Application of Impulse Oscillometry Combined with Bronchodilator Testing for Asthma Management: A Children's Hospital Experience in Taiwan

Technical Summary: Application of Impulse Oscillometry Combined with Bronchodilator Testing for Asthma Management

Problem Statement
Accurate diagnosis and management of asthma in pediatric patients remain challenging due to the limitations of traditional pulmonary function tests (PFTs), specifically spirometry. Standard spirometry requires substantial patient cooperation and effort, which is often difficult to obtain from young children, leading to potential underdiagnosis or misdiagnosis. While Impulse Oscillometry (IOS) offers a non-invasive alternative requiring minimal patient effort, there is a gap in the literature regarding the specific effectiveness of combining IOS with bronchodilator testing (BDT) for routine asthma diagnosis and management in children. Furthermore, the relationship between patient age and specific IOS parameters in the context of asthma has not been fully characterized in clinical practice.

Methodology
This retrospective study was conducted at China Medical University Children's Hospital in Taichung, Taiwan, involving 225 patients with clinician-diagnosed asthma who demonstrated obstructive airflow patterns and a positive bronchodilator response.

• Study Design: The study analyzed data collected between August 1, 2019, and May 31, 2020. It was approved by the hospital's Institutional Review Board as a continuous quality improvement initiative, waiving the need for informed consent.
• Inclusion/Exclusion: Patients were included if they met Global Initiative for Asthma (GINA) guidelines for diagnosis and showed a positive BDT via spirometry (≥12% and ≥200 mL increase in FEV1). Exclusion criteria included recent use of asthma controller medications (within 2 days), congenital heart disease, or co-existing pulmonary anomalies (e.g., bronchopulmonary dysplasia).
• Procedures: All participants underwent IOS using a Jaeger MasterScreen system prior to spirometry. Measurements were taken at 5 Hz (R5) and 20 Hz (R20), along with resonance frequency (Fres) and reactance (X5). A positive bronchodilator response for IOS was defined as a reduction in airway resistance of >30% for children <18 years and >40% for adults.
• Statistical Analysis: Data were stratified by age (<6, 6–20, and >20 years). Continuous variables were expressed as medians with interquartile ranges (IQR). The Wilcoxon signed-rank test was used for paired pre- and post-BDT comparisons, and Pearson correlation coefficients assessed relationships between age and IOS parameters.

Key Results

• Demographics: The cohort included 225 patients (123 males, 102 females) with a median age of 6 years (range 2–23).
• Baseline Resistance: At baseline, the median airway resistance at 5 Hz (R5) was 175.34% of the predicted value (95% CI: 171.66–178.62), and at 20 Hz (R20) was 121.68% (95% CI: 118.73–127.12).
• Bronchodilator Response: Following bronchodilator administration, median R5 decreased significantly to 123.56% (95% CI: 119.07–126.77). This represented a median reduction of 52.8% (95% CI: 49.48–56.08; P < 0.0001), confirming a clinically meaningful response in the majority of participants.
• Age Correlations: A moderate positive correlation was found between age and R20 (r = 0.51, P < 0.001), indicating that proximal airway resistance increases with age. Weak but statistically significant correlations were observed between age and both pre-BDT R5 (r = 0.16) and post-BDT R5 (r = 0.24). No significant correlations were found between age and X5 or AX5.
• Parameter Sensitivity: The study found that R5 was the most sensitive IOS marker for detecting bronchodilator responsiveness. Other parameters (R5–R20, Fres) showed smaller and more variable changes.

Key Contributions
The study provides empirical evidence supporting the utility of IOS combined with BDT as a practical diagnostic tool for asthma, particularly in young children who cannot perform standard spirometry. It establishes that IOS can reliably detect reversible airflow obstruction in a pediatric cohort, with a median reduction in R5 exceeding standard thresholds for positivity. Additionally, the research highlights an age-dependent physiological trend where proximal airway resistance (R20) increases with age, suggesting that IOS interpretation should be age-aware.

Significance and Claims
The authors claim that incorporating IOS with BDT into diagnostic protocols offers a feasible, non-invasive, and child-friendly alternative to traditional PFTs for assessing reversible airflow obstruction. The study suggests that this approach enhances diagnostic accuracy in suspected asthma cases, especially in preschool and young school-aged children.

The paper modestly concludes that while IOS is a valuable tool for monitoring treatment efficacy and diagnosing asthma, it does not replace the need for comprehensive assessment including lung volumes or diffusion capacity. The authors acknowledge limitations, including the retrospective nature of the study, the lack of a control group, and the absence of universally accepted reference values for IOS across diverse populations. They posit that future prospective studies are necessary to validate these findings, establish age-specific reference ranges, and determine if IOS-based markers can predict long-term asthma control or exacerbation risks. The findings support the routine use of IOS in settings where spirometry is challenging, aiming to improve long-term health outcomes for pediatric asthma patients.