Effect of inhaled corticosteroids on small airways in asthmatics using impulse oscillometry

Background The abnormalities in the small airways contribute to the symptoms of asthma. The small airways dysfunction may be attributed to many factors; mainly inflammation, remodeling, and changes in the surrounding tissue. Small airways affection associates with worse control of asthma, more frequent exacerbations, presence of nocturnal symptoms, more severe bronchial hyper-responsiveness, exercise-induced asthmatic symptoms, and the late-phase allergic response. Forced oscillation technique (FOT) was found to have higher sensitivity to inhaled corticosteroid (ICS) or to beta-agonist inhalation than spirometry. Both ICS and beta-agonists improve small-airway function, and FOT responses manifest eminent changes in indices of peripheral airway obstruction. In contrast, spirometric sensitivity to small-airway function is less eminent. Accordingly, it is expected that FOT might provide useful indices of peripheral airway change in response to therapeutic interventions. Aim The aim of this study was to evaluate the effect of regular use of ICS on small-airway function of asthmatic patients using impulse oscillometry (IOS). Patients and methods The study was carried out at Kobry El-Qobba Military Chest Hospital on 30 patients newly diagnosed as having mild and moderate bronchial asthma. Spirometric lung functions and IOS were done at baseline and then after 1 and 3 months of regular use of proper dosage of ICS to assess the effect on small-airway function. Results Results revealed that there was highly statistically significant improvement regarding changes in forced expiratory volume in 1 s, forced vital capacity, forced expiratory volume in 1 s/forced vital capacity, and maximum mid-expiratory flow (MMEF) 25-75 when comparing 1 day, 1 month, and 3 months. Moreover, there was statistically significant improvement regarding the R5, R20, and X5 when comparing 1 day, 1 month, and 3 months. Regular ICS use provides progressive improvement over time in both spirometry and IOS parameters. Both spirometric and IOS parameters were equally sensitive in detecting change of small-airway function. Conclusion Small-airway involvement in the pathogenesis of asthma will no longer be missed as it can be measured either qualitatively, as the presence or absence of high peripheral resistance values, or quantitatively through measuring the reactance. The more the patient is adherent to his or her daily recommended dose of ICS, the more evident is the improvement in his or her IOS and spirometric parameters including parameters that measure the small airways affection, starting from the very first few weeks of proper treatment. Using IOS is equally sensitive as spirometry in diagnosis and follow-up of adult asthmatic patients.