[Measurement of airway resistance by an interrupter technique in anesthetized dogs during methacholine induced...

Airway resistance was measured by an interrupter technique in anesthetized and paralyzed dogs. Bronchoconstriction was then induced by the inhalation of methacholine hydrochloride at a concentration of 25 or 50 mg . ml-1 for ten minutes. Airway resistance was measured again immediately after the inhalation of methacholine and 50 minutes later. Under normal conditions, airway resistance increased with a linear relationship to the expiratory airflow as expressed by a function of Y = K1 + K2X. K1 and K2 were calculated by a least square method. As a result, K1 increased markedly immediately after the inhalation of methacholine and returned to the control level thereafter. However, it was still higher than the control 50 minutes later. On the other hand, no statistically significant changes were observed because the changes in K2 were variable. In some cases, K2 increased, while in others it was unchanged. K2 decreased in more cases, however, and a negative value was often seen. This inverse correlation between flow and resistance was supposed to reflect the occurrence of small airway obstructions during the end expiratory phase. Therefore, it was considered that this method is capable of detecting small airway abnormalities which could not be detected by %FEV1.0.