Dual indifferent electrode pacemaker

• US 5,284,136 A
• Filed: 05/13/1991
• Issued: 02/08/1994
• 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): Howell, Kyle L.
• Assistant Examiner(s): Getzow, Scott M.
• Application Number:
  US07/698,789
• Time in Patent Office: 1,002 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 disposed thereon;

(c) a pacer housing including a conductive pacer can;

(d) a third electrode disposed on said housing and insulated from the pacer can;

(e) sense amplifier means having first and second inputs and an output;

(f) means coupling said source of alternating current carrier signals between said first electrode and one of said pacer can and said third electrode;

(g) means coupling said first and second inputs of said sense amplifier means individually to the other of said pacer can and said third electrode and to said second electrode, respectively, for sensing at said output of said sense amplifier a modulated signal proportional to the instantaneous tissue impedance within the thoracic cavity;

(h) demodulator and filter circuit means for demodulating said modulated signal and recovering a demodulated signal therefrom, said demodulated signal also being proportional to instantaneous impedance within the thoracic cavity wherefrom the demodulator and filter circuit means develops a control signal consistent with the instantaneous impedance in the thoracic cavity; and

(i) means for applying said control signal to said pulse generator for modifying the pacing rate thereof.

2. The apparatus of claim 1 wherein the modulating 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 or time-averaged ventilation.

3. The apparatus of claim 1 wherein the pacer apparatus includes an insulated top on said can 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 20000 Hz.

5. 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;

(c) a pacer housing including a conductive pacer can;

(d) a second electrode mounted on said pacer housing and insulated from the pacer can, in electrical contact with body tissue and structured and arranged to cooperate with the first electrode to form a pair of drive electrodes for said carrier signals;

(e) sense amplifier means being coupled to said first electrode and said pacer can for receiving and amplifying a modulated carrier signal developed across said first electrode and said pacer can;

(f) demodulator and filter circuit means for demodulating said modulated signal and recovering a demodulated signal therefrom, said demodulated signal being related to variations in thoracic impedance due to ventilatory activity wherefrom the demodulator and filter circuit means develops a control signal consistent with said ventilatory components; and

(g) means for applying said control signal to the pulse generator to vary its pacing rate.

6. The apparatus of claim 5 wherein the pacer housing includes an insulated top and the second electrode resides exposed through the insulated top.

7. The apparatus of claim 5 wherein the predetermined carrier signal frequency is in the range of from about 500 to 20000 Hz.

8. 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 disposed thereon;

(c) a pacer housing including a conductive pacer can;

(d) a third electrode disposed on said housing and insulated from the pacer can;

(e) sense amplifier means having first and second inputs and an output;

(f) means coupling said source of alternating current between only two of said pacer can, said first, said second and said third electrodes;

(g) means coupling said first and second inputs of said sense amplifier means individually to other than the two of said pacer can, said first, second and third electrodes to which said source of alternating current is connected, for sensing at the output of said sense amplifier a modulating signal proportional to the instantaneous tissue impedance within the thoracic cavity;

(h) demodulator and filter circuit means for demodulating said modulated signal and recovering a demodulated signal therefrom, said demodulated signal also being proportional to instantaneous impedance within the thoracic cavity wherefrom the demodulator and filter circuit means develops a control signal consistent with the instantaneous impedance in the thoracic cavity; and

(i) means for applying said control signal to said pulse generator for modifying the pacing rate thereof.

9. 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 one electrode disposed thereon;

(c) a pacer housing including a conductive pacer can;

(d) a button electrode disposed on said housing and insulated from the pacer can;

(e) sense amplifier means having first and second inputs and an output;

(f) means coupling said source of alternating current carrier signals between said conductive pacer can and said button electrode;

(g) means coupling said first and second inputs of said sense amplifier means individually to said one electrode and to said button electrode for sensing at the output of said sense amplifier a modulated signal proportional to the instantaneous tissue impedance within the thoracic cavity;

(h) demodulator and filter circuit means for demodulating said modulated signal and recovering a demodulated signal therefrom, said demodulated signal also being proportional to instantaneous impedance within the thoracic cavity wherefrom the demodulator and filter circuit means develops control signal consistent with the instantaneous impedance in the thoracic cavity; and

(i) means for applying said control signal to said pulse generator for modifying the pacing rate thereof.