Oxygen uptake in saline-perfused rabbit heart is decreased to a similar extent during reductions in flow and in arterial oxygen concentration.

In experiments reported in the literature, oxygen uptake in saline-perfused heart decreased after small reductions in arterial O2 concentration (CaO2) at constant perfusion flow. This may have resulted from the decrease in O2 supply, but may also have been due to decreased O2 demand caused by reduced perfusion pressure following hypoxic vasodilation (garden hose effect). We tested both possibilities in 8 isolated rabbit hearts, perfused with Tyrode solution at 37 degrees C, perfusion pressure 94 +/- 4 mm Hg (mean +/- SD). Vasodilation with 10 microM adenosine in the perfusate prevented changes in perfusion pressure during hypoxia. Oxygen uptake decreased significantly by 5.8 +/- 2.1% for a 10% decrease in CaO2 at constant flow, and by 4.4 +/- 1.8% per 10% decrease in flow at constant CaO2. In both cases a 10% reduction in oxygen supply was applied and the decrease in oxygen uptake was not significantly different. The decrease in perfusion pressure during flow reduction did therefore not cause a detectable decrease in oxygen consumption via the garden hose effect in addition to the decrease caused by reduced oxygen supply. The data show that oxygen uptake in saline-perfused rabbit heart, at 37 degrees C, is limited by O2 supply.