title: Quantitative assessment of regional alveolar ventilation and gas volume using 13N-N2 washout and PET.
abstract: Measurement of alveolar volume (Va) and regional ventilation (a) is crucial to understanding the pathophysiology of acute lung injury and ventilator-induced lung injury. PET has previously been used as a noninvasive, quantitative method to assess a, but formal validation of this technique in experimental lung injury is lacking. This study aims to validate Va and a regional assessment with PET, using inhaled (13)N-N(2) in pigs.
  
  
  METHODS
  Two normal and 2 oleic acid-injured pigs were tracheotomized, mechanically ventilated, and studied in 5 different levels of ventilation by changing respiratory rate. In each experimental condition, lungs were washed-in and then washed-out with (13)N-N(2) through an open circuit in the ventilator. Using this method, multiframe images were acquired with a dedicated PET camera. Regions of interest (ROIs) were drawn on each lung. Regional time-activity curves during washout were generated for each ROI and fitted to a mono- and a bicompartmental model. Validation of this method was performed in 2 ways. First, regional values of predicted Va (Va(emission)) were compared with regional volume obtained independently from density analysis on a transmission scan (Va(trans)). Second, regional values of predicted a were summed in each animal during each experimental condition and compared with minute-ventilation values set on the ventilator.
  
  
  RESULTS
  The bicompartmental model best fitted the experimental values in normal (94.7% [62.2%-100.0%] (median [interquartile range]) of the ROIs) as well as in injured animals (90.7% [81.6%-97.4%] of the ROIs) (P = 0.49). Va(emission) significantly correlated with Va(trans) (R(2) = 0.89, P < 0.001) but exceeded Va(trans) by 10%. Finally, a strongly and positively correlated with minute-ventilation in both normal (R(2) = 0.96, P < 0.001) and injured (R(2) = 0.96, P < 0.001) animals.
  
  
  CONCLUSIONS
  Measurement of (13)N-N(2) washout using PET is accurate to assess regional alveolar volume and ventilation during experimental acute lung injury.
authors.affiliation: Service de Réanimation Médicale et d'Assistance Respiratoire, Lyon, France.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Richard
authors.forename: Marc
authors.initials: M
authors.lastname: Janier
authors.forename: Franck
authors.initials: F
authors.lastname: Lavenne
authors.forename: Christian
authors.initials: C
authors.lastname: Tourvieille
authors.forename: Didier
authors.initials: D
authors.lastname: Le Bars
authors.forename: Nicolas
authors.initials: N
authors.lastname: Costes
authors.forename: Gerard
authors.initials: G
authors.lastname: Gimenez
authors.forename: Claude
authors.initials: C
authors.lastname: Guerin
mesh_terms: D000280:Administration, Inhalation; D000465:Algorithms; D000818:Animals; D003198:Computer Simulation; D005260:Female; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008657:Metabolic Clearance Rate; D008954:Models, Biological; D009584:Nitrogen / Q000008:administration & dosage / Q000493:pharmacokinetics*; D009590:Nitrogen Radioisotopes; D019301:Oleic Acid; D049268:Positron-Emission Tomography / Q000379:methods; D011650:Pulmonary Alveoli / Q000000981:diagnostic imaging* / Q000187:drug effects / Q000378:metabolism*; D012123:Pulmonary Ventilation; D011865:Radioisotope Dilution Technique; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D012128:Respiratory Distress Syndrome / Q000139:chemically induced / Q000000981:diagnostic imaging* / Q000378:metabolism*; D013552:Swine; D013990:Tidal Volume
chemical_list: D009590:Nitrogen Radioisotopes; D019275:Radiopharmaceuticals; D019301:Oleic Acid; D009584:Nitrogen