title: The relationship between airflow obstruction, emphysema extent, and small airways function in COPD.
abstract: BACKGROUND
  The severities of COPD (FEV(1) % predicted) and airflow obstruction (FEV(1)/FVC) are considered to be due to both emphysema and small airways disease. To our knowledge, this has not been previously confirmed by combined measurements of emphysema and of small airway function. We hypothesized that small airways disease and emphysema extent contribute independently to the severity of both COPD and airflow obstruction.
  
  
  METHODS
  Twenty-six subjects with COPD underwent measurements with forced oscillation technique (FOT) at 6 Hz and single-breath nitrogen washout. Respiratory system resistance, respiratory system reactance (Xrs), and expiratory flow limitation (EFL) index (measured as mean inspiratory Xrs − expiratory Xrs) were derived from FOT. Closing volume/vital capacity (CV/VC) was derived from the washout. Emphysema extent was measured as low attenuation areas < -910 Hounsfield units, expressed as a percentage of CT scan lung volume from multislice CT scans taken at total lung capacity.
  
  
  RESULTS
  Subjects were aged (mean ± SD) 69.6 ± 8.0 years. Postbronchodilator FEV(1) was 64.8 ± 19.8% predicted, and diffusing capacity of lung for carbon monoxide was 50.7 ± 15.8% predicted. Emphysema extent was 22.6% ± 15.0% CT scan volume. CV/VC was 16.9% ± 7.9%; Xrs, -3.72 ± 3.03 cm H(2)O/L/s; and EFL index, 3.88 ± 3.93 cm H(2)O/L/s. In multiple regression analyses, FEV(1)/FVC was predicted by both emphysema and CV/VC (model r(2) = 0.54, P < .0001) whereas FEV(1) % predicted was predicted by emphysema and EFL index (model r(2) = 0.38, P = .0014).
  
  
  CONCLUSIONS
  The severities of COPD and airflow obstruction are independently predicted by both small airways disease and emphysema extent.
authors.affiliation: Woolcock Institute of Medical Research, Australia; Cooperative Research Centre for Asthma and Airways, Glebe, St. Leonards, Australia; Department of Respiratory Medicine, Royal North Shore Hospital, St. Leonards, Australia; Sydney Medical School, University of Sydney, Sydney, NSW, Australia. Electronic address: stimmins@med.usyd.edu.au.
authors.forename: Sophie C
authors.initials: SC
authors.lastname: Timmins
authors.affiliation: Woolcock Institute of Medical Research, Australia; Cooperative Research Centre for Asthma and Airways, Glebe, St. Leonards, Australia.
authors.forename: Chantale
authors.initials: C
authors.lastname: Diba
authors.affiliation: Woolcock Institute of Medical Research, Australia; Cooperative Research Centre for Asthma and Airways, Glebe, St. Leonards, Australia; Sydney Medical School, University of Sydney, Sydney, NSW, Australia.
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Farrow
authors.affiliation: Woolcock Institute of Medical Research, Australia; Department of Respiratory Medicine, Royal North Shore Hospital, St. Leonards, Australia; Sydney Medical School, University of Sydney, Sydney, NSW, Australia.
authors.forename: Robin E
authors.initials: RE
authors.lastname: Schoeffel
authors.affiliation: Woolcock Institute of Medical Research, Australia; Cooperative Research Centre for Asthma and Airways, Glebe, St. Leonards, Australia; Sydney Medical School, University of Sydney, Sydney, NSW, Australia.
authors.forename: Norbert
authors.initials: N
authors.lastname: Berend
authors.affiliation: Woolcock Institute of Medical Research, Australia; Cooperative Research Centre for Asthma and Airways, Glebe, St. Leonards, Australia; Sydney Medical School, University of Sydney, Sydney, NSW, Australia.
authors.forename: Cheryl M
authors.initials: CM
authors.lastname: Salome
authors.affiliation: Woolcock Institute of Medical Research, Australia; Cooperative Research Centre for Asthma and Airways, Glebe, St. Leonards, Australia; Department of Respiratory Medicine, Royal North Shore Hospital, St. Leonards, Australia; Sydney Medical School, University of Sydney, Sydney, NSW, Australia.
authors.forename: Gregory G
authors.initials: GG
authors.lastname: King
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000403:Airway Resistance / Q000502:physiology; D055745:Bronchioles / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D004646:Emphysema / Q000150:complications* / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011650:Pulmonary Alveoli / Q000503:physiopathology*; D011653:Pulmonary Diffusing Capacity / Q000502:physiology; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology*; D012720:Severity of Illness Index; D014057:Tomography, X-Ray Computed; D014797:Vital Capacity / Q000502:physiology