title: [Repeated body position change training can improve human head-down tilt tolerance].
abstract: OBJECTIVE
  To verify the hypothesis that repeated body position change training can improve human head-down tilt (HDT) tolerance.
  
  
  METHODS
  Six young healthy subjects were trained with repeated position change for 9 times and 11 days according to protocol of alternative head-down and head-up tilts, each time of training lasted for about 35 min. Their HDT tolerance (- 30 degrees/30 min) were determined before and after training.
  
  
  RESULTS
  (1) Compared with the data before training, subjects' symptom scores during HDT test after training decreased significantly (6.00 +/- 3.79 vs 1.00 +/- 0.63, P < 0.05), magnitude of the decreased heart rate increased significantly (-0.6 +/- 2.5 vs -4.4 +/- 3.6, P < 0.01). (2) Before training, blood flow volume of internal jugular vein (IJV) during HDT decreased significantly and that of internal carotid artery (ICA) increased significantly at the beginning period of HDT compared with pre-HDT (P < 0.01), while blood flow volume of the common carotid artery (CCA) presented increasing trend. After training, there was no significant difference in blood flow volume of IJV between during HDT and pre-HDT, that of ICA and CCA presented decreasing trend in the final period of HDT compared with Pre-HDT.
  
  
  CONCLUSIONS
  Repeated body position change training can improve human head-down tilt tolerance. And its main causation is that headward shift of blood volume is restrained to some extend during HDT after training.
authors.affiliation: Department of Aerospace Medicine, Fourth Military Medical University, Xi'an 710032, China. wubinacc@sina.com
authors.forename: Bin
authors.initials: B
authors.lastname: Wu
authors.forename: Ping
authors.initials: P
authors.lastname: Wu
authors.forename: Yue-Ying
authors.initials: YY
authors.lastname: Xue
authors.forename: Xing-Hua
authors.initials: XH
authors.lastname: Liu
authors.forename: Yan-Lei
authors.initials: YL
authors.lastname: Wang
authors.forename: Shi-Zhong
authors.initials: SZ
authors.lastname: Jiang
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000293:Adolescent; D018480:Astronauts; D002320:Cardiovascular Physiological Phenomena; D018475:Head-Down Tilt; D006801:Humans; D008297:Male; D011187:Posture / Q000502:physiology*; D018474:Weightlessness Simulation; D055815:Young Adult