Diesel Exhaust Poses Risks for Men with Heart Disease

EDINBURGH, Scotland, Sept. 13 -- Breathing diesel fumes during exercise, even for a brief period, promoted myocardial ischemia in men who've had a heart attack, researchers here reported.

It also impaired thrombotic mechanisms, Nicholas L. Mills, M.D., of the University of Edinburgh, and colleagues wrote in the Sept. 13 issue of the New England Journal of Medicine.

The data emerged from a double-blind, randomized, crossover study in a controlled-exposure facility. The study included 20 middle-aged men who'd had a prior myocardial infarction and had primarily single-vessel disease.

The men were exposed in two separate sessions to dilute diesel exhaust (300 ?g per cubic meter) or filtered air for one hour during 15-minute periods of rest and moderate exercise on a bicycle ergometer.

During the combustion exposure, typical of heavy traffic in large cities, myocardial ischemia was quantified by ST-segment analysis using continuous 12-lead electrocardiography. Six hours after exposure, vasomotor and fibrinolytic function were assessed via intra-arterial agonist infusions.

During both exposure sessions, the men's heart rate increased with exercise (P

In an accompanying editorial, Murray A. Mittleman, M.D., of Harvard, wrote that this study may provide insight into the mechanisms responsible for the reported association between ambient air pollution and the onset of acute cardiovascular events, including the heightened risk during vigorous exertion.

Noting that dilute diesel exhaust is an extremely complex mixture of particles and gases, Dr. Mittleman said it was not possible from this study to determine which constituents of diesel exhaust were responsible.

Nonetheless, he said, if such exposures are causal, these findings may represent the "tip of an iceberg" for cardiovascular risk.

Dr. Mittleman noted important study limitations with respect to generalizability. For example, he said, different engines, fuels, and loads would result in different outputs.

In addition, the study did not directly address the cardiovascular consequences of air pollution from sources other than diesel combustion. Finally, he noted, these findings apply only to men with a history of myocardial infarction.

Considering the unequivocal benefits of regular exercise, including its role in decreasing the risk that an isolated episode of exertion might trigger an acute cardiovascular event, "the risk-benefit ratio may be optimized if people exercise away from traffic when possible," he concluded.

No potential conflict of interest relevant to this article was reported by the study authors or Dr. Mittleman, the editorial writer.