Introduction

Forced midexpiratory flow (FEF25%?75%), measured between 25% and 75% of forced vital capacity (FVC), assess small airways caliber (less than 2mm). There is increased interest in small airways as a therapeutic target in recent years with inhaled particles that are capable of better reaching these distal areas. This study?s aim is evaluating variability of FEF25%?75% with bronchodilator testing response.

Material and methods

A prospective cohort study, with 311 patients who underwent spirometry and bronchodilator testing during april and may 2021. Patients were classified in two groups: Positive/indeterminate test: increase in FEV1 > 12% and/or 200ml (n=64); Negative test: increase in FEV1<12% and <200ml (n=248). The mean variations of FEF25%?75% in both groups? pre and post-bronchodilator testing were compared.

Results

Volume and percentage difference of FEF25%?75% were evaluated. After performing the bronchodilator test, first group mean difference was 482mL and 31.5%, and second group mean variation was 224mL and 15.02%.

Subsequently, to reduce FEF25%?75% result variability by FVC difference due to the bronchodilator testing itself, patients with less than 150mL of their FVC change were selected. In the first group, the mean difference was 460 mL and 34.83%; on the other hand, the second group, showed an average variation of 269mL and 14.4%.

Conclusions

FEF25%?75% vary significantly after the application of a bronchodilator with a higher response in patients with positive bronchodilator testing.