A comparative study of asthma with airflow limitation and asthma-COPD overlap using the forced oscillation technique

The forced oscillation technique （ FOT ） , which requires breathing without forced action, is a useful tool that can measure respiratory impedance. We investigated the physiological differences between asthma with smoking-unrelated airflow limitation and asthma-chronic obstructive pulmonary disease （ COPD ） overlap （ ACO ） using the FOT. Among 275 patients with asthma who presented at the Showa University Hospital from April 2018 through March 2019, 211 were enrolled and assigned into the asthma （ BA ） , asthma with airflow limitation （ AL ） , or ACO groups. Respiratory impedance measured using the FOT were compared among the groups. There were no differences in spirometry data between the AL and the ACO group. The AL group had higher respiratory resistance at 5 Hz （ R5 ） , 20 Hz （ R20 ） , and reactance at 5 Hz than the ACO group, but there was no significant difference in subtracting R20 from R5 （ R5 - R20 ） . R5 and R20 were similar between the ACO and the BA groups, but R5 - R20, resonant frequency （ Fres ） , and low-frequency reactance area were significantly higher in the ACO group than the BA group. Fres yielded the highest area under the curve （ AUC ） to identify airflow limitation, and R20 yielded the highest AUC to identify the ACO group among patients with airflow limitation. 33 patients ACO. Therefore, FOT aids our understanding of the physiological characteristics and provides clues for the treatment in asthmatics with airflow limitation.