title: Expiratory flow limitation relates to symptoms during COPD exacerbations requiring hospital admission.
abstract: 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.
  
  
  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 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.
  
  
  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).
  
  
  CONCLUSIONS
  The presence of flow-limited breathing as well as abnormal respiratory system mechanics contribute independently to symptoms during COPD exacerbations.
authors.affiliation: Woolcock Institute of Medical Research, University of Sydney, Sydney, NSW, Australia ; Sydney Medical School, University of Sydney, Sydney, NSW, Australia.
authors.forename: Kanika
authors.initials: K
authors.lastname: Jetmalani
authors.affiliation: Woolcock Institute of Medical Research, University of Sydney, Sydney, NSW, Australia ; Department of Respiratory Medicine, Royal North Shore Hospital, Sydney, NSW, Australia ; Cooperative Research Centre for Asthma and Airways, George Institute of Global Health, Sydney, NSW, Australia.
authors.forename: Sophie
authors.initials: S
authors.lastname: Timmins
authors.affiliation: Woolcock Institute of Medical Research, University of Sydney, Sydney, NSW, Australia ; Cooperative Research Centre for Asthma and Airways, George Institute of Global Health, Sydney, NSW, Australia.
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Brown
authors.affiliation: Woolcock Institute of Medical Research, University of Sydney, Sydney, NSW, Australia ; Cooperative Research Centre for Asthma and Airways, George Institute of Global Health, Sydney, NSW, Australia.
authors.forename: Chantale
authors.initials: C
authors.lastname: Diba
authors.affiliation: Woolcock Institute of Medical Research, University of Sydney, Sydney, NSW, Australia ; Cooperative Research Centre for Asthma and Airways, George Institute of Global Health, Sydney, NSW, Australia ; Department of Respiratory Research, George Institute of Global Health, Sydney, NSW, Australia.
authors.forename: Norbert
authors.initials: N
authors.lastname: Berend
authors.affiliation: Woolcock Institute of Medical Research, University of Sydney, Sydney, NSW, Australia ; Sydney Medical School, University of Sydney, Sydney, NSW, Australia ; Cooperative Research Centre for Asthma and Airways, George Institute of Global Health, Sydney, NSW, Australia.
authors.forename: Cheryl M
authors.initials: CM
authors.lastname: Salome
authors.affiliation: Department of Medicine, West China Hospital, West China School of Medicine, Sichuan University, Chengdu, People's Republic of China.
authors.forename: Fu-Qiang
authors.initials: FQ
authors.lastname: Wen
authors.affiliation: Department of Medicine, West China Hospital, West China School of Medicine, Sichuan University, Chengdu, People's Republic of China.
authors.forename: Peng
authors.initials: P
authors.lastname: Chen
authors.affiliation: Woolcock Institute of Medical Research, University of Sydney, Sydney, NSW, Australia ; Sydney Medical School, University of Sydney, Sydney, NSW, Australia ; Department of Respiratory Medicine, Royal North Shore Hospital, Sydney, NSW, Australia ; Cooperative Research Centre for Asthma and Airways, George Institute of Global Health, Sydney, NSW, Australia.
authors.forename: Gregory G
authors.initials: GG
authors.lastname: King
authors.affiliation: Woolcock Institute of Medical Research, University of Sydney, Sydney, NSW, Australia ; Sydney Medical School, University of Sydney, Sydney, NSW, Australia ; Department of Respiratory Medicine, Concord Hospital, Sydney, NSW, Australia.
authors.forename: Claude S
authors.initials: CS
authors.lastname: Farah
mesh_terms: D000368:Aged; D000403:Airway Resistance; D001993:Bronchodilator Agents / Q000627:therapeutic use; D002681:China; D018450:Disease Progression; D045853:Exhalation / Q000187:drug effects; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D001239:Inhalation; D008168:Lung / Q000187:drug effects / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010343:Patient Admission; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology*; D020127:Recovery of Function; D013147:Spirometry; D013997:Time Factors; D016896:Treatment Outcome; D014797:Vital Capacity
chemical_list: D001993:Bronchodilator Agents
keywords: COPD; exacerbations; flow limitation; respiratory mechanics; symptoms