Interruption of the blood supply to part of the brain due to a sudden bleed in the brain (cerebral haemorrhage) or embolism or thrombosis. Strokes vary in severity from producing almost no symptoms to proving rapidly fatal. In between are those (often recurring) that leave a wide range of impaired function, depending on the size and location of the event.
Strokes involving the right side of the brain, for example, produce weakness of the left side of the body. Some affect speech. Around 80% of strokes are ischaemic strokes, caused by a blood clot blocking an artery transporting blood to the brain. Transient ischaemic attacks, or ‘mini-strokes’, with effects lasting only briefly (less than 24 hours), require investigation to try to forestall the possibility of a subsequent full-blown stroke.
The disease of the arteries that predisposes to stroke is atherosclerosis. High blood pressure (hypertension) is also a precipitating factor - a worldwide study in 1995 estimated that high blood pressure before middle age gives a tenfold increase in the chance of having a stroke later in life.
Strokes can sometimes be prevented by surgery (as in the case of some aneurysms), or by use of anticoagulant drugs or vitamin E or daily aspirin to minimize the risk of stroke due to blood clots. According to the results of a US trial in 1995, the clot-buster drug tPA, if administered within three hours of a stroke, can cut the number of stroke victims experiencing lasting disability by 50%. The best predictor of strokes among older people may be an echogram (sonogram) of carotid arteries. According to a 1999 medical study, a diet rich in fruit and vegetables can lower the risk of strokes.
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