Evaluation of a lumped parameter model for isolated working rat hearts

When a mechanical model of the rat aortic input impedance is perfused with a pulsatile pump, the computed values of the impedance components vary linearly with flow rate and are interactive. When the model is perfused by an isolated rat heart, the total load upon the left ventricle consists of the model and coronary impedances in parallel. Adenosine triphosphate induces changes in coronary impedance, and the redistribution of cardiac output from the model to the coronary circulation causes flow-related changes in the model impedance. Thus, the mechanical model does not provide a constant load for the isolated heart, because of variations in both the model and coronary impedances.