The Role of Impulse Oscillometry in Evaluating Disease Severity and Predicting the Airway Reversibility in Patients With Bronchiectasis

Abstract

Background: Impulse oscillometry (IOS) can be used to evaluate airway impedance in patients with obstructive airway diseases. Previous studies have demonstrated that IOS parameters differ between patients with bronchiectasis and healthy controls. This study aims to explore the usefulness of IOS in assessing disease severity and airway reversibility in patients with bronchiectasis.

Method: Seventy-four patients with non-cystic fibrosis bronchiectasis who visited our Respiratory Medicine outpatient clinic were consecutively recruited. Spirometry, plethysmography and IOS tests were performed. Patients were stratified into mild, moderate and severe disease according to Reiff, Bhalla, BSI, FACED, and BRICS scores. Airway reversibility was measured by bronchodilation test (BDT) and the result was classified as positive or negative. ROC curves of IOS parameters were used to assess the usefulness of IOS parameters in predicting airway reversibility. Correlations between the IOS, spirometric lung function and bronchiectasis severity parameters were analyzed.

Results: Many IOS parameters, such as airway resistance at 5 Hz (R5), small airways resistance (R5-R20), total airway reactance (X5), resonance frequency (Fres), total airway impedance at 5 Hz (Z5), and peripheral resistance (Rp) increased in patients with bronchiectasis who presented a moderate to severe severity as categorized by the FACED, BSI and Reiff scores. Large airway resistance (R20) and central resistance (Rc) were not significantly different among groups with different bronchiectasis severity. The difference between R5 and R20 (R5-R20) showed 81.0% sensitivity, and 69.8%specificity in predicting the airway reversibility in bronchiectasis with AUC of 0.794 (95%CI, 0.672-0.915).

Conclusion: IOS measurements are useful indicators of bronchiectasis severity and may be useful for predicting the airway reversibility.

Keywords: airway reversibility; bronchiectasis; impulse oscillometry; plethysmography; spirometry.

Figure 1

Results of respiratory impedance at rest stratified by different bronchiectasis severity scores (n = 74). (A–H) Correspond to the modified Reiff score, (I–P) correspond to the BSI score, and (Q–X) correspond to the FACED score. R5, respiratory system resistance at 5 Hz; R20, respiratory system resistance at 20 Hz; X5, respiratory system reactance at 5 Hz; Fres, resonant frequency; Z5, respiratory impedance; Rc, central resistance; and Rp, peripheral resistance. Statistics performed by Kruskal–Wallis test.

Figure 2

Receiver Operator Characteristic (ROC) curve: x-axis (1-specificity), y-axis sensitivity, each curve represents the predictability of each impulse oscillometry (IOS) parameter (in different colors). AUC values and p-values for the separate variables are detailed in the right table. R5, respiratory system resistance at 5 Hz; R20, respiratory system resistance at 20 Hz; Fres, resonant frequency; X5, respiratory system reactance at 5 Hz; Z5, respiratory impedance, and Rp, peripheral resistance.

Figure 3

Spearman correlation analysis. (A) between IOS parameters and lung function; (B) Between lung function and bronchiectasis severity scores. ^*p < 0.05; ^**p < 0.01; ^***p < 0.001; ^****p < 0.0001; ns, no significance. Rc, central resistance; Rp, peripheral resistance; Z5, the respiratory impedance; R5 and R20, respiratory system resistance at 5 and 20Hz, respectively; X5, respiratory system reactance at 5Hz; Fres, resonant frequency. FEV1, forced expiratory volume in one second; FVC, forced vital capacity; RV, residual volume; TLC, total lung capacity; MEF, maximal expiratory flow; MMEF, maximal mid-expiratory flow; PEF, peak expiratory flow.

Figure 4

Spearman correlation analysis between IOS parameters and bronchiectasis severity scores. (A–F) Correspond to the Reiff score, (G–L) correspond to the BSI score, (M–R) correspond to the FACED score, and (S–U) correspond to the Bhalla score. R5, respiratory system resistance at 5 Hz; R20, respiratory system resistance at 20 Hz; X5, respiratory system reactance at 5 Hz; Fres, resonant frequency; Z5, the respiratory impedance; Rc, central resistance; and Rp, peripheral resistance.

Figure 5

Correlation between IOS parameters and lobe engagement (with the lingula counted as an individual lobe). (A) R5, respiratory system resistance at 5 Hz; (B) R5–R20, difference between the respiratory system resistance at 5 Hz and 20 Hz; (C) Fres, resonant frequency; (D) X5, respiratory system reactance at 5 Hz; (E) Z5, the respiratory impedance; (F) Rp, peripheral resistance.