THE EFFECT OF THE COMPOSITION OF THE INSPIRED AIR ON THE CIRCULATION THROUGH THE BRAIN

¹ The Department of Physiology, University of Toronto

The flow of blood through the femoral vein and longitudinal sinus of dogs was examined by comparison of the A-V oxygen differences. Inhalation of 10 per cent. CO₂ in O₂ increased blood-flow through the brain of anæsthetised dogs to the estimated extent of from two to four times. At the same time flow through the hind leg was diminished, often to less than half the normal rate. These vascular changes indicate a differential vascular control giving a preferential consideration to the brain.

Alveolar O₂ deficiency did not cause the differential change, but the actual degree of anoxemia was not serious.

During CO₂ inhalation the R.Q. of the brain is much larger than in the leg. The R.Q. indicates the process of equilibration of the tissue with a change in pressure of CO₂, and demonstrates that the pressure of CO₂ changes more quickly in the brain than in the leg. The stimulus for differential control of flow may originate in the brain itself, but the result may be reinforced by, or it may even originate in a site extrinsic to the tissue.