title: Imaging the interaction of atelectasis and overdistension in surfactant-depleted lungs.
abstract: OBJECTIVE
  Atelectasis and surfactant depletion may contribute to greater distension-and thereby injury-of aerated lung regions; recruitment of atelectatic lung may protect these regions by attenuating such overdistension. However, the effects of atelectasis (and recruitment) on aerated airspaces remain elusive. We tested the hypothesis that during mechanical ventilation, surfactant depletion increases the dimensions of aerated airspaces and that lung recruitment reverses these changes.
  
  
  METHODS
  Prospective imaging study in an animal model.
  
  
  METHODS
  Research imaging facility.
  
  
  METHODS
  Twenty-seven healthy Sprague Dawley rats.
  
  
  METHODS
  Surfactant depletion was obtained by saline lavage in anesthetized, ventilated rats. Alveolar recruitment was accomplished using positive end-expiratory pressure and exogenous surfactant administration.
  
  
  RESULTS
  Airspace dimensions were estimated by measuring the apparent diffusion coefficient of He, using diffusion-weighted hyperpolarized gas magnetic resonance imaging. Atelectasis was demonstrated using computerized tomography and by measuring oxygenation. Saline lavage increased atelectasis (increase in nonaerated tissue from 1.2% to 13.8% of imaged area, p < 0.001), and produced a concomitant increase in mean apparent diffusion coefficient (~33%, p < 0.001) vs. baseline; the heterogeneity of the computerized tomography signal and the variance of apparent diffusion coefficient were also increased. Application of positive end-expiratory pressure and surfactant reduced the mean apparent diffusion coefficient (~23%, p < 0.001), and its variance, in parallel to alveolar recruitment (i.e., less computerized tomography densities and heterogeneity, increased oxygenation).
  
  
  CONCLUSIONS
  Overdistension of aerated lung occurs during atelectasis is detectable using clinically relevant magnetic resonance imaging technology, and could be a key factor in the generation of lung injury during mechanical ventilation. Lung recruitment by higher positive end-expiratory pressure and surfactant administration reduces airspace distension.
authors.affiliation: Department of Anesthesiology and Critical Care and Stavropoulos Sepsis Research Program, University of Pennsylvania, Philadelphia, PA, USA. maurizio.cereda@uphs.upenn.edu
authors.forename: Maurizio
authors.initials: M
authors.lastname: Cereda
authors.forename: Kiarash
authors.initials: K
authors.lastname: Emami
authors.forename: Yi
authors.initials: Y
authors.lastname: Xin
authors.forename: Stephen
authors.initials: S
authors.lastname: Kadlecek
authors.forename: Nicholas N
authors.initials: NN
authors.lastname: Kuzma
authors.forename: Puttisarn
authors.initials: P
authors.lastname: Mongkolwisetwara
authors.forename: Harrilla
authors.initials: H
authors.lastname: Profka
authors.forename: Stephen
authors.initials: S
authors.lastname: Pickup
authors.forename: Masaru
authors.initials: M
authors.lastname: Ishii
authors.forename: Brian P
authors.initials: BP
authors.lastname: Kavanagh
authors.forename: Clifford S
authors.initials: CS
authors.lastname: Deutschman
authors.forename: Rahim R
authors.initials: RR
authors.lastname: Rizi
mesh_terms: D000818:Animals; D018893:Bronchoalveolar Lavage; D038524:Diffusion Magnetic Resonance Imaging; D004195:Disease Models, Animal; D008168:Lung / Q000378:metabolism / Q000473:pathology; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D011650:Pulmonary Alveoli / Q000473:pathology*; D001261:Pulmonary Atelectasis / Q000473:pathology*; D011663:Pulmonary Surfactants / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014057:Tomography, X-Ray Computed; D055397:Ventilator-Induced Lung Injury
chemical_list: D011663:Pulmonary Surfactants