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Great Lakes Article:

Study connects smog to illness




Canadian scientists have demonstrated, for the first time, that inhaling smog can have an immediate effect on the hearts of healthy people.

And in those who already have cardiovascular disease, high levels of air pollution -- such as occur during rush hour in big cities on a hot day -- can trigger a heart attack.

The research is published in today's edition of Circulation, the journal of the American Heart Association.

There is a wealth of data linking air pollution to lung and heart problems, but researchers at the University of Toronto and Environment Canada have finally shown why they are linked.

Dr. Frances Silverman, a respiratory physiologist at the Gage Occupational and Environmental Health Unit at the U of T, found that inhaling smog sets off a chemical chain reaction in the body that causes blood vessels to constrict. This, in turn, reduces the flow of blood and increases the likelihood of blockages. Most heart attacks and strokes occur when a blood clot blocks a vessel.

The researchers believe the pollutants in the air affect a compound called endothelin, which causes blood vessels to constrict. Rats exposed to smog have abnormally high levels of endothelin.

"We now have a biological explanation in humans that helps explain the relationships we have seen in epidemiological and animal studies," Dr. Silverman said.

To conduct the research, 25 healthy volunteers breathed polluted air for two hours in a laboratory setting. Their brachial arteries -- key blood vessels that run from the shoulder to the elbow -- constricted between 2 per cent and 4 per cent on average.

The air that was pumped into the lab had high concentrations of fine particles plus ozone, making it similar to the smog that blankets Toronto at rush hour.

Fine particles are emitted from burning fossil fuels, and found principally in car-engine exhaust, and the emissions of coal-fired power plants and manufacturing plants. Ozone is created when sun shines on the emissions.

Dr. Robert Brook, a professor at the University of Michigan in Ann Arbor and a member of the research team, said it appears that it is the fine particles that are damaging to circulatory systems.

While large particles are trapped in the upper airways, fine particles travel down to the alveoli, tiny air sacs at the base of the lungs.

He said that people with atherosclerosis, whose blood vessels are already dangerously narrowed, are at greatest risk from air pollution, but that smog can also "adversely affect the blood vessels of healthy people."

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