Effect of Radial Position on Volume Measurements Using the Conductance Catheter

A finite-difference computer model has been used to determine the potential distributions arising from a dipole current source aligned parallel to the axis of bounding cylinders. The radial position of this source had large and nonlinear influence on the potentials along the dipole axis. The accuracy of the computer simulation was established from comparison with an analytic solution of a simple geometry. Measurements using a conductance catheter in saline-filled cylinders also demonstrated the dependence of the conductance on the radial position. The dependence of the potential distribution on the radial position of the dipole places limits on the ultimate accuracy of the conductance catheter technique when used for the measurement of ventricular volume. Radial movement of the catheter within the ventricular cavity, resulting in changes in the potential distribution, could explain some artefacts that appear on volume recordings from the conductance catheter.