Background:Asthma is a common, chronic heterogeneous disease. Tests of large airways function (FEV1) are commonly used to diagnose/monitor disease and bronchodilator responsiveness (BDR: measured by a change in FEV1) is considered the hallmark of asthma. Small airways (18 y) referred to the pulmonary function laboratory as part of an asthma assessment between January 2016 and April 2021. BDR was assessed 20 min after the administration of 2.5 mg of salbutamol using a jet nebulizer. Changes in FEV1 and FEF25-75 were assessed. The study was approved by the Research Ethics Committee and the Health Research Authority of the NHS (20/WM/0024). Results:219 patients were identified for this initial analysis. The population consisted of 104 (47.5%) males and the mean age was 44.7 y ± 18.9 with a BMI of 28.2 ± 6.5. 28 (12.8%) demonstrated airflow limitation in pre-BDR tests. The mean difference in pre and post bronchodilator %predicted FEV1was 9.7 (95% CI = 8.7-10.8) and 22.3 (95% CI = 19.7-24.9) %predicted FEF25-75; (P < 0.01 for both). In total 73 (33.3%) demonstrated BDR in FEV1, 101 (46.1%) in FEF25-75. All of those with significant BDR response in FEV1 had a significant response in FEF25-75. The BDR in FEF25-75 was noted to be the lowest in severe cases, with no distinctive differences in other patients' characteristics. Conclusions:This study confirms the presence of BDR in more adults with asthma using measures of small airways function than FEV1. It is unclear whether this represents a separate phenotype of asthma.
Almeshari et al. (Fri,) studied this question.