Disturbance of cerebral circulation during intracranial hypertension is not only caused by vasoparalytic effect of the cerbral vessel, but also caused by alteration of the perfusion pressure. The perfusion pressure, which is the difference between mean arterial pressure and cerebrospinal fluid pressure (Miller), does not always indicate real perfusion pressure during intracranial hypertension. Appearance of intercompartment pressure gradient during intracranial hypertension might be important to control perfusion pressure as reported by Symon et al. In the mechanism of alteration of cerebral circulation during intracranial hypertension, the change of the real perfusion perssure, vasopressor response and vasoparalysis have to be observed.
In 40 mongrel dogs under pentobarbital anesthesia with artificial respiration (PaCO2 35-38 mmHg), pressures at the epidural space, the cisterna magna, the sagittal sinus, the femoral artery, the cerebral pial artery, the vein and cerebral tissue fluid were continuously recorded during intracranial hypertension induced by incremental inflation of the extradural balloon placed at the right frontal region or at the posterior fossa.
The perfusion pressure was analysed by means of two factors: One is upstream perfusion pressure (mean arterial pressure —pial arterial pressure) and the other is downstream perfusion pressure (pial arterial pressure — pial venous pressure). Each perfusion pressure was divided by mean arterial pressure as indicated by the formula in Fig. 2.
