ollateral circulation, genetic make-up, and extent of brain area involved (Wright, 1998). When ischemia occurs, the affected brain tissue undergoes a series of complex neurochemical changes known as the "ischemic cascade," which, if uninterrupted, ends in infarction and neurologic disability. If adequate blood flow is restored within three hours after the stroke, the ischemic cascade can be interrupted, and neurologic function may return. During the first six to 12 hours after occlusion, the ischemic area becomes discolored and soft. Between 48 and 72 hours after a stroke, neuronal cells swell and myelin sheaths, axons, oligodendrites, and astrocytes disintegrate. The neural damage after a stroke is progressive, falling into two patterns: the ischemic core and ischemic penumbra. When blood flow is obstructed, a dense ischemic core of injury is formed with irreversible damage to this region occurring rapidly (minutes to an hour). This necrotic area is surrounded by tissue that receives a minimal amount of blood
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