Stroke
Medical Author: Benjamin C. Wedro, MD, FAAEM
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
Latest News
As Obesity Increases, So Does Stroke Risk
Jan. 21 (HealthDay News) -- The more overweight you are, the more likely you are to have a stroke, a new study reports.
The study, which followed 13,549 middle-aged Americans for 19 years, looked at stroke risk associated with several measures of obesity, emphasizing body mass index (BMI), a ratio of weight and height, but also such measures as waist circumference.
"We found that the risk of stroke was increased with each measure of obesity," said Dr. Hiroshi Yatsuya, a visiting associate professor of public health at the University of Minnesota and lead author of a report published online Jan. 21 in Stroke.
The degree of risk varied by sex and ethnic group. For example, people in the highest BMI category had a 1.43 to 2.12 times higher risk for stroke, with variations by race and sex. The risk ratios ranged from 1.65 to 3.19 when obesity was measured by waist circumference and from 1.69 to 2.55 when the ratio of waist to hip was used.
The risk was especially high for blacks, the study found. For example, the incidence of stroke was 1.2 per 1,000 person-years for white women and 4.3 per 1,000 person-years for black women. In the highest BMI category, rates ranged from 2.2 for white women to 8.0 for black men.
That higher incidence of stroke for blacks has been found in many previous studies, and it also is seen in Asians, Yatsuya said. The reason is unknown, but "there may be a genetic difference," he said.
Read the rest of As Obesity Increases, So Does Stroke Risk »
What is a stroke?
A stroke, or cerebrovascular accident (CVA), occurs when blood supply to part of the brain is disrupted, causing brain cells to die. When blood flow to the brain is impaired, oxygen and glucose cannot be delivered
to the brain. Blood flow can be compromised by a variety of mechanisms.
Blockage of an artery
- Narrowing of the small arteries within the brain can cause a so-called lacunar stroke, (lacune=empty space). Blockage of a single arteriole can affect a tiny area of brain causing that tissue to
die (infarct).
- Hardening of the arteries (atherosclerosis) leading to the brain. There are four major blood vessels that supply the brain with blood.
The anterior circulation of the brain that controls most motor, activity, sensation, thought, speech, and emotion is supplied by the carotid arteries.
The posterior circulation, which supplies the brainstem and the cerebellum, controlling the automatic parts of brain function and coordination, is supplied by the vertebrobasilar arteries.
If these arteries become narrow as a result of
atherosclerosis, plaque or
cholesterol, debris can break off and float downstream, clogging the blood supply to a part of the brain. As opposed to lacunar strokes, larger parts of the brain can lose blood supply, and this may produce more symptoms than a lacunar stroke.
- Embolism to the brain from the heart. In situations in which blood clots form within the heart, the potential exists for small clots to break off and travel (embolize) to the arteries in the brain and cause a stroke.
Rupture of an artery (hemorrhage)
- Cerebral hemorrhage (bleeding within the brain substance). The most common reason to have bleeding within the brain is uncontrolled high blood pressure. Other situations include
aneurysms that leak or rupture or arteriovenous malformations (AVM) in which there is an abnormal collection of blood vessels that are fragile and can bleed.
What causes a stroke?
Blockage of an artery
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.
As a result of the deprived blood and oxygen, the cells of that part of the brain die. Typically, a clot forms in a small blood vessel within the brain that has been previously narrowed due to a variety of risk factors including:
- high blood pressure (hypertension),
- high cholesterol,
- diabetes, and
- smoking.
Embolic stroke
Another type of stroke may occur 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.
Cerebral hemorrhage
A cerebral hemorrhage occurs when a blood vessel in the brain ruptures and bleeds into the surrounding brain tissue. A cerebral hemorrhage (bleeding in the brain) can cause a stroke by depriving blood and oxygen to parts of the brain. Blood is also very irritating
to the brain and can cause swelling of brain tissue (cerebral edema). Edema and the accumulation of blood from a cerebral hemorrhage increases pressure within the skull and causes further damage by squeezing the brain against the bony skull.
Subarachnoid hemorrhage
In a subarachnoid hemorrhage, blood accumulates in the space beneath the arachnoid membrane that lines the brain. The blood originates from an abnormal blood vessel that leaks or ruptures. Often this is from an aneurysm (an abnormal ballooning out of the wall of the vessel). Subarachnoid hemorrhages usually cause a sudden, severe headache and stiff neck. If not recognized and treated, major neurological consequences, such as coma, and brain death will occur.
Vasculitis
Another rare cause of stroke is vasculitis, a condition in which the blood vessels become inflamed.
Migraine headache
There appears to be a very slight increased occurrence of stroke in people with
migraine headache. The mechanism for migraine or vascular headaches includes narrowing of the brain blood vessels. Some migraine headache episodes can even mimic stroke with loss of function of one side of the body or vision or speech problems. Usually, the symptoms resolve as the headache resolves.
Next: What are the risk factors for stroke? »
Neurology RSS