title: Changes in the lung after prolonged positive pressure ventilation in normal baboons.
abstract: OBJECTIVE
  The effects of prolonged positive pressure ventilation on lung ultrastructure are not well defined in primates. This study was designed to measure cardiopulmonary and morphological responses to 4 days of positive pressure ventilation in normal baboons.
  
  
  METHODS
  Six adult male baboons were mechanically ventilated on air for 96 hours with 2.5 cm positive end-expiratory ventilation and a tidal volume of 12 to 15 mL/kg. Physiological measurements were obtained every 12 hours and serial measurements of ventilation-perfusion (VA/Q) were performed using the multiple inert gas elimination technique. Quantitative morphotometry, lung dry-to-wet ratio, and surfactant analysis were performed at the end of the experiment.
  
  
  RESULTS
  Cardiovascular variables, except for a small increase in mean pulmonary artery pressure at 84 and 96 hours, were not significantly affected by positive pressure ventilation. Arterial Po2 decreased, and shunt fraction increased from 0.7% of cardiac output to 5.4% (P < .01). Dispersion of perfusion increased threefold (P < .01), and dispersion of ventilation doubled (P < .01) indicating increased VA/Q mismatch mismatch. Respiratory system compliance decreased by 30% (P < .01). There was no lung edema or change in surfactant composition. Lung morphometry showed increases in polymorphonuclear cells and type II cell volume. Vacuolated endothelial cells and bare basement membrane were observed consistently.
  
  
  CONCLUSIONS
  Four days of positive pressure ventilation decreases lung compliance and worsens gas exchange by increasing shunt and VA/Q mismatch in healthy baboons. These effects are accompanied by only minor ultrastructural changes and mild inflammatory responses in the lung.
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: S G
authors.initials: SG
authors.lastname: Simonson
authors.forename: Y C
authors.initials: YC
authors.lastname: Huang
authors.forename: P J
authors.initials: PJ
authors.lastname: Fracica
authors.forename: K E
authors.initials: KE
authors.lastname: Welty-Wolf
authors.forename: R E
authors.initials: RE
authors.lastname: Moon
authors.forename: S L
authors.initials: SL
authors.lastname: Young
authors.forename: C A
authors.initials: CA
authors.lastname: Piantadosi
mesh_terms: D000818:Animals; D001485:Basement Membrane / Q000648:ultrastructure; D001706:Biopsy; D001784:Blood Gas Analysis; D018893:Bronchoalveolar Lavage; D002855:Chromatography, Thin Layer; D004797:Enzyme-Linked Immunosorbent Assay; D008168:Lung / Q000502:physiology* / Q000601:surgery; D008297:Male; D008854:Microscopy, Electron; D010101:Oxygen Consumption; D010215:Papio; D010743:Phospholipids / Q000032:analysis; D011175:Positive-Pressure Respiration; D011506:Proteins / Q000032:analysis; D011669:Pulmonary Wedge Pressure; D012121:Respiration, Artificial; D013990:Tidal Volume
chemical_list: D010743:Phospholipids; D011506:Proteins