Kanika Jetmalani,1,2 Sophie Timmins,1,3,4 Nathan J Brown,1,4 Chantale Diba,1,4 Norbert Berend,1,4,5 Cheryl M Salome,1,2,4 Fu-Qiang Wen,6 Peng Chen,6 Gregory G King,1-4 Claude S Farah1,2,7 1Woolcock Institute of Medical Research, 2Sydney Medical School, University of Sydney, 3Department of Respiratory Medicine, Royal North Shore Hospital, 4Cooperative Research Centre for Asthma and Airways, 5Department of Respiratory Research, George Institute of Global Health, Sydney, NSW, Australia; 6Department of Medicine, West China Hospital, West China School of Medicine, Sichuan University, Chengdu, People’s Republic of China; 7Department of Respiratory Medicine, Concord Hospital, Sydney, NSW, Australia Background: Expiratory flow limitation (EFL) is seen in some patients presenting with a COPD exacerbation; however, it is unclear how EFL relates to the clinical features of the exacerbation. We hypothesized that EFL when present contributes to symptoms and duration of recovery during a COPD exacerbation. Our aim was to compare changes in EFL with symptoms in subjects with and without flow-limited breathing admitted for a COPD exacerbation.Subjects and methods: A total of 29 subjects with COPD were recruited within 48 hours of admission to West China Hospital for an acute exacerbation. Daily measurements of postbronchodilator spirometry, resistance, and reactance using the forced oscillation technique and symptom (Borg) scores until discharge were made. Flow-limited breathing was defined as the difference between inspiratory and expiratory respiratory system reactance (EFL index) greater than 2.8 cmH2O·s·L-1. The physiological predictors of symptoms during recovery were determined by mixed-effect analysis.Results: Nine subjects (31%) had flow-limited breathing on admission despite similar spirometry compared to subjects without flow-limited breathing. Spirometry and resistance measures did not change between enrolment and discharge. EFL index values improved in subjects with flow-limited breathing on admission, with resolution in four patients. In subjects with flow-limited breathing on admission, symptoms were related to inspiratory resistance and EFL index values. In subjects without flow-limited breathing, symptoms related to forced expiratory volume in 1 second/forced vital capacity. In the whole cohort, EFL index values at admission was related to duration of stay (Rs=0.4, P=0.03).Conclusion: The presence of flow-limited breathing as well as abnormal respiratory system mechanics contribute independently to symptoms during COPD exacerbations. Keywords: COPD, exacerbations, flow limitation, respiratory mechanics, symptoms