Regulation of intracranial pressure in rat, dog, and man.

Intracranial resistance and compliance were assessed in the cerebrospinal fluid system of rat, dog, and man by means of low-volume, short-duration infusions of artificial CSF into the subarachnoid space. A family of pressure/time response curves was obtained for each species: at low flow rates, steady-state pressure elevations were associated with normal neurological function; at high flow rates, rapid linear pressure elevations were associated with marked neurological dysfunction. From these curves a mathematical model was developed which describes transport and pressure-dependent valvelike characteristics of the CSF outflow resistance. This resistance shows a progressive phylogenetic change in rat, dog, and man which increasingly enhances the species' abilities to vent fluid from the intracranial cavity into the venous circulation. Arachnoid villi appear to be the major structures modulating sustained, nonlethal elevations of intracranial pressure.