Assessing Pulmonary Pathology by Detailed Examination of Respiratory Function

Pulmonary inflammation causes multiple alterations within the lung, including mucus production, recruitment of inflammatory cells, and airway hyperreactivity (AHR). Measurement of AHR by direct, invasive means (eg, mechanical ventilation) or noninvasive techniques, like whole body plethysmography (WBP), assesses the severity of pulmonary inflammation in animal models of inflammatory lung disease. Direct measurement of AHR is acknowledged as the most accurate method for assessing airway mechanics, but analysis of all data obtained from WBP may offer insights into which inflammatory aspects of the lung are altered along with AHR. Using WBP, we compared the respiratory parameters of two groups of mice sensitized with cockroach allergen. One group was treated with dexamethasone (Dex) before final challenge (Dex-Asthma), while the other group received vehicle treatment (Asthma). Respiratory parameters from plethysmography revealed that Dex-Asthma mice compensated to maintain high minute ventilation, whereas Asthma mice showed significant impairment in minute ventilation despite increased peak expiratory flow (103 ± 5 ml/min vs. 69 ± 70 ml/min). The WBP data suggest that enhanced air exchange in the Dex-Asthma mice results from significant decreases in airway mucus production. Additional studies with quantitative morphometry of histological sections confirmed that Dex reduced airway mucus. In conclusion, a detailed examination of WBP parameters can accurately assess the respiratory health of mice and will help direct additional studies.