title: Positive expiratory pressure improves oxygenation in healthy subjects exposed to hypoxia.
abstract: BACKGROUND
  Positive end-expiratory pressure (PEEP) is commonly used in critical care medicine to improve gas exchange. Altitude sickness is associated with exaggerated reduction in arterial oxygenation. We assessed the effect of PEEP and pursed lips breathing (PLB) on arterial and tissue oxygenation under normobaric and hypobaric hypoxic conditions.
  
  
  METHODS
  Sixteen healthy volunteers were exposed to acute normobaric hypoxia (Laboratory study, FiO₂=0.12). The protocol consisted in 3-min phases with PEEPs of 0, 5 or 10 cmH₂O, PLB or similar ventilation than with PEEP-10, interspaced with 3-min phases of free breathing. Arterial (pulse oximetry) and quadriceps (near-infrared spectroscopy) oxygenation, ventilation, cardiac function, esophageal and gastric pressures and subjects' subjective perceptions were recorded continuously. In addition, the effect of PEEP on arterial oxygenation was tested at 4,350 m of altitude in 9 volunteers breathing for 20 min with PEEP-10 (Field study).
  
  
  RESULTS
  During the laboratory study, PEEP-10 increased arterial and quadriceps oxygenation (arterial oxygen saturation +5.6±5.0% and quadriceps oxyhemoglobin +58±73 µmol.cm compared to free breathing; p<0.05). Conversely, PLB did not increase oxygenation. Oxygenation improvement with PEEP-10 was accompanied by an increase in expiratory esophageal and gastric pressures (esophageal pressure swing +5.4±3.2 cmH₂O, p<0.05) but no change in minute ventilation, breathing pattern, end-tidal CO₂ or cardiac function (all p>0.05) compared to PEEP-0. During the field study, PEEP-10 increased arterial oxygen saturation by +6.7±6.0% after the 3(rd) minute with PEEP-10 without further significant increase until the 20(th) minute with PEEP-10. Subjects did not report any significant discomfort with PEEP.
  
  
  CONCLUSIONS
  These data indicate that 10-cmH₂O PEEP significantly improves arterial and muscle oxygenation under both normobaric and hypobaric hypoxic conditions in healthy subjects. PEEP-10 could be an attractive non-pharmacological tool to limit blood oxygen desaturation and possibly symptoms at altitude.
authors.affiliation: INSERM U1042, Grenoble, France ; University Grenoble Alpes, Hypoxia-Physiopathology Laboratory (HP2), Grenoble, France.
authors.forename: Hugo
authors.initials: H
authors.lastname: Nespoulet
authors.affiliation: INSERM U1042, Grenoble, France ; University Grenoble Alpes, Hypoxia-Physiopathology Laboratory (HP2), Grenoble, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Rupp
authors.affiliation: INSERM U1042, Grenoble, France ; University Grenoble Alpes, Hypoxia-Physiopathology Laboratory (HP2), Grenoble, France.
authors.forename: Damien
authors.initials: D
authors.lastname: Bachasson
authors.affiliation: INSERM U1042, Grenoble, France ; University Grenoble Alpes, Hypoxia-Physiopathology Laboratory (HP2), Grenoble, France.
authors.forename: Renaud
authors.initials: R
authors.lastname: Tamisier
authors.affiliation: INSERM U1042, Grenoble, France ; University Grenoble Alpes, Hypoxia-Physiopathology Laboratory (HP2), Grenoble, France.
authors.forename: Bernard
authors.initials: B
authors.lastname: Wuyam
authors.affiliation: INSERM U1042, Grenoble, France ; University Grenoble Alpes, Hypoxia-Physiopathology Laboratory (HP2), Grenoble, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Lévy
authors.affiliation: INSERM U1042, Grenoble, France ; University Grenoble Alpes, Hypoxia-Physiopathology Laboratory (HP2), Grenoble, France.
authors.forename: Samuel
authors.initials: S
authors.lastname: Verges
mesh_terms: D000328:Adult; D000399:Air Pressure; D000704:Analysis of Variance; D006334:Heart Function Tests; D006801:Humans; D000860:Hypoxia / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010100:Oxygen / Q000097:blood / Q000378:metabolism; D011175:Positive-Pressure Respiration / Q000379:methods*; D052097:Quadriceps Muscle / Q000378:metabolism; D012129:Respiratory Function Tests; D019265:Spectroscopy, Near-Infrared
chemical_list: D010100:Oxygen