title: Long-duration head-down bed rest: project overview, vital signs, and fluid balance.
abstract: BACKGROUND
  Spaceflight has profound effects on the human body. Many of these effects can be induced with head-down bed rest, which has been a useful ground-based analog. With limited resources aboard the International Space Station for human research, the bed rest analog will be a primary platform on which countermeasures will be developed and tested for lunar and Mars mission scenarios.
  
  
  METHODS
  NASA Johnson Space Center, in conjunction with the University of Texas Medical Branch (UTMB), has created the NASA Flight Analogs Project (FAP), a research program with the overall objective of using head-down bed rest to evaluate, compare, and refine candidate countermeasures to spaceflight deconditioning. This paper serves as an overview and describes the standard conditions, the standard set of subject screening criteria, and the standard set of measurements for all FAP bed rest subjects.
  
  
  RESULTS
  Heart rate and diastolic pressures decreased transiently at the onset of bed rest. Fluid balance showed an early diuresis, which stabilized within 3 d. In this supplement, detailed results from multiple disciplines are presented in a series of reports.
  
  
  CONCLUSIONS
  The following reports describe multi-disciplinary results from the standard measurements by which the responses to bed rest will be assessed and by which countermeasures will be evaluated. The data presented in this overview are meant to serve as a context in which to view the data presented in the discipline specific manuscripts. The dietary support and behavioral health papers provide additional information regarding those aspects of implementing bed rest studies successfully.
authors.affiliation: HumanAdaptation and Countermeasures Division, NASA Johnson Space Center, Houston, TX 77058, USA. janice.v.meck@nasa.gov
authors.forename: Janice V
authors.initials: JV
authors.lastname: Meck
authors.forename: Sherlene A
authors.initials: SA
authors.lastname: Dreyer
authors.forename: L Elisabeth
authors.initials: LE
authors.lastname: Warren
mesh_terms: D000328:Adult; D000337:Aerospace Medicine; D001510:Bed Rest; D001794:Blood Pressure; D005260:Female; D018475:Head-Down Tilt / Q000502:physiology; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D011446:Prospective Studies; D013026:Space Flight; D013781:Texas; D013997:Time Factors; D014481:United States; D018557:United States National Aeronautics and Space Administration; D014882:Water-Electrolyte Balance