Method and apparatus to correct for electric field non-uniformity in conductance catheter volumetry

• US 5,971,933 A
• Filed: 08/27/1997
• Issued: 10/26/1999
• Est. Priority Date: 09/17/1996
• Status: Expired due to Fees

• Current Assignee: Cleveland Clinic Foundation, Marquette Medical Systems, Inc. (GE Aerospace)
• Original Assignee: Cleveland Clinic Foundation, Marquette Medical Systems, Inc. (GE Aerospace)
• Inventors: Schluter, Paul, Gopakumaran, Balakrishnan, Petre, John H., Osborn, Peter K.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): EVANISKO, GEORGE ROBERT
• Application Number:
  US08/920,345
• Time in Patent Office: 790 Days
• Field of Search: 607/29, 600/505-508, 600/547, 600/526
• US Class Current: 600/526
• CPC Class Codes: A61B 2562/043 in a linear array
• 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
• CPC Class Codes: A61B 5/287 Holders for multiple electrodes, e.g. electrode catheters for electrophysiological study [EPS]

Abstract

A method of determining cardiac volume including the steps of positioning a catheter in a blood-filled chamber of a patient'"'"'s heart. The catheter comprises an elongated body having a distal end, a proximal end, a plurality of spaced electrodes arrayed on the outer surface of the catheter and spaced apart a predetermined distance from each other to define a distal electrode, a proximal electrode and a plurality of pairs of adjacent electrodes between the distal and proximal electrodes to define volume segments within the chamber. The method includes the steps of providing a constant alternating current to the distal and proximal electrodes, measuring the potential between pairs of electrodes located between a distal and proximal electrodes while the distal and proximal electrodes are energized with the constant amplitude alternating current; determining a set of correction factors from the measured raw segmental volumes and catheter curvature; and correcting for field non-uniformity by multiplying the raw volumes by the set of correction factors.

Claims

1. A method of determining cardiac volume by means of a catheter adapted to be positioned in a blood filled chamber of a human heart

the catheter comprising an elongated body having a distal end and proximal end, a plurality of spaced electrodes arrayed on the outer surface of the catheter and being spaced apart a predetermined distance from each other to define a proximal electrode and a distal electrode and a plurality of electrodes disposed therebetween, pairs of adjacent electrodes between the distal and proximal electrodes defining volume segments within the chamber,

the method comprising the steps of positioning the catheter in a blood filled chamber of a human heart, the catheter assuming an arcuate configuration so that the segments of the catheter between adjacent electrodes are curved,

providing a constant alternating electrical excitation to the distal and proximal electrodes,

measuring an electrical parameter between pairs of adjacent electrodes located between the distal and proximal electrodes while the distal and proximal electrodes are energized with the electrical excitation,

determining the uncorrected volume of each volume segment from the measured electrical parameters,

determining a correction factor CF for each volume segment from the accurate curvature of the segment, and

applying the correction factor CF to the uncorrected volume of each volume segment to provide a corrected volume for each segment.

2. The method set forth in claim 1 and including the step of determining the slope a_i and intercept b_i of the catheter segments, wherein the correction factor CF is determined from the uncorrected volume and the slope and intercept of the catheter segment in the volume segment.

3. The method set forth in claim 2 and wherein the correction factor is derived from the expression:

space="preserve" listing-type="equation">CF.sub.i =a.sub.i RV.sub.i +b.sub.i

where

CFi=Correction factors for segment `i`

a_i =slope for the i^th segment

b_i =intercept for the i^th segment

RV_i =Uncorrected or raw volume of segment i.

4. The method set forth in claim 3 wherein the step of determining the slope a_i and the intercept b_i from the curvature of the catheter is determined as follows:

space="preserve" listing-type="equation">a.sub.i =m.sub.i /Cur+n.sub.i

space="preserve" listing-type="equation">b.sub.i =p.sub.i /Cur+q.sub.i

where

`Cur`is the catheter curvature and constants m_i, n_i, p_i and q_i depend on the segment number `i`.

5. The method set forth in claim 1 including the step of determining catheter curvature wherein the correction factor CF for each segmental volume is determined from the curvature of the catheter segment in the volume segment.

6. The method set forth in claim 5 wherein the electrical excitation is an alternating current and the electrical parameter is the potential between pairs of adjacent electrodes.

7. An apparatus for determining cardiac volume comprising a catheter adapted to be positioned in a blood filled chamber of a human heart, the catheter comprising an elongate body having a distal end and a proximal end, a plurality of spaced electrodes arrayed on the outer surface of the catheter and being spaced apart a predetermined distance from each other to define a proximal electrode and a distal electrode and a plurality of electrodes disposed therebetween, pairs of adjacent electrodes between the distal and proximal electrodes defining volume segments within the chamber,

said catheter adapted to assume a curved configuration within a chamber so that segments of the catheter between adjacent electrodes are curved,

means for providing a constant alternating electrical excitation to the distal and proximal electrodes,

means for measuring an electrical parameter between pairs of adjacent electrodes located between the distal and proximal electrodes while the distal and proximal electrodes are energized with the electrical excitation,

a processor coupled to the means for measuring the electrical parameter for determining the uncorrected volume of each volume segment from the measured electrical parameter, and for determining a correction factor for each volume segment from the curvature of the catheter segment therein and for applying the correction factor for each volume segment to the uncorrected volume of that segment to provide a corrected segmental volume for each volume segment.

8. The apparatus set forth in claim 7 wherein the processor is operative to determine the slope a_i and b_i intercept of the curved catheter segments, and to determine the Correction Factor from the uncorrected volume and the slope and intercept of the curved catheter segments.

9. The apparatus set forth in claim 8 wherein said processor is operative for deriving the Correction Factor from the expression:

space="preserve" listing-type="equation">CF.sub.i =a.sub.i RV.sub.i +b.sub.i

where

CFi=Correction factors for segment `i`

a_i =slope for the i^th segment

b_i =intercept for the i^th segment

R=the resistance of the volume segment

V_i =the measured voltage across the i^th segment.

10. The apparatus set forth in claim 9 wherein the processor is operative to determine the slope a_i and the intercept b_i from the curvature of the catheter as follows:

space="preserve" listing-type="equation">a.sub.i m.sub.i /Cur+n.sub.i

space="preserve" listing-type="equation">b.sub.i =p.sub.i /Cur+q.sub.i

where

`Cur` is the catheter curvature and constants m_i, n_i, p_i and q_i depend on the segment number `i`.

11. The apparatus set forth in claim 7 and including means for determining catheter curvature, the processor being operative to determine the correction factor for each volume segment from the curvature of the catheter segment therein.

12. The apparatus set forth in claim 11 wherein the means for providing a constant alternating electrical excitation is an alternating current source and the means for measuring an electrical parameter comprises means for measuring the potential between pairs of adjacent electrodes.

13. A method of determining cardiac volume comprising the steps of positioning a conductance catheter in a blood filled chamber of a human heart, the catheter having a plurality of spaced apart electrodes,

positioning the catheter in a curved configuration so that a first one of spaced apart electrodes is adjacent to the tricuspid valve and a second one of the spaced electrodes is positioned adjacent to the aortic valve,

determining the number of electrodes between the first and second electrodes,

energizing the first and second electrodes,

determining a voltage between adjacent pairs of electrodes between the first and second electrodes, the adjacent pairs of electrodes defining segmental volumes within the chamber,

determining a distance between the exciting electrodes,

determining catheter curvature,

determining uncorrected segmental volumes of the chamber as defined by the adjacent pairs of electrodes,

determining correction factors for each segmental volume for the catheter curvature between adjacent pairs of electrodes defining the segmental volumes, and

multiplying the uncorrected segmental volume of each volume segment by the correction factor for that segment to determine the true segmental volume.

14. The method set forth in claim 13 including the steps of determining the slope a_i and intercept b_i the of catheter segments, wherein the correction factor CF is determined from the uncorrected volume and the slope and intercept of the catheter segment in the volume segment.

15. The method set forth in claim 14 and wherein the step of determining the correction factor is determined from the expression:

space="preserve" listing-type="equation">CF.sub.i =a.sub.i RV.sub.i +b.sub.i

where

CFi=Correction factors for segment `i`

a_i =slope for the i^th segment

b_i =intercept for the i^th segment

R=the resistance of the volume segment

V_i =the measured voltage across the i^th segment.

16. The method set forth in claim 15 and wherein the step of determining the slope a_i and the intercept b_i from the curvature of the catheter is determined as follows:

space="preserve" listing-type="equation">a.sub.i =m.sub.i /Cur+n.sub.i

space="preserve" listing-type="equation">b.sub.i =p.sub.i /Cur+q.sub.i

where

`Cur` is the catheter curvature and constants m_i, n_i, p_i and q_i depend on the segment number `i`.