Abstract

Objectives: To evaluate whether hourly changes in fine particle (PM_2.5, diameter<2.5 µm) exposure or outdoor particle concentrations are associated with rapid ischaemic responses.

Methods: 41 non-smoking elderly people with coronary heart disease were followed up with biweekly clinic visits in Helsinki, Finland. The occurrence of ST segment depressions >0.1 mV was recorded during submaximal exercise tests. Hourly variations in personal PM_2.5 exposure and outdoor levels of PM_2.5 and ultrafine particles (<0.1 µm) were recorded for 24 h before a clinic visit. Associations between particulate air pollution and ST segment depressions were evaluated using logistic regression.

Results: Both personal and outdoor PM_2.5 concentrations, but not outdoor ultrafine particle counts, were associated with ST segment depressions. The odds ratio (per 10 µg/m³) for personal PM_2.5 concentration during the hour preceding a clinic visit was 3.26 (95% CI 1.07 to 9.99) and for 4 h average outdoor PM_2.5 it was 2.47 (95% CI 1.05 to 5.85).

Conclusions: Even very short-term elevations in fine particle exposure might increase the risk of myocardial ischaemia. The precise mechanism is still unknown but could involve changes in autonomic nervous control of the heart.