title: Flow dependency and off-line measurement of exhaled NO in children.
abstract: Levels of exhaled nitric oxide (eNO) are flow-dependent, and the choice of an optimal flow rate for off-line and on-line eNO measurement has raised much debate. Recently, a flow rate of 50 ml/s was recommended, but children younger than 5-6 years are not capable of stabilizing their expiratory flow at low flow rates. The power of off-line eNO values to discriminate between normal and atopic children was therefore evaluated at different exhalation flow rates. At flow rates of both 8.3 ml/s and of 350 ml/s, children (8-12 years) sensitive to house dust mite have two-fold higher eNO values (p < 0.001) as compared with children lacking such a sensitivity. The power of eNO to discriminate between normal and atopic subjects was similar at the two flow rates (no difference in AUC of receiver operation curves, p = 0.89). All children from 4.5 to 5 years of age (n = 29) could perform a single off-line exhalation manoeuvre at high (>350 ml/s) but not at low (8.3 ml/s) flow rates. At high exhalation flow rate, eNO was 7.1 +/- 2.4 (mean +/- SD) median, 6.5 p.p.b. with a mean variation coefficient of 5.5%. Depending on their developmental level, about half of the younger children (35-46 months of age) could perform an off-line exhalation manoeuvre at high flow rate with good reproducibility (mean variation coefficient of 6.6%). It is concluded that an exhalation flow rate of 350 ml/s is feasible to determine off-line eNO-values in children from 3.5 years of age, and that this high flow rate does not compromise the power of eNO to detect allergic disease.
authors.affiliation: Laboratory of Health Effects Research, National Institute of Public Health and the Environment, PO Box 1, 3720 BA Bilthoven, The Netherlands. JGC.van.Amsterdam@rivm.nl
authors.forename: J G C
authors.initials: JG
authors.lastname: van Amsterdam
authors.forename: P
authors.initials: P
authors.lastname: Zanen
authors.forename: S
authors.initials: S
authors.lastname: Somer
authors.forename: H
authors.initials: H
authors.lastname: van Loveren
authors.forename: A
authors.initials: A
authors.lastname: Opperhuizen
authors.forename: P A
authors.initials: PA
authors.lastname: Steerenberg
mesh_terms: D000328:Adult; D000367:Age Factors; D019540:Area Under Curve; D002648:Child; D002669:Child Welfare; D002675:Child, Preschool; D045853:Exhalation / Q000502:physiology*; D005260:Female; D005540:Forced Expiratory Flow Rates / Q000502:physiology*; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000378:metabolism / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000378:metabolism*; D012372:ROC Curve; D016032:Randomized Controlled Trials as Topic; D015203:Reproducibility of Results
chemical_list: D009569:Nitric Oxide