title: G protection: interaction of straining maneuvers and positive pressure breathing.
abstract: BACKGROUND
  G protection in the 39 Gripen aircraft is provided by a full coverage anti-G suit, a pressure-breathing system, and anti-G straining maneuvers (AGSM). The purpose was to study (1) the interaction of pressure breathing and AGSM while wearing an anti-G suit; and (2) the G-protective properties of the anti-G suit alone and in combination with the pressure-breathing system.
  
  
  METHODS
  During rapid onset rate G-time profiles (< or =9 G), 10 subjects were investigated in 5 conditions: (I) sitting relaxed, without any G-protective garment; (II) sitting relaxed and wearing an anti-G suit; (III) sitting relaxed, wearing an anti-G suit, and pressure breathing; IV) wearing an anti-G suit and performing AGSM; and V) wearing an anti-G suit, pressure breathing, and performing AGSM. In supplementary experiments (n=9), the share of the anti-G suit protection afforded by the abdominal bladder was investigated.
  
  
  RESULTS
  G tolerance was 3.4 Gz (range: 2.8-4.3) in condition I, > or = 6.5 Gz (4.5-9.0) in II, > or = 8.0 Gz (6.5-9.0) in III, > or = 8.9 Gz (8.5-9.0) in IV and > or = 9.0 Gz (8.5-9.0) in V. In the supplementary experiments, the anti-G suit afforded a 2.8-G protection, a third of which was contributed by the abdominal bladder. In the relaxed state, pressure applied to the airways was transmitted undistorted to the intrathoracic space. During AGSM, intrathoracic pressure rose to 10-14 kPa, regardless of whether AGSM was performed with or without pressure breathing.
  
  
  CONCLUSIONS
  The anti-G suit and the pressure breathing system provide G protection of > or = 4.6 G, of which the anti-G suit contributes about 3.0 G. The C-protective properties of the anti-G suit and those of pressure breathing appears to be additive, whereas the G protection afforded by pressure breathing does not add to that provided by AGSM.
authors.affiliation: Swedish Defence Research Agency, Karolinska Institutet, Stockholm, Sweden. ola.eiken@foi.se
authors.forename: Ola
authors.initials: O
authors.lastname: Eiken
authors.forename: Roger
authors.initials: R
authors.lastname: Kölegärd
authors.forename: Eddie
authors.initials: E
authors.lastname: Bergsten
authors.forename: Mikael
authors.initials: M
authors.lastname: Grönkvist
mesh_terms: D000054:Acceleration / Q000009:adverse effects*; D000328:Adult; D000337:Aerospace Medicine; D000401:Aircraft; D002498:Centrifugation; D006112:Gravitation; D005676:Gravity Suits; D006801:Humans; D018471:Hypergravity / Q000009:adverse effects*; D008297:Male; D011175:Positive-Pressure Respiration; D019442:Space Suits; D013548:Sweden; D013997:Time Factors; D014636:Valsalva Maneuver / Q000502:physiology*