Analysis of Single-breath Profiles of Exhaled Nitric Oxide in Children with Allergy and Asthma: Guideline-derived Plateau Concentrations Compared to Results of Automatic Evaluation by Two Analyzers

Abstract

Current guidelines recommend the single-breath measurement of fractional concentration of exhaled nitric oxide (FE_NO) at the expiratory flow rate of 50 mL/s as a gold standard. The time profile of exhaled FE_NO consists of a washout phase followed by a plateau phase with a stable concentration. This study performed measurements of FE_NO using a chemiluminescence analyzer Ecomedics CLD88sp and an electrochemical monitor NIOX MINO in 82 children and adolescents (44 males) from 4.9 to 18.7 years of age with corticosteroid-treated allergic rhinitis (N = 58) and/or asthma (N = 59). Duration of exhalation was 6 seconds for children less than 12 years of age and 10 seconds for older children. The first aim was to compare the evaluation of FE_NO-time profiles from Ecomedics by its software in fixed intervals of 7 to 10 seconds (older children) and 2 to 4 seconds (younger children) since the start of exhalation (method A) with the guideline-based analysis of plateau concentrations at variable time intervals (method B). The second aim was to assess the between-analyzer agreement. In children over 12 years of age, the median ratio of FE_NO concentrations of 1.00 (95% CI: 0.99–1.02) indicated an excellent agreement between the methods A and B. Compared with NIOX MINO, the Ecomedics results were higher by 11% (95% CI: 1–22) (method A) and 14% (95% CI: 4–26) (method B), respectively. In children less than 12 years of age, the FE_NO concentrations obtained by the method B were 34% (95% CI: 21–48) higher and more reproducible (p < 0.02) compared to the method A. The Ecomedics results of the method A were 11% lower (95% CI: 2–20) than NIOX MINO concentrations while the method B gave 21% higher concentrations (95% CI: 9–35). We conclude that in children less than 12 years of age, the guideline-based analysis of FE_NO–time profiles from Ecomedics at variable times obtains FE_NO concentrations that are higher and more reproducible than those from the fixed interval of 2 to 4 seconds and higher than NIOX MINO concentrations obtained during a short exhalation (6 seconds). The Ecomedics FE_NO concentrations of children more than 12 years of age calculated in the interval of 7 to 10 seconds represent plateau values and agree well with NIOX MINO results obtained during a standard 10-second exhalation.

Keywords:

• fractional exhaled nitric oxide
• on-line measurement
• allergy
• asthma