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of the magnet over the reed switch after enabling of the timer to thereupon disable the timer before the preset period of time has expired. If the second pass of |
the magnet occurs after the exercise rate has begun, the element for increasing the rate is disabled to return the pulse generator to the lower pacing rate. The change in |
pacing rates is made in steps. 1. In combination with an implantable cardiac pacemaker for delivering electrical stimuli to the heart of a patient to pace the heart rate, said |
pacemaker comprising: pulse generator means for selectively producing said electrical stimuli at a fixed resting rate and at a higher exercise rate, lead means associated with said pulse generator for |
delivering said stimuli to a selected chamber of the heart, and timer means for stepping-up said pulse generator means from said resting rate to said exercise rate after an adjustable |
preset delay following activation of said timer means, said preset delay being of a duration perceptible by the patient; and external control means for patient initiation of a first command |
to said pacemaker to activate said timer means. 2. In combination with an implantable cardiac pacemaker for delivering electrical stimuli to the heart of a patient to pace the heart |
rate, said pacemaker comprising: pulse generator means for selectively producing said electrical stimuli at a fixed resting rate and a higher exercise rate, lead means associated with said pulse generator |
for delivering said stimuli to a selected chamber of the heart, and delay means for stepping-up said pulse generator means from said resting rate to said exercise rate after an |
adjustable preset delay following activation of said delay means, means associated with said pulse generator means and said delay means for maintaining said exercise rate for a predetermined time interval |
following said preset delay and then returning said pulse generator means to said resting rate; and an external control means for patient-initiation of a command to said pacemaker to activate |
said delay means. 3. The combination according to claim 2, wherein said delay means is responsive to a second command initiated by the patient from said external control means at |
any time after receipt of the first said command and before the expiration of said predetermined time interval, to cancel the activation of said delay means. 4. The combination according |
to claim 3, wherein the stepping up and returning of said rates at which said stimuli are produced by said pulse generator means is effected gradually. 5. An implantable pulse |
generator unit for a cardiac pacemaker for use with an external magnet to permit patient-initiated adjustment of pacing rate from a resting rate to an exercise rate and vice versa, |
said unit comprising: generator means for generating electrical stimuli at said resting rate, control means associated with said generator means responsive, when enabled, for controllably increasing the rate at which |
electrical stimuli are generated from said generator means from said resting rate to said exercise rate, and timer means responsive to positioning of said external magnet in proximity to said |
pulse generator unit for enabling said control means an adjustable preset delay period after said positioning, said preset delay period being of a duration perceptible to the patient. 6. An |
implantable pulse generator unit for a cardiac pacemaker for use with an external magnet to permit patient-initiated adjustment of pacing rate from a resting rate to an exercise rate and |
vice versa, said unit comprising: generator means for generating electrical stimuli at said resting rate, control means associated with said generator means responsive, when enabled, for controllably increasing the rate |
at which electrical stimuli are generated by said generator means from said resting rate to said exercise rate, said control means including timing means for maintaining the rate at which |
electrical stimuli are generated by said generator means at said exercise rate for a predetermined time interval; and delay means responsive to positioning of said external magnet in proximity to |
said pulse generator unit for enabling said control means an adjustable preset delay period thereafter. 7. The pulse generator unit of claim 6, wherein said control means automatically returns said |
generator means to said resting rate following the expiration of said predetermined time interval. 8. The pulse generator unit of claim 7, wherein said control means gradually increases the rate |
at which electrical stimuli are generated by said generator means from said resting rate to said exercise rate, and gradually returns said generator means to said resting rate following the |
expiration of said predetermined time interval. 9. The pulse generator unit of claim 6, wherein said delay means is responsive to a repositioning of said external magnet in proximity to |
said pulse generator unit after said control means has been enabled, for disabling said control means. 10. A cardiac pacemaker pulse generator for generating electrical stimuli to be delivered to |
the heart of a patient to pace the heart rate, said generator comprising: means for generating said electrical stimuli at a first pacing rate, means electrically connected to said stimuli |
generating means for selectively increasing the rate at which said stimuli are generated to a second higher pacing rate, timing means for triggering said rate increasing means to increase said |
first pacing rate to a second higher pacing rate upon passage of an adjustable preselected period of time after said timing means is enabled, said preselected period of time being |
of a duration perceptible by the patient, means responsive to a command signal from a patient-activated external device for enabling said timing means to commence timing. 11. The pulse generator |
according to claim 10, wherein said enabling means is further responsive to a second command signal after said timing means is enabled, to disable said timing means prior to passage |
of said preselected period of time. 12. The pulse generator according to claim 10, further including means responsive to a second command signal while said stimuli are being generated at |
said second higher pacing rate, for disabling said rate increasing means and thereby returning the rate at which said stimuli are generated by said stimuli generating means to said first |
pacing rate. 13. The pulse generator according to claim 12, wherein said rate increasing means is responsive, when disabled, to decrementally reduce the rate at which said stimuli are generated |
by said stimuli generating means. 14. The pulse generator according to claim 10, wherein said rate increasing means is responsive to said timing means reaching preset time intervals toward passage |
of said preselected period of time, for incrementally increasing the rate at which said stimuli are generated by said stimuli generating means in steps as each preset time interval is |
reached. 15. The method of pacing a pacemaker patient's heart rate using a magnet-controlled implantable pulse generator to adjust the stimulation rate from a resting rate to an exercise rate |
and vice versa, comprising the steps of maintaining the stimulation rate of said pulse generator at said resting rate, initiating a command signal to reset the stimulation rate of said |
pulse generator to said exercise rate after an adjustable programmed delay period following said command signal, and returning the stimulation rate of said pulse generator to said resting rate in |
increments following a predetermined interval of time at said exercise rate. The present invention relates generally to medical devices, and more particularly to implantable artificial cardiac pacemakers adapted to provide |
patient-variable stimulation rates appropriate to a condition of exercise by the patient. The resting heart rate of sinus rhythm, that is, the rate determined by the spontaneously rhythmic electrophysiologic property |
of the heart's natural pacemaker, the sinus node, is typically in the range from about 65 to about 85 beats per minute (bpm) for adults. Disruption of the natural cardiac |
pacing and propagation system may occur with advanced age and/or cardiac disease, and is often treated by implanting an artificial cardiac pacemaker in the patient to restore and maintain the |
resting heart rate to the proper range. In its simplest form, an implantable pacemaker for treatment of bradycardia (abnormally low resting rate, typically below 60 beats per minute (bpm)) includes |
an electrical pulse generator powered by a self-contained battery pack, and a catheter lead including at the distal end a stimulating cathodic electrode electrically coupled to the pulse generator. The |
lead is implanted intravenously to position the cathodic electrode in stimulating relation to excitable myocardial tissue in the selected chamber on the right side of the patient's heart. The pulse |
generator unit is surgically implanted in a subcutaneous pouch in the patient's chest, and has an integral electrical connector to receive a mating connector at the proximal end of the |
lead. In operation of the pacemaker, the electrical pulses are delivered (typically, on demand) via the lead/electrode system, including an anodic electrode such as a ring behind the tip for |
bipolar stimulation or a portion of the pulse generator case for unipolar stimulation, and the body tissue and fluid, to stimulate the excitable myocardial tissue. Pacemakers may operate in different |
response modes, such as asynchronous (fixed rate), inhibited (stimulus generated in absence of specified cardiac activity), or triggered (stimulus delivered in presence of specified cardiac activity). Further, present-day pacers range |
from the simple fixed rate device that offers pacing with no sensing (of cardiac activity) function, to fully automatic dual chamber pacing and sensing functions (so-called DDD pacemakers) which may |
provide a degree of physiologic pacing by at least a slight adjustment of heart rate according to varying metabolic conditions in a manner akin to the natural pacing of the |
heart. Thus, some DDD pacemaker patients experience an increased pacing rate with physical exertion, with concomitantly higher cardiac output, and thereby, an ability to handle low levels of exercise. Unfortunately, |
a significant percentage of the pacemaker patient population, who suffer from atrial flutter, atrial fibrillation or sick-sinus syndrome, for example, cannot obtain the benefit of exercise-responsive pacing with conventional atrial-triggered |
pacemakers. Moreover, the DDD-type pacemakers are complex and costly to manufacture, which is reflected in a higher price to the patient. It is a principal object of the present invention |
to provide a relatively simple and inexpensive pacemaker which provides pacing at a desired resting rate, and which is subject to limited control by the patient to provide a desired |
exercise rate for a preset period of time following which the pacemaker returns to the resting rate. Various types of rate responsive pacemakers have been proposed which would sense a |
physiological parameter that varies as a consequence of physical stress, such as respiration, blood oxygen saturation or blood temperature, or merely detect physical movement, and correspondingly adjust the pacing rate. |
Many of these rate responsive pacemakers may also be relatively complex, and therefore expensive to the patient. The present invention is directed toward a low cost pacemaker which can be |
adjusted at will by the patient, subject to the limited amount of control programmed into the device by the physician for that patient. According to the invention, patient control is |
manifested by bringing an external magnet into proximity with an implanted reed switch associated with the pacemaker. Of course, limited magnet control has been afforded to the patient in the |
past for some purposes, such as to enable transtelephonic monitoring of the pacemaker functions. Also, techniques are presently available which permit external adjustment of the stimulation rate of the pacemaker |
after implantation, as by means of a programming unit available to the physician. For obvious reasons, it is undesirable to give the patient the same latitude to control his pacemaker. |
In U.S. Pat. No. 3,623,486, Berkovits disclosed a pacemaker adapted to operate at either of two stimulation rates, and switchable from one to the other by the physician using an |
external magnet. In this manner, the physician would be able to control the pacer mode and rate according to the needs of the particular patient. The purpose, in part, was |
to provide a pacemaker which had some adaptability to the patient's requirements. However, once set by the physician, the selected resting rate was maintained for that patient by the implanted |
pacer. Another technique for external adjustment of pacing rate by the physician is found in the disclosures of U.S. Pat. No. 3,198.195 to Chardack, and U.S. Pat. No. 3,738,369 to |
Adams et al. In each, rate control is exercised by inserting a needle through a pacemaker aperture beneath the patient's skin to adjust a mechanism. In the Adams et al. |
disclosure, the needle is used to change the position of a magnet within the paper to actuate a rate-controlling reed switch. In U.S. Pat. No. 3,766,928, Goldberg et al. describe |
an arrangement for continuous adjustment of rate by a physician using an external magnet that cooperates with a magnet attached to the shaft of a rate potentiometer in the implanted |
pacemaker, to provide the initial setting of pacing rate desirable for the particular patient. More recent proposals offer the patient limited control over the pacing rate. In U.S. Pat. No. |
4,365,633, Loughman et al. disclose a pacemaker programmer which is conditioned by the physician to give the patient the capability to select any of three distinct rates: for sleep, for |
an awake resting state, and for exercise. The programmer generates a pulsating electromagnetic field, and allows the patient to select any of those three modes with an abrupt change in |
rate when the coil pod of the programmer is positioned over the implanted pacemaker. It is, of course, necessary to have the programmer at hand in order to change the |
stimulation rate, and the use of the device in public can be a source of extreme embarassment to the patient. In U.S. Pat. No. 4,545,380, Schroeppel describes a technique for |
manual adjustment of rate control contrasted with the activity sensing, automatic rate control disclosed by Dahl in U.S. Pat. No. 4,140,132. According to the Schroeppel patent, a piezoelectric sensor and |
associated circuitry are combined with the implanted pulse generator of the pacemaker to allow the patient to change from a resting rate to a higher rate by sharp taps on |
his chest near the site of the piezoelectric sensor. Such an arrangement requires that the sensor be sufficiently sensitive to respond to the patient's sharp taps, and yet be insensitive |
to the everyday occurrences the patient encounters while undergoing normal activities and which could otherwise result in false triggerings. These include presence in the vicinity of loud noise such as |
is generated by street traffic, being jostled in a crowd, experiencing bumps and vibrations while riding in a vehicle, and the like. Further, even when controlled in the manner described, |
this type of switching results in an abrupt, non-physiological change of rate. Accordingly, it is another object of the present invention to provide a pacemaker which is capable of being |
controlled externally by the patient to assume exercise and non-exercise rate modes, in a manner that allows discreet and yet reliable control. Yet another object of the invention is to |
provide a cardiac pacemaker whose stimulation rate is controllable by and according to a schedule selected by the patient. Briefly, according to the present invention a cardiac pacemaker is manually |
controllable by the patient to preset time intervals of operation at a relatively high (exercise) rate and lower (resting) rate according to the patient's own predetermined schedule of exercise and |
rest. An important aspect of the invention is that the pulse generator may be implemented to undergo an adjustment of stimulation rate from a fixed resting rate of, say, 75 |
bpm, to a preselected exercise rate of, say, 120 bpm, following a predetermined period of time after activation by the patient using an external magnet, that is, after a predetermined |
delay following a patient-initiated command signal, and to remain at the higher rate for a preselected time interval. Thus, the patient may effectively "set a clock" in his pacemaker to |
elevate his heart rate at the time and for the duration of a scheduled exercise session, such as a game of tennis. Moreover, he may activate the pacemaker in this |
manner in the privacy of his own home well in advance of the exercise session. According to another aspect of the invention, the pulse generator is implemented to return automatically |
to the resting rate at the expiration of the preselected exercise rate time interval. Hence, the patient need not carry his magnet with him to readjust the pacer to the |
resting rate at the completion of the scheduled exercise session. According to this aspect, after operating at the elevated stimulation rate for a time interval preselected to be suitable for |
the exercise session, say, one hour, the generator resets itself to return to the initial resting rate. According to another feature of the invention, the rate is incremented and decremented |
in steps from one rate setting to the other to avoid abrupt changes, and therefore to provide a more physiological rate control than has heretofore been available in manually controlled |
pacemakers. A further feature of the invention is that the pulse generator may be activated to disable the exercise rate command at any time after it has been given, including |
that to produce an early conclusion to an already-commenced exercise session. For example, if a scheduled tennis game or bicycling run is called off by the patient's partner after the |
patient has programmed in the higher rate, he need merely apply the magnet in proximity to the implanted pulse generator again to cancel the previous command and maintain the fixed |
resting rate. Similarly, if the exercise session is shortened, the rate may be returned to the resting rate by simply applying the magnet over the pulse generator. The above and |
still further objects, aspects, features and attendant advantages of the present invention will become apparent to those of ordinary skill in the field to which the invention applies from a |
consideration of the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawing, in which: FIG. 1 is a block circuit diagram of a pulse |
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