O2 cost of contractility but not of mechanical energy increases with temperature in canine left ventricle.

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 ( E max)-pressure-volume area (PVA; a measure of total mechanical energy)-myocardial oxygen consumption (Vo 2) 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 E max and increased the oxygen cost of E max, which was enhanced by dobutamine, in a linear manner. However, the slope of the Vo 2-PVA relation (reciprocal of contractile efficiency) and its Vo 2intercept remained constant. Q10values of E max, the oxygen cost of E max, 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 E max and augment its oxygen cost without affecting the oxygen cost of PVA as myocardial temperature increases by 10°C around normothermia.