title: Altitude decompression sickness at 7620 m following prebreathe enhanced with exercise periods.
abstract: BACKGROUND
  Over 80% altitude decompression sickness (DCS) was reported during a 4-h exposure with mild exercise to 7620 m (25,000 ft) without prebreathe. Prebreathe for more than 1 h would be necessary to reduce the DCS risk below 40%. Use of a single period of exercise to enhance prebreathe effectiveness has been successfully tested and used during some U-2 operations. The current tests used multiple exercise sessions to enhance prebreathe (MEEP) as a means of improving denitrogenation efficiency.
  
  
  METHODS
  Two MEEP profiles, 30 or 60 min, preceded 4-h exposures to 7620 m with mild, upper-body exercise while breathing 100% oxygen. Resting prebreathe controls were from published studies at the same laboratory. Both MEEP profiles involved 10 min of strenuous dual-cycle ergometry (75% of maximal oxygen uptake) at the beginning of prebreathe. After a 15-min rest period during the 60-min prebreathe, an additional 5 min of strenuous ergometry was performed. Mild exercise was performed during 15 of the last 20 min of both prebreathe profiles.
  
  
  RESULTS
  The 60-min MEEP resulted in 25% DCS and the 30-min MEEP 40% DCS (N.S.). The 25% incidence of DCS following the 60-min MEEP profile was significantly less than the 63% DCS following an equal-time, resting prebreathe control. Following the 30-min MEEP, DCS incidence was not greater than the incidence following a 60-min, resting prebreathe control. There was a lower incidence of venous gas emboli during the MEEP exposures than during resting control exposures.
  
  
  CONCLUSIONS
  Denitrogenation with multiple periods of exercise provides a shorter alternative to resting prebreathe for reducing DCS risk during exposure to 7620 m.
authors.affiliation: Wyle Laboratories, Life Sciences Systems Service, San Antonio, TX, USA. james.webb@brooks.af.mil
authors.forename: James T
authors.initials: JT
authors.lastname: Webb
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Pilmanis
authors.forename: Ulf I
authors.initials: UI
authors.lastname: Balldin
mesh_terms: D000293:Adolescent; D000328:Adult; D000401:Aircraft; D000531:Altitude; D003665:Decompression Sickness / Q000209:etiology / Q000517:prevention & control*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008889:Military Personnel; D010102:Oxygen Inhalation Therapy; D012307:Risk Factors; D013997:Time Factors