title: Circadian variation of heart rate variability among welders.
abstract: OBJECTIVE
  To compare the circadian variation of hourly heart rate variability (HRV) on work and non-workdays among boilermaker construction workers.
  
  
  METHODS
  A panel study of 18 males monitored by 24-h ambulatory ECG over 44 observation-days on paired work and non-workdays was conducted. ECGs were analysed and the SD of normal-to-normal beats index (SDNN(i)) was calculated from 5-min data and summarised hourly. SDNN(i)s over work and non-workdays were compared using linear mixed-effects models to account for repeated measures and harmonic regression to account for circadian variation.
  
  
  RESULTS
  Both work and non-work hourly HRV exhibited circadian variation with an increase in the evening and a decrease in the afternoon. SDNN(i) was lower on workdays as compared with non-workdays with the largest, statistically significant differences observed between 10:00 and 16:00, during active working. Lower SDNN(i), albeit smaller yet statistically significant differences, was also observed in the evening hours following work (17:00-21:00) and early morning (4:00). In regression models using all time periods, an average workday SDNN(i) was 8.1 ms (95% CI -9.8 to -6.3) lower than non-workday SDNN(i). The circadian pattern of HRV exhibited two peaks which differed on work and non-workdays.
  
  
  CONCLUSIONS
  While workday and non-workday HRV followed a circadian pattern, decreased HRV and variation of the circadian pattern were observed on workdays. Declines and changes in the circadian pattern of HRV is a concern among this exposed population.
authors.affiliation: Harvard School of Public Health, Department of Environmental Health, Environmental and Occupational Medicine and Epidemiology Program, 665 Huntington Ave, FXB-103, Boston, MA 02115, USA. jcavalla@hsph.harvard.edu
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Cavallari
authors.forename: Shona C
authors.initials: SC
authors.lastname: Fang
authors.forename: Murray A
authors.initials: MA
authors.lastname: Mittleman
authors.forename: David C
authors.initials: DC
authors.lastname: Christiani
mesh_terms: D000328:Adult; D000395:Air Pollutants, Occupational / Q000032:analysis / Q000633:toxicity; D002940:Circadian Rhythm / Q000502:physiology*; D015716:Electrocardiography, Ambulatory / Q000379:methods; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016273:Occupational Exposure / Q000009:adverse effects / Q000032:analysis; D014896:Welding
chemical_list: D000395:Air Pollutants, Occupational
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