Air Study: Short Exposure Can Result in Serious Effects

Research presented at the American Society of Hypertension's 23rd annual Scientific Meeting and Exposition (ASH 2008) shows that even a few hours of exposure to particulate matter (PM) is responsible for rapidly raising blood pressure and can impair blood vessel function in certain situations within 24 hours. These effects may explain why air pollution can trigger heart attack, heart failure, and stroke.

"Not everyone is equally at risk to the effects of poor air quality," said Dr. 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 PM, 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."

PM is the 13th cause of mortality worldwide, but until now, the explanation underlying this association remains incompletely understood.

In their study, researchers designed two randomized, double-blind exposure experiments – one in downtown Toronto and one in Ann Arbor, Mich. – to investigate how PM 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 PM (concentrated ambient fine particles [CAP] alone), CAP and ozone, ozone alone, or filtered air. Results showed that short-term exposure to air pollution that contains PM (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 PM, 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 point after all exposures, and blood pressure returned to normal within 10 minutes after exposure.

Results confirm that it is PM 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 increase in sympathetic nervous system activity is the most like cause.

Additionally, the study confirmed that PM does impair blood vessel function one day following exposure. But since this response occurred only in Toronto, the composition of PM 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.

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