Negative inotropism of hyperthermia increases oxygen cost of contractilityin canine hearts

Heart temperature affects left ventricular (LV) function and myocardial met abolism. However, how and whether increasing heart temperature affects LV m echanoenergetics remain unclear. We designed the present study to investiga te effects of increased temperature by 5 degreesC from 36 degreesC on LV co ntractility and energetics. We analyzed the LV contractility index (Emax) a nd the relation between the myocardial oxygen consumption (M(V) over dot O- 2) and the pressure-volume area (PVA; a measure of LV total mechanical ener gy) in isovolumically contracting isolated canine hearts during normothermi a (NT) and hyperthermia (HT). HT reduced E-max by 38% (P < 0.01) and shorte ned time to E-max by 20% (P < 0.05). HT, however, altered neither the slope nor the unloaded M(V) over dot O-2 of the M(V) over dot O-2-PVA relation. HT increased the oxygen cost of contractility (the incremental ratio of unl oaded M(V) over dot O-2 to Emax) by 49%. When Ca2+ infusion restored the re duced LV contractility during HT to the NT baseline level, the unloaded M(V ) over dot O-2 in HT exceeded the NT value by 36%. We conclude that HT-indu ced negative inotropism accompanies an increase in the oxygen cost of contr actility.