Bronchial length behavior with respect to lung volume histories in different bronchial sizes in excised dog lungs

The bronchial length behavior of three different-sized segments in seven excised dog lobes was examined in terms of the transpulmonary pressure (PL)-bronchial length relationship and the absolute lung volume (VL)-bronchial length relationship during lung inflation and deflation. The straight bronchi of the right lower lobes were used and the bronchial lengths were measured directly and continuously with a linear displacement transducer which was connected by a thin rod to a wedged bead in the bronchi. From PL 30 to 0 cmH2O, the lengths of proximal, intermediate and distal bronchi from the airway opening decreased by 25.2 +/- 4.0%; 36.5 +/- 10.4%; and 37.0 +/- 11.5% (mean +/- S.D.), respectively. Hysteresis of bronchial length existed in the lung volume histories at the same PL, but not at the same VL. With deflation of lung from PL 30 to 0 cmH2O, the more proximal bronchi less changed their length disproportionately with lung volume. It is suggested that nonhomogeneous expansion between lung parenchyma and the bronchi would be more intense in the proximal bronchi than the distal bronchi in terms of bronchial length.