Assessment of critical closing pressure in the cerebral circulation as a measure of cerebrovascular tone

Critical closing pressure (CCP) calculated from the blood how velocity (FV) and arterial blood pressure (ABP) waveforms has been previously reported t o be useful in the assessment of the dynamics of cerebral circulation. We i nvestigated the relationship between CCP and intracranial pressure (ICP) an d cerebrovascular tone in a model of intracranial hypertension in 22 anaest hetised New Zealand White rabbits during manipulations of arterial CO2, ABP and vasodilatation caused by hypoxia. Recordings were made of FV in the ba silar artery, ABP and ICP during subarachnoid infusion of saline. During in fusion ICP and CCP were significantly correlated (R = 0.68; p < 0.001), but the magnitude of increase in ICP and CCP during infusion were not correlat ed to each other. Linear regression between the difference: CCP-ICP (repres enting a factor due to vasogenic tone) and cerebral perfusion pressure (CPP = ABP-ICP) was highly significant (R = -0.87; p < 0.01). Generally, CCP de creased significantly (p < 0.05) with hypercarbia, arterial hypotension and after and post-hypoxia and the difference: CCP-ICP decreased consistently after each vasodilatatory manoeuvre studied. Our data confirmed the linear relationship between CCP and ICP, and between the difference: CCP-ICP and cerebrovascular tone. However, because the mag nitude of increase in ICP was not con-elated to magnitude of change.