title: Counteracting effect of head-up tilt on increased femoral venous compliance after simulated weightlessness in rabbits.
abstract: BACKGROUND
  The increased femoral venous compliance is one of the factors of orthostatic intolerance after space flight. The purpose of this study was to observe the effect of daily head-up tilt (HUT) on stress-strain relationship of femoral vein during simulated weightlessness in rabbits.
  
  
  METHODS
  Head-down tilt (HDT) 20 degrees rabbit model was used to simulate weightlessness. Twenty-four healthy male New-Zealand rabbits were randomly divided into three groups: simultaneous control, 21 d HDT, and 21 d HDT plus daily 2 h HUT 45 degrees, with 8 in each. Twenty-one days later, stress-strain relationship of femoral vein was examined.
  
  
  RESULTS
  Under the same stress, the circumferential strain both in the 21 d HDT group and the 21 d HDT plus daily 2 h HUT group increased significantly than those in the control group. There were no significant differences between these two groups. There were no significant changes in the longitudinal strain among three groups under the same stress.
  
  
  CONCLUSIONS
  The femoral venous compliance of rabbits increase significantly after 21 days simulated weightlessness. Daily 2 h HUT 45 degrees could not prevent increase of femoral venous compliance in rabbits induced by 21 days simulated weightlessness.
authors.affiliation: Department of Aeropsace Biodynamics, Fourth Military Medical University, Xi'an, China. sunxiqing@hotmail.com
authors.forename: Xi-Qing
authors.initials: XQ
authors.lastname: Sun
authors.forename: Hui-Pin
authors.initials: HP
authors.lastname: Sun
authors.forename: Yong-Jie
authors.initials: YJ
authors.lastname: Yao
authors.forename: Bing
authors.initials: B
authors.lastname: Wang
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D003187:Compliance; D005268:Femoral Vein / Q000166:cytology* / Q000502:physiology*; D018475:Head-Down Tilt; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D011187:Posture / Q000502:physiology*; D011817:Rabbits; D018474:Weightlessness Simulation