Clinical Utility of Impulse Oscillometry Parameters in Predicting Asthma Exacerbations

Impulse oscillometry (IOS) provides an effort-independent assessment of respiratory mechanics and is particularly sensitive to small airway dysfunction. Although IOS has been shown to complement spirometry in asthma, its association with exacerbation risk and its relationship with type 2 inflammatory biomarkers remain incompletely understood.

In this retrospective cross-sectional study, 128 adult patients with physician-diagnosed asthma who underwent both spirometry and IOS at a tertiary hospital between January 2023 and July 2024 were analyzed. Exacerbation events during 1-year follow-up were identified from medical records. IOS parameters included resistance at 5 and 20 Hz (R5 and R20), reactance at 5 Hz (X5), resonant frequency (Fres), area under the reactance curve (AX), and frequency dependence of resistance between R5 and R20 (R5-R20). Correlations between spirometric indices and IOS parameters were assessed. Diagnostic performance for exacerbation events was evaluated using receiver operating characteristic (ROC) analysis. Exploratory analyses examined associations between IOS indices, fractional exhaled nitric oxide (FeNO), and blood eosinophil counts.

Thirty-three patients (25.8%) experienced exacerbations. AX showed the strongest correlations with forced expiratory volume in 1 second (FEV₁)% predicted (r=-0.51, p<0.001) and FEF25-75% predicted (r=-0.42, p<0.001). Patients with exacerbations exhibited significantly higher R5, Fres, AX, and R5-R20 compared with those without exacerbations, with AX demonstrating the largest effect size (Cohen's d=0.91). In ROC analysis, AX showed the highest discriminative ability for exacerbation events (area under the curve=0.673). FeNO and blood eosinophil counts were not significantly correlated with IOS parameters and showed limited predictive performance when used alone; however, inclusion of AX significantly improved model discrimination.

IOS parameters, particularly AX, are significantly associated with asthma exacerbations and capture mechanical aspects of small airway dysfunction that are not fully reflected by spirometry or type 2 inflammatory biomarkers. IOS may provide clinically meaningful complementary information for risk stratification in asthma.