title: Effects of shift work on QTc interval and blood pressure in relation to heart rate variability.
abstract: OBJECTIVE
  There is evidence that shift work contributes to excess cardiovascular mortality. The purpose of this study was to determine the effects of shift work on heart rate-corrected QT (QTc) and blood pressure in relation to heart rate variability (CV(RR)).
  
  
  METHODS
  The study population consisted of 153 male shiftworkers and 87 male day workers who were employed at a copper-smelting plant. The QTc interval, total power spectral density (t-PSD) of 100 RR intervals, PSDs with frequencies of 0.01 Hz-0.15 Hz and 0.15 Hz-0.40 Hz (PSD(LF) and PSD(HF)), CV(RR), low frequency (LF) component variability and high frequency (HF) component variability (CCV(LF) and CCV(HF)) and %LF (PSD(LF)/(PSD(LF)+PSD(HF)) .100) were measured (LF and HF components are thought to reflect the sympathetic and parasympathetic activities, respectively).
  
  
  RESULTS
  The QTc interval was significantly longer in the shiftworkers than in the day workers, although there was no significant difference in systolic or diastolic blood pressure between the two groups. Also, the CCV(LF) and log(PSD(LF)) were significantly depressed in the shiftworkers. In the day workers, the QTc interval was significantly related to the CV(RR), log(t-PSD), CCV(HF), log(PSD(HF)),%LF, and log(LF/HF ratio) (partial correlation coefficient r=-0.305, -0.377, -0.312, -0.355, 0.297, and 0.277, respectively). In the shiftworkers only two relations of the QTc interval to non-specific CV(RR) and log(t-PSD) were significant.
  
  
  CONCLUSIONS
  The clear association between long QTc interval and reduced parasympathetic activity observed in the day workers did not exist in the shiftworkers. Rather, the shiftworkers had a selective reduction in sympathetic drive, which may have compensated for prolonged QTc interval due to shift work. On the other hand, the impact of shift work on hypertension remains unclear, although reduced sympathetic drive in the shiftworkers may explain the absence of differences in blood pressure between shiftworkers and day workers to some extent.
authors.affiliation: Division of Environmental Health Sciences, Department of Social Medicine, Akita University School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan. winestem@med.akita-u.ac.jp
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Murata
authors.forename: Eiji
authors.initials: E
authors.lastname: Yano
authors.forename: Hideki
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Kanae
authors.initials: K
authors.lastname: Karita
authors.forename: Miwako
authors.initials: M
authors.lastname: Dakeishi
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007564:Japan; D008297:Male; D008875:Middle Aged; D016272:Occupational Health; D010808:Physical Examination; D014940:Work Schedule Tolerance / Q000502:physiology*