HYPERTENSION AND THE BRAIN

Neurogenic mechanisms are important in the maintenance of most forms of hypertension, yet the brain is highly vulnerable to the deleterious effects of elevated blood pressure. Hypertensive encephalopathy results from a sudden, sustained rise in blood pressure sufficient to exceed the upper limit of cerebral blood flow autoregulation. The cerebral circulation adapts to chronic less severe hypertension but at the expense of changes that predispose to stroke due to arterial occlusion or rupture. Stroke is a generic term for a clinical syndrome that includes focal infarction or hemorrhage in the brain, or subarachnoid hemorrhage. Atherothromboembolism and thrombotic occlusion of lipohyalinotic small-diameter end arteries are the principal causes of cerebral infarction. Microaneurysm rupture is the usual cause of hypertension-associated intracerebral hemorrhage. Rupture of aneurysms on the circle of Willis is the most common cause of nontraumatic subarachnoid hemorrhage. Stroke is a major cause of morbidity and mortality, particularly among persons aged 65 years or older. Treatment of diastolic hypertension reduces the incidence of stroke by about 40%. Treatment of isolated systolic hypertension in persons aged 60 years and older reduces the incidence of stroke by more than one third. Blood pressure management in the setting of acute stroke and the role of antihypertensive therapy in the prevention of multi-infarct dementia require further study.