Variable rate cardiac pacer

• US 5,036,849 A
• Filed: 04/04/1990
• Issued: 08/06/1991
• Est. Priority Date: 04/04/1990
• Status: Expired due to Term

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Hauck, John A., Pederson, Brian D.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): Getzow, Scott M.
• Application Number:
  US07/503,991
• Time in Patent Office: 489 Days
• Field of Search: 128/419 PG
• US Class Current: 607/24
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance

Abstract

An endocardial lead having first and second spaced apart electrodes resides in a patient'"'"'s heart. The first electrode is a sensing electrode and the second electrode is a carrier signal driving electrode. The lead has a conductor coupling a source of alternating current carrier signals of a predetermined frequency to the second electrode. A third electrode is in electrical contact with body tissues. A cardiac pacer apparatus includes a pacer can which functions as a fourth electrode and has a plastic top wherein the third electrode is located. Said third electrode acts in cooperation with the first electrode to form a pair of sensing electrodes. The sensing electrode pair is further coupled to a sense amplifier for receiving an amplifying modulated electrical signals developed across the sensing electrode pair. A demodulator and filters circuit for demodulating the modulated carrier signal and recovering the modulating signal therefrom is connected to the output of the sense amplifier. The modulating signal is proportional to instantaneous stroke volume of the patient'"'"'s heart and the demodulator and filters circuit develops a control signal therefrom called a stroke volume signal. The control signal is applied to the pulse generator so as to control the rate of stimulating pulses.

Claims

1. A variable rate cardiac pacer apparatus responsive to metabolic needs of a patient, wherein the cardiac pacer apparatus includes a pulse generator, comprising:

(a) a source of alternating current carrier signals of a predetermined frequency;

(b) an endocardial lead having at least first and second electrodes wherein the second electrode is connected to the source of carrier signals so as to operate as a driver of the carrier signals;

(c) a pacer can wherein the pacer can is coupled to the source of carrier signals;

(d) a third electrode insulated from the pacer can, in electrical contact with body tissues and structured and arranged to cooperate with the first electrode to form a pair of sensing electrodes which sense a modulated signal proportional to instantaneous stroke volume of the patient'"'"'s heart;

(e) sense amplifier means coupling to the pair of sensing electrodes for receiving and amplifying the modulated signal;

(f) demodulator and filters circuit means for demodulating said amplified modulated signal and recovering a demodulated signal therefrom, said demodulated signal also being proportional to instantaneous stroke volume of the patient'"'"'s heart wherefrom the demodulator and filters circuit means develops a control signal consistent with the instantaneous stroke volume of the patient'"'"'s heart; and

(g) means applying said control signal to the pulse generator.

2. The apparatus of claim 1 wherein the demodulated further signal includes a ventilatory signal component, and following demodulation the ventilatory signal component is recovered, and said signal, being proportional to instantaneous ventilation, is used to develop a heart rate control signal consistent with instantaneous and/or time averaged ventilation.

3. The apparatus of claim 1 wherein the pacer apparatus includes an insulated top and the third electrode resides exposed through the insulated top.

4. The apparatus of claim 1 wherein the predetermined carrier signal frequency is in a range from about 500 to 20,000 Hertz.

5. In a variable rate cardiac pacer apparatus responsive to metabolic needs of a patient and including a conductive pacer can having an insulating member, a source of alternating current carrier signals of a predetermined frequency, wherein the pacer can is connected to the carrier signal source, and a pulse generator means for determining the rate at which heart stimulating pulses will be generated, the apparatus comprising:

(a) an endocardial lead having first and second electrodes wherein the second electrode is connected to the carrier signal source and operates as a driver for the carrier signal;

(b) a third electrode disposed on the insulating member wherein the first and third electrodes are structured and arranged to operate as a pair of sensing electrodes;

(c) sense amplifier means coupling to the pair of sensing electrodes for receiving and amplifying modulated signals developed across the sensing electrodes;

(d) demodulator and filters circuit means for demodulating the amplified modulated carrier signal and recovering the modulating signal therefrom, the modulating signal being proportional to instantaneous stroke volume of the patient'"'"'s heart wherein the demodulator and filters circuit develops a control signal therefrom; and

(e) means coupling the control signal to the pulse generator wherein the pulse generator operates to output stimulating pulses at a rate consistent with the control signal.

6. The apparatus of claim 5 wherein the carrier signals have a frequency in the range of about 500 to 20,000 Hertz.

7. A variable rate cardiac pacer apparatus responsive to metabolic needs of a patient, wherein the cardiac pacer apparatus includes a pulse generator, comprising;

(a) a source of alternating current carrier signals of a predetermined frequency;

(b) a unipolar lead having a first electrode wherein the first electrode is connected to the source of carrier signals so as to operate as a driver of the carrier signals;

(c) a pacer can wherein the pacer can is coupled to the source of carrier signals.

(d) a third electrode insulated from the pacer can, in electrical contact with body tissues and structured and arranged to cooperate with the first electrode to form a pair of sensing electrodes which sense a modulated signal proportional to instantaneous stroke volume of the patient'"'"'s heart;

(e) sense amplifier means coupling to the pair of sensing electrodes for receiving and amplifying the modulated signal developed across the sensing electrodes;

(f) demodulator and filters circuit means for demodulating said amplified modulated signal and recovering a demodulated signal therefrom, said demodulated signal also being proportional to instantaneous stroke volume of the patient'"'"'s heart wherefrom the demodulator and filters circuit means develops a control signal consistent with the instantaneous stroke volume; and

(g) means applying said control signal to the pulse generator. wherein the demodulator and filters circuit develops a control signal consistent with the instantaneous stroke volume; and

(g) means applying said control signal to the pulse generator.

8. The apparatus of claim 7 wherein the demodulated signal further includes a ventilatory signal component, and following demodulation the ventilatory signal component is recovered, and said signal, being proportional to instantaneous ventilation, is used to develop a heart rate control signal consistent with instantaneous and/or time averaged ventilation.

9. The apparatus of claim 7 wherein the pacer apparatus includes an insulated top and the second electrode resides exposed through the insulated top.

10. The apparatus of claim 7 wherein the predetermined carrier signal frequency is in a range from about 500 to 20,000 Hertz.

11. In a variable rate cardiac pacer apparatus responsive to metabolic needs of a patient and including a conductive can having an insulating member, a source of alternating current carrier signals of a predetermined frequency, wherein the pacer can is connected to the carrier signal source, and a pulse generator means for determining the rate at which heart stimulating pulses will be generated, the apparatus comprising:

(a) unipolar endocardial lead having a first electrode connected to the carrier signal source so as to operate as a driver for the carrier signal;

(b) a second electrode disposed on the insulating member wherein the first and second electrodes are structured and arranged to operate as a pair of sensing electrodes;

(c) sense amplifier means coupling to the pair of sensing electrodes for receiving and amplifying a modulated signal developed across the sensing electrodes;

(d) demodulator and filters circuit means for demodulating the amplified modulated signal and recovering a demodulated signal therefrom, the demodulated signal being proportional to instantaneous stroke volume of the patient'"'"'s heart wherein the demodulator and filters circuit develops a control signal therefrom; and

(e) means coupling the control signal to the pulse generator wherein the pulse generator operates to output stimulating pulses at a rate consistent with the control signal.

12. The apparatus of claim 11 wherein the carrier signals have a frequency in the range of about 500 to 20,000 Hertz.

13. In a variable rate cardiac pacer apparatus responsive to metabolic needs of a patient and including a conductive pacer can having an insulating member, a source of alternating current carrier signals of a predetermined frequency, wherein the pacer can is connected to the carrier signal source, a pulse generator means for determining the rate at which heart stimulating pulses will be generated and an endocardial lead having a first electrode wherein the first electrode is connected to the carrier signal source and operates as a driver for the carrier signal, the apparatus comprising a second electrode disposed on the insulating member wherein the first and second electrodes are structured and arranged to operate as a pair of sensing electrodes.