Raised Intracranial Pressure

CEREBRAL BLOOD FLOW (CBF)/CEREBRAL BLOOD VOLUME (CBV)

Blood flow is dependent on blood pressure and the vascular resistance:

Pressure

Resistance

Inside the skull, intracranial pressure must be taken into account:

Cerebral perfusion pressure (CPP)

_ (i.e. systemic BP - intracranial pressure)

Cerebral vascular resistance (CVR)

Under normal conditions the cerebral blood flow is coupled to the energy requirements of brain tissue. Various regulatory mechanisms acting on the arterioles maintain a cerebral blood flow sufficient to meet the metabolic demands.

FACTORS AFFECTING THE CEREBRAL VASCULATURE Chemoregulation

- Change in extracellular pH or an accumulation of metabolic by-products directly affects the vessel calibre.

- Any change in arteriolar PC02 has a direct effect on cerebral vessels, but only a reduction of P02 to < 50 mmHg has a significant effect.

Autoregulation

- A change in the cerebral perfusion pressure results in a compensatory change in vessel calibre.

Any change in blood vessel diameter results in considerable variation in cerebral blood volume and this, in turn, directly affects intracranial pressure.

Energy requirements differ in different parts of the brain. To meet such needs in the white matter, flow is 20 ml/100 g/min, whereas in the grey matter flow is as high as 100 74 ml/lOOg/min.

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