Method of determining the conductivity of blood

• US 5,827,192 A
• Filed: 08/21/1996
• Issued: 10/27/1998
• Est. Priority Date: 08/21/1996
• Status: Expired due to Fees

• Current Assignee: Cleveland Clinic Foundation
• Original Assignee: Cleveland Clinic Foundation, Marquette Medical Systems, Inc. (GE Aerospace)
• Inventors: Gopakumaran, Balakrishnan, Petre, John H., Osborn, Peter K.
• Primary Examiner(s): Jastrzab, Jeffrey R.
• Assistant Examiner(s): CARTER, RYAN CHRISTOPHER
• Application Number:
  US08/701,177
• Time in Patent Office: 797 Days
• Field of Search: 128/668, 128/673, 128/72, 128/642, 128/661.08, 128/713, 128/734, 128/693, 128/637, 600/481, 600/485-486, 600/454, 600/374, 600/526, 600/547, 600/506, 600/508, 600/381
• US Class Current: 600/481
• 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 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• 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
• CPC Class Codes: A61B 5/287 Holders for multiple electrodes, e.g. electrode catheters for electrophysiological study [EPS]
• CPC Class Codes: A61N 1/056 Transvascular endocardial electrode systems

Abstract

An in vivo method of determining the conductivity of a liquid such as human blood, including the steps of determining a location in a ventricle of a patient'"'"'s heart at which blood conductivity may be measured effectively, positioning a catheter having a plurality of spaced electrodes in the ventricle such that at least a pair of adjacent electrodes are positioned at the location, applying a current of known magnitude to the adjacent electrodes, measuring the voltage between the adjacent electrodes, and determining the conductivity of the patient'"'"'s blood from the known current and measured voltage.

Claims

1. In a process of determining cardiac volume by the conductance catheter method, the improvement comprising a method of determining the absolute electrical conductivity of blood as a part of said process comprising the steps of positioning in the ventricle of a mammalian heart a catheter comprising an elongate body having an outer surface and a plurality of spaced electrodes disposed on its outer surface, determining which pair of adjacent electrodes of the plurality of electrodes is optimally positioned to determine resistivity of the blood in the ventricle and selecting the pair of electrodes, applying a current of known magnitude to the selected pair of electrodes, measuring the voltage between the selected pair of electrodes and determining the absolute conductivity of the blood from the expression:

space="preserve" listing-type="equation">S=IKc/V

where

I=the applied current,

V=the measured voltage, and

Kc=a calibration ratio dependent upon electrode geometry and spacing.

2. The method set forth in claim 1 wherein the step of determining which pair of adjacent electrodes is optimally positioned comprises measuring the resistivity of successive pairs of adjacent electrodes and selecting the pair between which the least resistivity exists.

3. A conductive catheter method of determining cardiac volume comprising the steps of positioning a catheter in a ventricle of a patient'"'"'s heart, the catheter comprising an elongate body having a proximal end and a distal end and a plurality of spaced electrodes arrayed on the outer surface thereof, said electrodes being spaced a predetermined distance from each other between the proximal and distal ends of the catheter, wherein the electrode closest to the proximal end is the proximal electrode and the electrode closest to the distal end is the distal electrode with the remaining electrodes disposed at spaced apart intervals therebetween, providing a constant alternating current to the distal and proximal electrodes located within the ventricle, measuring the potential between pairs of electrodes located between the distal and proximal electrodes disposed within the ventricle, determining cardiac volume using an expression in which the conductivity of a patient'"'"'s blood is a variable, the improvement comprising the method of determining the absolute conductivity of the patient'"'"'s blood and including the steps of selecting a pair of adjacent electrodes between the proximal and distal electrodes from the plurality of electrodes and which pair of adjacent electrodes are positioned optimally for making conductivity measurements, applying a current of known magnitude to the selected pair of adjacent electrodes, measuring the voltage between the selected pair of adjacent electrodes, and determining the conductivity of the patient'"'"'s blood from the expression:

space="preserve" listing-type="equation">S=IKc/V

where

I=the applied current,

V=the measured voltage, and

Kc=a calibration ratio dependant upon electrode geometry and spacing.

4. The method set forth in claim 3 and including the steps of periodically terminating the cardiac output determination for a series of dwell periods and determining the conductivity of the patient'"'"'s blood during each dwell period, and resuming the cardiac output determination at the end of each dwell period using the blood conductivity determined during the dwell period preceding the determination of cardiac output.

5. A method of determining the absolute electrical conductivity of blood comprises the steps of positioning a catheter in a patient'"'"'s ventricle, the catheter comprising an elongate body having an outer surface and a plurality of spaced electrodes on the outer surface, positioning the catheter so that the plurality of electrodes are located within the ventricle, selecting a pair of adjacent electrodes between the proximal and distal electrodes from the plurality of electrodes and which pair of adjacent electrodes are positioned optimally for making conductivity measurements, applying a current of known magnitude to the selected pair of electrodes, measuring the voltage between the selected pair of electrodes and determining the conductivity of the blood from the expression:

space="preserve" listing-type="equation">S=IKc/V

where

I=the applied current,

V=the measured voltage, and

Kc=a calibration ratio dependant upon electrode geometry and spacing.

6. The method set forth in claim 5 wherein the step of selecting comprises measuring the resistivity of successive pairs of adjacent electrodes and selecting the pair having the least resistivity.