Microscopic Pollution May Trigger Heart Attacks And Strokes By Spurring
Blood Clots
ScienceDaily (Sep. 26, 2007) — It was a murder
mystery playing out in major cities across the country and perplexing
scientists. Thousands of people were dying from strokes and heart attacks
within 24 hours of a spike in microscopic pollution -- tiny particles that spew
from the exhaust of diesel trucks, buses and coal-burning factories.
But scientists didn't have a smoking gun. They couldn't figure out why the
pollution was triggering the deaths. All they had to go on was a vague lead:
the particles -- too small to be filtered by the nose or mouth -- caused
inflammation of the lungs. But what was the link between particles trapped in
the lungs to the strokes and heart attacks?
New research from the gumshoes at Northwestern
University's Feinberg
School of Medicine has solved a key piece of the mystery. The study identifies
how these tiny pieces of soot -- called particulate matter air pollution --
kill people at risk and tells how they can protect themselves from these
pollution-related strokes and heart attacks.
Northwestern researchers have discovered that this microscopic air pollution
-- smaller than 10 microns or less than one-tenth of the diameter of a human
hair -- spurs hyperclotting of the blood. The study found that lungs inflamed
by the pollution secrete a substance, interleukin-6, which causes an increased
tendency for blood to coagulate or clot. This raises the risk of a fatal heart
attack or stroke in people with cardiovascular disease such as coronary artery
disease, congestive heart failure or a history of stroke.
Previous epidemiological research has linked the pollution to cardiovascular
death and disease, but this is the first study to show how it actually happens
in an animal model.
"This is a critical missing piece of the puzzle that has eluded
scientists for decades," said Gokhan Mutlu, M.D., lead author of the study
and assistant professor of pulmonary and critical care medicine at the Feinberg School,
and a physician at Northwestern
Memorial Hospital.
"Now we know how the inflammation in the lungs caused by air pollutants
leads to death from cardiovascular disease."
The doctors also warned that heart attacks and strokes occur at relatively
low levels of particulate matter pollution. "We haven't found a safe level
yet," Mutlu said. He hopes the study helps encourages the EPA and local
regulators to reduce the limits on particulate matter levels.
The risk of dying from a heart attack or ischemic stroke jumps a whopping 30
percent with each additional 10 micrograms of pollution. medicine, and David
Green, M.D., professor of hematology and oncology, both at the Feinberg School
and physicians at Northwestern
Memorial Hospital.
The paper will appear on-line Sept. 20 in the Journal of Clinical
Investigation and will be published in the print issue October 1.
In the study, researchers used particles of pollution collected by the
United States Environmental Protection Agency, mixed them into a saline
solution and injected the pollution cocktail into the lungs of mice. The blood
of the mice exposed to the pollution clotted faster than mice not exposed.
Researchers observed a 15-fold increase in interleukin-6 24 hours after the
mice were exposed to the pollution.
In people, interleukin-6 also raises the levels of a substance called CRP,
which is correlated with death from cardiovascular disease.
Particulate matter pollution is highest near expressways or truck routes.
It's hard for commuters to escape. People are exposed to the pollution inside a
car (even with the windows rolled up), a train or walking outdoors, Mutlu said.
The only safe location with lower levels is indoors.
People with previous blockages in the coronary or carotid arteries are at
the highest risk. "It's important to get screened to see if you have one
of these conditions. If so, when there are high levels of particulate matter,
you should try to stay indoors and limit your exposure to the outside
air," Budinger said.
Exercising hikes the risk because it floods the lungs with more polluted
air. "If you're sitting down, the amount of air you get into your lungs is
about five to six liters per minute, but if you're running the amount is 20 to
25 liters," Mutlu noted. "If you're close to an expressway, you're
actually breathing more particulate matter into your lungs."
The doctors also warned that heart attacks and strokes occur at relatively
low levels of particulate matter pollution. "We haven't found a safe level
yet," Mutlu said. He hopes the study helps encourages the EPA and local
regulators to reduce the limits on particulate matter levels.
The American Lung
Association State
of the Air: 2007 report said the most "ominous trend" in air
pollution is the increase in particle pollution, particularly in the eastern United States.
Among the metropolitan areas, Los
Angeles has the most year-round particle pollution. Chicago ranks 11; New York,
17 and Washington D.C., 20. All received an "F" or
failing grade for their pollution , which was in excess of the EPA annual
average limit of 15 micrograms per cubic meter.
The risk of dying from a heart attack or ischemic
stroke jumps a whopping 30 percent with each additional 10 micrograms of
pollution