Prevalence of small airways dysfunction in asthma with- and without-fixed airflow obstruction and chronic obstructive pulmonary disease.

Abstract

Small airways dysfunction (SAD) is not uncommon in asthma without fixed airflow obstruction (FAO). We aimed to determine if SAD in non-FAO asthma is different from FAO-asthma and COPD. Cases of obstructive airway diseases who underwent spirometry, plethysmography, and impulse oscillometry [resistance at 5 Hz (R5) and at 20 Hz (R20), peripheral resistance (R5-R20), and reactance area (AX)] were reviewed, and classified as; 1) COPD, 2) FAO-asthma, and 3) non-FAO asthma. FAO was defined as post-bronchodilator (post-BD) FEV1/ FVC < 0.7. SAD was considered if 1) RV/TLC ≥ 40%, or 2) post-BD R5-R20 ≥ 0.075 kPa.L-1s. A total of 73 patients (22 COPD, 24 FAO-asthma, and 27 non-FAO asthma) were analyzed. RV/TLC ratio was higher in FAO-asthma and COPD (45 ± 5% and 42 ± 8%) than in non-FAO asthma (32 ± 8%), p < 0.001. Post-BD values of R5-R20 and AX (median; range) were higher in FAO-asthma (0.17; 0.08, 0.47, 13.24; 6.52, 82.11) than in non-FAO asthma (0.11; 0.03, 0.23, 8.63; 2.40, 22.02), p = 0.007 and p = 0.017, respectively. The prevalence of SAD among diagnosis group by RV/TLC criterion was different (95%, 59%, and 15% in FAO-asthma, COPD, and non-FAO asthma, p < 0.001), but those were not observed by R5-R20 criterion (95%, 68%, and 77%, p = 0.052). SAD in non-FAO asthma was less prevalent than FAO-asthma and COPD.