End-Systolic Pressure as Direct Determinant of Stroke Volume from Fixed End-Diastolic Volume in Isolated Canine Left Ventricle

Abstract

Ventricular systolic pressure as a whole has been considered the determinant of stroke volume of the ventricle which is contracting from a given end-diastolic (preload) volume under a given contractile state. However, the relative importance of the instantaneous ventricular pressure at different instants of systole remains unknown. In the present study, we investigated the effect of changing the magnitude of systolic ventricular pressure at the onset, middle, or end of ejection on stroke volume of isolated left ventricles, which contracted from a fixed end-diastolic volume. The results indicate that end-systolic pressure, rather than early or midsystolic pressure, is the direct determinant of stroke volume in the ventricle contracting from a given end-diastolic volume under a given contractile state.