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.
Nwasokwa
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ON
Division of Cardiology, Harris Chasanoff Heart Institute, Long Island Jewish Medical Center, New Hyde Park 11042.
Bodenheimer
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MM
D000818:Animals; D001775:Blood Circulation; D001803:Blood Transfusion; D003326:Coronary Circulation; D004285:Dogs; D005263:Femoral Artery / Q000502:physiology; D005268:Femoral Vein / Q000502:physiology; D007537:Isometric Contraction; D008433:Mathematics; D008955:Models, Cardiovascular; D009200:Myocardial Contraction; D010210:Papillary Muscles / Q000502:physiology*