Analysis of left ventricular pressure during isovolumic relaxation in coronary artery disease.

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Abstract
When a decrease in left ventricular isovolumic pressure is considered as an exponential, the rate of relaxation can be defined by a time constant (T). Previously, T was calculated from the slope of ln (pressure) against time, but this method is valid only when the asymptote of the exponential is zero. In this study, 2 estimates of T were made: Tln from the slope of ln (pressure) against time, and TEXP by a method of exponential analysis that also estimated the asymptote. These techniques were applied to measurements of left ventricular pressure made at increasing pacing rates in 3 groups of patients catheterized for chest pain: group 1 (n = 9), normal coronary arteriograms; group 2 (n = 9), coronary artery disease (CAD) but no angina or lactate production during pacing; and group 3 (n = 9), CAD and angina during pacing. Tln was always shorter than TEXP and, in groups 1 and 2, TEXP was dependent on heart rate while Tln was not. The asymptote was negative and increased toward zero during pacing in groups 1 and 2. The difference between TEXP and Tln could be related to the value of the asymptote. In 18 of 20 beats tested, pressures calculated from TEXP and the asymptote were in closer agreement with measured pressures than were the pressures predicted by Tln. Despite their different values, TEXP and Tln was each distinguished between the 3 groups. Although the choice of an exponential model is arbitrary, isovolumic pressure decrease approximates to a single exponential but this study suggests that both T and the asymptote are variable.