Dry air-induced mucosal cell injury and bronchovascular leakage in canine peripheral airways

The purpose of this study was to examine the relationship between hyperpnea-induced mucosal injury, bronchovascular hyperpermeability, and airway reactivity. Hyperpnea-induced bronchoconstriction was assessed by measuring peripheral airway resistance (Rp) in anesthetized mechanically ventilated male mongrel dogs. Either colloidal carbon or monastral blue was used to localize bronchovascular leakage after a 5-min exposure to either a 1000 ml/min dry, 2000 ml/min wet, or 2000 ml/min dry air challenge. Morphometric analyses of cross-sectioned bronchi revealed that hyperpnea with dry air stimulated goblet cell degranulation, damaged the bronchial mucosa, and increased bronchovascular permeability. Exposure to only a 2000 ml/min dry air challenge produced marked mucosal injury when compared with control. Regardless of treatment, bronchial vessels lying below normal mucosa characterized by goblet/ciliated cell (G/C) ratios > or = 0.3 did not leak. A G/C transition zone between 0 and 0.3 separated normal from damaged mucosa. Within this zone, vascular permeability was inversely correlated with G/C ratio. In addition, airflow-induced changes in Rp were inversely related to G/C ratio and positively correlated with bronchovascular leakage. Although these correlations are consistent with the speculation that bronchovascular leakage and edema formation are responsible for the dry air-induced changes in Rp, it is equally plausible that bronchovascular leakage is not the cause of but occurs in concert with airway narrowing to protect cells in the bronchial mucosa from excessive losses of heat and water.