Method and apparatus for measuring ventricular volume

• US 4,674,518 A
• Filed: 09/06/1985
• Issued: 06/23/1987
• Est. Priority Date: 09/06/1985
• 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.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US06/773,048
• Time in Patent Office: 655 Days
• Field of Search: 128/419 PG, 128/419 D, 128/668, 128/687, 128/693, 128/694, 128/695, 128/700, 128/713, 128/734, 128/784, 128/786
• US Class Current: 600/508
• 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 5/1073 Measuring volume, e.g. of limbs
• CPC Class Codes: G01F 17/00 Methods or apparatus for determining the capacity of containers or cavities, or the volume of solid bodies measuring linear dimensions to determine volume G01B

Abstract

A method and apparatus for the instantaneous measurement of venticular volume using an intracavity electrical impedance catheter having plural pairs of spaced surface electrodes driven by a corresponding plurality of electrical signals, each of the signals exhibiting a different discrete frequency, and having plural pairs of spaced surface electrodes for sensing the potentials at predetermined locations within the ventricle. Switching means are provided for selectively coupling the drive signals to predetermined pairs of surface electrodes and for selecting the sensing electrode pairs to be utilized at any given time for read-back of the sensed potentials. The read-back signals are demodulated and converted from an analog signal to a digital quantity. Then, a digital computer is used to determine from the sensed digital quantities the extrapolated value of impedance corresponding to sources spaced an infinite distance apart. Knowing the extrapolated impedance value, the volume of blood in the ventricle can be computed using the formula V=ρL² /R₀ wherein R₀ is the extrapolated impedance value, L is the distance between the spaced sensing electrodes spanning the ventricle and ρ is the resistivity of the blood.

Claims

1. A method for determining the instantaneous volume of blood in a chamber of an animal heart, 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 the proximal end of said catheter by conductors passing through said tubular catheter, the longitudinal spacing being such that the distal electrode and proximal electrode are located at the apex and proximate the entrance to said chamber, respectively;

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

(c) next driving the penultimate distal electrode and the second most proximal electrode as a second 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 said second pair of driving electrodes attributable to the application of said driving constant current source to the respective first and second pairs of driving electrodes, said potentials being proportional to the instantaneous impedance of the medium existing between the selected pairs of intermediate sensing electrodes;

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

(f) applying said digital quantities to a programmed digital computing device;

(g) generating a single corrected instantaneous impedance value for each pair of intermediate sensing electrodes from the two impedance values detected due to the application of the constant current source to said respective first and second pairs of driving electrodes;

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

(i) summing said segment volumes for each pair of sensing electrodes to produce said total instantaneous ventricular volume.

2. The method as in claim 1 wherein said reopective first and second pairs of driving electrodes are energized simultaneously by separate constant current sources of differing frequencies.

3. The method as in claim 1 wherein said single corrected instantaneous impedance value corresponds to that obtained between two of said intermediate sense electrodes due to said sources being spaced an infinite distance apart.

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

8. The method as in claim 1 or 5 and further including the step of multiplying said stroke volume quantity by the animal'"'"'s heartrate to provide a measured value of cardiac output.

5. A method for determining the instantaneous volume of blood in a chamber of an animal heart, 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 the proximal end of said catheter by conductors passing through said tubular catheter, the longitudinal spacing being such that the distal electrode and proximal electrode are located at the apex and proximate the entrance to said chamber, respectively;

(b) driving said distal electrode and proximal electrode with a constant current source of a first frequency;

(c) driving the penultimate distal electrode and the second most proximal electrode with a constant current source of a second frequency different from said first frequency;

(d) selectively and sequentially detecting the potential signal developed between pairs of sensing electrodes located intermediate said penultimate distal electrode and the second most proximal electrode attributable to said constant current source of a first frequency and to said constant current source of a second frequency, said potentials being proportional to the instantaneous impedance of the medium existing between the selected pairs of intermediate sensing electrodes;

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

(f) applying said digital quantities to a programmed digital computing device;

(g) generating a single corrected instantaneous impedance value for each pair of intermediate sensing electrodes from two impedance values corresponding to said first and second frequencies;

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

(i) summing said segment volumes for each pair of sensing electrodes to produce said total instantaneous ventricular volume.

6. The method as in claim 5 wherein said single corrected instantaneous impedance value corresponds to that obtained between two of said intermediate sense electrodes due to said sources being spaced an infinite distance apart.

7. The method as in claim 5 and further including the step of detecting the maximum and minimum excursions of said total instantaneous ventricular volume and determining the stroke volume of said chamber therefrom.

9. Apparatus for measuring the instantaneous volume of blood in a chamber of the heart, comprising in combination:

(a) an elongated tubular intravascular catheter having a proximal end and a distal end with a first pair of drive electrodes attached to the exterior surface thereof and spaced apart from one another by a predetermined distance, d₁, which is less than the length dimension of said chamber, a second pair of drive electrodes attached to the exterior surface thereof and spaced apart from one another by a predetermined distance, d₂, where d₂ is less than d₁, said second pair of drive electrodes being spanned by said first pair of drive electrodes and a plurality of pairs of sense electrodes attached to the surface thereof and longitudinally spaced therealong between said second pair of drive electrodes, said first and second pairs 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 first constant current source of a frequency, f₁ ;

(c) a second constant current source of a frequency, f₂ ;

(d) switching means joined to said terminals for coupling said first constant current source to said first pair of drive electrodes and for coupling said second constant current source to said second pair of drive electrodes;

(e) 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 the sense electrode pair selected by said switching means attributable to said first and second constant current sources;

(f) means operatively 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; and

(g) computing means coupled to receive said digital values, said computing means being programmed to extrapolate from said impedance values measured at the drive frequencies f₁ and f₂ an effective impedance value as if said distances d₁ and d₂ were infinitely large and computing the volume of the segments between selected pairs of said sense electrodes using the formula V=ρ

L² /R₀ where L is the distance between electrodes of said selected pair of sense electrodes, ρ

is the resistivity of the medium and R₀ is said effective impedance value.

10. Apparatus for measuring the instantaneous volume of blood in a chamber of the heart, comprising in combination:

(a) an elongated tubular intravascular catheter having a proximal end and a distal end with a first pair of drive electrodes attached to the exterior surface thereof and spaced apart from one another by a predetermined distance, d₁, which is less than the length dimension of said chamber, a second pair of drive electrodes attached to the exterior surface thereof and spaced apart from one another by a predetermined distance, d₂, where d₂ is less than d₁, said second pair of drive electrodes being spanned by said first pair of drive electrodes and a plurality of pairs of sense electrodes attached to the surface thereof and longitudinally spaced therealong between said second pair of drive electrodes, said first and second pairs 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) constant current source;

(c) switching means joined to said terminals for coupling said constant current source sequentially to said first pair of drive electrodes and to said second pair of drive electrodes;

(d) 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 the sense electrode pair selected by said switching means attributable to said constant current source being coupled to first pair of drive electrodes and to said second pair of drive electrodes;

(e) means operatively 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; and

(f) computing means coupled to receive said digital values, said computing means being programmed to extrapolate from said impedance values measured due to said constant current source coupled to said first pair of drive electrodes and to said second pair of drive electrodes and effective impedance value as if said distances d₁ and d₂ were infinitely large and computing the volume of the segments between selected pairs of said sense electrodes using the formula V=ρ

L² /R₀ where L is the distance between electrodes of said selected pair of sense electrodes, ρ

is the resistivity of the medium and R₀ is the effective impedance value.

11. The apparatus as in claims 9 or 10 wherein said computer is further programmed to sum the individual segment volumes to provide a total instantaneous volume for said chamber.