Fig. 1

Hypothetical shape of cerebrospinal pressure-volume curve. For small increases in volumes (left part of the graph), pressure responds slowly and proportionally. This is a zone of good compensatory reserve: changes in volume produce low-pressure response. After the first breakpoint, ICP responds exponentially to a volume increase. This is an area of compromised compensatory reserve. Above a certain critical threshold of ICP (sources say that this threshold may vary between patients from 25 to 55 mmHg) the arterial bed starts to collapse and the curve tends to flatten, indicating exaustion of compensatory reserve along with decreasing CBF. RAP: correlation between amplitude and mean value of ICP (see text for details)