Quantitative data on the afterload dependence of left ventricular dp/dtmax in isolated canine hearts.

In 15 canine heart-lung preparations the effect of an increase in aortic pressure on left ventricular dP/dtmax was tested. Abrupt elevation of aortic pressure by 20-80 mm Hg during diastole without change in enddiastolic pressure did not influence left ventricular dP/dtmax in the following heart beat. Left ventricular circumference increased slightly. Stepwise elevation of aortic pressure from 60 to 130 mm Hg (LVEDP maintained constant) resulted in an augmentation of the steady-state values of dP/dtmax by only 42 mmHg/s per 10 mmHg pressure rise. If the enddiastolic pressure was not maintained constant, the increase in dP/dtmax was 77 mm Hg/s per 10 mm Hg pressure rise. Aortic pressure alterations exhibit a slight but significant influence on left ventricular contractility in the steady-state phase, while an acute effect is not detectable, thus demonstrating that a sudden increase in coronary perfusion pressure is without immediate effect on the cardiac performance.