Small Airway Pathology is Related to Increased Closing Capacity and Abnormal Slope of Phase III in Excised Human Lungs1–3

Single-breath nitrogen and static pressure-volume curves were obtained from 29 excised human lungs. The lungs were separated into 2 groups based on values predicted for closing capacity; “normal” lungs (n = 19) had normal closing capacities, and “abnormal” lungs (n = 10) had closing capacities that were larger than normal. Closing pressure (the pressure at the onset of closing capacity) differed between the 2 groups. The group of abnormal lungs had a higher mean closing pressure (2.25 cm H2O) than that of the group of normal lungs (0.98 cm H2O) (p < 0.01). A grading system was used to estimate the extent of pathologic changes in the small airways of each whole lung. Mural inflammation and squamous metaplasia were 2 lesions of the small airways that differed significantly in degree (p < 0.05) between the 2 groups. Data from both groups were combined to determine whether any of the pathologic variables examined were correlated with the data from the single-breath nitrogen curves. Among the small airway lesi...