title: Alterations in feline tracheal permeability after mechanical ventilation.
abstract: OBJECTIVE
  Previous investigations of ventilator-induced airway injury focused on histopathologic changes associated with various ventilators and strategies for their use. We hypothesized that mechanical ventilation is associated with alterations in tracheal epithelial permeability, and designed a study using an animal model to evaluate changes in tracheal epithelial permeability after administering different types of mechanical ventilation to test this hypothesis.
  
  
  METHODS
  Prospective, multiple-group, controlled trial. Five groups of animals were studied and compared. Eight animals were studied without intubation or mechanical ventilation. A total of 28 animals (seven in each group) were studied after conventional mechanical ventilation, high-frequency positive-pressure ventilation, high-frequency jet ventilation, or high-frequency flow interruption at respiratory rates of 20, 150, 400, and 900 breaths/min, respectively. Comparison of data for each group was done using the Kruskall-Wallis analysis of variance. Between-group comparisons were made using standard error of the mean comparisons. For airway pressures and other physiologic data, one-way analysis of variance was performed. Between-group comparisons were made using the Student-Newman-Keuls' test.
  
  
  METHODS
  Small animal physiology laboratory.
  
  
  METHODS
  Thirty-six adult cats.
  
  
  METHODS
  Mechanically ventilated animals were treated for 8 hrs and then killed. Inspired oxygen concentration, BP, and mean airway pressures were comparable in mechanically ventilated animals. Spontaneously breathing control animals were killed without endotracheal intubation or exposure to mechanical ventilation.
  
  
  RESULTS
  Permeability values in isolated tracheal segments were calculated for 14C-sucrose, 3H-inulin, and fluorescein isothiocyanate-dextran-20. Tracheal epithelial permeability to all studied molecules increased after exposure to mechanical ventilators. These different mechanical ventilators increased epithelial permeability in a progressive manner that paralleled ventilatory frequency. The changes were greatest after ventilation at the highest frequency. These observed changes in tracheal permeability are consistent with previously observed alterations in tracheal histopathology after exposure to mechanical ventilation.
  
  
  CONCLUSIONS
  Mechanical ventilation was associated with increases in tracheal permeability to large and small nonionic molecules. These changes occurred with all studied ventilators, used as they are clinically. Permeability changes paralleled ventilatory rate changes.
authors.affiliation: Infant Pulmonary Research Center, Children's Hospital of St. Paul, University of Minnesota, Minneapolis.
authors.forename: R C
authors.initials: RC
authors.lastname: Maynard
authors.forename: O D
authors.initials: OD
authors.lastname: Wangensteen
authors.forename: J E
authors.initials: JE
authors.lastname: Connett
authors.forename: K K
authors.initials: KK
authors.lastname: Holloman
authors.forename: S J
authors.initials: SJ
authors.lastname: Boros
authors.forename: M C
authors.initials: MC
authors.lastname: Mammel
mesh_terms: D000818:Animals; D002415:Cats; D004848:Epithelium / Q000378:metabolism; D006611:High-Frequency Jet Ventilation / Q000009:adverse effects; D006612:High-Frequency Ventilation / Q000009:adverse effects; D010539:Permeability; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000009:adverse effects*; D014132:Trachea / Q000293:injuries / Q000378:metabolism*