Small Airways Dysfunction in Asthmatics: Insights into Lung Oscillometry, Spirometry Indices, Phenotypes, and Comorbidities from a Multicentric Study in India

Introduction: Small Airways Disease (SAD) is increasingly recognized as an important phenotype of asthma, characterized by distinct clinical manifestations and a notable prevalence, reported in up to 50% of asthmatics. This underscores the significance of identifying SAD as a distinct subtype within asthma. Its recognition is crucial for optimizing treatment, as it may require targeted therapeutic strategies focusing on small airways to alleviate symptoms and enhance patient outcomes. Methods: Pulmonologists from 5 centres across India, who were members of the International Network for Lung Oscillometry Research (ARISE) took part in the study. Oscillometry was performed using Antlia FOT (iCALTECH, Bangalore. India) and spirometry was performed using devices meeting ATS/ERS standards, among asthmatic patients visiting their clinics. SAD was defined using cut-off of ≥1 for R5-R20 and ≤65% for FEF25%-75%. Results: From a cohort of 1969 asthmatic patients, 1629 met the eligibility criteria for final analysis, among whom 746 (45.7%) were identified with Small Airways Disease (SAD) by R5-R20 ≥ 1 and 865 (53.1%) by FEF25%-75% ≤ 65. The lung oscillometric and spirometric parameters for these patients are detailed in Table 1 highlighting reduced lung function with mean FEV1 % predicted at 56.3% and significant small airway involvement, evidenced by an elevated mean R5-R20 of 2.28 cmH2O/L/sec. Among SAD asthmatics, common symptoms included breathlessness (69.8%), wheeze (55.7%), and chest tightness (35.8%). Additionally, comorbidities such as hypertension, diabetes, and a history of hospitalizations for lung-related conditions were more prevalent with a proportion of 20.3%, 8.4% and 7.1% respectively. Conclusion: SAD is a prevalent phenotype in asthma, affecting nearly half of the studied population. It is associated with reduced lung function, distinct clinical symptoms, and higher comorbidities, emphasizing the need for its recognition in routine asthma management. Targeted evaluation using oscillometry and spirometry can guide personalized therapeutic strategies to improve patient outcomes.