The Relations between Structural Changes in Small Airways and Pulmonary-Function Tests

TLDR

Small‑airway lesions arise from progressive inflammation that leads to fibrosis and connective‑tissue deposition in airway walls. The study aimed to investigate the relationship between small‑airway abnormalities and specific lung functions by performing pulmonary‑function tests on 36 patients shortly before open‑lung biopsy. Lesions were reliably identified using tests for closing capacity and the slope of phase III of the single‑breath washout curve, which assess airway caliber, elastic recoil, and ventilation evenness. Greater small‑airway disease was associated with worsened lung function, and these tests detected abnormalities when pathological changes were still potentially reversible and other tests remained unchanged.

Abstract

To examine the relation between small-airways abnormalities and specific lung functions, we performed pulmonary-function tests in 36 patients, of whom two were nonsmokers, one to three days before open-lung biopsy for localized pulmonary lesions. The primary lesion in the small airways was a progressive inflammatory reaction leading to fibrosis with connective-tissue deposition in the airway walls. Increase in disease in small airways correlated with deterioration in lung function. Lesions could be reliably detected (P less than 0.05) by tests for closing capacity, the volume at which air and helium flow ere equal (a test of airway caliber and elastic recoil), and the slope of phase III of the single-breath washout curve (which tests evenness of ventilation). These tests showed abnormalities at a time when the pathologic changes were still potentially reversible and when other tests were not appreciably changed.