Small airway dimension and size distribution in human lungs with an increased closing capacity

Pulmonary function tests were obtained in 7 emphysema-free and 27 emphysematous lungs with minimal small airway disease. The lungs were divided into 2 groups on the basis of whether they had a small or large, i.e., increased closing capacity. The lungs were subsequently fixed and the small airways (less than or equal to 2.00 mm) from 6 to 10 blocks of tissue were counted and inside diameters were measured. There was a significant increase in the number of airways measuring 0.40 mm or less (p less than 0.03) and a decrease of airways measuring 0.81 to 1.0 mm (p less than 0.03) in the lungs that had larger closing capacities. When the data of both groups were combined there was a negative correlation between the mean bronchiole inside diameter as a function of the percentage of predicted closing capacity (r = -0.381, p less than 0.03) and a positive correlation between small airway inside diameter and the forced expiratory volume in one second (r = 0.595, p less than 0.001) and the maximal mid-expiratory flow rate (r = 0.527, p less than 0.01). We conclude that in lungs that are normal or involved with minimal lung disease, function can be related to the caliber of the small airways.