Cardiac contraction time and relaxation time with change in temperature: four half-logistic time constants

Abstract

High temperature shortens cardiac contraction time and relaxation time, and low temperature extends them. Goodness of half-logistic (h-L) function fits are superior to goodness of mono-exponential (m-E) function fits for the four phases; the first half of the ascending phase, second half of the ascending phase, first half of the descending phase, and second half of the descending phase of the isovolumic left ventricular pressure-time curve in the excised, cross-circulated canine heart at any temperatures. Four h-L time constants obtained by the h-L curve fittings extend with decreasing temperature and shorten with increasing temperature. Moreover, goodness of h-L function fits are superior to goodness of m-E function fits for the four phases of the isometric force-time curve and intracellular free calcium transient-time curve observed in the rat right ventricular papillary muscle and mouse left ventricular papillary muscle at low temperature. Four h-L time constants can be indices to evaluate cardiac or myocardial inotropic and lusitropic functions, and contraction process and relaxation process of intracellular free calcium transient accurately regardless of change in temperature.