Small airways involvement is associated with bronchial hyperresponsiveness in asthma

Background: Bronchial hyperresponsiveness (BHR) is a hallmark of asthma. Although, the role of small airways involvement in asthma has been well established, little is known about the association between BHR and small airways obstruction. We hypothesize that small airways disease contributes to BHR. Methods: A total of 119 patients with a doctor9s diagnosis of asthma were included. All subjects underwent spirometry and a BHR testing (PD 20 histamine). Small airways involvement was defined as an MEF 50 ≤ the lower limit of normal (LLN). We compared the severity of BHR between asthmatics with and without small airways involvement. Results: We found 36 patients with and 83 patients without small airways involvement (MEF 50 ≤LLN and MEF 50 >LLN respectively). Patients with small airways involvement showed a more severe BHR than patients without (PD 20 histamine 0.2 vs. 1.1 mg). In addition, FEV 1 , FEV 1 /FVC and reversibility were lower in patients with small airways involvement. Both a lower MEF 50 and FEV 1 were independent predictors of more severe BHR in multivariate linear regression models. Conclusion: Small airways involvement is associated with more severe BHR in asthma. Since FEV 1 is used as a read-out in current BHR tests, we hypothesize that further research with small airways measurements during BHR tests will provide more insight into the relation between BHR and small airways involvement.