Airway eosinophilic inflammation indicates small airway dysfunction (SAD) in patients with mild stable or at risk for COPD – results from CAPTO-COPD

<b>Background:</b> Airway eosinophilic inflammation is usually linked to recurrent exacerbations in COPD. However, little is known about its role in SAD in patients with mild or at risk for COPD. We aimed to describe the association between airway eosinophilic inflammation and SAD in these patients. <b>Methods:</b> We induced sputum in 45 patients with mild stable COPD (post FEV₁/FVC&lt;70% + FEV₁≥70%pred) and in 24 smokers at risk (post FEV₁/FVC≥70%, ≥10py and CAT ≥10 or long-acting bronchodilator) from CAPTO-COPD. Lung function included spirometry, body plethysmography and SF₆ multiple breath washout (MBW). Patients were stratified based on sputum eosinophil count in eosinophil-high (≥2%) and eosinophil-low. <b>Results:</b> 19% of patients (8 COPD, 5 at risk) were eosinophil-high (mean eosinophil count: 5.6± 6.0%). Markers of SAD indicated increased acinar (S_acin 0.66±0.51 vs 0.38±0.27), global (LCI 10.6±1.2 vs 9.5±1.5) ventilation inhomogeneity and air trapping (RV/TLC 48±7 vs 41±6%) in eosinophil-high patients. Age (64±8 vs 65±8y), smoking (43±16 vs 45±25 py), airway neutrophilia (72±11 vs 70±17%) and airflow obstruction (FEV₁/FVC 58±9 vs 62±8%, FEV₁ 75±12 vs 83±13%pred) did not differ between both groups. Significant correlation between airway eosinophils and SAD (r=0.48 to 0.30, all p&lt;0.05) was found while no correlation between eosinophils and airflow obstruction was be established. <b>Conclusion:</b> In a subgroup of smokers at risk or patients with mild stable COPD, eosinophilic airway inflammation was associated with more severe SAD. Interventional trials are needed to demonstrate the benefit of early targeting airway eosinophilia on disease progression.