Localization of airway constriction using gases of varying density and viscosity

The relationship between the major site of airway constriction and change in total pulmonary resistance while breathing gases of varying density and viscosity was studied in five anesthetized dogs pretreated with atropine. Using an airway catheter, central and peripheral components of pulmonary resistance were measured by forced oscillation. Total pulmonary resistance was measured at 0.5 1/s with lungs air-filled, at 0.25 1/s with the lungs filled with 80% helium-20% oxygen (RL-He), and at 1.0 1/s with 80% sulfur hexafluoride-20% oxygen (RL-SF6). Intravenous histamine infusion resulted in a predominantly peripheral resistance increase as determined by the airway catheter and a much larger percentage increase in RL-He than in RL-SF6. Tracheal banding produced a purely central resistance increase and a greater change in RL-SF6 than in FL-He. These results support theoretical predictions that the predominant site of airways constriction can be determined without on airway catheter by comparing relative changes in total pulmonary resistance using different flow regimes.