Oscillometry-defined small airway dysfunction as a predictor of moderate-to-severe exacerbations in COPD: a systematic review and meta-analysis

Small airway dysfunction (SAD) is a pivotal feature of chronic obstructive pulmonary disease (COPD), yet spirometry has limited sensitivity for peripheral airway impairment. Oscillometry offers effort-independent assessment of respiratory mechanics during tidal breathing. We systematically reviewed longitudinal studies reporting the association between baseline oscillometry and subsequent moderate-to-severe acute exacerbations (AE) in COPD. Ratio estimates (OR, HR, IRR) were pooled using a DerSimonian–Laird random-effects model, with sensitivity analyses for effect metric, follow-up, study quality and estimate selection. Six studies (1,317 unique patients; follow-up 1–5 years) met inclusion criteria, and four independent cohorts ( n = 1,236) contributed to the meta-analysis. Oscillometry-defined SAD was associated with a higher risk of moderate-to-severe AE (pooled estimate 2.28, 95% CI 1.77–2.94; I² = 0%; 95% prediction interval 1.31–3.98). The association persisted when restricted to hazard and rate ratios (2.23, 95% CI 1.67–2.98) and when the lowest available estimate from each study was pooled (1.60, 95% CI 1.16–2.22). Evidence on discrimination relative to FEV₁ was limited to a single cohort, in which R5–R20 and FEV₁ performed similarly (AUC 0.775 vs. 0.777). Within this small evidence base, oscillometry-defined SAD was associated with exacerbation risk; larger cohorts should define outcome-anchored thresholds and incremental value over spirometry.