Background: Some patients with asthma have high levels of exhaled nitric oxide fraction (FE
NO) despite inhaled corticosteroids (ICS) therapy. Early studies suggested that this might be explained by the presence of heterogeneous airway inflammation. We aimed to assess the predictors for identifying the efficacy of systemic corticosteroids on residual FE
NO elevations in severe asthma.
Methods: Twenty severe asthmatics with persistent FE
NO elevation (≥40ppb) despite maintenance therapy including high-daily-dose ICS were enrolled. Asthma Control Questionnaire (ACQ), lung function, blood eosinophils, and FE
NO were assessed before and after 14 days treatment with 0.5mg/kg oral prednisolone/day.
Results: ACQ, blood eosinophils, FE
NO level, FVC, FEV
1, FEV
1/FVC ratio and the slope of the single nitrogen washout curve (ΔN
2) were significantly improved by treatment with prednisolone. 70% of the subjects showed ≥20% reductions in the FE
NO levels. The reduction in FE
NO levels was significantly correlated with the improvements in ACQ (
p < 0.0001), FVC (
p < 0.01), FEV
1 (
p < 0.0001), and ΔN
2 (
p < 0.05). Among the measurements at baseline, the FE
NO levels and blood eosinophil numbers were identified as significant predictors of ≥20% reductions in the FE
NO levels by systemic steroid therapy.
Conclusions: Systemic corticosteroids could suppress the residual FE
NO elevations in more than half of the patients with severe asthma and the reduction in FE
NO levels was associated with improvements in asthma control and airflow limitation. The FE
NO levels and blood eosinophil numbers were the predictors of improved residual airway inflammation by systemic steroid therapy in severe asthma.
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