Diagnostic accuracy of respiratory impedance parameters to detect airflow obstruction in adults

OBJECTIVE: The present study was aimed to evaluate the diagnostic accuracy of impedance parameters to detect airflow obstruction and the severity of airflow obstruction in adults. METHODS: The spirometry parameters (forced expiratory volume in 1 s [FEV1], forced vital capacity [FVC], FEV1/FVC, FVC3/FVC, and FEF25-75) and respiratory impedance parameters (R5, R19, R5-19, and X5) measured by forced oscillation technique of consecutive 299 adults (male: 186) were included in the present analysis. The Spearman correlation coefficient (ρ) was used to assess the correlations of impedance parameters with spirometry indices. The area under the curve (AUC) was used to assess respiratory impedance parameters' diagnostic accuracy. RESULTS: The mean age of the study population was 54.1 ± 12.3 years, and 99 individuals (33%) had airflow obstruction (FEV1/FVC < 0.70) in spirometry. All spirometry indices (% of predicted) showed a weak negative correlation with R5, R19, R5-19, and weak positive correlation with X5. The R5 >142% predicted and X5 >136% predicted had the maximum AUC (0.75) with a sensitivity of up to 56% and specificity up to 86% to identify airflow obstruction. The impedance parameters showed low concordance with the severity of airflow obstruction. CONCLUSION: Respiratory impedance parameters had insufficient sensitivity to diagnose airflow obstruction and the severity of obstruction in adults. Thus, impedance parameters cannot a substitute for spirometry in diagnosing obstructive lung function.