What is a stroke?
A stroke or cerebrovascular accident (CVA) occurs when the blood supply to a part of the brain is suddenly interrupted by occlusion (an ischemic stroke) or by hemorrhage (a hemorrhagic stroke). The former, ischemia, is a reduction of blood flow due to occlusion (an obstruction). The latter, hemorrhagic stroke, occurs when a blood vessel in the brain bursts, spilling blood into the spaces surrounding the brain cells or when a cerebral aneurysm ruptures. Stroke is literally a "brain attack",
caused when the vital supply of blood and oxygen is cut off to part of the brain. If a portion of the brain loses its supply of nutrient-rich blood and oxygen, the bodily functions controlled by that part of the brain (vision, speech, walking, etc.) are impaired. Like a heart attack, every minute counts in getting a stroke victim emergency medical treatment so that brain damage and possible future disability will be minimized.
A stroke is a sudden interruption in the blood supply of the brain. Most strokes are caused by an abrupt blockage of arteries leading to the brain (ischemic stroke). Other strokes are caused by bleeding into brain tissue when a blood vessel bursts (hemorrhagic stroke). Because stroke occurs rapidly and requires immediate treatment, stroke is also called a brain attack. When the symptoms of a stroke last only a short time (less than an hour), this is called a transient ischemic attack (TIA) or mini-stroke. Stroke has many consequences. The blockage of an artery in the brain by a clot (thrombosis) is the most common cause of a stroke. The part of the brain that is supplied by the clotted blood vessel is then deprived of blood and oxygen. The cells of that part of the brain die as a result. Typically, a clot forms in a small blood vessel within the brain that has been previously narrowed due to the long-term, damaging effects of high blood pressure (hypertension) or diabetes. The resulting strokes are called lacunar strokes because they look like little lakes. In other situations, usually because of hardening of the arteries (atherosclerosis), a blood clot can obstruct a larger vessel going to the brain, such as the carotid artery in the neck.
Another type of stroke occurs when a blood clot or a piece of atherosclerotic plaque (cholesterol and calcium deposits on the wall of the inside of the heart or artery) breaks loose, travels through open arteries, and lodges in an artery of the brain. When this happens, the flow of oxygen-rich blood to the brain is blocked and a stroke occurs. This type of stroke is referred to as an embolic stroke. For example, a blood clot might originally form in the heart chamber as a result of an irregular heart rhythm, such as occurs in atrial fibrillation. Usually, these clots remain attached to the inner lining of the heart, but occasionally they can break off, travel through the blood stream, form a plug (embolism) in a brain artery, and cause a stroke. An embolism can also originate in a large artery (for example, the carotid artery, a major artery in the neck that supplies blood to the brain) and then travel downstream to clog a small artery within the brain.
Risk factors (for atherosclerosis and small vessel disease) are hypertension (high blood pressure), diabetes mellitus, elevated blood lipid levels and cigarette smoking. High blood pressure is the main cause of stroke. Atrial fibrillation and other arrhythmias can lead to clot formation in the heart, which embolise to the brain. Some forms of thrombophilia (increased coagulation tendency) have a predilection for arterial thrombosis and stroke; these include polycythemia vera and the rare paroxysmal nocturnal hemoglobinuria.
Symptoms of stroke develop suddenly. Symptoms of a stroke depend on the area of the brain affected. The most common symptom is weakness or paralysis of one side of the body with partial or complete loss of voluntary movement or sensation in a leg or arm. There can be speech problems and weak face muscles, causing drooling. Numbness or tingling is very common. A stroke involving the base of the brain can affect balance, vision, swallowing, breathing and even unconsciousness. In cases of severe brain damage there may be deep coma, paralysis of one side of the body, and loss of speech, followed by death or permanent neurological disturbances after recovery. If the brain damage sustained has been slight, there is usually complete recovery, but most survivors of stroke require extensive rehabilitation. Hypertension, which is a major cause of intracranial hemorrhage and stroke, can be treated by preventive measures using diet (e.g., increasing nutrients such as antioxidants and folate), drug therapy, and stress reduction techniques. Other preventive measures for people at high risk include daily aspirin to retard clot formation and surgical correction of the narrowed carotid artery. Sometimes surgical removal of the clot is possible on larger vessels, but it is usually pointless after the stroke or when blockage is widespread. The thrombolytic drug tissue plasminogen activator, widely used to treat heart attacks, has been approved for use within three hours of the onset of strokes caused by clots.
The effects of a stroke depend on which part of the brain is injured, and how severely it is injured. Strokes may cause sudden weakness, loss of sensation, or difficulty with speaking, seeing, or walking. Since different parts of the brain control different areas and functions, it is usually the area immediately surrounding the stroke that is affected. Sometimes people with stroke have a headache, but stroke can also be completely painless. It is very important to recognize the warning signs of stroke and to get immediate medical attention if they occur.
Although death rates from stroke have declined over the recent years, it remains the third leading cause of death in the United States. Most stroke symptoms are not associated with pain, causing people to delay medical treatment. Signs and symptoms of stroke can range from a sudden difficulty with speech to sudden numbness or weakness in the face or limbs. Prevention is of primary importance, and proper prevention requiras reduction of risk factors in persons at the highest risk. |
