Effects of changes in the aortic input impedance on systolic pressure-ejected volume relationships in the isolated supported XXXX left ventricle.

@entity235 @entity64
We examined the effects of aortic input impedance alteration on left ventricular pressure, aortic flow and ejected volume (integral value of aortic flow), in an isolated blood perfused ejecting @entity235 heart, with special reference to end-systolic values. A hydraulic model which stimulates an aortic input impedance was attached to the aortic root of an excised heart. Left ventricular end-diastolic pressure was kept constant by electrical pacing. Three coronary arteries were perfused with arterial blood from support @entity235 . When the peripheral resistance in the hydraulic model was changed, there were inverse linear relationships between @entity64 volume and mean left ventricular systolic pressure and between ejected volume and pressure at end-systole. Time interval from the onset of contraction to end-systole did not change. Thus the relation between @entity64 volume and mean left ventricular pressure obtained by changes in peripheral resistance is governed by a source resistance, which can be considered as the contractile state of the ventricle. When the capacitance (arterial compliance) was changed, there was no inverse linear relation between @entity64 volume and mean systolic pressure. In many cases, there was an inverse linear relationship between ejected volume and pressure at end-systole. However, an increase in capacitance prolonged the time interval from the onset of contraction to end-systole. We conclude that the end-systolic pressure-ejected volume relationship in the ejecting heart is governed not only by contractility but also by arterial capacitance.
