title: First-time imaging of effects of inspired oxygen concentration on regional lung volumes and breathing pattern during hypergravity.
abstract: OBJECTIVE
  Aeroatelectasis can develop in aircrew flying the latest generation high-performance aircraft. Causes alleged are relative hyperoxia, increased gravity in the head-to-foot direction (+Gz), and compression of legs and stomach by anti-G trousers (AGT). We aimed to assess, in real time, the effects of hyperoxia, +Gz accelerations and AGT inflation on changes in regional lung volumes and breathing pattern evaluated in an axial plane by electrical impedance tomography (EIT).
  
  
  METHODS
  The protocol mimicked a routine peacetime flight in combat aircraft. Eight subjects wearing AGT were studied in a human centrifuge during 1 h 15 min exposure of +1 to +3.5Gz. They performed this sequence three times, breathing AIR, 44.5 % O2 or 100 % O2. Continuous recording of functional EIT enabled uninterrupted assessment of regional lung volumes at the 5th intercostal level. Breathing pattern was also monitored.
  
  
  RESULTS
  EIT data showed that +3.5Gz, compared with any moment without hypergravity, caused an abrupt decrease in regional tidal volume (VT) and regional end-expiratory lung volume (EELV) measured in the EIT slice, independently of inspired oxygen concentration. Breathing AIR or 44.5 % O2, sub-regional EELV measured in the EIT slice decreased similarly in dorsal and ventral regions, but sub-regional VT measured in the EIT slice decreased significantly more dorsally than ventrally. Breathing 100 % O2, EELV and VT decreased similarly in both regions. Inspired tidal volume increased in hyperoxia, whereas breathing frequency increased in hypergravity and hyperoxia.
  
  
  CONCLUSIONS
  Our findings suggest that hypergravity and AGT inflation cause airway closure and air trapping in gravity-dependent lung regions, facilitating absorption atelectasis formation, in particular during hyperoxia.
authors.affiliation: Hedenstierna Laboratory, Department of Surgical Sciences, Section of Anaesthesiology & Critical Care, Uppsala University, Uppsala, Sweden, joao.batista_borges@surgsci.uu.se.
authors.forename: João Batista
authors.initials: JB
authors.lastname: Borges
authors.forename: Göran
authors.initials: G
authors.lastname: Hedenstierna
authors.forename: Jakob S
authors.initials: JS
authors.lastname: Bergman
authors.forename: Marcelo B P
authors.initials: MB
authors.lastname: Amato
authors.forename: Jacques
authors.initials: J
authors.lastname: Avenel
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Montmerle-Borgdorff
mesh_terms: D000328:Adult; D005676:Gravity Suits; D006801:Humans; D018471:Hypergravity / Q000009:adverse effects*; D018496:Hyperoxia / Q000503:physiopathology*; D001239:Inhalation; D008168:Lung / Q000187:drug effects / Q000502:physiology*; D008297:Male; D010100:Oxygen / Q000633:toxicity*; D012119:Respiration; D013990:Tidal Volume; D014054:Tomography
chemical_list: D010100:Oxygen