[Editor's note: This article is from 2007. Some newer treatments and current statistics may not be included. See further information on BrainWeb]
sections include: what causes ischemia?, diagnosis and treatment, recovery from ischemic stroke
Each year in the United States, nearly 750,000 individuals have a stroke. Of those people, 150,000 (90,000 women and 60,000 men) die from the resulting brain injury. Strokes are the country’s third leading cause of death, and the number one cause of persistent disability. The chance that you will have some type of stroke during your lifetime is about one out of seven. All told, there are about 2 million stroke survivors in the United States today. In other parts of the world, strokes are even more common. In China, for instance, 1.5 million people die annually because of strokes.
There are two major kinds of stroke. Four strokes out of five are due to ischemia, meaning that part of the brain stops receiving enough blood. The other 20 percent are caused by bleeding, or hemorrhage, into the brain or the fluid surrounding it; these hemorrhagic strokes are discussed here.
In a brain ischemia, the blood flow to part of your brain is cut off, and the cells in that region do not receive the oxygen and fuel (sugar) they need. The neurons stop functioning and die unless the blood flow is restored quickly. The brain damage caused by deprivation of blood is called ischemic stroke, and the region of damage is called a brain infarct.
Brain ischemia usually develops abruptly, most often in the morning. The symptoms depend on the area of the brain that stops receiving blood. Sometimes a person notices vision loss or problems in one eye, or in the left or right half of the visual field in both eyes. A person may notice weakness or diminished feeling in the face, arm, hand, and leg on one or both sides of the body, or have trouble walking. He or she may suddenly have difficulty with memory (amnesias, dementia), or with speaking, understanding speech, reading, or writing. Some people notice dizziness and double vision. The symptoms can also fluctuate in severity for hours and even days.
These same symptoms can also appear temporarily, lasting a few minutes or hours only, in which case they are called transient ischemic attacks (TIAs). For instance, you might sense a gray shade blocking the vision in your right eye for a couple of minutes, or feel your left hand and arm suddenly becoming numb and weak for an hour. Such problems indicate a temporary halt in blood flow to particular parts of your brain. Some people try to ignore these problems—after all, they go away—but that is unwise. TIAs signal the possibility of a longer loss of blood supply. As troubling as these symptoms are, people who have them are actually lucky. Other people who have strokes lose brain functions with no such warning.
The symptoms of a stroke or TIA demand immediate medical attention. Any possible stroke is an emergency. The sooner a person having a stroke arrives at a hospital, the more likely that treatment will be effective. The more time it takes for a person to seek care, the more damage the brain undergoes. That has given rise to this medical reminder: Time = Brain.
What Causes Ischemia?
Brain ischemia is most often caused by blockage of an artery that brings oxygenated blood to some portion of the brain. The obstruction can occur where arteries pass through the neck or within the skull, with varying results.
Sometimes the clog develops in the artery itself, a process called thrombosis. Most commonly, this starts with plaques forming inside an artery due to atherosclerosis, or a hardening of the arterial walls. These plaques are composed of cholesterol and fibrous and connective tissue. They grow in and under the inner lining of arteries and jut out into the space where blood should flow. Other vascular diseases can also narrow the artery, decreasing blood flow. These conditions include overgrowth of muscle and fibrous tissue in arteries (fibromuscular dysplasia), the tearing of arterial walls, and inflammation (arteritis). Plaques and other abnormalities of arteries’ inner lining also release chemicals that make blood platelets stick together and adhere to irregular crevices in the plaques. Whatever the cause, narrowing of the artery impedes blood flow and causes a clot (thrombus) to form, perhaps completely clogging the artery.
Alternatively, an artery can be blocked by material that originates elsewhere in the cardiovascular system and travels there. This process is called embolism. The material (an embolus) is usually a clot that originates in the heart, the aorta, or other blood vessels and then moves through the circulatory system. Sometimes illnesses like cancer and infections can start the clotting process. Occasionally, abnormalities in a person’s clotting system can lead to a thrombus in an artery that has no major disease. An embolus travels until it gets stuck in, and blocks, the first artery too small for it to pass through.
Doctors customarily divide brain ischemias by location. What we call vertebrobasilar strokes, or posterior circulation strokes, occur when the clog is in the vertebral arteries in the back of the neck, in the basilar artery formed in the head where the two vertebral arteries join, or in their branches. This type of ischemia affects the brain stem, cerebellum, or the very back of the cerebral hemispheres. It can result in loss of memory, dizziness, slurred speech, difficulty swallowing, abnormal gait, and impaired vision on one or both sides. When blood is blocked in the carotid arteries or their branches in what we call the anterior circulation, a person can lose function in the cerebral hemisphere on the side of the blockage. The symptoms produced by such ischemia often include loss of vision in the eye on that side, and weakness, numbness, and loss of vision on the opposite side of the body. When a stroke develops in the left anterior circulation, a person often loses spoken and written language skills because those are centered on the left side of the brain. When the damage is to the right carotid artery system, people have difficulty with visual-spatial skills and with giving and understanding emotional messages.
Both genes and lifestyle can promote the formation of atherosclerotic plaques and lead to degenerative changes in the heart and blood vessels that bring on ischemic stroke. Risk factors for stroke include a strong family history of heart disease and stroke, hypertension (high blood pressure), diabetes, high levels of cholesterol in the blood, cigarette smoking, obesity, a sedentary lifestyle, and high blood homocysteine levels. You can take steps to counteract all those factors but the first.
Diagnosis and Treatment
Physicians diagnose ischemic stroke and brain ischemia based on people’s descriptions of their symptoms, physical and neurological examinations, and the results of blood tests, brain images, and blood vessel tests. If a stroke seems to have occurred, a neurologist should usually direct diagnosis and treatment.
Brain images (computed tomography, or CT, and magnetic resonance imaging, or MRI, scans) can differentiate between the two types of stroke—ischemia and hemorrhage. This is important because the two conditions are treated differently.
Brain imaging technology can also show the regions of the brain damaged by ischemia and yield information about blood flow to those areas. CT and MRI are now sophisticated enough to produce images of a person’s arteries; these techniques are called CT angiography (CTA) and MR angiography (MRA). Sometimes it is necessary to inject a dye into the arteries to obtain clear pictures. Ultrasound checks of the neck and head can also provide important information about arterial blockage and blood flow. Since the heart and aorta are often the source of emboli, doctors use electrocardiograms (ECGs) and echocardiograms of the heart to identify the cause of the brain ischemia. Blood tests can determine whether a person’s system contains too many or too few red blood cells or platelets, and whether the blood is clotting normally.
As noted earlier, fast diagnosis and treatment of strokes are vital to helping a person recover successfully. The sooner the patient comes to the hospital to be examined, the more effective any therapy is likely to be. The treatment of patients with brain ischemia depends very much on what caused the problem. Blocked arteries can sometimes be opened by surgery, by placing balloons or tubes in these blood vessels to push back their walls, or by administering drugs that break up clots, such as recombinant tissue plasminogen activator (rt-PA) and urokinase.
To prevent further brain damage and strokes, doctors often prescribe drugs that change how platelets work (such as aspirin, clopidogrel, and dipyridamole), or anticoagulant drugs (such as heparin and Coumadin), which decrease the formation of red-blood-cell clots. Controlling blood pressure while ensuring an adequate volume of blood within the body is also helpful in minimizing brain damage. Strokes are usually signs of suboptimal cardiovascular health, so doctors and patients must take steps to avoid heart attacks and related problems.
People who have had strokes often lose some physical abilities, such as eating, walking, or using a limb as easily as they once did. Sometimes they must lie in bed for extended periods. These physical disabilities can lead to complications that prolong recovery from the stroke and even endanger a person’s life. Such problems include:
- lung and urinary tract infections
- blood clots in little-used legs, which can travel to the lungs (pulmonary embolism)
- joints rendered stiff or weak by immobility
- loss of bone on the paralyzed side because of lack of exercise
- breathing food or throat contents into the lungs (aspiration)
Therefore, part of therapy after a stroke involves teaching the person and any caregivers ways to prevent those problems, and to recognize and treat them quickly if they do develop.
Some people sustain such damage from strokes that they do not even realize how badly they have been impaired. Others know that they have lost some mental or physical ability—to express themselves as they did before, to walk, to do detailed work—and this can be very frustrating. A person’s outlook for recovery depends mostly on the cause of the brain ischemia and the amount of the damage. Rehabilitation specialists can help people relearn tasks, or learn to do them in a different way, perhaps using different parts of the body. The brain’s plasticity is a great asset in this process. If the damaged area is not too large, the neurons can often create new channels for their electrochemical signals and restore functions a person enjoyed before a stroke.
RECOVERY FROM ISCHEMIC STROKE
Most gains in a person’s ability to function in the first 30 days after a stroke are due to spontaneous
recovery. Further rehabilitation depends on:
■ the extent of the brain injury
■ the patient’s attitude
■ the rehabilitation team’s skill
■ the cooperation of family and friends
The success of rehabilitation therapy often depends on both the location and the extent of damage to the brain, but the determination of the patient can be no less important. Studies have shown that the brain has plasticity: the lifelong ability to adapt to change, overcome injury, and compensate for loss of function in one portion of the brain by working harder in another area. Complete recovery may not be a reasonable expectation, but the goal of rehabilitation therapy is some level of improvement. Improvement in function after stroke can make the difference between hospital stays and home recovery. For a stroke survivor, the goal of rehabilitation is to be as independent and productive as possible, given the limitations resulting from the stroke.
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