Assessment of small airway dysfunction and symptoms in COPD

<bold>Background:</bold> Small airway dysfunction (SAD) may be a key comorbidity in COPD but its association with symptoms is poorly understood. Impulse oscillometry (IOS) is a forced oscillation technique that is currently used for clinical assessment of SAD in asthma, while much less is known about its application in COPD. <bold>Aims:</bold> To characterise SAD in relation to symptoms in a real-life cohort of COPD patients. <bold>Methods:</bold> We utilized clinical data from patients with severe COPD referred for clinical evaluation to Karolinska Severe COPD Center (2021-23). IOS was performed before dynamic spirometry as a part of the clinical evaluation at all visits. We present data from the first clinical visit to our center. <bold>Results:</bold> 60 patients (mean age 70.4 years, 54% females) were included. Among these patients, 20% were current smokers, 73 % ex-smokers (average tobacco load 39.4 packyears) and 7% never smokers. Emphysema was reported as a comorbidity in the medical records of 62% of the patients. Out of all patients, 83.3 % had SAD as assessed by IOS. All patients in GOLD stage IV had SAD. Table 1. Spirometry and IOS results <table-wrap><object-id>erj;64/suppl_68/PA1227/TB1</object-id><object-id>T1</object-id><object-id>TB1</object-id><table><colgroup><col></col><col></col><col></col><col></col></colgroup><tbody><tr><td></td><td>GOLD II n= 12</td><td>GOLD III n=41</td><td>GOLD IV n= 7</td></tr><tr><td>FEV₁ % predicted^*</td><td>57.1 (9.3)</td><td>39.5 (6.7)</td><td>24.8 (4.4)</td></tr><tr><td>R₅-R₂₀, kPa/L/s^#</td><td>0.22 (0.38)</td><td>0.27 (0.67)</td><td>0.35 (0.81)</td></tr><tr><td>AX kPa/L^#</td><td>2.34 (4.12)</td><td>3.2 (9.6)</td><td>5.26 (11.5)</td></tr></tbody></table></table-wrap> R₅-R₂₀: frequency dependent resistance, AX: area of reactance ^*mean (SD)^#median (range) Both R₅-R₂₀ (r=0.3076, p=0.0178) and AX (r=0.2604, p=0.0464) displayed a positive correlation with the CAT total score. <bold>Conclusion:</bold> SAD was frequent in all disease stages but most frequent in GOLD stage IV. Two different assessments of SAD increased with symptom score, suggesting that SAD plays a prominent role for clinical pathology in severe disease.