Small airways in fibrosing alveolitis

Pulmonary function, including lung elastic recoil, was measured in 9 subjects with fibrosing alveolitis. Closing volume and upstream conductance were studied to assess small airway function. Lung volumes, diffusing capacity, and transfer coefficient were decreased. Peak expiratory flow and the ratio of 1-sec forced expiratory volume to forced vital capacity were normal, whereas total lung resistance was low, suggesting that large airways were not narrowed. Lung elastic recoil was increased, but the changes could be accounted for by the loss of lung volume. Closing volume and closing capacity were increased when expressed as a percentage of vital capacity and total lung capacity, respectively; but again, this could be accounted for by the decrease in lung volume, because the absolute lung volume at which airway closure occurred was normal. Upstream conductance was not reduced. We conclude that there is no evidence of narrowing of functional small airways in ventilated parts of the lung. The mechanical findings are compatible with the patchy involvement seen pathologically in fibrosing alveolitis.