Causes of Primary Disturbance of the Cerebral Circulation
There may be several different causes of disturbance of the cerebral circulation. In conformity with the general plan of this book, in this chapter we shall examine only those disorders of blood flow in the brain which are produced by primary disturbances of the normal functional behavior of the vascular mechanisms of the brain, and we shall not consider circulatory disturbances of the type that are caused by sclerotic changes in the cerebral vessels or by their thrombosis and embolism. In general, functional disturbances of the cerebral circulation can depend, on the one hand, on extrinsic causes: significant changes in the level of the systemic arterial and venous pressures and, consequently, changes in the inflow of blood into the brain or its outflow from the skull. On the other hand, they can be due to intrinsic causes: a local increase of resistance in the vessels of the brain itself.
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