Small Airways of the Lung

Abstract

Recent findings have emphasized the importance of the bronchiole to the function of the lung. The surface of the bronchiole differs from that of the alveolus. Rather than being covered by a thin coat of phospholipid, the surface is covered with cilia that are surrounded by a low-viscosity fluid. This permits the removal of foreign particles. Surface forces are important to the function of the bronchiole. The diameter of the bronchiole is a function of the volume of the lung. When the lung is partially collapsed, the bronchiole acts as a capillary tube and is readily obstructed by fluid. In chronic bronchitis, obstruction is related to narrowing by fibrosis and inflammation, alteration in the secretion, and loss of traction on the walls. Obstruction of the bronchiole by fluid in edema of the lung contributes to hypoxemia. Positive end expiratory pressure may prevent obstruction by increasing the bronchiolar diameter.