Effects of Inhalation of Oxygen on Blood Flow and Microvasculature of Ischemic and Nonischemic Cerebral Cortex

The right middle cerebral artery was occluded in cats, and PaO2 was increased by increasing the amount of oxygen inhaled by the animals at atmospheric pressure. Cortical blood flow (CBF) was measured with Krypton-85, and observations and photographs of the superficial cortical microvasculature were made bilaterally. In two of five animals, increasing the PaO2 caused constriction of surface arterioles of the nonischemic hemispheres, with an associated decrease of CBF; in the three other animals, there were no circulatory responses to the increased PaO2. In seven animals, increasing the PaO2 had no apparent effect on CBF or arteriolar caliber of the ischemic cerebral hemispheres. In four animals, at PaO2 greater than 400 torr, reactivity to increases of PaO2 was preserved in nonischemic cortex but impaired in ischemic cortex. Reddening of venous blood of the microvasculature of ischemic cerebral cortex occurred when PaO2 was increased, indicating that more oxygen was made available to the ischemic cerebral tissue. However, no beneficial effects could be demonstrated on the changes in the microvasculature produced by ischemia.