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When it Comes to Air Pollution, What You Can't See Can Hurt You

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"Not everyone is equally at risk to the effects of poor air quality," said Robert Brook, Assistant Professor of Medicine of the Division of Cardiovascular Medicine at the University of Michigan. "Yet, as traffic worsens and millions of vulnerable people are exposed to particulate matter, it is incumbent upon us to understand how and why people are affected so that we can take steps to limit our personal exposure – and consider making broader changes to the public agenda to control air pollution."

Although it is known that particulate matter is the 13th cause of mortality worldwide, the explanation underlying the association remained incompletely understood until now. In their particulate matter health study, the researchers designed two randomized, double-blind exposure experiments – one in downtown Toronto and one in Ann Arbor, Michigan – to investigate how particulate matter raises blood pressure in healthy adults, aged 18 to 50, and what air pollution constituents are responsible. In Toronto, researchers compared the effect on blood pressure and blood vessel functions among 30 adults for two hours in four different exposure situations: concentrated ambient particulate matter (CAPS alone), CAPS and ozone, ozone alone or filtered air.

Results showed that short term exposure to air pollution that contains particulate matter (CAP or CAP and ozone) – but not ozone alone – significantly raised diastolic blood pressure by 3.6 mm Hg on average (a significant difference from filtered air), and only during the exposure period of two hours. Blood vessel function was impaired 24 hours after all exposures containing particulate matter, but not ozone alone, and not immediately after any exposure type (within five minutes).

In Ann Arbor, researchers compared the effect of CAP and ozone in 50 adults pre-treated with the anti-oxidant vitamin C, a blocker of the vasoconstrictor hormone endothelin (bosentan) and placebo. Diastolic blood pressure increased to a similar degree, between 2.5 and 4.0 mm Hg, during all exposure types. Blood vessel function was not impaired at any time point after all exposures, and blood pressure returned to normal within 10 minutes after exposure.

Results confirm that it is particulate matter and not ozone that is responsible for the rapid raise in diastolic blood pressure and that the pro-hypertensive response occurs only during the actual inhalation of the particles. The very rapid and transient nature of the increase in blood pressure, and the fact that pre-treatment with vitamin C did not block the response, suggest that a sudden increased in sympathetic nervous system activity is the most like cause.

Additionally, the study confirmed that particulate matter does impair blood vessel function one day following exposure. But since this response occurred only in Toronto, the composition of particulate matter or its source may likely play a role in determining the health response.

"These findings are a springboard for further study that will specifically determine how the sympathetic nervous system responds and to what types of particles in air pollution," said Dr. Brook. "But this glimpse helps us determine the triggers behind a range of cardiovascular events – some deadly. Learning how this dangerous cascade starts can help the medical and public health community make advances toward limiting their impact in the future."
Last modified on Thursday, 03 December 2009 14:25
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