title: Effect of positive end-expiratory pressure on regional ventilation distribution during mechanical ventilation after surfactant depletion.
abstract: BACKGROUND
  Ventilator-induced lung injury occurs due to exaggerated local stresses, repeated collapse, and opening of terminal air spaces in poorly aerated dependent lung, and increased stretch in nondependent lung. The aim of this study was to quantify the functional behavior of peripheral lung units in whole-lung lavage-induced surfactant depletion, and to assess the effect of positive end-expiratory pressure.
  
  
  METHODS
  The authors used synchrotron imaging to measure lung aeration and regional specific ventilation at positive end-expiratory pressure of 3 and 9 cm H2O, before and after whole-lung lavage in rabbits. Respiratory mechanical parameters were measured, and helium-washout was used to assess end-expiratory lung volume.
  
  
  RESULTS
  Atelectatic, poorly, normally aerated, hyperinflated, and trapped regions could be identified using the imaging technique used in this study. Surfactant depletion significantly increased atelectasis (6.3±3.3 [mean±SEM]% total lung area; P=0.04 vs. control) and poor aeration in dependent lung. Regional ventilation was distributed to poorly aerated regions with high (16.4±4.4%; P<0.001), normal (20.7±5.9%; P<0.001 vs. control), and low (5.7±1.2%; P<0.05 vs. control) specific ventilation. Significant redistribution of ventilation to normally aerated nondependent lung regions occurred (41.0±9.6%; P=0.03 vs. control). Increasing positive end-expiratory pressure level to 9 cm H2O significantly reduced poor aeration and recruited atelectasis, but ventilation redistribution persisted (39.2±9.5%; P<0.001 vs. control).
  
  
  CONCLUSIONS
  Ventilation of poorly aerated dependent lung regions, which can promote the local concentration of mechanical stresses, was the predominant functional behavior in surfactant-depleted lung. Potential tidal recruitment of atelectatic lung regions involved a smaller fraction of the imaged lung. Significant ventilation redistribution to aerated lung regions places these at risk of increased stretch injury.
authors.affiliation: Université de Picardie Jules Verne, EA4285 Péritox-INERIS and Pediatric Lung Function Laboratory, CHU Amiens, Amiens, France.
authors.forename: Sam
authors.initials: S
authors.lastname: Bayat
authors.forename: Liisa
authors.initials: L
authors.lastname: Porra
authors.forename: Gergely
authors.initials: G
authors.lastname: Albu
authors.forename: Heikki
authors.initials: H
authors.lastname: Suhonen
authors.forename: Satu
authors.initials: S
authors.lastname: Strengell
authors.forename: Pekka
authors.initials: P
authors.lastname: Suortti
authors.forename: Anssi
authors.initials: A
authors.lastname: Sovijärvi
authors.forename: Ferenc
authors.initials: F
authors.lastname: Peták
authors.forename: Walid
authors.initials: W
authors.lastname: Habre
mesh_terms: D000818:Animals; D018893:Bronchoalveolar Lavage; D002245:Carbon Dioxide / Q000097:blood; D007091:Image Processing, Computer-Assisted; D008168:Lung / Q000000981:diagnostic imaging; D008176:Lung Volume Measurements; D008297:Male; D010100:Oxygen / Q000097:blood; D011175:Positive-Pressure Respiration; D001261:Pulmonary Atelectasis / Q000503:physiopathology; D011663:Pulmonary Surfactants / Q000378:metabolism*; D011817:Rabbits; D012121:Respiration, Artificial; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics; D017356:Synchrotrons; D014057:Tomography, X-Ray Computed
chemical_list: D011663:Pulmonary Surfactants; D002245:Carbon Dioxide; D010100:Oxygen