Neural regulation of canine skeletal muscle blood flow during hypoxic hypoxia

Vascular resistance in canine limb skeletal muscle first increases and then decreases with prolonged arterial hypoxia, but whether neural sympathetic activity decreases with time is unknown. To assess the effectiveness of neurally mediated vasoconstrictor tone, the authors periodically cooled and rewarmed the sciatic nerve while nine anesthetized, paralyzed, pump-ventilated dogs were made hypoxic for 60 min by ventilation with 9.1% O sub(2) in N sub(2). The results showed that not only was neurally mediated vasoconstriction to skeletal muscle maintained throughout the hypoxic period, but that its intensity must have been increasing to overcome the local vasodilatory forces that were responsible for flow increasing even further with nerve cooling in prolonged hypoxia.