Contribution of brain distortion and displacement to CSF dynamics in experimental brain compression.

The present study was designed to determine the contribution of brain distortion and displacement to changes in cerebrospinal fluid (CSF) dynamics [pressure-volume index (PVI), compliance (C), and outflow resistance (Ro)] during progressive brain compression and the effect of compression on brain mechanical properties. In 10 dogs measurements were made of CSF dynamics, brain elastic behavior, cerebral perfusion pressure, local cerebral blood flow, and suprainfratentorial intracranial pressure (ICP) during the incremental expansion of a supratentorial extradural balloon. PVI appeared more as a measure of the compressibility of the cerebral vascular compartment than of intracranial bulk compliance. Reciprocal changes in CSF dynamics behaved as expected when the balloon expanded predominantly supratentorially causing a moderate increase in ICP. A significant increase in ICP, however, caused a rise in PVI and a decrease in compliance. Under these conditions PVI alone could not differentiate between a falling cerebral perfusion pressure and an increasing suprainfratentorial ICP gradient. In contrast, the compliance decreased with balloon expansion while the outflow resistance showed an inverse correlation with compliance and a linear correlation with baseline ICP; Go, an elastic response parameter, consistently decreased, implying that C, Ro, and Go can be used as a trend of intracranial compensatory reserve during intracranial mass expansion.