INCREASED MAXIMAL AIRWAY RESPONSE TO METHACHOLINE DURING SEASONAL ALLERGIC RHINITIS IN NONASTHMATIC SUBJECTS - RELATIONSHIPS WITH AIRWAY WALL THICKNESS AND INFLAMMATION

This study was carried out to determine whether the increase in airway responsiveness induced by natural antigenic exposure in nonasthmatic subjects is associated with an increase in maximal bronchoconstrictor response (MBR), and if these changes could be due to an increase in airway wall thickness from allergen-induced increase in airway inflammation. In 11 nonasthmatic subjects with seasonal allergic rhinitis, a methacholine challenge was obtained monthly, during and out of pollen exposure, Each subject had a high-resolution chest tomography in and out of the pollen season, to determine the relative thickness of the right intermediary bronchus over its total diameter (T/D), as well as inflammatory cell counts, apparent basement membrane thickness as an indication of subepithelial fibrosis and epithelial desquamation in bronchial biopsy specimens. In season, the mean provocative concentration of methacholine producing a 20% decrease in forced expiratory volume in one second (PC20) decreased from 51.5 to 25.8 mg . mL(-1), and the maximal post-methacholine fall in forced expiratory volume in one second (Delta FEV1,max) or forced vital capacity (Delta FVC) and the slope of the dose response curve (DRS) increased compared with out of season: Delta FEV1,max 44+/-5 vs 25+/-5%; Delta FVC 34+/-5 vs 16+/-4%; and slope of DRS 14.1+/-2.8 vs 6.9+/-1.3%/mg . ml(-1). No significant change was observed in T/D ratio, The seasonal change in Delta FVC was positively correlated with the Delta FEV1,max (rs=0.891) and the change in DRS (rs=0.909), but not with the change in PC20, nor with changes in bronchial biopsy inflammatory features or T/D ratio. In conclusion, we found an increase in airway responsiveness and maximal bronchoconstrictor response after natural allergen exposure in nonasthmatic rhinitic patients, However, there was no significant increase in bronchial inflammatory features or large airway wall thickness, This could indicate that the statistical power of this study is limited, or alternatively, that the small airways are more important in determining the physiological responses to pollen exposure.