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10.1016_j.ejrh.2020.100692.txt
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TITLE: Temporal and spatial variability of shallow soil moisture across four planar hillslopes on a tropical ocean island, San Cristóbal, Galápagos
AUTHORS:
- Percy, Madelyn S.
- Riveros-Iregui, Diego A.
- Mirus, Benjamin B.
- Benninger, Larry K.
ABSTRACT:
Study region
This paper provides a summary of findings from temporal and spatial studies of soil water content on planar hillslopes across the equatorial island of San Cristóbal, Galápagos (Ecuador).
Study focus
Soil water content (SWC) was measured to generate temporal and spatial records to determine seasonal variation and to investigate how the behavior of surface and near-surface root-zone soil water may support island-wide hydrogeology models. SWC probes were installed at four weather stations in a climosequence to generate a temporal record, and spatial surveys of shallow SWC across the selected sites were completed during wet and dry seasons. Temporal differences in SWC were driven by seasonal variations in rainfall and evapotranspiration, while spatial variability remained high during both wet and dry seasons. Unsaturated hydraulic conductivity determined by mini-disk infiltrometers was highly variable across the slopes, as were other hydrologic variables.
New hydrological insights for the region
The high heterogeneity of soil water and hydrologic characteristics provides a means to explain why little runoff is observed at the study sites: soils do not saturate uniformly across hillslopes, allowing for runoff generated in one part of the hillslope to be conducted into the soil in adjacent parts of the hillslope. The lack of connected surface runoff helps explain how water enters the groundwater system of the island.
BODY:
1 Introduction Knowledge of near-surface soil water content and the amount of water in pore spaces in the top of a soil (0−15 centimeters) contributes to the understanding of climate, energy balance, and plant health. Soil water content distributions across hillslopes can affect energy fluxes by: (1) controlling the partitioning of rainfall into evapotranspiration, runoff, and recharge ( Mirus and Loague, 2013 ; Rasmussen et al., 2011 ); (2) facilitating soil development and changes in chemistry by serving as a means of solute transport and changing the oxidation state of soils ( Bailey et al., 2014 ); and (3) serving as the source of water for soil microbiota ( Graham et al., 2010 ). Soil water content distributions also affect hydrologic processes at varying scales ( Western and Blöschl, 1999 ), ranging from centimeters (e.g., capillary flow versus macropore flow, solute transport) to kilometers (e.g., surface-atmosphere interactions, large-scale flooding). The distribution of soil water across hillslopes is affected by a number of factors, including season ( Martinez et al., 2008 ; Western and Grayson, 2000 ), topography ( Beven and Kirkby, 1979 ), flora ( Chandler et al., 2018 ; Metzger et al., 2017 ), land use ( Foster et al., 2003 ), and physical properties of the soil ( Dong and Ochsner, 2018 ; Zhu and Mohanty, 2003 ). We investigated the effect of seasonal variations in rainfall and evapotranspiration on the temporal and spatial distributions of soil water on San Cristóbal, a tropical ocean island located in the Galápagos archipelago in the equatorial Pacific ( Fig. 1 ). Previous work on soil moisture patterns and dynamics has largely focused on subtropical or temperate landscapes, where a hillslope’s aspect affects the soil water content, not just through evapotranspiration, but by fundamental changes to the hillslope’s hydrology. Slope aspect affects the types of plants growing on the hillslope, the amount of solar radiation that each side of the slope receives during the summer and the winter, and the shape of the slopes ( Pelletier et al., 2018 ). Authors have noted that polar-facing slopes (south-facing in the southern hemisphere and north-facing in the northern hemisphere) are usually cooler, wetter and steeper, while equator-facing slopes are drier and more likely to approach wilting point, and less steep ( Ebel, 2013 ). Low-elevation equatorial sites, like those on San Cristóbal, are largely unaffected by aspect because solar radiation is direction-independent, providing an opportunity to explore the seasonal change, at constant aspect, in the distribution of soil water. The relationship between temporal and spatial variability in soil water content based on season has been extensively studied in subtropical and temperate climates. The Shale Hills Critical Zone Observatory (Pennsylvania, USA) has served as the site of numerous spatial and temporal soil water surveys. The results of the temporal studies show that while root-zone and shallow soil water probes (less than 0.3 m deep) recorded strong seasonal differences in the distributions of soil moisture, deeper soil moisture probes (inserted to depths between 0.3 and 1.1 m) showed greater temporal persistence ( Takagi and Lin, 2012 ). At the Wüstebach catchment in Germany, authors noted that seasonal, and even event-driven variations in precipitation affected the topsoil’s soil moisture content, while deeper soil water content was affected by the depth to the water table more than the local precipitation ( Rosenbaum et al., 2012 ). A study of soils in France, Spain, and Tunisia found that while precipitation caused the mean soil water content across a field to change, the distribution of soil water, especially minima and maxima, remained constant through time ( Vachaud et al., 1985 ). Other authors have noted similar examples of spatially heterogeneous soil water distributions that are stable inter- or intra-annually ( Brocca et al., 2009 , and references therein; Grayson et al., 1997 ). At all these sites, an extensive network of soil moisture monitoring probes, weather stations, and groundwater observation wells and piezometers were in place, facilitating detailed quantitative understanding of the temporal and spatial dynamics of soil moisture. Tropical sites like the Galápagos often lack the scientific infrastructure to support studies like those carried out in subtropical and temperate climates, despite the importance of the temporal behavior and spatial distribution of soil water to the island-wide hydrology. Previous studies have used electromagnetic resistivity ( D’Ozouville et al., 2008a ), seismic refraction ( Adelinet et al., 2018 ), numerical modeling ( Domínguez et al., 2016 , 2017 ), and noble gas and stable isotope geochemistry ( Warrier et al., 2012 ) to create a conceptual model for the behavior of water as it enters the groundwater system (summarized in Percy et al., 2016 ). In general, the current conceptual models of the island’s hydrogeological system require that water infiltrates through soils and into perched aquifers that either drain via springs to the surface or deeper into the island’s groundwater system. However, little work has been done to understand the behavior of shallow soil water across the island’s planar hillslopes. San Cristóbal’s seasonal variability in precipitation amounts and type ( Percy et al., 2016 ; Schmitt et al., 2018 ) makes it a prime study site to understand how seasonal variability affects the temporal and spatial behavior and distribution of soil water across hillslopes on a tropical island. This study uses new data collected from soil moisture and weather monitoring stations at four different altitudes on San Cristóbal, coupled with intensive spatial sampling of shallow soil water content distributions across these four hillslopes during two different seasons, to address three primary questions: 1 Does the soil water saturation differ seasonally on the studied hillslopes? 2 Do we observe differences in the spatial patterns of near-surface soil water content across these hillslopes based on seasonal differences in stochastic variables like rainfall and evapotranspiration? 3 Could spatial patterns of shallow soil water affect runoff generation? Through geostatistical analysis of spatial patterns, time-series analysis of the hydrologic response monitoring across the hillslopes, and characterization of soil hydraulic properties, we provide further insights into variations in the hillslope-scale water balance across a climosequence in a tropical equatorial island setting. 2 Methods and materials 2.1 Site selection and description San Cristóbal Island, a basaltic volcanic island that is part of the Galápagos Archipelago ( Fig. 1 ), is estimated to have emerged from the Pacific around 2.4 Ma ( Geist et al., 2014 ), and the youngest dated eruption on the southwest side of the island, where our study sites are located, occurred 0.65 Ma ago. The bedrock across the archipelago is basaltic and ranges from tholeiitic to alkaline in nature; across San Cristóbal, at least six mineralogically and chemically distinct basalts were identified that range in age between 2.35 ± 0.03 and 0.7 Ma on the southwest side of the island to nearly modern on the northeast side of the island ( Geist et al., 1986 ). Despite its equatorial latitude, San Cristóbal experiences seasons due to the latitudinal migration of the Intertropical Convergence Zone ( Trueman and D’Ozouville, 2010 ). From January through May, San Cristóbal generally experiences weather typical of the tropics, with large convective rainstorms across the entire island. From June until December, southeast trade winds blow across cool upwelled ocean water to create an inversion layer, resulting in a dry and sunny coastal zone while the summit at roughly 700 m above sea level receives rainfall and is often cloudy (see Schmitt et al., 2018 , for details of upland climate). The seasonal shift from highly variable, island-wide precipitation to consistent, highland-only precipitation has resulted in a climosequence that is strongly dependent on elevation, ranging from very arid at the coastline to very humid at the summit ( Colinvaux, 1972 ). Vegetation ranges from native scrub and cacti at the coastline to grassy pastures, broadleaf shrubs, and trees at middle elevations, and native herbs and shrubs at the highest elevations ( Huttel, 1986 ). We selected four hillslope sites across the island, co-located with weather stations deployed in 2015 ( Fig. 1 ), two on the windward side and two on the leeward side. The weather stations were installed to capture as many climate zones as possible while facilitating routine maintenance, instrument security, and data downloads. El Junco (EJ) is the highest site on the windward side of the island and is located in the very humid zone. The hillslope is convex-linear (see classification of Schoeneberger et al., 2012 , for explanation of slope shapes) and is bounded on the east side by a bedrock outcrop. The studied portion of the slope covers an area of 48 × 50 m 2 . Sitio Mirador (SM) and Cerro Alto (CA) are located on the leeward side of the island and span the transition zone between dry (SM) and humid (CA) climates. CA’s slope shape is convex-concave and has cow paths that we observed to affect runoff at the site; the studied portion of the slope is 54 × 40 m 2 . SM, with a study area of 96 × 40 m 2 , is the most gently sloping of the sites and is bounded on three sides by bedrock cliffs. Finca Merceditas (FM) is the lowest site, but because it is on the windward side of the island, it remains in the transition zone between the dry and humid climate zones. The slope shape at FM is linear-linear and was partially covered by a study area of 75 × 50 m 2 . With these four sites, we have hillslopes in most of San Cristóbal’s climate zones except for the arid zone. The arid coastal zone’s soils are thin and unevenly distributed, found mostly in cracks in lava flows, and so are not included in this study. We visited the sites during the Galápagos wet season of 2015 and the dry season of 2016; wet season 2015 was during an El Niño and was wet (161 mm of measured precipitation at EJ over five weeks of the study period, from the weather station at each site), while the study during 2016 occurred during an eight-month drought (46 mm of precipitation measured over the eight-week study period at EJ). Summary details about each site are provided in Table 1 . Between the field seasons, a wildfire affected CA and SM, probably in July according to farmers. At CA, the majority of the sampling points were unaffected by the wildfire and the site remained a pasture; only the downslope points experienced the fire. SM’s land use changed following the fire from a carefully maintained natural area that served as a nursery for native plants to a garden with little ground cover. 2.2 Measurement of climate variables and temporal soil water data The deployed weather stations collected data on rainfall, wind speed and direction, relative humidity, temperature, and solar radiation, and were co-located with soil moisture probes at three depths. Data gaps at the stations were the result of inclement weather and biological activity that resulted in the failure of instruments. To record the volumetric soil water content, we installed soil water sensors (Model CS616, Campbell Scientific Inc., Utah, United States) horizontally at depths of 10, 20, and 40 cm at EJ, and 10, 20, and 30 cm at the other three sites. However, because of equipment failure after deployment, continuous soil moisture data at SM are not available. The data were recorded every 15 min, with the exception of the station at FM which recorded data every 5 min for the first 300 days. A complete description of the equipment used to measure climate variables is found in Schmitt et al. (2018) . To calculate the reference evapotranspiration rates, we used the FAO Penman-Monteith method ( Zotarelli et al., 2010 ) because of the available weather station data. We used the grass reference surface in our calculations because none of the weather stations were installed under trees and because three of the four sites were grassy, while the last site (EJ) is characterized by low herbs. 2.3 Physical properties and site characterization We made hillslope-scale and point measurements to describe the physical properties of the studied hillslopes. We recorded physical variables at each point for which near-surface soil water content was collected, as described below. Digital elevation models available for San Cristóbal were insufficient because their resolution was too coarse for this study (20 m from ENVISAT, D’Ozouville et al., 2008b ), so we surveyed the four hillslopes across the 2-m grid via tape-and-compass measurements (Fig. S1). From the generated 2-m resolution DEM, we calculated the slopes and upslope accumulation area for each site using ArcGIS ( Esri, 2011 ). We noted the overlying plant type (bramble, fern, herb, grass, tree, and bare soil) at the point at which we inserted the soil water content probe, and recorded the presence of trees, tree roots, or rocky outcrops within 2 m of each measurement point. We present maps of the plants at each measurement point for both seasons in Figure S2. We used a soil step probe (33″ Plated Step Probe with Handle, AMS, Idaho, United States) to measure the depth of soil (hereafter, depth to refusal) after measuring the soil water content at each point. Excavations show that the depth to refusal is the depth to a clay-rich horizon or rock and provide an adequate proxy for the depth to which soils are heavily rooted. Maps of the depth to refusal are presented in Fig. S3. 2.4 Soil water content and hydrologic properties During the field seasons, we measured the near-surface soil water content using a Hydrosense II (HS2) CS659 portable soil water content probe (12-cm rods, Campbell Scientific Inc., Utah, United States) with a support volume (the volume of soil over which the soil water content is measured) of approximately 460 cm 3 . The output from the HS2 is electrical period (microseconds, μs) and a conversion is used to calculate volumetric water content (volume%). The period is strongly related to the dielectric permittivity of the material around the probe rods (Campbell Scientific Hydrosense II User Guide). Tropical soils on volcanic parent material can have a range of clay and amorphous material contents that will affect the calibration of soil water content probes ( Noborio, 2001 ; Regalado et al., 2003 ), so we noted both period and calculated soil water content. We calibrated the HS2 in the laboratory using minimally disturbed soil core samples collected in 130 cm 3 metal cylinders. In the 2015 wet season, we took at least 100 shallow soil moisture measurements within a 20 × 20 m 2 grid to provide adequate spatial coverage on the small hillslopes. We made additional measurements down slopes in transects extending from grid lines. The dry season campaign in 2016 included the same 100 points measured during the 2015 campaign. We measured additional points during both field campaigns that are included in the geospatial analysis. We collected measurements over several days at each site; during the wet season campaign, the weather stations were not yet operational at EJ, CA, and FM, but field notes indicate that it rained every day at EJ and for one of the six measurement days at CA. During the dry season, only EJ received rain during data collection (Fig S4). We also measured hydraulic properties of the soils to support the temporal and spatial observations of the soil’s volumetric water content. To measure the hydraulic properties of the soils on the four hillslopes, we used in situ experiments to quantify the unsaturated hydraulic conductivity and laboratory analyses to measure bulk density, grain size distributions, pH, and the weight percentage of amorphous material in the soils. In the field, we measured the sorptivity of water and unsaturated hydraulic conductivity using Meter Group mini-disk infiltrometers (MDI) with an applied suction of −2 cm for sites CA, SM, and FM, and −0.5 cm for site EJ (due to slow infiltration across the site). We applied the MDI to the soil after clearing the leaf litter and made at least two measurements of unsaturated hydraulic conductivity within 1 m of each other at SM and FM. We used the Excel macro provided by the manufacturer to calculate the sorptivity and unsaturated hydraulic conductivity. We measured the bulk density of the soils using the saran method ( Blake and Hartge, 1986 ) to aid in the calibration of the Hydrosense II, as well as estimate what the maximum volumetric water content could be. We calculated the bulk porosity in samples from the sites using an average particle density value of 2.60 g/cm 3 , the average density of kaolinite, gibbsite, halloysite, and illite, all of which are expected to be important components of the soil (porosity = 1 – [bulk density/particle density]). In the laboratory, we measured grain size distributions from each site by dry sieving the fine earth fraction (<2 mm particles) on a shaker, followed by gravimetric determination to yield the percent of the total weight of the sample, with chemical dispersion of clays accomplished using sodium hexametaphosphate ( Soil Survey Staff, 2014 ). The pH of the mineral soil was measured by combining 5 g of fine earth mixed in 20 mL of distilled water and allowed to equilibrate for at least one hour before allowing the particles to settle and measuring the pH of the supernatant ( Pansu and Gautheyrou, 2006 ). Naturally occurring amorphous materials in soils are noncrystalline and poorly crystalline material, usually composed of compounds of Si, Fe, and Al that coordinate with free oxides and hydroxides. We measured the weight percentage of amorphous material in the bulk soil using the ammonium oxalate extraction method ( Jackson et al., 1986 ) at least once per site because amorphous materials can adsorb water and affect the hydrophobicity of soil. 2.5 Data processing We analyzed the soil water content and climate time-series data using R computing software ( R Core Team, 2017 ). To examine relative temporal changes in soil moisture, we normalized the measured volumetric water content to the maximum observed values during saturation to calculate relative soil saturations. To examine the observations spatially, we used semivariogram analysis to calculate the autocorrelation distance across the four sites during each season; semivariograms show the autocorrelation over distance across hillslopes and can be used to understand the distributions of soil water ( Western et al., 2004 ). Understanding autocorrelation distance at the four sites provides a quantitative metric for the degree of hillslope connectivity, which is important to the understanding of runoff generation on the hillslopes. We input our gridded data into the geoR package in R ( Ribeiro and Diggle, 2001 ) to test omnidirectional, exponential ( Western et al., 2004 ) and spherical models ( Bi et al., 2009 ). Different studies have found that the exponential or spherical models fit data better in different landscape types: the exponential model’s covariance along the sill asymptotically approaches zero variance, while the spherical model’s sill represents where the covariance is zero. We compared the raw output data from the HS2 (period) and the calculated soil water content to complete the semivariogram analysis using the different models. We tested correlation relationships between soil water content and topographic measures, including slope and upslope accumulation area, and the depth to refusal. We also analyzed the relationship between hillslope-averaged variables like bulk density, pH, fraction of amorphous material, unsaturated infiltration rates, soil texture, and the mean soil moisture and standard deviation of the soil water content for the wet and dry seasons. 3 Results 3.1 Temporal record of soil moisture The temporal record of rainfall, soil moisture, and evapotranspiration is presented in Fig. 2 for sites EJ, CA, and FM. Summary data from the weather stations at all four sites are in Table 2 . The wet season on San Cristóbal usually falls between January and May, and the dry season falls between June and December, with interannual variability in the beginning and end of the seasons. However, the beginning of the study fell within the strong 2015−2016 El Niño, which ended in May–June 2016 ( Hu and Fedorov, 2019 ), resulting in very wet conditions throughout the first part of the study. As shown in Fig. 2 a, almost 65% of the precipitation at EJ fell between October 2015 and February 2016. During this period, the wind was at its most variable, and the solar radiation was lower than during dryer parts of the year. On the island of Santa Cruz, researchers found that fog can account for approximately 20% of the net precipitation at high elevation sites at comparable elevations to EJ ( Pryet et al., 2012b ). Because of the configuration of the weather station, we did not measure the amount of occult precipitation at EJ, which means that an important source of water into the hillslope is not considered within the precipitation data. Within the soil, the deepest soil moisture probe (40 cm) recorded soil moisture levels that regularly approached saturation; the data show that soil moisture decreased more slowly from saturation than the shallow soil moisture. The dry period (February 2016 until the end of the data record, January 2017) had fewer rainstorms and the reference evapotranspiration was higher due to both higher windspeeds and greater solar radiation. This corresponds with a decline in the recorded soil moisture through the season, with rainstorms resulting in sudden increases in the shallower soil moisture data (10 and 20 cm) and much smaller increases in the deep soil moisture data (40 cm). CA ( Fig. 2 b), located on the drier leeward side of the island, receives precipitation from large convective storms, rather than the fog that characterizes the “dry” season at EJ. In calculating the reference ET for site CA, the solar radiation term of ET was consistent across the year, but the wind term was highly variable and was the dominant control of the calculated reference evapotranspiration for the site. The data recorded by the soil moisture probes at CA show that the deepest soil moisture probe (30 cm) most often approached saturation, and the 20 cm deep probe was only slightly drier. The shallow probe (10 cm) recorded the greatest percent change in measured soil water content after precipitation events compared to the deeper soil probes and also indicated that the soil dried most quickly near the surface. At the low-elevation windward site FM, the average reference ET remained around 2.40 mm/day throughout the seasons, in part because the windspeed remained consistent throughout the seasons. Changes in the daily reference ET are due to changes in radiation fluxes. The soil moisture data show that the shallowest soil moisture probe (10 cm) recorded the highest saturation across the study period, while the two deeper soil moisture probes (20 and 30 cm) had similar saturation values recorded through time. At all of the sites, the temporal soil moisture record reflects different responses to precipitation events. For example, at EJ ( Fig. 3 a), the surface soil moisture probe at 10 cm showed a daily decline in the percent saturation until a large event, at which point the record reflects an increase to 100% saturation. The 10- and 20-cm probes first responded to the storm event at the same time; however, the 20-cm deep probe did not record as steep of a rate in the increase of saturation. The 40-cm probe had the highest percent saturation prior to the storm event and did not respond to the storm event until hours after the surface soil probes. Several days after the precipitation event, the 40-cm deep probe reached saturation during smaller precipitation events, while the 10- and 20-cm soils had lower percent saturation values. Fig. 3 b shows the response in percent saturation at CA to two storm events. The first storm event resulted in a nearly simultaneous increase in the percent saturation at all three probe depths within 30 min after the start of the event, indicative of preferential flow in the surface soil which may be an important mechanism at this site. The second storm event was recorded by all three soil probes simultaneously (within the same 15-minute measurement period). At CA, the surface soil dried most quickly. At FM ( Fig. 3 c), the 10-cm deep probe recorded the highest percent saturation throughout the considered time period, while the 20- and 30-cm deep probes recorded very similar percent saturations. The shallowest probe recorded an increase in the percent saturation approximately 50 min before the 20- and 30-cm root-zone probes began to record an increase in the percent saturation. The second, smaller event did not affect the 30-cm deep probe, and only marginally increased the percent saturation for the 20-cm deep probe but resulted in a 3% increase in the percent saturation for the surface probe, from 92% saturation to 94.8% saturation. 3.2 Spatial soil water patterns and statistics The number of sampling points and summary statistics of the spatial soil water survey measurements ( Table 3 ) show that the mean, maximum, and minimum measured values of soil water content during the wet seasons are, not surprisingly, higher than during the dry season. The standard deviation and coefficient of variation (a measure of the relative variability of the soil water content) are higher for the dry period than they are for the wet period at all four sites. While changes in soil water between field seasons are associated with the precipitation, the cross-site relationship between site-wide precipitation and mean soil water content is not linear, likely because of differences in physical properties of soils at the sites. For example, despite its location in the very humid highlands and the highest annual precipitation record, EJ has the lowest mean of spatial soil water content for the wet season, and the second highest mean of spatial soil water content for the dry season. CA’s mean of spatial soil water content is the second highest during the wet season but has a low mean of spatial soil water content during the dry season. SM and FM display similar means of spatial soil water values during the wet season, but because SM is on the leeward side of the island and FM is on the windward side, the mean of the spatial soil water content during the dry season is higher at FM than SM. There are no easily discernible spatial patterns in the distribution of near-surface soil moisture across the hillslopes ( Fig. 4 ). At EJ, the most humid site, neither of the spatial surveys show a relationship between soil moisture distribution and topography across the hillslope, although the lower portion of the slope for the dry season was slightly wetter than the upper portion of the slope, collected the day before, because of a rainstorm that occurred on the day we made the measurements on the low slope segment (Supplementary Fig. 4 ). Any possible pattern present at CA is difficult to identify because of the rock faces and thin soils that dominate the middle of the hillslope at this site. In the areas with spatially continuous data, soil moisture increased slightly in the middle of the saddle at the top of the hill at CA, at a point with the greatest convergence at the study site. For SM, the distribution of soil moisture appears random during both the wet and dry season, although less data were collected during the wet season. The noticeably wet area at SM during the wet season occurred where taller trees and thick herbs shaded the ground. At FM, the distribution of soil moisture appears random during both the wet and dry seasons. The distribution of the soil water content data varies from site to site, with the Shapiro-Wilk test of normality indicating that none of the sites’ soil water content distributions are normal. Previous authors used the gamma distribution (e.g., Kaiser and McGlynn, 2018 ) to describe the probability distribution of data because it resembles the positive skewness often observed with soil pore size distributions ( Tuller and Or, 2005 ) and it has been experimentally tested in a variety of catchments (e.g., McGuire et al., 2005 ). We examined histograms of the soil water content for each site and applied gamma distributions ( Fig. 5 ). For all but FM, the dry season’s distributions are positively skewed, while for all of the sites, the wet season’s distributions are negatively skewed. Other studies note that negative skewness is observed when the bounded function approaches the upper bound of porosity and the soil water content has reached saturation ( Kaiser and McGlynn, 2018 ; Western et al., 2002 ), whereas positive skewness corresponds to the soil water content approaching the wilting point. We tested the temporal stability of the soil moisture spatial distributions by ranking the soil moisture values and comparing the ranks of the points that we measured during both seasons. Across the four sites, there was no temporal stability in the spatial distribution of soil moisture. However, it is crucial to note that other studies that have observed temporal stability of soil moisture distribution patterns incorporated significantly more time points, including studies that collected soil moisture data over years ( Dari et al., 2019 ; Gao et al., 2019 ; Starks et al., 2006 ; Western et al., 1999 ). Additional interpretations of the temporal stability of soil moisture distributions across our hillslopes would require additional spatial surveys of the slopes to capture not just wet and dry seasons, but the transition between the seasons. 3.3 Geostatistical analysis We used semivariogram analysis at each site to evaluate spatial correlations between measured soil moisture. We made the models of semivariance using the directly measured period (μs) rather than the calculated soil water content because the Hydrosense II does not report volumetric water content values above 52.2% due to internal calibration within the sensor, while the measured period is reported from the sensor for every point. The soil’s electrical response is affected by soil moisture, but also by the clay content, organic material content, and soil salinity ( Topp et al., 1980 ). While the use of period rather than volumetric water content affected the autocorrelation distances calculated with the semivariogram analysis, this introduced less error into the interpretations of the results because of greater spatial coverage across the hillslopes. We tested a range of input values for the nugget, the partial sill, and the range parameter, selected based on the measured data for each model semivariogram and reported the model with the lowest sum-of-squares fit. The values used for each of the best-fit models are in Table 4 . The spherical model type provided a lower sum-of-squares fit than does the exponential model for all but four of the models. For three models (CA during the dry season and FM during the wet and dry seasons), the type of model did not affect the sum-of-squares fit and is listed as Sph/Exp. For SM during the dry season, the exponential model had a lower sum-of-squares fit. We also tested whether the model required a nugget; for all of the models, setting a nugget provided a better model fit than reducing the nugget to zero. Beyond the presence of a nugget, the semivariogram models (lines) show no consistent trends in autocorrelation related to either season or site wetness and do not fit the calculated semivariance of the measured data well ( Fig. 6 ). In the wet season (right panel), the wet sites’ semivariance does not reach a plateau, suggesting that the autocorrelation distance is longer than the measured length of the hillslopes. For the dry season (left panel), the models of the semivariance (lines) fail to capture the calculated semivariance at CA and FM because there is no spatial correlation across the hillslopes. 3.4 Soil hydrologic properties The results of the MDI experiments measured over the course of one day at each site show that the soils’ sorptivity and measured unsaturated hydraulic conductivity (hereafter, K unsat ) were heterogeneous during both wet and dry field seasons. We report both values in Table 5 because the sorptivity, which represents a soil’s ability to draw water ( Stewart et al., 2013 ), does not depend upon the soil wetness when measured, unlike unsaturated hydraulic conductivity measurements. Because the MDI experiments are completed over very small areas (the diameter of the steel disk applied to the soil surface is 4.5 cm), this heterogeneity is expected, but even in settings with massive spatial variability in hydraulic conductivity, enough measurements with a mini disk can be used to provide useful estimates of effective infiltration capacity at the catchment scale ( McGuire et al., 2018 ). Regardless of the mean soil water content for each hillslope, the unsaturated hydraulic conductivity did not exhibit patterns based on the distance downslope from the datum at each site, suggesting that shallow soil water was not accumulating downslope. We measured the soil saturation at each point prior to running the MDI experiments and saw no relationship between shallow soil saturation, the soil sorptivity, and the unsaturated hydraulic conductivity. Other hydrologic properties at the four sites, including bulk density and calculated porosity, grain size distributions, pH, and the weight percentage of amorphous material, are reported along with the results of the MDI experiments in Table 5 . Because we made all of the soil moisture measurements in the upper soil layer, only topsoil (0−15 cm, samples from the O or Ah horizons; Lasso and Espinosa, 2018 ) properties are included. During the dry field season, we collected surface bulk density samples at the same location we made the MDI measurements at FM and EJ; however, there is no apparent relationship between the two properties. The other measured hydrologic properties at FM and EJ have no correlation with the MDI-measured K unsat values at FM and EJ. We compared the K unsat data to the intensity of rainfall during the field seasons for all of the sites ( Fig. 7 ). At all of the sites, the range of measured unsaturated hydraulic conductivity spanned orders of magnitude. The smallest values measured for the unsaturated hydraulic conductivity at each site are within the same order of magnitude of rainfall intensity ( Table 5 ), while the largest values are much higher than the measured rainfall intensity. However, because we avoided obvious macropores (observed at Sitio Mirador, the only site at which surficial expression of the presence of macropores was clear) and adjusted the suction for the MDI to exclude macropore flow, the calculated K unsat values only apply to the soil matrix. Because we did not account for macropore flow in our measurements of K unsat , the precipitation and K unsat values may not overlap at all if macropore flow is important and rapid infiltration through macropores dominates infiltration. Additionally, we calculated the rainfall intensities from the total precipitation collected in a tipping bucket rain gauge and integrated over the data logger’s recording time (5−15 min). Likely some of the instantaneous rainfall intensities were slightly higher than the values integrated over the relatively short measurement periods. While in the field, we excavated soil pits across the hillslopes; at EJ, we observed water exfiltrating along the O and A horizon boundary in the profile wall (between 8 and 15 cm deep across the entire hillslope) when there was heavy rain (every day during the wet season, one day during the dry season). At CA, we observed water moving along a boundary between less clay-rich and clay-rich layers only during the wet season. At SM and FM, we did not observe water exfiltration from the exposed face of the soil pits. Although numerous studies indicate that saprolite that underlies many tropical sites may have bimodal pore size distributions ( Navarre-Sitchler et al., 2013 ), we observed no evidence of such a distribution within the saprolites from the soil pits. 4 Discussion 4.1 Do the soil water saturation states differ seasonally? At the three study sites with temporally continuous records of soil saturation (EJ, CA, and FM), we observed changes in the percent saturation for all depths between the wet season and the dry season ( Table 6 ). This shift in the seasonal percent saturation was unsurprisingly supported by changes in the mean soil saturation measured by the two areal studies. EJ had one rain event during the dry season for which there are both temporal and spatial data. Over the course of the event, the soil water saturation of the areal study increased by a percent change of 18.5%, and the soil water saturation measured by the weather station increased by a percent change of 20.3%. With additional spatial surveys and in situ soil moisture probes, determining if the weather stations provide a representative measurement of the change in the percent saturation would be possible. Because this study fell during an El Niño, the seasonal changes that we described represent extreme cases of wet and dry. The highest intensity and amount of precipitation measured at EJ corresponds to the record of the greatest saturation of soils at all depths. When rainfall declined during the dry season, the calculated reference evapotranspiration was higher and more variable, reflecting an increase in solar radiation and windspeed. El Niño usually results in more convective rainfall and less fog in the Galápagos ( Trueman and D’Ozouville, 2010 ), so it is possible that during non-El Niño years, the soils at EJ do not dry as much as they did during our study period, which occurred during an intense El Niño year. At CA, the rainy periods corresponded to the highest measured soil saturation, while the reference evapotranspiration was variable throughout the year, reflecting the site’s leeward position and the fact that it receives less consistent rainfall and fog during dry seasons compared to the windward sites. Because island-wide convective storms are more common during El Niño years, the high soil saturation observed during this study at CA may be uncharacteristic of the site. FM also has a distinct rainy and dry season, although it received more dry season precipitation than the leeward CA. Higher soil saturation was associated with the rainy seasons, but the reference evapotranspiration stayed consistent throughout the year, reflecting the fact that the site receives less precipitation than EJ, but more than CA. We examined the change in variance in the temporal soil water content record and observed shifts through time. The sites showed different relationships between the saturation state and the variance, with higher measured variance during the dry season at EJ and lower variance during the dry season at CA. The variance around the mean percent saturation at FM remains nearly the same for both seasons. Many authors have observed that the highest variance in soil moisture is associated with mid-range mean soil moisture measurements in near-surface soils ( Choi et al., 2007 ; Famiglietti et al., 2008 ), although researchers have also noted that variance can both increase or decrease with changes in the mean soil moisture ( Pan and Peters-Lidard, 2008 ). For example, at a temperate site in Virginia (USA), it was noted that the lowest variance around mean soil moisture is associated with extreme wet and dry periods ( Lawrence and Hornberger, 2007 ). The authors determined that during dry periods, the variance is controlled by the wilting point of plants; during temperate periods, the variance is dictated by the hydraulic conductivity of soils; and during wet periods, the variance is controlled by the soil porosity. In the case where authors working in sodic soils observed that while the highest variance was associated with mid-range soil moisture measurements at depths below 20 cm, they still observed that the shallowest soil moisture measurements (0−6 cm) exhibited the highest variance associated with the extreme wet and dry soil moisture periods ( Peterson et al., 2019 ). Additionally, their observation of high variance associated with extreme wet and dry values in deeper soils is likely the result of the chemical properties of the soils affecting the conductivity of clay pans at depths greater than 20 cm. The depth to the point of refusal, which is generally the depth to a clay-rich horizon, is deeper than the shallowest soil moisture probe at each weather station, and the chemistry of the soils do not display sodic characteristics ( Percy, 2020 ), so we assume that the sites’ variance decreases as conditions approach extreme wet and dry conditions. To this end, we compared the wet and dry seasons to understand what possible factors may affect the percent saturation at the sites, using Lawrence and Hornberger’s (2007) drivers of variance for different saturation states. At EJ, we observed a shift between the wet and dry seasons from lower to higher variance, suggesting a possible shift from the control of soil saturation by maximum soil porosity to the control of the soil saturation by hydraulic conductivity and other hydrologic properties. EJ’s surface soil remained more saturated than any of the other sites throughout the year ( Table 2 ), resulting in the plants on the planar hillslope unlikely to demonstrate water stress during any part of the study period. Conversely, the variance in CA declined between the wet and the dry periods, suggesting that CA shifted from a state where soil saturation was controlled by hydrologic factors to a point where the plants’ wilting points were being reached. Field observations of dried grasses and herbs support this hypothesis, although matric pressure was not measured so this hypothesis cannot be further tested. The lack of a statistically significant change in the variance at FM led us to conclude that there was not a major shift in what factors are controlling the soil saturation at this site. Conversely, it is possible that the control of the saturation of soils at FM had shifted from porosity to the wilting point of plants, but we find this to be unlikely based on field observations at FM during the dry season, when grasses and herbs were still green, and because the deeper probes rarely recorded full saturation values. Further field campaigns would benefit from a longer temporal record and the installation of additional in situ soil moisture probes to account for variable changes in the percent saturation across the sites. 4.2 Do the spatial patterns of near-surface soil water shift seasonally? With the spatial surveys of soil moisture, we intended to test whether observable differences in the spatial patterns of near-surface soil moisture (12 cm) across the hillslopes are based on the season. Our findings indicate that the heterogeneity of soil water across the hillslopes remained high during both wet and dry seasons, but based on only two spatial surveys, determining the temporal stability of the heterogeneity is not yet possible. The semivariogram analysis indicates that the autocorrelation distance was longer than the length of the studied hillslopes. The lack of spatial autocorrelation on our measured scales may reflect the size of the hillslopes, their planar morphology, or the heterogeneity of soil properties across the hillslopes. We used simple regressions to test whether topography, depth to refusal, or slope could be used to predict the percent saturation, but no relationship was observed between any of these variables and the spatial soil moisture measurements. We used Wilcoxan signed rank tests to test whether plant type led to distinguishable differences in percent saturation, but differences between plant types were not statistically significant at any of the sites. This suggests that at the scales of the plots in which we worked a combination of these variables affects the surface soil moisture, in addition to the microclimatic conditions associated with each measurement point. Previous studies noted that plot-scale variability in soil moisture can be very high when compared to landscape-scale variability ( Kaiser and McGlynn, 2018 ); because this study was limited to the hillslopes at which weather stations were installed, we did not measure catchment-scale variability in soil water content. We noted from the temporal soil moisture record that EJ’s variance in percent saturation was higher in the dry season than in the wet season, while CA’s variance was lower in the dry season than in the wet season, and FM’s variance was the same throughout the seasons (Section 4 .1). However, the variance from the spatial soil moisture measurements from the seasonal surveys was consistently higher during the dry season compared to the wet season. Although the temporal and spatial variance are not directly comparable because of the nature of the study design, the dry season’s higher spatial variance may be due to surface soils drying and approaching wilting points. Reasons why the spatial patterns of soil water remained highly heterogeneous throughout both seasons are numerous, despite differences in stochastic variables like precipitation and evapotranspiration. Previous work completed across a much larger catchment at Tarrawarra (Victoria, Australia) noted a change in the heterogeneity of spatial soil moisture observations between the wet and dry season, with soil water content increasing in the convergent portions of the catchment during wet periods ( Western and Grayson, 1998 , 2000). The planar nature of the studied hillslopes, coupled with their small size, make it unlikely that we captured sufficient data in convergent areas where flowlines meet, possibly explaining the lack of recorded seasonal reorganization of soil water. Additionally, the interpretation of the spatial distribution of soil water is convoluted by the fact that each site’s soil water survey took several days to complete. The weather stations were installed after we completed the spatial surveys in the wet season, so we are unable to show the change in soil water content through time for the first spatial survey; however, we can show how the soil moisture changed during the dry season over the course of the surveys (Fig. S4). At FM and CA, the weather station recorded a mean value of volumetric water content of 29.7% and 25.4%, respectively, with a standard deviation of 0.2% over the time period during which we collected spatial data. However, a rainstorm at EJ on one of our measurement days caused the soil water content to rise and the resulting standard deviation of the soil water measured at the weather station during the four days of the spatial survey is an order of magnitude higher at EJ (2.3%) compared to FM and CA. Further surveys of spatial distributions of soil water will benefit from single-day collection, which was not possible with the limited resources and narrow scope of this project. 4.3 Do spatial patterns of soil water affect runoff generation? Despite intense rainfall at all of the sites during the rainy season, we did not observe evidence of connected surface runoff across the studied hillslopes at EJ, SM, and FM, including little evidence of gully formation at the agricultural sites or bottom-slope wetness. The only runoff that we observed was at CA along a cow trail, and then only when the trail passed beneath a basalt bluff. Based on the spatial distribution of soil moisture across the hillslopes and the semivariogram analyses of the spatial distributions, we propose that the lack of runoff at the four sites is due to low spatial connectivity across each hillslope and variable responses to wetting and drying at different depths of the soil, coupled with generally high hydraulic conductivity in surface soils. The low spatial connectivity of the surface soil water, identified using semivariogram analysis, affected runoff because the amount of water in soils varied spatially. From the temporal record of soil water content, we noted variable responses to wetting and drying between the surface soil probes (10 cm) and the deeper soil moisture measurements made within the root zone. The delays between the arrival of water at the surface soil probe and the deeper probes suggest vertical infiltration is largely matrix-flow dominated. We also observed a large range of sorptivity and unsaturated hydraulic conductivity ( Fig. 7 , Table 5 ). The range of the unsaturated hydraulic conductivities ( Table 5 ) suggests that some parts of the hillslopes were more conductive than others. From the MDI experiments, we know these areas may be very close to one another (within 1 m). Incorporating the observations of spatial and vertical heterogeneity, we propose two possible explanations for the lack of runoff observed at the sites. The first is that highly permeable, unsealed surface material distributed across the hillslopes allows water to vertically infiltrate into the soil column. Previous authors modeling arid and semiarid catchments found that the sealing status of the shallowest portions of a soil profile were a more important factor in generating runoff than spatial heterogeneity ( Assouline and Mualem, 2006 ). They showed that simulations of catchments with no surface seal formation generated little cumulative runoff. However, this explanation does not fit our observations, as we did not observe soil sealing on any of the hillslopes, and the hydrologic properties and soil water distributions are highly heterogeneous at each site. Instead of uniform, highly permeable soil surfaces, we suggest that surface soil that becomes saturated simply becomes a source of soil water to adjacent soil that is less saturated and can accommodate the excess water by serving as a sink. The high variability in unsaturated hydraulic conductivity provides further evidence that intense precipitation does not saturate a soil and start flowing overland because areas with lower soil moisture and higher hydraulic conductivity are nearby and can serve as sinks for excess water. This supports the hypothesis of more “transmissive” and “retentive” parts of the hillslopes that prevent the accumulation of observable and measurable overland flow across hillslopes. Thus, any patches of runoff are not connected with another downslope and limit the occurrence and impacts of overland flow. Transmissive soils conduct water more easily when wet (higher hydraulic conductivities), while retentive soils conduct water poorly when wet (lower hydraulic conductivities) but can retain soil moisture for longer periods of time. High-intensity rainfall may produce localized runoff from retentive soils that infiltrates into adjacent parcels of more transmissive soil ( Nimmo et al., 2009 ). On San Cristóbal, this model may explain the lack of runoff on the planar hillslopes: because of the high heterogeneity in hillslope-scale characteristics, like soil texture and the amount of amorphous material, both of which affect hydraulic conductivity, parcels of transmissive and retentive soils may be adjacent to each other. The lack of autocorrelation across small distances (less than 100 m) on the hillslopes provides support for this model of a patchwork of transmissive and retentive soils. Runoff generation at temperate sites may depend on whether lateral or vertical flow paths are dominant along the hillslopes, where the presence of lateral flow paths depends on the morphology of the landscape ( Elsenbeer, 2001 ; Fitzjohn et al., 1998 ). For our study, none of the studied slopes featured gullies or other areas of high convergence (Fig. S1), so it is unlikely that large amounts of surface lateral flow were driven by hillslope morphology. At CA, the uppermost portion of the site was saddle shaped and crisscrossed by cow paths. Soil water may have accumulated due to lateral flow in the slightly convergent portion of the saddle ( Fig. 4 ), but the remainder of the data from the spatial survey at the site demonstrated no similar accumulation. Most soil water evaporates directly from the soil surface, is used by plants, or infiltrates vertically until the water reaches an aquitard and begins to flow laterally. In excavated soil pits during the wet season, we observed water seeping out of the upslope walls along the horizon boundaries, supporting lateral redistribution of water at depth. At CA, also a “water meadow” at the base of a nearby hillslope wetted after small rain events, despite no evidence of runoff along the hillslope, supporting the idea that water may be laterally redistributed deeper within the soil. Our hypothesis to explain the lack of observed surface runoff on the hillslopes corroborates work completed on other tropical ocean islands. On the island of Santa Cruz, Galápagos (to the west of San Cristóbal), soil profiles were instrumented with tensiometers to measure the pressure head within soil profiles under two different land cover types (forest, pasture; Domínguez et al., 2016 ). Those data were then incorporated into a soil water transfer model, which showed that runoff was negligible because the soil water input never exceeded the infiltration capacity of the soils, as we observed at the sites on San Cristóbal. Based on the model, deep percolation into the groundwater system occurred in both land use regimes, suggesting that vertical flow paths through the soil results in groundwater recharge. Previous work on Hawaii observed a similar phenomenon—the surface soil had little connectivity, resulting in negligible runoff, but after vertical infiltration, lateral redistribution of soil water was observed at horizon boundaries due to the change in the hydraulic conductivity between different horizons ( Lohse and Dietrich, 2005 ). Future work on San Cristóbal should include the measurement of hydraulic conductivity across broader areas and in different horizons to better characterize spatial variations in conductivity that control runoff and groundwater recharge. 4.4 Soil water and island-wide hydrogeology Previous work on the hydrogeology of San Cristóbal has related the island’s groundwater system to that of Hawaii ( Violette et al., 2014 ). Consecutive lava flows, separated by baked paleosols or tuffs, have led to a complicated groundwater system of perched aquifers, some of which drain to a basalt aquifer and some that result in springs. This is similar to the hydrogeology of many other basalt systems, including continental basalts like those found on the Snake River Plain ( Mirus et al., 2011 ) and other ocean islands, like Piton de la Fournaise on La Reúnion ( Violette et al., 1997 ). San Cristóbal is the only island in the archipelago with multiple perennial streams, maintained by springs that drain the perched aquifers. This understanding has come through geophysical ( Adelinet et al., 2018 ; Auken et al., 2009 ; Pryet et al., 2012a ) and geochemical ( Warrier et al., 2012 ) observations. Little research has previously connected inputs into the island’s hydrologic system with the groundwater system. From this study, we propose that water that has been transmitted through the soil’s root zone and into the deeper horizons of the soil will either flow laterally along horizons of low hydraulic conductivity, resulting in high soil water contents and seeps that emerge in areas of convergence (like the water meadow at the base of CA), or will infiltrate further through the unconsolidated saprolite to enter the deeper groundwater system. Due to the lack of monitoring wells on San Cristóbal, exact determination of the amount of infiltrated water that enters the groundwater system is unknown, but the research on the behavior of surface and root zone soil water helps provide an important step in further understanding water cycling on San Cristóbal. This study is far from comprehensive, but the data provide ample opportunities for further testing of conceptual and numerical models of hillslope hydrologic response on San Cristóbal and similar tropical island settings. Additional efforts must also be made to improve instrumentation of hillslopes in diverse climates across San Cristóbal to track how seasonality affects the distribution and behavior of soil water. 5 Conclusions We have compared the temporal and spatial records of soil water on four planar hillslopes on San Cristóbal, Galápagos, to develop a qualitative model of water in near-surface soils in different climate zones. This work aims to provide a component of our understanding of the hydrogeology of San Cristóbal, and possibly, other ocean islands. We initially sought to answer three questions: (1) does soil water differ seasonally; (2) does the spatial distribution of soil water differ through time; and (3) could spatial patterns of soil water affect runoff generation. The findings of this study confirm that temporal differences in saturation states on the studied hillslopes are driven by seasonal differences in precipitation and evapotranspiration, and the position of the hillslopes on San Cristóbal’s climosequence and their windward/leeward position. Thus, our dataset is a valuable resource for future hydrologic and soil-atmosphere modeling efforts. We complemented the temporal differences in saturation state with surveys of the spatial variability of the soil water across the studied hillslopes, showing that during both wet and dry seasons, the soil water content was highly variable spatially and randomly distributed across the hillslope. This spatial variability is likely the result of the heterogeneity of a number of factors, including physical and hydrologic characteristics of the soil and the microclimate and microtopography around each of the measurement points. While in the field, we did not observe evidence of runoff at most of the sites except along the cow path at CA, despite numerous heavy rain events. Because near-surface soil moisture was not spatially connected and the hydraulic conductivity is higher than rainfall intensity, we conclude that retentive patches of soil which can generate runoff are adjacent to transmissive patches of soil. Transmissive soils have higher hydraulic conductivities and can transmit potential runoff into deeper horizons of the soil system. This may explain observations that uncultivated hillslopes on San Cristóbal have little surface-runoff connectivity, as well as explaining how water enters the shallow groundwater system that is drained by numerous springs. Fieldwork in the Galápagos remains challenging, and our measurement and monitoring campaigns were restricted by access and resources. Our results confirm what might be presumed based on initial site assessments and field trips, namely that seasonal changes in precipitation and elevation-dependent precipitation inputs affect the soil saturation across the sites. However, our study provides concrete evidence to support the conceptual model for hillslope hydrology on San Cristóbal. These baseline data can be expanded to improve our understanding of the behavior of water through the surface soil across San Cristóbal’s climate gradient. Additional fieldwork on the hillslopes can capture the spatial distribution of soil water across the hillslopes with different precipitation inputs to accurately model the temporal stability of soil moisture distributions. The installation of more research infrastructure, especially piezometers and additional soil water probes at different points across the currently instrumented sites, will yield valuable information to help track the fate of soil water that infiltrates beneath the clay layer at each site. Testing soil-water models using the data presented in this paper can also facilitate improved quantitative understanding of factors affecting the distribution of soil water across the hillslopes, as well as predict the fate of the soil water through the water cycle on the island. Acknowledgments This work was supported by a NSF Graduate Research Fellowship grant ( DGE-1650116 ), a G eological Society of America Student Research Grant ( 10804-15 ), the NSF Science Across Virtual Institutions International Critical Zone Observatory Grant, and UNC’s Department of Geological Sciences Martin Fund awarded to M.S. Percy. All the data described in this work can be obtained by emailing the corresponding author ( madelynp@live.unc.edu ). The authors appreciate logistical collaboration with the UNC-USFQ Galápagos Science Center, particularly Leandro Vaca and Juan Pablo Muñoz. We thank Juliana Borja, Rebecca Chaisson, Sara Guevara, Claris Orellana, Sarah Schmitt, Kayla Seiffert, and Erin VanderJeudgt for field assistance. The manuscript benefited enormously from feedback provided by Kim Perkins of the U.S. Geological Survey and two anonymous reviewers. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Appendix A Supplementary data Supplementary material related to this article can be found, in the online version, at doi: https://doi.org/10.1016/j.ejrh.2020.100692 . Appendix A Supplementary data The following is Supplementary data to this article:
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10.1016_j.heliyon.2024.e39709.txt
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TITLE: A study of intergenerational support and the health relationship of the elderly population: Evidence from CHARLS
AUTHORS:
- Wang, Jinzhen
- Peng, Wenjia
- Miao, Changjun
- Bao, Yuekui
- Yang, Danhong
ABSTRACT:
Background
Currently, the relationship of intergenerational support on health is mainly focused on physical health and mental health, and there are fewer studies on the relationship of intergenerational support on self-assessed health. Therefore, this paper discusses and analyzes the possible relationship of intergenerational support on the self-assessed health of older adults in terms of the bidirectional support of various forms of support between older parents and their adult children in terms of financial, living, and emotional support(CHARLS).
Methods
This study was conducted on participants aged 65 and over, using the CHARLS 2020 survey, involving 6359 (3069 men and 3290 women) elderly people.
Health was measured in three dimensions: physical, psychological, and self-assessment; intergenerational support was measured in three dimensions: financial, life care, and spiritual comfort; and regression models analysed the relationship between intergenerational support and the health of the elderly population.
Results
Children's life care support (p < 0.05) had a significant positive association on physiological health, but a significant negative association on the elderly's psychological and self-assessed health, children's spiritual comfort support (p < 0.05) had a positive association on the elderly's physiological health, psychological health, and self-assessed health, and children's financial support (p < 0.05) was positively correlated with the elderly's psychological, and children's financial support had a positive association, but not related to physical health and self-rated health of the elderly.
Conclusions
The relationship between intergenerational support and the health of the older population is complex, with life-care support significantly contributing to physical health but negatively affecting mental health and self-assessed health; spiritual comfort support positively affecting physical, mental and self-assessed health; and financial support having a primarily positive effect on mental health. Therefore, children should fully respect and utilise the ‘autonomy’ of the elderly when providing intergenerational support to the elderly in their families. It is also important to improve intergenerational communication abilities and skills, which will help to better understand and fulfil the needs of older people, thereby promoting their physical and mental health.
BODY:
1 Introduction Globally, population ageing has become a common and increasingly serious social phenomenon [ 1–3 ]. With the advancement of medical technology and socio-economic development, the life expectancy of human beings continues to increase, the proportion of elderly people is growing rapidly, and the issue of elderly health has gradually become a hot field of social science research around the world [ 4–6 ]. Most studies have examined the impact of intergenerational support on health in old age from a single dimension, and there are differences between urban and rural areas. With the shift to smaller family structures, the role of intergenerational support in the health protection of the elderly has become more prominent, emphasizing the need to pay attention to the needs of different groups of elderly people and to develop differentiated support strategies. Elderly health is not only related to the quality of life of individuals, but also has a far-reaching impact on socio-economic development, healthcare system and social security system. However, the elderly are currently facing various health threats, such as depression and other mental health problems, which are highly prevalent among the elderly population, with a prevalence rate of 25.6 % and on the rise [ 7 , 8 ], while the proportion of disabled and semi-disabled elderly people also accounts for 18.3 % of the elderly population, a figure that is also worrying [ 9 ]. These health problems place a tremendous pressure of life and financial burden on older persons and their families. In order to address this global challenge, governments and international organizations have promoted healthy ageing as an important strategy, such as the introduction of China's "Healthy China 2030" planning document [ 10 ]; the Japanese Government's implementation of a long-term care insurance system [ 11 ]; and the European Union's development of a healthy ageing strategy [ 12 ]. These policy documents not only emphasize the need to sustain the development and maintenance of healthy lives for older persons, but also propose specific goals and measures to promote healthy ageing. Within the framework of the theory of health ecology, the factors influencing the health of older persons involve the individual, family and social levels. However, with the changes in family structure and the diversification of residence patterns globally, the intergenerational supportive role of the family in providing life care, economic support and spiritual comfort is also changing. Although a large number of studies have examined the relationship of child support on the health of the elderly population [ 13–16 ], there is a large inconsistency in the findings due to differences in study locations, study populations, and measurement indicators. This inconsistency may stem from sample selection bias, one-sidedness of indicators, and ignorance of the complexity and inter-causality of social factors. Therefore, in order to gain a deeper understanding of the relationship between intergenerational support and the health of the elderly population and to overcome the limitations of existing studies, this study intends to analyze the data based on a national survey in China. The health status of older adults was comprehensively assessed in terms of three dimensions: physical, psychological and self-assessment, while intergenerational support was comprehensively measured in terms of three dimensions: economic, life care and spiritual comfort. We speculated that life-care support significantly promoted physical health but had a negative impact on mental health and self-rated health; spiritual comfort support had a positive impact on physical, mental and self-rated health; and financial support had a positive effect mainly on mental health. Through this research design, we aim to reveal the specific relationship of intergenerational support on the health of the elderly population in different dimensions and its mechanism of action, so as to provide a scientific basis for the formulation of more effective health promotion policies. 2 Methods 2.1 Study population The current study is based on the China Health and Retirement Longitudinal Study (CHARLS), an ongoing, nationally representative longitudinal program. Inclusion criteria: 1) age ≥45 years; 2) residence in China; and 3) informed consent for this study. Residents are aged 45 years and older, including more than 19,000 people in 150 county-level units, 450 village-level units, and about 10,000 households.A baseline survey was conducted in 2011, and waves 2, 3, 4, and 5 were followed in 2013, 2015, 2018, and 2020, respectively in Fig. 1 . The questionnaire included the basic personal and family status of the elderly, their social and economic background and family structure, self-evaluation of their health and quality of life status, personality and psychological characteristics, cognitive functioning, lifestyle, ability to perform daily activities, economic sources, financial status, life care, caregivers when sick, whether they could get timely treatment and medical bill payers, and other ninety questions with more than 180 Details of the research design and sampling methodology of the CHALRS have been described by Zhao et al. [ 17 ]. This study uses data from the 2020 cross-sectional survey with a total valid sample of 6359 participants. Participants were excluded based on the following exclusion criteria: 1) age ≥65 years; 2) groups with missing values for key indicators; and 3) health conditions, such as memory-related disorders or psychiatric problems. A valid sample of 6359 participants remained.The CHARLS survey was approved by the Biomedical Ethics Committee of Peking University (IRB00001052-11015), and all participants were required to sign an informed consent form. 2.2 Variable selection 2.2.1 Independent variables Intergenerational support was used as the independent variable in this study, which was comprehensively measured in three separate areas: life care, spiritual comfort, and financial support. The corresponding measurement questions were, "Is life care support received?", "Do they receive spiritual comfort support?" and "Do they receive financial support?" The corresponding questions were: "Do you receive care support? A value of 1 was assigned to a "yes" answer and a value of 0 to a "no" answer. 2.2.2 Dependent variables In this study, the health status of older adults was used as the dependent variable, and three dimensions of physical health, mental health, and self-assessed health were comprehensively assessed. In terms of physical health, the Ability to Perform Activities of Daily Living (ADL) scale was used to measure the basic mobility of older adults, which is a relatively objective measure. The questions in the scale cover six daily activities: bathing, dressing, eating, toileting, bowel control, and getting in and out of bed, and the ability to take care of themselves is assessed by asking the elderly whether they need help from others in these activities. According to the level of assistance needed, the answers were categorized into three options: "No difficulty, no help needed", "Some difficulty, need help", and "Can't do it, must get help". The answers were categorized as "no difficulty, no need help", "some difficulty, need help" and "can't do it, must get help". Based on the study by Yen Yueh-Ping, if an elderly person can complete all six activities in the ADL scale on his/her own without assistance, he/she is considered as not disabled (ADL = 0); if he/she has difficulties in one or more activities or is unable to complete them, he/she is considered as disabled (ADL = 1). In terms of mental health, this study used the Depression Scale, a relatively subjective measure, to assess the psychological state of the elderly. The scale consists of 10 entries with response options including "always", "often", "sometimes", "seldom ", "never", and "refused to answer". The total score ranges from 10 to 50, with higher scores indicating more depressive tendencies and poorer mental health. In this study, we refer to the depression evaluation criteria of the scale, and consider older adults with a score of 30 or more as having a tendency to depression, while those with a score of less than 30 are considered to be psychologically healthy. In terms of self-assessment of health, the question "What do you think about your health condition?" to find out the elderly's subjective assessment of their health. Answer options included "very good", "good", "fair", "not good" and "still very bad". "still very bad". Based on previous research, self-assessed health was set as a dichotomous variable: it took the value of 1 when the respondent answered "very good" or "good", and "fair" when the respondent answered "fair", "not good" or "very bad" and 0 when respondents answered "fair", "not good" or "very bad". 2.2.3 Covariates A total of six Covariates were included in this study based on the results of previous studies and the data provided by CLHLS2020, including gender, age, marital status, alcohol consumption, pension status, and nature of residence of the elderly. The details are shown in Table 1 . 2.3 Statistical methods The qualitative data in this study are represented in relative quantities and proportions, and the Chi-square test is employed to analyze the correlation between intergenerational support and the health of the elderly population. After considering endogeneity, a logistic regression model is used to analyze the relationship between intergenerational support and the physical health, mental health, and self-rated health of the elderly population. All statistical analyses were performed using R software, version 4.1.0 (University of Auckland, New Zealand). p-value <0.05 was considered statistically significant. 3 Results 3.1 Basic characteristics of study population Finally, a total of 6359 participants were enrolled. The detailed selection process was presented in Fig. 2 .In this study, a total of 6359 elderly people were surveyed, of whom 3069 (48.26 %) were male and 3290 (51.74 %) were female; their ages were mainly concentrated in the age range of 65–74 years, with a total of 4722 (74.26 %); in terms of life support, 63.58 % of elderly people did not receive life support, 78.35 % of elderly people received spiritual comfort, and 66.80 % of elderly people received financial support. In terms of health, 24.19 of the elderly were disabled, 12.96 per cent were psychologically depressed, and 79.59 per cent were self-assessed as unhealthy. Marriage and residence show that 72.95 per cent of older persons have a spouse, 84.84 per cent receive a pension and 72.62 per cent live in rural areas. In terms of living habits, 76.33 per cent of older persons do not drink alcohol and 76.08 per cent do not smoke, as detailed in Table 2 . 3.2 Correlation analysis between intergenerational support and health of the elderly population According to the results analysed in Table 3 , intergenerational support is significantly correlated with the psychology of the elderly population, while life care support and spiritual comfort support are also significantly correlated with both physiological health and self-assessed health of the elderly population. In terms of physiological health, 60.96 % of the non-disabled elderly did not receive life care support, 16.59 % did not receive mental comfort support, and 33.64 % did not receive financial support; while only 71.78 % of the disabled elderly did not receive life care support, and also 37.52 % did not receive mental comfort support, and 31.79 % did not receive financial support. In terms of mental health, 62.89 per cent of the elderly without a tendency to depression did not receive support for living care, 20.43 per cent did not receive support for mental comfort, and 33.75 per cent did not receive financial support; 68.20 per cent of the elderly with a tendency to depression did not receive support for living care, 29.85 per cent did not receive support for mental comfort, and 29.49 per cent did not receive support for mental comfort. 29.49 per cent did not receive financial support. With regard to self-assessed health, 64.43 per cent of the elderly who considered themselves unhealthy did not receive life-care support, while 22.43 per cent did not receive spiritual comfort support and 32.76 per cent did not receive financial support; while 60.25 per cent of the elderly who considered themselves healthy did not receive life-care support, 18.64 per cent did not receive life-care support and 34.90 per cent did not receive financial support. elderly people did not receive financial support, as shown in Table 3 . 3.2.1 Logistic regression model analysis of intergenerational support and health of the elderly population Analysis of the regression results shows that in Model 1, there is a significant positive correlation between life care support, spiritual comfort and the physical condition health of the elderly population, with specific coefficients of 1.533 and 2.280, respectively. however, there is no significant correlation between financial support and the physical health condition of the elderly population. In model 2, life care support and financial support are significantly negatively associated with the tendency to depression in the elderly population with a coefficient of −1.198; on the contrary, spiritual comfort support is significantly positively associated with the tendency to depression in the elderly population with a coefficient of 1.226. In model 3, it is found that life care support has a significant negative correlation with the self-assessed health status of the elderly population, with a coefficient of −0.842, and spiritual comfort support has a significant positive correlation with the self-assessed health status of the elderly population, with a specific coefficient of 1.533 and 2.280. population's self-assessed health status with a significant positive correlation and a coefficient of 0.814. It is worth noting that in this model, there is no significant relationship between financial support and the physical health and self-assessed health status of the elderly population, as detailed in Table 4 . 4 Discussion 4.1 Life care has a significant positive association on the physical health of older people, but a negative association on mental health and self-assessed health status After in-depth exploration, this study found that the positive association of life care support on the physical health of older adults was particularly significant, a finding that coincides with previous research by Zheng Zhidan and several other scholars [ 18–20 ]. Analysing the reasons for this, we hypothesize that this is mainly attributed to the meticulous care provided by children to the elderly. Such care not only effectively reduces the mobility stress of the elderly in their daily lives and frees them from heavy housework, but more importantly, it largely reduces the risk of potential physical damage to the elderly [ 21 ]. In addition, citing Hu Chenpei's research findings, we found that the caregiving support provided by children also empowered the elderly to have more leisure time and abundant energy to engage in appropriate physical exercise, which undoubtedly had a profound positive association on their physical health [ 22 ]. However, caregiving support had a negative association on older people's mental health and self-rated health. This may be due to the fact that excessive caregiving leads to dependency among older people, reducing their sense of autonomy and self-efficacy, which in turn has a negative association on psychological well-being. At the same time, over-care may also make older people feel less well, which may affect their self-rated health [ 23 ]. This finding suggests the need for moderation and attention to the psychological needs of older people when providing them with life care support in order to promote their overall health [ 24 ]. 4.2 Children's spiritual comfort support has significant positive association on physical health, psychological health and self-rated health of older people This study further found that spiritual comfort has a significant positive contribution to physical health and mental health of older adults, a result that is in line with previous studies [ 25–27 ].Spiritual comfort has a significant positive contribution to the self-rated health of older adults, which is consistent with the findings of Wang Dan et al. [ 28 ]. On the one hand, this may be because as they grow older, older adults may face challenges such as changes in physical health, adjustments in their living environment, and narrowing of their social circle, which bring anxiety and loneliness; children's care, listening, and understanding provide older adults with an outlet for emotional catharsis, enabling them to release their inner repression and dissatisfaction, thus effectively relieving psychological stress and maintaining a good psychological state (c) Children can make the elderly feel the warmth and care of the family through companionship, communication and the provision of emotional support. This kind of support not only makes the elderly feel that they are still needed and cherished, but also stimulates their love and confidence in life [ 29 , 30 ]. At the same time, the spiritual comfort of their children can also help the elderly to better cope with the difficulties and challenges in their lives and improve their mental resilience, thus positively contributing to their physical and mental health. 4.3 Children's financial support has a positive association on the psychological health of the elderly, but is not related to their physical health and self-rated health The results of the study show that children's financial support can positively influence the mental health of older adults, which is consistent with the findings of Sun Jingkai et al. [ 31–33 ]. It may be on the one hand because as they age, older adults may face financial problems such as insufficient pensions and increased medical costs. Financial support from their children, whether regular living expenses are given or irregular financial assistance, can improve the financial situation of the elderly to a certain extent, so that they don't have to worry about the basic living expenses and medical costs, and this sense of financial stability helps to reduce the level of anxiety and stress among the elderly, which in turn positively affects their mental health; on the other hand, the elderly who receive financial help from their children [ 34 ]. On the other hand, when the elderly receive financial help from their children, they will also feel the care and love of their children, which will make them feel that they are still valuable to their families, thus enhancing their self-esteem and sense of self-worth [ 35 ]. 4.4 Strengths and limitations of this study The innovation of this study is that it is the first time to comprehensively assess the impact of intergenerational support on geriatric health from the three dimensions of physiological, psychological, and self-assessed health, which fills the gap of single-dimension research; at the same time, it utilises the CHARLS dataset, which is nationally representative, which enhances the representativeness and reliability of the study; and it explores in depth the specific mechanisms of action of the different types of intergenerational support, which provides a precise geriatric health policy with a scientific basis. However, there are limitations in this study, including the cross-sectional design cannot effectively observe the long-term cumulative impact of intergenerational support, it may be difficult to completely avoid endogeneity problems due to the large health disparities caused by the fact that the study population is a special group, and it is difficult to comprehensively reflect the dynamic changes of intergenerational support with a single point in time observation. In summary, with the gradual trend of empty nesting and miniaturisation of elderly families in China, the association of intergenerational support on the health of the elderly has become increasingly complex. There is a bidirectional relationship between intergenerational support and health in old age: on the one hand, intergenerational support will have an association on the health status of the elderly; on the other hand, the health status of the elderly will also lead families to adjust the way of intergenerational support. At the same time, different types of intergenerational support will have different associations on the health of the elderly. When providing support to the elderly in the family, children should focus on the appropriateness and reasonableness of the approach, respect the autonomy of the elderly, and support the elderly to play the role of self-supporting, avoiding excessive intervention in the lives of the elderly. It is recommended that a health management information system integrating health monitoring, emergency contact, personalized advice, interactive learning and social functions be established to enhance the self-management capacity of older persons and to promote healthy ageing in conjunction with the Government, the community and the family. Elderly people generally do not have enough knowledge about health and their health behaviours need to be improved [ 36 ]. Through communication with their children, older people can acquire more health knowledge and improve their ability to self-support themselves in the process of strengthening their children's interaction. The government and society should pay attention to interpersonal communication training and counselling for elderly families, enhance the ability of both children to provide mental comfort, promptly resolve negative emotions arising from children's support, and correct erroneous health perceptions and lifestyles in order to maintain the mental health of the elderly. At the same time, family support policies should be improved, social resources should be integrated, and the development of community-based home care services should be promoted [ 37 ], so as to raise children's awareness of their responsibility to care for the elderly. Comprehensive and differentiated interventions should also be adopted to address the characteristics of different elderly people, strengthen geriatric health care and enhance health literacy, so as to strengthen the supportive role of family elderly care and promote the realisation of healthy ageing [ 38 ].Future research could further explore: the use of longitudinal studies to track the cumulative effects of changes in intergenerational support on the health of older persons over time; in-depth analyses of the mechanisms of action and interaction effects of different types of intergenerational support; and the expansion of the scope of research to explore the similarities and differences in the relationship between intergenerational support and health of older persons in different regions and cultural contexts. CRediT authorship contribution statement Jinzhen Wang: Writing – original draft, Formal analysis, Data curation. Wenjia Peng: Writing – review & editing, Resources. Changjun Miao: Project administration, Methodology. Yuekui Bao: Writing – review & editing, Software. Danhong Yang: Writing – review & editing, Supervision. Contributors PW and YD were responsible for drafting and revising the manuscript. WJ analysed and interpreted the data and prepared the figures and tables. BY and MC revised the manuscript, while WJ refined the language. The final version of the manuscript was read and approved by all authors. Patient consent to publication Not applicable. Ethical approval The CHARLS survey project received approval from the Peking University Biomedical Ethics Committee (IRB00001052-11015), and all participants provided written informed consent prior to the survey. Data availability statement The CHARLS datasets generated and analysed during the current study are available on the CHARLS website at http://charls.pku.edu.cn/en . CHARLS data are de-identified. Respondents are identified by a unique ID number. Funding This research did not receive any specific grants from any funding bodies in the public, commercial, or not-for-profit sectors. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements We express gratitude to the CHARLS team for providing the datasets and training. This study was supported by the Health Committee of Jinshan District , Shanghai ( JSKJ-KTMS-2021-10,2022-WS-59 ).
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1. ROSEMARY G (2023)
2. TODA K (2023)
3. S M (2023)
4. XIAOMENG W (2022)
5. PEJMAN S (2022)
6. BO T (2021)
7. PEYMAN M (2023)
8. RONG J (2020)
9. LI C (2023)
10. ZHANG X (2020)
11. YOICHIRO Y (2022)
12. CRISTEA M (2020)
13. LANLAN C (2023)
14. ZHAO L (2023)
15. PATAPORN S (2023)
16. LIANLIAN L (2022)
17. YAOHUI Z (2014)
18. ZHIDAN Z (2017)
19. ZUO D (2011)
20. HOU J (2021)
21. HU P (2024)
22. HU C (2016)
23. IOST P (2023)
24. SBIRAKOS V (2021)
25. AJROUCH K (2007)
26. FENGJEN T (2013)
27. QINGYAN S (2022)
28. WANG D (2023)
29. WILLIAMS W (2018)
30. KEENOY J (2023)
31. HAN S (2024)
32. SUN J (2021)
33. ROMERO F (2024)
34. ROSTAN Z (2022)
35. ALVES S (2022)
36. YIMIN Q (2023)
37. PIERLUC T (2020)
38. LUO L (2021)
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10.1016_j.chpulm.2024.100119.txt
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TITLE: A 77-Year-Old Man With Unexplained Hypoxemia
AUTHORS:
- Pasqualicchio, Patrick
- Siow, Maria
- Peiris, Shanaka
- Arif, Imran
- Sukhija, Rishi
- Elwing, Jean
- Jose, Arun
ABSTRACT: No abstract available
BODY:
Case Presentation A 77-year-old male with small cell lung cancer and recently diagnosed radiation pneumonitis presented to the emergency department after he was found to be hypoxemic at an outpatient appointment, with pulse oximetry demonstrating an oxygen saturation (Sp o 2 ) of 60% to 70%, refractory to supplemental oxygen up to 6 L/min. Before admission, he did not require supplemental oxygen. His medical history was notable for hypertension and hyperlipidemia with no known history of intracardiac defects. On arrival to the emergency department, he was escalated to 15 L/min, with improvement in Sp o 2 to 80%. He demonstrated worsening hypoxemia when sitting upright, which was relieved when recumbent in the left lateral decubitus position. An expedited workup for hypoxemic respiratory failure was pursued. CT imaging was negative for acute pulmonary thromboembolism, but demonstrated widespread bilateral ground glass opacities ( Fig 1 ). Review of current CT imaging compared with 1 month prior demonstrated interval progression of radiographic abnormalities. A transthoracic echocardiogram with agitated saline demonstrated dyssynergic interventricular septal motion, with large right-to-left atrial shunting evidenced by early appearance of bubbles within 3 to 5 cardiac cycles. There was no dilation of the right-sided heart chambers, and function of the left and right ventricles was subjectively normal. No tricuspid regurgitant jet was visualized, and pulmonary artery systolic pressure was unable to be calculated. Laboratory testing (CBC count, comprehensive metabolic panel, and coagulation studies) was unremarkable, with the exception of an A-a gradient of 351.3 mm Hg on arterial blood gas. Given the findings on chest imaging, the patient was given a diagnosis of radiation pneumonitis resulting in acute hypoxemic respiratory failure, thought to precipitate right-to-left intraatrial shunting due to an underlying intracardiac defect and concomitant elevated pulmonary vascular pressures. As a result, the patient was treated with supplemental oxygen, systemic glucocorticoids, and diuretics. After 14 days of 500-mg daily IV methylprednisolone therapy, an unusually high dose and duration because of the patient’s severity on presentation and do-not-intubate code status limiting therapeutic options in the event of deterioration, repeat CT imaging demonstrated a marked improvement in the extent of parenchymal abnormalities ( Fig 2 ). However, the patient’s acute hypoxic respiratory failure had paradoxically worsened with an Sp o 2 of 75% to 85% while on 100% F io 2 and 70 L/min via high-flow oxygen therapy, prompting a more extensive workup. Right heart catheterization performed 16 days after admission demonstrated low filling pressures in the absence of pulmonary hypertension or a step-up in oxygenation ( Tables 1, 2 ). An incomplete shunt run and the absence of pulmonary vein or wedge position saturation precluded calculation of the pulmonary to systemic blood flow (Qp/Qs) ratio for shunt quantification. The cardiac output listed in Table 1 refers to the Qs systemic values. A transesophageal echocardiogram (TEE) was also performed, identifying a large patent foramen ovale (PFO) and a small fenestrated atrial septal defect (ASD) measuring 1.0 cm, composed of a bidirectional atrial level shunt with a prominent eustachian valve and concomitant atrial septal aneurysm, which we will refer to as a complex PFO ( Fig 3 ). What is the diagnosis? Diagnosis: Platypnea-orthodeoxia syndrome secondary to a complex PFO Given the patient’s refractory hypoxemia, closure of the atrial shunt was attempted. Intracardiac echocardiography (ICE) evaluation of the interatrial septum confirmed the presence of a complex PFO ( Fig 4 A). A 37-mm Gore Cardioform ASD Occluder was deployed under fluoroscopic and echocardiographic guidance, allowing for closure of the communication with no visible shunting with Doppler. Immediately after device deployment, the patient’s oxygen saturation improved from 84% to 100%, and he was rapidly weaned off supplemental oxygen. Discussion Clinical Discussion Platypnea-orthodeoxia syndrome (POS) is a rare disorder characterized by hypoxemia that worsens when upright, improving with recumbency. First described in 1949, the prevalence is unknown; however, the incidence is increasing, mainly due to increased awareness and improvements in diagnosis. It can be caused by intracardiac shunts, pulmonary arteriovenous shunts, or ventilation/perfusion mismatch in the lungs and can lead to significant hypoxemia in the absence of elevated right-sided pressures, which often complicates diagnosis. 1 Intracardiac shunts constitute 87% of POS cases, and can consist of either a PFO or an ASD, with or without concomitant or atrial septal aneurysm. 1 2 In POS due to intracardiac shunts, postural changes are thought to create a pressure gradient favoring blood flow from right-to-left across the atrial septum, resulting in hypoxemic respiratory failure. The mechanisms behind these postural hemodynamic abnormalities are not well understood, but stretching and horizontalization of the atrial septum creating a jet-like flow directly from the vena cava through a (low-resistance) interatrial communication are thought to play a role. This process is also thought to contribute to the positional variation in hypoxemia observed in POS; the upright position more closely aligns flow from the vena cava with the atrial septum as the heart is pulled down by gravity, widening the defect, while simultaneously decreasing venous return to the heart, and reducing right atrial pressure. Calculating the shunt ratio of pulmonary to systemic blood flow (Qp/Qs) can be helpful in quantifying the presence and directionality of an intracardiac shunt; however, this requires oxygen saturation recorded from the pulmonary artery and pulmonary vein/wedge position (for Qp), and the aorta and both inferior and superior vena cava (to calculate true mixed venous saturation for Qs). In this case, the lack of a full shunt run prevented calculation of the Qp:Qs ratio; however, we were able to support the diagnosis of POS secondary to a complex PFO by relying on advanced imaging (TEE and ICE) and postural oxygenation changes seen in the patient. Positional pulse oximetry (not performed in this case) can be useful in characterizing orthodeoxia platypnea when evaluating challenging cases. Though present in this case, dyssynergic interventricular septal motion is not thought to contribute to the pathophysiology of POS resulting hypoxemic respiratory failure and may have been a spurious finding further complicating the diagnosis. 1 It is unclear exactly why the patient suddenly manifested acute hypoxemic respiratory failure from shunting through a preexisting (undiagnosed) complex PFO, or what process acutely changed the position of the atrial septum relative to the PFO to result in POS. Although we did not have direct radiographic evidence confirming an acute shift in atrial position, this sequence of events is supported by the persistence of hypoxemic respiratory failure despite improvement in the burden of pulmonary parenchymal abnormalities with empirical treatment for radiation pneumonitis and resolution of hypoxemia only after closure of the cardiac defect. When an intracardiac shunt is identified in the setting of POS, definitive management involves closure of the defect. Percutaneous PFO closure is preferred to a surgical approach because it has lower morbidity and has been proven to be effective with minimal long-term complications. 2 2 , The 2008 American College of Cardiology/American Heart Association 3 guidelines recommend closure of an ASD in the setting of documented POS (class IIa). Given the patient’s refractory hypoxemia and complex PFO, closure of the atrial defect was attempted using a 37-mm Gore Cardioform ASD Occluder under fluoroscopic and ICE guidance ( 4 Fig 4 C). Although a 27-mm device would be typical for a defect of 1.0 cm, a larger device was selected given the patient’s hypermobile and redundant atrial septum to maximize stability and cover both defects with 1 device. After device placement, ICE confirmed correction of interatrial shunting ( Fig 4 D), and the patient’s oxygen saturation immediately improved from 84% to 100%. In the days after the procedure, the patient was rapidly weaned off supplemental oxygen, maintaining oxygen saturations > 90% on ambient air. Radiologic Discussion Plain chest radiograph was deferred on admission in lieu of dedicated CT imaging of the chest, which demonstrated interval worsening of pulmonary parenchymal disease, with widespread bilateral ground glass opacities with areas of consolidation, supporting the initial diagnosis of radiation pneumonitis ( Fig 1 ) precipitating secondary right-to-left interatrial shunt and acute hypoxemic respiratory failure. However, the presence of refractory acute hypoxemic respiratory failure despite improvement in the burden of pulmonary parenchymal disease appreciated on CT imaging ( Fig 2 ) raised the possibility of an alternate diagnosis, supporting more aggressive investigation of the underlying interatrial shunting and justifying the invasiveness of TEE imaging. Subsequent TEE investigation revealed a bidirectional atrial level shunt concerning for a large PFO involving a fenestrated ASD ( 5 Figs 3 A, 3B), prompting ICE evaluation. ICE is an imaging modality that provides the same quality images as TEE for diagnostic purposes, but also simultaneously guides catheter-based interventions. In this patient, ICE was able to confirm the presence of bidirectional interatrial shunting ( 6 Fig 4 A) due to a complex PFO ( Fig 4 B). Additionally, a prominent eustachian valve was observed where the inferior vena cava met the right atrium, which may have played a role in channeling blood through the atrial defect ( Fig 3 C). A single closure device rather than 2 separate devices for the ASD and PFO components was used given the characteristics of the defect. The use of ICE allowed for simultaneous confirmation of a complex cardiac defect and real-time visualization of corrective intervention ( Fig 4 C) that completely corrected the patient’s interatrial shunting ( Fig 4 D) and almost immediately resulted in resolution of the patient’s hypoxemic respiratory failure without the need for general anesthesia. Conclusions • In patients with refractory hypoxemia, particularly those with positional variation of their hypoxemia and a diagnostic workup incongruent with their clinical course, the appropriate application of advanced diagnostics (eg, TEE, ICE) can be helpful to reconcile discordant data and identify unusual etiologies of hypoxemia (eg, POS). • Although rare, POS caused by intracardiac shunt responds well to closure, with 95% of patients experiencing symptomatic and clinical improvement. • ICE is a powerful tool that can simultaneously characterize a patient’s physiology and guide intervention in cases of POS with intracardiac shunting without the need for TEE and general anesthesia. Financial/Nonfinancial Disclosures None declared (P. P., M. S., I. A., and R. S.). A. J. reports investigator-initiated research supported by United Therapeutics, and has served on the Consultant or Advisory board for Merck and Janssen. J. M. E. has received research grant support from Janssen, United Therapeutics, Liquidia, Phase Bio, Gossamer Bio, Bayer, Merck, Altavant, Aerovate, Tenax, and Pharmosa, and serves on the consultant or advisory board of United Therapeutics, Altavant, Aerovate, Bayer, Gossamer Bio, Liquidia, Merck, and Janssen. Acknowledgments Author contributions: P. P. is the guarantor of this case and had full access to all the data in the case and takes responsibility for the integrity of the data and the accuracy of its analysis. P. P. aided in writing and revising the paper and coordinated discussions between coauthors. M. S. aided in interpreting data and writing and revising the paper. S. P. aided in selecting and analyzing TEE and ICE images, and in responding to reviewer requests. I. A. and R. S. aided in selecting TEE and ICE images, labeling and interpreting them and incorporating them into the case. J. E. supervised the writing and revision of the case and provided guidance on key components of the paper. A. J. supervised the writing and revision of the case and provided guidance on key components of the paper. Other contributions: CHEST Pulmonary worked with the authors to ensure that the Journal policies on patient consent to report information were met.
REFERENCES:
1. RODRIGUES P (2012)
2. AGRAWAL A (2017)
3. DELGADO G (2004)
4. WARNES C (2008)
5. DEBELDER M (1992)
6. VITULANO N (2015)
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10.1016_j.nbd.2012.06.008.txt
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TITLE: Activation of the γ-secretase complex and presence of γ-secretase-activating protein may contribute to Aβ42 production in sporadic inclusion-body myositis muscle fibers
AUTHORS:
- Nogalska, Anna
- D'Agostino, Carla
- Engel, W. King
- Askanas, Valerie
ABSTRACT:
The muscle-fiber phenotype of sporadic inclusion-body myositis (s-IBM), the most common muscle disease associated with aging, shares several pathological abnormalities with Alzheimer disease (AD) brain, including accumulation of amyloid-β 42 (Aβ42) and its cytotoxic oligomers. The exact mechanisms leading to Aβ42 production within s-IBM muscle fibers are not known.
Aβ42 and Aβ40 are generated after the amyloid-precursor protein (AβPP) is cleaved by β-secretase and the γ-secretase complex. Aβ42 is considered more cytotoxic than Aβ40, and it has a higher propensity to oligomerize, form amyloid fibrils, and aggregate. Recently, we have demonstrated in cultured human muscle fibers that experimental inhibition of lysosomal enzyme activities leads to Aβ42 oligomerization.
In s-IBM muscle, we here demonstrate prominent abnormalities of the γ-secretase complex, as evidenced by: a) increase of γ-secretase components, namely active presenilin 1, presenilin enhancer 2, nicastrin, and presence of its mature, glycosylated form; b) increase of mRNAs of these γ-secretase components; c) increase of γ-secretase activity; d) presence of an active form of a newly-discovered γ-secretase activating protein (GSAP); and e) increase of GSAP mRNA. Furthermore, we demonstrate that experimental inhibition of lysosomal autophagic enzymes in cultured human muscle fibers a) activates γ-secretase, and b) leads to posttranslational modifications of AβPP and increase of Aβ42. Since autophagy is impaired in biopsied s-IBM muscle, the same mechanism might be responsible for its having increased γ-secretase activity and Aβ42 production. Accordingly, improving lysosomal function might be a therapeutic strategy for s-IBM patients.
BODY: No body content available
REFERENCES:
No references available
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10.1016_j.nbd.2008.01.002.txt
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TITLE: Cerebellar granule cells transplanted in vivo can follow physiological and unusual migratory routes to integrate into the recipient cortex
AUTHORS:
- Williams, Ian Martin
- Carletti, Barbara
- Leto, Ketty
- Magrassi, Lorenzo
- Rossi, Ferdinando
ABSTRACT:
CNS repair by cell transplantation requires new neurons to integrate into complex recipient networks. We assessed how the migratory route of transplanted granule neurons and the developmental stage of the host rat cerebellum influence engraftment. In both embryonic and postnatal hosts, granule cells can enter the cerebellar cortex and achieve correct placement along their natural migratory pathway. Donor neurons can also reach the internal granular layer from the white matter and integrate following an unusual developmental pattern. Although the frequency of correct positioning declines in parallel with cortical development, in mature recipients correct homing is more frequent through the unusual path. Following depletion of granule cell precursors in the host, more granule neurons engraft, but their ability for achieving correct placement is unchanged. Therefore, while the cerebellar environment remains receptive for granule cells even after the end of development, their full integration is partially hindered by the mature cortical architecture.
BODY: No body content available
REFERENCES:
No references available
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10.1016_j.rineng.2025.105468.txt
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TITLE: Chaos game optimization for extracting global MPP of PV System based high-efficiency triple-junction solar cell
AUTHORS:
- Ghadbane, Houssam Eddine
- Rezk, Hegazy
- Benhammou, Aissa
- Mohamed, Ahmed F.
ABSTRACT:
High-efficiency triple-junction solar cells (TJSC) have received more attention in concentrated solar photovoltaic (PV) systems because of their ultimate feathers. In this paper, chaos game optimization (CGO) is used for extracting the global maximum power point (MPP) of high efficiency InGaP/InGaAs/Ge TJSC based PV system considering partial shading (PS). With PS, the power versus voltage characteristics comprises some local MPPs and unique global ones. Consequently, traditional MPP tracking approaches cannot discriminate between global and local points and are always stuck with local MPP. In this case, the PV power is reduced, and hence, an optimization algorithm such as CGO is highly required to mitigate the PCS of the PV system. To prove the dependability of CGO in extracting the global MPP, four PS patterns are used to test the superiority of CGO in cases of changing the position of the global MPP. A comparison with another optimzation algorithms also considered and the results confirmed the superiority of CGO compared with other algorithms. As an example, in the first PS pattern, the average PV power levels were between 865.67 W and 993.89 W. The maximum power that CGO can achieve is 993.89 W whereas when using COOT, the lowest power output is 865.67 W. In addition, CGO achieves the lowest STD of 0.032.
BODY:
1 Introduction Multi-junction solar cell (MJSC) combines materials with different energy band-gaps into one PV solar cell (SC) [ 1 , 2 ]. This permits promising high-efficiency solar cells because the MJSC extends the usable spectrum of solar energy makes the SC efficiency far more than the best efficiencies achievable by traditional single-junction SCs [ 3 , 4 ]. The efficiency of MJSC reached to 44 % with a concentration ratio of 947 suns [ 3 ]. Generally, the triple-junction solar cell (TJSC) uses GaAs as a middle sub-cell since its near-perfect material quality, despite its bandgap being higher than optimal for the global spectrum [ 5 ]. A new mathematical model to simulate the MJSC is proposed by Ferhati et al. [ 1 ]. The model is based on the aspect of interfacial potential. Zilong et al. examined the characterization of the InGaP/InGaAs/Ge TJSC with a two-stage dish-style concentration [ 3 ]. The results demonstrated that with a solar irradiance level of 450 W/m2 and a temperature lower than 64.9 C, the output power and efficiency are 1.52 W/cm 2 and 29.3 %, respectively. Under this case, the output power and efficiency increased by 23.3 % and 9.1 % respectively compared to single stage concentrating system [ 6 ]. The relation between the TJSC temperature and efficiency was investigated by Almonacid et al. [ 6 ]. The results demonstrated that the InGaP/lnGaAs/Ge TJSC efficiency diminished from 39 % to 31 % with increasing the temperature 25 C to 100 C under a geometric concentration ratio of 200. The characteristics of TJSC are non-linear; under uniform distribution of solar radiation, there is one maximum power point (MPP) which can be easily extracted using any conventional MPP tracker such as perturb and observe, hill climbing and fuzzy logic [ 7 ]. Samavat et al. used modern optimzation algorithms to optimize the membership functions and rules of the fuzzy logic [ 7 ]. At the same time, Partial shading condition (PSC) has a significant impact on PV systems [ 8 ]. Under PSCs, several MPPs appear on the power against the voltage curve [ 9 , 10 ]. This poses a challenge for conventional MPP methods to precisely extract the global MPP because conventional MPP methods cannot distinguish between global and local MPPs. Accordingly, the conventional MPP method frequently converges to a local MPP, leading to declined harvested energy from the PV system [ 11 ]. To mitigate the shading condition and ensure extracting the global MPP, optimzation algorithms such red-tailed hawk algorithm [ 12 ], modified tunicate swarm algorithm [ 13 ], musical chairs algorithm [ 14 ], grey wolf optimizer [ 15 ], Archimedes optimization algorithm [ 16 ] and Marine predator algorithm [ 17 ] as are used. In the current research work, CGO is used to extract the global MPP of high-efficiency InGaP/InGaAs/Ge TJSC-based PV systems while considering PSC. To demonstrate the reliability of CGO n tracking the global MPP, four different shading scenarios are taken into consideration. The idea is to use different shading scenarios to change the position of the global MPP. A comparison with recent optimization algorithms was also carried out, including eel & grouper optimizer (EGO) [ 18 ], COOT algorithm [ 19 ], puzzle optimization algorithm (POA) [ 20 ], northern goshawk optimization (NGO), leaders harris hawk optimization (LHHO), harris hawk optimization (HHO), ant lion optimizer (ALO), red kite optimization (ROA), gradient-based optimizer (GBO), equilibrium optimizer (EO), Marine predators’ algorithm (MPA) and particle swarm optimization (PSO) [ 21 ]. The contributions of the paper can be summarised as follows. • For the first time, CDO is applied to extract the global MPP of a high-efficiency InGaP/InGaAs/Ge TJSC-based PV system. • A comprehensive comparison with recent optimzation algorithms is carried out. • Validating the superiority of the proposed global MPPT The rest of the paper is organized as follows. The model of InGaP/InGaAs/Ge TJSC and related formulas are explained in Section 2 . Section 3 presents the methodology which contains two parts: chaos game optimization algorithm and problem formulation. The obtained results are discussed in Section 4 and finally the conclusions were highlighted in Section 5 . 2 Model of InGaP/InGaAs/Ge TJSC The parameters of each sub-cell are included in the TJSC model. Think about the diode reverse saturation currents and how the temperature changes affect the energy gap of each sub-cell. One light-current, one parallel-resistance, and one series-resistance are all part of the single-diode model of TJSC, as shown in Fig. 1 . Three sub-cells—the upper, medium, and lower—make up the TJSC model. From highest to lowest, the energy disparities decrease. This equation describes the current that is taken out of the TJSC: (1) I c e l l = I p h i − I d i − I p i ∀ i = [ 1 , 2 , 3 ] The photocurrent is defined using the following relation in terms of solar irradiance level: where (2) I p h i = G X s [ I s c i + α ( T − T s t c ) ] T stc is the standard temperature, α is the short circuit current temperature coefficient, X is the concentration ratio, and s G is the solar irradiance level in W/m 2 . The current, voltage drop, and saturation current of the diode are experssed by the following relations: (3) I d i = I O i [ exp ( q V d i A i K B T ) − 1 ] (4) V d i = V i + I c e l l × r i (5) I O i = K i × T ( 3 + γ i / 2 ) [ exp ( − E g i A i K B T ) ] ∀ i = [ 1 , 2 , 3 ] The terminal voltage of the Triple-Junction solar cell can be expressed as follows: where; (6) V c e l l = n 1 K B T q ln [ I p h 1 − I c e l l I O 1 + 1 ] + n 2 K B T q ln [ I p h 2 − I c e l l I O 2 + 1 ] + n 3 K B T q ln [ I p h 3 − I c e l l I O 3 + 1 ] − I c e l l × R where (7) R = r 1 + r 2 + r 3 q is the electron charge, n i is the diode ideality factor, K B is Boltzmann's constant, E g is the bandgap energy, K and γ are constants, T is the absolute temperature, and R is the cell series resistance. 3 Methodology 3.1 Chaos game optimization Chaos theory is a mathematical branch that examines the behavior of dynamical systems. It focuses on their sensitivity to initial conditions and their self-similarity, highlighting the importance of initial conditions. Chaos Game Optimization (CGO) is a novel metaheuristic optimization method that utilizes ideas from chaos theory. It leverages the configuration of fractals through the chaotic game concept and focuses on the self-similarity aspects of fractals. The CGO algorithm employs a Sierpinski triangle as the search space for solution candidates. Each solution candidate ( X = 1,2…, i , i n ) comprises decision variables that denote the position of eligible seeds, where n is the population size. The mathematical model aims to create eligible seeds within a search space to complete the Sierpinski triangle shape. It creates new seeds within a Sierpinski triangle, drawing a temporary triangle with three seeds for each eligible seed. The purpose of creating temporary triangles is to generate new eligible seeds in the search space. Four approaches are developed to achieve this. The first iteration uses a temporary triangle with n available seeds and three vertices of a Sierpinski triangle. Three seeds are placed in the triangles: X , best seed ( i X ), and the mean of all seeds ( best X ). mean where – For the 1st temporary seed, a dice with green and red faces is rolled, and the seed is moved based on the color. Random integer generation functions are used to create two integers for each face. Randomly generated factorials are used to control seed movement in the search space. This process can be modelled as follows: (8) X T 1 = X i + α i ( β i X b e s t − γ i X m e a n ) α is a random factorial generated for the i i th seed expressing its motion limitations, β and i γ are random gains (0–1) expressing the possibility of rolling a dice. i α can be defined as one of the following forms: i where (9) α i = { r a n d 2 × r a n d ( δ × r a n d ) + 1 ( ε × r a n d ) + ( ∼ ε ) δ and ε are random numbers (0,1). – The 2nd temporary seed is rolled using a dice with three blue and three red faces. Depending on the color, the seed moves toward the X (blue face) or i X (red face). The second seed can move toward a point on the connected lines using randomly generated factorials. This process can be modelled as follows: mean (10) X T 2 = X b e s t + α i ( β i X i − γ i X m e a n ) – For the 3rd temporary seed, a dice with blue and green faces rolls, determining the seed's direction. Random integer generation creates 0 and 1 for selecting colors. Seed can move along connected lines between X and i X . This process can be modelled as follows: best (11) X T 3 = X m e a n + α i ( β i X i − γ i X b e s t ) – An additional random 4th temporary seed ( X ) is added to implement the mutation phase while updating the new seeds. T4 – The fitness of each temporary generated seed will be calculated, and temporary best solutions ( X ) will be assigned. If Tbest X is better than Tbest X , this list will be updated. best The CGO can be described using the following pseudocode: start the cgo random initialization fitness evaluation and x best assignment for t = 1:t max for i = 1:n calculate X mean calculate α i , β i and γ i calculate x t1 , x t2 , x t3 and x t4 limit the temporary seeds within the search space limits fitness evaluation and x tbest assignment update x best return x best end The evolution of the optimization process can be described using the flowchart explained in Fig. 2 . 3.2 Problem formulation The main target is extracting the global MPP from the InGaP/InGaAs/Ge TJSC-based PV system, which is considering PS. While the extracted PV power defines the maximum cost function, the array current is the suggested design variable. The output PV voltage of the TJSC-based array may be defined using the following relation: (12) V a r r a y = N s m × n C ( ∑ i = 1 i = 3 ( n i K B T q ln [ I p h i − I I O i + 1 ] ) − I × R ) The variable Nsm represents the number of solar PV modules linked in series, whereas n represents the total number of cells per module. The photovoltaic power generated by the array can be approximated using the following equation: C (13) P a r r a y = V a r r a y × I c = ( N s m × n C ( ∑ i = 1 i = 3 ( n i K B T q ln [ I p h i − I I O i + 1 ] ) − I × R ) ) × I c The suggested objective function is maximizing the PV output power provided in Eq. (13) through seeking the PV current at global MPP. The steps of the solution methodology using CGO are given on Fig. 3 . At first, the optimization process starts with random initial values for PV current. Then at every value of PV current, the PV system operated, and the PV power is required. After each iteration, the updating process is initiated if the power obtained is more than the preceding run. Once all the iterations have been completed, the best power from each iteration is combined to generate global power. 4 Results and discussion The analysis is performed on a based PV module containing 20 series-connected solar cells and provides 480 W of nominal maximum power at 800 W/m 2 and 20 °C (STC). The InGaP/InGaAs/Ge TJSC parameters are presented in Table 1 . The InGaP/InGaAs/Ge TJSC is built in MATLAB, as demonstrated in Fig. 4 . The electrical characteristics of the TJSC-based PV module are presented in Table 2 and Fig. 5 . The PV power characteristics are nNar and vary with the solar irradiance and temperature. Fig. 6 a and 6 b illustrate the results of the simulation of the PV model's output current-voltage and output power-voltage characteristics at a constant temperature and increasing solar radiation, respectively, with the effect of solar radiation taken into account. Varying the amount of sunlight has a significant impact on the maximum power point. As the solar radiation varies between 450 W/m 2 and 1000 W/m 2 , the MPP is adjusted from 280 W to 570 W. However, changing the solar radiation has a significant impact on the I-V characteristics of the cell up until the output voltage hits the maximum power point. Then it has a little effect beyond that. To prove the consistency of the proposed global MPPT based CGO, four PS patterns are carried out. The results are compared to EGO, COOT, POA, NGO, LHHO, HHO, ALO, ROA, GBO, EO, MPA and PSO. The performance of the algorithms is analyzed through the best value of the objective function, standard deviation, variance, minimum value and average value under different PS patterns. Four arrangements of PV array are employed: three series-PV modules, four series-PV modules, five series-PV modules and six series-PV modules. Four PS patterns are used during the evaluation process, which have different global MPP locations, such as 2nd right, 3rd right, 2nd left, and centre. The idea of changing the location of the global MPP is to test the reliability of the proposed tracker. Table 3 and Fig. 7 demonstrate the detailed explanation of the specifications of PS patterns. In order to maintain objectivity in the comparison, all algorithms have the same starting point of five populations and ten iterations. To be fair in comparison, the number of populations (5) and iterations (10) are kept fixed with all algorithms. MATLAB software version R2022b has been used with OMEN X by HP Laptop, Intel(R) Core (TM) i9–9880H CPU @ 2.30 GHz 32.0 GB RAM. During the optimization process, a cost function that was meant to be improved upon was the product of PV current voltage. After 30 trials, all optimizers were used to prove that the global MPPT-based CGO that was suggested was reliable. As shown in Table 4 , all approaches were statistically evaluated. Table 5 shows the specifics of the first shading pattern and Table 6 shows the features of the thirs pattern, while both have 30 runs. The initial PV configuration, which makes use of three series-PV modules, follows the steps outlined in Fig. 6 a and employs the first PS pattern. Solar irradiation ranges from 300 W/m 2 to 700 W/m 2 . Two local points at 524.93 W and 681 W, as well as a single global peak at 993.89 W, make up the power vs voltage graph under this PS pattern. In the middle of the graph, you can see the worldwide MPP. At this point, the PV voltage is 103.55 V, and the current is 9.59 A. Table 3 shows that when compared to other algorithms, the proposed global MPPT based CGO performs the best. In the first PS pattern, the average PV power levels were between 865.67 W and 993.89 W. The maximum power that CGO can achieve is 993.89 W and followed by POA (993.54 W). When using COOT, the lowest power output is 865.67 W. The standard deviations range from 0.032 to 134.28. After POA (1.32), CGO achieves the lowest STD (0.032). According to ALO, the worst possible STD value is 134.28. Fig. 8 shows the convergence during the optimization process. CGO is faster than other algorithms in finding the global MPP. The final values of the mean cost function for EGO, COOT, POA, NGO, LHHO, HHO, ALO, ROA, GBO, EO, MPA, PSO, and CGO are 973.76 W, 865.67 W, 993.54 W, 976.8 W, 992.91 W, 992.19 W, 882.55 W, 980.73 W, 986.48 W, 983.42 W, 991.16 W, 992.4 W, and 993.89 W, respectively, as shown in Table 3 . This demonstrates that the proposed CGO is better than competing algorithms. However, one of the main challenges in integrating CGO into practical PV systems is time-consuming nature, especially when they involve complex shading patterns. This can delay real-time MPP tracking. To address this issue, the optimization process end criteria must be adaptive in nature and the optimizer stops the search just in case global MPP is obtained. As shown in Fig. 7 b, the second PS pattern is utilized in the second PV configuration that makes use of four series-PV modules. At 900 W/m 2 , 700 W/m 2 , 400 W/m 2 , and 200 W/m 2 , the sun irradiance levels are as follows. The power-versus-voltage graph in this PS pattern has four peaks: a single global peak at 993.89 W and three local peaks at 524.93 W, 903.58 W, and 614.3 W. In the middle of the graph, on the left side, you can see the global MPP. At this point, the PV voltage is 103.55 V, and the current is 9.59 A. Table 3 shows that, when compared to other algorithms in this PS pattern, the proposed global MPPT-based CGO performs the best. Between 993.89 W and 896.64 W were the mean values of the PV power. The most significant power that CGO can achieve when flowed via PSO is 993.89 W (989.52 W). In terms of PV power, ALO achieves the lowest value of 896.64 W. From 0.0009 to 129.69, the STD values range. With an STD of 0.0009, CGO achieves the lowest value, while PSO comes in second with 7.19. When using ALO, the lowest possible STD value is 129.69. The optimization process's impact on the mean cost function is seen in Fig. 9 . With reference to Table 3 , the final mean cost function values for EGO, COOT, POA, NGO, LHHO, HHO, ALO, ROA, GBO, EO, MPA, PSO, and CGO are 966.89 W, 879.52 W, 985.76 W, 973.38 W, 986.27 W, 974.2 W, 896.64 W, 982.7 W, 980.41 W, 972.08 W, 985.19 W, 989.52 W, and 993.89 W, respectively. This demonstrates that the proposed CGO is better than competing algorithms. Regarding the third PS pattern is utilized in the third PV arrangement with five series-PV modules, as shown in Fig. 7 c. Sunlight irradiance readings range from 1000 W/m 2 to 250 W/m 2 . The PS pattern causes the power-voltage graph to have five peaks: a single global peak at 1692.34 W and four local peaks at 571.25 W, 1259.35 W, 1571.61 W, and 977.5 W. Second from the right on the graph is where you can find the global MPP. The current flowing through the PV system is 7.58 A, and the voltage is 223.05 V. Table 3 shows that, when compared to other algorithms in this PS pattern, the proposed global MPPT-based CGO performs the best. Values for the mean PV power varied from 1692.33 W to 1544.66 W. The highest power flowed by PSO (1681.37 W) to CGO is 1692.33 W. At its lowest, ALO achieves a PV power of 1544.66 W. From 0.032 to 209.46, the STD values range. After LHHO (0.8), CGO achieves the lowest STD of 0.032. According to ALO, the worst possible value of STD is 209.46. The mean cost function fluctuates throughout the optimization process, as shown in Fig. 10 . The mean cost functions for EGO, COOT, POA, NGO, LHHO, HHO, ALO, ROA, GBO, EO, MPA, PSO, and CGO were determined to be 1630.47 W, 1565.72 W, 1684.05 W, 1676.02 W, 1691.93 W, 1675.38 W, 1544.66 W, 1659.81 W, 1677.12 W, 1680.12 W, 1675.05 W, 1681.37 W, and 1692.33 W, respectively. This demonstrates that the proposed CGO is better than competing algorithms. As shown in Fig. 7 d, the fourth PS pattern is then applied to the fourth PV configuration, which makes use of six series-PV modules. There are 950 W/m 2 , 750 W/m 2 , 600 W/m 2 , 500 W/m2, 350 W/m 2 , and 250 W/m 2 of solar irradiation. A power-versus-voltage graph exhibiting this PS pattern has six peaks, including five local points at 548.4 W, 1061.81 W, 1348.68 W, 1359.9 W, and 1171.1 W, and one unique global peak at 1534 W. On the third right-hand side of the graph, you can see the global MPP. At this point, the PV voltage is 223.08 V, and the current is 6.91 A. Table 3 shows that, when compared to other algorithms in this PS pattern, the proposed global MPPT-based CGO performs the best. Values for the mean PV power varied from 1692.33 W to 1372.99 W. The highest power that CGO may get from LHHO (1533.47 W) is 1534.03 W. In terms of PV power, ALO achieves the lowest value of 1372.99 W. The range of STD values is from 0.032 to 157.17. After PSO (9.9), CGO achieves the lowest STD of 0.032. The ALO method yields the worst possible STD result of 157.17. The optimization process's impact on the mean cost function is illustrated in Fig. 11 . If we look at Table 3 , we can see that the final values of the mean cost functions for EGO, COOT, POA, NGO, LHHO, HHO, ALO, ROA, GBO, EO, MPA, PSO, and CGO are 1466.44 W, 1412.97 W, 1530.44 W, 1503.28 W, 1533.47 W, 1524.51 W, 1372.99 W, 1524.46 W, 1520.26 W, 1523.04 W, 1530.83 W, 1527.53 W, and 1534.03 W, respectively. This demonstrates that the proposed CGO is better than competing algorithms. Table 7 displays the results of an analytical study that evaluated the algorithms under consideration using the ANOVA test. The degree of freedom ( DF ), the sum of squares ( SS ), mean squared error ( MS ) (= DF/SS ), the ratio of mean squared errors ( F ), and the likelihood that the computed test statistic can take on a value more significant than the test statistic itself ( P ) are all variables used in this test. With a P value that is significantly smaller than the F value in every instance, we can see that the mean values in the columns are very different from one another. At the same time, the rankings are shown graphically in Fig. 12 , which proves that the CGO algorithm is very stable and accurate. A Tukey test has been carried out to support the results gained by ANOVA. The results of the Tukey test were demonstrated in Fig. 13 . For the 1st PS pattern, CGO has the best performance followed by POA, whereas the worst performance is assigned to the original COOT and ALO. For the 2nd PS pattern, CGO has the best performance, followed by PSO, whereas the worst performance is assigned to COOT and ALO. For the 3rd PS pattern, CGO has the best performance, followed by LHHO, whereas the worst performance is assigned to COOT and ALO. Lastly, for the 4th PS pattern, CGO has the best performance, followed by LHHO, whereas the worst performance is assigned to EGO, COOT and ALO. 5 Conclusion Chaos game optimization (CGO) has been implemented to extract the global MPP of high-efficiency InGaP/InGaAs/Ge triple-junction solar cell (TJSC) based PV system while considering the partial shading (PS) issue. Four different PS patterns are used throughout the assessment procedure. The tracking performance of CGO is compared with another recent optimzation methods. The results demonstrated the superiority of CGO; for the 1st PS pattern as an example, the mean PV power values ranged between 993.89 W and 865.67 W. CGO attains the maximum power of 993.89 W flowed by POA (993.54 W). COOT obtains the lowest power of 865.67 W. The STD values vary between 0.032 to 134.28. The lowest STD of 0.032 is attained by CGO, followed by POA (1.32). ALO obtains the worst value of STD of 134.28. In sum, A comparison with recent optimzation algorithms was also carried out, and the results confirm the superiority of CGO compared with other algorithms. Integrating the high-efficiency InGaP/InGaAs/Ge TJSC with thermoelectric generator to build hybrid system will be examined in the future work considering shading and heterogeneous heat distribution conditions. CRediT authorship contribution statement Houssam Eddine Ghadbane: Writing – review & editing, Writing – original draft, Software, Methodology, Investigation, Formal analysis, Conceptualization. Hegazy Rezk: Writing – review & editing, Writing – original draft, Software, Methodology, Funding acquisition, Conceptualization. Aissa Benhammou: Writing – review & editing, Writing – original draft, Software, Formal analysis. Ahmed F. Mohamed: Writing – review & editing, Writing – original draft, Methodology, Formal analysis, Conceptualization. Declaration of competing interest The authors declare that they have no conflicts of interest to report regarding the present study. Funding “This research work was funded by Umm Al-Qura University , Saudi Arabia, under grant number 25UQU4290444GSSR05 ”. Acknowledgments “The authors extend their appreciation to Umm Al-Qura University , Saudi Arabia, for funding this research work through grant number 25UQU4290444GSSR05 .”.
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10.1016_j.jctube.2015.11.003.txt
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TITLE: Mycobacterium avium intracellulare complex causing olecranon bursitis and prosthetic joint infection in an immunocompromised host
AUTHORS:
- Tan, Eugene M.
- Marcelin, Jasmine R.
- Mason, Erin
- Virk, Abinash
ABSTRACT:
Case
A 73-year-old immunocompromised male presented with recurrent left elbow swelling due to Mycobacterium avium intracellulare complex (MAC) olecranon bursitis. 3 years after completing MAC treatment, he underwent right total knee arthroplasty (TKA). 1 year later, he developed TKA pain and swelling and was diagnosed with MAC prosthetic joint infection (PJI). He underwent TKA resection, reimplantation, and 12 months of anti-MAC therapy. This patient is the seventh case report of MAC olecranon bursitis and the third case report of MAC PJI. He is the only report of both MAC olecranon bursitis and PJI occurring in the same patient.
Informed consent
This patient was informed and agreed to the publication of this material.
BODY:
Introduction Nontuberculous mycobacteria (NTM) comprise over 125 species and are ubiquitous in soil, water, and animals. Mycobacterium avium intracellulare complex (MAC) is the most common pathogenic NTM species and consists of M. avium and M. intracellulare , which are indistinguishable based on traditional laboratory testing. MAC usually causes pulmonary disease but may also cause lymphatic, skin/soft tissue, skeletal, or disseminated disease. Water sources, such as recirculating hot-water systems, are the reservoir for most MAC infections. [1] We illustrate a rare case of MAC causing both olecranon bursitis and prosthetic joint infection (PJI) in an immunocompromised host. Case report A 73-year-old male with history of multiple myeloma (in remission for 3 years after thalidomide and dexamethasone treatment) and chronic cough, presented to the Emergency Department with 3 days of left elbow swelling, which was diagnosed as olecranon bursitis based on clinical presentation and X-ray ( Fig. 1 ). There was no history of elbow trauma. His bursitis improved with a steroid injection but recurred 2 months later and was treated with a repeat steroid injection. Unfortunately, his bursitis recurred again 2 months later, and bursa aspirate yielded a white blood cell (WBC) count of 45,708 with 98% neutrophils, suspicious for septic bursitis. Bacterial cultures were negative, and he had not been on antibiotics previously. He received a 14-day course of cephalexin. Because the elbow was still edematous after 8 days of cephalexin, he underwent elbow debridement, which revealed purulent fluid with erythematous grayish-brown tissue. Histology showed acutely inflamed synovium consistent with infection. 2 out of 3 samples were smear-positive for acid-fast bacilli. All 3 operative mycobacterial cultures and the initial aspiration grew MAC. On review of systems, he mentioned a chronic productive cough. The patient smoked a pipe for 10 years but quit 65 years ago. He had no formal diagnosis of COPD. Sputum cultures grew MAC. A chest X-ray showed basal atelectasis and multiple bilateral calcified pleural plaques, consistent with prior asbestos exposure ( Fig. 2 ). There was no significant change compared to a chest X-ray done 3 years prior to presentation, and tuberculosis skin testing was negative. Other exposures included gardening, hot-tub use, and a pet dog. The MAC isolate was susceptible to rifabutin, ethambutol, and clarithromycin; intermediate to rifampin, streptomycin, and moxifloxacin; and resistant to ciprofloxacin, kanamycin, cycloserine, ethionamide, and amikacin. His initial treatment regimen included clarithromycin 500 mg PO BID, ethambutol 1600 mg PO daily, and rifabutin 300 mg once daily. The rifabutin was discontinued 3 weeks into therapy due to neutropenia and transaminitis. His bursitis resolved after a 12-month course of ethambutol and clarithromycin. Repeat sputum cultures were not obtained after completion of therapy. One year later, his multiple myeloma recurred, and he was started on lenalidomide and dexamethasone. Around this time, he was also diagnosed with seronegative rheumatoid arthritis (RA) and initiated methotrexate. 3 years after completing his MAC treatment, he underwent an elective right total knee arthroplasty (TKA) for degenerative joint disease. This procedure was performed at an outside facility with presumed peri-operative prophylaxis. One year later, he developed right TKA pain, instability, and swelling. X-ray showed a well-seated right TKA with a large effusion ( Fig. 3 ). C-reactive protein (CRP) was elevated at 13.5 mg/L (reference range < 8 mg/L), and erythrocyte sedimentation rate (ESR) was elevated at 65 mm/h. Synovial fluid aspiration yielded 4524 total nucleated cells; 57% neutrophils, and 39% monocytes. The synovial fluid aspirate grew MAC. He underwent TKA resection with placement of a vancomycin/tobramycin impregnated spacer. Histology was negative for acute inflammation or granulomas. All 4 surgical tissue samples grew MAC. His multiple myeloma chemotherapy and methotrexate for RA were held. His TKA MAC isolate was still susceptible to ethambutol and clarithromycin. Although it was previously susceptible to rifabutin, it now demonstrated intermediate susceptibility. He was initially started on clarithromycin, ethambutol and rifabutin, but due to recurrent transaminitis and neutropenia, he was continued on dual therapy with ethambutol and clarithromycin for 6 months prior to consideration for reimplantation. Pre-reimplantation CRP was normal at 4.8 mg/L, and ESR was 49 mm/h. Although still on therapy, the right knee synovial fluid was aspirated prior to reimplantation and found to be negative for mycobacterial growth. Six weeks later, he underwent reimplantation. All 4 surgical tissue samples from reimplantation remained negative for MAC. One of 4 cultures grew coagulase-negative staphylococci, which was considered a contaminant. Pathology was negative for acute inflammation. He continued ethambutol and clarithromycin for another 6 months, to complete a total of 12 months. Then, he was placed on chronic suppression with azithromycin 1200 mg orally once a week. Fifteen months later, he successfully underwent an elective contralateral TKA, again for degenerative joint disease. His multiple myeloma went into remission, precluding further chemotherapy. His methotrexate for RA was switched to hydroxychloroquine. He continues to do well at 7 years of follow-up after the 2-stage exchange of his MAC-infected right TKA. Discussion Nontuberculous mycobacteria (NTM) olecranon bursitis is very rare, with only 21 reported cases, 6 of which were due to MAC ( Table 1 ). 38% of cases occurred in immunocompromised patients. Minor elbow trauma or bursa injection can provide a portal of entry for NTM if contaminated with soil [2,3] . Most patients with NTM olecranon bursitis typically present with mild pain that improves with multiple corticosteroid injections, but bursal swelling may worsen. Diagnosis is delayed more than 6 months in most cases. 13 out of the 21 reported cases required surgical intervention followed by prolonged anti-mycobacterial therapy [2] . This patient's subsequent MAC infection of the TKA was also interesting. In general, the microorganisms causing PJI are S. aureus (31.0%), coagulase-negative Staphylococcus (20.2%), culture-negative (15.8%), polymicrobial (7.4%), Streptococcus (5.8%), Enterococcus (3.9%), fungi (2.3%), anaerobes (0.9%), and lastly mycobacteria (0.6%) [4] . Mycobacterial species previously reported to cause PJI include M. tuberculosis, M. bovis, and the rapidly growing mycobacteria: M. abscessus, M. chelonae, M. fortuitum, M. kansasii, M. smegmatis, and M. wolinskyi . However, MAC PJI is relatively rare [5] . The pathogenesis of his infection is unclear – whether it was contamination at surgery or subsequent hematogenous spread. He had chronic respiratory tract colonization, but there is no clear mechanism to explain how MAC respiratory colonization could potentially lead to joint infection in his case. Currently, there are 2 known case reports of MAC PJI ( Table 2 ) [5,6] . Because of the rarity of MAC PJI, optimal management is undefined. A 3-drug regimen of a macrolide, ethambutol, and a rifamycin is recommended for 6–12 months, but accepted treatment guidelines have not been established [1] . Regarding reimplantation, treatment decisions must be extrapolated from the available literature on other mycobacterial PJI's. In a 1998 case series, only 2 out of 7 patients with M. tuberculosis PJI underwent reimplantation, one at 20 months and other at 30 months post-resection [7] . In a 2007 case series of PJI due to rapidly growing mycobacteria (RGM), 2 patients underwent reimplantation (one at 3.5 months and one at 7.5 months post-resection) and required chronic antibiotic suppression [8] . ESR and CRP are helpful to assess clearance of bacterial infections prior to reimplantation but may be unreliable in determining timing of second-stage reimplantation in NTM PJIs [9] . Our patient's ESR of 49 mm/h done one day prior to reimplantation may have been confounded by his multiple myeloma and RA; however CRP had normalized. In a 2007 case series of RGM PJI, the median ESR at diagnosis was 70.5 mm/h, and the median CRP was 6 mg/dL. In the two patients who underwent reimplantation, ESR and CRP had normalized [8] . Synovial fluid WBC count less than 1102.5 cells/uL may be an adjunctive perioperative test but only has a sensitivity of 75% and specificity of 61% and has not been studied in NTM PJI [9] . Suppressive therapy is another important question. One patient with M. chelonae PJI underwent resection, reimplantation, and suppressive therapy with clarithromycin and moxifloxacin. Two patients with M. fortuitum PJI were able to retain their prosthesis and remained asymptomatic on suppressive regimens of moxifloxacin, trimethoprim-sulfamethoxazole and azithromycin and levofloxacin/trimethoprim-sulfamethoxazole, respectively. However, suppressive therapy may not be feasible with other species such as M. abscessus , which are often resistant to most oral antibiotics [8] . This patient's MAC olecranon bursitis and PJI were separated by approximately 4 years, suggesting long-term colonization. MAC has been known to colonize the respiratory and gastrointestinal tract of patients especially those with immune compromise such as AIDS or those with structural lung disease, such as COPD or bronchiectasis. Our patient was immunocompromised with his multiple myeloma and treatment of seronegative RA [10–12] . Other risk factors for pulmonary NTM colonization include white race, age greater than or equal to 60 years, female sex, birth and residency in Canada for at least 10 years. Our patient possesses the risk factors of white race and age greater than 60 years and immune suppression for his long-term colonization with MAC [12] . This patient's MAC olecranon bursitis, followed by a MAC PJI 4 years later, is a rare phenomenon and likely related to chronic relatively asymptomatic respiratory MAC colonization. In summary, mycobacterial PJIs are very rare, and patients often experience a delay in diagnosis. Mycobacterial cultures should be obtained in immunocompromised patients with persistent symptoms and negative bacterial cultures [2] . This is the seventh case report of MAC olecranon bursitis and the third case report of a MAC PJI. This patient is unique, as he is the only known case of both MAC olecranon bursitis and PJI occurring in the same patient. This case also highlights the rare risk of MAC PJI in immunocompromised patients who may be colonized with MAC. Learning points for clinicians 1. Obtain mycobacterial cultures for persistent join pain or swelling despite empiric antibiotics, especially if the patient is immunocompromised. 2. ESR, CRP, and synovial WBC count may be helpful to determine timing of reimplantation for patients with PJI's. 3. Discuss the option of long-term antibiotic suppression for patients with MAC PJI.
REFERENCES:
1. GRIFFITH D (2007)
2. GARRIGUES G (2009)
3. ZHIBANG Y (2002)
4. AGGARWAL V (2014)
5. GUPTA A (2009)
6. MCLAUGHLIN J (1994)
7. BERBARI E (1998)
8. EID A (2007)
9. KUSUMA S (2011)
10. WEINSTOCK D (2003)
11. BERMUDEZ L (1992)
12. HERNANDEZGARDUNO E (2010)
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10.1016_j.asej.2014.04.014.txt
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TITLE: Blood flow analysis of Prandtl fluid model in tapered stenosed arteries
AUTHORS:
- Akbar, Noreen Sher
ABSTRACT:
In the present article we have discussed the blood flow analysis of Prandtl fluid model in tapered stenosed arteries. The governing equations for considered model are presented in cylindrical coordinates. Perturbation solutions are constructed for the velocity, impedance resistance, wall shear stress and shearing stress at the stenosis throat. Attention has been mainly focused to the analysis of embedded parameters in converging, diverging and non-tapered situations. Streamlines have been plotted at the end of the article for considered arteries. It is observed that due to increase in Prandtl fluid parameters, the stenosis shape and maximum height of the stenosis the velocity profile decreases.
BODY:
Nomenclature V ¯ velocity vector n stenosis shape Q flow rate T ¯ temperature u velocity component in r -direction w velocity component in z -direction P ¯ pressure S ¯ Cauchy stress tensor A , B material constant of Prandtl fluid model ξ tapering parameter b length of stenosis Greek symbols α , β Prandtl fluid parameter μ Kinmatic viscosity δ height of the stenosis ρ Density of the fluid ν Kinematic viscosity ϕ tapered angle 1 Introduction Arteries which are basically considered as a living tissues need a supply of metabolites including oxygen and removal of waste products. Aroesty and Gross [1] have discussed the pulsatile flow of blood in small blood vessels. Blood flow in artery has some important aspects due to the engineering as well as from the medical applications point of view. The hemodynamic behavior of the blood flow is influenced by the presence of the arterial stenosis. If the stenosis is present in an artery, normal blood flow is disturbed. Thurston [2] and Chien et al. [3] present the viscoelastic properties of blood. According to them the arterial configuration is closely connected with blood flow. Blair and Spanner [4] discussed that blood as a Casson fluid is valid for moderate shear rate and validity of Casson’s and Herschel–Bulkley for blood flow is same. Chaturani and Samy [5] reported the theory of Aroesty and Gross [1] and study pulsatile flow of blood in stenosed arteries modeling blood as a Casson fluid. Mandal [6] analyzed unsteady analysis of non-Newtonian blood flow through tapered arteries with a stenosis. Unsteady flow and mass transfer in models of stenotic arteries considering fluid–structure interaction discussed by Valencia and Villanueva [7] . Pulsatile flow of blood for a modified second-grade fluid model is presented by Massoudi and Phuoc [8] . In another article Siddiqui et al. [9] discussed Casson fluid in arterial stenosis. Blood flow analysis for micropolar fluid model for axisymmetric but radially symmetric mild stenosis tapered artery is presented by Mekheimer and Kot [10] . According to their observation the magnitude of the resistance impedance is higher for a micropolar fluid than that for a Newtonian fluid model. In another article Mekheimer and Kot [11] presented the same model with the influence of magnetic field and Hall currents on blood flow through a stenotic artery and visualized that the wall shear stress and the shearing stress on the wall at the maximum height of the stenosis possess an inverse characteristic to the resistance to flow with respect to any given value of the Hartmann number and the Hall parameter. Varshney et al. [12] coated the influence of magnetic field on the blood flow in artery having multiple stenosis and made a numerical study. Simulation of heat and chemical reactions on Reiner Rivlin fluid model for blood flow through a tapered artery with a stenosis was presented by Akbar and Nadeem [13] . Numerical simulation of generalized Newtonian blood flow past a couple of irregular arterial stenoses is investigated by Mustafa et al. [14] . They presented that in comparison to the corresponding Newtonian model the generalized Newtonian fluid experiences higher pressure drop, lower peakwall shear stress and smaller separation region. Recently a mathematical model for blood flow through an elastic artery with multistenosis under the effect of a magnetic field in a porous medium is presented by Mekheimer et al. [15] . Some important articles describing the features of blood flow are cited in the Refs. [16–34] . The objective of the present study was to discuss the blood flow analysis of Prandtl fluid in tapered stenosed arteries. The governing equations for considered model are presented in cylindrical coordinates. This model is not discussed for blood flow problem so far. Perturbation solutions are constructed for the velocity, impedance resistance, wall shear stress and shearing stress at the stenosis throat. Attention has been mainly focused to the analysis of embedded parameters in converging, diverging and non-tapered situations. Streamlines have been plotted at the end of the article. 2 Mathematical model For an incompressible fluid the balance of mass and momentum are given by (1) div V ¯ = 0 , (2) ρ d V ¯ dt = - ∇ P ¯ + div S ¯ , The constitutive equation for Prandtl fluid model is given by Akbar et al. [19] (3) S ¯ = A sin - 1 1 C ∂ u ¯ ∂ z ¯ 2 + ∂ w ¯ ∂ r ¯ 2 1 2 ∂ u ¯ ∂ z ¯ 2 + ∂ w ¯ ∂ r ¯ 2 1 2 ∂ w ¯ ∂ r ¯ , 3 Mathematical development We examine an incompressible flow of Prandtl fluid with constant viscosity and density μ in a tube having length ρ L . The cylindrical coordinate system is chosen such that ( r , θ , z ) and u ¯ are the velocity components in the w ¯ and r ¯ directions respectively. Here z ¯ is selected the axis of the symmetry of the tubes. The consideration of stenosis is represented as Mekheimer and Kot r = 0 [10] : with (4) h ( z ) = d ( z ) 1 - η 1 b n - 1 ( z - a ) - ( z - a ) n , a ⩽ z ⩽ a + b , = d ( z ) , otherwise In above equations (5) d ( z ) = d 0 + ξ z . is the radius of the tapered arterial segment in the stenotic region, d ( z ) is the radius of the non-tapered artery in the non-stenoic region, d 0 is the tapering parameter, ξ b is the length of stenosis, is a parameter determining the shape of the constriction profile and referred to as the shape parameter the symmetric stenosis occurs for ( n ⩾ 2 ) and n = 2 a indicates its location (see in Fig. 1 ). The parameter is defined by the expression η in which maximum height of stenosis located at (6) η = δ ∗ n n n - 1 d 0 b n ( n - 1 ) , is in Mekheimer and Kot z = a + b n n n - 1 [10] . The equations governing the flow are (7) ∂ u ¯ ∂ r ¯ + u ¯ r ¯ + ∂ w ¯ ∂ z ¯ = 0 , (8) ρ u ¯ ∂ ∂ r ¯ + w ¯ ∂ ∂ z ¯ u ¯ = - ∂ p ¯ ∂ r ¯ + 1 r ¯ ∂ ∂ r ¯ r ¯ S ¯ r ¯ r ¯ + ∂ ∂ z ¯ S ¯ r ¯ z ¯ - S ¯ θ ¯ θ ¯ r ¯ , (9) ρ u ¯ ∂ ∂ r ¯ + w ¯ ∂ ∂ z ¯ w ¯ = - ∂ p ¯ ∂ z ¯ + 1 r ¯ ∂ ∂ r ¯ r ¯ S ¯ r ¯ z ¯ + ∂ ∂ z ¯ S ¯ z ¯ z ¯ . Defining (10) r = r ¯ d 0 , z = z ¯ b , w = w ¯ u 0 , u = b u ¯ u 0 δ , p = d 0 2 p ¯ u 0 b μ , h = h ¯ d 0 , Re = ρ bu 0 μ , S rr = b S ¯ rr u 0 μ , S ∼ rz = d 0 S ¯ rz u 0 μ , S zz = b S ¯ zz u 0 μ , S θ θ = b S ¯ θ θ u 0 μ , α = A μ c , β = Au 0 2 6 d 0 2 μ c 3 . Using Eqs. (1)–(3) and (10) along with the additional conditions Mekheimer and Kot [10] : (10a) ( i ) Re δ ∗ n 1 n - 1 b ≪ 1 , and for mild stenosis (10b) ( ii ) d 0 n 1 n - 1 b ∼ O ( 1 ) , Eqs. δ ∗ d 0 ≪ 1 (8) and (9) take the form (11) ∂ P ∂ r = 0 , (12) ∂ P ∂ z = 1 r ∂ ∂ r r α ∂ w ∂ r + β ∂ w ∂ r 3 . The boundary conditions are now given by (12a) ∂ w ∂ r = 0 , at r = 0 , (12b) w = 0 , at r = h ( z ) , and (13) h ( z ) = ( 1 + ξ z ) 1 - η 1 z - σ 1 - z - σ 1 n , σ 1 ⩽ z ⩽ σ 1 + 1 , in which (13a) η 1 = δ n n n - 1 ( n - 1 ) , δ = δ ∗ d 0 , σ 1 = a b , ξ ′ = ξ b d 0 , ξ = tan ϕ , is represents the tapered angle. Further, we consider three types of arteries ( ϕ i ) converging tapering or , non-tapered artery ( ( ϕ < 0 ) ϕ = 0) and the diverging tapering . ( ϕ > 0 ) 4 Solution of the problem 4.1 Perturbation solution Eq. (11) is a non-linear equation, therefore we seek the perturbation solution. For perturbation solution, we expand and w , F 1 P by taking as perturbation parameter β (14) w = w 0 + β w 1 + O ( β 2 ) , (15) P = P 0 + β P 1 + O ( β 2 ) , (16) F 1 = F 10 + β F 11 + O ( β 2 ) . The perturbation results for small parameter , satisfying the conditions β (12a) and (12b) , the expression for velocity field and pressure gradient are directly written as (17) w = r 2 - h 2 4 α dP dz + β 16 ( 2 F 1 ) 3 r 4 - h 4 α h 12 , (18) dP dz = - 8 α ( 2 F 1 + h 2 ) h 4 + β - 256 ( 2 F 1 + h 2 ) 3 3 h 10 . The pressure drop across the stenosis between the section ( Δ p = p at z = 0 and Δ p = - p at z = L ) and z = 0 can be obtained using the expression given below z = L (19) Δ p = ∫ 0 L - dp dz dz . 4.2 Resistance impedance The resistance impedance is given by in which (20) λ ̃ = Δ p Q = ∫ 0 a F ( z ) h = 1 dz + ∫ a a + b F ( z ) dz + ∫ a + b L F ( z ) h = 1 dz , F ( z ) = 16 α h 4 + 2048 β F 1 2 3 h 10 . On simplification, Eq. ( 20 ) yields (21) λ ̃ = ( L - b ) 16 α + 2048 β F 1 2 3 + ∫ a a + b F ( z ) dz . 4.3 Expression for the wall shear stress The expression for dimensionless shear stress is (22) S ∼ rz = α ∂ w ∂ r + β ∂ w ∂ r 3 . The wall shear stress is of the form (23) S ∼ rz = α ∂ w ∂ r + β ∂ w ∂ r 3 r = h . The shearing stress at the stenosis throat i. e the wall shear at the maximum height of the stenosis located at can be expressed as z = a b + 1 n n n - 1 (24) τ ̃ s = S ∼ rz h = 1 - δ . The final expressions for the dimensionless resistance to , wall shear stress λ and the shearing stress at the throat S rz are τ s (25) λ = λ ¯ λ 0 = 1 3 1 - b L 16 α + 2048 β F 1 2 3 + 1 L ∫ a a + b R ( z ) dz , with (26) τ rz = S ∼ rz τ 0 , τ s = τ ̃ s τ 0 , (27) λ 0 = 3 L , τ 0 = 4 Q . 5 Numerical solution To see the validity of perturbation results, I have also solved Eq. (12) numerically using shooting technique and results are presented through tables and graphs see Table 1 and Fig. 8 (a) and (b). The results are in good agreement for Converging tapering (CT), diverging tapering (DT) and non-tapered arteries (NT) (see Table 2 ). 6 Graphical discussion Our interest in this section is to analyze the effects of the Prandtl fluid parameter , the stenosis shape α , β n and maximum height of the stenosis for converging tapering, diverging and non-tapered arteries in JeffreyPrandtl fluid. For that purpose we have plots δ Figs. 2–7 . The variation of axial velocity for and α , n , β in converging, diverging and non-tapered arteries are displayed in the δ Fig. 2 (a)–(d). We observed that due to increase in and α , n , β the velocity profile decreases. It is also seen that for the case of converging tapering the velocity gives larger values as compared to the case of diverging tapering and non-tapered arteries. δ Fig. 3 (a)–(d) show how the converging , diverging and non-tapered arteries influence on the wall shear stress . Interestingly with an increase in S rz the shear stress increases and decreases with an increase in α and β , δ n . It is also seen that the stress yield diverging tapering with tapered angle , converging tapering with tapered angle ϕ > 0 and non-tapered artery with tapered angle ϕ < 0 . In the ϕ = 0 Fig. 4 (a)–(c) it has been noticed that the impedance resistance increases for converging , diverging and non-tapered arteries when we increase and α , β n . We also observed that resistive impedance in a diverging tapering appear to be smaller than in converging tapering because the flow rate is higher in the former case when compared with the later. Impedance resistance attains its maximum values in the symmetric stenosis case . ( n = 2 ) Figs. 5–7 show the streamlines for different values of and n , α . Streamlines for different values of the Prandtl fluid parameter β is shown in Fig. 5 . Here it is noticed that the size of the trapping bolus increases while the number of bolus decreases, when we increase the Prandtl fluid parameter . α Fig. 6 is plotted to see the streamlines for different values of Prandtl fluid parameter . Here the size of the trapping bolus decreases with an increase in Prandtl fluid parameter β . Streamlines for different values of stenosis shape β n is presented through Fig. 7 . It is seen that the size of the trapping bolus increases while the number of bolus decreases, when we increase the stenosis shape n . 7 Conclusions Blood flow analysis of Prandtl fluid model in tapered stenosed arteries is discussed. Analytical solution have been evaluated using regular perturbation technique. The main points of the performed analysis are as follows: 1. We observed that due to increase in Prandtl fluid parameter , the stenosis shape α , β n and maximum height of the stenosis the velocity profile decreases. δ 2. It is also seen that for the case of converging tapering the velocity gives larger values as compared to the case of diverging tapering and non-tapered arteries. 3. Interestingly with an increase in the shear stress increases and decreases with an increase in α and β , δ n . 4. It is also seen that the stress yield diverging tapering with tapered angle , converging tapering with tapered angle ϕ > 0 and non-tapered artery with tapered angle ϕ < 0 . ϕ = 0 5. It has been noticed that the impedance resistance increases for converging , diverging and non-tapered arteries when we increase and α , β n . 6. We also observed that resistive impedance in a diverging tapering appear to be smaller than in converging tapering because the flow rate is higher in the former case when compared with the later. 7. Impedance resistance attains its maximum values in the symmetric stenosis case . ( n = 2 ) 8. The size of the trapping bolus increases while the number of bolus decreases, when we increase the Prandtl fluid parameter . α 9. It is seen that the size of the trapping bolus increases while the number of bolus decreases, when we increase the stenosis shape n . 10. The size of the trapping bolus decreases with an increase in Prandtl fluid parameter . β
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1. AROESTY J (1972)
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3. CHIEN S (1975)
4. SCOTTBLAIR G (1974)
5. CHATURANI P (1986)
6. MANDAL P (2005)
7. VALENCIA A (2006)
8. MASSOUDI M (2008)
9. SIDDIQUI S (2009)
10. MEKHEIMER K (2008)
11. MEKHEIMER K (2008)
12. VARSHNEY G (2010)
13. AKBAR N (2010)
14. MUSTAFA N (2011)
15. MEKHEIMER K (2011)
16. NADEEM S (2011)
17. NADEEM S (2011)
18. NADEEM S (2011)
19. AKBAR N (2012)
20. AKBAR N (2012)
21. AKBAR N (2012)
22. MEKHEIMER K (2010)
23. MEKHEIMER K (2008)
24. MEKHEIMER K (2011)
25. ELLAHI R (2013)
26. ELLAHI R (2014)
27. ELLAHI R (2013)
28. ELLAHI R (2014)
29. SHEIKHOLESLAMI M (2013)
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10.1016_j.therwi.2024.100114.txt
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TITLE: Sperm storage in males of the Neotropical rattlesnake Crotalus durissus (Squamata: Viperidae): Structure and seasonal variation of the distal ductus deferens
AUTHORS:
- Carvalho, Leonardo
- Avelar, Gleide Fernandes de
- Resende, Flávia Cappuccio de
ABSTRACT:
In species with asynchronous reproductive cycles, where gamete production is not aligned with the mating season, either males or females must store sperm. This reproductive tactic is an obligatory feature of male rattlesnakes’ reproductive cycle due to asynchrony between spermatogenesis and mating. Given that the ductus deferens is the primary site of sperm storage in male snakes, we aimed to investigate the morphological and histochemical changes in the distal ductus deferens of C. durissus throughout its reproductive cycle. In this species, spermatogenesis begins in spring and peaks in summer, while testes regress during autumn and winter. The distal ductus deferens of 28 mature male specimens was evaluated using histomorphometric and histochemical methods. Spermatozoa were consistently observed within the lumen of the ductus deferens in almost all specimens. The principal cells of the distal region of ductus deferens reacted positively for Periodic Acid-Schiff and Bromophenol Blue. Secretions were observed in the apical region of the principal cells' cytoplasm and along the epithelium edge, which may be related to gamete maintenance. Increased secretory activity of the principal cells was observed during periods of testicular activity. A reduction in the lumen of ductus deferens occurs during testicular regression, indicating possible fluid resorption by epithelial cells. Fluid resorption might be one of the mechanisms to ensure stored sperm viability, as it provides an increase in the glycoprotein’s concentration.
BODY:
1 Introduction The male reproductive system of Squamata consists of a pair of testes, epididymis, ductus deferens, a sexual segment of the kidney, and hemipenes [1,2] . The testes of most snakes have an elongated and cylindrical shape, generally present bilateral asymmetry, and are located in the coelomic cavity [3] . Snakes and other squamates possess a system of efferent ducts that originate from the testis, and these ducts function not only in the passage of spermatozoa but also in its storage and as accessory sex glands [4] . After spermiation, spermatozoa pass through the seminiferous tubules, which are connected to the rete testis, and follow a sequential path to the ductuli efferentes, ductus epididymis, and ductus deferens [4] . The latter typically exhibits bilateral asymmetry, with the right duct being longer than the left, and develops tight coiling as it passes caudally toward the ampulla [5] . Studies on Lepidosauria and Testudines have shown that the ductus deferens presents pseudostratified epithelium, muscular tissue, and dense connective tissue containing blood vessels [6,7] . Sever [6] and Rojas et al. [8] , working with Seminatrix pygaea and Dipsas mikanii , respectively, reported two epithelial cell types in the ductus deferens: principal and basal cells, with the latter arranged between the principal cells along the basal lamina of the epithelium. The ductus deferens is the primary site for sperm storage for snakes [4,9] . Long or short-term gamete storage in ductus deferens may be related to seasonal patterns of spermatogenesis and mating periods [10] . The reproductive cycle of male snakes, as other squamates, can be classified by considering the temporal relationship between spermatogenesis and mating [10,11] . In species with dissociated (or asynchronous) cycles, the gonadal activity does not occur in the period of copulation, requiring gamete storage in males [10,11] . This type of cycle is also called postnuptial spermatogenesis [10,12] . On the other hand, in species with associated (or synchronous) cycles, the production of spermatozoa occurs in the mating period [10,11] . This type of cycle is also called prenuptial spermatogenesis [10,12] . In snakes with asynchronous cycle, spermatozoa are observed in the lumen of the distal ductus deferens during the entire year [10] . Conversely, in snakes with synchronous cycles, spermatozoa are not seen in the ductus deferens after the mating season [10] . The Neotropical rattlesnake Crotalus durissus is a venomous species from the Viperidae family with a wide distribution in South America [13,14] . In Brazil, this species is found in the Cerrado, Caatinga, and Pampas biomes, as well as in open areas of the Amazon and the Atlantic Forest [13,14] . Previous studies have shown that C. durissus spermatogenic activity begins in spring and peaks in summer, while testicular regression occurs in autumn and winter [15,16] . Resende and Avelar [16] observed a peak in the hypertrophy of the sexual segment of the kidney and elevated testosterone levels in summer, when the species shows increased testicular activity. Additionally, individuals of C. durissus have been found to be more active during summer and autumn [17–20] . Combat rituals and mating have been reported in autumn for captive animals [21] , and in summer in the wild [22] . Vitellogenic females of C. durissus are observed from late summer to late autumn [23] . After mating, females store spermatozoa in the uterus throughout the winter, with fertilization occurring in spring [24] . To date, most studies have focused on determining the reproductive cycle of Neotropical male snakes using only macroscopic morphological characteristics [10] . While these studies have provided valuable insights into overall reproductive timing and gross anatomical changes, they offer limited understanding of the finer microstructural and cellular process involved. Notably, there remains a lack of information regarding the microstructural characteristics underlying reproductive tactics [21,25,26] . Although the ductus deferens is the primary site for gamete storage in male snakes, few studies have detailed the changes in this structure throughout the reproductive cycle [6,9,21,27] . Therefore, we aimed to investigate morphological and histochemical changes in the distal ductus deferens of C. durissus throughout the periods of testicular activity and regression. To our knowledge, this is the first detailed study of the distal ductus deferens of a Neotropical snake species. 2 Material and methods 2.1 Specimens and sampling area For this study, we used 28 mature males of C. durissus : 14 exhibiting active testes, collected during the austral summer and spring, and 14 exhibiting testicular regression, collected during the austral autumn and winter. The snakes were collected in the southeastern Brazilian state of Minas Gerais between July 2015 and February 2017 ( Table S1 ), under a license granted by the Chico Mendes Institute for Biodiversity Conservation (ICMBio, # 48897-1). The animals were collected in a Cerrado area, where the dry season corresponds to the period from May to September. The months from November to February present the highest rainfall in the collected area [28] . After inducing unconsciousness through hypoxia using carbon dioxide, animals were euthanized via intracoelomatic injection of barbiturate (Thiopental® 100 mg/kg) [29] . All procedures involving animals were conducted in accordance with the institutional animal care protocols and guidelines approved by the Ethics Committee in Animal Experimentation of Federal University of Minas Gerais (CEUA/UFMG, # 130/2015) and Ezequiel Dias Foundation (CEUA/Funed, # 079/2015). After dissection and collection of organs, the specimens were fixed in formalin and transferred to the Scientific Collection of Snakes of the Ezequiel Dias Foundation, Brazil. After euthanasia, the snakes were weighed, and their snout-vent length (SVL) was measured. The testes of all specimens were weighed, and their gonadosomatic index (GSI) was calculated using the formula: [(testes mass/body mass) × 100]. 2.2 Tissue sampling and preparation Fragments of the distal region of the ductus deferens were removed and fixed by immersion in Bouin’s solution (left fragment) or 5 % buffered glutaraldehyde (right fragment) for 24 h. The fixatives were then replaced with 70 % ethanol and 0.05 M phosphate buffer (pH 7.3), respectively. Samples fixed in glutaraldehyde were dehydrated in graded ethanol series and embedded in glycol methacrylate. Tissue fragments fixed in Bouin’s solution were processed following standard protocols for embedding in Paraplast® (Sigma-Aldrich Corporation, St. Louis, USA). Sections of 4 and 5 μm thickness were obtained from tissue embedded in glycol methacrylate and Paraplast®, respectively, using a Leica RM 2165 microtome (Leica Biosystems, Wetzlar, Germany). Alternating slides were used for the different stain procedures and subsequent analyses. Tissue embedded in glycol methacrylate were used for histomorphometric evaluation and for histochemical analysis of Periodic Acid-Schiff (PAS) and Bromophenol Blue (BB). Tissue embedded in Paraplast® were used for Alcian Blue (AB) staining. The slides were observed under a compound light microscope Olympus BX40 (Olympus Corporation, Tokyo, Japan), and images were obtained using an Olympus DP25 microscope camera (Olympus Corporation, Tokyo, Japan). Morphometric analyses were performed using Image J 1.47t software [30] . 2.3 Ductus deferens morphometry To investigate seasonal variation and spermatozoa storage in the distal ductus deferens, we used fragments on the right side. These slides were stained with toluidine blue and 1 % sodium borate. To measure the diameter of the distal ductus deferens (DDD) and the diameter of the lumen of distal ductus deferens (DDLD), we used 20 cross-sections with a circular shape. We obtained the ductus deferens epithelium height (DDEH) from 30 measures per specimen exhibiting either regressed or active testes. The synthetic activity of the ductus deferens cells was correlated with the nuclear volume of the principal cells, since cells with intense protein synthesis activity may have euchromatic nuclei, with less condensed chromatin, which can alter nuclear volume. Thus, the nuclear diameter was measured from 20 nuclei, considering only those with a spherical shape. The nuclear volume of principal cells (NVPC) was calculated using the formula 4/3πr³, where r = nuclear diameter/2 [31] . The percentage of ductus deferens components during active and regressed testes was obtained through the volume density approach. A grid with 475 intersections was created on ImageJ 1.47t software and placed over images of the distal ductus deferens obtained at 200 × magnification. Fifteen randomly selected fields were analyzed per specimen, resulting in a total of 7125 points per snake. The components evaluated were connective tissue, muscular tunica, epithelium, lumen, lumen with spermatozoa, cytoplasmatic vesicles in the lumen, secretion in the lumen, and detached cells in the lumen (testicular somatic cells and germ cells, except spermatozoa). 2.4 Ductus deferens histochemistry Histochemical methods assessed ductus deferens secretions, with BB staining detecting noncarbohydrate-conjugated proteins and AB staining identifying acidic glycoproteins. The protocols of BB and AB are described in detail in Resende and Avelar [16] . Neutral glycoprotein was evaluated through PAS staining. Slides were washed in distilled water for five minutes and then incubated in 0.5 % periodic acid for 20 min, followed by another five-minute wash in distilled water. After drying, the tissues were incubated in Schiff’s reagent for 45 min. Subsequently, the slides were washed in three baths of sulfurous water for three minutes each and then rinsed under running water for 30 min. We performed the counterstaining with hematoxylin for five minutes and washed the slides under running water for 10 min. Finally, after drying, Entellan (Merck KGaA, Darmstadt, Germany), a water-free mounting medium, was used for obtaining permanent slides from the three histochemical techniques. 2.5 Quantification of secretion activity To quantify the amount of secretions with different histochemical compositions, fifteen cross-sections stained with PAS and BB were analyzed. Areas of interest (secretory granules) were marked, and artifacts or non-relevant structures were removed using the Image-Pro Plus 4.5 software (Media Cybernetics, Silver Spring, USA). The software automatically counted the number of selected objects per field [30] . This approach was used to compare the composition of the secretions present in the epithelium and lumen of the ductus deferens between snakes exhibiting active and regressed testes. 2.6 Statistical analysis We examined both distal ductus deferens to assess structural changes in animals with either active or regressed testes. The number and distribution of animals used for each evaluation in the present study are shown in Table S2 . The normality of the data was verified using the Shapiro-Wilk test. The Student’s t-test was used to analyze the parametric data, including body mass, testes mass, gonadosomatic index, ductus deferens diameter, ductus deferens lumen diameter, nuclear volume of the principal cells, volume density of connective tissue and epithelium, and the secretion activity (PAS and BB). For the non-parametric data (ductus deferens epithelium height, and volume density of the total tubule, total lumen, muscular tunica, lumen, lumen with spermatozoa, cytoplasmic vesicles, secretions in the lumen, and detached cells), we applied the Mann-Whitney test. The results were expressed as the mean ± standard deviation (SD). Statistical analysis was performed using GraphPad Prism 8 software (GraphPad Software, San Diego, USA), and significance was set at P < 0.05. 3 Results 3.1 Biometric data of the snakes A total of 28 males of the Neotropical rattlesnake ( C. durissus ) were collected throughout the year ( Table S1 ). The specimens’ mean SVL was 83.9 cm. The body mass ranged from 250 g to 1050 g for snakes with active testes and from 282 g to 1383 g for snakes with regressed testes, with no statistically significant difference between the two groups (t = 0.7; df = 25; P = 0.459, Table 1 ). In contrast, the testes mass (t = 4.2; df = 25; P = 0.0003, Table 1 ) and GSI (t = 8.5; df = 23; P < 0.0001, Table 1 ) were significantly higher in animals with active testes than in those with testicular regression. 3.2 Histology The distal ductus deferens of C. durissus consists of a pseudostratified epithelium containing principal and basal cells ( Fig. 1 A). The principal cells are columnar in shape, extending from the basement membrane to the luminal edge, while the basal cells are confined to the basal compartment of the epithelium. The muscular tunica is formed by smooth muscle cells, and the outermost layer of the ductus consists of dense, well-organized connective tissue and blood vessels ( Fig. 1 B). Spermatozoa were observed occupying the lumen of the ductus deferens in almost all animals analyzed, regardless of the histologic classification of the testicular parenchyma. It is worth noting that in one of the specimens sampled in January, during mid-summer season in Brazil, the distal ductus deferens contained either no spermatozoa or only a few ( Fig. 1 C). 3.3 Morphometry Morphometric data showed no significant differences in the distal ductus diameter (DDD) (t = 1.2; df =15; P = 0.247, Fig. 2 A) nor in the lumen diameter (DDLD) (t = 1.0; df = 15; P = 0.322, Fig. 2 B) between snakes with different testicular conditions. The nuclear volume of principal cells (NVPC) remained constant across specimens with different testicular conditions (t = 1.23; df = 18; P = 0.232, Fig. 2 C). However, the distal ductus deferens epithelium height (DDEH) was significantly higher in specimens with regressed testes ( ) when compared with those with active testes ( 18.31 ± 5.57 µm 1.77 10.32 ± ) (t = 5.1; df = 26; µm P < 0.0001, Fig. 3 A–C). 3.4 Stereology When analyzing the distribution of components in the distal ductus deferens, we observed the total tubule (epithelium + lumen + lumen with spermatozoa + cytoplasmic vesicles + secretions in the lumen + detached cells) (U = 2987; P = 0.0037, Table 2 ) and total lumen (lumen + lumen with spermatozoa + cytoplasmatic vesicles + secretions in the lumen + detached cells) (U = 17; P = 0.0005, Table 2 , Fig. 4 A–B) percentages were higher in snakes with active testes than in those with regressed testes. The analysis of each component separately revealed significant differences in the percentages of the muscular tunica, epithelium, luminal secretions, and detached cells in the lumen among snakes with different testicular conditions ( Table 2 ). The epithelium (t = 2.3; p = 0.0258, Table 2 ) and muscular tunica (U = 45; p = 0.0141, Table 2 ) occupied a larger proportional space in the ductus deferens of snakes with testicular regression ( Fig. 4 C–D). The increase was approximately 75 % for the muscular tunica and 60 % for the epithelium ( Table 2 ). Conversely, significantly greater proportions of secretions (more than 100 times) and detached cells (5 times) were observed in the lumen of snakes with active testes ( Fig. 4 E–F; Table 2 ). Connective tissue, lumen, lumen with spermatozoa, and cytoplasmic vesicles in the lumen did not show significant variation among the groups analyzed ( Table 2 ). 3.5 Histochemistry Our histochemical analysis demonstrated that the distal ductus deferens of C. durissus reacts positively to PAS ( Fig. 5 A; 5D) and BB ( Fig. 5 B; 5 E) in animals with both active and regressed testes. However, a negative reaction was observed with AB ( Fig. 5 C; 5 F). Secretions were present in the apical region of the principal cells’ cytoplasm and in the epithelial border. Quantification of PAS- and BB-positive secretions revealed more intense secretory activity in the principal cells during testicular activity compared to the testicular regression period (PAS: t = 2.5; df = 8; P = 0.0364; BB: t = 2.7; df = 8; P = 0.0242, Fig. 6 ). 4 Discussion Our results indicate that, despite C. durissus exhibiting seasonal testicular activity [15,16] , no variation was found in the proportion of spermatozoa in the distal ductus deferens. The presence of spermatozoa in the lumen of the distal ductus deferens of snakes with regressed testes, along with the lack of variation in the proportion of gametes between specimens with active and inactive gonads, provides strong evidence for the occurrence of sperm storage in C. durissus . Almeida-Santos et al. [21] demonstrated through laparotomy and extraction of sperm from the ductus deferens that spermatozoa are present throughout the year. However, during winter (the period of testicular regression), a lower quantity of spermatozoa was observed in the ductus. Notably, in their study, sperm extraction was performed along the entire length of the ductus deferens. Although mating among captive C. durissus has been recorded in autumn, the period when males exhibit regressed testes [21] , in the wild, copulation has been observed in summer [22] , when the testes are active. Based on the recent observation of copulation in summer, the species' reproductive cycle could be classified as associated (or synchronous) [11] . Conversely, copulation in autumn would suggest a dissociated (or asynchronous) cycle [11,32] . In this context, the dissociation between gamete production and mating implies that sperm storage is an obligatory tactic for this species [33] . Other studies found dissociated cycle patterns in Neotropical snakes, such as Bothrops erythromelas [34] , B. cotiara [35] , and Spilotes pullatus [36] . The presence of spermatozoa in the ductus deferens throughout the year has been reported in various snake species, such as Vipera berus [37] , Xerotyphlops vermicularis [38] , Seminatrix pygaea [1,5] , C. durissus [21] , Austrelaps superbus, Hemiaspis signata, Notechis scutatus, and Suta gouldii [39] . Prolonged storage of gametes has been described only in snakes among Squamata, and it may play a fundamental role in the reproductive success of species with dissociated cycles [10] . We observed secretory activity in the distal ductus deferens of C. durissus , with the presence of neutral glycoproteins and proteins not conjugated to carbohydrates. These findings are similar to those reported for Agkistrodon piscivorus [9] , Dipsas mikanii [8] , and B. erythromelas [36] . Consistent with the present study, Barros et al. [36] and Rojas et al. [8] found stronger PAS and BB reactions in the apical region of the ductus deferens epithelium, while AB did not result in a positive reaction. According to Rojas et al. [8] , these secretions may be responsible for nourishing spermatozoa during storage. As we demonstrated, the proportion of spermatozoa in the distal ductus deferens did not vary during the main phases of the male reproductive cycle of C. durissus , despite the morpho-functional changes observed for this segment, which clearly followed the gonadal activity cycle. In this context, the percentage of total tubule and lumen in snakes with active testes increased, corresponding to a reduction in these same parameters in snakes with regressed testes. Similarly, Amer and Elshabka [40] described this same response of ductus deferens for the colubrid snakes Psammophis sibilans and Spalerosophis diadema during the active breeding season. Studies that observed secretory activity in the ductus deferens of snakes did not assess variations in secretions during the reproductive cycle [8,9,36] . However, the results and analyses of the amount of secretions in our study indicate that the ductus deferens are more active during spermatogenic activity, when concentrations of plasma testosterone are higher [16] . During this period, we observed stronger histochemical reactions to PAS and BB, indicating that the principal cells of the epithelium exhibit significant secretory activity. No relationship was found between nuclear volume and the biosynthetic activity of the principal cells of the ductus deferens. Further electron microscopy analyses investigating the protein synthesis machinery may clarify the differences in secretory activity. Although the ductus deferens is more active during the spermatogenesis phase, the epithelium height is lower compared to the testicular regression period. Spermatogenesis is when maximum testicular activity occurs; therefore, the distal region of ductus deferens would be receiving spermatozoa, testicular fluid, and possible secretions from the efferent ductus and the epididymis [4] . According to Amer and Elshabka [40] these alterations in epithelium height during spermatogenesis are due to an expansion of the ductus deferens for sperm storage, resulting in a thinner epithelium during this phase. We believe that the pressure exerted by these fluids on the epithelium may alter the overall cell morphology and decrease the epithelium height, which, for some yet-undetermined reason, does not affect the tubular diameter of the ductus deferens. On the other hand, the higher percentage and height of the epithelium in C. durissus with regressed testes, as observed here, follow the findings obtained for snake species from temperate areas, such as the viperid Cerastes vipera [41] and the colubrids Psammophis sibilans and Spalerosophis diadema [40] . Additionally, Viana et al. [7] observed similar changes in the epithelium of the Neotropical turtle, Kinosternon scorpioides . It is likely, that the epithelium height is regulated by luminal pressure, which is low in individuals with regressed testes, as previously suggested by Aldridge et al. [10] for other snake species. A lower epithelium is not necessarily associated with reduced secretory activity by the principal epithelium cells; on the contrary, secretory activity in the ductus deferens is higher in specimens with active testes. Our results suggest that principal epithelium cells might be responsive to androgens, as has been observed in various vertebrates [42–45] . Therefore, seasonal variation in morphology and function of the distal ductus deferens is likely to be affected by testosterone levels, which were higher during testicular activity [16] . Since the evidence suggests that epithelium enlargement is not associated with increased secretory activity, we propose a hypothesis that, during testicular regression, the epithelial cells of the distal ductus deferens assume a role in water reabsorption. This mechanism might be one of the aspects that allow sperm storage in the ductus deferens, the fluids containing glycoprotein produced in the organ itself and in the epididymis would become more concentrated [46,47] . Sever [6] found apical vesicles in the epithelial cells of the ductus deferens of a colubrid, indicating a possible role in fluid absorption. The muscular tunica is responsible for the contractile movements that push the spermatozoa toward to the ampulla of the ductus deferens. Despite this function, the muscular tunica also appears to play a role in maintaining the total diameter of the ductus throughout the reproductive cycle. As observed, the smooth muscle cells were stretched in active testes and contracted in snakes with regressed testes. This suggests a fine volumetric adjustment mechanism that allows the ductus deferens to adapt to the filling condition of its lumen without altering its total diameter. Similarly, in colubrid snakes, the muscular tunica exhibited the same response throughout the reproductive cycle [40] . The presence of few spermatozoa in the lumen of the distal ductus deferens in only one specimen collected during summer may indicate post-copulation, given that mating was recently observed in the wild during this season [22] . Additionally, Resende and Avelar [16] suggested the possibility that C. durissus could also copulate in summer, based on certain reproductive observations. Males collected from December to March (summer in Brazil) exhibited a hypertrophied sexual segment of the kidney, high spermatogenic activity, and elevated plasma testosterone levels [16] . Together, our findings support the hypothesis that males could also copulate in the summer. The mechanism of spermatozoa storage has evolved convergently among species belonging to different groups and constitutes a biological tactic that ensures males can copulate after a long period of hibernation. This is particularly important for species native to temperate areas. In this context, it is well known that the genus Crotalus originated in North America, and later migrated to South America via Central America [48,49] . Rattlesnakes from North America hibernate during winter and become reproductively active in the spring [32,50–52] . A critical question remains: what stimuli trigger spermatozoa storage in the ductus deferens of the Neotropical rattlesnake C. durissus ? While we propose that this phenomenon may be linked to the retention of an ancestral evolutionary trait, as suggested by Barros et al. [36] for B. erythromelas , this hypothesis raises numerous questions. Moreover, we must also consider the marked differences in the reproductive cycles among C. durissus populations in Brazil [53] . Understanding the mechanisms behind this adaptation is crucial for advancing our knowledge of the reproductive biology of this highly adaptable Neotropical genus. In summary, the presence of spermatozoa in the distal ductus deferens of C. durissus across different phases of testicular activity indicates sperm storage, as suggested by the consistent proportion of spermatozoa among the groups analyzed. The intense secretory activity of the epithelial principal cells during the spermatogenic period, marked by PAS- and BB-positive secretions, appears to be associated with gamete maintenance. Furthermore, the reduction in luminal fluid in regressed rattlesnakes is suggestive of the resorptive function of the epithelial cells. We hypothesize that this mechanism may also ensure the viability of stored spermatozoa by increasing the concentration of glycoproteins. However, the duration of sperm viability within the ductus deferens of this species remains unknown [4] . To address this, we are currently evaluating the rattlesnake sperm lifespan inside the lumen of the ductus deferens using the cell tracker bromodeoxyuridine. As final remarks, although sperm storage is considered an obligatory part of the male Neotropical rattlesnake reproductive cycle, based on the dissociation between summer spermatogenesis and autumn mating, a recent study demonstrated a summer copulation for C. durissus [22] . Our results indicate that the maintenance of spermatozoa inside the ductus deferens is a strong evolutionary trait that persists in this species, possibly due to the reduced likelihood of encountering a receptive female in the wild. Understanding the functional mechanisms that support long-term sperm storage may, therefore, unlock new biotechnological opportunities, such as improving assisted reproductive technologies, enhancing conservation efforts for threatened species, and developing novel approaches for sperm preservation and fertility management in both wild and captive populations. 5 Conclusion The present study used histomorphometry and histochemistry techniques to investigate variations in the distal ductus deferens of C. durissus throughout the males’ reproductive cycle. Our approach contributes to a better understanding of sperm storage tactic in males of a Neotropical snake species, highlighting increased secretory activity of the principal cells during testicular activity. Ongoing immunohistochemistry studies focusing on determining whether the epithelial cells are responsive to androgens stimulation and whether their absorptive function is mediated by aquaporins will further contribute to a more detailed understanding of the physiology of the distal ductus deferens. CRediT authorship contribution statement Flávia Cappuccio Resende: Writing – review & editing, Writing – original draft, Supervision, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Gleide Fernandes de Avelar: Writing – review & editing, Resources, Formal analysis, Conceptualization. Leonardo Carvalho: Writing – original draft, Methodology, Investigation, Formal analysis, Data curation. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments We would like to thank S. M. Almeida-Santos and T. O. Farias for their suggestions regarding data analysis and manuscript development. We are grateful to the Ezequiel Dias Foundation for financial and logistical support and to the Chico Mendes Institute for Biodiversity Conservation (ICMBio) for providing the license to capture the snake specimens. We also appreciate the technical support of M. L. Santos and J. A. G. Cabral. Special thanks go to Giselle Agostini Cotta and Heloísa Marques for their administrative assistance in the laboratory. We are deeply grateful to Anthony Wagner for the English language revision. Appendix A Supporting information Supplementary data associated with this article can be found in the online version at doi:10.1016/j.therwi.2024.100114 . Appendix A Supplementary material Supplementary material
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| "TITLE: Colonoscopic resection of appendiceal endometriosis \n\nAUTHORS:\n- Nieto, Jose\n- Deshmukh,(...TRUNCATED)
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