HIGH FLOW DOES NOT ABOLISH THE REDUCED MAXIMUM OXYGEN UPTAKE IN DOG MUSCLE PERFUSED WITH 2, 3-DIPHOSPHOGLYCERATE-DEPLETED BLOOD

Abstract

To clarify the limiting factors for maximum oxygen consumption (⩒ₒ₂max) in contracting skeletal muscle, we perfused isolated dog gastrocnemius muscle at a high flow rate with two kinds of blood which have different affinities for oxygen. ⩒ₒ₂max was decreased significantly in the perfusion with DPG-depleted blood and the reduction was shown to have resulted from a lower O₂ extraction ratio. ⩒ₒ₂ and O₂ extraction were closely proportional to the reciprocal of resistance to blood flow. Furthermore, the different O₂ affinities of the perfusion blood affected these relationships : the slopes for ⩒ₒ₂ and O₂ extraction against the reciprocal of resistance for DPG-restored blood were signifi- cantly higher than those for DPG-depleted blood. We assumed that red cell transit time is inversely proportional to the resistance to blood flow and that high O₂-affinity blood is inherently slow to unload O₂ from red cells. The present results are well explained by our assumption. The results suggest that ⩒ₒ₂max may be determined by red cell transit time and O₂ unloading from the red cell.