title: Accuracy of whole-body plethysmography requires biological calibration.
abstract: BACKGROUND
  Specific airway resistance (sRaw) measured by whole-body plethysmography in young children is increasingly used in research and clinical practice. The method is precise and feasible. However, there is no available method for calibration of the resistance measure, which raises concern of accuracy. Our aim was to determine the agreement of sRaw measurements in six centers and expand normative sRaw values for nonasthmatic children including these centers.
  
  
  METHODS
  Identical hardware with different software versions was used at the six centers. Measurements followed a standard operating procedure: (1) seven healthy young children were brought to each of the six centers for sRaw measurements; and (2) 105 healthy preschool children (52 boys; mean age, 5.1 years; interquartile range, 4.3 to 6.0) were recruited locally for sRaw measurements.
  
  
  RESULTS
  (1) The sRaw of the seven-children study group was significantly lower at two centers compared with the other four centers, and one center had significantly higher sRaw than all the other centers (p < 0.05). Error in the factory settings of the software was subsequently discovered in one of the deviating centers. (2) Normative data (105 preschool children) were generated and were without significant difference between centers and independent of height, weight, age, and gender. We subsequently pooled these normative data (105 children) with our previous data from 121 healthy young children (overall mean sRaw, 1.27; SD, 0.25).
  
  
  CONCLUSIONS
  Control using biological standards revealed errors in the factory setting and highlights the need for developing methods for verification of resistance measures to assure accuracy. Normative data were subsequently generated. Importantly, other centers using such normative data should first consider proper calibration before applying reference values.
authors.affiliation: Pediatric Department, Naestved Hospital, Naestved, Denmark.
authors.forename: Porntiva
authors.initials: P
authors.lastname: Poorisrisak
authors.affiliation: Pediatric Department, Naestved Hospital, Naestved, Denmark.
authors.forename: Carsten
authors.initials: C
authors.lastname: Vrang
authors.affiliation: Pediatric Department, Aarhus University Hospital, Skejby, Denmark.
authors.forename: Jorn Molgaard
authors.initials: JM
authors.lastname: Henriksen
authors.affiliation: Pediatric Department, Copenhagen University Hospital, Hvidovre, Denmark.
authors.forename: Bent
authors.initials: B
authors.lastname: Klug
authors.affiliation: Pediatric Department, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Birgitte
authors.initials: B
authors.lastname: Hanel
authors.affiliation: Copenhagen Prospective Study on Asthma in Children, Danish Pediatric Asthma Center, Health Sciences, University of Copenhagen, Copenhagen University Hospital, Gentofte, Denmark. Electronic address: Bisgaard@copsac.dk.
authors.forename: Hans
authors.initials: H
authors.lastname: Bisgaard
mesh_terms: D000403:Airway Resistance / Q000502:physiology*; D002675:Child, Preschool; D003718:Denmark; D005260:Female; D006801:Humans; D008297:Male; D015588:Observer Variation; D010993:Plethysmography, Whole Body / Q000379:methods* / Q000592:standards*; D012016:Reference Values; D012680:Sensitivity and Specificity