title: Circadian Disruptions of Heart Rate Variability among Weekly Consecutive-12-hour 2 Shift Workers in the Automobile Factory in Korea.
abstract: OBJECTIVE
  The objective of this study is to compare the circadian patterns of heart rate variability assessed by 24-hour ambulatory electrocardiographic (ECG) recordings during day shift and night shift among the workers in the 5 days-concecutive- 12-hour shift in an automobile factory in Korea.
  
  
  METHODS
  The study population consisted 300 workers, who were randomly selected among the 8700 total workers in one car factory. To analyse circadian variation, the 24-hour ECG recordings (Marquette) were measured during day shift (08: 00-20: 00 h) and night shift (20: 00-08: 00 h). Analysis was performed for all time and frequency domain measures of HRV. 233 workers completed taking 24-hour ECG recordings.
  
  
  RESULTS
  This study shows that the 24 hourcircadian variation mainly follows work/sleep cycle rather than day/night cycle among shift workers. This study also shows that among the night shift, the circadian variation between work and sleep cycle decreased compared to the work/sleep cycle among day shift workers. All time and frequency domain parameters (except LF/HF ratio) show significantly different between work and sleep in the day shift and night shift.
  
  
  CONCLUSIONS
  These changes in heart rate variability circadian rhythms reflect significant reductions in cardiac parasympathetic activity with the most marked reduction in normal vagal activity among the shift workers. Especially, it suggests the circadian rhytm has blunted among the night workers. The quantification of the circadian variation in HRV can be a surrogates of workers' potential health risk, as well as suggests possible mechanisms through which the shift works compromise workers' health.
authors.affiliation: Kangwon National University, Medical College, Department of Preventive Medicine, Korea. sonmia@kangwon.ac.kr.
authors.forename: Mia
authors.initials: M
authors.lastname: Son
authors.affiliation: Kangwon National University, Medical College, Department of Preventive Medicine, Korea. sonmia@kangwon.ac.kr.
authors.forename: Juhon
authors.initials: J
authors.lastname: Sung
authors.affiliation: Kangwon National University, Medical College, Department of Preventive Medicine, Korea. sonmia@kangwon.ac.kr.
authors.forename: Myunggul
authors.initials: M
authors.lastname: Yum
authors.affiliation: Kangwon National University, Medical College, Department of Preventive Medicine, Korea. sonmia@kangwon.ac.kr.
authors.forename: Jung Ok
authors.initials: JO
authors.lastname: Kong
authors.affiliation: Kangwon National University, Medical College, Department of Preventive Medicine, Korea. sonmia@kangwon.ac.kr.
authors.forename: Hye Un
authors.initials: HU
authors.lastname: Lee
authors.affiliation: Kangwon National University, Medical College, Department of Preventive Medicine, Korea. sonmia@kangwon.ac.kr.
authors.forename: In A
authors.initials: IA
authors.lastname: Kim
authors.affiliation: Kangwon National University, Medical College, Department of Preventive Medicine, Korea. sonmia@kangwon.ac.kr.
authors.forename: Jung Yeon
authors.initials: JY
authors.lastname: Kim
keywords: 24-hour ECG recordings; Circadian variation; Heart rate variability; shift