On the functional consequences of bronchial basement membrane thickening

Reticular basement membrane (RBM) thickness and airway responses to inhaled methacholine (MCh) were studied in perennial allergic asthma (n = 11), per ennial allergic rhinitis (n = 8), seasonal allergic rhinitis (n = 5), and c hronic obstructive pulmonary disease (COPD, n = 9). RBM was significantly t hicker in asthma (10.1 +/- 3.7 mum) and perennial rhinitis (11.2 +/- 4.2 mu m) than in seasonal rhinitis (4.7 +/- 0.7 mum) and COPD (5.2 +/- 0.7 mum). The dose (geometric mean) of MCh causing a 20% decrease of 1-s forced expir atory volume (FEV1) was significantly higher in perennial rhinitis (1,073 m ug) than in asthma (106 mug). In COPD, the slope of the linear regression o f all values of forced vital capacity plotted against FEV1 during the chall enge was higher, and the intercept less, than in other groups, suggesting e nhanced airway closure. In asthma, RBM thickness was positively correlated (r = 0.77) with the dose (geometric mean) of MCh causing a 20% decrease of FEV1 and negatively correlated (r = -0.73) with the forced vital capacity v s. FEV1 slope. We conclude that 1) RBM thickening is not unique to bronchia l asthma, and 2) when present, it may protect against airway narrowing and air trapping. These findings support the opinion that RBM thickening repres ents an additional load on airway smooth muscle.