Abstract: A method for operating an implantable medical device to control a stimulation therapy includes the steps of: sensing an acoustic energy; producing acoustic signals indicative of heart sounds of the heart of the patient over predetermined periods of a cardiac cycle during successive cardiac cycles; extracting a signal corresponding to a first heart sound (S1) from a measured acoustic signal; calculating an energy value corresponding to the extracted signal; storing the energy value corresponding to the first heart sound; and initiating an optimization procedure, the optimization procedure comprising the steps of: iteratively controlling a delivery of the pacing pulses based on successive energy values corresponding to successive first heart sound signals and determining an optimal PV interval or AV interval with respect to the energy values. A medical device and a computer readable medium to implement the method.

Abstract: The present invention includes a method for controlling pacemaker therapy in a patient with an implanted biological pacemaker. The method may include pacing a heart at a predetermined rate using an electronic pacemaker and configuring the pacemaker to periodically enter a biological pacemaker weaning mode. The weaning mode may include ceasing pacing for at least a predetermined length of time and monitoring the heart to detect electrical depolarizations of a ventricle of the heart during the predetermined length of time. The weaning mode may further include determining the length of time between the cessation of pacing and the detected electrical depolarization and determining if the length of time between the cessation of pacing and the detected electrical depolarization is less than a maximum predetermined interval. The pacemaker therapy may be withheld as long as the length of time is less than the maximum predetermined interval.

Abstract: A medical device delivers a therapy to a patient. Posture events are identified, e.g., a posture of the patient is periodically determined and/or posture transitions by the patient are identified, and each determined posture event is associated with a current therapy parameter set. A value of at least one posture metric is determined for each of a plurality of therapy parameter sets based on the posture events associated with that therapy parameter set. A list of the therapy parameter sets is presented to a user, such as a clinician, for evaluation of the relative efficacy of the therapy parameter sets. The list may be ordered according to the one or more posture metric values to aid in evaluation of the therapy parameter sets. Where values are determined for a plurality of posture metrics, the list may be ordered according to the one of the posture metrics selected by the user.

Abstract: Systems, devices and methods for detecting and monitoring cardiac dysfunction. The devices include motion sensors for detecting signals representative of the total movement of the heart, and of the apex of the heart in particular.

Abstract: Methods for evaluating motion of a cardiac tissue location, e.g., heart wall, are provided. In the subject methods, timing of a signal obtain from a strain gauge stably associated with the tissue location of interest is employed to evaluate movement of the cardiac tissue location. Also provided are systems, devices and related compositions for practicing the subject methods. The subject methods and devices find use in a variety of different applications, including cardiac resynchronization therapy.

Abstract: An implantable cardiac device is configured and programmed to assess a patient's cardiopulmonary function by evaluating the patient's minute ventilation response. Such evaluation may be performed by computing a minute ventilation response slope, defined as the ratio of an incremental change in minute ventilation to an incremental change in measured activity level. The minute ventilation response slope may then be compared with a normal range to assess the patient's functional status.

Abstract: A motion sensor, and an implantable cardiac stimulator incorporating such a motion sensor, has a fluid-type housing containing a fluid that includes at least one type of anisotropic molecules, the anisotropic molecules exhibiting an anisotropic property having a state that changes dependent on motion. The housing of the motion sensor is located externally on an animate subject, or is implanted in the animate subject, and includes externally accessible electrodes that detect a change in the state of the anisotropic property and emit an output signal representative of an activity level of the subject.

Abstract: A heart stimulator for enhancing cardiac performance of a patient suffering from ventricular rhythms that tend to overdrive the patient's atrial rhythm, has sensing circuitry that detects atrial events and ventricular events, and an atrial stimulator that generates and supplies stimulation pulses to the atrium. A timer generates a detection window having a predetermined duration for the ventricular sensing, the detection window starting upon detection of an intrinsic or stimulated atrial event. If an R-wave is sensed from the ventricle during the detection window, a control unit determines that a focus, that pre-depolarizes the ventricles, exists, and the control unit operates the atrial stimulator to increase the atrial stimulation rate for a predetermined number of consecutive heart cycles.

Abstract: A method and device for delivering cardiac function therapy on a demand basis. An implantable device for delivering cardiac function therapy is programmed to suspend such therapy at periodic intervals or upon command from an external programmer. Measurements related to hemodynamic performance are then taken using one or more sensing modalities incorporated into the device. Based upon these measurements, the device uses a decision algorithm to determine whether further delivery of the cardiac function therapy is warranted.

Abstract: An active implantable medical device having a function for monitoring the sympathico-vagal activity by an analysis of endocardiac acceleration. The device collects at least one physiological parameter of the patient, analyzes that collected parameter and delivers at an output data representative of the sympathico-vagal activity of the patient. The physiological parameter is an endocardiac acceleration (EA), and the representative data include at least one value function of the endocardiac acceleration, in particular a function of a first peak (PEA I) at the time of the phase of isovolumic ventricular contraction and/or of a second peak (PEA II) at the time of the phase of isovolumic ventricular relieving.

Abstract: Techniques are provided for tracking patient respiration based upon intracardiac electrogram signals or other electrical cardiac signals. Briefly, respiration patterns are detected by integrating cardiac electrical signals corresponding to individual paced cardiac cycles. The integrals may be obtained between consecutive pairs of ventricular pacing pulses or between consecutive pairs of atrial pacing pulses. In either case, cyclical changes in the integrals of the individual cardiac cycles are tracked. The cyclical changes are representative of respiration. Once respiration patterns have been identified, episodes of abnormal respiration, such as apnea, hyperpnea, nocturnal asthma, or the like, may be detected and therapy automatically delivered.

Abstract: A method and device for delivering cardiac function therapy on a demand basis. An implantable device for delivering cardiac function therapy is programmed to suspend such therapy at periodic intervals or upon command from an external programmer. Measurements related to hemodynamic performance are then taken using one or more sensing modalities incorporated into the device. Based upon these measurements, the device uses a decision algorithm to determine whether further delivery of the cardiac function therapy is warranted.

Abstract: An implantable cardiac device is configured and programmed to assess a patient's cardiopulmonary function by evaluating the patient's minute ventilation response. Such evaluation may be performed by computing a minute ventilation response slope, defined as the ratio of an incremental change in minute ventilation to an incremental change in measured activity level. The minute ventilation response slope may then be compared with a normal range to assess the patient's functional status.

Abstract: A method and device for treating myocardial ischemia are described in which the stress experienced by a myocardial region identified as vulnerable to becoming ischemic is varied with pre-excitation pacing. In an unloading mode, pacing is applied in proximity to the vulnerable region to reduce stress and the metabolic demand of the region. In a loading mode, pacing is applied to a region remote from the vulnerable region in order to produce a conditioning effect.

Abstract: An apparatus and method for reversing ventricular remodeling with electro-stimulatory therapy. A ventricle is paced by delivering one or more stimulatory pulses in a manner such that a stressed region of the myocardium is pre-excited relative to other regions in order to subject the stressed region to a lessened preload and afterload during systole. The unloading of the stressed myocardium over time effects reversal of undesirable ventricular remodeling.

Abstract: Heart treatment equipment and a heart treatment method directed to prevention of a fatal arrhythmia by detecting a physical exercise or a mental stress by using a sensor and thereafter controlling the vagus nerve stimulation, wherein sensor means for detecting various living body information for generating a signal which designates degree of a sympathetic tone is provided and heart rate threshold for carrying out the vagus nerve stimulation is adjusted according to the living body information detected by the sensor means. Further, a nerve stimulation parameter for adjusting the strength of the vagus nerve stimulation is adjusted in response to the degree of the patient sympathetic tone.

Abstract: An exemplary method includes detecting a change in position, measuring cardiac output after the detecting a change in position and, based at least in part on the measuring cardiac output, deciding whether to increase a cardiac pacing rate. An exemplary method may rely on activity in lieu of or in addition to position to decide whether to increase a cardiac pacing rate. Various exemplary methods aim to compensate for orthostatic effects such as those associated with dysautonomia. Various other exemplary methods are disclosed along with various exemplary devices, systems, etc.

Abstract: A medical device delivers a therapy to a patient. The medical device may identify posture events, e.g., periodically determine a posture of the patient and/or identify posture transitions by the patient, and associate each determined posture event with a current therapy parameter set. A value of at least one posture metric is determined for each of a plurality of therapy parameter sets based on the posture events associated with that therapy parameter set. A list of the therapy parameter sets is presented to a user, such as a clinician, for evaluation of the relative efficacy of the therapy parameter sets. The list may be ordered according to the one or more posture metric values to aid in evaluation of the therapy parameter sets. Where values are determined for a plurality of posture metrics, the list may be ordered according to the one of the posture metrics selected by the user.

Abstract: The invention is directed to sensing techniques that can be executed by an implantable medical device (IMD). The sensing techniques exploit the fact that useful information can be sensed during the periods where the sympathetic and vagal tone balance changes in a patient's nervous system. This balance generally changes when a patient is falling asleep or waking up from sleep. In accordance with the invention, sensed information is recorded specifically during the times where a patient is either falling asleep or waking up. The IMD can be designed to sense or identify when a patient is falling asleep or waking up, and can record the useful sensed information specifically during those times.

Abstract: A method of predicting an arrhythmia, such as ventricular tachycardia, for example, in a medical device using a quantitative measure in order to allow assessment of patient risk and to enable preventative interventions by the device and clinicians. The trending of day and night average heart rates, along with patient physical activity can be analyzed to provide prediction of impending arrhythmia within weeks. By examining day and night average heart rate for crossover points, where the night heart rate equals or exceeds the day rate, and monitoring for a concomitant elevation in the night heart rate from a reference value, specific days heralding an increased risk of arrhythmia can be determined and therapy can be updated accordingly.

Abstract: A medical device, programmer, or other computing device may determine values of one or more activity and, in some embodiments, posture metrics for each therapy parameter set used by the medical device to deliver therapy. The metric values for a parameter set are determined based on signals generated by the sensors when that therapy parameter set was in use. Activity metric values may be associated with a postural category in addition to a therapy parameter set, and may indicate the duration and intensity of activity within one or more postural categories resulting from delivery of therapy according to a therapy parameter set. A posture metric for a therapy parameter set may indicate the fraction of time spent by the patient in various postures when the medical device used a therapy parameter set. The metric values may be used to evaluate the efficacy of the therapy parameter sets.

Abstract: A cardiac rhythm management device in which an accelerometer is used to detect diaphragmatic or other skeletal muscle contraction associated with the output of a pacing pulse. Upon detection of diaphragmatic contraction, the device may be configured to automatically adjust the pacing pulse energy and/or pacing configuration.

Abstract: A device and method for delivering electrical stimulation to the heart in a manner which provides a protective effect against subsequent ischemia is disclosed. The protective effect is produced by configuring a cardiac pacing device to intermittently switch from a normal operating mode to a stress augmentation mode in which the spatial pattern of depolarization is varied to thereby subject a particular region or regions of the ventricular myocardium to increased mechanical stress.

Abstract: A system comprising an implantable medical device (IMD). The IMD comprises a ventricular heart signal sensing circuit to provide a ventricular heart signal, at least one sensor operable to provide an electrical signal representative of patient activity, a sensor interface circuit coupled to the at least one sensor to provide an activity signal, and a controller circuit coupled to the heart signal sensing circuit and the sensor interface circuit. The controller circuit is operable to determine whether ventricular ectopy occurs during recovery from exercise using the heart signal, and to set at least one warning indicator if ventricular ectopy occurs during the recovery from exercise.

Abstract: An implantable cardiac device is configured and programmed to assess a patient's cardiopulmonary function by evaluating the patient's heart rate response. Such evaluation may be performed by computing a heart rate response slope, defined as the ratio of an incremental change in intrinsic heart rate to an incremental change in measured activity level. The heart rate response slope may then be compared with a normal range to assess the patient's functional status.

Abstract: A method and device for delivering ventricular resynchronization pacing therapy in conjunction with electrical stimulation of nerves which alter the activity of the autonomic nervous system is disclosed. Such therapies may be delivered by an implantable device and are useful in preventing the deleterious ventricular remodeling which occurs as a result of a heart attack or heart failure. The device may perform an assessment of cardiac function in order to individually modulate the delivery of the two types of therapy.

Abstract: An implantable medical device includes a dual-use sensor such as a single accelerometer that senses an acceleration signal. A sensor processing circuit processes the acceleration signal to produce an activity level signal and a heart sound signal. The implantable medical device provides for rate responsive pacing in which at least one pacing parameter, such as the pacing interval, is dynamically adjusted based on the physical activity level. The implantable medical device also uses the heart sounds for pacing control purposes or transmits a heart sound signal to an external system for pacing control and/or diagnostic purposes.

Abstract: A method and device for sensing cardiac activity that includes a first plurality of electrodes forming a first electrode configuration to sense cardiac activity, a second plurality of electrodes forming a second electrode configuration to sense cardiac activity, and a third plurality of electrodes to deliver a stimulation pulse in response to the sensed cardiac activity. A microprocessor determines whether an escape interval associated with the delivered stimulation pulse is less than a rate limit interval, and a control circuit switches from the first plurality of electrodes to the second plurality of electrodes in response to the escape interval being less than the rate limit interval.

Abstract: A system and method are provided for compensating for the drop in blood pressure upon standing. Upon transition from prolonged sitting, lying down, or standing position, the pacemaker abruptly increasing its pacing rate upon postural transition. This pacing rate is triggered when a patient stands after a prolonged reclined or supine/prone position.

Abstract: A method of data management for optimizing the patient outcome from the provision of cardiac resynchronization therapy (CRT) is described. This method describes a process by which sets of dynamic cardiopulmonary dependent variables are measured during steady-state conditions, displayed, and translated into quantitative and qualitative measurements while the independent variables of CRT, device lead placement and atrial-ventricular and interventricular delay settings of bi-ventricular pacemaker systems, are altered by a physician. In combination with visual observation and computer-assisted ranking of the dependent variables, a physician can utilize the resulting information to render decisions on the optimal choice of the independent variables.

Abstract: A cardiac rhythm management system includes an implantable device executing a dynamic pacing algorithm after an myocardial infarction (MI) event. The dynamic pacing algorithm dynamically adjusts one or more pacing parameters based on a person's gross physical activity level. Examples of the one or more pacing parameters include atrioventricular pacing delays and pacing channels/sites. The dynamic pacing algorithm provides for improved hemodynamic performance when a person's metabolic need is high, and post MI remodeling control when the person's metabolic need is low.

Abstract: An implantable cardiac stimulation device is configured to measure selected ventricular contraction parameters and possibly apply stimulation therapy based on the ventricular contraction parameters. In accordance with one aspect, the ventricular contraction parameters include impedance values that correspond to the volume of fluid in the right ventricle and the left ventricle. In accordance with another aspect, the ventricular contraction parameters include motion values that correspond to heart sounds/motion in the right ventricle and the left ventricle. The ventricular contraction parameters can be used to form pseudo P-V loop from which treatment decisions can be made.

Abstract: A cardiac rhythm management system provides for assessment of cardiac mechanical dyssynchrony based on heart sound morphology and optimization of pacing parameters based on the effect of pacing on the cardiac mechanical dyssynchrony assessment. A degree of cardiac mechanical dyssynchrony is measured by the time delay between tricuspid valve closure and mitral valve closure and/or the time delay between pulmonary valve closure and aortic valve closure. A cardiac resynchronization therapy is optimized by determining therapy parameters to provide an approximately minimum degree of cardiac mechanical dyssynchrony by cardiac pacing.

Abstract: A system and automated method for assessing ventricular synchrony in ambulatory patients is provided including at least one mechanical sensor (e.g., accelerometer, tensiometric sensor, force transducer, and the like) operatively coupled to a first myocardial location in order to measure a wall motion signal of a first chamber, and a second mechanical sensor operatively coupled to a second myocardial location in order to measure a wall motion signal of a second chamber. The wall motion signals are processed in order to identify the time at which a fiducial (e.g., an inflection point, a threshold crossing, a maximum amplitude, etc.) occurs for each respective signal. The temporal separation between the fiducial points on each respective signal is measured as a metric of ventricular synchrony and can be optionally utilized to adjust pacing therapy timing to improve synchrony.

Abstract: Techniques for detection and treatment of myocardial ischemia are described that monitor both the electrical and dynamic mechanical activity of the heart to detect and verify the occurrence of myocardial ischemia in a more reliable manner. The occurrence of myocardial ischemia can be detected by monitoring changes in an electrical signal such as an ECG or EGM, and changes in dynamic mechanical activity of the heart that are sensed by an accelerometer sensor. The heart acceleration signal can be obtained from an single- or multiple-axis accelerometer and/or a pressure sensor deployed within or near the heart. The techniques correlate contractility changes detected by an accelerometer or pressure sensor with changes in the ST electrogram segment detected by the electrodes to increase the reliability of ischemia detection.

Abstract: An exemplary method includes detecting movement of an in vivo oscillator using one or more in vivo sensors, receiving information from at least one of the one or more sensors, and deciding whether to switch an implanted cardiac therapy device from a lower tier of anti-arrhythmia therapy to a higher tier of anti-arrhythmia therapy based at least in part on the information. An exemplary implantable device includes a micro-electromechanical system (MEMS) capable of measuring acceleration and logic capable of determining postural sway based at least in part on acceleration measured by the MEMS. Various other exemplary methods, devices and systems are also disclosed.

Abstract: An implantable device that can automatically monitor and record patient activity as sensed by an activity monitor. In certain variations, the activity monitor can include an accelerometer providing three-axis acceleration signals and in other variations the activity sensor can include a position sensor, such as a GPS receiver. The implantable device automatically determines if patient activity exceeds a determined threshold and monitors and records a total equivalent distance traveled for a determined period, which may be set equal to a standard measure such as a six minute period. The device can monitor and record multiple periods of activity and the periods may be consecutive, overlapping, and/or separate in time. The device may store all activity records or selected records which may correspond to daily, weekly, or other periodic maxima.

Abstract: Techniques are provided for detecting and tracking heart failure based on heart rate, rest rate and activity levels. Briefly, histograms are generated based on rest-rate adjusted heart rate values and corresponding activity level values. Heart failure is then detected and tracked based on an analysis of the histogram. In one example, so long as the activity level of the patient exceeds some minimum threshold, the ratio of adjusted heart rate to activity level is periodically calculated and resulting values are stored in a histogram. Each day, the histogram is compared against a previous histogram to detect any overall trend. For example, the centroid of the histogram can be calculated each day with any changes in the centroid values used to track progression of heart failure.

Abstract: Energy efficient methods and systems for using multi-dimensional activity sensors with implantable cardiac devices are provided. In certain embodiments the output of a passive activity sensor (used for rate responsive pacing) is used to trigger temporary use of a relatively high power multi-dimensional activity sensor. In other embodiments, the output of a relatively low power oxygen saturation sensor is used to trigger temporary use of a relatively high power multi-dimensional activity sensor. This description is not intended to be a complete description of, or limit the scope of, the invention.

Abstract: A rate-adaptive pacemaker is disclosed in which a sensor-indicated rate is calculated by adding a function of the measured exertion level to a programmed lower rate limit. In the case where the function of the measured exertion level is the difference between a short-term average and a long-term average of the measured exertion level, the lower rate limit is modulated as a function of the long-term average of the measured exertion level and maximum and minimum values of the long-term average of the measured exertion level during a defined extended time period.

Abstract: Time-varying spatial signals are detected by accelerometers mounted within the patient. The signals, representative of the actual 3-D trajectory of the patient, are compared with information representative of expected trajectories retrieved from memory to identify a current patient posture, which may be either a dynamic posture such as walking or running or a change in posture such as rising from a seated position to a standing position. In this manner, a change in posture of the patient is identified based upon a full 3-D trajectory, rather than merely the orientation of the patient at the beginning and the end of the change in posture. In an example described herein, the implantable device stores information representative of expected 3-D trajectories in the form of pre-calculated comparison matrices derived from orthonormal kernels employing Laguerre functions or Lagrange functions.

Abstract: Time-varying spatial signals are detected by accelerometers mounted within the patient. The signals, representative of the actual 3-D trajectory of the patient, are compared with information representative of expected trajectories retrieved from memory to identify a current patient posture, which may be either a dynamic posture such as walking or running or a change in posture such as rising from a seated position to a standing position. In this manner, a change in posture of the patient is identified based upon a full 3-D trajectory, rather than merely the orientation of the patient at the beginning and the end of the change in posture. In an example described herein, the implantable device stores information representative of expected 3-D trajectories in the form of pre-calculated comparison matrices derived from orthonormal kernels employing Laguerre functions or Lagrange functions.

Abstract: Methods and apparatus are provided for an accelerometer. The apparatus includes first, second, and third substrates. The first substrate includes the first plate of a first capacitor. The second substrate includes a moveable mass that is coupled to the second substrate by at least one spring. The moveable mass is the second plate of the first capacitor and the first plate of a second capacitor. The third substrate includes the second plate of the second capacitor. The moveable mass is prevented from moving in any direction where the at least one spring is inelastically flexed. The first substrate couples to the second substrate. The third substrate couples to the second substrate. The method includes forming a moveable mass in a substrate. The moveable mass is formed having a plurality of springs coupling the moveable mass to the substrate. The moveable mass is released using a dry etch.

Abstract: A cardiac stimulation device and method monitor and store discrepancies in sensor indicated rates determined from two or more sensors generating signals related to metabolic demand. One feature included in the present invention is a sensor cross-check record that stores the time, duration and sensor indicated rates whenever individual sensor indicated rates differ by more than a discrepancy threshold. This record allows a clinician to monitor an abnormal patient condition or determine if a sensor is not functioning properly or is programmed sub-optimally. Another feature provided by the present invention is a sensor cross-check histogram in which sensor indicated rate differences are stored. Histogram data aids the clinician in selecting programmable operating parameters that control the calculation of sensor indicated rates and the rate response of the cardiac stimulation device.

Abstract: Methods and systems for providing cardiac therapy are described. In some embodiments, methods and systems are configured to deliver atrial tachyarrhythmia therapy by confirming that a patient is asleep and thereafter administering the therapy. Sleep can be confirmed, in some embodiments, through the use of a histogram that can be calculated using one or more parameters that are monitored by an implantable stimulation device. Parameters can include both physiological and non-physiological parameters. In other embodiments, atrial tachyarrhythmia therapy is delivered by determining desirable times to administer such therapy. Other various systems and methods for administering cardiac therapy are described.

Abstract: An implantable medical device delivers augmentation therapy to intervene in a pattern of sleep-disordered breathing. Augmentation therapy includes the delivery of electrical stimulation to cardiac tissue above and/or below a capture threshold. PESP and NES/CCM are possible augmentation therapies that are used alone or in combination. In addition, augmentation therapies can be used with other pacing therapies such as atrial overdrive pacing and atrial coordinated pacing as a therapy for sleep-disordered breathing.

Abstract: An implantable neural stimulation device and method treats peripheral vascular disease of a patient. The device includes a pulse generator that provides stimulation pulses and an implantable lead that applies the stimulation pulses to neural tissue. An activity sensor senses activity level of the patient and a processor, responsive to the activity sensor, controls the provision of the stimulation pulses by the pulse generator. The processor causes the pulse generator to provide stimulation therapy any time the patient is active or when the patient is at rest. The processor further provides long term activity monitoring and closed loop control of neural tissue stimulation levels to adapt the stimulation therapy to changes in the patient's condition.

Abstract: An implantable cardiac device is programmed to monitor short term activity changes that occur while a patient is at rest to produce a sleep disturbance metric that is useful in analyzing and/or treating sleep apnea. After the implantable cardiac device confirms that a patient is at rest, the device monitors an instantaneous signal from an activity sensor to detect variances from normal rest mode activity. When the variances exceed a preset threshold for a short time period (e.g., less than 30–40 sec.), the patient is presumed to be experiencing a form of sleep disturbance as opposed to conscious or wakeful activity. These short term events are recorded as sleep disturbance events. The sleep disturbance metric are reported to a physician as a diagnostic to help ascertain the severity of sleep apnea or to evaluate the effectiveness of pacing therapies being applied to treat sleep apnea.

Abstract: The present invention relates to monitoring septal wall motion of the atrial and/or ventricular chambers of a heart for optimizing cardiac pacing intervals based on signals derived from the monitored wall motion. At least one lead of medical device is equipped with a motion sensor adapted to couple to septal tissue. The device receives and may post-process (e.g., suitably filter, rectify and/or integrate) motion signals to determine acceleration, velocity and/or displacement. During pacing interval optimization the wall motion is measured for those pacing intervals and the pacing interval setting(s) that produce minimal wall motion for chronic therapy delivery. In addition, methods for periodically determining whether to cease or resume delivery of a bi-ventricular pacing therapy to a patient that may have experienced beneficial reverse remodeling of the heart.

Abstract: A method and system for automatically adjusting the operating parameters of a rate-adaptive cardiac pacemaker in which maximum exertion levels attained by the patient are measured at periodic intervals and stored in order to compute or update a maximum exercise capacity. The slope of the rate-response curve is then adjusted to map an exertion level corresponding to the updated maximum exercise capacity to a maximum allowable pacing rate. In accordance with the invention, a maximum exercise capacity is determined by cross-checking periodic maximum exertion level sensor values with a motion-level sensor value.