Optimal arterial resistance for the maximal stroke work studied in isolated canine left ventricle

In a previous analysis of ventricular arterial interaction (Sunagawa et al., 1983), we represented the left ventricle as an elastic chamber which periodically increases its volume elastance to a value equal to the slope of the linear end-systolic pressure-volume relationship. Similarly, the arterial load property was represented by an effective elastance which is the slope of the arterial end-systolic pressure-stroke volume relationship. Since the maximal transfer of potential energy from one elastic chamber to another occurs when they have equal elastance, we hypothesized that the left ventricle would do maximal external work if the ventricular elastance and the effective arterial elastance were equal. We tested this hypothesis in 10 isolated canine left ventricles, ejecting into a simulated arterial impedance, by extensively altering arterial resistance and finding the optimal resistance that maximized left ventricular stroke work under various combinations of end-diastolic volume, contractility, heart rate, and arterial compliance. Each of these parameters was set at one of three levels while others were at control. The optimal resistance varied only slightly with arterial compliance, whereas it varied widely with contractility and heart rate. We thus determined that the ratio of the optimal effective arterial elastance to the given ventricular elastance remained nearly unity. This result supports the hypothesis that the left ventricle does maximal external work to the arterial load when the ventricular and arterial elastances are equalized.