Cerebral Blood Flow & Its Regulation

Cerebral Blood Flow & Its Regulation


- Inhaled nitrous oxide (N2O) (Kety method). The average cerebral blood flow in young adults is 54 mL/100 g/min. The average adult brain weighs about 1400 g, so the flow for the whole brain is about 756 mL/min. In resting humans, the average blood flow in gray matter is 69 mL/100 g/min compared with 28 mL/ 100 g/min in white matter.

- Because brain tissue and spinal fluid are essentially incompressible, the volume of blood, spinal fluid, and brain in the cranium at any time must be relatively constant (Monro–Kellie doctrine).

- In the brain, auto regulation maintains a normal cerebral blood flow at arterial pressures of 65–140 mm Hg.

- O2 consumption by the human brain (cerebral metabolic rate for O2, CMRO2) averages about 3.5 mL/ 100 g of brain/min (49 mL/min for the whole brain) in an adult. This figure represents approximately 20% of the total body resting O2 consumption.

- Glucose enters the brain via GLUT 1 in cerebral capillaries.

- Blood Flow in Various Parts of the Brain – Best is P.E.T (2 Deoxy Glucose).

- CPP = MAP – CVP/ICP (whichever is higher), (Normal CPP 80-100 mmHg, ICP <10mm Hg.)

- Most important extrinsic influence on CPP is Arterial pCO2.

- Cerebral Blood Flow changes by 5-7 % with 10C change of temperature.