Computer simulation of the effects of ventricular interdependence on indices of left ventricular systolic function

The influence of ventricular interdependence on cardiovascular function has been convincingly demonstrated. In the intact cardiovascular system ventricular interdependence is always present, and thus measures of cardiac function include the contribution of ventricular interdependence (VI). A cardiovascular system model is presented and used to discuss how VI affects selected indices of left ventricular (LV) systolic function. Indices of LV function studied were the ejection fraction, stroke work, peak time derivative of ventricular pressure (dP/dT) and the LV end-systolic pressure-volume relationship. The effects of right ventricular (RV) volume through systolic VI on these indices are conveniently studied by comparing the model responses to pulmonary artery (PA) and vena caval (VC) occlusions; both PA and VC occlusion reduce LV volume, but the RV volume is increased by PA but reduced by VC occlusions. Through systolic VI the increase in RV volume with PA occlusion shifted the LV end-systolic pressure-volume relationship to the left and thus affected measures of LV maximum elastance. The LV ejection fraction, peak dP/dT and stroke work were all augmented by the increase in RV volume associated with the PA occlusion. Experimental studies comparing the responses to PA and VC occlusions are in broad agreement with the results described here. Systolic VI also shifted the cardiac function curve, a global measure of cardiac function, to the left. The results thus suggest that commonly used indices of LV systolic function are dependent on RV function and do not solely reflect LV function.