Hydraulic regulation of brain parenchymal volume

Abstract

A mechanism for the hydraulic regulation of brain parenchymal volume is hypothesized. Ventricular fluid pressure is transmitted to parenchymal capillaries and affects the pressure difference across the capillary wall, thereby influencing the rate of movement of fluid from the capillary lumen to interstitial fluid. The tendency for brain parenchyma to expand results from the resistance encountered by interstitial fluid as it slowly passes through the complex interstices of extracellular space. The tendency for the brain parenchyma to become smaller results, not from compression of tissue by ventricular fluid, but from an inherent elasticity of brain tissue. The parenchymal volume is stable only when the opposing tendencies are balanced. The critical site of action for the hydraulic control of parenchymal volume is the capillary wall, and the fundamental relationship governing this can be expressed mathematically.