Clinical Neuroscience (Illustrated Colour Text) by Paul Johns

Author:Paul Johns [Johns, Paul]
Language: eng
Format: epub, mobi, pdf
ISBN: 9781455742127
Publisher: Elsevier Health Sciences UK
Published: 2014-04-02T00:00:00+00:00

Brain blood flow and ICP

The main factors determining cerebral blood flow (CBF) are illustrated in Figure 9.13. Blood flow to the brain is proportional to the cerebral perfusion pressure (CPP) and inversely proportional to the cerebral vascular resistance (CVR). The cerebral perfusion pressure can be thought of as the ‘driving force’ for cerebral blood flow.

Fig. 9.13 The relationship between cerebral blood flow and intracranial pressure.

NB: The upper and lower expressions are the same, but the lower part of the figure shows the main determinants of the cerebral perfusion pressure (coloured purple).

Under normal circumstances perfusion pressure is mainly determined by the mean arterial blood pressure (MABP) which is essentially unopposed when the intracranial pressure is normal (0–10 mmHg). If the ICP rises significantly, the mean arterial blood pressure is gradually offset and it becomes increasingly difficult to drive blood into the cranium. In other words, the net cerebral perfusion pressure drops as the ICP increases (assuming constant arterial pressure). If the intracranial pressure were to equal the mean arterial blood pressure, then the net cerebral perfusion pressure would be zero (and brain blood flow would cease). Raised intracranial pressure thus compromises cerebral perfusion.

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