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 (ΔX_rs) occurs. However, flow limitation can vary from breath to breath, and so we compared a multiple-breath ΔX_rs 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 ΔX_rs when used as a continuous measurement over multiple breaths. In addition, we examined how multiple-breath ΔX_rs 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 ΔX_rs approached zero in healthy controls with little variation between measurements. COPD patients generally had higher ΔX_rs and higher variability. The COPD patients with ΔX_rs >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 ΔX_rs 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 ΔX_rs >0.1 kPa·L⁻¹·s⁻¹, as a way to identify COPD patients who are more likely to report dyspnoea.