Clinical features and airway inflammation in mild asthma versus asymptomatic airway hyperresponsiveness

SummaryRationaleWe still do not know why some subjects with airway hyperresponsiveness (AHR) experience no respiratory symptoms.ObjectivesOur aim was to compare pulmonary function, perception of bronchoconstriction, and airway inflammation in atopic subjects with mild recently diagnosed (<5 years, n=30n=30) or longer-standing (5 years or more, n=30n=30) symptomatic asthma in comparison with atopic subjects with asymptomatic AHR (n=27n=27).MethodsAll subjects had measurements of expiratory flows, PC20 methacholine, perception of breathlessness and induced sputum cell differential, eosinophil cationic protein and α2α2-macroglobulin levels.ResultsCompared with the other groups, PC20 was significantly lower in longer-standing asthma and perception score for breathlessness at 20% fall in FEV1 was lower in asymptomatic subjects. Markers of airway inflammation were similar in all groups. There were no significant correlations between sputum eosinophils, α2α2-macroglobulin and/or eosinophil cationic protein levels and FEV1, FVC or PC20 in either group.ConclusionSubjects with mild asthma or asymptomatic AHR are similar in regard to induced sputum markers of airway inflammation. Although perception of bronchoconstriction was slightly lower in asymptomatic subjects, additional factors are probably involved to explain why they report no respiratory symptoms. Further studies are needed to determine why these last are asymptomatic.