Association of heart rate variability in taxi drivers with marked changes in particulate air pollution in Beijing in 2008

Background: Heart rate variability (HRV), a marker of cardiac autonomic function, has been associated with particulate matter (PM) air pollution, especially in older patients and those with cardiovascular diseases. However, the effect of PM exposure on cardiac autonomic function in young, healthy adults has received less attention. Objectives: We evaluated the relationship between exposure to traffic-related PM with an aerodynamic diameter ≤ 2.5 μm (PM_2.5) and HRV in a highly exposed panel of taxi drivers. Methods: Continuous measurements of personal exposure to PM_2.5 and ambulatory electrocardiogram monitoring were conducted on 11 young healthy taxi drivers for a 12-hr work shift during their work time (0900-2100 hr) before, during, and after the Beijing 2008 Olympic Games. Mixed-effects regression models were used to estimate associations between PM_2.5 exposure and percent changes in 5-min HRV indices after combining data from the three time periods and controlling for potentially confounding variables. Results: Personal exposures of taxi drivers to PM_2.5 changed markedly across the three time periods. The standard deviation of normal-to-normal (SDNN) intervals decreased by 2.2% [95% confidence interval (CI), -3.8% to -0.6%] with an interquartile range (IQR; 69.5 μg/m³) increase in the 30-min PM_2.5 moving average, whereas the low-frequency and high-frequency powers decreased by 4.2% (95% CI, -9.0% to 0.8%) and 6.2% (95% CI, -10.7% to -1.5%), respectively, in association with an IQR increase in the 2-hr PM_2.5 moving average. Conclusions: Marked changes in traffic-related PM_2.5 exposure were associated with altered cardiac autonomic function in young healthy adults.