Evidence of Time-Varying Myocardial Contribution by In Vivo Magnitude and Phase Measurement in Mice

Cardiac volume can be estimated by a conductance catheter system. Both blood and myocardium are conductive, but only the blood conductance is desired. Therefore, the parallel myocardium contribution should be removed from the total measured conductance. Several methods have been developed to estimate the contribution from myocardium, and they only determine a single steady state value for the parallel contribution. Besides, myocardium was treated as purely resistive or mainly capacitive when estimating the myocardial contribution. We question these assumptions and propose that the myocardium is both resistive and capacitive, and its contribution changes during a single cardiac cycle. In vivo magnitude and phase experiments were performed in mice to confirm this hypothesis.