Figure 1. Lung function measurements in chronic obstructive pulmonary disease patients with and without expiratory flow limitation (EFL)23. (A) EFL patients have worse airflow obstruction and more hyperinflation measured by residual volume (RV) and total lung capacity (TLC). (B) EFL patients have more impulse oscillometry evidence of small airway disease (R5 and R5–R20). All differences between groups in panels (A) and (B) are statistically significant (p<0.05). FEV₁: forced expiratory volume in 1 second.