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

BackgroundImpulse oscillometry is a noninvasive pulmonary function test performed during quiet breathing and requires minimal patient cooperation. It is useful for detecting small airway disease and provides increased sensitivity for diagnosing asthma in younger children who may have difficulty completing standard spirometry. Bronchodilator testing, a standard assessment of airflow obstruction reversibility, is recommended in patients with suspected asthma who present obstructive airflow patterns. ObjectiveTo evaluate impulse oscillometry parameters before and after bronchodilator administration across different age groups and to examine the relationship between age and airway resistance in patients with clinician-diagnosed asthma. MethodsThis retrospective study included patients with clinician-diagnosed asthma who demonstrated obstructive airflow patterns and a positive bronchodilator response. Participants were grouped by age: younger than 6 years, 6 to 20 years, and older than 20 years. Key impulse oscillometry parameters--airway resistance at 5 Hz, airway resistance at 20 Hz, the difference between these values, and resonance frequency--were collected and compared across groups. A positive bronchodilator response was defined as a reduction in airway resistance of more than 30% in individuals younger than 18 years and more than 40% in adults. ResultsA total of 225 patients (123 males and 102 females) were included, with a median age of 6 years. At baseline, the median airway resistance at 5 Hz was 175.34% of the reference value (95% CI, 171.66-178.62), and airway resistance at 20 Hz was 121.68% (95% CI, 118.73-127.12). The median difference between these values was 52.32% (95% CI, 49.89-57.14), and the median resonance frequency was 5.11 Hz (95% CI, 4.62-5.35). After bronchodilator administration, airway resistance at 5 Hz decreased to 123.56% (95% CI, 119.07-126.77), corresponding to a median reduction of 52.8% (95% CI, 49.48-56.08; P < 0.0001). Age demonstrated a moderate positive correlation with airway resistance at 20 Hz (r = 0.51, P < 0.001). ConclusionsProximal airway resistance increases with age among patients with asthma, suggesting age-related differences in airway inflammation. Impulse oscillometry combined with bronchodilator assessment provides a practical approach for evaluating airflow reversibility and enhances diagnostic accuracy in suspected asthma.