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The term "stroke" or "paralytic stroke" is commonly used to describe a sudden neurological affliction that is usually related to cerebral blood supply. A "stroke," therefore, can be due to cerebral ischemia, infarction, or hemorrhage, and usually implies permanent neurological deficits.(1) All three of these causes, cerebral ischemia, infarction, or hemorrhage, would be characterized as manifestations of cerebrovascular disease.
Cerebrovascular disease can be further defined as any type of pathophysiologic vascular disease of the brain. This vascular pathology can include any abnormality of the vessel, blood flow, or quality of the blood.(2) Other terms for this abrupt onset neurologic deficit include apoplexy, or cerebrovascular accident (CVA). In the United States, the term stroke is most often used to describe cerebral infarction. It is preferable to use the more precise terms, cerebral ischemia, cerebral infarction, or intracranial hemorrhage. Cerebral ischemia is caused by a reduction in blood flow that lasts for several seconds or a few minutes. If the cessation of flow lasts for more than a few minutes, infarction of brain tissue results.
Ischemia and infarction constitute 85-90 percent of strokes in western countries, with 10-15 percent being caused by intracranial hemorrhages. The morbidity and mortality from cerebrovascular diseases has actually decreased in recent years, due mostly to better recognition and treatment of underlying factors such as hypertension and cardiac diseases that increase the risk of stroke.
General population studies show atherothrombotic infarction is the most common type of stroke, representing almost 65 percent of the reported cases of the 85 percent caused by ischemia. Therefore, the majority of strokes are caused by ischemia and infarction secondary to disease of the large, small, and medium-sized arteries supplying the brain. Cerebral embolism causes stroke about 20 percent of the time. Hemorrhage into the brain tissue (cerebral or intraparenchymal hemorrhage) and subarachnoid hemorrhages account for about 15 percent of all strokes.
Ischemic cerebrovascular disease is divided into two broad categories: thrombotic and embolic. When it occurs in elderly patients, particularly those with manifestations of atherosclerosis, the term atherothrombotic, or atherothromboembolic may be used. Although the precise reason for ischemia may not be determined, the term is used when it seems likely that atherosclerosis-induced thrombosis occurred and the thrombus then lysed, or embolized, distally and fragmented. Thrombotic strokes occur without warning symptoms in 80-90 percent of patients. Between 10 and 20 percent are heralded by one or more transient ischemic attacks. Thrombotic strokes often present with stuttering, fluctuating symptoms that worsen over several minutes or hours. Embolic strokes usually present with a neurologic deficit that is maximum at onset.(3)
Cerebral ischemia is further divided into focal and general, or global, ischemia. Global ischemia refers to a situation where little or no collateral circulation exists and irreversible brain damage occurs in a short period of time. In focal ischemia, however, there is some degree of collateral circulation, which may allow for survival of brain cells and reversal of neuronal damage after periods of ischemia.
Normal cerebral blood flow in humans is about 53ml/100g of brain tissue per minute. Reductions in the cerebral blood flow to the range of 15-18ml/100g/min result in abnormal brain electrical activity. At a flow of 10ml/g/min, alterations in intracellular calcium and extracellular potassium homeostasis occur. Also, free fatty acids are released, and adenosine triphosphate (ATP) is depleted. A severe intracellular acidosis ensues in cells in the ischemic area.(2)
Within 10 seconds after cerebral blood flow ceases, m
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