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Stroke

blood brain vessel clot

A stroke, also called a cerebral vascular accident or CVA, is a sudden, often crippling disturbance in blood circulation in the brain. Interruption in blood circulation may be the result of a burst artery or of an artery that has become closed off because a blood clot has lodged in it. Blood circulation to the area of the brain served by that artery stops at the point of disturbance, and the brain tissue beyond that is damaged or dies.

Stroke is the third leading cause of death in the United States. Heart attack is the leading cause of death, and all forms of cancer are second. Approximately 500,000 strokes, new and recurrent, are reported each year. Of these, about 150,000 will be fatal. Today approximately three million Americans who have had a stroke are alive.

The death rate from stroke has been steadily declining since the early 1970s. A great part of this success has been the efforts of various agencies to make physicians and the general population aware of the danger of high blood pressure. The importance of regular blood pressure checks has begun to infiltrate the general public's knowledge. High blood pressure, or hypertension, is the most important risk factor for stroke.

The brain requires a constant and steady infusion of blood to carry out its functions. Blood delivers the oxygen and nutrients needed by the brain cells, so the circulation to the brain is copious. The carotid arteries on each side of the throat and the vertebral arteries in the back of the neck carry blood to the brain. As the arteries enter the brain they begin to divide into smaller and smaller vessels until they reach the microscopic size of capillaries. The venous system to drain blood from the brain is equally large.

A burst blood vessel, which may occur in a weak area in the artery, or a blood vessel that becomes plugged by a floating blood clot no longer supplies blood to the brain tissue beyond the point of the occurrence. The effect of the interruption in circulation to the brain depends upon the area of the brain that is involved. Interruption of a small blood vessel may result in a speech impediment or difficulty in hearing or an unsteady gait. If a larger blood vessel is involved the result may be the total paralysis of one side of the body. Damage to the right hemisphere of the brain will result in injury to the left side of the body, and vice versa. The onset of the stroke A hemorrhagic stroke (left) compared to a thrombotic stroke (right). Illustration by Hans & Cassidy. Courtesy of Gale Group. may be so sudden and severe that the patient is literally struck down in his tracks. Some patients have early warnings that a stroke may be developing, however.

These people have what is called transient ischemic attacks, or TIAs. These usually result when a cerebral artery is closing because of the build-up of fatty deposits inside the vessel, a condition called atherosclerosis. Slight disturbances in circulation occur at intervals in such a case and the patient will experience momentary symptoms such as unexplained dizziness, blurring of vision, loss of hearing, or other event. It is important in this case to consult a physician so that proper testing can be carried out to determine the cause of the TIAs and steps taken to prevent development of a full stroke.

A stroke that results from a burst blood vessel is called a hemorrhagic stroke. In addition to the damage to brain tissue caused by lack of blood, damage may be brought about by the blood clot formed from the bleeding. The doctor may need to surgically remove the clot to relieve pressure on the brain.

A stroke caused by a clot sealing a blood vessel is called a thrombotic stroke, a derivation of the technical name for a clot, a thrombus. The clot can be formed elsewhere in the body and be carried in the circulating blood until it reaches a vessel too small for it to pass through. At that point it will lodge and dam up the flow of blood, inflicting damage on the tissue beyond the blockage. A thrombotic stroke, if attended quickly, sometimes can be minimized in terms of damage.

People who are known to form blood clots in their circulatory system can be given medications to prevent it. Also, current therapy includes medications that can be given to dissolve clots (a process called thrombolysis) and remove the barrier to blood flow. Some brain function may be preserved in this way that would otherwise be lost if the clot is allowed to remain in place.

Not all vascular events bring on a stroke. Pathologists often find areas in the brain in which a small blood vessel has ruptured but the patient was not reported to have suffered a stroke. Blood vessels that form what is called collateral circulation often make up for the blood circulation lost by a plugged or ruptured vessel. Collateral circulation is carried by other vessels that help to supply blood to a given area of the brain.

Strokes can be prevented by effective treatment of high blood pressure and by taking an aspirin tablet every day, for those who can tolerate such medication. The aspirin helps to prevent clot formation and a number of clinical trials have shown it to be effective in stroke reduction.

Recovery from a stroke varies from one person to the next. Swift treatment followed by effective physical therapy may restore nearly full function of an affected area of the body. Some individuals have experienced severe enough damage that their recovery is minimal and they may be confined to a wheelchair or bed for the remainder of their lives.

Because stroke is a major cause of disability and death, much research effort is being put into this topic. Research is looking at a variety of ways to improve the odds of stroke patients, investigating substances which could be "neuroprotective," by protecting the cells from certain events that occur after stroke, and result in increasing damage to brain tissue; vasodilators (medications that work to increase the diameter of blood vessels, thereby allowing a greater flow of blood to areas served by those vessels), which hold the potential to increase blood flow and therefore oxygen delivery to areas of the brain threatened by or injured by stroke; genetic engineering which holds the future hope of allowing genes to be inserted in the brain, to provoke brain cells into producing chemicals which could be either neuroprotective or perhaps reparative to areas damaged by stroke; animal hibernation, to increase understanding of how a hibernating animal can have decreased blood flow to the brain without brain damage; and specialized magnets to ascertain whether application of a magnetic field to areas of the brain damaged by stroke could potentially help stroke victims recapture functioning to those areas.

See also Thrombosis.

Resources

Periodicals

Aldhous, P. "A Hearty Endorsement for Aspirin." Science 263 (January 7, 1994):24.

Other

National Heart, Lung, and Blood Institute. Report of the Joint

National Committee on Detection, Evaluation, and Treatment of High Blood Pressure Bethesda, MD: 1993.


Larry Blaser

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cerebral

—Refers to the brain. Cerebral vascular is reference to the blood supply to the brain.

Death rate

—The number of deaths from a given cause per specified number of people. The death rate from a disease may be given as 30 per 10,000 population.

Pathologist

—A physician who studies the disease process. He/she learns by conducting autopsies on people who have died.

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