Assessment of cardiac contractility. The relation between the rate of pressure rise and ventricular pressure during isovolumic systole.

It was considered that the relationship between dp/dt and simultaneously developed pressure during the course of isovolumic contraction might afford a more accurate measure of contractility than the maximum rate of intraventricular pressure rise (peak dp/dt). In six cat papillary muscles contracting isometrically from any given preload, the ratio of the rate of tension development (dT/dt) to simultaneously occurring isometric tension always varied directly with the contractile state. This ratio rose slightly as preload was increased, but it was not affected by changes in afterload. In 17 experiments in an intact canine heart preparation in which left ventricular end-diastolic