Analysis of myocardial isometric dynamics using parameters of a global model.

Despite previous efforts, a global empirical relation has not been described for the myocardial isometric curve, F(t). We propose here that a useful relation is F(t) = CtB-1e-AtB. A, B, and C are global parameters. We evaluated this model and the effect of change in muscle length (L) and dobutamine on the parameters in nine in situ canine papillary muscles. A servo-system clamped muscle length to produce isometric twitches. For each twitch, the parameters were determined by curve fitting. The model fit the observed curves of F(t) closely; the correlation coefficient was 0.997 +/- 0.001. Whereas C changed with L, A and especially B varied little with L averaging 28.6 +/- 5.2 and 2.42 +/- 0.08, respectively. Our predictions that A reflects chronotropic state, B lusitropic, and C heterometric and inotropic states, were verified with dobutamine. We also derived relations for various attributes of the F(t) curve in terms of A, B, and C only. An excellent correlation was noted between the calculated and the observed values of these attributes. The empirical relation F(t) = CtB-1e-AtB therefore provides a valid cohesive reference frame for analysis of myocardial dynamics.