| Night Heart Rate Variability and Particulate Exposures among Boilermaker Construction Workers Jennifer M. Cavallari,1 Ellen A. Eisen,1 Jiu-Chiuan Chen,1,2 Shona C. Fang,1 Christine B. Dobson,1 Joel Schwartz,1 and David C. Christiani1,3,4 1Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA; 2Department of Epidemiology, UNC School of Public Health, Chapel Hill, North Carolina, USA; 3Harvard Medical School, Boston, Massachusetts, USA; 4Massachusetts General Hospital, Boston, Massachusetts, USA Abstract
Background: Although studies have documented the association between heart rate variability (HRV) and ambient particulate exposures, the association between HRV, especially at night, and metal-rich, occupational particulate exposures remains unclear. Objective: Our goal in this study was to investigate the association between long-duration HRV, including nighttime HRV, and occupational PM2.5 exposures. Methods: We used 24-hr ambulatory electrocardiograms (ECGs) to monitor 36 male boilermaker welders (mean age of 41 years) over a workday and nonworkday. ECGs were analyzed for HRV in the time domain ; rMSSD (square root of the mean squared differences of successive intervals) , SDNN (SD of normal-to-normal intervals over entire recording) , and SDNNi (SDNN for all 5-min segments) were summarized over 24-hr, day (0730–2130 hours) , and night (0000–0700 hours) periods. PM2.5 (particulate matter with an aerodynamic diameter ≤ 2.5 µm) exposures were monitored over the workday, and 8-hr time-weighted average concentrations were calculated. We used linear regression to assess the associations between HRV and workday particulate exposures. Matched measurements from a nonworkday were used to control for individual cardiac risk factors. Results: Mean (± SD) PM2.5 exposure was 0.73 ± 0.50 mg/m3 and ranged from 0.04 to 2.70 mg/m3. We observed a consistent inverse exposure–response relationship, with a decrease in all HRV measures with increased PM2.5 exposure. However, the decrease was most pronounced at night, where a 1-mg/m3 increase in PM2.5 was associated with a change of –8.32 [95% confidence interval (CI) , –16.29 to –0.35] msec nighttime rMSSD, –14.77 (95% CI, –31.52 to 1.97) msec nighttime SDNN, and –8.37 (95% CI, –17.93 to 1.20) msec nighttime SDNNi, after adjusting for nonworking nighttime HRV, age, and smoking. Conclusion: Metal-rich particulate exposures were associated with decreased long-duration HRV, especially at night. Further research is needed to elucidate which particulate metal constituent is responsible for decreased HRV. Keywords: environmental cardiology, heart rate variability, occupational, particulate exposures, welders. Environ Health Perspect 115:1046–1051 (2007) . doi:10.1289/ehp.10019 available via http://dx.doi.org/ [Online 5 April 2007]
Address correspondence to D.C. Christiani, Environmental and Occupational Medicine and Epidemiology, Harvard School of Public Health, 665 Huntington Ave., SPH1-1402, Boston, MA 02115 USA. Telephone: (617) 432-3323. Fax: (617) 432-3441. E-mail: dchristi@hsph.harvard.edu We thank R. Hauser, B. Herrick, J.Y. Kim, S. Magari, A. Mehta, E. Rodrigues, L. Su, M. Wang, and the International Brotherhood of Boilermakers, Local 29, Massachusetts. This work was supported by grants ES009860 and ES00002 from the National Institute of Environmental Health Sciences. J.C. was supported by a training grant T42 OH008416 from the National Institute for Occupational Safety and Health and a Taplin Fellowship. The authors declare they have no competing financial interests. Received 20 December 2006 ; accepted 5 April 2007. Correction The authors note that Yeatts et al. have recently published an article on the association between particulate exposures and long-duration HRV [Yeatts K, Svendsen E, Creason J, Alexis N, Herbst M, Scott J, et al. Coarse particulate matter (PM2.5–10) affects heart rate variability, blood lipids, and circulating eosinophils in adults with asthma. Environ Health Perspect 115:709–714 (2007) ].
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