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Biomarkers 2 and Reproduction 2
  1. J. C. Cavallari,
  2. S. C. Fang,
  3. E. A. Eisen,
  4. J. Schwartz,
  5. R. Herrick,
  6. R. Hauser,
  7. D. C. Christiani
  1. Harvard School of Public Health

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    Although recent research demonstrates associations between particulate exposures and decreased heart rate variability (HRV), it is unclear whether exposures alter the natural circadian rhythm of HRV. In a cohort of boilermaker welders, we compared the circadian variation of hourly HRV on a workday during exposure to high levels of metal-rich particulates to a non-workday when particulate exposures were low.


    We conducted a panel study among 36 males who were monitored by 24 h ambulatory electrocardiograms (ECG) over both a workday (exposure period) and non-workday (control period). ECGs were analysed and the standard deviation of normal-to-normal beats index (SDNNi) was calculated from 5 min data and summarised hourly over the 24 h measurement. Work and non-work periods were compared using a paired t-test.


    Welders were exposed to a mean (SD) workday PM2.5 concentration of 1.14 (0.76) mg/m3. There was conservation of the circadian rhythm of HRV on workdays, with an increase in HRV during the sleeping hours, peaking at 5 am, and a decrease in the afternoon, reaching a nadir at 1 pm. However, we observed lower hourly SDNNi on workdays as compared to non-workdays. Furthermore, the largest difference between work and non-work HRV was during the time that most participants reported active working. For example, at 1 pm the mean (SD) hourly SDNNi was 52.47 (20.21) ms on a non-workday and 40.67 (15.13) ms on a workday. The difference between work and non-work hourly SDNNi was statistically significant (p<0.05) between 8 am and 3 pm. Lower SDNNi was also observed in the hours following work and in the early morning; at 5 and 6 am the difference was statistically significant.


    Although the circadian variation in HRV was preserved following workday exposure, HRV was decreased as compared to a non-workday. While the largest differences between work and non-work HRV …

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