Biomedical method and apparatus for controlling the administration of therapy to a patient in response to changes in physiologic demand

• US 4,686,987 A
• Filed: 03/29/1982
• Issued: 08/18/1987
• Est. Priority Date: 06/18/1981
• Status: Expired due to Term

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Salo, Rodney W., Pederson, Brian D.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US06/362,903
• Time in Patent Office: 1,968 Days
• Field of Search: 128/419 PG, 128/693, 128/694, 128/713, 128/723, 128/734, 128/782
• US Class Current: 607/24
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance

Abstract

A biomedical apparatus capable of sensing changes in the heart'"'"'s ventricular volume or stroke volume and then changing the operating performance of the device in a fashion as a function of stroke volume. A relatively low frequency signal (under 5 KHz) is applied between spaced electrodes disposed in the heart and the beating action of the heart serves to modulate this signal due to changes in impedance being sensed between these or other electrodes within the heart. The modulated carrier signal is then processed to remove R-wave and other electrical artifacts and then demodulated to remove the carrier frequency component leaving the envelope which is proportional to instantaneous ventricular volume. This envelope signal then contains stroke volume and ventricular volume information which can be used by the biomedical apparatus to vary its operating parameters. For example, a current proportional to changes in stroke volume may be injected into the timing circuit of a demand-type cardiac pacer pulse generator whereby the interpulse interval of the pulse generator is varied as a function of stroke volume.

Claims

1. Apparatus for applying therapy to a patient based upon the hemodynamic state of said patient'"'"'s body, comprising in combination:

(a) intracardiac ventricular impedance sensing means for sensing the stroke volume in only one ventricular chamber of the heart;

(b) means coupled to said sensing means for developing a control signal varying as a function of changes in said stroke volume;

(c) patient therapy means having controllable rate means for establishing the rate at which prescribed therapy is administered to the patient; and

(d) means for applying said control signals to said controllable rate means to change said rate in relation to said changes in stroke volume.

2. Apparatus as in claim 1 wherein said intracardiac impedance sensing means comprises:

(a) an elongated electrical lead having a plurality of conductors extending the length thereof within an insulating sheath, said conductors individually terminating distally at plural spaced apart electrode means exposed on the exterior of said sheath with said electrode means located in one of the ventricular chambers of the heart;

(b) a source of an alternating current carrier signal whose frequency is in the range of from 500 to 5,000 Hertz electrically coupled to the proximal ends of said plurality of conductors for creating an alternating current voltage between said spaced electrodes; and

(c) further means coupled to said conductor means for detecting modulation of said alternating current carrier signal occasioned by the beating action of said patient'"'"'s heart, said modulation being a function of electrical impedance changes between ones of said electrode means in said one of said ventricular chambers.

3. Apparatus as in claim 2 wherein said means for developing an electrical control signal proportional to changes in stroke volume comprises:

(a) signal processing means coupled to said further means for converting the modulation envelope waveform of said carrier signal into an output proportional to changes in stroke volume.

4. Apparatus as in claim 3 and further including means in said signal processing means for establishing a fixed reference value such that said output is proportional to changes in stroke volume from said fixed reference value.

5. A variable rate cardiac pacer apparatus responsive to metabolic needs of the patient comprising in combination:

(a) a source of alternating current carrier signals of a predetermined frequency in the range of from 500 to 5,000 Hertz

(b) an endocardial electrical lead having at least two spaced apart sensing electrodes and a stimulating electrode, said sensing electrodes being located proximally of said stimulating electrode such that when said stimulating electrode is proximate the apex of one ventricular chamber, said sensing electrodes are also within said one chamber said lead having conductors coupling said source of carrier signals to said pair of sensing electrodes;

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

(d) high pass filter means connected to receive the output from said sense amplifier means for passing said carrier signals while attenuating any electrical artifacts picked up at said sensing electrodes of a frequency which is less than said predetermined frequency of said carrier signals;

(e) demodulator circuit means including low pass filter means coupled to the output of said high pass filter means for demodulating said modulated carrier signal and recovering the modulating signal therefrom, said modulating signal being proportional to instantaneous stroke volume of the patient'"'"'s heart;

(f) means coupled to said low pass filter for developing a control current proportional to changes in said modulating signal;

(g) a cardiac pacer pulse generator having a timing means for determining the rate at which heart stimulating pulses will be generated;

(h) means applying said control current to said timing means; and

(i) means coupling said generated stimulating pulses to said stimulating electrode on said lead.

6. Apparatus as in claim 5 wherein said means for developing a control current proportional to changes in said modulating signal comprises:

(a) means for establishing a fixed reference potential; and

(b) integrator circuit means coupled to receive said modulating signal and said fixed reference potential for integrating the difference between said modulating signal and said fixed reference potential.

7. A method of controlling the rate at which cardiac stimulating impulses are generated by a cardiac pacer pulse generator of the type having a variable timing means defining the period of said stimulating impulses, comprising:

(a) positioning an endocardial lead having spaced apart electrodes proximate its distal end in the vascular system such that said electrodes are in only one ventricular chamber of the heart;

(b) applying a high frequency carrier signal to said lead and across said spaced electrodes;

(c) detecting the modulation of said carrier signal occasioned by the inflow and outflow of blood in said one chamber during diastole and systole;

(d) developing a control signal proportional to changes in the detected modulation; and

(e) applying said control signal to said variable timing means of said cardiac pacer pulse generator to alter the rate at which stimulating pulses are generated.

8. A method of controlling the rate at which therapy is administered to a patient as a function of the hemodynamic state of said patient'"'"'s body, comprising:

(a) positioning an endocardial lead having spaced apart electrodes proximate its distal end in the vascular system such that said electrodes are in only one ventricular chamber of the heart;

(b) applying a high frequency carrier signal to said lead and across said spaced electrodes;

(c) detecting the modulation of said carrier signal occasioned by the inflow and outflow of blood from said one chamber during diastole and systole;

(d) developing a control signal indicative of the changes in the detected modulation; and

(e) utilizing said control signal to vary the rate at which said therapy is administered.

9. Cardiac stimulating apparatus having means for adjusting the frequency of stimulation as a function of physiologic demand, comprising in combination:

(a) a pulse generator having timing means therein for determining the frequency at which cardiac stimulating pulses are produced;

(b) means for conveying said cardiac stimulating pulses to a patient'"'"'s heart;

(c) impedance plethysmographic means including sensing means for measuring the stroke volume solely within one ventricular chamber of said heart; and

(d) means coupled to said impedance plethysmographic means for producing a control signal proportional to changes in stroke volume of the patient'"'"'s heart; and

(e) means coupling said control signal to said pulse generator for altering the operation of said timing means whereby the frequency at which stimulating pulses are produced varies with changes in stroke volume.

10. Apparatus as in claim 9 wherein said means for producing a control signal comprises:

(a) endocardial lead means having a pair of spaced-apart electrodes proximate the distal end of said lead means such that when said lead means is inserted in the vascular system, said electrodes are in only one ventricular chamber of the heart;

(b) means for applying a carrier signal via said lead means to said electrodes, said carrier signal having a frequency which is in the range of from 500 to 5,000 Hertz;

(c) demodulation means coupled to said lead means for detecting changes in amplitude of said carrier signal picked up by said electrodes which are occasioned by instantaneous changes in the volume of the heart;

(d) integrating means coupled to said demodulation means for producing a direct current signal proportional to said changes in said carrier signal over a predetermined time interval; and

(e) means for applying said control signal to said timing means in said pulse generator for changing the frequency at which cardiac stimulating pulses are produced in accordance with changes in the stroke volume of the heart.

11. Apparatus as in claim 10 wherein said carrier signal applied to said electrodes is of an amplitude and frequency insufficient to evoke electrically stimulated systoles.

12. A cardiac pacer system comprising:

(a) pulse generator means having a variable timing means for producing a cardiac stimulating impulses at a rate determined by said variable timing means;

(b) an endocardial lead coupled to the output of said pulse generator means and having a stimulating tip electrode and at least two additional electrodes proximally spaced a predetermined distance from said tip electrode so as to be located solely within one ventricular chamber of the heart when said stimulating tip electrode is disposed at the apex of the heart;

(c) means for applying an alternating current carrier signal of a predetermined amplitude and frequency between said two additional electrodes, said amplitude and frequency of said carrier signal being such that electrically stimulating systoles are not evoked by said carrier signal and said predetermined frequency being in the range of from 500 to 5,000 Hertz;

(d) high-pass filter means coupled to said pair of additional electrodes for attenuating signals picked up by said pair of electrodes which are of a lesser frequency than said predetermined frequency;

(e) demodulator means coupled to the output of said high-pass filter means for developing a control signal proportional to changes in amplitude of said alternating current carrier signal; and

(f) means for applying said control signal to said timing means in said pulse generator means whereby the rate of the stimulating pulses produced at said tip electrode is determined in part by said control signal.

13. Apparatus as in claim 12 wherein said demodulator means comprises:

(a) a half-wave rectifier circuit having an input and an output, said input being coupled to receive modulated carrier signals from said high-pass filter means;

(b) first low-pass filter means having an input for receiving the output from said half-wave rectifier and a cut-off frequency characteristic which is less than the frequency of said carrier signal, but greater than the expected frequency of a heartbeat; and

(c) second low-pass filter means coupled to receive the output from said first low-pass filter means, said second low-pass filter means having a cut-off frequency which is lower than the expected frequency of a heartbeat for producing a direct current voltage proportional in amplitude to changes in amplitude of said modulated carrier signals.

14. A variable rate cardiac pacer apparatus responsive to metabolic needs of the body, comprising in combination:

(a) intracardiac impedance plethysmography means for sensing changes in stroke volume in only one ventricular chamber of a mammalian heart;

(b) means coupled to said intracardiac impedance plethysmography means for developing a control signal proportional to said changes;

(c) cardiac pacer pulse generating means having timing means for determining the rate at which said pulse generator means produces output cardiac stimulating signals; and

(d) means for applying said control signals to said timing means to change said rate in relation to said changes in stroke volume.