WEDNESDAY, May 14 (HealthDay News) -- Just a few hours of exposure to particulate matter air pollution can increase blood pressure and harm blood vessel function within 24 hours, a new study finds.

The findings may explain why air pollution can trigger a range of cardiovascular events such as heart attack, heart failure and stroke, the researchers said.

Particulate matter (PM) is a component of air pollution emitted from vehicles, power plants, and factories. It's believe that PM is the 13th leading cause of death worldwide, but the link between PM and death hasn't been well understood.

"Not everyone is equally at risk to the effects of poor air quality," researcher Robert Brook, an assistant professor of medicine, division of cardiovascular medicine, University of Michigan, said in a prepared statement.

"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," Brook said.

In the study, researchers looked at adults living in Toronto and Ann Arbor, Mich.

In Toronto, 30 adults, aged 18 to 50, were exposed for two hours to concentrated ambient PM (CAPS alone), CAPS and ozone, ozone alone, or filtered air. Exposure to air pollution that contains PM (CAP or CAP and ozone) resulted in an average diastolic blood pressure increase of 3.6 mm/Hg. Blood vessel function was impaired 24 hours after (but not immediately after) all exposures to all exposures containing PM, but not ozone alone.

In Ann Arbor, 50 adults were pre-treated with either the antioxidant vitamin C -- which blocks the vasoconstrictor hormone endothelin (bosentan) -- or placebo. Diastolic blood pressure increased between 2.5 and 4.0 mm/Hg during all exposures. However, blood pressure function was not impaired at any time after all exposures, and blood pressure returned to normal within 10 minutes after exposure.

The fact that vitamin C didn't block the blood pressure response suggests that it's likely caused by a sudden increase in sympathetic nervous system activity.

The findings confirm that PM, not ozone, is responsible for the rapid increase in diastolic blood pressure and that this occurs only during actual inhalation of PM. The research also confirms that PM impairs blood vessel function one day after exposure. However, this blood vessel function response occurred only in Toronto, which suggests that the composition of PM or its source may play a role in determining that kind of response, the researchers said.

The study was expected to be presented Wednesday at the American Society of Hypertension annual meeting, in New Orleans.

"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," Brook said. "But this glimpse helps us determine the triggers behind a range of CV 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."

More information

The American Academy of Family Physicians has more about air pollution and health.

SOURCE: American Society of Hypertension, news release, May 14, 2008

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