title: Effects of rapid ascent on the heart rate variability of individuals with and without acute mountain sickness.
abstract: OBJECTIVE
  Through time- and frequency-domain analysis, we compared the effects of acute hypobaric hypoxia on the changes in heart rate variability (HRV) following night sleeping and morning awakening in individuals with and without acute mountain sickness (AMS).
  
  
  METHODS
  Thirty-nine nonacclimatised healthy individuals were transported by bus from sea level to 3150 m within 3 h. Short-term HRV was measured two times a day-before sleeping (BS) and after awakening (AA)- at 3 days before ascent (T0), two consecutive nights at 3150 m (T1 and T2), and 2 days after descent (T3). AMS was diagnosed using the self-reported Lake Louise score questionnaire.
  
  
  RESULTS
  AMS developed in 19 of 39 participants (48.7%). At sea level, individuals had higher HRV at AA than at BS, and the trend of increased HRV at AA remained unchanged at high altitude, irrespective of AMS. At T1 BS, low-frequency power in normalised unit was significantly lower in participants with AMS than in those without AMS. Compared with those at T1 BS, the square root of the mean squared differences of successive normal-normal (NN) intervals, the number of interval differences of successive NN intervals more than 50 ms (NN50), and the proportion derived by dividing NN50 by the total number of NN intervals at T1 AA significantly increased in participants without AMS but nonsignificantly decreased in those with AMS.
  
  
  CONCLUSIONS
  After rapid ascent, individuals with AMS did not demonstrate sympathetic hyperactivity but did exhibit withdrawal of cardiac vagal modulation in the morning following the first night's sleep.
authors.affiliation: Institute of Emergency and Critical Care Medicine, School of Medicine, National Yang-Ming University, #155 Section 2, Linong Street, Taipei, 112, Taiwan, Republic of China.|Department of Chest Medicine, Taipei Veterans General Hospital, #201 Section 2, Shih-Pai Road, Taipei, 112, Taiwan, Republic of China.
authors.forename: Ming Ling
authors.initials: ML
authors.lastname: Yih
authors.affiliation: Department of Chest Medicine, Taipei Veterans General Hospital, #201 Section 2, Shih-Pai Road, Taipei, 112, Taiwan, Republic of China.|Department of Medicine, School of Medicine, National Yang-Ming University, Taipei, Taiwan, Republic of China.
authors.forename: Fang-Chi
authors.initials: FC
authors.lastname: Lin
authors.affiliation: Department of Chest Medicine, Taipei Veterans General Hospital, #201 Section 2, Shih-Pai Road, Taipei, 112, Taiwan, Republic of China.|Department of Medicine, School of Medicine, National Yang-Ming University, Taipei, Taiwan, Republic of China.|Institute of Biomedical Informatics, National Yang-Ming University, Taipei, Taiwan, Republic of China.
authors.forename: Heng-Sheng
authors.initials: HS
authors.lastname: Chao
authors.affiliation: Department of Nursing, Taipei Veterans General Hospital, Taipei, Taiwan, Republic of China.
authors.forename: Han-Chen
authors.initials: HC
authors.lastname: Tsai
authors.affiliation: Institute of Emergency and Critical Care Medicine, School of Medicine, National Yang-Ming University, #155 Section 2, Linong Street, Taipei, 112, Taiwan, Republic of China. scchang@vghtpe.gov.tw.|Department of Chest Medicine, Taipei Veterans General Hospital, #201 Section 2, Shih-Pai Road, Taipei, 112, Taiwan, Republic of China. scchang@vghtpe.gov.tw.
authors.forename: Shi-Chuan
authors.initials: SC
authors.lastname: Chang
mesh_terms: D000064:Acclimatization; D000328:Adult; D000532:Altitude Sickness / Q000503:physiopathology*; D016022:Case-Control Studies; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D014630:Vagus Nerve / Q000502:physiology
keywords: Acute hypobaric hypoxia; Acute mountain sickness; Frequency domain analysis; Heart rate variability; Time domain analysis