Current status of small airways disease

There is very convincing evidence that inflammatory changes in the small airways are common in cigarette smokers, but do not necessarily lead to emphysema which is usually the cause of the clinical condition of chronic airflow obstruction. The tests of small airway function appear to be quite sensitive for detecting early airflow obstruction which is probably synonomous with inflammatory disease in the small airways. The relatively high sensitivity of the tests of small airway function is not, however, matched by a high specificity or a high predictive value in identifying the individual who is going to progress from mild airflow obstruction to clinical airflow obstruction. This is probably because inflammatory disease in the small airways, although associated with emphysema in that both conditions are found in cigarette smokers, is not causally related to emphysema. The tests of small airway function still have an important place in epidemiologic studies and in other research studies. Clinically, the measurements obtained from the spirogram and from the MEFV curve are useful in identifying the individual with mild airflow obstruction. The single breath N₂ test and the MEFV curve breathing gases of different densities, on the other hand, are still largely research tools and will probably remain so unless it can be clearly demonstrated that they have a high predictive value identifying the individual who is most likely to progress to chronic airflow obstruction.