Improvement of FeNO and FEF25-75 After Inhaled Corticosteroid Treatment of Asthma

Current guideline-defined asthma control cannot be applied to the level of airway inflammation because neither symptoms nor the results of basic pulmonary function tests can reflect ongoing airway inflammation.Consequently, asymptomatic or minimally symptomatic patients are usually considered to have controlled asthma even if they have subclinical airway inflammation. Measures of airway inflammation are thus required to identify patients with silent airway inflammation which does not manifest itself as symptoms or impaired lung function. In addition, measurement should be easy to perform, reproducible, and associated with a high degree of acceptance by patients. In this regard, the advent of FeNO measurements represents a significant advance in monitoring airway inflammation of asthmatic patients. High FeNO values above certain cut-point may indicate active eosinophilic airway inflammation and the likelihood of deterioration in asthma control. However, it is still unclear that high FeNO in asymptomatic patients implies the need for the anti-inflammatory treatment. Current guidelines for asthma management recommended forced expiratory volume in the first second (FEV1) as a principle spirometric parameter to assess airflow limitation. However, asthmatic subjects have air trapping in the presence of normal FEV1. Air trapping in asthmatic subjects has been demonstrated to be better correlated with forced expiratory flow between 25% and 75% of vital capacity % predicted (FEF25-75 % predicted) than FEV1 % predicted. In fact, impaired FEF25-75 is one of the most common abnormalities in pulmonary function in cross-sectional studies in asymptomatic patients. In addition, high FeNO in asymptomatic or minimally symptomatic patients may be accompanied by impairment of FEF25-75 because both parameters have been suggested to be measures of residual small airway disease. Therefore, there is a possibility that the improvement of FEF25-75 happens concomitantly with the decrease of FeNO during the anti-inflammatory treatment. In this study, we recruited previously well-documented atopic asthmatic children who required no medication to maintain asthma control for more than 3 months and had high FeNO levels (\> 25 ppb). We aimed to assess whether the decrease of FeNO occurs simultaneously with improvement of FEF25-75 after treatment with inhaled corticosteroid (ICS) in these patients.