Effect of inhaled corticosteroids on small airways in asthma: Investigation using impulse oscillometry

BackgroundSmall airways appear to have an important role in asthma. Hydrofluoroalkane-134a beclomethasone dipropionate (HFA-BDP) has ultrafine particles and accordingly greater deposition in the small airways than chlorofluorocarbon (CFC)-BDP. Impulse oscillometry systems (IOS), a new and non-invasive measure of pulmonary function, can examine the resistance of total (R5), large (R20), and small airways (R5–R20) separately, and low-frequency reactance area (AX), also considered a measure of small airways dysfunction.MethodsMild-to-moderate asthmatics who were inhaled corticosteroid naïve were randomized to receive 200 mcg HFA-BDP bid (n = 26) or 400 mcg CFC-BDP bid (n = 12) for 12 weeks in an open-label manner. Following baseline measurements, IOS and spirometry were repeated every 4 weeks, and methacholine challenge to separately assess airway sensitivity and airway reactivity and lung volumes at 12 weeks.ResultsModerate correlations were found between R5–R20 or AX and spirometry and lung volume indices of small airways, and between R20 and peak expiratory flow at baseline. The two groups did not significantly differ in baseline clinical or functional parameters. At 12 weeks, all IOS indices improved in the HFA-BDP group, whereas all but R5–R20 improved with CFC-BDP. R5–R20 and AX progressively improved with HFA-BDP; these changes achieved statistical significance at 12 weeks versus the CFC-BDP group. Other IOS and spirometry indices failed to show such trends. HFA-BDP significantly attenuated methacholine airway sensitivity; the degree of this attenuation strongly correlated with R5–R20 and AX baseline values, and with improvement of AX with treatment.ConclusionHFA-BDP is an effective treatment of small airways in asthma. Prolonged treatment provides a progressive effect over time, which is associated with an attenuation of airway responsiveness.