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

Newswise — Research presented at American Society of Hypertension's Twenty Third Annual Scientific Meeting and Exposition (ASH 2008) shows that even a few hours of exposure to particulate matter (PM), which is not ozone but a component of air pollution emitted from power plants, factories and motor vehicles, among other sources, 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 a large host of CV events including heart attack, heart failure and stroke.

"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 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, Michigan " 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 (CAPS alone), CAPS 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 time 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 increased 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. "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." About the American Society of HypertensionThe American Society of Hypertension (ASH) is the largest U.S. professional organization of scientific investigators and healthcare professionals committed to eliminating hypertension and its consequences. ASH is dedicated to promoting strategies to prevent hypertension and to improving the care of patients with hypertension and associated disorders. The Society serves as a scientific forum that bridges current hypertension research with effective clinical treatment strategies for patients.