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Thorax 2001;56:285-289 doi:10.1136/thorax.56.4.285
  • Original article

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

  1. Q Jöbsisa,c,
  2. H C Raatgeepa,
  3. W C J Hopb,
  4. J C de Jongstea
  1. aDepartment of Paediatrics, Division of Paediatric Respiratory Medicine, Erasmus University Medical Center/Sophia Children's Hospital, Rotterdam, The Netherlands, bDepartment of Epidemiology and Biostatistics, cDepartment of Paediatrics, University Hospital Maastricht, The Netherlands
  1. Professor Dr J C de Jongste, Department of Paediatrics/Respiratory Medicine, Sophia Children's Hospital , P O Box 2060, 3000 CB Rotterdam, The Netherlandsdejongste{at}lons.azr.nl
  • Received 28 February 2000
  • Revision requested 17 May 2000
  • Revised 11 December 2000
  • Accepted 20 December 2000

Abstract

BACKGROUND The aim of this study was to validate exhaled nitric oxide (eNO) values obtained with an alternative off 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 different sampling techniques at three different 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 off 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 off line eNO values were significantly higher than the on line values at all flows. At 50 ml/s the geometric mean (SE) off 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, off line and on line values were similar: at 50 ml/s off line eNO was 17.7 (1.0) ppb and on line eNO 16.0 (1.2) ppb. There was a good agreement between off line eNO values without dead space air and on line eNO: for 50 ml/s the mean on/off line ratio was 0.95 (95% agreement limits 0.63 to 1.27). The off 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, off 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 differentiate between groups of otherwise healthy school children with and without self-reported asthma, allergy, and/or colds. We propose that, for off line sampling, similar low flow rates should be used as are recommended for on line measurements.

Footnotes

  • Funding: This work was supported by research grant 94.14 from The Netherlands Asthma Foundation.

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