Less small airway dysfunction in asymptomatic bronchial hyperresponsiveness than in asthma

Abstract

Background: Bronchial hyperresponsiveness (BHR) can be present in subjects without any respiratory symptoms. Little is known about the role of the small airways in asymptomatic subjects with BHR.

Methods: We investigated small airway function assessed by spirometry and impulse oscillometry, as well as Borg dyspnea scores at baseline and during a methacholine provocation test in 15 subjects with asymptomatic BHR, 15 asthma patients, and 15 healthy controls.

Results: At baseline, small airway function (R5 -R20 and X5 ) was comparable between subjects with asymptomatic BHR and healthy controls, whereas asthma patients showed small airway dysfunction as reflected by higher R5 -R20 and lower X5 values. During methacholine provocation, small airway dysfunction was more severe in asthma patients than in subjects with asymptomatic BHR. Interestingly, a higher increase in small airway dysfunction during methacholine provocation was associated with a higher increase in Borg dyspnea scores in subjects with asymptomatic BHR, but not in asthma patients.

Conclusion: Subjects with asymptomatic BHR may experience fewer symptoms in daily life because they have less small airway dysfunction.

Keywords: asthma; asymptomatic bronchial hyperresponsiveness; small airways.