Usefulness of Impulse Oscillometry in Predicting the Severity of Bronchiectasis

Abstract

Background: Bronchiectasis is a chronic respiratory disease that leads to airway inflammation, destruction, and airflow limitation, which reflects its severity. Impulse oscillometry (IOS) is a non-invasive method that uses sound waves to estimate lung function and airway resistance. The aim of this study was to assess the usefulness of IOS in predicting the severity of bronchiectasis.

Methods: We retrospectively reviewed the IOS parameters and clinical characteristics in 145 patients diagnosed with bronchiectasis between March 2020 and May 2021. Disease severity was evaluated using the FACED score, and patients were divided into mild and moderate/severe groups.

Results: Forty-four patients (30.3%) were in the moderate/severe group, and 101 (69.7%) were in the mild group. Patients with moderate/severe bronchiectasis had a higher airway resistance at 5 Hz (R5), a higher difference between the resistance at 5 and 20 Hz (R5-R20), a higher resonant frequency (Fres), and a higher area of reactance (AX) than patients with mild bronchiectasis. R5 ≥0.43, resistance at 20 Hz (R20) ≥0.234, R5-R20 ≥28.3, AX ≥1.02, reactance at 5 Hz (X5) ≤-0.238, and Fres ≥20.88 revealed significant univariable relationships with bronchiectasis severity (p<0.05). Among these, only X5 ≤-0.238 exhibited a significant multivariable relationship with bronchiectasis severity (p=0.039). The receiver operating characteristic curve for predicting moderate- to-severe bronchiectasis of FACED score based on IOS parameters exhibited an area under the curve of 0.809.

Conclusion: The IOS assessed by the disease severity of FACED score can effectively reflect airway resistance and elasticity in bronchiectasis patients and serve as valuable tools for predicting bronchiectasis severity.

Keywords: Bronchiectasis; Disease Severity; Impulse Oscillometry.

Figure 1.

Flowchart of the study patients. IOS: impulse oscillometry.

Figure 2.

Histogram of new bronchiectasis severity scoring based on a cut-off score of 2.3. A bronchiectasis severity model incorporating the impulse oscillometry parameters was developed based on the beta coefficient of the multivariable logistic regression analysis. The scoring system categorized participants into two groups using a cut-off score of 2.3.

Figure 3.

Area under the curve (AUC) based on the new scoring for the severity of bronchiectasis based on the FACED score. The AUCs of the new scoring tool using impulse oscillometry for predicting moderate-to-severe bronchiectasis of FACED scores are 0.823 (training data) and 0.809 (validation data). CI: confidence interval.

Figure 4.

The scatter plots and correlation values between the FACED score and four variations of the iFACED score. “iFACED score” is a data that replaces the forced expiratory volume in 1 second % predicted in the FACED score with the impulse oscillometry parameter. (A) Difference between resistance at 5 and 20 Hz (R5−R20), (B) area of reactance (AX), (C) reactance at 5 Hz (X5), and (D) resonant frequency (Fres).

Figure 5.

The receiver operating characteristic curves and area under the curve (AUC) values for the parameters used in the iFACED, indicating a very strong correlation between the FACED score and the iFACED score with AUC values exceeding 0.9. “iFACED score” is a data that replaces the forced expiratory volume in 1 second % predicted in the FACED score with the impulse oscillometry parameter. CI: confidence interval; AX: area of reactance; Fres: resonant frequency; R5−R20: difference between the resistance at 5 and 20 Hz; X5: reactance at 5 Hz.