title: Day-to-day variability of oscillatory impedance and spirometry in asthma and COPD.
abstract: Variability in airway function may be a marker of disease activity in COPD and asthma. The aim was to determine the effects of repeatability and airway obstruction on day-to-day variability in respiratory system resistance (Rrs) and reactance (Xrs) measured by forced oscillation technique (FOT). Three groups of 10 subjects; normals, stable asthmatic and stable COPD subjects underwent daily FOT recordings for 7 days. Mean total and inspiratory Rrs and Xrs, and expiratory flow limitation (EFL) Index (inspiratory - expiratory Xrs), were calculated. The ICC's were high for all parameters in all groups. Repeatability, in terms of absolute units, correlated with airway obstruction and was therefore lowest in COPD. Day-to-day variability was due mostly to repeatability, with a small contribution from the mean value for some parameters. FOT measures are highly repeatable in health, stable asthma and COPD in relation to the wide range of measures between subjects. For home monitoring in asthma and COPD, either the coefficient of variation or individualized SDs could be used to define day-to-day variability.
authors.affiliation: The Woolcock Institute of Medical Research, Glebe, NSW 2037, Australia. stimmins@med.usyd.edu.au
authors.forename: Sophie C
authors.initials: SC
authors.lastname: Timmins
authors.forename: Nicholas
authors.initials: N
authors.lastname: Coatsworth
authors.forename: Gaurie
authors.initials: G
authors.lastname: Palnitkar
authors.forename: Cindy
authors.initials: C
authors.lastname: Thamrin
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Farrow
authors.forename: Robin E
authors.initials: RE
authors.lastname: Schoeffel
authors.forename: Norbert
authors.initials: N
authors.lastname: Berend
authors.forename: Chantale
authors.initials: C
authors.lastname: Diba
authors.forename: Cheryl M
authors.initials: CM
authors.lastname: Salome
authors.forename: Gregory G
authors.initials: GG
authors.lastname: King
mesh_terms: D000328:Adult; D000403:Airway Resistance / Q000502:physiology*; D001249:Asthma / Q000503:physiopathology*; D017097:Electric Impedance; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology*; D006801:Humans; D008297:Male; D019370:Observation; D009991:Oscillometry; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D013147:Spirometry; D018709:Statistics, Nonparametric; D014797:Vital Capacity / Q000502:physiology*