Demographic and clinical characteristics
Overall, 21 patients with mild asthma, 36 with moderate asthma, 47 with severe asthma and 31 control subjects were included in Study 1. The gender distribution, age, body-mass index and BSA were comparable (allP >0.05, Table 1 ). The difference in atopic status, sputum and peripheral blood eosinophil counts was unremarkable among asthmatic patients with varying severity (allP >0.05). Patients with severe asthma had a longer disease duration than those with mild asthma. Furthermore, compared with patients with mild asthma and control subjects, patients with moderate-to-severe asthma had markedly lower percentage predicted value of forced expiratory volume in one second (FEV1) and the ratio between FEV1 and forced vital capacity (FVC). The percentage predicted of FEV1 and maximal mid-expiratory flow (MMEF) was significantly lower in patients with mild asthma than in control subjects (all P <0.05). The magnitude of abnormality of IOS parameters was greater in patients with asthma than in control subjects (Table E1 ). Patients with severe asthma had significantly higher R5, R5-R20, X5 and Z5 compared with those with moderate asthma (allP <0.05). The magnitudes of abnormality of Fres, R5, R5-R20, X5, AX and Z5 were markedly higher in patients with severe asthma than those with mild asthma (allP <0.05).
In Study 2, we recruited 16 patients with moderate asthma and 16 with severe asthma. The baseline clinical characteristics of patients with moderate-to-severe asthma in Study 1 did not differ from those in Study 2 (Table E2 ) .