title: Useful marker of oscillatory lung function in methacholine challenge test-comparison of reactance and resistance with dose-response slope.
abstract: BACKGROUND
  There are few studies focusing on the comparison of resistance (Rrs) and reactance (Xrs) in impulse oscillometry system (IOS) in the bronchial challenge test using dose-response slope (DRS), a quantitative index of bronchial hyperresponsiveness.
  
  
  METHODS
  We conducted a case-control study of 144 asthmatic and 218 non-asthmatic children to compare the diagnostic accuracy of two-point linear DRS for FEV1 , Rrs5 , and Xrs5 (DRS_FEV1 , DRS_Rrs5 , and DRS_Xrs5 ) and assessed various diagnostic cut-off points of provocation concentrations (PC) using receiver operating characteristic (ROC) curves.
  
  
  RESULTS
  DRS_FEV1 had a stronger correlation with DRS_Xrs5 (r = 0.739, P < 0.001) than with DRS_Rrs5 (r = 0.652, P < 0.001) and the area under the ROC curves of DRS_Xrs5 (0.737) was similar to that of DRS_FEV1 (0.732) and higher than that of DRS_Rrs5 (0.668). The area under the ROC curves in order of greater value was as follows: absolute change of Xrs5 (Abs_Xrs5 ) (0.759) > percent change of FEV1 (Pch_FEV1 ) (0.735) > Pch_Xrs5 (0.727) > Abs_Rrs5 (0.690) > Pch_Rrs5 (0.630). PC78 _Xrs5 and PC0.17 _Xrs5 of IOS showed considerably good sensitivity and specificity comparable to those of PC20 _FEV1 by spirometry. Additional 18 (13%) children who showed normal spirometric measures were identified as asthmatics with the use of IOS.
  
  
  CONCLUSIONS
  The utility of the DRS_Xrs5 to differentiate asthmatics from controls was comparable to that of the DRS_FEV1 and better than that of the DRS_Rrs5 . In addition, IOS could detect additional asthmatic patients who did not show positive responses in spirometry.
authors.affiliation: Department of Pediatrics, CHA University School of Medicine, Seongnam, Korea.
authors.forename: Jung Won
authors.initials: JW
authors.lastname: Yoon
authors.forename: Youn Ho
authors.initials: YH
authors.lastname: Shin
authors.forename: Hye Mi
authors.initials: HM
authors.lastname: Jee
authors.forename: Sun Jung
authors.initials: SJ
authors.lastname: Chang
authors.forename: Ji Hyeon
authors.initials: JH
authors.lastname: Baek
authors.forename: Sun Hee
authors.initials: SH
authors.lastname: Choi
authors.forename: Hyeong Yun
authors.initials: HY
authors.lastname: Kim
authors.forename: Man Yong
authors.initials: MY
authors.lastname: Han
mesh_terms: D000293:Adolescent; D001249:Asthma / Q000175:diagnosis*; D015415:Biomarkers; D016535:Bronchial Hyperreactivity / Q000175:diagnosis*; D001985:Bronchial Provocation Tests / Q000379:methods*; D016085:Bronchoconstrictor Agents; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D003937:Diagnosis, Differential; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008297:Male; D016210:Methacholine Chloride; D009991:Oscillometry / Q000379:methods*; D012372:ROC Curve; D012680:Sensitivity and Specificity; D013147:Spirometry / Q000379:methods
chemical_list: D015415:Biomarkers; D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride
keywords: asthma; bronchial hyperresponsiveness; dose-response slope; impulse oscillometry system