title: Short and long term variability of the interrupter technique under field and standardised conditions in 3-6 year old children.
abstract: BACKGROUND
  The short and long term variability of the interrupter technique was assessed to determine whether interrupter resistance is a stable individual characteristic over time. The effect of field and standardised measurement conditions on the within-subject variability of the interrupter technique was also examined.
  
  
  METHODS
  The interrupter technique was studied under field and standardised conditions in children aged 3-6 years. Under field conditions, five investigators performed the measurements using two different measurement devices in random sequence. Both short term (20-30 minutes) and long term variability (median 38 days) were assessed in 32 children. Under standardised conditions, a single investigator conducted all measurements using a single device; the repeated measurements were conducted at the same time of day in a familiar quiet classroom. Long term variability (median 11 days) was estimated in 15 children. Within-subject standard deviations were estimated by analysis of variance with adjustment for the effects of different investigators and measurement devices on within-subject variability under field conditions.
  
  
  RESULTS
  Under field conditions within-subject standard deviations for short and long term variability were 0.10 kPa/l/s (adjusted 0.10 kPa/l/s) and 0.13 kPa/l/s (adjusted 0.14 kPa/l/s), respectively. Under standardised conditions the within-subject standard deviation for long term variability was 0.10 kPa/l/s.
  
  
  CONCLUSIONS
  Measurement of interrupter resistance under field conditions only slightly increased the within-subject variability compared with standardised conditions. The results indicate that interrupter resistance is a stable individual characteristic over a period of some weeks.
authors.affiliation: Department of Environmental and Occupational Health, Institute for Risk Assessment Sciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: R M J
authors.initials: RM
authors.lastname: Beelen
authors.forename: H A
authors.initials: HA
authors.lastname: Smit
authors.forename: R T
authors.initials: RT
authors.lastname: van Strien
authors.forename: L P
authors.initials: LP
authors.lastname: Koopman
authors.forename: J E
authors.initials: JE
authors.lastname: Brussee
authors.forename: B
authors.initials: B
authors.lastname: Brunekreef
authors.forename: J
authors.initials: J
authors.lastname: Gerritsen
authors.forename: P J F M
authors.initials: PJ
authors.lastname: Merkus
mesh_terms: D000403:Airway Resistance / Q000502:physiology*; D000704:Analysis of Variance; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D015588:Observer Variation; D012129:Respiratory Function Tests / Q000295:instrumentation* / Q000592:standards; D012680:Sensitivity and Specificity