THE EFFECTS OF ALTERED ARTERIAL TENSIONS OF CARBON DIOXIDE AND OXYGEN ON CEREBRAL BLOOD FLOW AND CEREBRAL OXYGEN CONSUMPTION OF NORMAL YOUNG MEN 1

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Abstract
The effects of inhalation of 5-7% CO2, 85-100% O2, and 10% O2, were studied on the composition of arterial and internal jugular blood; on blood flow, O2 consumption, and vascular resistance of the brain; on cardiac output and blood pressure. CO2 inhaled in concns. of 5-7% produces an increase in cerebral blood flow averaging 75%. O2 inhaled in concns. of 85-100% is associated with a reduction in cerebral blood flow of 13%, while 10% O2 produced an increase of 35% in this function. These changes are satistically significant. Calculation of cerebrovascular resistance indicates that in every case the change in blood flow is due to a change in the vascular resistance of the brain. Cerebral O2 consumption is not significantly altered by changes in the composition of inspired air over the ranges studied. Mean arterial blood pressure rose significantly during the CO2 and high O2 inhalations and fell slightly with 10% O2. The only significant change in cardiac minute volume was an increase which occurred during 10% O2 inhalation and resulted from an increase in rate rather than stroke volume.