What does the above graph (Fig. 78.1) depict?

Define cerebral perfusion pressure, and how is it derived?

How is cerebral autoregulation achieved during normal states?

What are the conditions in which this balance of cerebral perfusion is upset?

The image depicts a normal cerebral autoregulation. The brain maintains a constant blood flow to itself despite changes in cerebral perfusion pressure. The ability of the organ to achieve this is called cerebral autoregulation.

Cerebral perfusion pressure (CPP) is defined as the difference between the mean arterial pressure (MAP) and intracranial pressure (ICP) {CPP = MAP − ICP}. If the central venous pressure (CVP) is greater than the ICP, then CPP = MAP − CVP. The cerebral flow is then modulated by the greater of the two pressures—CVP or ICP. The classic understanding is that autoregulation is maintained between MAPs of 50–150 mmHg [1]. As the ICP is generally in the range of 5–12 mmHg, MAP then becomes the main determinant of the cerebral blood flow. This can be affected by various factors such as sympathetic neural activity, the renin-angiotensin system, and changes in the arterial carbon dioxide partial pressure.