BRONCHOMOTOR AGENTS AND HYSTERESIS OF COLLATERAL RESISTANCE IN DOG LOBE

The effect of smooth muscle tone on hysteresis of collateral channels was examined and compared with that of airways, in freshly excised dog lobes. A double lumen catheter was sealed into a branch off the main bronchus, and air (Vs) flowed through the outer lumen while the pressu re in the segment (Ps) was measured by the inner lumen. Collateral con ductance (Gcoll) was calculated as Gcoll = Vs/Ps. In another series of experiments a pleural capsule was used to measure either segmental ai rway flow (Vsaw) or capsule pressure (Pcap). Segmental airway conducta nce (Gsaw) was calculated as Gsaw = Vsaw/(Ps-Pcap). Hysteresis for Gco ll vs lung volume (VL) curves were almost absent in control and after isoproterenol inflation Gcoll was greater than deflation Gcoll at a gi ven VL (clockwise history). Conversely, after histamine Gcoll vs VL cu rves showed a counterclockwise history. The behaviors of Gcoll and Gsa w against a bronchomotor agent were similar. We conclude that major co llateral channels have muscular walls, and being that of an airway typ e.