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GENERAL CARDIOLOGY

Cardiovascular effects of air pollution highlighted

Both short and long-term exposure to air pollution has been associated with an increase in cardiovascular morbidity and mortality, and the WHO estimates that air pollution causes 800 000 premature deaths each year. However, the exact mechanisms for this association remain relatively unexplored.

Mills et al performed a double-blind, randomised, crossover study of the effect of dilute diesel exhaust on 20 men with a previous history of myocardial infarction. In two separate sessions, the men were exposed to dilute diesel exhaust (300 μg per cubic metre) or filtered air for 1 hour during periods of both rest and moderate exercise. During the exposure experiment, continuous 12-lead electrocardiography was used to assess ST-segment changes. Six hours later, vasomotor and fibrinolytic function was assessed by means of intra-arterial agonist infusions.

Exercise-induced ST-segment depression was seen in all patients, but the changes seen were greater during exposure to diesel exhaust (−22 (SD 4) vs −8 (SD 6) millivolt seconds, p<0.001). Although vasomotor dysfunction was not made worse by exposure to diesel exhaust, the acute release of endothelial tissue plasminogen activator was reduced (35% decrease in area under the curve).

Although this study demonstrates the deleterious effects of diesel fumes, it does not allow us to determine exactly which components of the fumes caused the effects seen. Furthermore diesel exhaust forms only one part of ambient air pollution, and the authors thus plan future studies to try to pinpoint exactly which elements are to blame. In the meantime patients with coronary artery disease may well be advised to exercise away from traffic when possible.

Mills NL, Tornqvist H, Gonzalez MC,. Ischemic and thrombotic effects of dilute diesel-exhaust inhalation in men with coronary heart disease. N Engl J Med 2007;357:1075–82.

Mittleman MA. Air pollution, exercise, and cardiovascular risk. N Engl J Med 2007;357:1147–49.

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