Preservation of cerebral autoregulation in the unanesthetized hypoxemic newborn dog.

Studies were conducted to determine the effects of hypoxemia on cerebral blood flow and the influence of hyperoxia and hypoxemia on autoregulation of cerebral blood flow in the unanesthetized newborn dog. Twenty-one newborn dogs less than 2 weeks of age were studied. Cerebral blood flow was measured using radioactive microspheres during successive periods of normotension, hypotension (produced by blood withdrawal) and normotension (produced by infusion of previously withdrawn blood). In the hyperoxic animals, arterial pO2 was maintained above 250 torr by having the animal breathe 100% oxygen, while in the hypoxemic animals arterial pO2 was maintained between 30 and 35 torr by having the animal breathe 12% O2. Cerebral blood flow increased significantly with hypoxemia. In both hypoxemic and hyperoxic animals cerebral blood flow was maintained constant in spite of a large fall in arterial blood pressure and cardiac output, demonstrating the presence of autoregulation. Calculated oxygen transport to the brain was constant during hypoxemia and hypotension in all animals. Thus autoregulation of cerebral blood flow is present in newborn animals and is preserved under conditions of moderate hypoxemia.