Abstract: An implantable device which acquires physiological data and status information. The physiological data is compressed, reducing the memory requirement of the implantable device and/or increasing the amount of data that can be stored. The compression technique uses variable resolution while maintaining desired accuracy. The physiological data, such as heart beat interval time, is converted into a digital value. The digital representation then is divided into sub-ranges, and various resolution values are assigned to each sub-range. Each resolution is selected to stay within the desired accuracy. The interval time is divided by the particular resolution to obtain a digital value for the interval time within that range. The digital value then is corrected based upon the sub-range to obtain the compressed encoded digital value, which can then be stored in memory together with other desired data.

Abstract: A cardiac simulation system including a patient warning apparatus. The cardiac stimulator is an implantable pacemaker or defibrillator or combination which can be programmed to automatically alter the voltage of its output stimulus, in particular, to increase the voltage of the output stimulus whenever a condition exists requiring patient notification or warning. A specialized auxiliary lead with a shunt circuit can be connected to a standard socket of a cardiac stimulator header and a standard lead, such as a cardiac pacemaker lead, can then be connected to the auxiliary lead. The auxiliary lead allows a stimulation electrode to be implanted near excitable tissue in a secure fashion to assure stimulation of tissue. The auxiliary lead includes an apparatus for shunting electrical current from the standard stimulation electrode implanted in or near the patient's heart to the auxiliary electrode in the presence of a stimulation pulse with a voltage at or above a preselected level.

Abstract: An implantable subcutaneous data port for transferring data received from a sensor implanted within a subject. The data port electrically connects to the sensor and includes a control circuit electrically connected to an access port. The control circuit includes a current loop transmitter which modulates a current loop signal with voltage outputs from the sensor. This current loop signal transmits through the access port to an externally located current loop receiver which converts the current loop signal into an output voltage. Needle electrodes are insertable through the skin of the subject to the access port and provide an electrical interface between the control circuit and current loop receiver.

Abstract: An improved transcutaneous energy transmission device is disclosed for charging rechargeable batteries in an implanted medical device and to minimize peak temperature rises in the implanted device. A current with a sinusoidal waveform is applied to a resonant circuit comprising a primary coil and a capacitor. Current is induced in a secondary coil attached to the implanted medical device. Two solid state switches are used to generate the sinusoidal waveform by alternately switching on and off input voltage to the resonant circuit. The present invention charges the batteries using a charging protocol that either reduces instantaneous charging current or duty cycle of a fixed charging current as the charge level in the battery increases. Peak temperature rises are less while delivering comparable electrical charge of the battery than for prior charging systems.

Abstract: Disclosed are apparatus and method for detecting electromagnetic interference (EMI), or noise, that may disrupt the proper operation of medical devices implantable in patients, such as cardiac stimulators. Circuitry of the detector of the invention is independent of other circuitry of the medical device. EMI is magnetically induced on an antenna that may be within the metal housing of the device in a receiver circuit, and the EMI signals are output to the noise detector. A variety of alert signals may be provided to the medical device circuitry to warn of the presence of EMI so that appropriate responses may be taken to insure the safety of the patient dependent on the device. The detector may share the telemetry antenna of the medical device, or utilize a separate, dedicated antenna to receive EMI. Alternative antennas external to the metal housing of the medical device include leads from the device to the heart of the patient, and a dedicated antenna in the non-metal header of the device.

Abstract: An optically-controlled high-voltage switch for an implantable defibrillator. A three-terminal high-voltage-tolerant semiconductor switch exhibits high conductivity between its high-voltage terminal and its common terminal in response to a low control voltage applied between its control terminal and its common terminal, where the low control voltage exceeds a characteristic threshold value, and exhibits low conductivity between same where the control voltage is less than the characteristic threshold value. A photovoltaic coupler/isolator having a light emitting device and a photovoltaic device, optically coupled to and electrically isolated from each other, is in circuit communication across the control and common terminals. A low voltage current source drives the light emitting device of the photovoltaic coupler/isolator.

Abstract: An improved transcutaneous energy transmission device is disclosed for charging rechargeable batteries in an implanted medical device. A current with a sinusoidal waveform is applied to a resonant circuit comprising a primary coil and a capacitor. Current is induced in a secondary coil attached to the implanted medical device. Two solid state switches are used to generate the sinusoidal waveform by alternately switching on and off input voltage to the resonant circuit. The sinusoidal waveform reduces eddy current effects in the implanted device which detrimentally increases the temperature of the implanted device. The present invention charges the batteries using a charging protocol that reduces charging current as the charge level in the battery increases. The controller preferably is constructed as a pulse width modulation device with a variable duty cycle to control the current level applied to the primary coil.

Abstract: The invention relates to an improved stimulation electrode for cardiac pacing and defibrillating, methods of manufacturing same, and methods of using same. Specifically, the electrodes of the invention by virtue of the methods of manufacturing and using, demonstrate improved capabilities of stimulating and sensing neuromuscular tissues. The electrodes have enhanced electrically-accessible surface areas which are coated with oxides of valve metals.

Abstract: A method for making a lead body for use in a conductive insulated lead for a cardiac stimulator. Alternating layers of conductive and insulative thermosetting polymers are extruded through successively arranged heated nozzles of increasing outlet diameter. As the inner layer emerges from its nozzle in a thermoset state, it is passed through a following nozzle while surrounded by another thermosetting polymer that is extruded through that following nozzle. The second polymer becomes thermoset and bonded to the already thermoset inner layer. Successive nozzles can be provided to form successive layers of alternating conductive and insulative polymers, where the conductive layers serve as the electrical conductors of the lead.

Abstract: The invention relates to methods of making an improved stimulation electrode for cardiac pacing and defibrillating. Specifically, the electrodes of the invention by virtue of the methods of manufacturing and using, demonstrate improved capabilities of stimulating and sensing neuromuscular tissues. The electrodes have enhanced electrically-accessible surface areas which are coated with oxides of valve and noble metals.

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: An implantable cardiac stimulation system having a patient warning system and an elongated electrode mounted near the can of the system for providing reliable stimulation for warning. The electrode has an extended length and a short width. The length is preferably at least double the width and more preferably at least four times the width. This extended length increases the probability that contact with the surrounding tissue will be achieved. The short width and rounded profile of the width, forming an "edge", on the other hand, increases the probability that a high enough current density will be achieved, causing stimulation to occur. The electrode may also be curved along its length, which tends to promote a "point" or small area contact between the electrode and the patient's tissue. The electrode may be mounted directly on the can or header of the cardiac stimulator or may be part of a separate pin electrode.

Abstract: A cardiac simulation system with a patient warning apparatus, including a pin electrode insertable into a standard female socket in the header of a dual chamber pacer or multi-function cardiac stimulator. The cardiac stimulator has at least two sockets in a header, such as is commonly found in a dual chamber pacemaker. Rather than stimulating both chambers of the heart, the dual chamber pacemaker is programmed to function as a single chamber pacemaker, with a standard lead connecting one socket and its associated circuitry to a selected chamber of the heart, usually the ventricle. The pin electrode is inserted in the other socket, usually used for the sensing and stimulation of the atrium, and additional programming is provided to the pacemaker or stimulator to automatically produce an output stimulus through the atrial socket to the pin electrode whenever a condition exists requiring patient notification or warning. The pin electrode includes a hood which fits around a selected part of a header.

Abstract: A cardiac simulation system including a patient warning apparatus. The cardiac stimulator is an implantable pacemaker or defibrillator or combination which can be programmed to automatically alter the voltage of its output stimulus, in particular, to increase the voltage of the output stimulus whenever a condition exists requiring patient notification or warning. A specialized auxiliary lead with a shunt circuit can be connected to a standard socket of a cardiac stimulator header and a standard lead, such as a cardiac pacemaker lead, can then be connected to the auxiliary lead. The auxiliary lead allows a stimulation electrode to be implanted near excitable tissue in a secure fashion to assure stimulation of tissue. The auxiliary lead includes an apparatus for shunting electrical current from the standard stimulation electrode implanted in or near the patient's heart to the auxiliary electrode in the presence of a stimulation pulse with a voltage at or above a preselected level.

Abstract: A method and apparatus is disclosed for use in an implantable device that communicates with an external device through pulse position modulation. A timing generator is provided as part of the implantable device that determines the phase uncertainty between an external signal and an internal cock signal. The phase uncertainty then is added to the preset delay period to more precisely control the position of the response. The phase uncertainty is measured by a dual slope circuit that varies a state variable (which can be a digital timer, a capacitor voltage, or the like) at a fixed rate with either a positive or negative slope. When the external signal is detected, the stat variable is reset and then decreased at a fixed rate until the next positive edge of the clock signal. The state variable then is increased at the same rate until the subsequent positive clock edge. The resulting variable value is proportional to the phase uncertainty.

Abstract: A system for lead removal of both heart pacemaker leads and cardioverter-defibrillator endocardial leads comprising a flexible coil of flattened ribbon. Preferably, the ribbon is comprised of polyethylene or another suitable biologically compatible material. At a distal end of the coil, a cutting surface may be provided, such as a chisel-like edge at the distal end of the coil. A handle may be provided for twisting the coil onto the lead. The coil should be at least partially radiopaque or provided with a surface which is radiopaque so that its use may be observed in the body by fluoroscopy or other suitable means.

Abstract: A cardiac simulator including a patient warning apparatus, having a sensor for detecting patient reaction to a warning stimulus and means for adjusting the magnitude of said warning stimulus to obtain a preselected level of reaction. The cardiac stimulator is an implantable pacemaker or defibrillator or combination which can be programmed to produce a warning stimulus whenever a condition exists requiring patient notification or warning. A warning pulse stimulus generator directs electrical current to a warning electrode. Alternatively, a controlled switch may re-direct a stimulation pulse to the warning electrode. The sensor for detecting the reaction of the patient to the applied warning stimulus may be an accelerometer or motion/vibration transducer or other sensor capable of detecting a reaction to a warning stimulus. Means for adjusting the level of the stimulus directed to the patient's skeletal muscle regulate the stimulus until a pre-selected magnitude of reaction has been achieved.

Abstract: A cardiac simulator including a patient warning apparatus, having an electrically conductive suture point in electrical communication with the patient warning apparatus. An electrically conductive suture passed through the suture point connects said stimulator mechanically and electrically to excitable tissue such as skeletal tissue. Inside the suture point is a connection for assuring a reliable electrical contact between the suture point and the suture. The cardiac stimulator automatically alters the peak voltage of its output stimulus whenever a condition exists requiring patient notification or warning. A specialized shunt circuit mounted within the stimulator or in the header of the stimulator re-directs electrical current from the standard stimulation electrode to the electrically conductive suture point. A controlled switch may be mounted within a hermetically sealed can of the stimulator to re-direct a stimulation pulse to the suture point. The controlled switch could also be mounted in the header.

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 femoral knee prosthesis having a box internal geometry adjacent the femur which has four intersecting planes which extend from the medial side of the prosthesis to the lateral side. Shims of varying thickness can be added which retain the same internal box geometry. The internal geometry of the shims comprises three intersecting planes. Medial and lateral shims are provided. The internal geometry of the shims is translated slightly anteriorly as they increase in thickness. The shims may be added to either condyle independently, with different thickness on each side.