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, we 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 contracility. We, 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.

Preload-induced curvilinearity of left ventricular end-systolic pressure-volume relations. Effects on derived indexes in closed-chest dogs.

“…This produces a depression of end-systolic pressure when end-diastolic volume is large compared with the value that would be expected from the ESPVR obtained with small end-diastolic volumes. This agrees with results obtained in isolated hearts by Suga and Yamakoshi,6 who showed that ESPVR is affected by ejection, particularly when stroke volume is large. Kass and Maughan'8 recently insisted on the difference between the true Emax (obtained in isolated hearts from differently loaded beats synchronized in time) and ESPVR obtained in the in situ heart, which can lead to Emax significantly steeper than Ees.…”

End-systolic pressure-volume relation estimated from physiologically loaded cat papillary muscle contractions.

“…The ventricular end-systolic pressure-volume relation was, however, no longer unique when ventricular stroke volume was varied. In a similar set of experiments, the endsystolic pressure at a given end-systolic volume was dependent both on stroke volume and ejection velocity (Suga and Yamakoshi, 1977). In these experiments, however, the pattern of ejection flow and, therefore, also the pattern of ventricular loading was different as peak velocity occurred much later in systole.…”

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

“…However, a similar magnitude of change in the end-systolic pressure can be ascribed to a change in the contractile state if the end-systolic, end-diastolic, and hence stroke volume and ejection fraction are unchanged as in run IV. Suga and Yamakoshi (1977) performed a similar study concerning the effects of ejection fraction and of the onset and velocity of ejection on end-systolic pressure. There are obvious differences between the two studies in the effects of changes in the onset and velocity of ejection on the end-systolic pressure.…”