The Impact of Airway Obstruction on Feno Values in Asthma Patients

Background Exhaled nitric oxide (Feno) is used as a marker of type-2 airway inflammation in asthma management. Studies with airway challenges demonstrated that a reduction in airway caliber decreases Feno levels. Objective To evaluate the impact of airway caliber reduction occurring spontaneously in patients with asthma on Feno values in daily clinical practice. Methods In this post hoc analysis, Feno, FEV1, and asthma control questionnaire scores were recorded on each visit for 120 (1073 visits) adult patients with asthma. Blood eosinophils were measured intermittently. The intraindividual relationship between Feno and FEV1 was evaluated via a linear mixed model. The determinants of the individual mean Feno were measured by a stepwise multivariate linear model including individual mean FEV1, inhaled corticosteroid dose, asthma control questionnaire score, and blood eosinophils. Results Variations in the negative Feno-FEV1 relationship within individuals at different times were significantly determined by the individual's mean FEV1. This relationship did not hold for individuals above the 75th and below the 25th quartiles. The best explanatory variables for individual mean Feno were FEV1 (+4.3 parts per billion/10%pred) and blood eosinophil count (+1 part per billion per 100 cells/mm3). Discussion In the presence of variable degrees of heterogeneous patterns of airway inflammation, airway caliber is shown to be an independent and significant determinant of Feno when measured in patients with asthma. We would propose a +4-parts-per-billion correction factor to the measured Feno value for each 10% reduction below 100% predicted FEV1. Doing this should improve the rigor of interpretation of Feno as an indicator of type-2 inflammation in patients with low FEV1. Exhaled nitric oxide (Feno) is used as a marker of type-2 airway inflammation in asthma management. Studies with airway challenges demonstrated that a reduction in airway caliber decreases Feno levels. To evaluate the impact of airway caliber reduction occurring spontaneously in patients with asthma on Feno values in daily clinical practice. In this post hoc analysis, Feno, FEV1, and asthma control questionnaire scores were recorded on each visit for 120 (1073 visits) adult patients with asthma. Blood eosinophils were measured intermittently. The intraindividual relationship between Feno and FEV1 was evaluated via a linear mixed model. The determinants of the individual mean Feno were measured by a stepwise multivariate linear model including individual mean FEV1, inhaled corticosteroid dose, asthma control questionnaire score, and blood eosinophils. Variations in the negative Feno-FEV1 relationship within individuals at different times were significantly determined by the individual's mean FEV1. This relationship did not hold for individuals above the 75th and below the 25th quartiles. The best explanatory variables for individual mean Feno were FEV1 (+4.3 parts per billion/10%pred) and blood eosinophil count (+1 part per billion per 100 cells/mm3). In the presence of variable degrees of heterogeneous patterns of airway inflammation, airway caliber is shown to be an independent and significant determinant of Feno when measured in patients with asthma. We would propose a +4-parts-per-billion correction factor to the measured Feno value for each 10% reduction below 100% predicted FEV1. Doing this should improve the rigor of interpretation of Feno as an indicator of type-2 inflammation in patients with low FEV1. Further Fine-Tuning of the Interpretation of FeNO Measurement in AsthmaThe Journal of Allergy and Clinical Immunology: In PracticeVol. 12Issue 1PreviewMeasurement of FeNO has been extensively studied over the past 3 decades. The method is noninvasive and easy to perform, which has enabled the generation of a lot of research data. This, in turn, has facilitated the identification of several individual factors that influence FeNO. Early on, it was identified that bronchoconstriction leads to a reduced FeNO, and subsequent bronchodilation normalizes FeNO.1,2 In this issue of The Journal of Allergy and Clinical Immunology (JACI): In Practice, Michils et al3 report on the independent effect of reduced lung function on FeNO in a relatively large real-life sample of patients with asthma, and suggest a way to correct for this effect in the clinic. Full-Text PDF