Comparison of online single-breath vs. online multiple-breath exhaled nitric oxide in school-age children

Introduction: Standards for online multiple-breath (mb) exhaled nitric oxie (eNO) measurements and studies comparing them with online single-breath (sb) eNO measurements are lacking, although eNOmb requires less cooperation in children at school age or younger. Methods: Online eNOmb and eNOsb were measured in 99 healthy children and (in order to observe higher values) in 21 children with suspected asthma at a median age of 6.1 and 11.7 y, respectively. For eNOmb, we aimed for 20 tidal breathing maneuvers; eNOsb was measured according to standards. The two techniques were compared by standard methods after computing NO output or extrapolating eNOmb to the standard flow of 50ml/s (eNOmb ₅₀). Results: Measurements were acceptable in 82 (eNOmb) and 81 (eNOsb) children. Paired data were available for 65 children. On a log-log scale, eNOmb ₅₀ (geometric mean SD ± 13.1 ± 15.5 parts per billion, ppb) was correlated with eNOsb (12.5 ± 15.8 ppb), with r ² = 0.87. The mean difference between eNOsb and eNOmb ₅₀ was 0.7 ppb, with limits of agreement (LOAs) of 4.0 and 5.3 ppb. Discussion: Despite its correlation with eNOsb, the LOA range hampers eNOmb use in research, where exact values across the whole range are warranted. However, eNOmb might be an alternative tool especially at preschool age, when cooperation during measurements is crucial.