Abstract
Background: Small airways disease in asthma is common; however, the optimal approach to diagnosis and treatment is not established. Clinically useful tests of small airways involvement in asthma are limited, and these are required if we are to accurately diagnose and treat patients with this asthma phenotype (for example, with specific treatments to penetrate the small airways, such as extra-fine particle inhaled therapy). FeNO is a biomarker that has been extensively studied for its association with eosinophilic airways inflammation and steroid responsiveness in asthma. Its behaviour in response to bronchodilation may be helpful in the assessment of small airways disease.
Objective: The aim of the study was to determine whether the change (or absence of change) in FeNO post-bronchodilator was associated with physiological parameters related to small airways disease (IOS markers of small airways resistance and reactance and MBNW markers of ventilation heterogeneity).
Method: Forty participants aged 18 and above with physician-diagnosed asthma completed the study. Respiratory function tests that included baseline FeNO, impulse oscillometry, multiple breath nitrogen washout and spirometry was completed. 600μg of salbutamol (6 actuations of 100μg salbutamol from a metered dose inhaler via spacer) was given as bronchodilator treatment. All test were repeated after treatment. A subgroup of ten participants repeated the visit >4 weeks later.
Results: Three FeNO groups were identified and all 40 participants were stratified into the groups. 23 participants showed no significant change in FeNO post-bronchodilator treatment (FeNO=), 13 decreased (FeNO-) and 4 increased (FeNO+). Demographics differences between FeNO= and FeNOD group (FeNO+ and FeNO-) include sex, FEV1/FVC%, FEV1% predicted% and FeNO. Small airways baseline measures between the two groups were also different in LCI2.5, iiiFRC, Sacin, FEF25-75. Lastly, differences in treatment effects between the two groups were seen in X5Hz, AX, and FEF25-75.
Conclusion: Differences between the FeNO= and FeNOD groups were consistent with them representing large and small airways disease respectively. Change in FeNO after bronchodilator therefore has the potential to be a useful biomarker of small airways disease in asthma. Further research is required to define this group and determine whether such patients might derive benefit from specific treatments.