A canine model of bronchial injury induced by nitric acid. Lung mechanics and morphologic features

We created a model of airway obstruction that avoids long-term toxic exposure. Bronchial injury was induced in 7 dogs by exposure to nebulized 1% nitric acid (HNO3) on alternate days for 4 wk. Lung mechanics were measured prior to exposure and after 2 and 4 wk. Both TLC and VC decreased and the FRC/TLC ratio increased. Expiratory flows decreased while breathing air and an 80% helium-20% oxygen mixture; the volume of isoflow increased. Pulmonary resistance increased and dynamic compliance decreased. On single-breath nitrogen washout, there were increases in the slope of phase III and in closing capacity. Histologically, there was widespread chronic airway inflammation, slight epithelial changes, slight peribronchiolar fibrosis, and an increase in smooth muscle. Pathologic scores were significantly higher in the HNO3-exposed group than in the control group. Scores for peripheral and central airway pathology were correlated with results of tests of airway obstruction.