Are we overlooking persistent small airways dysfunction in community-managed asthma?
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Background Whether small airways dysfunction persists in patients with asthma receiving standard community treatment is unknown. Impulse oscillometry (IOS) is a sensitive measure of small airways function. Objective To assess the degree of small airways dysfunction in a cross-section of patients with community-managed asthma. Methods We analyzed primary care referral data from patients with persistent asthma (n = 378) receiving standard community therapy, screened using spirometry and IOS. We compared patients by British Thoracic Society asthma treatment step (2–4). Results Step 2 patients were not different from step 3 patients receiving long-acting beta-agonist (LABA). Step 4 patients differed from step 2 by: higher inhaled corticosteroid (ICS) dose (P < .0001); lower forced expiratory volume in 1 second (FEV1%; P = .02) and forced mid-expiratory flow (FEF25–75%; P = .001); higher frequency of resonance (Fres; P = .02) and peripheral airway resistance (R5-R20; P = .006); whereas for steps 3 vs 4 there were differences in Fres (P < .05) and R5-R20 (P = .006). There were high proportions of abnormality for R5-R20 (>0.03 kPa/L/s) at steps 2, 3, and 4, respectively: 64.6%, 63.5%, and 69.9%. Step 2 patients receiving extra-fine particle ICS demonstrated lower total airway resistance at 5Hz (R5) vs patients receiving standard ICS (124.1% vs 138.3%, P < .05), with no difference in FEV1. At step 4, R5 remained elevated at 141.3% despite concomitant LABA, with only 2.4% using extra-fine ICS. Conclusion Persistent small airways dysfunction occurs despite treatment at steps 2 through 4 of current asthma guidelines. Extra-fine ICS may reduce airway resistance at step 2. Prospective studies with extra-fine ICS ± LABA at steps 2 through 4 are required to discern whether improving small airways function might result in long-term improved control.