289 Introduction A number of studies have assessed the health efects of ambient air pollution exposure on human cardiovascular system in recent years, with the strongest evidence shown for particulate matter (PM) ≤2.5 µm in aerodynamic diameter (PM 2.5 ) (Brook et al., 2010; Sun et al., 2010). Speciically, PM related to traic pollution has been associated with adverse cardiac efects among diferent populations (Riediker et al., 2004; Schwartz et al., 2005; Peretz et al., 2008; Fan et al., 2009; Delino et al., 2010; Wu CF et al., 2010; Zanobetti et al., 2010). he cardiac efects of gaseous air pollutants, such as carbon monoxide (CO), have also been reported previously (Dales et al., 2004; Schwartz et al., 2005; Riojas-Rodríguez et al., 2006; Min et al., 2009). he mechanisms that air pollution inluences the cardiovascular system are complex and still not well- RESEARCH ARTICLE he relationship between traic-related air pollutants and cardiac autonomic function in a panel of healthy adults: a further analysis with existing data Shaowei Wu 1,* , Furong Deng 1,* , Jie Niu 2 , Qinsheng Huang 2 , Youcheng Liu 3 , and Xinbiao Guo 1 1 Department of Occupational and Environmental Health Sciences, Peking University School of Public Health, Beijing, China, 2 Peking University hird Hospital, Beijing, China, and 3 Department of Environmental and Occupational Health Sciences, School of Public Health, University of North Texas Health Science Center, Fort Worth, TX, USA Abstract Context: Epidemiological studies have linked particulate matter (PM) and carbon monoxide (CO) exposures with alterations in cardiac autonomic function as measured by heart rate variability (HRV) in populations. Recently, we reported association of several HRV indices with marked changes in particulate air pollution around the Beijing 2008 Olympic Games in a panel of healthy adults. Objective: We further investigated the cardiac effects of traffic-related air pollutants over wide exposure ranges with expanded data set in this panel of healthy adults. Methods: We obtained real-time data on nine taxi drivers’ in-car exposures to PM ≤2.5 μm in aerodynamic diameter (PM 2.5 ) and CO and on multiple HRV indices during a separate daily work shift in four study periods with dramatically changing air pollution levels around the Beijing 2008 Olympic Games. Mixed effect models and a loess smoother method were used to investigate the associations of exposures with HRV indices. Results: Results showed overall negative associations of traffic-related air pollutants with HRV indices across periods, as well as differences in period-specific and individual associations. After stratifying the individuals into two different response groups (positive/negative), cardiac effects of air pollutants became stronger within each group. Exposure– response modeling identified changed curvilinear relationships between air pollution exposures and HRV indices with threshold effects. Discussion and conclusion: Our results support the association of exposure to traffic-related air pollution with altered cardiac autonomic function in young healthy adults free of cardiovascular compromises. These results suggest a complicated mechanism that traffic-related air pollutants influence the cardiovascular system of healthy adults. Keywords: Air pollution, carbon monoxide, cardiac autonomic function, heart rate variability, panel study, particulate matter *hese authors contributed equally to this study. Address for Correspondence: Xinbiao Guo, Department of Occupational and Environmental Health Sciences, Peking University School of Public Health, 38 Xueyuan Road, Beijing 100191, China. Tel: 86-10-82801176. Fax: 86-10-62375580. E-mail: guoxb@bjmu.edu.cn (Received 27 November 2010; revised 28 February 2011; accepted 02 March 2011) Inhalation Toxicology, 2011; 23(5): 289–303 © 2011 Informa Healthcare USA, Inc. ISSN 0895-8378 print/ISSN 1091-7691 online DOI: 10.3109/08958378.2011.568976 Inhalation Toxicology Downloaded from informahealthcare.com by Peking University on 04/21/11 For personal use only.