Quantitative assessment of regional alveolar ventilation and gas volume using 13N-N2 washout and PET.
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.
Richard
Jean-Christophe
JC
Service de Réanimation Médicale et d'Assistance Respiratoire, Lyon, France.
Janier
Marc
M
Lavenne
Franck
F
Tourvieille
Christian
C
Le Bars
Didier
D
Costes
Nicolas
N
Gimenez
Gerard
G
Guerin
Claude
C
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
D009590:Nitrogen Radioisotopes; D019275:Radiopharmaceuticals; D019301:Oleic Acid; D009584:Nitrogen