The changes in airways structure associated with reduced forced expiratory volume in one second.

We compared the structure of the membranous and respiratory bronchioles of resected lungs from 111 patients with a normal predicted forced expiratory volume in one second (FEV1) to the structure of these airways from 45 patients with an FEV1 reduced below the 95% confidence limits for height and age. Membranous and respiratory bronchioles of less than 2 mm in internal diameter were counted and their diameter and wall thickness were measured. The data show that there were more membranous bronchioles of internal diameter less than 0.4 mm in patients with reduced FEV1. The wall thickness of respiratory bronchioles was increased in the obstructed group and there was also an increase in the ratio of wall thickness to lumen diameter in these airways. The walls of membranous bronchioles were not increased in thickness but there was an increase in the ratio of wall thickness to lumen diameter. Although the data is consistent with the hypothesis that airways obstruction in patients with chronic obstructive pulmonary disease is due to thickening of the airway wall and narrowing of the airway lumen, we cannot rule out distortion of the membranous bronchioles by loss of elastic recoil.