Negative inotropism of hyperthermia increases oxygen cost of contractility in canine hearts
Heart temperature affects left ventricular (LV) function and myocardial metabolism. However, how and whether increasing heart temperature affects LV mechanoenergetics remain unclear. We designed the present study to investigate effects of increased temperature by 5°C from 36°C on LV contractility and energetics. We analyzed the LV contractility index ( Emax) and the relation between the myocardial oxygen consumption (MV˙o2) and the pressure-volume area (PVA; a measure of LV total mechanical energy) in isovolumically contracting isolated canine hearts during normothermia (NT) and hyperthermia (HT). HT reduced Emaxby 38% ( P < 0.01) and shortened time to Emaxby 20% ( P < 0.05). HT, however, altered neither the slope nor the unloaded MV˙o2of the MV˙o2-PVA relation. HT increased the oxygen cost of contractility (the incremental ratio of unloaded MV˙o2to Emax) by 49%. When Ca2+infusion restored the reduced LV contractility during HT to the NT baseline level, the unloaded MV˙o2in HT exceeded the NT value by 36%. We conclude that HT-induced negative inotropism accompanies an increase in the oxygen cost of contractility.