Besides determination by pressure gradients and vascular resistance, cerebral blood flow is tightly regulated by the arterial partial pressures of CO2 & oxygen. The association between low intracranial compliance and linear obstruction of arterial blood vessels due to an increase in ICP is obvious. In healthy blood vessels, the reactive lumen narrowing in physiological blood pressure ranges occurs automatically in such a way that the flow (and thus indirectly perfusion) is kept constant (Bayliss effect). Passive pressure dilation only occurs when blood pressure values are very high. The normal blood flow requirement of brain parenchyma (gray and white s.) is >50ml/min/100g with an oxygen requirement of 3-3.5ml/min/100g (adults).
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