Prevalence of Small-Airway Dysfunction among COPD Patients with Different GOLD Stages and Its Role in the Impact of Disease

<b><i>Background:</i></b> In chronic obstructive pulmonary disease (COPD) patients, small-airway dysfunction (SAD) is considered a functional hallmark of disease. However, the exact role of SAD in the clinical presentation of COPD is not yet completely understood; moreover, it is not known whether SAD may have a relationship with the impact of disease. <b><i>Objectives:</i></b> To evaluate the prevalence of SAD among COPD patients categorized by the old and the new GOLD classification and to ascertain whether there is a relationship between SAD and impact of disease measured by the COPD Assessment Test (CAT) questionnaire. <b><i>Methods:</i></b> We prospectively enrolled COPD outpatients from the University Hospital of Parma. Using the impulse oscillometry system (IOS), we assessed the fall in resistance from 5 to 20 Hz (R5-R20), reactance at 5 Hz (X5), and resonant frequency (<i>F</i>_Res) as markers of peripheral airway dysfunction. According to R5-R20 ≥0.07 or <0.07, the cohort was also categorized in patients with and without SAD, respectively. <b><i>Results:</i></b> We studied 202 patients. In both GOLD classifications, a progressive increasing distribution of R5-R20 and <i>F</i>_Res was reported with a decreasing of X5. Moreover, there was a significant correlation between R5-R20 and CAT (<i>r</i> = 0.527, <i>p</i> < 0.001). Finally, the presence of SAD (OR 11.96; 95% CI 4.53-31.58; <i>p</i> < 0.001) and use of ICS + LABA + LAMA (OR 5.31; 95% CI 1.88-15.02; <i>p</i> = 0.002) were independent predictors of higher impact (CAT score ≥10). <b><i>Conclusion:</i></b> In COPD patients, the presence of SAD, as assessed by IOS, progressively increases with GOLD classifications and it is closely related to the high impact of disease on health status.