title: Staged decompression to 3.5 psi using argon-oxygen and 100% oxygen breathing mixtures.
abstract: BACKGROUND
  The current extravehicular activity (EVA) space suit at 4.3 psia causes hand and arm fatigue and is too heavy for Martian EVA. A 3.5 psia EVA pressure suit requires increased preoxygenation time but would reduce structural complexity, leak rate, and weight while increasing mobility, comfort, and maintainability. On Mars, nitrogen and argon are available to provide the inert gas necessary for a fire-resistant habitat atmosphere, eliminating need for transport. This study investigated breathing argon/oxygen and 100% oxygen gas mixtures during staged decompression prior to exposure to 3.5 psia.
  
  
  METHODS
  During this study, 40 subjects each completed 3 hypobaric exposures to 3.5 psia for 3 h in a reclined position: (A) a 4-h 25-min 14.7-psia (ground level) denitrogenation (100% oxygen breathing) prior to exposure to 3.5 psia; (B) the same as A, utilizing a 7.3-psia stage denitrogenation; and (C) the same as B, with 62% argon-38% oxygen (ARGOX) during the stage. Venous gas emboli (VGE) were monitored with echocardiography.
  
  
  RESULTS
  Decompression sickness (DCS) incidence at 3.5 psia with ARGOX at 7.3 psia (C) was significantly higher than with oxygen breathing with or without staged decompression: there was 78% DCS for C compared with 33% and 55% DCS, respectively, for A and B. The corresponding VGE incidences were 73% (C) compared with 33% (A) and 45% (B).
  
  
  CONCLUSIONS
  Preoxygenation at a 7.3-psia stage resulted in a higher DCS risk at 3.5 psia than ground level preoxygenation. It is suggested that an 8.0-psia stage pressure could eliminate this difference. Unfavorable results after preoxygenation with ARGOX indicate argon on-gassing was significant.
authors.affiliation: Biodynamics and Protection Division, Air Force Research Laboratory, Brooks City-Base, San Antonio, TX 78235-5105, USA. andrew.pilmanis@brooks.af.mil
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Pilmanis
authors.forename: Ulf I
authors.initials: UI
authors.lastname: Balldin
authors.forename: James T
authors.initials: JT
authors.lastname: Webb
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Krause
mesh_terms: D000293:Adolescent; D000328:Adult; D000337:Aerospace Medicine; D001128:Argon / Q000008:administration & dosage*; D001272:Atmosphere; D003664:Decompression; D003665:Decompression Sickness / Q000503:physiopathology*; D004618:Embolism, Air / Q000209:etiology / Q000517:prevention & control; D005676:Gravity Suits; D006801:Humans; D008297:Male; D018535:Mars; D008875:Middle Aged; D010102:Oxygen Inhalation Therapy; D012307:Risk Factors
chemical_list: D001128:Argon