Plenty of epidemiological studies support a link between pollution and compromised lung function. Now scientists have detected a physical response to common air pollutants. According to a report published online by Circulation: Journal of the American Heart Association, exposure to contaminated air similar to that found in urban areas during peak smog periods causes constriction of the blood vessels in healthy individuals.

Robert D. Brook of the University of Michigan and his colleagues recruited 25 healthy nonsmokers willing to breathe air containing elevated levels of fine particles and ozone in the name of science. Each subject spent two sessions in the so-called human exposure facility at the University of Toronto breathing either filtered air or polluted air. Using ultrasound, the researchers measured the brachial artery (which runs from the shoulder to the elbow) before and after two-hour exposures. They found that the volunteers' arteries constricted between 2 and 4 percent in response to the polluted air but saw no change after their exposure to filtered air. The degree of constriction detected, though measurable, is small and unlikely to produce problems in healthy individuals, Brook says. He adds, however, that "these findings suggest a possible reason why the rate of heart attacks and other cardiovascular events increases with exposure to air pollution for people with known heart and blood vessel disease."

Because of the small size of the study, the findings are preliminary, and the scientists caution that more research is required to understand the mechanism responsible for air pollution's negative effects on blood vessels. But Brook says that as a starting point, the "results are a clear demonstration that environmentally relevant concentrations of common air pollutants that can occur in urban settings adversely affect the blood vessels of healthy people." As such, he notes, they call attention to the need for further research into the pollution problems that plague many of the world's largest cities.