AJP - Heart and Circulatory Physiology, Vol 257, Issue 4 1275-H1286, Copyright © 1989 by American Physiological Society
Analysis of myocardial isometric dynamics using parameters of a global model
O. N. Nwasokwa and M. M. Bodenheimer
Division of Cardiology, Harris Chasanoff Heart Institute, Long Island Jewish Medical Center, New Hyde Park 11042.
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.
