Figure 1.
Diagram illustrating the homeostasis of oxygen delivery and consumption in the brain. Arterial (Ya) and venous (Yv) oxygenation levels are the percentage of hemoglobin in the blood that is bound to oxygen. Ya is close to unity and, relative to Yv, does not vary much across individuals. Arterial vessels deliver blood to brain tissue, the flow rate of which is denoted by CBF. When the blood transits through capillary beds, a portion of the carried oxygen is extracted by brain tissue for its metabolism, the rate of which is denoted by CMRO2. The portion that remains in the blood will determine the value of Yv and is drained through veins.