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Diesel Exhaust Chokes Human Arteries

'Exposure chamber' study shows fumes narrow vessels, raise clot risk

MONDAY, Dec. 19, 2005 (HealthDay News) -- Fumes belched from 18-wheelers and other diesel-powered vehicles and engines may be especially tough on the human cardiovascular system, new research reveals.

In a carefully controlled study, the arteries of healthy volunteers exposed to diesel exhaust lost part of their ability to expand, while their blood became more likely to clot.

"People have wondered for a long time whether diesels were harmful, and if so, how," said Dr. Russell V. Luepker, a professor of epidemiology at the University of Minnesota, and a spokesman for the American Heart Association. "This study is a building block. It shows that when you look hard for mechanisms, you find them."

Luepker was not involved in the study, which was conducted by Scottish researchers at the University of Edinburgh and published in the Dec. 20 issue of Circulation.

The research relied on a specially built "exposure chamber" at the University's Center for Cardiovascular Science. In two one-hour sessions, 30 healthy young men were exposed either to filtered air or to exhaust from an idling diesel engine. The researchers then injected vasodilators -- drugs that cause the arteries to expand -- and took blood samples to measure clotting levels.

Response to the vasodilators was reduced significantly after the diesel exposure, and levels of an enzyme that keeps clots from forming were reduced, the researchers reported.

The findings have potentially important implications for the U.S. Environmental Protection Agency, which is currently sponsoring a voluntary program to outfit diesel-powered vehicles with devices that trap fine particles in exhaust fumes.

"Diesel exhaust consists of a complex mixture of particles and gases," said study author Dr. Nick Mills, a clinical research fellow at the Edinburgh center. "Before we can advocate the widespread use of particle traps in diesel engines, we need to verify that combustion-derived particles are the responsible component."

A number of real-world studies have linked diesel fume exposure to heart attacks and other cardiovascular problems, Mills noted.

"However, observational studies cannot prove causality," he said. "In human exposure studies, we can control for all potential confounding factors and assess the direct effect of particulates on the cardiovascular system. Our findings provide further support for the observational studies and a plausible mechanism to explain association between particles and acute cardiovascular events."

It's not clear whether the findings apply to gasoline-powered engines, Mills said, because their emissions are very different from those of diesel-powered engines. In particular, diesel exhausts generate 100 times more pollutant particles, he said.

Because the study was so carefully controlled, Luepker labeled the results "interesting initial data." But he added that "the controlled study in the laboratory is not totally dissimilar to what people out on the street can be exposed to."

"If this study were done in mice, I would say, 'very interesting,'" Luepker said. "A study done in healthy humans gets my attention more."

More information

For more on diesel pollution, head to the U.S. Environmental Protection Agency.

SOURCES: Nick Mills, M.D., clinical research fellow, University of Edinburgh Center for Cardiovascular Research, Scotland; Russell V. Luepker, M.D., professor, epidemiology, University of Minnesota, Minneapolis, and spokesman, American Heart Association; Dec. 20, 2005, Circulation
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