PERSONAL EXPOSURE TO SUBMICROMETER PARTICLES AND HEART RATE VARIABILITY IN HUMAN SUBJECTS

We conducted a study on two panels of human subjects-9 young adults and 10 elderly patients with lung function impairments-to evaluate whether submicrometer particulate air pollution was associated with heart rate variability ( HRV). We measured these subjects' electrocardiography and personal exposure to number concentrations of submicrometer particles with a size range of 0.02-1 mum (NC0.02-1) continuously during daytime periods. We used linear mixed- effects models to estimate the relationship between NC0.02-1 and log(10)-transformed HRV, including standard deviation of all normal-to-normal intervals (SDNN), square root of the mean of the sum of the squares of differences between adjacent NN intervals (r-MSSD), low frequency (LF, 0.04-0.15 Hz), and high frequency (HF, 0.15-0.40 Hz), adjusted for age, sex, body mass index, tobacco exposure, and temperature . For the young panel, a 10,000-particle/cm(3) increase in NC0.02-1 with 1-4 hr moving average exposure was associated with 0.68-1.35% decreases in SDNN, 1.85-2-58% decreases in r -MSSD, 1.32-1.61% decreases in LF, and 1.57-2.60% decreases in HF. For the elderly panel, a 10,000-particle/cm(3) increase in NC0.02-1 with 1-3 hr moving average exposure was associated with 1.72-3.00% decreases in SDNN, 2.72-4.65% decreases in r-MSSD, 3.34-5.04% decreases in LF, and 3.61-5. 61% decreases in HF. In conclusion, exposure to NC0.02-1 was associated with decreases in both time-domain and frequency-domain HRV indices in human subjects.