Bifurcated sleep in night shift workers alters circadian relationships in cardiovascular and temperature rhythms

Abstract Shift workers are faced with sleep deficits and circadian disruption, a risk factor for hypertension. We recorded daily rhythms of body temperature and blood pressure (BP) of 28 healthy healthcare workers using thermometers and ambulatory BP monitors, respectively. Participants worked in in regular day (D) shift, regular night (N) shift or rotational shift (RS, i.e., RD/RN during day/night shift) work routines. Different shift regimes had variable effects on sleep quality and duration, thus affecting the waveform of daily BP/temperature rhythms. Therefore, this study aimed to assess circadian misalignment of BP/temperature rhythms under shift-work regimes. In D, 8-h night sleep and robust bimodal rhythmic patterns in SBP, DBP and temperature were observed. Among shift workers, N exhibited bifurcated sleep with long work-hour naps commensurate to the daily peak and dip in BP/temperature. The amplitude of the daily rhythm of BP and temperature was dampened in RS. Overall, cardiovascular rhythm disruption was greater in SBP than in DBP. RS exhibited higher temperatures throughout day-night shifts. Sleep bifurcation, although it immediately recompenses sleep deficits, may be associated with altered circadian waveforms of physiological rhythms, rendering long-term health consequences.