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.