O2cost of contractility but not of mechanical energy increases with temperature in canine left ventricle

Abstract

We investigated the effects of myocardial temperature on left ventricular (LV) mechanoenergetics in the excised, cross-circulated canine heart. We used the framework of the LV contractility ( Emax)-pressure-volume area (PVA; a measure of total mechanical energy)-myocardial oxygen consumption (Vo2) relationship. We have shown this framework to be useful to integrative analysis of the mechanoenergetics of a beating heart. In isovolumic contractions at a constant pacing rate, increasing myocardial temperature from 30 to 40°C depressed Emaxand increased the oxygen cost of Emax, which was enhanced by dobutamine, in a linear manner. However, the slope of the Vo2-PVA relation (reciprocal of contractile efficiency) and its Vo2intercept remained constant. Q10values of Emax, the oxygen cost of Emax, and the oxygen cost of PVA were 0.4, 2.1 and 1.0, respectively, around normothermia. We conclude that the temperature-dependent processes of cross-bridge cycling and Ca2+handling integratively depress Emaxand augment its oxygen cost without affecting the oxygen cost of PVA as myocardial temperature increases by 10°C around normothermia.