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·Lwere 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. @ERSpublications Within-breath reactance in COPD correlates with dyspnoea and adds information beyond that of spirometry alone

Telemonitoring in Chronic Obstructive Pulmonary Disease (CHROMED). A Randomized Clinical Trial

“…FOT measurements were cleaned automatically from artefacts using previously published filtering rules 29 and automatically sent to the study server. An algorithm generated respiratory alerts if a trend of worsening was detected in at least one of the following FOT parameters measured at 5Hz: inspiratory resistance (Rinsp), inspiratory reactance (Xinsp) or the difference between inspiratory and expiratory reactance (∆Xrs), an index of the presence of tidal expiratory flow limitation 30,31 . Specifically, a worsening was deemed to occur when a statistically significant (p<0.05) linear increase of Rinsp or ∆Xrs or a decrease of Xinsp and a correlation coefficient of at least 0.4 was detected in a time window of ten days including the current measurement (see ONLINE DATA SUPPLEMENT).…”

Clinical characteristics of COPD patients with tidal expiratory flow limitation

“…Aarli et al 6 Note: Data are presented as mean (95% CI), median (interquartile range), and percentages as appropriate. Abbreviations: EFL, expiratory flow limitation; ICS, inhaled corticosteroid; LABA, long-acting beta agonist; LAMA, long-acting muscarinic antagonist; BD, bronchodilator; FeV 1 , forced expired volume in 1 second; FVC, forced vital capacity; SGRQ, St George's Respiratory Questionnaire; CAT, COPD Assessment Test; VAS, visual analog scale (dyspnea); 6MWD, 6-minute walk distance; DLCO, diffusing capacity of the lungs for carbon monoxide; KCO, carbon monoxide transfer coefficient; VA, alveolar volume; TLC, total lung capacity; RV, residual volume; FRC, functional residual capacity; R5, total resistance; R20, central resistance; R5-R20, peripheral resistance; R5insp-R20insp, peripheral resistance during inspiration; X5, total reactance; ∆X5, difference in total reactance between inspiration and expiration; AX, reactance area; Fres, resonance frequency; R5exp, total expiratory resistance; R5insp, total inspiratory resistance; X5exp, total expiratory reactance; X5insp, total inspiratory reactance; CI, confidence interval.…”

“…COPD patients with higher ∆X5 values have greater dyspnea. 6 The aim of this study was to quantify the proportion of COPD patients with EFL, and to further characterize the clinical characteristics of patients with EFL. We also studied whether the presence of EFL is stable after 2 years of follow-up.…”

“…COPD patients typically have increased total airway resistance and a greater negative reactance compared to healthy subjects. 6 Small airway narrowing and closure during expiration can prevent low-frequency oscillometric signals from traveling to the distal lung. 6 These regional "choke points" within the airway tree are present during expiration but not during inspiration, and cause expiratory flow limitation (EFL).…”

“…6 Small airway narrowing and closure during expiration can prevent low-frequency oscillometric signals from traveling to the distal lung. 6 These regional "choke points" within the airway tree are present during expiration but not during inspiration, and cause expiratory flow limitation (EFL). EFL can be detected by a marked change in reactance during tidal breathing.…”