title: Use of an impedance meter for measuring airways responsiveness to histamine.
abstract: We compared spirometry (FEV1) and airway impedance (z) in the assessment of airway responsiveness to histamine. Airway impedance was measured by the oscillator technique during quiet breathing; both measurements were made twice after each increment of histamine during the challenge. Percentage change in impedance was related to percentage change in FEV1 according to: -delta z = 1.09-2.66 (delta FEV1), r = -0.73, p less than 0.01, ie, impedance increased on average 2.7 times as much as FEV1 fell. The cut-off point for the standard test is the histamine concentration giving a 20 percent fall of FEV1 (PC20(FEV1)). The corresponding cut-off value chosen for impedance was a 30 percent increase (PC30(z)). (PC30(z)) = 0.74 (PC20(FEV1))-0.48, rs = 0.88, where rs is the Spearman rank correlation coefficient. Thus, impedance is a more sensitive index than FEV1 because a smaller dose of histamine gave a diagnostic result. Impedance is a practical alternative to FEV1, being less arduous for the patient and requiring little cooperation.
authors.affiliation: Department of Medicine, Charing Cross Hospital, London, England.
authors.forename: P D
authors.initials: PD
authors.lastname: Snashall
authors.forename: S
authors.initials: S
authors.lastname: Parker
authors.forename: P
authors.initials: P
authors.lastname: Ten Haave
authors.forename: D
authors.initials: D
authors.lastname: Simmons
authors.forename: M I
authors.initials: MI
authors.lastname: Noble
mesh_terms: D000328:Adult; D000403:Airway Resistance / Q000502:physiology*; D001985:Bronchial Provocation Tests / Q000379:methods*; D005260:Female; D005541:Forced Expiratory Volume; D006632:Histamine; D006801:Humans; D008297:Male; D009991:Oscillometry / Q000295:instrumentation*; D013147:Spirometry
chemical_list: D006632:Histamine