Effects of hypercapnia and arterial hypotension and hypertension on cerebrospinal fluid pulse pressure and intracranial volume-pressure relationships.

In twelve anaesthetised, ventilated dogs the effects of hypercapnia and pharmacologically induced arterial hypotension and hypertension on the interrelation between volume-pressure response (VPR) and cerebro-spinal fluid (CSF) pulse pressure were studied during continuous inflation of a supratentorial extradural balloon. Hypercapnia did not significantly affect the intracranial volume-pressure relationships, but did cause a significant increase in gradient of the relationship between CSF pulse pressure and intracranial pressure (ICP). Alteration of the arterial blood pressure showed opposite effects on VPR and CSF pulse pressure. A decrease in VPR and an increase in pulse pressure were observed during arterial hypotension; the reverse was found during arterial hypertension. The discrepancy between the effects on VPR and CSF pulse pressure of the variables under study was explained by changes in the transient increase in cerebral blood volume per cardiac cycle. On the basis of the results of this study it will be possible, during clinical ICP monitoring, to interpret changes in the CSF pulse pressure to ICP ratio in terms of changes in intracranial volume-pressure relationships.