Isovolume pressure-flow relationships in intrapulmonary bronchi of excised dog lungs

From excised dog lungs we isolated airtight the intrapulmonary main bronchi (5-6 cm in length) with beads according to the technique described by Takishima et al. (J. Appl. Physiol. 38: 875-881, 1975), except for the most distal bronchus in which a retrograde catheter was inserted into the pleural surface of the lung. Air flowed from the retrograde catheter to the isolated main lobar bronchi at a given transpulmonary pressure (PL) with variable dynamic rates of driving pressure. We studied isovolume pressure-flow (IVPF) curves in the isolated intrapulmonary bronchi. The IVPF curves showed maximum expiratory flow (Vmax) and negative effort dependence. Vmax increased with increased PL and with increased dynamic rate of driving pressure and decreased with increased peripheral airway resistance added to the retrograde catheter. Bronchograms showed that dynamic compression occurred near the outlet of the isolated bronchi. When the isolated bronchi were dissected free from the surrounding parenchyma, Vmax decreased by 20-30% compared with Vmax in intact bronchi. We concluded that Vmax in intrapulmonary bronchi is preserved by mechanical interdependence between bronchi and parenchyma.