Varying temperature affects cardiac systolic and diastolic function and the left ventricular (LV) pressure-time curve (PTC) waveform that includes information about LV inotropism and lusitropism. Our proposed half-logistic (h-L) time constants obtained by fitting using h-L functions for four segmental phases (Phases I-IV) in the isovolumic LV PTC are more useful indices for estimating LV inotropism and lusitropism during contraction and relaxation periods than the mono-exponential (m-E) time

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... stants at normal temperature. In this study, we investigated whether the superiority of the goodness of h-L fits remained even at hypothermia and hyperthermia. Phases I-IV in the isovolumic LV PTCs in eight excised, cross-circulated canine hearts at 33°C, 36°C, and 38°C were analyzed using h-L and m-E functions and the least-squares method. The h-L and m-E time constants for Phases I-IV significantly shortened with increasing temperature. Curve fitting using h-L functions was significantly better than that using m-E functions for Phases I-IV at all temperatures. Therefore, the superiority of the goodness of h-L fit vs. m-E fit remained at all temperatures. As LV inotropic and lusitropic indices, temperature-dependent h-L time constants could be more useful than m-E time constants for Phases I-IV. Page 2 of 30 https://mc06.manuscriptcentral.com/cjpp-pubs Canadian Journal of Physiology and Pharmacology Page 3 of 30 https://mc06.manuscriptcentral.com/cjpp-pubs Canadian Journal of Physiology and Pharmacology In the present study, we investigated the potential application of the h-L and m-E functions to the analyses of Phases I, II, and III in the isovolumic LV PTC at hypothermia and hyperthermia, how temperature affects the h-L and m-E time constants, and whether the superiority of the goodness of h-L fits vs. that of m-E fits remained at different temperatures.