Dependence of collateral and small airway resistances of CO 2 and volume in dog lobes

Abstract

We examined the hypothesis that collateral channels were identical within small airways and ducts, therefore both should respond similarly to chemical and mechanical stresses. A double lumen catheter was wedged into a segmental bronchus of the dog and humidified air or 10% CO 2 in air (V̇s) flowed at a segmental bronchial pressure (Pb) of 2 cm H 2O. A small circular area about 1 cm diameter was peeled from the wedged segment and covered with a capsule glued to the surrounding pleura for measuring either a small airway flow (V̇saw) or capsule pressure (Pcap). Collateral resistance (Rcoll) and small airway resistance (Rsaw) were calculated as Rcoll = Pb/(V̇s − V̇saw), Rsaw = (Pb-Pcap)/V̇saw, respectively. Hypocapnia (air) resulted in increases in Rcoll and Rsaw, while hypercapnia (10% CO 2) generally had the opposite effect. Gcoll and Gsaw both increased linearly with lung volume (V l). The pattern of the responses of Rsaw closely paralleled those of Rcoll to local hypercapnia and hypocapnia, and to changing V l, implying that the major sites of resistance along collateral channels and along the airways are functionally and structurally similar.