Effects of fine particulate on heart rate variability in Beijing: a panel study of healthy elderly subjects

Purpose This study aims to investigate the effects of ambient fine particulate (particulate matter with an aerodynamic diameter of 2.5 mu m or less, PM2.5) exposure within several minutes on Heart Rate Variability (HRV) of the healthy elderly subjects in the general environments (indoor and outdoor). Methods This study is conducted by measuring the real-time indoor and outdoor exposure variables (PM2.5, Temperature, and relative humidity) and heart rate variability (HRV), a marker of cardiac autonomic function measured by 24-h ambulatory electrocardiogram monitoring in a panel of 30 healthy elderly subjects in Beijing. Associations between personal 5-min PM2.5 concentrations and concurrent 5-min HRV frequency indices are investigated using the mixed linear model. Results High Frequency (HF) and Low Frequency (LF) increase, respectively by 1.30% (95% CI, 0.16-2.45%) and 1.34% (95% CI, 0.38-2.30%) per 10 mu g/m(3) increases of PM2.5 in the polled data analysis after the potential confounders are adjusted. When the indoor and outdoor periods are separated, positive associations are found between PM2.5 and HRV when the subjects are indoors; however, there is no association when the subjects are outdoors. Conclusions We conclude that PM2.5 exposure within several minutes leads to increases of HRV of the healthy older subjects, which may increase the cardiac risks. Prominent effect of PM2.5 on HRV is found when they are indoors, while the effect is not obvious in outdoor environment.