Stability of intrapulmonary bronchial dimensions during expiratory flow in excised lungs

The length and diameter of intrapulmonary airways (4.8-9.0 mm ID) were measured from tantalum bronchograms in lobes of excised dog lungs. Twenty retrograde catheters were inserted into the lobe around the perimeter and airflow passed from the periphery to the lobar cannula. During expiratory flow the lateral intrabronchial pressure (Pib) in the larger airways was lowered relative to alveolar pressure (Palv) keeping lung volume constant. Airway dimensions were compared under no flow (static) conditions when Pib = Palv, and during expiratory flow (dynamic) with Pib < Palv. When Palv was held constant at +5 or +10 cmH₂O the change of bronchial diameter per unit change of Pib was significantly less than under static conditions, suggesting that the parenchyma confers a stiffness upon intrapulmonary airways during expiratory flow by virtue of tissue attachments. Interdependence of airway and airspace expansion was less at low lung recoil pressures. At isovolume it was estimated that peribronchial pressures decreased relative to pleural pressure by up to 10 cmH₂O. There was no reduction in length as Pib was lowered at constant lung volume.