• Kanika Jetmalani, Sophie Timmins, Nathan J Brown, Chantale Diba, Norbert Berend, Cheryl M Salome, Fu-Qiang Wen, Peng Chen, Gregory G King, and Claude S Farah.
• Woolcock Institute of Medical Research, University of Sydney, Sydney, NSW, Australia ; Sydney Medical School, University of Sydney, Sydney, NSW, Australia.
• Int J Chron Obstruct Pulmon Dis. 2015 Jan 1; 10: 939-45.

BackgroundExpiratory 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 MethodsA total of 29 subjects with COPD were recruited within 48 hours of admission to West China Hospital for an acute exacerbation. Daily measurements of post-bronchodilator 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.ResultsNine 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).ConclusionThe presence of flow-limited breathing as well as abnormal respiratory system mechanics contribute independently to symptoms during COPD exacerbations.

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