Abstract
BACKGROUND: Forced Oscillation Technique (FOT) is an innovative tool to measure within-breath reactance at 5 Hz (ΔXrs(5Hz)) but its feasibility and utility in acute exacerbations of COPD (AECOPD) is understudied. METHODS: A prospective observational study was conducted in 82 COPD patients admitted due to AECOPD. FOT indices were measured and the association between these indices and spirometry, peak inspiratory flow rate, blood inflammatory biomarkers and patient-reported outcomes including assessment of dyspnoea, quality of life, anxiety and depression and frailty at admission and discharge were explored. RESULTS: All patients were able to perform FOT in both sitting and supine position. The prevalence of expiratory flow limitation (EFL) in the upright position was 39% (32 out of 82) and increased to 50% (41 out of 82) in the supine position. EFL (measured by ΔXrs(5Hz)) and resistance at 5 Hz (Rrs(5Hz)) negatively correlated with forced expiratory volume in 1 s (FEV(1)); those with EFL had lower FEV(1) (0.74±0.30 versus 0.94±0.36 L, p = 0.01) and forced vital capacity (1.7±0.55 versus 2.1±0.63 L, p = 0.009) and higher body mass index (27 (21-36) versus 23 (19-26) kg·m(-2), p = 0.03) compared to those without EFL. During recovery from AECOPD, changes in EFL were observed in association with improvement in breathlessness. CONCLUSION: FOT was easily used to detect EFL during hospitalisation due to AECOPD. The prevalence of EFL increased when patients moved from a seated to a supine position and EFL was negatively correlated with airflow limitation. Improvements in EFL were associated with a reduction in breathlessness. FOT is of potential clinical value by providing a noninvasive, objective and effort-independent technique to measure lung function parameters during AECOPD requiring hospital admission.