Supplementary Material for: Clinical value of impulse oscillometry in chronic obstructive pulmonary disease: a systematic review and meta-analysis

Introduction: Impulse oscillometry (IOS) is an effortless test compared to spirometry. Numerous studies explored the role of IOS in spirometry-based chronic obstructive pulmonary disease (COPD), but most of them had limited sample sizes with poor statistical power. This systematic review and meta-analysis aimed to pool the individual data and quantitatively analyze the clinical value of IOS in COPD.
Methods: PubMed, Web of Science, Ovid, Cochrane Library, China National Knowledge Internet and Wanfang were searched for studies with comparisons of IOS indicators between COPD patients and healthy controls, including respiratory resistance at 5Hz (R5) and 20Hz (R20), difference between R5 and R20 (R5-R20), respiratory reactance at 5 Hz (X5), resonant frequency (Fres), and area of reactance (Ax). Meta-analyses were conducted to calculate the weighted mean differences (WMDs) and 95% confidence intervals (CIs).
Results: 39 eligible studies were enrolled, involving 6144 COPD patients and 4611 healthy controls. Relative to healthy controls, COPD patients had significantly higher R5 (WMD: 0.17, 95% CI: 0.14, 0.20), R5-R20 (WMD: 0.13, 95% CI: 0.11, 0.15), Fres (WMD: 9.04, 95% CI: 7.66, 10.42), Ax (WMD: 1.24, 95% CI: 0.86, 1.61) and lower X5 (WMD: -0.15, 95% CI: -0.18, -0.11), and such differences became even greater as the Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage escalated. Pooled correlation coefficients presented that R5, R5-R20, Fres and X5 were significantly related to post-bronchodilator forced expiratory volume in the first second (FEV1)/forced vital capacity (FVC) ratio (meta r = -0.37, -0.45, -0.53 and 0.42 respectively) and FEV1 as a percentage of predicted value (FEV1% pred) (meta r = -0.43, -0.54, -0.59 and 0.56 respectively).
Conclusion: IOS may be a supplement to spirometry in diagnosing and assessing COPD, especially when spirometry is inappropriate. More well-designed, large sample sized, prospective studies are warranted to establish an IOS-based criterion for COPD management.