title: Abbreviation modalities of nitrogen multiple-breath washout tests in school children with obstructed lung disease.
abstract: BACKGROUND
  Nitrogen multiple-breath washout (N2 MBW) is a promising tool for assessing early lung damage in children with chronic obstructive pulmonary disease, but it can be a time-consuming procedure. We compared alternative test-shortening endpoints with the most commonly reported N2 MBW outcome, the lung clearance index, calculated as lung volume turnovers required to reach 2.5% of the starting N2 concentration (LCI2.5 ).
  
  
  METHODS
  Cross-sectional study of triplicate N2 MBW measurements obtained in cystic fibrosis (CF) patients (N = 60), primary ciliary dyskinesia (PCD) patients (N = 28), and matched healthy controls (N = 48) aged 5-18 years. Bland-Altman analysis was used to compare LCI2.5 with earlier LCI endpoints (3%, 4%, 5%, 7%, and 9% of starting N2 concentration), Cn@TO6 (defined as % of N2 starting concentration when reaching six lung volume turnovers), and LCI derived from only two N2 MBW runs in each session. N2 MBW endpoints were analyzed as z-scores calculated from healthy controls.
  
  
  RESULTS
  In PCD, Cn@TO6 and LCI2.5 exhibited similar values (mean [95%CI] difference: 0.33 [-0.24; 0.90] z-scores), reducing the test duration by one-third (5.4 min; 95%CI: 4.0; 6.8). All other tested alternative endpoints exhibited increasing disagreement with increasing LCI2.5 . With an average reduction in test duration of 40%, LCI2.5 derived from two runs exhibited good agreement in all children.
  
  
  CONCLUSIONS
  Cn@TO6 may be suggested as a potential test-shortening endpoint in school children with PCD. In CF, early test termination may reduce measurement power with advancing pulmonary disease, suggesting differences in underlying pathophysiology. Two technically acceptable N2 MBW runs may be sufficient in school children irrespective of diagnosis with CF or PCD. Pediatr Pulmonol. 2016;51:624-632. © 2015 Wiley Periodicals, Inc.
authors.affiliation: Department of Pediatric and Adolescent Medicine, Danish PCD and chILD Centre, CF Centre Copenhagen, Pediatric Pulmonary Service, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.|Research Unit on Women's and Children's Health, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Kent
authors.initials: K
authors.lastname: Green
authors.affiliation: Department of Pediatric and Adolescent Medicine, Danish PCD and chILD Centre, CF Centre Copenhagen, Pediatric Pulmonary Service, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Jacob S
authors.initials: JS
authors.lastname: Ejlertsen
authors.affiliation: Department of Pediatric and Adolescent Medicine, Danish PCD and chILD Centre, CF Centre Copenhagen, Pediatric Pulmonary Service, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Astrid
authors.initials: A
authors.lastname: Madsen
authors.affiliation: Department of Pediatric and Adolescent Medicine, Danish PCD and chILD Centre, CF Centre Copenhagen, Pediatric Pulmonary Service, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Frederik F
authors.initials: FF
authors.lastname: Buchvald
authors.affiliation: Department of Pediatric and Adolescent Medicine, Danish PCD and chILD Centre, CF Centre Copenhagen, Pediatric Pulmonary Service, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.|Research Unit on Women's and Children's Health, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kongstad
authors.affiliation: Department of Pediatric and Adolescent Medicine, Danish PCD and chILD Centre, CF Centre Copenhagen, Pediatric Pulmonary Service, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.|Research Unit on Women's and Children's Health, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Helene
authors.initials: H
authors.lastname: Kobbernagel
authors.affiliation: Department of Pediatrics, Central Hospital, Skövde, Sweden.
authors.forename: Per M
authors.initials: PM
authors.lastname: Gustafsson
authors.affiliation: Department of Pediatric and Adolescent Medicine, Danish PCD and chILD Centre, CF Centre Copenhagen, Pediatric Pulmonary Service, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Kim G
authors.initials: KG
authors.lastname: Nielsen
mesh_terms: D000293:Adolescent; D001944:Breath Tests / Q000379:methods*; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D003550:Cystic Fibrosis / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D005652:Functional Residual Capacity; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008173:Lung Diseases, Obstructive / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D009585:Nitrogen Dioxide / Q000032:analysis*; D011446:Prospective Studies; D012129:Respiratory Function Tests; D013990:Tidal Volume; D014109:Total Lung Capacity
chemical_list: D009585:Nitrogen Dioxide
keywords: cystic fibrosis; lung function; multiple-breath washout; observational study; primary ciliary dyskinesia