Study connects smog to illness
By ANDRé PICARD PUBLIC HEALTH REPORTER
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
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
and Environment Canada have finally shown why they are
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
in Ann Arbor
and a member of the research team, said it appears that
it is the fine particles that are damaging to circulatory
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