title: Bench testing of a new hyperbaric chamber ventilator at different atmospheric pressures.
abstract: OBJECTIVE
  Providing mechanical ventilation is challenging at supra-atmospheric pressure. The higher gas density increases resistance, reducing the flow delivered by the ventilator. A new hyperbaric ventilator (Siaretron IPER 1000) is said to compensate for these effects automatically. The aim of this bench test study was to validate the compensation, define its limits and provide details on the ventilator's output at varied atmospheric pressures.
  
  
  METHODS
  Experiments were conducted inside a multiplace hyperbaric chamber at 1, 2.2, 2.8 and 4 atmospheres absolute (ATA), with the ventilator connected to a test lung. Transducers were recalibrated at each ATA level. Various ventilator settings were tested in volume and pressure control modes. Measured tidal volumes were compared with theoretical predictions based on gas laws.
  
  
  RESULTS
  Results confirmed the ventilator's ability to provide compensation, but also identified its limits. The compensation range could be predicted and depended on the maximal flow attainable, decreasing linearly with increasing atmospheric pressure. With settings inside the range, tidal volumes approximated set values (mean error 10 ± 5 %). With settings outside the range, the volume was limited to the predicted maximal value calculated from maximal flow. A practical guide for clinicians is provided.
  
  
  CONCLUSIONS
  The IPER 1000 ventilator attempted to deliver stable tidal volume by adjusting the opening of the inspiratory valve in proportion to atmospheric pressure. Adequate compensation was observed, albeit only within a predictable range, which can be reliably predicted for each setting and ATA level combination. Setting a tidal volume outside this range can result in an unwanted decrease in minute ventilation.
authors.affiliation: Intensive Care Department, Geneva University Hospital, 4 Rue Gabrielle Perret-Gentil, 1211, Genève 14, Switzerland. jclefebvre31@hotmail.com
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Lefebvre
authors.forename: Aissam
authors.initials: A
authors.lastname: Lyazidi
authors.forename: Miguel
authors.initials: M
authors.lastname: Parceiro
authors.forename: Giuseppe F
authors.initials: GF
authors.lastname: Sferrazza Papa
authors.forename: Evangelia
authors.initials: E
authors.lastname: Akoumianaki
authors.forename: Deborah
authors.initials: D
authors.lastname: Pugin
authors.forename: Didier
authors.initials: D
authors.lastname: Tassaux
authors.forename: Laurent
authors.initials: L
authors.lastname: Brochard
authors.forename: Jean-Christophe M
authors.initials: JC
authors.lastname: Richard
mesh_terms: D001273:Atmosphere Exposure Chambers; D001274:Atmospheric Pressure; D006801:Humans; D006931:Hyperbaric Oxygenation / Q000295:instrumentation*; D007320:Inspiratory Capacity; D013990:Tidal Volume; D012122:Ventilators, Mechanical