All organs in the body, particularly the brain, rely on an adequate supply of oxygenated blood. There are some conditions and diseases, however, that result in a loss of blood flow to the brain, starving it from oxygen and glucose. This loss of blood flow is called cerebral ischemia.
The most common cause of cerebral ischemia is a stroke. A stroke is a focal, neurological deficit that occurs when vessels supplying blood to the brain become either blocked or start bleeding, causing either an occlusive stroke or a hemorrhagic stroke. Occlusive strokes occur as a result of a thrombus, or blood clot, in vessels supplying blood to the brain, whereas hemorrhagic strokes are generally the result of ongoing high blood pressure.
Cerebral ischemia causes a reduction of oxygen and glucose delivered to the brain, and, as a result, toxic metabolites, such as lactic acid, are unable to be removed. Once delivery of oxygenated blood to the brain is reduced, a brief loss in consciousness, called syncope, can also occur. A lack of oxygen to the brain as a result of cerebral ischemia is called hypoxia. Hypoxia can permanently destroy neurons by a process called necrosis, which can lead to brain damage. Necrotic cell death happens when a cell membrane is rapidly destroyed and, during autopsy, the cell membrane appears softer in texture.
Two different types of cerebral ischemia can occur because of a stroke: focal cerebral ischemia and global ischemia. An individual suffering focal cerebral ischemia will still have some degree of circulation to parts of the brain; however, a patient with global ischemia will have no blood flow to any area of the brain. Transient ischemic attack (TIA) is the term applied to ischemic symptoms that are focal and last for a short period of time. These attacks can precede strokes, but can also occur independently and are generally the result of a vascular disease, such as atherothrombosis. Recognizing and treating a TIA early is very important, as a patient may be at risk of developing cerebral infarction or stroke in the future.
There are many different medications prescribed to patients suffering TIA's. One such treatment is aspirin, which is effective in preventing embolic and thrombotic strokes. Aspirin works by reducing and preventing platelet aggregation. If patients are unable to tolerate this medication, the platelet aggregate inhibitor clopidogrel, or other similar drugs, are also effective.