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E-M:/ Particle air pollution increases ischemic strokes -- Detroit included in study


American Heart Assn News Release
4 p.m. EDT, Thursday
Oct. 27, 2005
American Heart Association rapid access journal report:
Air pollution linked to ischemic strokes

DALLAS, Oct. 28 ? Already a factor in heart attacks, air pollution also increases the risk for ischemic strokes ? those caused by a blood clot ? according to a study in Stroke: Journal of the American Heart Association.

Hemorrhagic strokes, which occur when a blood vessel ruptures, were not affected by the level of pollution.

Compared to days with relatively low air pollution levels, the risk of ischemic stroke ? the most common type of stroke ? was 1 percent higher on days with relatively higher air pollution, said Gregory Wellenius, Sc.D., postdoctoral fellow in cardiology at Beth Israel Deaconess Medical Center in Boston.

 ?It appears that air pollution has only a small effect on acute ischemic events of either the heart or brain, but everybody in those cities is exposed.  So, while the relative risk may be small, the absolute risk in terms of excess number of strokes can be quite high, especially when you realize that someone in the United States has a stroke every 45 seconds,? Wellenius said.

According to American Stroke Association statistics, 700,000 Americans suffer strokes every year.

Previous studies have shown that exposure to air pollution increases the risk of heart attack, hospitalization for heart failure, and the triggering of implantable cardioverter-defibrillators (electronic devices that shock the heart to end dangerous heartbeat disturbances).
Studies also have suggested that air pollution might increase the risk for stroke, but most have not distinguished between ischemic and hemorrhagic strokes.

      Wellenius and his co-authors evaluated the association between daily levels of particulate matter smaller than 10 micrometer in diameter (PM10) and hospital admission for ischemic and hemorrhagic stroke among Medicare recipients in nine U.S. cities: Birmingham, Ala., Chicago, Cleveland, New Haven, Conn., Detroit, Minneapolis, Pittsburgh, Salt Lake City and Seattle.

The researchers used standard measurements of PM10 concentration, which includes particles from car and truck exhaust, power plants, refineries and other substances that make up air pollution.  Particulate matter measurements provided by the U.S. Environmental Protection Agency covered more than 37,000 days in the nine cities.  Daily and hourly measurements were also obtained for the pollutants carbon monoxide, nitrogen dioxide and sulfur dioxide.

Medicare data for the nine cities revealed 155,503 hospital admissions for ischemic stroke.  Those patients were an average age of 79, 75 percent were white and 61 percent were female.  The data found 19,314 admissions for hemorrhagic stroke.  Hemorrhagic stroke patients were on average 78 years old, 78 percent white and 59 percent female.

After separating the patients into quartiles according to particulate matter readings, Wellenius found that an increase in pollution concentration from the lowest to the highest quartile was associated with a 1.03 percent rise in risk for hospital admissions due to ischemic stroke on that day.  Similar associations were seen for carbon monoxide, nitrogen dioxide and sulfur dioxide.

In contrast, the rate of hemorrhagic stroke did not rise with increases in quartiles of air pollution levels.  The null findings for hemorrhagic stroke may be due to the small number of hospital admissions for hemorrhagic stroke and lack of statistical power.

This study supports earlier findings that link air pollution to diseases of the heart and lungs, and suggests that ambient particles may also trigger other cardiovascular events such as stroke.

?Taken together with previous work, these results support the idea that reducing exposure to particulate matter may reduce the risk of strokes and heart attacks.?

The researchers theorize that air pollution may increase ischemic stroke risk by promoting atherosclerotic plaque disruption and blood clot formation.  However, they said more studies are needed to better understand the mechanisms related to the increased stroke risk.

 ?We need to replicate this study in other populations and do more studies to see which components of air pollution are most toxic and whether there are individuals within the population that are more susceptible than others to the effects of air pollution,? Wellenius said.
Co-authors are Joel Schwartz, Ph.D. and Murray Mittleman, M.D., Dr.PH.

The study was funded by the National Institutes of Health and the U.S. Environmental Protection Agency.


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