Relationships between fractional exhaled nitric oxide levels and FEF25%-75% in children with asthma

Abstract

Purpose: Fractional exhaled nitric oxide (FeNO) is considered an indirect marker of airway inflammation, and forced expiratory flow between 25% and 75% of vital capacity (FEF25%-75%) is widely used as a sensitive indicator of small airway obstruction in asthma. The aim of this study was to investigate relationships between FeNO and FEF25%-75% in children with asthma. Methods: A total of 118 children with asthma underwent spirometry and measurement of eosinophil markers. FeNO levels were measured, and skin prick tests to 13 common allergens were done. Study subjects were divided into 2 groups according to FEF25%-75% values (group 1, normal FEF25%-75% >= 65%pred, n=90; group 2, impaired FEF25%-75%<65% pred, n=28). Results: The mean (+/- standard deviation, SD) age was not significantly different between groups 1 and 2 (10.3 +/- 2.8 years vs. 11.1 +/- 3.4 years), and the sex ratio was also not significantly different between 2 groups. The geometric mean (range of 1 SD) concentration of FeNO was significantly higher in group 2 than in group 1 (25.8 ppb [14.2-46.9 ppb] vs. 37.2 ppb [24.2-57.2 ppb], P=0.008). A significant inverse correlation between FeNO and FEF25%-75% was observed in group 2 (r=-0.493, P=0.038), but not in group 1 (r=-0.037, P=0.749) after adjustment for confounders, such as atopy, age, sex, weight, and height. Conclusion: FeNO levels were higher in group of asthmatic children with impaired FEF25%-75% level. FeNO levels were inversely correlated with FEF25%-75% only in impaired small-airway obstruction group after adjustment for atopy. These results suggest that small-airway obstruction may relate more closely to airway inflammation in asthmatic children with impaired small-airway function.