title: Pressure breathing without a counter-pressure vest does not impair acceleration tolerance up to 9 G.
abstract: BACKGROUND
  This study was to determine whether safe and adequate G-protection by pressure breathing during G (PBG) could be maintained if the COMBAT EDGE counter-pressure vest were eliminated to ensure aircrew do not unnecessarily endure a possible in-flight discomfort or distraction.
  
  
  METHODS
  Centrifuge exposures up to +9 Gz were completed by 11 subjects, including 5 F-15 aircrew, using PBG at 60 mmHg pressure with and without the counter-pressure vest. Additional G-exposures using pressures of 0, 30, and 45 mmHg were performed without the vest.
  
  
  RESULTS
  Elimination of the COMBAT EDGE counter-pressure vest did not significantly reduce G-tolerance. During gradual onset G exposure, the mean G level reached with PBG was 8.4 G without the vest and 8.2 G with the vest. In comparison, 6.7 G was reached without PBG. Mean times at G with rapid onset G exposure were 59 and 60 s, respectively, compared with 49 s without PBG. PBG, with or without the vest, was preferred by all test subjects. PBG at 60 mmHg produced the highest G protection and was preferred by the test subjects over lesser pressures. Subjects reported no adverse effects from the use of PBG without chest counter-pressure.
  
  
  CONCLUSIONS
  The use of PBG and the anti-G straining manuever (AGSM) together enhances G tolerance and comfort more than AGSM alone. Elimination of the counter-pressure vest during use of PBG does not hinder an individual's ability to reach +9 Gz or complete a short duration simulated aerial combat maneuver G exposure. Further research is needed to determine if use of PBG without chest counter-pressure increases fatigue during multiple sorties or produces other aeromedical problems in operational environments.
authors.affiliation: Wyle Laboratories, AFRL/HEP, Brooks City-Base, TX 78235-5105, USA. ulf.balldin@brooks.af.mil
authors.forename: Ulf I
authors.initials: UI
authors.lastname: Balldin
authors.forename: Robert B
authors.initials: RB
authors.lastname: O'Connor
authors.forename: Wayne M
authors.initials: WM
authors.lastname: Isdahl
authors.forename: Paul M
authors.initials: PM
authors.lastname: Werchan
mesh_terms: D000054:Acceleration; D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D001274:Atmospheric Pressure; D005260:Female; D005676:Gravity Suits; D006801:Humans; D018471:Hypergravity; D008297:Male; D017060:Patient Satisfaction; D012143:Respiratory Physiological Phenomena; D013647:Task Performance and Analysis