Significance of Small Airway Tests in Middle-Aged Smokers1–3

In 54 asymptomatic lifelong nonsmokers and 105 current smokers, all steelworkers 45 to 55 yr of age, we measured several lung function indexes in order to assess the significance of small airway tests, slope of phase III of the N2 single-breath washout (ΔN2), and bolus closing volume and closing capacity (CC/TLC). Smokers had all mean indexes significantly different from nonsmokers, with CC/TLC and ΔN2 being the most frequently impaired tests. Smokers with small airway disease (abnormal CC/TLC or ΔN2) but normal forced expiratory volume in one second (FEV1) / vital capacity had a significantly lower FEV1 / height3 (p < 0.001) than subjects without small airway disease. The latter had indexes similar to nonsmokers. Our data suggested that smokers with small airway disease experience a more rapid decline in their FEV1 and thus are more susceptible to long-term smoking than smokers without small airway disease. The latter appear to be resistant to tobacco-induced chronic airflow obstruction.