title: [Changes of cardiac function during 21 d head-down tilt bed rest and the effect of lower body negative pressure in the last week].
abstract: OBJECTIVE
  To investigate the change of cardiac function during 21 d head-down tilt (HDT) bed rest and the effect of lower body negative pressure (LBNP) in the last week in human.
  
  
  METHODS
  12 healthy male served as subjects which were randomly divided into control and LBNP groups, with 6 in each group. All of them were exposed to -6 degrees HDT for 21 d. The LBNP group received -4.0 kPa LBNP training 1 h/d in the last week of the test. The cardiac pump function and cardiac systole function were measured before, during and after HDT.
  
  
  RESULTS
  Cardiac output, cardiac index and stroke volume decreased significantly, whereas total peripheral resistance, pre-ejection period (PEP), isovolumetric contraction time/left ventricular ejection time (LVET) and PEP/LVET increased significantly during HDT in both control and LBNP groups, compared to pre-HDT values, and they returned to normal level on day 2 post HDT. PEP and PEP/LVET in LBNP group were significantly higher than those in control group on day 21 of HDT and day 2 post HDT.
  
  
  CONCLUSIONS
  The reduction of cardiac pump function and cardiac systole function induced by 21 d HDT could not be prevented by LBNP training in the last week of 21 d HDT.
authors.affiliation: Department of Aerospace Biodynamics, Faculty of Aerospace Medicine, The Fourth Military Medical University, Xi'an, China.
authors.forename: X Q
authors.initials: XQ
authors.lastname: Sun
authors.forename: Y J
authors.initials: YJ
authors.lastname: Yao
authors.forename: X Y
authors.initials: XY
authors.lastname: Wu
authors.forename: W Y
authors.initials: WY
authors.lastname: Hao
authors.forename: S Z
authors.initials: SZ
authors.lastname: Jiang
authors.forename: Z L
authors.initials: ZL
authors.lastname: Qiao
mesh_terms: D000293:Adolescent; D000328:Adult; D001510:Bed Rest; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D002320:Cardiovascular Physiological Phenomena; D018475:Head-Down Tilt; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D013318:Stroke Volume / Q000502:physiology; D013599:Systole / Q000502:physiology; D014655:Vascular Resistance / Q000502:physiology; D018474:Weightlessness Simulation