Dissociation of end ejection from end systole of ventricle.

Previous experiments showed the cases in which end ejection of the ventricle did not always coincide with end systole as identified by the time for Emax corresponding to the maximally contracted pressure-volume relationship line of the ventricle. The purpose of the present study is to obtain a better insight into the ventricular afterloading conditions that enable end ejection to coincide with end systole of the ventricle by a simulation method. The left ventricle was simulated by a time-varying elastance, E(t), and the afterload by a constant pressure connected to the ventricle via a valve with resistance R and inertance L in series. A sinusoidal wave starting from 0 at onset of systole, reaching Emax at end systole, and returning to 0 at end diastole in each cycle was assigned for E(t). Parameters of the system elements were changed individually. Ventricular pressure, volume and flow were computed by solving the system of ordinary differential equations with a time-varying parameter, E(t). Results indicate that end ejection coincides with end systole only when R and L values fall on a specific curve in an R-L domain for a given set of the other system parameters, and otherwise the 2 ends variably dissociate from each other. Consequently, end ejection should not blindly be used as a substitute for end systole when Emax and end-systolic pressure-volume relations are to be assessed.