Time course of heart rate variability decline following particulate matter exposures in an occupational cohort.

Although research suggests that particles influence cardiac autonomic response as evidenced by decreases in heart rate variability (HRV), the time course of the response remains unclear. Using a crossover panel study, we monitored 36 male boilermaker welders, occupationally exposed to metal-rich particulate matter (PM) to investigate the temporal trend of hourly HRV subsequent to PM exposure. Ambulatory electrocardiograms were collected over work (exposure) and non-work (control) periods and the mean of the standard deviations of all normal-to-normal intervals for all 5-min segments (SDNN(i)) was calculated hourly for up to 14-hrs post-work. The exposure-response relationship was examined with linear mixed effects regression models to account for participants monitored over multiple occasions. Models were adjusted for non-work HRV to control for diurnal fluctuations and individual predictors of HRV. The mean (SD) work PM(2. 5) concentration was 1.12 (0.76) mg/m(3). Hourly SDNN(i) was consistently lower post-work as compared to the same time period on a non-work day. HRV was inversely associated with work PM(2. 5) exposures in each of the 14-hrs post-work. The hourly associations suggested an early and later phase response, with the largest regression coefficients observed 2-3 hrs (beta = -6.86 (95% CI: -11.91, -1.81) msec/1 mg/m(3) at 3-hrs), and then 9-13 hrs (beta = -8.60 (95% CI: -17.45, 0.24) msec/1 mg/m(3) at 11-hrs), after adjusting for non-work HRV, smoking status, and age. This investigation demonstrates declines in HRV for up to 14 hours following PM exposure and a multiphase cardiovascular autonomic response with immediate (2 hrs) and delayed (9-13 hrs) responses.