by Anthony J. Brown, MD

Last Updated: 2007-09-12 19:39:52 -0400 (Reuters Health)

NEW YORK (Reuters Health) – In a study of men with coronary heart disease, inhalation of dilute diesel exhaust increases myocardial ischemia and inhibits fibrinolysis, according to a report in The New England Journal of Medicine for September 13.

In light of these findings, "environmental health policy interventions targeting reductions in urban pollution should be considered in order to decrease the risk of adverse cardiovascular events," lead author Dr. Nicholas L. Mills, from the University of Edinburgh in the UK, and colleagues conclude.

"We are the first group to directly assess the effects of air pollution on the heart and blood vessels in patients with coronary heart disease," Dr. Mills told Reuters Health. "Previous observational studies are limited by imprecision in the measurement of pollution exposure, the effect of potential confounding environmental and social factors, and the lack of mechanistic data."

The findings stem from a randomized, crossover study of 20 men with a prior MI who were exposed to dilute diesel exhaust or filtered air for 1 hour during two separate sessions while resting and during moderate exercise.

Continuous 12-lead ECG was used to assess myocardial ischemia. Six hours after exposure, intraarterial infusions of three endothelium-dependent vasodilators (acetylcholine, sodium nitroprusside, and bradykinin, which also releases tissue plasminogen activator) were used to determine vasomotor and fibrinolytic function.

Heart rate rose to a similar extent during exercise while exposed to both diesel exhaust and filtered air, the report indicates.

Both exposure conditions were also associated with exercise-induced ST-segment depression, although the increase in ischemic burden was significantly greater during exhaust exposure.

Diesel exhaust exposure did not seem to cause vasomotor dysfunction, but it was associated with a significant reduction in the release of tissue plasminogen activator.

"It will be important to determine the components of diesel exhaust responsible for the adverse effects on the heart and blood vessels in future work. We believe these effects are mediated by fine particle emissions," Dr. Mills said.

"Considering the unequivocal benefit of habitual exercise, including its established role in decreasing the risk that isolated episodes of exertion may trigger the onset of an acute cardiovascular event, the risk-benefit ratio may be optimized if people exercise away from traffic when possible," Dr. Murray A. Mittleman, from Beth Israel Deaconess Hospital in Boston, comments in a related editorial.

N Engl J Med 2007;357:1075-1082,1147-1149.