From small airways disease to pre-COPD through pulmonary function tests

<bold>Background:</bold> Small airways disease (SAD) can only indirectly be evaluated through airflow limitation, air trapping, elevated airway resistance or ventilation heterogeneity. COPD diagnosis is pathophysiologically related to SAD. Pre-COPD diagnosis could be based on SAD diagnosis. <bold>Aim:</bold> To identify the extent of SAD by various methods in asymptomatic smokers. <bold>Methods:</bold> Spirometry, impulse oscillometry, lung volumes and single breath N₂ washout were performed in a single visit in 88 smokers. SAD was defined as either of FEF_25-75<60%, FRC>120%, RV>100%, RV/TLC>35%, R₅-R₂₀>0.07 or N₂Delta (%)>1.5%. <bold>Results:</bold> In 88 consecutive smokers, N₂Delta was the most sensitive tool for SAD diagnosis. Combination of N₂Delta with FEF_25-75 resulted in higher sensitivity for SAD diagnosis (Fig. 1A). COPD was diagnosed in 21 smokers based on spirometry. In this subgroup, FEF_25-75 and N₂Delta were found to have 100% sensitivity for SAD diagnosis. (Fig 1B). In the 67 asymptomatic smokers with normal spirometry values, the most sensitive tool for SAD diagnosis was N₂Delta (sensitivity:93%). Combination of N₂Delta with FEF_25-75 resulted in 94.7% sensitivity for SAD diagnosis in asymptomatic smokers (Fig. 1C). <bold>Conclusions:</bold> Single breath N₂ washout appears as the most sensitive tool for SAD diagnosis in smokers. Combining spirometry with single breath N₂ washout can be used for SAD and pre-COPD diagnosis with high sensitivity in clinical practice. <fig><object-id>erj;64/suppl_68/OA4652/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig>