Myocardial oxygen consumption in the sea raven, Hemitripterus americanus: The effects of volume loading, pressure loading and progressive hypoxia

Abstract

1. Myocardial oxygen consumption (V̇O2) was measured using an in situ, perfused heart preparation at 10°C. V̇O2 increased in a linear fashion with power output when cardiac output (V̇b) was elevated (volume loading). The increased V̇O2 was possible through improved O2 delivery (increased V̇b), but Δ PO2 (input PO2 - output PO2) was reduced. The mechanical efficiency of the heart was improved. 2. V̇O2 also increased in a linear fashion with power output when output pressure was increased with V̇b constant (pressure loading). The increased V̇O2 was supported by increased O2 removal from the perfusate since oxygen delivery (V̇b and input PO2) was constant. Once more, improved mechanical efficiency was observed. 3. V̇O2 decreased as O2 delivery was reduced with progressive hypoxia. Even so, power output was maintained at a perfusate input PO2 of 81 Torr. Five of 11 hearts survived a 30-Torr PO2 exposure, but with a 29% decrease in power output and a 5-fold reduction in V̇O2. The increase in the apparent aerobic efficiency which enabled this is discussed.