Lung function measurement of small airway obstruction in idiopathic interstitial pneumonia

Small airway obstruction in idiopathic interstitial pneumonia was studied in 54 cases of interstitial pneumonia accompanied by restrictive, but not obstructive impairment (%VC less than 80%, FEV1/FVC% greater than 70%). Correlation analysis of %VC showed that small airway obstruction seemed to play a role in the decrease in VC in these cases. Cases were then divided into two groups. In group A, restrictive impairment was caused by the decrease in TLC (%TLC less than 80% & %RV less than 120%) and in group B, it was caused by increase in RV (%TLC greater than 80% & %RV greater than 120). Cases of idiopathic interstitial pneumonia (IIP) were preferentially categorized into group A. Statistical comparison of the lung function measurements revealed that lung parenchyma was altered less severely whereas small airway obstruction was more advanced in group B than group A. Group B was divided into two subgroups, the subgroups of IIP cases and of the other disease cases, and the latter had a larger lung volume and more severely impaired small airway function. Furthermore, IIP cases from group A had less severely altered lung parenchyma than IIP cases from group B. Smoking habits did not seem to be related to these results. The results indicate that in most cases of interstitial pneumonia other than IIP, the lung function was characterized by small airway obstruction rather than decreased lung volume, and some cases of IIP also showed a similar trend. In addition, a long-term study of lung function was made in some cases of interstitial pneumonia and it was shown that small airway obstruction could change in severity after a time interval.