title: Variability of within-breath reactance in COPD patients and its association with dyspnoea.
abstract: The forced oscillation technique can identify expiratory flow limitation (EFL) when a large difference in inspiratory and expiratory reactance (ΔXrs) occurs. However, flow limitation can vary from breath to breath, and so we compared a multiple-breath ΔXrs approach to the traditional breath-by-breath assessment of EFL. We investigated the within- and between-day reproducibility and the factors that affect the size of ΔXrs when used as a continuous measurement over multiple breaths. In addition, we examined how multiple-breath ΔXrs relates to the sensation of breathlessness. 425 moderate to very severe chronic obstructive pulmonary disease (COPD) patients and 229 controls were included. Spirometry and impedance measurements were performed on a MasterScope CT Impulse Oscillation System. Median ΔXrs approached zero in healthy controls with little variation between measurements. COPD patients generally had higher ΔXrs and higher variability. The COPD patients with ΔXrs >0.1 kPa · L(-1) · s(-1) were prone to be more breathless and had a higher modified Medical Research Council dyspnoea scale score. In controls, the 95th percentile of ΔXrs was as low as 0.07 kPa · L(-1) · s(-1). We describe a new method to assess EFL at a patient level and propose a cut-off, mean ΔXrs >0.1 kPa · L(-1) · s(-1), as a way to identify COPD patients who are more likely to report dyspnoea.
authors.affiliation: Institute of Clinical Science, University of Bergen, Bergen, Norway Dept of Thoracic Medicine, Haukeland University Hospital, Bergen, Norway bernt.aarli@k2.uib.no.
authors.forename: Bernt B
authors.initials: BB
authors.lastname: Aarli
authors.affiliation: Clinical Science Centre, University Hospital Aintree, Liverpool, UK.
authors.forename: Peter M A
authors.initials: PM
authors.lastname: Calverley
authors.affiliation: LDS Hospital, Pulmonary Division, Salt Lake City, UT, USA.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Jensen
authors.affiliation: Institute of Clinical Science, University of Bergen, Bergen, Norway Dept of Thoracic Medicine, Haukeland University Hospital, Bergen, Norway.
authors.forename: Tomas M L
authors.initials: TM
authors.lastname: Eagan
authors.affiliation: Institute of Clinical Science, University of Bergen, Bergen, Norway.
authors.forename: Per S
authors.initials: PS
authors.lastname: Bakke
authors.affiliation: Institute of Clinical Science, University of Bergen, Bergen, Norway.
authors.forename: Jon A
authors.initials: JA
authors.lastname: Hardie
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D016022:Case-Control Studies; D004417:Dyspnea / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology; D005260:Female; D005540:Forced Expiratory Flow Rates; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway; D009991:Oscillometry / Q000379:methods; D010991:Plethysmography / Q000379:methods; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013147:Spirometry / Q000379:methods