Intracranial physiology and biomechanics. Clinical data on pressure-volume relationships and their interpretation.

The intracranial pressure-volume (PV) relationship was examined postoperatively after removal of brain tumors in two groups of patients (13 in all). Changes of ventricular fluid pressure were analyzed by a method involving fluid injection into the lateral ventricle. A technique has been developed which provides quantitative data on the PV relationship with minimal error. The results confirm the exponential nature of the PV relationships. Various parameters characterizing the intracranial volume compliance, the cerebrospinal fluid pressure, and their interrelationship were investigated. It was found that 1) intracranial PV dependence is accurately defined by three parameters; 2) in patients who are not critically ill delta P/ delta V at P = P mean does not vary statistically, and may be used as one of the important parameters to determine the regulation of the intracranial PV relationships. Examples are presented of the use of the data from the PV test for the control o the intracranial PV relationship. Examples are also given of the computation of volume redistribution in the cranium, both spontaneous and evoked by clinical tests. Analysis of the results allows the conclusion that the intracranial volume compliance concerned is an active compliance, which is controlled by the systems maintaining brain function.