title: Exposures to PM₂.₅ components and heart rate variability in taxi drivers around the Beijing 2008 Olympic Games.
abstract: BACKGROUND
  Carbonaceous and metallic components of particles have been shown to play a role in particles' effects on cardiac autonomic function as measured by heart rate variability (HRV). Previously we reported the association of HRV with marked changes in traffic-related particulate air pollution around the Beijing 2008 Olympic Games in a panel of taxi drivers.
  
  
  OBJECTIVE
  We further investigated the relationship between exposures to the carbonaceous and metallic components of traffic-related particles and HRV in the same population.
  
  
  METHODS
  Repeated measurements of in-car exposures to particulate matter ≤ 2.5 μm in aerodynamic diameter (PM₂.₅), carbon monoxide and nitrogen oxides were conducted in a group of 14 taxi drivers for one work shift in four study periods around the Beijing 2008 Olympics. The quantities of organic/elemental carbons and 27 elements of the in-car PM₂.₅ mass were determined laboratorially. Linear mixed-effects models were used to evaluate the impact of exposures to different PM₂.₅ components on HRV while controlling for potential confounders.
  
  
  RESULTS
  Taxi drivers' exposures to in-car PM₂.₅ and its components showed dramatic changes across the four study periods around the Beijing 2008 Olympics. Differences in associations of in-car PM₂.₅ components with HRV were found. An interquartile range (IQR: 917.9 ng/m³) increase in calcium was associated with a 5.48 millisecond [ms, 95% confidence interval (CI): 0.71, 10.24] increase in standard deviations of normal-to-normal (SDNN) intervals, while an IQR (4.1 ng/m³) increase in nickel was associated with a 1.53 ms (95% CI: 0.14, 2.92) increase in SDNN index. Additionally, a decline of 8.11 ms (95% CI: -15.26, -0.97) in SDNN per IQR (481.4 ng/m³) increase in iron was also found.
  
  
  CONCLUSIONS
  The results support associations of PM₂.₅ metallic components with HRV in younger healthy individuals. Future studies are needed to clarify the interaction among different PM₂.₅ components or the role of PM₂.₅ mixtures.
authors.affiliation: Department of Occupational and Environmental Health Sciences, Peking University School of Public Health, Beijing, China.
authors.forename: Shaowei
authors.initials: S
authors.lastname: Wu
authors.forename: Furong
authors.initials: F
authors.lastname: Deng
authors.forename: Jie
authors.initials: J
authors.lastname: Niu
authors.forename: Qinsheng
authors.initials: Q
authors.lastname: Huang
authors.forename: Youcheng
authors.initials: Y
authors.lastname: Liu
authors.forename: Xinbiao
authors.initials: X
authors.lastname: Guo
mesh_terms: D000328:Adult; D000395:Air Pollutants, Occupational / Q000032:analysis* / Q000633:toxicity; D000397:Air Pollution / Q000706:statistics & numerical data*; D002248:Carbon Monoxide / Q000032:analysis / Q000633:toxicity; D002681:China; D002947:Cities; D005260:Female; D006321:Heart / Q000187:drug effects / Q000502:physiology; D006339:Heart Rate; D006801:Humans; D019570:Inhalation Exposure / Q000706:statistics & numerical data*; D008297:Male; D016273:Occupational Exposure / Q000706:statistics & numerical data; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis* / Q000633:toxicity; D013177:Sports
chemical_list: D000395:Air Pollutants, Occupational; D052638:Particulate Matter; D002248:Carbon Monoxide