Continuous cardiac output by impedance measurements in the heart

• US 4,951,682 A
• Filed: 04/26/1989
• Issued: 08/28/1990
• Est. Priority Date: 06/22/1988
• Status: Expired due to Term

• Current Assignee: Cleveland Clinic Foundation
• Original Assignee: Cleveland Clinic Foundation
• Inventors: Petre, John H.
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): GETZOW, SCOTT M
• Application Number:
  US07/343,953
• Time in Patent Office: 489 Days
• Field of Search: 128/642, 128/713, 128/709, 128/712, 128/784, 128/786, 128/692, 128/693, 128/734
• US Class Current: 600/526
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/0538 invasively, e.g. using a catheter

Abstract

A diagnostic catheter for use in measuring cardiac output in the right ventricular chamber of a heart includes a catheter body having an outer periphery and a distal section terminating in a distal end and a proximal section terminating in a proximal end. A plurality of spaced electrodes are secured to the body outer periphery along the body distal section. A plurality of electrical leads extend in the catheter body from a respective one of the electrodes to the proximal end of the catheter body. An elongated rigid member is provided for stiffening a portion of the catheter body. One end of the rigid member is located adjacent a proximal most one of a plurality of electrodes. The rigid member so locates the plurality of electrodes as to space them away from endocardial tissue. The catheter is used with a cardiac output monitoring system. Signals from the catheter are acquired by a signal conditioning and catheter control unit and, are thereafter fed to a microcomputer. The catheter and the system are used in a method for determining the instantaneous volume of blood in a heart chamber.

Claims

1. A method for determining the instantaneous volume of blood in a chamber of an animal heart over an extended period of time, comprising the steps of:

(a) inserting an elongated tubular catheter percutaneously into said chamber, said catheter having a plurality of longitudinally-spaced electrodes on the surface thereof which are individually connected to a corresponding plurality of terminals at a proximal end of said catheter by conductors passing through said tubular catheter, the longitudinal spacing being such that a distal electrode and a proximal electrode are located adjacent a pulmonic valve and a tricuspid valve of the heart, respectively;

(b) driving said distal electrode and proximal electrode as a pair of driving electrodes with a constant current source;

(c) selectively and sequentially detecting the potential signal developed between pairs of sensing electrodes located intermediate the pair of driving electrodes attributable to the application of said constant current source to the pair of driving electrodes, said signal being proportional to the instantaneous impedance of the medium located between selected pairs of intermediate sensing electrodes;

(d) converting the detected potential signals to digital quantities;

(e) applying said digital quantities to a programmed digital computer device;

(f) generating a single corrected instantaneous impedance value for each pair of intermediate sensing electrodes determined to lie within the chamber, wherein the impedance value detected is due to the application of the constant current source to said pair of driving electrodes;

(g) calculating from said single corrected instantaneous impedance value a ventricular segment volume for each pair of sensing electrodes;

(h) summing said segment volumes for each pair of sensing electrodes to produce a total instantaneous ventricular volume;

(i) rejecting pacemaker pulses to prevent such pulses from interfering with processing of said detected potential signal.

2. The method of claim 1 wherein said single corrected instantaneous impedance value corresponds to a signal obtained between two of said intermediate sensing electrodes as if said driving electrodes were being spaced an infinite distance apart.

3. The method of claim 1 further including the step of detecting maximum and minimum excursions of said total instantaneous ventricular volume and determining the stroke volume of said chamber therefrom.

4. The method of claim 3 further including the step of multiplying said stroke volume quantity by a heart rate to provide a measured value of cardiac output.

5. The method of claim 1 wherein any electrode pair can be selected as drive electrodes.

6. The method of claim 1 wherein any electrode pair can be selected as sense electrodes.

7. The method of claim 1 further comprising the step of determining the location of said catheter in the heart by scanning said electrodes.

8. Apparatus for measuring the instantaneous volume of blood in a chamber of the heart over an extended period of time, comprising in combination:

(a) an elongated tubular intravascular a catheter having a proximal end and a distal end with a pair of drive electrodes attached to a exterior surface thereof and spaced apart from one another by a predetermined distance, d₁, which is less than the length dimension of catheter section held in said chamber and a plurality of pairs of sense electrodes attached to the surface thereof and longitudinally spaced there along between said pair of drive electrodes, said pair of drive electrodes and said plurality of pairs of sense electrodes being electrically coupled, individually, to a terminal at said proximal end of said catheter;

(b) a constant current source of frequency, F₁ ;

(c) a switching means joined to said terminal for coupling said constant current source to said pair of drive electrodes;

(d) a signal detector means connectable through said switching means to predetermined pairs of said plurality of pairs of sense electrodes for producing signal waves corresponding to the impedance of the medium present between a sense electrode pair selected by said switching means attributable to said constant current source;

(e) a computing means coupled to said signal detector means for sampling said signal waves at a predetermined rate and converting said signal waves to digital values representative of impedance values, said computing means being programmed to compute the volume of segments between selected paris of said sense electrodes using the formula;

space="preserve" listing-type="equation">Volume=(I.sub.c ×

ρ

×

L.sup.2)/V.sub.EE

where I_c is a known constant current source, ρ

is the resistivity of the medium, L is the distance between said selected pair of electrodes and V is a voltage measured from end to end of the catheter; and

(f) an auto-positioning means for positioning the signal waves within a predetermined window, whereby changes in ρ

over extended time periods can be accounted for such that extended monitoring can be accurately accomplished.

9. The apparatus of claim 8 wherein said computing means is further programmed to sum the individual segment volumes to provide a total instantaneous volume for said chamber.

10. A continuous cardiac output monitoring system, comprising:

an elongated tubular intravascular catheter adapted for insertion into a patient'"'"'s heart, said catheter including a plurality of spaced electrodes positioned on a periphery of said catheter, a distal most one and a proximal most one of said electrodes being configured as drive electrodes and the remaining electrodes being configured as sense electrodes, each of said electrodes being connected to a terminal located at a proximal end of said catheter;

a signal conditioning and control unit which is in electrical contact with said catheter through said catheter terminal, said unit comprising;

a constant current source,

a selector means for coupling said constant current source to said drive electrodes, and

a signal processing means for processing a signal received by said unit;

a computing means electrically connected to said unit for converting signal waves from said unit to digital values and then computing a stroke volume of the heart; and

a means for rejecting pacemaker pulses to prevent such pulses from being transmitted to said signal processing means.

11. The system of claim 10 further comprising a display means for displaying information concerning stroke volume, said display means being electrically connected to said computing means.

12. The system of claim 11 further comprising a housing means for holding said constant current source, said computing means and said display means.

13. The system of claim 12 wherein said housing means comprises a frame and wheels on which said frame is mounted so that said housing means is readily movable.

14. The system of claim 10 wherein said unit further comprises a signal and control isolation means for isolating the patient from all control signals in said unit and all sampled patient data.

15. The apparatus of claim 10 further comprising means for sampling signals from five pairs of electrodes.

16. The apparatus of claim 10 wherein said computing means comprises:

a keyboard entry means for enabling control parameters to be programmed in said computing means;

an input/output buffer means through which said computing means provides an output signal for an associated printer;

a video processor means through which said computing means provides an output signal for an associated cathode ray tube display;

a memory for storing data; and

,

a power supply for powering said computing means.