The association between personal measurements of environmental exposure to particulates and heart rate variability

Background. Epidemiologic evidence indicates that airborne particulates are associated with mortality risk, predominately from heart disease. This may occur through changes in the cardiac autonomic nervous system, witnessed by changes in heart rate variability. Methods. This short,term longitudinal study used continuous personal particulate matter measurements to examine the effects of exposure to particulate matter less than 2.5 mum in diameter (PM2.5) on heart rate and rate variability in 20 relatively young, healthy male workers. Continuous exposure and cardiac monitoring were per-formed on each subject on a nonwork day. The 5-minute standard deviation of the normal-to-normal interval was used as the main measure of heart rate variability. Results. Mixed-effects regression models estimate an average 1.4% (95% confidence limits = -2.1, -0.6) decrease in the 5-minute standard deviation of the normal-to-normal interval for each 100 mug/m(3) increase in the 3-hour PM2.5 moving average, and small increases in heart rate, after adjustment for potential confounding factors. Predicted effects of exposure were greatest using the 3-hour averaging interval for PM2.5 and decreased in magnitude using shorter and longer intervals. Conclusions. These results reveal an association between cardiac autonomic function and environmental PM2.5 exposure. These observed associations may result from decreased vagal or increased sympathetic tone.