Temporal relationship between left ventricular and arterial system elastances.

Arterial compliance is an important component of ventricular afterload. Although its pressure dependence has been recognized, its temporal relationship to ventricular elastance (Elv(t)) has not been established. We investigated this in five open chest anesthetized dogs where simultaneous aortic pressure and flow and left ventricular pressure were measured. Elv(t) was derived using an elastance-resistance model of the left ventricle assuming an ejection fraction of 0.50 and a dead volume (Vd) of 3.0 mL. The nonlinear pressure-dependent compliance (C(P)) of the arterial system was incorporated in a three-element Windkessel model and determined by accurate prediction of aortic pressure from aortic flow. The resulting arterial elastance (Eas(t)) was computed as Eas(t) = 1/C(P). Results show that Eas(t) reaches a minimum value at or near the start of ventricular ejection and attains its peak value at or near the same time maximum LV elastance (Emax) is reached, at end-systole. Finally, numerical simulation of the model demonstrates its ability to adequately reproduce measured pressure and flow. Thus, the arterial system, in terms of elastance, is dynamically and temporally coupled to the left-ventricle during ejection.