The response of brain to transient elevations in intraventricular pressure.

A mathematical theory has been developed to evaluate the change in size of the cerebral ventricles in response to a square-wave pressure pulse within the ventricles. Specifically, the theory utilizes a lumped compartment viscoelastic spherical shell model of the brain and takes into account available creep compliance data. The pressure change in the cortical subarachnoid space plays a critical role in determining the net displacement of the brain. The rise in cortical subarachnoid pressure is governed by a rate constant gamma which is nearly proportional to the absorption coefficient when absorption is rate-limiting, inversely proportional to the compliance of the spinal subarachnoid space, and also depends upon the resistance to flow through CSF pathways. A rapid rise in pressure within the cortical subarachnoid space results in an inward displacement of the ventricles immediately after the ventricular pressure pulse has ceased. Thereafter, the ventricles return toward their initial size as the pressure in the cortical subarachnoid space decays. A slow rise, on the other hand, favors permanent ventricular enlargement. Decreased absorption of CSF, long duration pulses, and bulk flow of CSF into brain, which are observed in hydrocephalus, all favor the development of ventricular enlargement.