title: Modeling the effects of exercise during 100% oxygen prebreathe on the risk of hypobaric decompression sickness.
abstract: BACKGROUND
  Several previous studies indicated that exercise during prebreathe with 100% O2 decreased the incidence of hypobaric decompression sickness (DCS). We report a meta-analysis of these investigations combined with a new study in our laboratory to develop a statistical model as a predictive tool for DCS.
  
  
  OBJECTIVE
  Exercise during prebreathe increases N2 elimination in a theoretical 360-min half-time compartment decreasing the incidence of DCS.
  
  
  METHODS
  A dose-response probability tissue ratio (TR) model with 95% confidence limits was created for two groups, prebreathe with exercise (n = 113) and resting prebreathe (n = 113), using nonlinear regression analysis with maximum likelihood optimization.
  
  
  RESULTS
  The model predicted that prebreathe exercise would reduce the residual N2 in a 360-min half-time compartment to a level analogous to that in a 180-min compartment. This finding supported the hypothesis. The incidence of DCS for the exercise prebreathe group was significantly decreased (Chi-Square = 17.1, p < 0.0001) from the resting prebreathe group.
  
  
  CONCLUSIONS
  The results suggested that exercise during prebreathe increases tissue perfusion and N2 elimination approximately 2-fold and markedly lowers the risk of DCS. Based on the model, the prebreathe duration may be reduced from 240 min to a predicted 91 min for the protocol in our study, but this remains to be verified. The model provides a useful planning tool to develop and test appropriate prebreathe exercise protocols and to predict DCS risks for astronauts.
authors.affiliation: KRUG Life Sciences Inc., Houston, TX 77058, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Loftin
authors.forename: J
authors.initials: J
authors.lastname: Conkin
authors.forename: M R
authors.initials: MR
authors.lastname: Powell
mesh_terms: D002985:Clinical Protocols; D003665:Decompression Sickness / Q000209:etiology / Q000517:prevention & control*; D004305:Dose-Response Relationship, Drug; D005081:Exercise Therapy / Q000379:methods*; D006801:Humans; D015994:Incidence; D016013:Likelihood Functions; D010102:Oxygen Inhalation Therapy / Q000379:methods*; D011237:Predictive Value of Tests; D012044:Regression Analysis; D015203:Reproducibility of Results; D013997:Time Factors; D014018:Tissue Distribution