title: Increased day-to-day variability of forced oscillatory resistance in poorly controlled or persistent pediatric asthma.
abstract: BACKGROUND
  Pediatric asthma lacks sensitive objective measures for asthma monitoring. The forced oscillation technique (FOT) offers strong feasibility across the pediatric age range, but relationships between FOT parameter day-to-day variability and pediatric asthma severity and control are unknown.
  
  
  METHODS
  Day-to-day variability in FOT respiratory system resistance (Rrs) and respiratory system reactance (Xrs) compared with peak expiratory flow (PEF) were defined in 22 children with asthma (mean ± SD age, 10.4 ± 1.1 years) during a 5-day asthma camp. FOT was performed at 6 Hz in triplicate on each test occasion. Relationships between day-to-day FOT variability (expressed as within-subject SD [SDW] and asthma control and severity (defined according to GINA [Global Initiative for Asthma] recommendations) were explored. For comparison, normal baseline FOT values and variability, measured on two occasions, were defined in a separate cohort of 38 healthy children (age, 9.5 ± 1.0 years).
  
  
  RESULTS
  Day-to-day Rrs variability was greater in persistent (n = 16) vs intermittent (n = 6) asthma (mean SDW, 0.69 cm H2O/L/s vs 0.39 cm H2O/L/s; P ≤ .01). Day-to-day Rrs variability was increased in uncontrolled (n = 13) vs partly controlled asthma (n = 9) (mean SDW, 0.75 cm H2O/L/s vs 0.42 cm H2O/L/s; P ≤ .05). PEF variability did not differentiate the groups. Day-to-day variability of Rrs and Xrs but not baseline values were increased in children with asthma vs control children (Rrs mean SDW, 0.61 cm H2O/L/s vs 0.33 cm H2O/L/s [P ≤ .05]; Xrs mean SDW, 0.24 cm H2O/L/s vs 0.15 cm H2O/L/s [P ≤ .05]).
  
  
  CONCLUSIONS
  Increased day-to-day FOT variability exists in school-aged children with asthma. Day-to-day Rrs variability was associated with asthma severity and asthma control. FOT may be a useful objective monitoring tool in pediatric asthma and warrants further study.
  
  
  BACKGROUND
  Australian and New Zealand Clinical Trials Registry; No.: ACTRN12614000885695; URL: www.anzctr.org.au.
authors.affiliation: Woolcock Institute of Medical Research, Sydney; The University of Sydney, Sydney; Department of Respiratory Medicine, The Children's Hospital at Westmead, Westmead; Cooperative Research Centre for Asthma and Airways, Sydney. Electronic address: dr.pdrobinson@gmail.com.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Robinson
authors.affiliation: Woolcock Institute of Medical Research, Sydney; The University of Sydney, Sydney; Cooperative Research Centre for Asthma and Airways, Sydney.
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Brown
authors.affiliation: Woolcock Institute of Medical Research, Sydney; The University of Sydney, Sydney; Cooperative Research Centre for Asthma and Airways, Sydney.
authors.forename: Martin
authors.initials: M
authors.lastname: Turner
authors.affiliation: The University of Sydney, Sydney; Department of Respiratory Medicine, The Children's Hospital at Westmead, Westmead.
authors.forename: Peter
authors.initials: P
authors.lastname: Van Asperen
authors.affiliation: The University of Sydney, Sydney; Department of Respiratory Medicine, The Children's Hospital at Westmead, Westmead.
authors.forename: Hiran
authors.initials: H
authors.lastname: Selvadurai
authors.affiliation: Woolcock Institute of Medical Research, Sydney; The University of Sydney, Sydney; Cooperative Research Centre for Asthma and Airways, Sydney; Department of Respiratory Medicine, Royal North Shore Hospital, St. Leonards, NSW, Australia.
authors.forename: Gregory G
authors.initials: GG
authors.lastname: King
mesh_terms: D000403:Airway Resistance / Q000502:physiology*; D001249:Asthma / Q000503:physiopathology*; D002648:Child; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D009991:Oscillometry / Q000379:methods*; D012720:Severity of Illness Index; D013147:Spirometry