Lung Function Assessment With Impulse Oscillometry (IOS) in Adolescents with Severe Asthma During the Asymptomatic Period: A Preliminary Study

Introduction: Impulse oscillometry (IOS), a non-invasive forced oscillation technique for assessing lung functions during quiet breathing, is an alternative method to the gold standard spirometry. Normal spirometry during asymptomatic periods is a major obstacle to diagnosing asthma.
Objectives: To assess lung functions of adolescents with severe asthma from the municipal council area of Anuradhapura, Sri Lanka using IOS during their asymptomatic period.
Methodology: A preliminary study was conducted in a convenient sample of 15 adolescents aged 13-14 years with severe asthma detected using the validated International Study of Asthma and Allergy in Childhood (ISAAC) questionnaire during the asymptomatic period. IOS was conducted per European Respiratory Society and American Thoracic Society guidelines with standard calibration, adequate training, and height and weight measurement. The best values of reactance (X) and resistance (R) were calculated at frequencies 5 to 20 Hz (R5, R10, R20, and X5). The standard cut-off of 150% of the predicted value was considered. Bronchodilator administration was conducted with a short-acting inhaled bronchodilator (200 μg MDI salbutamol with spacer) repeating IOS 15 minutes later.
Results: The study sample consisted of 7 boys and 8 girls. Most participants (n=13, 86.67%) had normal IOS results. Significantly increased total (R5) and mid-airway (R10) resistance, with normal large airway (R20) resistance, indicative of significant peripheral airway resistance (R5-20), was detected in one participant. Another participant had significantly increased resonance frequency with normal R and X indicative of either obstructive or restrictive disease.
Conclusion: Evidence suggestive of airway obstruction was found in 2(13.3%) participants highlighting the utility of IOS in diagnosing asthma even in the asymptomatic period.