Controlled low flow oV line sampling of exhaled nitric oxide in children

Background—The aim of this study was to validate exhaled nitric oxide (eNO) values obtained with an alternative oV line, single breath, low flow balloon sampling method against on line sampling according to ERS and ATS guidelines in children who could perform both methods. Methods—One hundred and twenty seven white children of median age 14.1 years, all pupils of a secondary school, participated in the study. They performed the two diVerent sampling techniques at three diVerent flows of 50, 100, 150 ml/s. Additional measurements were done in random subgroups to determine the influence of the dead space air on eNO values obtained oV line by excluding the first 220 ml of exhaled air. All children completed a questionnaire on respiratory and allergic disorders and underwent spirometric tests. Results—The oV line eNO values were significantly higher than the on line values at all flows. At 50 ml/s the geometric mean (SE) oV line eNO was 18.7 (1.1) ppb and the on line eNO was 15.1 (1.1) ppb (p<0.0001). However, when dead space air was discarded, oV line and on line values were similar: at 50 ml/s oV line eNO was 17.7 (1.0) ppb and on line eNO 16.0 (1.2) ppb. There was a good agreement between oV line eNO values without dead space air and on line eNO: for 50 ml/s the mean on/oV line ratio was 0.95 (95% agreement limits 0.63 to 1.27). The oV line eNO level at 50 ml/s in 80 children with negative questionnaires for asthma, rhinitis, and eczema was 13.6 (1.0) ppb compared with 33.3 (1.1) ppb in the remaining children with positive questionnaires on asthma and allergy and/or recent symptoms of cold (p<0.0001). Conclusions—In children, oV line assessment of eNO using constant low flow sampling and excluding dead space air is feasible and produces similar results as on line assessment with the same exhalation flow rate. Both sampling methods are sufficiently sensitive to diVerentiate between groups of otherwise healthy school children with and without self-reported asthma, allergy, and/or colds. We propose that, for oV line sampling, similar low flow rates should be used as are recommended for on line measurements. (Thorax 2001;56:285–289)