Improvements in the accuracy of estimation of left ventricular volume from measurements of complex admittance using a tetrapolar catheter

Abstract

Cardiac volume has been estimated using conductance technology that generates an instantaneous volume-dependant conductance signal. Unfortunately, the measured conductance is a combination of blood and myocardium, but only the blood conductance is desired. Hence, the instantaneous parallel myocardial contribution must be determined and removed from the total measured conductance signal in order to accurately measure cardiac volume. The currently adopted method assumes that the conductance-volume relationship is linear and the myocardial contribution to the total measured conductance is constant during a cardiac cycle. It also ignores either myocardial conductance or capacitance when estimating the myocardial contribution. This dissertation deals with these issues, and derives and validates a nonlinear conductance-to-volume conversion equation. It also proves that myocardial contribution varies during the cardiac cycle and develops a new method to calculate myocardial contribution using the fact that myocardium is both conductive and capacitive.