Abstract: A dry electrode system for the detection of biopotentials existing on the surface of the skin of a living body, including a dry electrode pad with a resilient conductive pad adhering to at least one adhesive pad or otherwise opposed adhesive surfaces, one of which is adapted to engage the skin of the living body. The dry electrode pad makes electrical connection to an amplifying circuit which transmits a biopotential derived from the conductive pad to a monitor. The amplifying circuit includes a conductive input contact for making electrical contact to the conductive pad, a lead amplifier having an input coupled to the input contact, and a voltage driven shield coupled to the output of the lead amplifier and surrounding portions of the input contact not in engagement with the dry electrode pad. In a preferred embodiment, conductive adhesive layers are applied to opposed sides of a conductive foam pad to construct the dry electrode pad.

Abstract: An amplifying circuit for amplifying a bipotential input signal, including an insulating housing having a conductive input contact mounted on the housing and adapted to engage a human body so that the bipotential input signal applied to the contact; a lead amplifier having inverting and non-inverting inputs, one of which is coupled to the input contact, and an output; first and second diodes connected in parallel inverse polarity across the inputs of the lead amplifier; third and fourth diodes connected in parallel inverse polarity from the inverting input of the lead amplifier to a circuit common potential; and an output resistor connected from the inverting input to the output of the lead amplifier. Portions of the input contact are surrounded by a voltage drive shield connected to the output of the lead amplifier.

Abstract: Isolation circuitry for use with diagnostic ECG devices provides high common mode rejection and low leakage current using optoisolators in conjunction with an isolating operational amplifier. A predetermined pattern of binary input signals selectively energizes, via the optoisolators, a plurality of switches interposed between electrodes positioned on a patient's skin and the isolating operational amplifier. This selection couples a predetermined combination of electrodes to the isolating operational amplifier to provide the desired ECG output. The output from the isolating operational amplifier may be coupled directly to a recording device or coupled to a circuit which processes the ECG signal before the signal is recorded.

Abstract: A cardiac pacer which generates pacing pulses at a predetermined pacing rate includes a device for making a body activity measurement. The measured body activity signal is non-linearly amplified such that signal portions having higher amplitudes are more amplified than signal portions having lower amplitudes. The non-linearly amplified body activity signal is integrated over a period of time. The predetermined pacing rate is varied dependent on the integrated signal.

Abstract: A bank of differential amplifier circuits includes specialized circuits to provide multi-channel differencing with a minimum number of active devices such that the differences between pairs of analog input signals, such as available from patient monitoring electrodes, are derived with half the number of active devices normally utilized. In one embodiment, two operational amplifier circuits are used in a differencing channel which functions together to provide differencing, a properly delayed input signal for use in another differencing channel, high input impedance buffering, a low impedance output for each differential amplifier channel, time-coincident, matched outputs for each differential amplifier channel, and with an additional operational amplifier, a DC rejection circuit which does not affect the low output impedance or the differencing function, thereby to eliminate the necessity of providing separate buffers and active delay circuits which can result in the use of twice the number of active devices.

Abstract: An unsaturable cardiac sense amplifier includes first and second amplifying stages, each of which is subject to saturation by excessive input voltage. Input voltage to the first amplifier stage is limited to less than a saturating level by means of a pair of parallel, oppositely sensed, diodes. Saturation of the second amplifier stage is prevented by a degenerative feedback loop formed by a pair of serially connected zener diodes. An artifact squelch circuit, connected to the output of the second amplifier stage, limits the maximum output voltage of the sense amplifier.

Abstract: A dry electrode system for the detection of biopotentials existing on the surface of the skin of a living body, including a dry electrode pad with a resilient conductive pad adhering to at least one adhesive pad or otherwise having opposed adhesive surfaces, one of which is adapted to engage the skin of said living body. The dry electrode pad makes electrical connection to an amplifying circuit which transmits a biopotential derived from the conductive pad to a monitor. The amplifying circuit includes a conductive input contact for making electrical contact to the conductive pad, a lead amplifier having an input coupled to the input contact, and a voltage driven shield coupled to the output of the lead amplifier and surrounding portions of the input contact not in engagement with the dry electrode pad.

Abstract: A sense amplifier for a cardiac pacemaker which has an amplifier section with two feedback paths. One path contains small valued capacitors and clock activated switches to form a discrete time feedback path. The other path contains unclocked passive components to form a continuous time feedback path. The sense amplifier generates a detect signal in response to a depolarization of cardiac tissue.

Abstract: A circuit for detecting and indicating an interruption in the electrical connection between a signal device and a signal processing device, which has been provided with an amplifier at its input. The signal device has a relatively low impedance and the signal processing device has a relatively high impedance. The circuit includes an alarm device which generates an alarm when the predetermined upper limit of the amplifier input voltage has been exceeded. Also included are a supply circuit to feed an auxiliary dc current into the connection between the signal device and the signal processing device. The supplied auxiliary current is controlled by the amplifier input voltage to rise during an increased amplifier input voltage. As a result, a lower current supply can be provided under normal circumstances, which reduces misinterpretations. Preferably, the circuit is used in connection with ECG measuring devices.

Abstract: A pacemaker sense amplifier circuit exhibiting a very high common mode rejection ratio for detecting intracardiac electrogram signals is disclosed. The circuit includes a sampling capacitor which is differentially charged by the intracardiac signal. The voltage stored on the sampling capacitor is periodically applied to a high input impedance differential voltage amplifier which is referenced to the battery ground. The signal is smoothed and reconstructed by a bandpass filter, and is applied to a comparator to generate a logic level pulse indicative of the occurrence of a cardiac depolarization.

Abstract: An implantable cardiac pacer having atrial and ventricular electrodes includes an input/output circuit which can be programmed for use with either unipolar or bipolar pacer leads. The circuit can be reprogrammed by the physician after implant to accommodate physiological changes in the patient or chronic changes in pacer lead characteristics, and can be utilized with single channel or dual channel cardiac pacers.

Abstract: Disclosed herein is a pacer signal reject circuit wherein an entire ECG waveform signal is applied to one input of an operational amplifier, while only the initial portion of the pacer signal including the main pulse and a portion of the tail, is applied to the second input of such operational amplifier, to cause cancellation of that initial portion from the ECG signal. Also, a synthesized version of the remainder of such pacer tail is generated and applied to the second input. Thus, by isolating the ECG signal from the second input except for a timed period of the pacer signal, and by applying the synthesized tail signal to such second input, the entire pacer signal may be cancelled.

Abstract: A sensing circuit for a cardiac stimulator which can adapt to the use therewith of either bipolar leads or unipolar leads without the need for telemetric programming of a switch internal to the implanted pacemaker. If a unipolar lead is plugged into the terminal receptacle of the pacer at the time of implant, the pacer will sense R-wave activity and other artifacts between a distal tip electrode and the metal body of the pacemaker, but if a bipolar lead is plugged into that same receptacle at the time of implant, the pacer will sense such artifacts between a tip electrode and a ring electrode spaced a predetermined short distance proximally of the tip electrode along the surface of the lead body.

Abstract: The purpose of the present invention is to provide a physiological signal amplifier circuitry exhibiting higher common mode rejection ratio with no necessity of adjustment. To realize this, outputs of the differential amplifiers are average to produce reference potential which is supplied, through a high gain amplifier, to invert terminals of the same differential amplifier as well as to invert terminals of other differential amplifiers connected to other electrodes. In the embodiment employed for the electrocardiograph, the reference potential is produced by the differential amplifier connected to extremity electrodes, and other differential amplifiers are connected to the chest electrodes.

Abstract: An electrocardiographic amplifier having an integrator in the feedback loop between the amplifier's input and output whose time constant is varied by the duty cycle of a series switch to vary the low frequency 3 dB roll-off point as a function of the detected low frequency noise in the amplifier output signal. A capacitor is switched in parallel with the inverting feedback resistor to lower the high frequency 3 dB roll-off point in response to detected high frequency noise.

Abstract: A monitoring electrode system is provided in which just two electrodes and their corresponding lead lines may be utilized for a monitoring unit, such as an ECG, having three input terminals and normally requiring signals from three electrodes. To achieve such a two lead system, a body tissue impedance simulating circuit is included to provide an automatic reference line signal at the third input terminal. Protection against high voltages and radio frequency interference is provided by various circuits, such as a high voltage protection circuit, a low pass filter network or an RF choke filter network. In the preferred embodiment hereof, a pair of electrodes are provided with a connecting plug which engages a corresponding connector at the end of a cable extending from the ECG monitor. Preferably, the body tissue impedance simulating circuit and any protective circuits are located in the connector at the end of the ECG cable.

Abstract: A biological signal source amplifier having a rapid overload recovery capability and an output reference level translation feature. The amplifier responds to input signals of excessive amplitude by actively decreasing the response time of a reactive input coupling circuit when the input signal crosses predetermined dynamic limits. A differential amplifier is used in such a way as to produce an output referenced to a voltage level other than power supply ground. A level translation feature is provided for translating the output signal to the input of a subsequent circuit having a different reference level without introducing a dc offset or other associated amplitude distortion, or effects of capacitive coupling on low-frequency response.

Abstract: An improved electrocardiography system displays and records electrocardiograph (ECG) signals provided on multiple pickup leads attached to a patient. The system has the capability of selectively displaying standard preprogrammed lead configurations or lead groups, and provides the operator with the additional capability of programming selected leads from various groups to form a "monitor group". Selected ECG signals are routed to a four-channel oscilloscope and a three-channel strip-chart recorder, the system providing the operator with a "freeze" capability such that a signal appearing on one of the oscilloscope channels may be displayed in a stationary state on the fourth oscilloscope channel, and subsequently printed out on the strip chart recorder.

Abstract: A cardiac amplifier system with several patient electrodes includes an amplifier with a capacitor coupled input and a switch for coupling different ones of the patient electrodes to the amplifier. A circuit including a time delay, a pair of sequentially operated controlled conduction devices and a resistive network shunts the amplifier input and charges the coupling capacitors in a controlled fashion when the selector switch is operated to prevent switching transients from being applied to the amplifier.

Abstract: A signal processing device composed of: a signal input for receiving an electrocardiographic signal containing a succession of QRS complexes; a signal output; a digitally operating unit having a transmission factor which is variable in discrete steps and connected between the signal input and output for supplying to the signal output a signal containing representations of the QRS complexes contained in the signal received by the signal input, with the relation between the amplitude of the signal at the signal output and the amplitude of the corresponding portions of the signal received by the signal input being proportional to the existing transmission factor of the digitally operating unit; and a transmission factor control unit connected to monitor the signal at the signal output for increasing the transmission factor of the digitally operating unit by one step in response to each appearance at the signal output of a QRS complex representation having a peak value between selected first and second threshold

Abstract: In signal measurement circuits which are referred to a floating ground and which derive their input signals from electrodes attached to a patient's body, the effects of common mode potentials on the patient's body are minimized without requiring any patient electrodes other than those acting as signal sources, by using a unity gain amplifier to drive the floating ground toward the common mode potential on the patient's body.This process is accomplished without significantly degrading the isolation impedance between the measurement circuits and true ground.The patient is protected from hazardous electrical shock by incorporating current limiting devices in the unity gain amplifier.

Abstract: There is disclosed an apparatus for the selective detection and controlled gain of intranuclear and intracellular potentials. Such apparatus contains an amplifier with a gain control, such amplifier having an input terminal and an output terminal and several stages each containing an integrated active electronic device. The input terminal is the input terminal of the integrated active device of the first stage, such input terminal being directly coupled by a double screened lead with a metallic microelectrode for collecting intracell and intranuclear biopotentials.

Abstract: In an electrocardiographic system there is a multielement electrode at two skin locations for providing an ECG signal of negligible magnitude between elements because of the close spacing while the pair of elements are sufficiently separated so that the motion of one element is at least partially independent of the motion of the other. Parallel ECG signals are obtained from different elements of two multielement electrodes. The difference between the signals is detected by logical circuitry to produce a signal indicating baseline shift. The elements are coaxial with a 250 K resistor in series with each outer element.