| Summary: | 碩士 === 輔仁大學 === 公共衛生學系碩士班 === 105 === Background
In recent years, the changes in the frequency and intensity of extreme weather and climate events have been outgoing frequently. Numerous studies have indicated that exposure to air pollutants and variation in ambient temperature are associated with elevated risks in cardiovascular morbidity and mortality. In addition, the measurement of heart rate variability (HRV) indices has been a common physiological indicator to reflect the function of cardiac autonomic system. At present, many governmental and research units use not only the traditional temperature and relative humidity, but also wet bulb globe temperature (WBGT) as thermal environment indices. The purpose of this study is to explore the effects of temperature, humidity and WBGT on HRV changes in the healthy subjects by adjusting the microenvironment air pollutants exposures, and to compare the differences between these two thermal indices to evaluate the effects of HRV.
Methods
In this study, a variety of direct reading instruments were used for the monitoring of microenvironmental air pollutants, hygrothermal parameters and WBGT in healthy adults and the elderly, and for synchronous monitoring of heart rate(HR) and HRV indices. After adjusting the demographic variables and each kind of pollutant, we calculated the 5-minutes, 1, 4, 8, 12, and 24-hour moving average of thermal environment indices with the HR/HRV time synchronization. Generalized additive mixed model (GAMM) was applied to evaluate the effects of thermal indices on HRV. Vuong’s closeness test was used to compare the model fitness between the thermal environment indices and HRV change.
Results
The study found that age, gender, season and case activity were the important factors affecting HRV. The association between WBGT and HR/HRV had nonlinear relationship, and the inflection points appeared in mostly between 15-20℃ and 20-25℃ in the smooth function graph, forming M-shaped curve. The smooth function curve of the low-frequency (LF) and WBGT showed the most obvious variation. The GAMM analysis results of the linear relationship between temperature and HR/HRV founded that increases in temperature were associated with declines in the percentage change of HR/HRV, and the cumulative effect could last up to 24 hours. The inflection points appeared mostly at 28℃ in the non-linear relationship curve between temperature and HR/HRV, as well as in 5-minute and 1-hour time series. The non-linear relationship between relative humidity and HR/HRV appeared frequently in 4-hour time series. In the comparison of model fitness between the thermal environment indices, regardless of the timing, temperature/humidity and their interaction term were more appropriate than WBGT for evaluating the change of high-frequency (HF). Besides, temperature/humidity and their interaction term were also more suitable than WBGT for evaluating the changes of 4-hour HR and 1-hour LF. Moreover, temperature and humidity were appropriate than WBGT for evaluating 5-min HR and 1-hour LF changes.
Conclusion
The real time effects of WBGT on HRV showed the non-linear relations. The temperature and humidity had linear and non-linear influence to HRV along with cumulative effect. After overall evaluating the model fitness of thermal environment indices, it was found that temperature, humidity and their interaction term were better than WBGT for evaluating the changes of some HRV indices.
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