Hemodynamic determinants of maximum negative dP/dt and periods of diastole

The canine right heart bypass preparation was utilized to examine the effects of heart rate, stroke volume, and arterial pressure on the maximum rate of fall of left ventricular pressure (negative dP/dt) and the duration of isovolumic diastole and the diastolic filling period. Maximum negative dP/dt was most closely related to the magnitude of the peak aortic systolic pressure. Large rapid increases in stroke volume from 2-4 ml to 15-20 ml at constant heart rate and constant peak aortic systolic pressure did result, though, in small increases in maximum negative dP/dt (5-13%). With changes in mean aortic pressure from 75 to 125 mmHg, there was no significant change in the diastolic isovolumic or filling period as a result of the more rapid fall of ventricular pressure. The isovolumic period shortened and the filling period lengthened at higher stroke volumes due to the rise in left atrial pressure and thus early mitral valve opening. Higher heart rates shortened the total diastolic duration per beat principally as a result of a briefer filling period. Despite a fall in the dicrotic notch pressure with increasing heart rate and constant cardiac input, isovolumic diastole did not shorten, due primarily to a lower left atrial pressure and delayed mitral valve opening. There was a small statistically insignificant decrease in isovolumic diastole per beat at higher heart rates with constant stroke volume. The duration of isovolumic diastole and of the diastolic filling period reflects interrelationships between the duration of systolic events, the aortic dicrotic notch pressure, ventricular relaxation rate, and left atrial pressure.