End-systolic pressure determines stroke volume from fixed end-diastolic volume in the isolated canine left ventricle under a constant contractile state.

Abstract

The effects of systolic pressure and volume changes on the end-systolic pressure at a fixed end-systolic volume in the left ventricle of excised, cross-circulated canine hearts were studied. Instantaneous ventricular volume was controlled and end-diastolic and end-systolic volumes were clamped, as preprogrammed by a volume servo pump system. Ventricular ejection was completed at the end of natural systole. When onset and velocity of ejection varied widely during contractions with end-diastolic and end-systolic volumes, end-systolic pressure was little affected by systolic pressure and volume changes in a stable contractile state. When end-diastolic volume increased from isovolumic condition, end-systolic pressure at the same end-systolic volume decreased (P < 0.05) from peak isovolumic pressure by 5-14%, for an ejection fraction of 40-70%. When end-systolic volume decreased while end-diastolic volume was fixed, the end-systolic pressure decreased in proportion to end-systolic volume. When ejection ends at the end of systole, stroke volume of the ventricle with a given end-diastolic volume is apparently determined predominantly by end-systolic pressure rather than by the entire systolic courses of the pressure and volume.