The effect of ischemia and edema on membrane capacitance

The myocardial impedance between 25 kHz and 1 MHz was monitored in 29 porcine hearts during experimental preservations using a 4-electrode sensor placed in the left ventricle. Ischemia and edema were induced using three protocols. The changes observed in the elements of the equivalent circuit model of the myocardium were (i) compared between the different protocols and (ii) correlated with the measured weight increase (attributed to the presence of edema). The largest changes were observed in the magnitude of the pseudo-capacitance and the characteristic frequency. The strongest correlation was observed during long term preservations between the final weight increase and the initial change in the characteristic frequency. Apart from this prognostic ability, the characteristic frequency has also the advantage to be directly calculable from the experimental data, independently of any equivalent circuit model.