DEPENDENCE OF COLLATERAL AND SMALL AIRWAY RESISTANCES OF CO2 AND VOLUME IN DOG LOBES

We examined the hypothesis that collateral channels were identical wit hin small airways and ducts, therefore both should respond similarly t o chemical and mechanical stresses. A double lumen catheter was wedged into a segmental bronchus of the dog and humidified air or 10% CO2 in air (Vs) flowed at a segmental bronchial pressure (Pb) of 2 cm H2O. A small circular area about 1 cm diameter was peeled from the wedged se gment and covered with a capsule glued to the surrounding pleura for m easuring either a small airway flow (Vsaw) or capsule pressure (Pcap). Collateral resistance (Rcoll) and small airway resistance (Rsaw) were calculated as Rcoll = Pb/(Vs - Vsaw), Rsaw = (Pb-Pcap)/Vsaw, respecti vely. Hypocapnia (air) resulted in increases in Rcoll and Rsaw, while hypercapnia (10% CO2) generally had the opposite effect. Gcoll and Gsa w both increased linearly with lung volume (VL). The pattern of the re sponses of Rsaw closely paralleled those of Rcoll to local hypercapnia and hypocapnia, and to changing VL, implying that the major sites of resistance along collateral channels and along the airways are functio nally and structurally similar.