EFFECT OF BRAIN DISTENSION ON CEREBRAL CIRCULATION

Abstract

It is contended that distension of the brain secondary to regressive changes—e.g., brain atrophy— is common in the higher age-groups. The distension may be, and often is, the cause of diminished blood-flow in the ageing brain. This hypothesis is supported by recent investigations, initiated by the discovery of a pathological condition termed normal-pressure hydrocephalus. With this type of hydrocephalus the cerebrospinal-fluid (C.S.F.) pressure is normal or not pathologically increased, but the cerebral blood-flow is reduced. This reduction in flow is correlated with the degree of ventricular dilatation. The condition of those affected improves after drainage of the C.S.F. by shunt procedures which cause a concomitant increase in cerebral blood-flow. The brain can be said to form an elastic container around the ventricular system, and the tensile strength of this container is diminished by atrophic processes due to ageing. These processes allow the ventricular system to expand even without an increase in the intraventricular pressure. Pneumoencephalographic investigations confirm that such distension is the rule rather than the exception at higher ages. This distension reduces the cerebral blood-flow by compressing the cerebral vessels. Probably there is a complex interaction between, on the one hand, morphological changes due to ageing in the brain tissue, in the C.S.F. valves, and in the cerebral blood-vessels, and, on the other hand, physiological disturbances in the cerebral blood circulation and in the C.S.F. circulation.