Airway hyper-responsiveness and small airway function in children with well-controlled asthma.

BACKGROUND: Airway hyper-responsiveness (AHR) and small airway function are critical to children with asthma. Little is known about the role of the small airway in well-controlled subjects with AHR. We aimed to evaluate AHR and small airway function in children with well-controlled asthma, and to investigate the association between them. METHODS: We studied 116 cases of children with well-controlled asthma (group A), 46 cases healthy children as controls (group C). Spirometry, impulse oscillometry (IOS), and methacholine challenge test (MCT) were conducted on all the children. RESULTS: (i) Group A and group C had no differences in forced expiratory volume in 1 s (FEV1) and FEV1/forced vital capacity (FVC) ratio (P > 0.05). Forced expiratory flow between 25 and 75% of vital capacity (FEF25-75) and reactance at 5 Hz (X5) in group A were significantly lower than those in group C. (ii) One hundred and five cases (90.5%) of group A proved positive to MCT. (iii) FEF25-75 in group A proved positive to MCT but were lower than those proved negative (P < 0.05). CONCLUSION: AHR persisted in majority of children with well-controlled asthma. Among children with well-controlled asthma, small airway function was lower in those with AHR than those without AHR.