Abstract: A patient monitoring and/or therapy delivery system and method employing an implantable medical device for sensing absolute physiologic signal values within the body of a patient, e.g., absolute blood pressure, temperature, etc., and an external monitoring device for monitoring and conveying ambient signal values to the implantable medical device, wherein the absolute physiologic signal values and the ambient signal values are combined to derive relative physiologic signal values for storage and/or control of a therapy provided by the implantable medical device. In the context of an implantable physiologic monitor, the relative and optionally, the absolute and/or ambient physiologic signal values are stored in memory for telemetry out to an external programmer in an uplink RF telemetry transmission initiated by medical personnel operating the external programmer. In the context of an implantable therapy delivery device, the relative physiologic signal values are also employed in therapy delivery algorithms.

Abstract: A system and method for a pacemaker are provided, for monitoring cardiac performance and adjusting a pacing regime to ensure hemodynamically optimal pacing therapy. The pacemaker includes a sensor for measuring a physiological parameter as an indicator of cardiac performance. A processing system dithers various programmable pacing parameters and notes the resulting changes in cardiac performance. The processor analyzes the changes in cardiac performance corresponding to changes in the pacing parameters and selects those parameters resulting in maximum cardiac performance. An activity sensor may be provided to allow the processing system to consider the activity level of a patient when determining a hemodynamically optimal pacing regime.

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: The present invention concerns a device for temporarily closing a canal in a body, in particular for assisting the function of the heart by application of counter-pressure. The device is characterised in that it comprises a first inflatable structure (1) which, in the inflated state, defines a sleeve shaped to match the internal surface of the canal, providing a central conduit (4). The device further comprises a second inflatable structure which expands radially, preferably from the exterior to the interior, is held by the first structure (1) and shaped such that, in the inflated state, it permits substantially complete closure of the central conduit (4) formed after inflation of the first structure. The device finally comprises means allowing each of these first and second inflatable structures to be in fluid communication with a fluid delivery source.

Abstract: A cardiac stimulating apparatus and method which optimizes cardiac performance by determining, from a filtered waveform transmitted from an accelerometer contained within the cardiac pacer, an optimum timing interval between at least one of intrinsic and paced stimulations of pre-selected chambers of the heart. Digitized data of the accelerometer signal, corresponding with identified R--R intervals, are stored for a plurality of preselected timing intervals for analysis and comparison. The accelerometer signal is filtered to isolate features of the waveform associated with specific cardiac events including for example, the first heart sound, the second heart sound or an amplitude in the frequency domain thereof. Characteristic values of these features of the accelerometer signal are calculated over a plurality of complete R--R intervals for each of the preselected timing intervals. The characteristic values are analyzed and compared to determine which timing interval optimizes cardiac performance.

Abstract: A medical therapy device includes at least one sensor for detecting a varle that can be measured on the body of a patient. An evaluating and control device is connected to the output of the sensor. A therapy device is connected to the output of the evaluating and control device and provides different therapies or therapy variables as a function of the value of the therapy control variable. A processing unit has an input connected to the output of a time controlled fluctuation-value generator which is connected between the output of the sensor and the input of the evaluating and control device.

Abstract: A rate responsive pacemaker is provided having the capability of automatically adjusting the lower rate limit (LRL) for sleep, or nighttime. The pacemaker has a temperature sensor for determining patient blood temperature, and processes patient blood temperature data to obtain an average daily low value of nighttime blood temperature. The pacemaker monitors blood temperature to determine a drop below a threshold which is coupled to the average daily low value, as well as when the rate of temperature change exceeds a predetermined limit, these two coincident conditions suggesting onset of nighttime and/or sleep. Lower rate limit is decremented, preferably by a predetermined amount at onset of nighttime, and is automatically incremented when patient blood temperature and/or time of day indicate the end of nighttime.

Abstract: A physiologic rate responsive pacer which alters the pacer's escape interval in response to the patient's respiratory minute ventilation derived from the electromyogram of selected respiratory muscle groups. The directly detected electromyogram (EMG) signal is amplified and band passed filtered, processed to remove any electrocardiogram (ECG) or pacing impulse signal, full-wave rectified, processed to develop a moving time average signal from which the peak, the maximal slope, and the average slope of the EMG moving time average may be calculated and processed in conjunction with the inspiratory and expiratory times between successive slope detections of the moving time average EMG to develop a rate control signal representative of minute ventilation.

Abstract: A rate responsive pacemaker includes a detector for detecting the anaerobic threshold of the patient. The threshold can be logged or can be used to manipulate the pacing regime of the pacemaker. The detector may include two metabolic demand sensors: one which is sensitive to the anaerobic threshold and one that is not. In this manner, the anaerobic threshold can be detected by monitoring the correlation between the two parameters. The parameter sensitive to the anaerobic threshold may be a parameter dependent on the patient's breathing cycle, such as minute volume, while the other parameter is preferably a threshold dependent on the sympathetic control of the body such as the QT interval.

Abstract: In an implantable rate responsive pacemaker a metabolic demand parameter is mapped in accordance with a rate response function into a corresponding metabolic indicated rate for pacing a patient's heart. In addition, a physical fitness monitor is also provided which monitors the patient's physical fitness and generates a long term true and accurate physical indicia. This indicia is used to adjust the rate response function so that it is automatically adjusted to the physical fitness of the patient.

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: 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: 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: An implantable cardiac pacemaker especially designed for treatment of CHF includes an accelerometer for sensing heart sounds and processing circuitry for deriving from the heart sound information the mechanical AV delay of the patient's heart. The pacemaker's applied AV delay is then adjusted until the measured mechanical AV delay falls in a range of between 180 ms and 250 ms. Further optimization of the heart as a pump can then be achieved by incrementally adjusting the pacemaker's applied AV delay interval until a point is reached where a measure of cardiac performance such as aortic pulse pressure is optimized.

Abstract: An electronic pacemaker generating pacing signals includes both a metabolic rate responsive sensor monitoring a physiological parameter and an activity rate responsive sensor monitoring movement of a patient's body during exercise. The measurements from each of the sensors are used to develop a corresponding rate signal and the two signals are combined to generate a dual sensor rate used to determine the timing of the pacing signals. The physiological parameter may be for example minute volume variation while the body movement may be monitored for example by using an accelerometer. The activity rate responsive sensor output is preferably used as an indication of a transition of a level of exercise, when a faster change in the pacing rate is desirable.

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: A body-implantable rate-responsive cardiac pacemaker is provided with circuitry for sensing a plurality of physiologic parameters known to be indicative of a patient's metabolic demand for increased cardiac output. In one embodiment, a rate-responsive pacemaker is provided with an activity sensor for detecting the patient's level of physical activity, and is further provided with an impedance sensing circuit for detecting the patient's level of minute ventilation by monitoring cardiac impedance. A rate-response transfer function, implemented by the pacemaker's control circuitry, periodically computes a rate-responsive pacing rate as a function of the outputs from both physiologic sensing circuits. The pacemaker's pacing rate is variable within a rate range defined by predetermined (programmable) upper and lower limits. In the preferred embodiment, the influence of activity sensing and minute ventilation parameters varies in accordance with the current pacing rate.

Abstract: An acoustic sensor is located in association with a patient's heart to detect abnormal heart sounds and a processor isolates abnormal heart sounds therefrom. The characteristics of these heart sounds are monitored while adjustments are made to the timing of pacing pulses to achieve a better heart function through pacing therapy. Particular adaption to cardiomyopathy is shown.

Abstract: A cardiac stimulating system incorporating a microprocessor-based controller is designed to automatically optimize both the pacing mode and one or more pacing cycle parameters in a way that results in optimization of a cardiac performance parameter, such as cardiac output. For each of a plurality of modes in which a DDD cardiac pacer can operate, a pacing parameter such as the AV interval of the pacer is incrementally adjusted and following that, an observation is made as to the effect of the adjustment on cardiac output. After the process has been repeated for all possible pacing modes, a determination is made to find the pacing mode and the AV interval or other pacing parameter that results in the maximum cardiac output or other optimal cardiac performance parameter. It is these pacing parameters that are then programmed into the microcontroller for causing the pacemaker to function in the desired mode and at the desired parameter values.

Abstract: A multiple sensor cardiac pacemaker blends the outputs from a fast-reacting Activity sensor and a slower-reacting Minute Ventilation sensor to achieve an optimally desirable pacing rate. The pacemaker conserves battery energy by forcing the Minute Ventilation sensor output to be at its minimum value by disabling the Minute Ventilation algorithm for a predetermined time period when the Activity sensor is at its minimum observed value. Power is conserved because the Minute Ventilation sensor and associated algorithms which normally consume power to operate the circuitry, and to measure impedance are disabled temporarily only during selected periods where the Activity sensor is at its minimum observed value, thereby maintaining optimal blending of the pacemaker sensor outputs in achieving the desired pacing rates.

Abstract: A device for generating a therapeutic value for a patient as a function of t least one variable parameter picked up within the body and constituting a first input value, with a change in the first parameter being a function of a second parameter which also constitutes an input value. The device includes circuitry for varying the generation of the therapeutic value by varying the second parameter so that the difference of the values of the first parameter, at selected limits of a variation range of the first parameter, constitutes a maximum in an intended treatment range of the patient. A memory retains a value of the second parameter for which the variation range of the first parameter constitutes a maximum. Control circuitry changes the therapeutic value as a function of the first parameter while maintaining the previously stored second parameter.

Abstract: A myocardial lead is provided with at least one sensor for sensing at least one of heart rate, physiological demand, or arrhythmia. Preferably, the sensor is a piezoelectric crystal, and is designed to flex with the beating of the human heart. Other suitable sensors include accelerometers, hemo-reflectance sensors, and strain gauge sensors. Each sensor is provided on a separate conductive segment of the electrode assembly. The signals can be monitored by appropriate electronics to detect changes in heart rate or arrhythmias of the heart.

Abstract: A cardiac pacemaker having an automatic pulse rate response gain factor responsive to at least one cardiac-related physiological characteristic of a patient. The pacemaker includes a rate controller that comprises a detector for detecting a plurality of individual measurements of at least one physiological characteristic over each of a plurality of pre-determined time periods, with each of the individual measurements being an average of values detected over each of a respective multiple number of incremental time periods occurring within each of the pre-determined time periods. The pacemaker saves the highest measurement from one incremental time period of each of several consecutive pre-determined time periods, and these highest measurements are averaged. Thereafter, the rate controller adjusts the rate response gain factor or slope of the pulse rate in relation to the physiological characteristic measurement and a pre-determined target pulse rate.

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: An implantable monitor/stimulator is disclosed that monitors and assesses indices of cardiac function, including the strength and timing of cardiac contraction, then automatically executes a physician-selected mode of therapy. It accomplishes this by assessing impedance, electrocardiogram, and/or pressure measurements, then calculating various cardiac parameters. The results of these calculations may be stored within the device, telemetered to an external monitor or display and/or may be used by the physician to determine the mode of therapy to be chosen. If indicated, therapy is administered by the device itself or by telemetering control signals to various peripheral devices for the purpose of enhancing either contraction or relaxation of the heart. The cardiac parameters that are calculated all provide an assessment of level of cardiac function by monitoring changes in ventricular filling and ejection or by calculating isovolumic phase indices of heart contraction.

Abstract: A cardiac pacemaker which automatically tests for changes in and adjusts output or other parameters in response to detected changes in environmental or physiologic conditions. One or more passive sensors detect environmental or physiologic conditions which may correlate to stimulation thresholds or other parameters. If a change in such conditions is detected, a test or search is initiated to achieve an energy efficient output, to optimize cardiac output, to improve sensing, etc.

Abstract: A rate adaptive cardiac pacer is described in which the impedance versus time information derived using impedance plethysmography or the pressure versus time information derived from a pressure transducer in a ventricular chamber is signal processed to recover a modulating envelope due to volume or pressure changes occasioned by respiratory activity. Either or both of the respiratory interval or respiratory depth may be combined in an appropriate rate control algorithm with other parameters also derived from the impedance versus time signal to develop a rate control signal for an implanted pacer.

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. The pacemaker also includes a memory circuit for selectively storing the sensor parameters from each of the plurality of sensors. The stored sensor parameters may thereafter be downloaded from the pacemaker memory and evaluated in non-real time with the various sensor parameters assuming different weighting (scaling) factors and different processing parameters (e.g.

Abstract: A multi-sensor blending circuit for use in a rate responsive cardiac pacemaker. The blending logic circuit blends delta pacing rate signals from two or more sensors which measure physical and physiological parameters of a patient. Programmable equations stored in the blending logic circuit determine which percentages or a ratio of the delta pacing rate sensor signals comprise a single delta pacing rate signal as a function of the delta pacing rate. This delta pacing rate signal is provided to the pacing control circuitry of a pacemaker. The blending ratios are dynamically determined based on the pacing rate established at the most recent cardiac cycle. The blending equations are comprised of several programmable variables, wherein the equations can be programmed by the external programmer in view of clinical data.

Abstract: A pacemaker capable of automatically adjusting the sensitivity of its sense amplifier to electrical cardiac signals is disclosed. In one embodiment, a pacemaker having a pressure sensor disposed on the distal end of its pacing/sensing lead counts the number of pressure events and electrical events which occur during an autosensitivity timing period. If the number of electrical events exceeds the number of pressure events by more than a predetermined margin, the sense amplifier's sensitivity threshold is decreased. If the number of electrical events does not exceed the number of pressure events by more than the predetermined margin, the sense amplifier's sensitivity threshold is increased. In another embodiment, the pacemaker maintains a running average of the peak voltages of sensed electrical events over a predetermined history period.

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 cardiac pacemaker control system includes a stress detector system (1) for producing a controlled basic stimulation rate based on signals picked up within a patient's body related to physical stress and derived from a pre-ejection period of the patient. A detection device (10, 15) detects a spatial orientation of the patient, and produces an output switching signal (20) for changing the controlled basic stimulation rate depending upon the position of the patient which represents an additional measure of physical stress.

Abstract: A rate controlled cardiac pacemaker stimulates the heart of a patient at a stimulation rate and includes a stress sensor for sensing actual physical stress of the patient. The device includes control logic for adapting the stimulation rate of the pacemaker to the actual physical stress of the patient and determining circuitry for determining the activity of the patient. The determining circuitry includes an activity sensor for sensing the activity state of the patient and a rate control circuit having an input connected with an output of the activity sensor. A timer generates a signal based on a 24-hour rhythm indicating a rest phase or an activity phase, and is synchronized by the activity sensor in a 24-hour rhythm with patient activity and rest phases that occur in continuous alternation.

Abstract: A dual-chamber metabolic demand, rate adaptive pacemaker that automatically calibrates the correlation between a metabolic demand measurement and an appropriate metabolic demand pacing rate according to the true physiological needs of the body, as determined by a patient's sinus rate when the natural sinus rate is functioning in a reliable manner in the absence of cardiac arrhythmia.

Abstract: An implantable medical apparatus for stimulating a heart at a variable stimulation rate dependent on the respiratory rate, tidal volume, heart rate and stroke volume includes a measurement apparatus which measures impedance around the heart, a filter unit which splits the impedance signal into high-frequency and a low-frequency signal portions and two analyzers which respectively evaluate the signal portions and which emit the four parameter values as output signals. The product of respiratory rate times tidal volume is formed in a control apparatus. This product corresponds to respiratory minute volume, and the product of heart rate times stroke volume corresponds to cardiac output. Cardiac output is multiplied by a constant, and respiratory minute volume is subtracted from the product thus formed. The resulting different is equal to zero when blood oxygenation is optimum. The control apparatus controls the stimulation rate on the basis of the magnitude and sign of the difference.

Abstract: A system for monitoring a patient and treating the malfunctioning heart of the patient, either in an automatic mode or in a semiautomatic mode, includes means which derive at least one electrical signal resulting from action of the patient's heart and means which derive at least one physiologic signal from or related to the patient's circulatory system. A central processing unit, which may be a programmable microprocessor, with a RAM and a ROM, receives and responds to the at least one electrical signal and to the at least one physiologic signal. Output means, which may include a heart assist pump, pacers, drug delivery devices and cardioverting/-defibrillating apparatuses, controlled by the central processing unit provides corrective measure(s) to the patient. Adjustable or variable baselines, against which a representation of the current, short-term magnitude of the selected physiologic parameter or parameters are provided.

Abstract: An implantable pacemaker provides three types of hysteresis for use in dual chamber and/or atrial tracking modes, such as VDI, VDD, DDI, DDD, VDIR, VDDR, DDIR or DDDR. The pacemaker defines a basic atrial escape interval (AEI) that defines the maximum time between a ventricular event and a subsequent atrial event, as well as an AV delay (AVD) that defines the maximum time between an atrial event and the next ventricular event. The sum of AEI plus AVD thus sets the rate at which stimulation pulses are generated in the absence of sensed natural cardiac activity. A first type of hysteresis, atrial escape rate hysteresis, causes the AEI to be extended upon sensing natural atrial beats (P-waves). The increased AEI remains in force so long as natural P-waves continue to be sensed during the AEI. Should a P-wave not be sensed during the AEI, a stimulation pulse is generated and the AEI reverts to its initial value.

Abstract: A multi-axis, multi-purpose sensor for use with implantable medical devices, and for simultaneously detecting the patient's posture and activity level. The sensor includes a hermetically sealed, fluid-tight, bio-compatible housing. The housing is formed of a plurality of adjacently secured sides, and a plurality of side electrodes coupled to the sides. A central electrode is disposed at the geometric center of symmetry of the housing, to allow measurement of voltage changes between the central electrode and the side electrodes. A non-toxic electrically conductive electrolyte fills about half the housing, and immerses part of the central electrode and the side electrodes. The sensor further includes a low frequency bandpass filter for passing low frequency signals indicative of the patient's posture, and a high frequency bandpass filter for passing high frequency signals indicative of the patient's activity.

Abstract: A cardiac pacemaker and related pacing method. The cardiac pacemaker includes atrial and ventricular sense amplifiers for generating atrial and ventricular sense signals. An activity control circuit measures the activity level and initiates an activity interval. A control circuit responds to the atrial sense signals, the ventricular sense signals, and the activity control circuit, for controlling the atrial and ventricular stimuli generation, by matching the activity interval with the depolarization of the atrial tissue, in order to differentiate true exercise induced sinus tachycardia from atrial arrhythmias and retrograde atrial events, and to permit a selective ventricular rate control. The control circuit initiates a 2 to 1 ventricular to atrial response when the activity interval is greater than a VV interval, which is the sum of the interval between the last sensed or paced ventricular event and the atrial intrinsic depolarization (VA.sub.

Abstract: A pacemaker capable of automatically adjusting the activity threshold setting of its activity sensor signal processing circuitry to its optimal value is disclosed. In one embodiment, the pacemaker maintains a running average of zero activity time and a cumulative summation of zero activity time over a predetermined history period. Periodically, the pacemaker computes a time difference between the running average of zero activity time and the cumulative summation of zero activity time, and adjusts the activity threshold of the activity sensor signal processing circuitry according to this computation. By basing the adjustment of activity threshold on a long-term average of zero activity time, the effects of cycle-to-cycle variation in sensed zero activity time are minimized. In another embodiment, the pacemaker periodically computes a time difference between a preprogrammed margin value and the cumulative summation of zero activity time.