title: A metabolic simulator for unmanned testing of breathing apparatuses in hyperbaric conditions.
abstract: BACKGROUND
  A major part of testing of rebreather apparatuses for underwater diving focuses on the oxygen dosage system.
  
  
  METHODS
  A metabolic simulator for testing breathing apparatuses was built and evaluated. Oxygen consumption was achieved through catalytic combustion of propene. With an admixture of carbon dioxide in the propene fuel, the system allowed the respiratory exchange ratio to be set freely within human variability and also made it possible to increase test pressures above the condensation pressure of propene. The system was tested by breathing ambient air in a pressure chamber with oxygen uptake (Vo₂) ranging from 1-4 L · min(-1), tidal volume (VT) from 1-3 L, breathing frequency (f) of 20 and 25 breaths/min, and chamber pressures from 100 to 670 kPa.
  
  
  RESULTS
  The measured end-tidal oxygen concentration (Fo₂) was compared to calculated end-tidal Fo₂. The largest average difference in end-tidal Fo₂during atmospheric pressure conditions was 0.63%-points with a 0.28%-point average difference during the whole test. During hyperbaric conditions with pressures ranging from 100 to 670 kPa, the largest average difference in Fo₂was 1.68%-points seen during compression from 100 kPa to 400 kPa and the average difference in Fo₂during the whole test was 0.29%-points.
  
  
  CONCLUSIONS
  In combination with a breathing simulator simulating tidal breathing, the system can be used for dynamic continuous testing of breathing equipment with changes in VT, f, Vo2, and pressure.
authors.affiliation: Environmental Physiology Unit at the School of Technology and Health, Royal Institute of Technology KTH, Stockholm, Sweden.
authors.forename: Oskar
authors.initials: O
authors.lastname: Frånberg
authors.forename: Mario
authors.initials: M
authors.lastname: Loncar
authors.forename: Åke
authors.initials: Å
authors.lastname: Larsson
authors.forename: Hans
authors.initials: H
authors.lastname: Ornhagen
authors.forename: Mikael
authors.initials: M
authors.lastname: Gennser
mesh_terms: D001273:Atmosphere Exposure Chambers; D002245:Carbon Dioxide / Q000032:analysis; D004242:Diving; D004867:Equipment Design; D006801:Humans; D008422:Materials Testing; D008954:Models, Biological; D010100:Oxygen / Q000032:analysis; D012119:Respiration; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen