Changes in Exhaled Nitric Oxide Measured by Two Offline Methods Predict Improvements in Bronchial Hyperresponsiveness after Inhaled Steroid Therapy in Japanese Adults with Asthma

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Background: The fraction of exhaled nitric oxide (FeNO) is a useful marker of eosinophilic airway inflammation in asthmatics. No studies have examined the relationship between the change in FeNO levels measured offline and changes in bronchial hyperresponsiveness (BHR) in asthmatic patients treated with inhaled corticosteroids (ICS). The objective of this study was to investigate the relationship between the change in FeNO levels measured offline and the change in BHR to acetylcholine in asthmatic patients taking ICS.
Methods: The study population comprised 41 ICS-treated asthmatics from our outpatient clinic. We measured FeNO levels by two methods -with a Sievers kit ("FeNOs") and with a kit from the Center for Environmental Information Science, Japan ("FeNOc") at baseline and after 1 year of regular treatment. We also used spirometry to test BHR to acetylcholine (PC_20Ach).
Results: The mean of duration of observation was 406 days. There were significant relationships between ΔlogPC_20Ach and logPC_20Ach (r = -0.877, P < 0.001), FeNOs (r = 0.465, P = 0.002), and FeNOc (r = 0.524, P = 0.004) at baseline, but not with age, the dose of ICS, FEV₁, or %FEV₁. Moreover, there was a significant relationship between ΔlogPC_20Ach and ΔFeNOs (r = -0.386, P = 0.013) and ΔFeNOc (r = -0.473, P = 0.004), but not with ΔFEV₁.
Conclusions: Changes in FeNOs and FeNOc correlated with improvements in BHR to acetylcholine in adult asthmatics after ICS therapy. Our findings suggest that offline monitoring of FeNO will facilitate the management of bronchial asthma in patients treated with ICS.