PHYSIOLOGY OF CEREBRAL BLOOD-FLOW AND METABOLISM

At a normal blood flow and oxygen consumption, the brain uses exclusively glucose as metabolic substrate. Coupling between blood flow and metabolism takes place on a local level. This adjustment occurs in two different ways: 1. Short-term, dynamic coupling mediated by local vasoactive factors that ensure second-to-second regulation. Such reactions appear to be partly dependent on the vascular endothelium. 2. Long-term, static coupling apparently mediated by capillary density and developed in response to local functional and metabolic activity. Recognizing these two mechanisms permits the distinction of apparent uncoupling during physiological conditions from real uncoupling during brain ischemia.