Usefulness of the forced oscillation technique in diagnosing asthma-COPD overlap syndrome

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Introduction: Distinguishing asthma from COPD, especially in smokers and older adults, can be difficult; hence, determining clinical parameters that differentiate asthma, asthma-COPD overlap syndrome (ACOS), and COPD is essential to achieve successful treatment. Aims and objectives: We hypothesized that the forced oscillation technique (FOT) could differentiate ACOS form asthma and COPD. In this cross-sectional study, we assessed the usefulness of FOT in diagnosing ACOS. Methods: Spirometry, FOT (MostGraph-01), and fractional exhaled nitric oxide (FeNO) measurement were performed in asthma (117), ACOS (41), and COPD (44) patients. Asthma patients fulfilled the definition of GINA guidelines (regardless of FEV1/FVC values; smoking history, <10 pack-years). COPD patients fulfilled the definition of GOLD guidelines (FEV1/FVC, <0.7; smoking history, ≥10 pack-years). ACOS was diagnosed if asthma patients had FEV1/FVC <0.7 and smoking history ≥10 pack-years or COPD patients had FEV1/FVC <0.7 and FeNO >50 ppb without receiving inhaled corticosteroids. Results: ROC curve analyses for diagnosing asthma and COPD revealed that the areas under the curve of resistance at 20 Hz (R20) and the difference between inspiratory and expiratory reactance at 5 Hz (ΔX5) were largest (0.632 and 0.720, respectively) with the best cut-off values (2.710 and 0.221 cmH2O/L/s, respectively). The accuracy of the diagnosis of ACOS based on these cut-off values (R20 <2.710 and ΔX5 <0.221 cmH2O/L/s) was as follows: odds ratio, 3.97; 95% confidence interval, 1.84 to 8.72; sensitivity 58.5%; and specificity, 87.5%. Conclusions: Combined assessment of resistance and reactance may be useful in diagnosing ACOS.