Estimation of time constant of left ventricular relaxation.

Abstract

When the fall in left ventricular pressure during isovolumic relaxation is treated as a monoexponential the rate of relaxation can be measured by a time constant. Though an empirical measurement, the time constant has been used extensively to study relaxation. It can be accepted, however, as a valid measurement only if isovolumic pressure fall approximates very closely to a monoexponential in a wide range of circumstances.We analysed 60 beats recorded at different heart rates in 20 patients with a variety of left ventricular disease. In the first part of the study a powerful non-linear regression program was used off-line to test three exponential models: (1) a monoexponential, the asymptote of which is zero, (2) a monoexponential with a variable asymptote, and (3) a biexponential. The pressures predicted by models 2 and 3 were in very close agreement with measured pressure, whereas the predictions of model 1 were consistently less accurate. Model 3 had no advantage over model 2. Thus, in all the beats tested isovolumic pressure fall approximated very closely to a monoexponential of which both the time constant and asymptote are variable. A second exponential term does not increase precision, and is an unnecessary complication.In the second part of the study the same 60 beats were analysed by a small program on the catheter laboratory computer. The time constant was estimated by two methods, corresponding to models 1 and 2 described above: (1) from the slope of In (pressure) against time, and (2) by a method of exponential analysis. The first method underestimated the time constant of model 1, particularly in beats where pressure fell to low levels. The second method accurately estimated the time constant of model 2.It is concluded that isovolumic pressure fall approximates closely to a monoexponential in a wide variety of circumstances, and it is legitimate, therefore, to describe the rate of relaxation by a time constant. But the time constant must be estimated by a method based upon an exponential model of which both the time constant and asymptote are variable. We have shown that such a time constant can be estimated reliably by a small program suitable for use on-line. The usual method of estimating the time constant, from the slope of In (pressure) against time, provides an unreliable estimate of the time constant of an unsatisfactory model.During isovolumic relaxation the fall in left ventricu-must decay exponentially during relaxation. Its use lar pressure from the point of its maximum rate of can be justified only if isovolumic pressure fall change until it reaches the level of end-diastolic pres-approximates closely to a monoexponential in a wide sure of the preceding beat approximates to a monoex-range of circumstances. In addition, the estimate of ponential and can be characterised by a time con-the time constant is highly dependent upon its stant. 14 Though it has been used widely to study method of calculation.89 The purpose of this study relaxation of the intact ventricle' -7 the time constant was ...

Overexpression of the rat sarcoplasmic reticulum Ca2+ ATPase gene in the heart of transgenic mice accelerates calcium transients and cardiac relaxation.

“…5, C and D). Since dP/dt min may be affected by loading conditions, the preload independent measure of isovolumic relaxation, Tau (40,41), was calculated for both control and SERCA2 mice under basal conditions. Tau was significantly shorter in SERCA2 mice compared with the negative controls indicating faster relaxation (Tau shortened by 20%, control at 16.6 ms versus in SERCA2 13.4 ms) (P Ͻ 0.01).…”

“…The time constant of isovolumic pressure decay (Tau) was determined assuming the fall in LV pressure (P LV ) during isovolumic relaxation to be monoexponential with variable asymptote. The equation P LV ϭ P o e Ϫt/T ϩ P B allows calculation of extrapolated LV pressure assuming diastole to be infinite in duration (40,41), where P O is the pressure at peak negative dP/dt, t is the time from peak negative dP/dt, P B is the asymptote and T is Tau. Calculation of Tau was performed using ‫ف‬ 20-22 points from the decay of LV pressure for both control and transgenic animals.…”

Comparison of effects of dobutamine and ouabain on left ventricular contraction and relaxation in closed-chest dogs.

“…Because relaxation is an active process, isovolumic relaxation can be considered part of systole (1). During this period LV pressure declines exponentially (1,15,(26)(27)(28). Thus, the rate offall ofLV pressure can be quantified using the time constant (T) of the pressure fall.…”

Superior Logistic Model for Decay of Ca2+ Transient and Isometric Relaxation Force Curve in Rabbit and Mouse Papillary Muscles

“…The residual mean squares (RMS) also quantifies the goodness of fit, and this was calculated as the residual sum of squares divided by the residual degrees of freedom, which indicates the number of data points analyzed minus the number of parameters in the function. 35) Logistic and monoexponential RMS values were compared using the Wilcoxon signed-rank test.…”