Objective To compare the circadian variation of hourly heart rate variability (HRV) on work and non-workdays among boilermaker construction workers.
Method 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 (SDNNi) was calculated from 5-min data and summarised hourly. SDNNis 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. SDNNi 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 SDNNi, 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 SDNNi was 8.1 ms (95% CI −9.8 to −6.3) lower than non-workday SDNNi. The circadian pattern of HRV exhibited two peaks which differed on work and non-workdays.
Conclusion 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.
- circadian rhythms
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Funding Other funders: NIH; Flight Attendants Medical Research Institute.
Competing interests None declared.
Ethics approval This study was conducted with the approval of the Harvard School of Public Health.
Provenance and peer review Not commissioned; externally peer reviewed.