Hourly variation in fine particle exposure is associated with transiently increased risk of ST segment depression.

Abstract

To evaluate whether hourly changes in fine particle (PM(2.5), diameter<2.5 microm) exposure or outdoor particle concentrations are associated with rapid ischaemic responses. 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 microm) were recorded for 24 h before a clinic visit. Associations between particulate air pollution and ST segment depressions were evaluated using logistic regression. 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 microg/m(3)) 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). 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.