Individual-level PM2.5 exposure and the time course of impaired heart rate variability: the APACR Study

In 106 community-dwelling middle-aged non-smokers we examined the time-course and the acute effects of fine particles (PM2.5) on heart rate variability (HRV), which measures cardiac autonomic modulation (CAM). Twenty-four hours beat-to-beat ECG data were visually examined. Artifacts and arrhythmic beats were removed. Normal beat-to-beat RR data were used to calculate HRV indices. Personal PM2.5 nephelometry was used to estimate 24-h individual-level real-time PM2.5 exposures. We use linear mixed-effects models to assess autocorrelation- and other major confounder-adjusted regression coefficients between 1-6 h moving averages of PM2.5 and HRV indices. The increases in preceding 1-6 h moving averages of PM2.5 was significantly associated with lower HF, LF, and SDNN, with the largest effect size at 4-6 h moving averages and smallest effects size at 1 h moving average. For example, a 10 mu g/m(3) increase in 1 and 6-h moving averages was associated with 0.027 and 0.068 ms(2) decrease in log-HF, respectively, and with 0.024 and 0.071 ms(2) decrease in log-LF, respectively, and with 0.81 and 1.75 ms decrease in SDNN, respectively (all P-values <0.05). PM2.5 exposures are associated with immediate impairment of CAM. With a time-course of within 6 h after elevated PM2.5 exposure, with the largest effects around 4-6 h. Journal of Exposure Science and Environmental Epidemiology (2011) 21, 65-73; doi: 10.1038/jes.2010.21; published online 7 April 2010