Springer Online Journal Archives 1860-2000
Abstract The instantaneous left intraventricular pressure-volume ratio, e(t)= p(t)/[v(t)−v d], in which p(t), v(t) and v d are intraventricular pressure, volume and a correction factor, respectively, was shown by our experimental studies to be independent of mechanical loading conditions and yet vary markedly with changes in contractile state of the ventricle. The studies also indicated that the e(t) curve under a given contractile state could be described as e(t)=αe o(βt), in which e o(t) represents e(t) under arbitrarily defined control contractile state and heart rate, and α and β are magnitude and duration parameters of the given e(t) with respect to e 0(t). The present mathematical analysis of mechanical relationship between ventricular performance represented by e(t) and myocardial contraction shows that the α and β parameters related to myocardial force, F, and shortening velocity of contractile element, V ce, respectively. Using a two-element model of myocardium and a thick-wall sphere or cylinder model of the ventricle we found that F(t)=αHe 0(βt) and V ce(t)=βK j[de 0(βt)/d(βt)]/e 0(βt). Both H and K j are functions of ventricular volume and are specific to the geometric model used, whereas the mode of afterload affects K j only. The mathematically derived F−V ce curves and their shifts owing to variations of α, β, H and K j under isotonic, isobaric and isovolumetric contractions simulated the experimentally established F−V ce curves from papillary muscle and their characteristic shifts reported by other investigators. On these bases we conclude that e(t) explicitly expresses the dynamic characteristics of myocardial contractions, which further supports our experimental contention that e(t) can be used as a useful index of contractile state of the ventricular chamber.
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