Effects of stroke volume and velocity of ejection on end systolic pressure of canine left ventricle. End systolic volume clamping

Abstract

To study the effects of contraction mode on ventricular end-systolic pressure-volume relationship, the authors compared the end-systolic pressure of isovolumic contraction with that of ejecting contraction at an identical end-systolic volume. The left ventricle of excised cross-circulated canine hearts was fitted with a water-filled balloon. The balloon was connected to a hydraulic pump that allowed the ventricle to contract to a preset constant end-systolic volume (19-37 ml) from a variable end-diastolic volume. At each of control, enhanced, and depressed levels of contractility, differences of end-systolic pressures of steady state isovolumic and ejecting contractions were evaluated while stroke volume and velocity of ejection were widely varied. The end-systolic pressure in the ejecting contraction tended to decrease by 5-15% from that of the isovolumic beat with increases in either stroke volume to 20-25 ml or peak velocity of ejection to about 800 ml/sec. There was no obvious difference in the results at different levels of contractility. The magnitude of the end-systolic pressure depression due to ejection was, however, relatively small as compared to 4-fold changes in end-systolic pressure due to the changes in contractility. The authors, therefore, conclude that the ventricular end-systolic pressure-volume relationship is affected slightly by ejection, and that this effect is much smaller than the maximal effect of changing contractility on the end-systolic pressure-volume relationship.