I. INTRODUCTION

Due to its very high metabolic demands, the brain depends on a constant supply of glucose and oxygen from the circulation, and on the removal of metabolic waste,, primarily in the form of carbon dioxide. Homeostatic mechanisms provide for the maintenance of adequate cerebral blood flow in the event of systemic changes in perfusion pressure, although pathological changes in the vasculature may impair these mechanisms. Disorders resulting from impairment in brain circulation are the greatest single cause of neurological disability in the adult population. "Strokes", which include ischemic infarction and intracerebral hemorrhage, are the most common of the cerebrovascular lesions. Cerebrovascular disease is less prevalent in children, since atherosclerosis, hypertension and diabetes mellitus, major determinants of such disease in adults, are rare in children.
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