Small Airway Dysfunction Links Asthma Severity with Physical Activity and Symptom Control

Science and Research

BACKGROUND: Little is known about the role of small airway dysfunction (SAD) and its complex relationship with asthma control and physical activity (PA). OBJECTIVE: to investigate the interrelationship between SAD, risk factors of asthma severity, symptom control and PA. METHODS: We assessed SAD by impulse oscillometry and other sophisticated lung function measures including inert gas washout in adults with asthma (mild to moderate, n=140; severe, n=128) and 69 healthy controls from the ALLIANCE cohort. We evaluated SAD prevalence and its interrelation with risk factors of asthma severity (older age, obesity, smoking), type-2 inflammation (sputum and blood eosinophils, FeNO), systemic inflammation (hsCRP), asthma control (AC) and physical activity (PA, accelerometer for one week). We applied a clinical model based on Structural Equation Modeling (SEM) that integrated causal pathways between these clinical variables. RESULTS: The prevalence of SAD ranged from 75% to 90% in patients with severe asthma and from 53% to 64% in mild to moderate asthma. Severe SAD was associated with poor AC and low PA. SEM indicated that age, obesity, obesity related systemic inflammation, T2-inflammation and smoking are independent predictors of SAD. SAD was the main determinant factor of AC, which in turn affected PA. Obesity affected AC directly and through its contribution to SAD and low PA. In addition, PA had bi-directional associations with obesity, SAD and AC. SEM also indicated an interrelation between distal airflow limitation, air trapping and ventilation heterogeneity. CONCLUSION: SAD is a highly prevalent key feature of asthma that interrelates a spectrum of distal lung function abnormalities with risk factors of asthma severity, asthma control and physical activity.