Heart rate variability associated with particulate air pollution

Background Epidemiologic studies have linked fine particulate air pollution with cardiopulmonary mortality, yet underlying biologic mechanisms remain unknown. Changes in heart rate variability (HRV) may reflect changes in car diac autonomic function and risk of sudden cardiac death. This study evalua ted changes in mean heart rate and HRV in human beings associated with chan ges in exposure to particulate air pollution. Methods Repeated ambulatory electrocardiographic monitoring was conducted o n 7 subjects for a total of 29 person-days before, during, and after episod es of elevated pollution. Mean HR, the standard deviation of normal-to-norm al (NN) intervals (SDNN), the standard deviation of the averages of NN inte rvals in all 5-minute segments of the recording (SDANN), and the square roo f of the mean of squared differences between adjacent NN intervals (r-MSSD) were calculated for 24-hour and 6-hour time segments. Associations of HRV with particulate pollution levels were evaluated with fixed-effects regress ion models. Results After controlling for differences across patients, elevated particu late levels were associated with (1) increased mean HR, (2) decreased SDNN, a measure of overall HRV, (3) decreased SDANN, a measure that corresponds to ultralow frequency variability, and (4) increased r-MSSD, a measure that corresponds to high-frequency variability. The associations between HRV an d particulates were small but persisted even after controlling for mean HR. Conclusions This study suggests that changes in cardiac autonomic function reflected by changes in mean HR and HRV may be part of the pathophysiologic mechanisms or pathways linking cardiovascular mortality and particulate ai r pollution.