Dynamics and Control Mechanisms in Maintenance of Regional Cerebral Blood Flow

Experiments with rabbits, cats, and monkeys during recording of complex physiological processes (LEPG, ThG, Po2, Pco2, and ECoG) in functionally discrete brain regions of awake animals have shown that functional changes, expressed as desynchronization effects on ECoG, are followed by an increase of local blood flow (LCBF) in regional brain cortex up to 0.3 to 0.4 ml per minute per 1 gm brain tissue or an increase of 35% to 45% of resting levels of LCBF. Under normal physiological conditions LCBF and Po2 change periodically without any external interference at frequency ranges 0.005 to 0.2 cps. This is characteristic of all brain regions and all species of animals investigated. These variations range in amplitude as much as 28% of the mean level of LCBF. Changes of LCBF have no correlation with changes of systemic blood pressure (SAP). Local control mechanisms appear to be responsible for them. The interrelationships of changes of functional activity and CBF in local regions of awake brain are characterized by a very short time delay (less than one second), but under narcosis it increased up to ten seconds. All these facts taken together suggest that control mechanisms responsible for local brain vascular reactions have two components; the first is metabolic and the second is neurogenic in nature.