Muscle perfusion and oxygenation during local hyperoxia.

Ventilation with O2 was previously shown to decrease whole-body and hindlimb muscle O2 uptake (VO2) in anesthetized dogs, particularly during anemia. To determine whether this was a purely local effect of hyperoxia (HiOx), we pump perfused isolated dog hindlimb muscles with autologous blood made hyperoxic (PO2 greater than 500 Torr) in a membrane oxygenator while the animals were ventilated with room air. Both constant-flow and constant-pressure protocols were used, and half the dogs were made anemic by exchange transfusion of dextran to hematocrit (Hct) approximately 15%. Thus there were four groups of n = 6 dogs each. A 30-min period of HiOx was preceded and followed by similar periods of perfusion with normoxic blood. In HiOx all four groups showed increased leg hindrance, increased leg venous PO2, and no significant changes in leg O2 inflow. Limb blood flow and VO2 decreased approximately 20% in HiOx with constant-pressure perfusion, regardless of Hct. In the constant-flow protocol, leg VO2 in HiOx was maintained by the anemic animals and actually increased in the normocythemic group. We conclude that HiOx directly affected vascular smooth muscle to cause flow restriction and maldistribution. Constant flow offset these effects, but the increased limb VO2 may have been a toxic effect. Anemia appeared to exaggerate the microcirculatory maldistribution caused by HiOx.