Effects of inhaled steroids on methacholine-induced bronchoconstriction and gas trapping in mild asthma

According to a recent hypothesis, airway smooth muscle regulates airway cal ibre mostly at high lung volume, whereas the mucosa and adventitia dimensio ns dominate at low lung volumes. It was thought that if inhaled steroids de crease the thickness of airway wall in asthma, then forced vital capacity ( FVC), which reflects the functional changes at low lung volume, should decr ease less during induced bronchoconstriction than flow at high volume. The study was conducted in 31 mild asthmatics under control conditions and during a methacholine challenge before and after 4-weeks treatment with inh aled fluticasone dipropionate (1.5 mg daily, 16 patients) or placebo (15 pa tients). After fluticasone dipropionate treatment, control forced expiratory volume in one second (FEV1), and maximal flow at 50% of control FVC during forced expiration after a maximal (V'max,50) and a partial inspiration (V'p,50) si gnificantly increased. During methacholine challenge, PVC decreased less th an did FEV1 or V'max,50, and so did inspiratory vital capacity compared to V'p,50, Both the provocative dose of methacholine causing a 20% fall in FEV 1 and the bronchodilator effect of deep inhalation significantly increased. The latter was assessed by means of the regression coefficient of all V'ma x,50 plotted against V'p,50. No significant changes in these parameters occ urred after placebo, These data show that inhaled steroids remarkably blunt the occurrence of ga s trapping during induced bronchoconstriction in mild bronchial asthma, pos sibly due to their effect on airway wall remodelling.