Abstract: An ischemia detector has a patient workload sensor and a patient breathing sensor which emits a signal representing sensed workload, and a patient breathing sensor which emits a signal representing sensed breathing activity of a patient. These signals are supplied to a detector unit which identifies a state of ischemia upon an occurrence of a predetermined relation between the sensed workload and the sensed breathing activity. This predetermined relation is a sensed low workload and a simultaneously sensed high breathing activity.

Abstract: An implanted defibrillator provides a device-implemented method of delivering cardiac pacing, cardioversion and defibrillation therapies in selective response to dysrhythmia detection of an implant patient's cardiac signal. The patient's heart rate is sensed, and cardioversion/defibrillation therapies are delivered by the device by producing electrical shocks of adjustable energy level for application to the patient's heart in response to applicable detected levels of pathologic accelerated heart rate. A match between the generated cardiac pacing rate and the contemporaneous hemodynamic needs of the implant patient under conditions of rest and physical activity is optimized by sensing periods of patient physical activity and rest and generating a signal representative thereof to control the cardiac pacing rate accordingly and according to the extent of activity by means of an accelerometer mounted on hybrid electronic circuitry of the device.

Abstract: A medical device system such as a pacemaker system is provided wherein pressure signals representative of a patient's cardiac movements are transmitted through a pacing lead to the pacemaker, where they are sensed and utilized for control of pacemaker operation. In a preferred embodiment, the invention utilizes a standard pacing lead, which may already be in place within the patient, the lead having a lumen through which relative pressure signals are transmitted from the patient's heart to the proximal end of the lead. The proximal end of the lead is connected to a pressure sensor, mounted either in the pacemaker header portion or within the hermetically sealed pacemaker can. The sensor signals are coupled to appropriate processing circuitry and are used for control of one or more pacing parameters, such as pacing rate.

Abstract: An implantable medical interventional device responds to detection of any of a plurality of cardiac dysrhythmias in a human patient by performing an appropriate therapy which may include cardiac pacing, cardioversion or defibrillation according to the nature of the detected dysrhythmia. A first sensor detects whether and what type of dysrhythmia is occurring. A generator produces pulses and/or shocks for delivery to the patient's heart according to whether a detected dysrhythmia is bradycardia or slow pathologic tachycardia on the one hand, or fast tachycardia or fibrillation on the other hand. An optimizer in the device at all times maintains a substantial match of the cardiac pacing rate to the hemodynamic needs of the implant patient under conditions of rest and physical activity; including sensing and distinguishing periods of patient physical activity and rest, and generating a signal representative thereof to control the cardiac pacing rate accordingly.

Abstract: A rate adaptive cardiac pacemaker having a first sensor for measuring a physiologic parameter reflecting metabolic demand and a second sensor for measuring a parameter reflecting the physical motion or activity of the patient, wherein the second sensor is used to generate a dynamic target pacing rate which the first sensor is optimized to over time, thereby reducing the time constant for the adaptation of the first sensor and minimizing the amount of clinical time required to initialize the cardiac pacemaker.

Abstract: An implantable medical device has a housing containing an accelerometer which detects vibrations of the housing. The accelerometer generates a vibration signal in response to the detected vibrations, which is supplied to a signal processing unit. The signal processing unit generates, for each of a number of predetermined frequency ranges, a parameter value indicative of a defined attribute of the vibration signal. The signal processing unit forms a ratio between any two of these parameter values, and emits at least one status value dependent on this ratio. The status value is uniquely indicative of a predetermined type or level of cardiac activity, and the status values can be used as a control signal for controlling therapy, such as cardiac stimulation, administered by the implantable medical device.

Abstract: An accelerometer and sensor assemblies for medical implantable devices such as pacemakers, cardioverters, IPGs, PCDs, defibrillators, ICDs, and the like, includes at least one intermediate metallization layer sandwiched between a first lower surface of at least one upper sheet formed from a piezoelectric material surface, and a second upper surface of at least one lower sheet formed from a piezoelectric material. The at least one upper sheet has a first outer edge disposed between its first upper and first lower surfaces. The at least one lower sheet has a second outer edge disposed between its second upper and second lower surfaces. The at least one intermediate metallization layer is not disposed at all locations between the first lower surface and the second upper surface, but extends to an external region disposed between the first outer edge and the second outer edge, and is electrically connected to the external region.

Abstract: An apparatus and method for assessing the status of well-being of patients being treated for CHF using cardiac pacing as a therapy. By sampling the output from an activity sensor or the like, and by noting the frequency with which the averaged rectified sensor output exceeds a preset threshold following changes in the pacing mode, the efficacy of the new mode compared to the previous one can be evaluated.

Abstract: A process of using a heart rate monitor to construct a user's personal heart rate curve, and using the heart rate curve to forecast the user's personal caloric expenditure on the basis of the user's heart rate while walking or running. A sub-unit installed within or otherwise connected to the electronic circuitry of a conventional heart rate monitor operates under control of a microprocessor. The sub-unit receives exogenous inputs by the user for conducting various calculations from a plurality of test data which is stored in memory by the user. The sub-unit utilizes the test data to calculate a rate of calories burned per pound for each test exercise, where the calculation is performed using a pre-programmed formula which differs according to the form of exercise. Next the sub-unit calculates a rate of calories burned per minute for each test exercise by multiplying the user's weight by the previously calculate rate per pound.

Abstract: A processing system and method are provided for deriving an improved hemodynamic indicator from cardiac wall acceleration signals. The cardiac wall acceleration signals are provided by a cardiac wall motion sensor that responds to cardiac mechanical activity. The cardiac wall acceleration signals are integrated over time to derive cardiac wall velocity signals, which are further integrated over time to derive cardiac wall displacement signals. The cardiac wall displacement signals correlate to known hemodynamic indicators, and are shown to be strongly suggestive of hemodynamic performance. An implantable cardiac stimulating device which uses cardiac wall displacement signals to detect and discriminate cardiac arrhythmias is also provided.

Abstract: An improved sensor and related method for multi-axial measurement of motion for an implantable medical device is disclosed. The sensor has a wide variety of applications, including use as a cardiac wall motion sensor or a physical activity sensor. The sensor includes first and second conductors over which the motion measurements are made. A first transducer provides a first motion measurement indicative of sensor acceleration during a first phase, while a second transducer provides a second motion measurement indicative of sensor acceleration during a second phase. The first and second transducers are connected in parallel so as to provide the first and second motion measurements to an implantable medical device over the first and second conductors. The first and second phases are non-overlapping periods of time so that the motion measurements from each transducer are time division multiplexed. The sensor provides motion measurements that may either be compensated or uncompensated for temperature effects.

Abstract: An implantable cardiac stimulation device, such as a pacemaker or an implantable cardioverter-defibrillator, that includes an accelerometer-based activity sensor that processes one or more signals from the activity sensor to obtain parameters that are indicative of the heartbeat of the patient. The implantable cardiac stimulation device determines when the patient is at rest and the activity sensor provides a signal that corresponds to the acceleration of the sensor due to the heartbeat of the patient. This acceleration signal is integrated over time once to provide a contractility parameter, which is indicative of the contractility of the heart and is integrated over time twice to provide a displacement parameter, which is indicative of the displacement of the heart wall during the heartbeat. This displacement parameter is thereby indicative of the volume of blood pumped by the heart.

Abstract: An annunciator for an implantable medical device encapsulated within a casing comprises a magnetically permeable stationary ring member including an integral inwardly projecting peripheral flange having opposed sides on which electrically conductive coils are mounted. An oscillating member encompassed by the stationary ring member includes a planar magnet member having opposed surfaces of opposite polarity and planar pole pieces are mounted to the first and second surfaces, respectively, in a sandwich-like construction. The oscillating member is movable along a longitudinal axis between extreme positions whereat the first pole piece, then the second pole piece is proximate the ring flange. Cyclic energization of the electrically conductive coils generates a cyclically alternating magnetic field, which interacts with the magnetic field of the oscillating member causing its oscillation between the first and second extreme positions.

Abstract: An electromagnetic accelerometer includes a rigid shell with a cavity in which two magnets are fixed at either and of the rigid shell and one magnet is allowed to move between the fixed magnets. The three magnets are arranged so that the movable magnet is suspended between the fixed magnets by magnetic forces from the fixed magnets. A coil of wire surrounds the shell and magnets. An acceleration of the accelerometer causes a displacement of the movable magnet with the cavity. As a result, an electrical current is induced in the coil of wire. The voltage in the coil of wire is proportional to the acceleration experienced by the accelerometer. The electromagnetic accelerometer is particular useful in an implantable pacemaker or defibrillator and can be included in either or both a lead or the housing of the pacemaker. Further, the accelerometer generates its own voltage in response to acceleration and the resulting electrical energy can be used as a power source.

Abstract: An active implantable medical device, particularly a cardiac pacemaker, which is enslaved to a signal representative of acceleration, having a measuring circuit (10) comprising at least one sensor (12) delivering a signal of acceleration, and circuits (22-24) to deliver, in response to the signal of acceleration, a parameter of enslavement of at least one function of the device, particularly that of a cardiac stimulation frequency. According to the invention, a circuit (24) operates to limit, in the detection of increase in acceleration, a value linked to the module of the signal of acceleration. Preferably, the limitation is operated on a value proportional to the square of the signal of acceleration, more particularly on a quadratic sum of individual acceleration components (X.sub.i, Y.sub.i, Z.sub.i) according to at least two distinct axes delivered by a respective number of sensors.

Abstract: Accelerometer and sensor assemblies for implantable medical devices such as pacemakers, cardioverters, IPGs, PCDs, defibrillators, ICDs, and the like includes at least one intermediate metallization layer sandwiched between a first lower surface of at least one upper sheet formed from a piezoelectric material surface, and a second upper surface of at least one lower sheet formed from a piezoelectric material. The at least one upper sheet has a first outer edge disposed between its first upper and first lower surfaces. The at least one lower sheet has a second outer edge disposed between its second upper and second lower surfaces. The at least one intermediate metallization layer is not disposed at all locations between the first lower surface and the second upper surface, but extends to an external region disposed between the first outer edge and the second outer edge, and is electrically connected to the external region.

Abstract: The present invention relates to accelerometer assemblies for implantable medical devices such as pacemakers, IPGs, PCDs, defibrillators, ICDs and the like. The accelerometer assembly of the present invention comprises a beam that deflects in response to being subjected to an externally provided force. Deflection of the beam generates a voltage in a piezoelectric material disposed in the assembly. At least one stop is provided to limit the vertical range of motion through which the beam may deflect to prevent failure, fracturing or breakage of the beam resulting from excessive deflection of the beam that might otherwise occur were the stop not present.

Abstract: An antitachycardia stimulation device that automatically adjusts its detection rate threshold as a function of a sensed physiological parameter indicative of cardiac rate. The implantable antitachycardia stimulation device includes heart rate detection circuitry and antitachycardia therapy circuitry for applying a specific antitachycardia therapy in the event that the detected heart rate falls within at least one tachycardia rate zone. The tachycardia rate zone is defined by a lower threshold limit, and may also be defined by an upper threshold limit if more than one rate zone is used. The lower threshold limit is automatically adjusted as a function of an independently sensed physiological parameter that predicts a normal or natural change in the heart rate. If more then one rate zone is used, other threshold limits may also be adjusted automatically as a separate function of the same sensed physiological parameter.

Abstract: In a system for detecting changes in body posture, electrocardiograms are recorded. The recorded electrocardiograms analyzed are to determine changes in the body posture of a patient from changes in the morphology of the recorded electrocardiograms. The electrocardiogram analysis can be augmented by obtaining and analyzing an accelerometer signal as well.

Abstract: A rate responsive implantable pacemaker generates a metabolic demand parameter which is converted into a corresponding metabolic indicated parameter. The parameter is used to determine certain characteristics related to an exercise period and the patient, including exercise duration and intensity. These characteristics are used to dynamically calculate an exercise recovery period during which the pacing rate is elevated above a rate indicated by the metabolic parameter. Preferably, fuzzy logic circuitry is used for this purpose.

Abstract: An accelerometer-based, multi-axis physical activity sensor for use with a rate-responsive pacemaker, and a method for fabricating the sensor, are provided. The multi-axis physical activity sensor includes a cantilever beam having a film of a piezoelectric polymer adhered to each surface of an electrically conductive substrate. The piezoelectric films are highly resistant to fracturing during manufacture and in use, and they provide a strong output signal when stressed in response to bodily accelerations. A mass is mounted to a free end of the cantilever beam, and is substantially offset with respect to a planar surface of the beam so as to impart multi-axis sensitivity to the physical activity sensor. The accelerometer-based, multi-axis physical activity sensor provides an output signal that is communicated to pacemaker circuitry using a pair of electrical conductors.

Abstract: A rate responsive implantable pacemaker generates a metabolic demand parameter such as a thoracic impedance which is converted into a corresponding metabolic indicated parameter. During the conversion, intermediate parameters, such as either tidal volume and respiration rate, or a derivative of the metabolic demand parameter are used by a cross-check circuit to insure that artefacts due for example to stroke volume noise are eliminated. The peak limiter is used to limit the metabolic indicated rate to an acceptable range. Both protection circuits use fuzzy logic components.

Abstract: An implantable cardiac rhythm management device includes an accelerometer along with apparatus for processing the analog signal output from the accelerometer for deriving therefrom the time of occurrence of a selected heart sound in relation to a previously occurring ventricular depolarization event. The thus-derived heart sound information can be used to establish a hemodynamic upper rate limit for a rate adaptive pacemaker.

Abstract: An implantable cardiac pacemaker having a housing containing pacing circuitry, a signal generator, and an electromagnetic transducer. The transducer has an electrical input line connected to the signal generator, and an electrical output line connected to the pacing circuitry. Consequently, a forcing motion on the transducer sends an electrical signal to the pacing circuitry, and operation of the signal generator causes the transducer to vibrate. The pacemaker may also include a disablement switch connected to the signal generator, with the signal generator operating in response to activation of the switch to cause the transducer to generate an audible warning tone while the pacemaker is disabled.

Abstract: A programmable pacemaker and program therefor are disclosed, wherein the pacer is programmed to operate in a first pacing mode whenever the measured atrial rate is less than a certain threshold switching rate R.sub.T, and to operate in a second pacing mode whenever the measured atrial rate is greater than the threshold switching rate R.sub.T. The threshold switching rate R.sub.T is varied based on either a programmed algorithm or the measured value of one or more sensed parameters. In another embodiment, a hysteresis is introduced, so that the rate at which the pacer switches back to its low-activity mode is lower than the rate that triggers a switch to the high-activity mode.

Abstract: A rate responsive pacemaker senses an instantaneous metabolic indicative parameter such as minute volume and monitors this parameter over an extended time period of 30 days. A corresponding cumulative rate control parameter is generated. The cumulative rate parameter is converted into a metabolic pulsing rate for generating pulses in accordance with a set of physical activity parameters.

Abstract: A comparator for comparing the operation of activity monitors of the type having internal sensors responsive to excitation forces in order to record the activity of a wearer, includes a housing having a test platform and a monitor-receiving test fixture for holding an activity monitor motionless during testing. The comparator further includes an electromagnet for applying an excitation force to the monitor, by converting a prerecorded digital signal, or waveform, into analog voltage signals which are applied to the electromagnet for testing the monitor. The monitor may be subjected to a variety of test patterns of activity.

Abstract: In a dual sensor pacer/defibrillator the output of a metabolic sensor is used to calibrate the output a second sensor over a long time period. In this manner the two sensor outputs track accurately the metabolic demand of the patient and no recalibration by a clinician is necessary.

Abstract: A sensor that is implantable within the body of a patient that provides an indication of movement and orientation of the patient. The sensor is comprised of a cylindrical enclosure having a central electrode positioned within the cavity formed by the enclosure that is co-axial with the axis of the cylinder. One or more peripheral electrodes are positioned within the cavity and extend in a direction parallel to the central electrode. An electrolytic fluid is positioned in the enclosure so that movement of the sensor results in variations in the amount of electrolytic solution between the central electrode and the one or more peripheral electrodes. An alternating current signal is applied to the central electrode and the one or more peripheral electrodes and the resulting voltage signal is measured between the central electrode and the one or more peripheral electrodes.

Abstract: A method of and apparatus for pacing a patient's heart at a pacing rate dependent on patient activity and posture particularly during stair climbing. A dual chamber, rate responsive pacemaker for pacing a patient's heart includes at least one DC accelerometer mounted in the pacemaker pulse generator for implantation such that the sensitive axis of the DC accelerometer is sensitive to the effects of gravity during forward lean of the patient characteristic of stair climbing posture. The DC and AC signal outputs of the accelerometer are processed to develop a tilt signal and an activity signal. A target rate control signal is derived from the activity signal dependent on the level of activity. A stair climbing rate is selected for controlling the physiologic pacing rate between a lower and an upper pacing rate in the presence of an activity signal indicative of a patient walking rate and a tilt signal value falling within a tilt window.

Abstract: Disclosed are method and apparatus for creating a cantilever accelerometer beam by mechanically forming an accelerometer from a piezoelectric substrate. The inherent structure of the accelerometer provides a means for employing surface mount technology (SMT), or a protective package may be utilized to couple the accelerometer to the hybrid circuit within an implantable pacemaker. The sensor's structure is defined by three members. The first and second members are used to couple the sensor to the hybrid circuit and the third member defines the cantilever accelerometer beam, which generates an electrical output signal indicative of a patient's activity.

Abstract: A variable rate cardiac pacemaker is adapted to be implanted in a human patient for automatically adapting pacing rate to metabolic need of the patient when the patient is walking in an ascending path, a descending path, or on a level plane. An accelerometer senses the activity of the patient walking, and produces an electrical sensor signal representative of the activity. The accelerometer signal has variable parameters indicative of morphology, including amplitude, of the sensor signal according to status of activity of the patient and to the upward, downward, or horizontal direction of the patient's walking. A pulse generator generates pacing pulses at a variable rate according to an applied control signal to electrically stimulate the patient's heart at a pacing rate which varies according to patient activity.

Abstract: Process of control of the base frequency of a cardiac pacemaker having at least one sensor monitoring a physiological parameter. Rest phases and resumption of activity phases are detected to adapt automatically the base frequency of the pacemaker to the relative periods of rest and activity of the patient. Thus, the base frequency is allowed to decrease below the normally programmed base frequency in response to actual patient rest, to encourage a low spontaneous cardiac rhythm to inhibit pacing.

Abstract: An automatic atrial defibrillator which includes a mechanism for sensing the occurrence of atrial fibrillation in a patient's heart and in response thereto delivers an atrial defibrillation pulse. The device also has the ability to determine whether the patient is likely to be asleep. Defibrillation pulses which are at energy levels which would normally be painful to the patient are delivered only in response to occurrences of atrial fibrillation while the patient is determined to likely be asleep. Defibrillation pulses at lower, non-painful levels may be delivered while the patient is not determined to be asleep.

Abstract: A programmable dual-chamber artificial cardiac pacemaker senses atrial activity and normally tracks the sensed atrial activity in pacing the ventricular activity. An accelerometer located in the case of the pulse generator portion senses physical exercise by a patient when the pacemaker is implanted in the patient, and generates a rate control signal indicative of extent of the sensed physical exercise. The pulse generator is programmed for ventricular pacing rate control in multiple rate zones bounded by rate limits including a ventricular tracking limit (VTL) that varies dynamically with sensed physical exercise and a higher mode switch rate. The ventricular pacing rate tracks the sensed atrial activity on a 1:1 basis for atrial rates below the dynamic VTL (DVTL) during a predetermined interval of time for which the DVTL applies, and tracks the sensed atrial activity in Wenckebach behavior for atrial rates above the DVTL up to the mode switch rate with the ventricular pacing rate limited by the DVTL.

Abstract: A method of and apparatus for determining the physical posture of a patient's body, having a superior-inferior body axis, an anterior-posterior body axis and a lateral-medial body axis, in relation to earth's gravitational field. A medical device having first, second and, optionally, third DC accelerometers having sensitive axes mounted orthogonally within an implantable housing is adapted to be implanted with the sensitive axes generally aligned with the patient's body axes. Each DC accelerometer generates DC accelerometer signals having characteristic magnitudes and polarities on alignment of the sensitive axis with, against or normal to earth's gravitational field and DC accelerometer signals of varying magnitudes and polarities when not so aligned. Body position may be determined through comparison of the magnitudes and polarities of the DC accelerometer signals with the characteristic magnitudes and polarities.

Abstract: A two-conductor bus system is provided to electrically interconnect a plurality of physiologic sensors to a pacemaker, each sensor being adapted for placement along a pacing lead. The conductors of the bus extend longitudinally through the insulating material of the lead, connecting to each sensor. The pacemaker provides a supply voltage on the bus to provide power to the sensors. The sensors modulate the supply voltage on the bus to transmit information to the pacemaker. This information may be used by the pacemaker to adaptively pace the heart. In one embodiment, the sensors include bus monitoring circuitry for receiving control signals from the pacemaker.

Abstract: An implantable, rate responsive pacemaker, sensitive to impedance changes in the heart as an indicator of cardiac stroke volume, wherein the baseline impedance is eliminated from the measurement of impedance. In one embodiment, an adaptively controlled, balanced bridge is utilized to eliminate the baseline. A Wein bridge is provided having a variable reactance whose impedance is controlled continuously. In another embodiment, an impedance measurement is modified by a signal conditioner providing an appropriate varying offset through the use of a sample and hold circuit and other signal modifying circuits prior to converting the impedance measurement to digital information. In a third embodiment, a sample and hold circuit may be used to provide digital information through an A to D converter to a microprocessor which directly controls a variable reactance. The end voltage of a pacing capacitor is used as an indication of a baseline impedance.

Abstract: The sensor is intended preferably for use in conjunction with a heart pacemaker whose stimulation rate is variable in dependence on the physical activity of the wearer. The sensor includes a mass of mercury which, in use, can assume a shape determined by the gravitational force and variable as a result of the forces applied to the mass due to movement. Detector means sensitive to the variations in shape generate signals which can be used as activity monitoring signals.

Abstract: A dual chamber, rate-responsive pacemaker for pacing a patient's heart novelly allows tracking of the patient's sinus rate when the sinus rate is slightly less than the sensor rate; i.e., within a predetermined "Sinus Preference Window Maximum Rate Drop." Pacing at the sensor rate occurs when the sensor rate exceeds the sinus rate by more than the Sinus Preference Window Maximum Rate Drop. In the preferred embodiment a Sinus Preference Window, which occurs at the end of the ventricle-to-atrium interval, is decremented with successive heart beats by a programmable delta to increase the pacing rate until the Sinus Preference Window reaches zero, in which case the pacemaker paces at the sensor rate. The Sinus Preference Window is reset to its maximum value upon either the detection of an atrial sensed event, or upon the expiration of a programmable Sinus Check Interval.

Abstract: A rate-responsive pacemaker measures a patient's level of activity and stores the results in an activity level histogram. The patient's average level of activity is maintained as a running average. Based on a prescribed base pacing rate, a prescribed maximum pacing rate, the average level of activity, and the measured levels of activity stored in the activity level histogram, the rate-responsive pacemaker automatically calculates the slope of the pacemaker transfer function. An activity deviation histogram is also maintained. Analysis of the activity deviation histogram allows the pacemaker to determine if the patient was usually inactive for an extended period of time, and to inhibit an automatic slope calculation under such conditions. If a patient desires to reach a prescribed target heart rate during exercise, the slope may be calculated using the target heart rate and a prescribed fraction of time each week that the patient devotes to exercise.

Abstract: A pyroelectric suppressor circuit for preventing undesirable thermally induced signals generated by a piezoelectric physical activity sensor from reaching processor circuitry within an implantable medical device is provided. The thermally induced signals typically have frequencies below a frequency in the range from about 0.1 mHz to about 10 mHz. The suppressor circuit provides a high-pass filter that rejects signals that have frequencies associated with thermally induced signals. Signals having frequencies greater than a frequency in the range from about 0.1 mHz to about 10 mHz, which correspond to patient activity, are passed on to processing circuitry of the implantable medical device.

Abstract: An implantable medical device including a piezoelectric accelerometer activity sensor. The activity sensor includes a thin film piezoelectric cell within a frame structure. A mass imposes a load based upon acceleration to apply lateral or transverse forces which cause the generation of an electrical potential within the piezoelectric cell, which can be used by a rate control algorithm within the device to control operation of the device.

Abstract: A medical interventional device adapted to be implanted in the body of a patient provides a plurality of cardiac therapeutic functions including bradycardia pacing, rate adaptive pacing, antitachycardia pacing, cardioversion and defibrillation on demand. An accelerometer in or associated with the device senses accelerational and gravitational effects indicative of at least one of position, posture and physical activity of the patient, and generates an electrical signal representative of the position, posture and physical activity of the patient of which the sensed effect is representative. The accelerometer acts as a transducer to convert mechanical movement to an electrical output representative of such movement. Another sensor detects a physiologic parameter of the patient indicative of cardiac activity of the patient, and generates another electrical signal representative of the cardiac activity.

Abstract: Heart function is monitored by monitoring the momentum or velocity of the heart masses, preferably by means of a sensor implanted in the heart mass.

Abstract: A variable rate implantable pacemaker responsive to patient exercise senses and distinguishes between distinct and different types of physical activity by the patient, and is programmed to respond by generating different response functions to control the pacing rate according to the specific type of physical activity detected. The response functions are algorithms, taken from the behavior of a healthy person with normally functioning cardiovascular system, of heart rates versus an appropriate parameter of a signal produced by a sensor carried by the patient, for the different types of activity requiring different algorithms, in which the parameter value varies in a predetermined way with exercise.

Abstract: A demand cardiac pacemaker implantable in a patient which includes a pulse generator which generates stimulating pulses at a controllable variable rate and has electrodes for applying stimulating pulses from the pulse generator to the heart of a patient. The length of the pre-ejection period (PEP) for the left ventricle in each heart cycle, which length is a function of the physiological demand of the patient, is detected and an output signal which is a function of the length of the pre-ejection period is produced. This output signal is used to control the pulse generator to produce stimulating pulses at a rate based on the output signal, and to apply the stimulating pulses to the electrodes in the absence of spontaneous heart action.

Abstract: An accelerometer-based, multi-axis physical activity sensor for use with a rate-responsive pacemaker, and a method for fabricating the sensor, are provided. The multi-axis physical activity sensor includes a cantilever beam having a film of a piezoelectric polymer adhered to each surface of an electrically conductive substrate. The piezoelectric films are highly resistant to fracturing during manufacture and in use, and they provide a strong output signal when stressed in response to bodily accelerations. A mass is mounted to a free end of the cantilever beam, and is substantially offset with respect to a planar surface of the beam so as to impart multi-axis sensitivity to the physical activity sensor. The accelerometer-based, multi-axis physical activity sensor provides an output signal that is communicated to pacemaker circuitry using a pair of electrical conductors.

Abstract: A rate-response pacemaker includes a plurality of sensors that each sense a physiologic-related parameter suggestive of the physiological needs of a patient, and hence indicative of the pacing rate at which the rate-responsive pacemaker should provide pacing pulses on demand. The pacemaker includes appropriate selection circuitry for selecting which of the sensor parameters or weighted combinations thereof, should be used as the sensor indicated rate (SIR) signal to control the pacing rate of the pacemaker at any given time. In a preferred embodiment, a maximum sensor rate signal (MR.sub.i) is computed for each sensor, and a maximum sensor rate (MSR) signal is defined for the pacemaker, and the SIR signal is selected as the lesser of: (i) the MSR signal; (ii) the largest of the sensed sensor parameters; or (iii) the respective MR.sub.i signals.

Abstract: A miniature, hybrid-mountable, accelerometer-based, physical activity sensor for use with a rate-responsive implantable stimulation device is provided. The physical activity sensor is constructed as a cantilever beam having a film of a piezoelectric polymer adhered to each surface of an electrically conductive substrate. The piezoelectric films are highly resistant to fracturing during manufacture and in use, and they provide a strong output signal when stressed in response to bodily accelerations. A pair of electrically conductive supports serve to anchor the physical activity sensor to a substrate and deliver the output signal provided by the sensor to circuitry within the rate-responsive implantable stimulation device. The physical activity sensor is adapted to be mounted directly to conductive traces on a suitable substrate, preferably an implantable stimulation device hybrid.