Blood flow and oxygen consumption in avian skeletal muscle during hypoxia

Birds are known to be much more tolerant than mammals to high altitude [low oxygen pressure (PO2)], and it is therefore of interest to know the responses of their muscles to low oxygen. We studied the influence of hypoxia on the rate of blood flow, oxygen extraction, and oxygen consumption (VO2) in resting hindlimb muscle of ducks. We found that during normoxia the VO2 in this muscle mass was similar to resting mammalian red muscle. However, blood flow rate (45 ml x 100 g-1 x min-1) and venous PO2 (70 Torr) were much higher than in resting red or white mammalian muscle. Hypoxia down to 35-40 Torr resulted in no change in blood flow, but oxygen extraction increased dramatically as arterial PO2 fell below 70 Torr. The resting VO2 was maintained even at the lowest arterial oxygen content (5 ml/100 ml). From these experiments it appears as though duck skeletal muscle has a "luxuriant" resting blood flow rate that is sufficient to supply skeletal muscle with adequate oxygen.