Impacts of In-Cabin Exposure to Size-Fractionated Particulate Matters and Carbon Monoxide on Changes in Heart Rate Variability for Healthy Public Transit Commuters

Chin-Sheng Tang,Hsiao-Chi Chuang,Shih-Chun Candice Lung,Kai-Jen Chuang,Tzu-Yi Wu,Ta-Yuan Chang,Li-Te Chang

doi:10.3390/atmos10070409

Abstract

To evaluate the cardiovascular impact of traffic-related pollutant exposure on healthy young adults, the research team has collected the primary data of in-cabin exposure to air pollutants and heart rate variability (HRV). Twenty young healthy college students were recruited in Taipei metropolitan area. In addition to electrocardiogram, personal exposure to air pollutants, i.e., particulate matter (PM) and carbon monoxide (CO), and weather conditions, including temperature and relative humidity (RH), on campus, bus, and mass rapid transit were monitored continuously. The following HRV parameters were evaluated using generalized additive mixed model to adjust for personal and meteorological variables: heart rate (HR), the square root of the mean of the sum of the squares of differences between adjacent normal-to-normal (NN) intervals (r-MSSD), the standard deviation of all NN intervals (SDNN), the percentage of successive NN interval differences greater than 50 ms (pNN50), low-frequency power (LF), high-frequency power (HF), total power (TP), and LF/HF. They were assessed to find out the association between in-cabin exposure and HRV parameters. Compared with the HRV parameters measured on campus, the percent changes in r-MSSD, SDNN, pNN50+1, LF, HF, and TP decreased when the participants were in public transits. After adjusting for all locations, 5 min moving averages of PM2.5–10 and PM1 were significantly associated with the increase in the percent changes in HR and SDNN. Additionally, 5 min moving averages of PM2.5–10 exposure were significantly associated with the decrease in the percent change in HF, while it was significantly associated with the increase of the percent change in LF/HF. The reduction of the percent change in HR was also found to be significantly associated with 5 min CO moving averages. To conclude, current analyses have shown that size-fractionated PMs and CO exposure in public transits might lead to significant changes of HRV parameters for healthy young adults.

Highlights

In the past few decades, industry, transportation, and economy in Asian countries have developed and even flourished
The current study found that along with each increase of 1 μg/m3 in PM1–2.5 to which participants were exposed on the bus, the percentage change of high-frequency range (HF) for them decreased by 57.76%, and PM1 caused the percentage changes of HF in healthy adults to decrease by 58.15%
Results of the generalized additive mixed model (GAMM) analysis showed that both PM2.5–10 and PM1 caused the percentage change of heart rate (HR) to increase significantly, and the percentage change of standard deviation of all NN intervals (SDNN), a time domain heart rate variability (HRV) parameter, to increase significantly; PM2.5–10 caused the percentage change of HF, a frequency domain HRV parameter, to decrease significantly and the percentage change of low-frequency power (LF)/HF

Summary

Introduction

In the past few decades, industry, transportation, and economy in Asian countries have developed and even flourished. Air pollution exposure can be viewed as a function of the concentration of contaminants in a microenvironment and the time an individual is exposed to the microenvironment. Air pollutants in traffic-related microenvironments are undoubtedly mainly derived from traffic emissions. Commuters are often exposed to high concentrations of pollution that do not meet air quality standards. Traffic-related air pollution exposure intensity varies with routes, traffic loads, and commuting modes [3,4,5,6,7]. Previous studies have indicated that commuters using engine vehicles, i.e., cars, trains, subways, trams, or buses, have higher air pollution exposure than those who adopt active commuting, i.e., walking or cycling [8]. Previous studies have found that pedestrians and cyclists have higher PM exposure on high-traffic routes when compared with on low-traffic routes, while commuters travelling in diesel-powered buses have three to four times the PM exposure in comparison with gasoline-powered bus commuters [9,10,11,12]

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Discussion

Conclusion