title: Effects of cold exposure on autonomic changes during the last rapid eye movement sleep transition and morning blood pressure surge in humans.
abstract: BACKGROUND
  Various studies have linked the occurrence of cardiovascular events and low ambient temperatures as well as the morning blood pressure surge (MBPS). We hypothesized that low ambient temperatures produce a higher sympathetic change during the last rapid eye movement (REM) sleep transition and that this may play an important role in cold-related cardiovascular events.
  
  
  METHODS
  All experiments were carried out on 12 healthy male adults, aged 24.00±0.74 years, who participated in two experimental conditions randomly (>1 day apart): warm (23 °C) and cold (16°C). Blood pressure (BP) was measured every 30 min for 24 h by autonomic ambulatory BP monitoring. The electroencephalograms, electrocardiograms, ambient temperature, near-body temperature, and physical activity were recorded by miniature polysomnography for 24 h.
  
  
  RESULTS
  The cold conditions resulted in: (i) higher MBPS than under warm conditions; (ii) significant and greater sympathetic index changes during the sleep-wake transition than during cover-to-uncover and supine-to-sit position tests; (iii) the non-REM-REM transition-related sympathetic elevation during the cold conditions being significantly higher in late sleep period than in early sleep period; (iv) at 1h prior to morning awakening, the value of total power of heart rate variability changes being significantly negatively correlated with the changes of near-body temperature; and (v) significantly higher arousal index and shorter average interval of REM periods than in warm conditions.
  
  
  CONCLUSIONS
  Cold exposure elevates the amplitude of MBPS and is associated with late sleep stage transition sympathetic activation, which might have important implications for cold-related cardiovascular events.
authors.affiliation: Sleep Research Center, School of Medicine, National Yang-Ming University, Taipei, Taiwan; Institute of Brain Science, School of Medicine, National Yang-Ming University, Taipei, Taiwan; Institute of Biophotonics, School of Medicine, National Yang-Ming University, Taipei, Taiwan; Department of Education and Research, Taipei City Hospital, Taipei, Taiwan.
authors.forename: Terry B J
authors.initials: TB
authors.lastname: Kuo
authors.affiliation: Sleep Research Center, School of Medicine, National Yang-Ming University, Taipei, Taiwan; Institute of Brain Science, School of Medicine, National Yang-Ming University, Taipei, Taiwan.
authors.forename: Cian-Hui
authors.initials: CH
authors.lastname: Hong
authors.affiliation: Sleep Research Center, School of Medicine, National Yang-Ming University, Taipei, Taiwan; Institute of Brain Science, School of Medicine, National Yang-Ming University, Taipei, Taiwan; Institute of Biophotonics, School of Medicine, National Yang-Ming University, Taipei, Taiwan.
authors.forename: I-Te
authors.initials: IT
authors.lastname: Hsieh
authors.affiliation: Institute of Brain Science, School of Medicine, National Yang-Ming University, Taipei, Taiwan; Faculty of Medicine, School of Medicine, National Yang-Ming University, Taipei, Taiwan; Department of Education and Research, Taipei City Hospital, Taipei, Taiwan.
authors.forename: Guo-She
authors.initials: GS
authors.lastname: Lee
authors.affiliation: Sleep Research Center, School of Medicine, National Yang-Ming University, Taipei, Taiwan; Institute of Brain Science, School of Medicine, National Yang-Ming University, Taipei, Taiwan; Department of Education and Research, Taipei City Hospital, Taipei, Taiwan. Electronic address: cchyang@ym.edu.tw.
authors.forename: Cheryl C H
authors.initials: CC
authors.lastname: Yang
mesh_terms: D001341:Autonomic Nervous System / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology; D003080:Cold Temperature; D006801:Humans; D008297:Male; D017286:Polysomnography; D012895:Sleep, REM / Q000502:physiology*; D055815:Young Adult
keywords: Cold exposure; Heart rate variability; Morning blood pressure surge; NREM–REM transition; Near-body temperature; Sleep