Dry air-induced late phase responses in the canine lung periphery

Although controversial, late phase responses in asthmatic subjects have been reported several hours after exercise. We previously showed that exposure to dry air increases collateral system resistance (Rcs) in the canine lung periphery, and produces acute airway responses analogous to those that characterize human exercise-induced asthma. We used a dual wedged bronchoscope technique in anaesthetized male mongrel dogs to monitor Rcs in: 1) control segments continuously exposed to 200 ml·min^-1 of 5% CO₂ in air and 2) dry air challenged segments exposed to 2000 ml·min^-1 5% CO₂ for 5 min. We examined Rcs at 5 min and ~5 h post-challenge in an attempt to document late phase airway obstruction. Five min after dry air challenge Rcs initially increased 114±SE 22%; contralateral control segments remained unchanged (n=9). Five hour post-challenge, Rcs in dry air exposed segments was elevated 81±20% above pre-challenge baseline (p<0.01); contralateral control segments did not change significantly over the 5 h period. Cell profile analyses of lavage samples at 5 hours revealed that neutrophils and eosinophils were significantly increased (p<0.03) in dry air challenged segments when compared to controls. Leukotriene C₄/D₄ concentration in lavage was correlated (p<0.02) with neutrophil infiltration. Thus, we conclude that the canine lung periphery represents a reproducible model of a dry air-induced late phase reaction.