Effect of lung surface tension on bronchial collapsibility in excised dog lungs

Bronchial collapsibilities were studied in air- and saline-filled excised dog lungs. The intrapulmonary bronchi were isolated from the rest of the lung parenchyma with beads placed at their tributary bronchi as described previously by Takishima et al. (J. Appl. Physiol. 38: 875-881, 1975). Pressure-volume relations of the isolated bronchi were obtained while lung volume (VL) was kept constant. When lung recoil pressure (PL) was reduced by filling the lung with saline at a given VL, bronchial areas were smaller and bronchial collapsibilities were larger than in the air-filled lung. When bronchial areas and bronchial collapsibilities in air- and saline-filled lungs were compared at a given PL, they were approximately identical. We concluded that bronchial areas and collapsibilities were primarily determined by PL rather than VL, and lung surface tension itself made bronchial collapsibility equal to or even less than the degree of collapsibility due to forces applied from surrounding lung tissues that distended the bronchi.