Feature Article
The type of stroke that results when a blood clot travels
to the brain -- called an ischemic stroke -- is more likely
to occur on days when the air contains a larger
concentration of particulate matter, according to a study
published online in Stroke: Journal of the American Heart
Association.
Researchers at Beth Israel Deaconess Medical Center (BIDMC)
and the Harvard School of Public Health (HSPH) examined air
quality on a total of 37,000 days in nine cities. Risk of
hospitalization for ischemic stroke was 1 percent higher on
days with relatively high levels of air pollution, compared
with low-air pollution days, reports lead author Gregory
Wellenius, ScD, postdoctoral fellow in cardiology at BIDMC.
Third Cause of Death in US
"Although these effects sound relatively small," says
Wellenius, "given the large number of people exposed to air
pollution and the large number of people at risk for stroke
... the actual number of strokes could be significant."
Stroke is the third leading cause of death in the US,
affecting more than 700,000 individuals each year.
A "consistent increased risk" for cardiac health problems
associated with exposure to ambient air particles was
established in earlier research by Wellenius and coauthors
Murray Mittleman, MD, DrPH, of BIDMC's Cardiovascular
Epidemiology Research Unit and Joel Schwartz, PhD, of HSPH.
"Air pollution has been shown to trigger heart attacks and
to aggravate the conditions of patients with congestive
heart failure," says Mittleman, who is also an associate
professor of medicine at Harvard Medical School.
"These new findings, demonstrating that incidence of
clot-based strokes also increase, [are] in keeping with our
earlier data showing a relationship between air pollution
and heart and lung disorders," he notes.
The researchers also looked at the incidence of hemorrhagic
stroke, which is caused by bleeding in the brain, during
the same "high pollution" days, notes Wellenius, but found
no association between the two.
Reducing Exposure May Lower Risk
The air pollution in question -- particulate matter smaller
than 10 micrometers in diameter -- includes particles from
car and truck exhaust, power plants and refineries. The
measurements were provided by the US Environmental
Protection Agency from nine US cities: Birmingham, Ala.,
Chicago, New Haven, Conn., Cleveland, Detroit, Minneapolis,
Pittsburgh, Salt Lake City and Seattle.
The authors analyzed hospital admissions among a group of
Medicare patients with an average age of 79. Seventy-five
percent of the patients were white, and 61 percent were
female. Their findings showed that during the course of
their study, there were 155,503 hospital admissions for
ischemic stroke.
The final analysis demonstrated a 1.03 percent rise in
ischemic stroke on the days with the highest pollution
measures.
"We don't know exactly what mechanisms are involved that
trigger these cardiac events," says Wellenius. "However, we
do know that particulates in the air promote inflammation,
which is a significant risk factor for cardiac events; that
exposure to particulates can lead to changes in heart rate
and blood pressure; and that pollution can cause changes in
coaguable states (related to blood clotting abilities)."
The authors say that future research will focus on finding
out which pollutants are most toxic, as well as which
patients are at greatest risk for health problems stemming
from air pollution.
"Taken together with previous work, these latest results
support the idea that reducing exposure to particulate
matter may reduce the risk of strokes and heart attacks,"
they conclude.
About this: - Rita Jenkins is a health journalist for Daily News Central,
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