Cerebral blood flow, cerebral blood volume, cerebral oxygen and glucose metabolism

1. Big picture

This topic is the physiological basis of stroke, raised intracranial pressure, syncope, hypoxic-ischemic encephalopathy, brain edema, perfusion CT, SPECT, PET, and acute stroke treatment decisions.

For the exam, the key idea is simple:

The brain has very high metabolic demand, almost no energy reserve, and depends continuously on cerebral blood flow for oxygen and glucose.

So whenever cerebral blood flow falls, the brain first compensates by autoregulation and increased oxygen extraction. If this fails, neuronal function stops first, then irreversible structural damage follows.

The most important exam links are:

• Normal cerebral blood flow (CBF): about 50 ml/100 g/min

• Penumbra: about 10-20 ml/100 g/min

• Ischemic core: usually <10 ml/100 g/min

• Global cerebral ischemia: irreversible injury after about 3-5 minutes

• Most important ischemic cascade mechanism: calcium influx

• Regulation of cerebral circulation: neurogenic regulation, metabolic regulation, and autoregulation

• Cerebral perfusion pressure (CPP): mean arterial pressure minus intracranial pressure