Multiscale entropy, a novel non-linear method, better reflected the detrimental impact of ambient air pollution on 24-hour heart rate variability than linear method or detrended fluctuation analysis

Abstract Background/Introduction Prior studies revealed exposure to ambient air pollution would increase cardiovascular disease–related mortality and nonfatal events, but the underlying mechanism was not fully elucidated. Disruption of autonomic regulation might be a possible cause of increased cardiovascular morbidity and mortality, but previous work showed inconsistent relationship between ambient air pollution and heart rate variability analyzed by traditional linear methods. Our previous study showed the relationship between ambient air pollution and home blood pressure was non-linear, thus non-linear methods, such as detrended fluctuation analysis (DFA) and multi-scale entropy (MSE), could be more useful tools while assessing the effect of ambient air pollution on biomedical parameters. Purpose To use both traditional linear and novel non-linear methods to evaluate the impact of ambient air pollution on 24-hour heart rate variability. Methods From 2015/01 to 2015/12, patients undergoing 24-hour Holter ECG study in a tertiary medical center were enrolled as the study population. The patients were divided into two groups based on the severity of air pollution in their living areas (severe and mild air pollution groups). The two groups were matched by propensity-score matching. Linear and non-linear methods, including DFA and MSE, were used to calculate 24-hour heart rate variability. Results A total of 568 patients (284 patients in each group) were enrolled in this study. Traditional linear analysis of HRV didn’t show significant difference between the two groups regarding any time- or frequency-domain parameters. In non-linear analysis of HRV, DFA failed to detect significant difference between the two groups, while most MSE parameters (Area1-5, LnArea1-5, Area6-20 and LnArea6-20) were significantly lower in the severe air pollution group. The MSE analysis revealed significant differences across all scales (1 to 20). Conclusion (s) Ambient air pollution was associated with decreased 24-hour heart rate variability, and the impact was better evaluated by non-linear analysis (specifically multi-scale entropy) than traditional linear method. Table Figure