- There is a linear correlation between cerebral blood flow and CMR
- Known as ‘flow–metabolism coupling’
- Exact mechanisms are unclear but are likely due to accumulation of vasodilatory metabolic by-products (e.g. CO2, H+, K+ and adenosine
- Occurs on a local level to match CBF to metabolically active areas of the brain:
- Demonstrated by the higher blood flow to the more metabolically active grey matter (70ml/100g/min) than white matter (20ml/100g/min)
- Also occurs on total brain level with CBF matched to total brain metabolism:
- Increase in overall CMR (during pyrexia or seizures) results in increased CBF
- Decreased CMR (during general anaesthesia or hypothermia) results in decreased CBF
