title: Association Between Expiratory Central Airway Collapse and Respiratory Outcomes Among Smokers.
abstract: OBJECTIVE
  Central airway collapse greater than 50% of luminal area during exhalation (expiratory central airway collapse [ECAC]) is associated with cigarette smoking and chronic obstructive pulmonary disease (COPD). However, its prevalence and clinical significance are unknown.
  
  
  OBJECTIVE
  To determine whether ECAC is associated with respiratory morbidity in smokers independent of underlying lung disease.
  
  
  METHODS
  Analysis of paired inspiratory-expiratory computed tomography images from a large multicenter study (COPDGene) of current and former smokers from 21 clinical centers across the United States. Participants were enrolled from January 2008 to June 2011 and followed up longitudinally until October 2014. Images were initially screened using a quantitative method to detect at least a 30% reduction in minor axis tracheal diameter from inspiration to end-expiration. From this sample of screen-positive scans, cross-sectional area of the trachea was measured manually at 3 predetermined levels (aortic arch, carina, and bronchus intermedius) to confirm ECAC (>50% reduction in cross-sectional area).
  
  
  METHODS
  Expiratory central airway collapse.
  
  
  METHODS
  The primary outcome was baseline respiratory quality of life (St George's Respiratory Questionnaire [SGRQ] scale 0 to 100; 100 represents worst health status; minimum clinically important difference [MCID], 4 units). Secondary outcomes were baseline measures of dyspnea (modified Medical Research Council [mMRC] scale 0 to 4; 4 represents worse dyspnea; MCID, 0.7 units), baseline 6-minute walk distance (MCID, 30 m), and exacerbation frequency (events per 100 person-years) on longitudinal follow-up.
  
  
  RESULTS
  The study included 8820 participants with and without COPD (mean age, 59.7 [SD, 6.9] years; 4667 [56.7%] men; 4559 [51.7%] active smokers). The prevalence of ECAC was 5% (443 cases). Patients with ECAC compared with those without ECAC had worse SGRQ scores (30.9 vs 26.5 units; P < .001; absolute difference, 4.4 [95% CI, 2.2-6.6]) and mMRC scale scores (median, 2 [interquartile range [IQR], 0-3]) vs 1 [IQR, 0-3]; P < .001]), but no significant difference in 6-minute walk distance (399 vs 417 m; absolute difference, 18 m [95% CI, 6-30]; P = .30), after adjustment for age, sex, race, body mass index, forced expiratory volume in the first second, pack-years of smoking, and emphysema. On follow-up (median, 4.3 [IQR, 3.2-4.9] years), participants with ECAC had increased frequency of total exacerbations (58 vs 35 events per 100 person-years; incidence rate ratio [IRR], 1.49 [95% CI, 1.29-1.72]; P < .001) and severe exacerbations requiring hospitalization (17 vs 10 events per 100 person-years; IRR, 1.83 [95% CI, 1.51-2.21]; P < .001).
  
  
  CONCLUSIONS
  In a cross-sectional analysis of current and former smokers, the presence of ECAC was associated with worse respiratory quality of life. Further studies are needed to assess long-term associations with clinical outcomes.
authors.affiliation: Division of Pulmonary, Allergy and Critical Care Medicine, University of Alabama at Birmingham2UAB Lung Health Center, University of Alabama at Birmingham3UAB Lung Imaging Core, University of Alabama at Birmingham.
authors.forename: Surya P
authors.initials: SP
authors.lastname: Bhatt
authors.affiliation: UAB Lung Imaging Core, University of Alabama at Birmingham4Department of Radiology, University of Alabama at Birmingham.
authors.forename: Nina L J
authors.initials: NL
authors.lastname: Terry
authors.affiliation: UAB Lung Imaging Core, University of Alabama at Birmingham4Department of Radiology, University of Alabama at Birmingham.
authors.forename: Hrudaya
authors.initials: H
authors.lastname: Nath
authors.affiliation: Quantitative Imaging Laboratory, National Jewish Health, Denver, Colorado.
authors.forename: Jordan A
authors.initials: JA
authors.lastname: Zach
authors.affiliation: VIDA Diagnostics, Coralville, Iowa.
authors.forename: Juerg
authors.initials: J
authors.lastname: Tschirren
authors.affiliation: UAB Lung Imaging Core, University of Alabama at Birmingham4Department of Radiology, University of Alabama at Birmingham.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Bolding
authors.affiliation: Department of Radiology, National Jewish Health, Denver, Colorado.
authors.forename: Douglas S
authors.initials: DS
authors.lastname: Stinson
authors.affiliation: Department of Biostatistics and Bioinformatics, National Jewish Health, Denver, Colorado.
authors.forename: Carla G
authors.initials: CG
authors.lastname: Wilson
authors.affiliation: Department of Biostatistics and Bioinformatics, National Jewish Health, Denver, Colorado.
authors.forename: Douglas
authors.initials: D
authors.lastname: Curran-Everett
authors.affiliation: Quantitative Imaging Laboratory, National Jewish Health, Denver, Colorado7Department of Radiology, National Jewish Health, Denver, Colorado.
authors.forename: David A
authors.initials: DA
authors.lastname: Lynch
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland.
authors.forename: Nirupama
authors.initials: N
authors.lastname: Putcha
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, University of California San Diego.
authors.forename: Xavi
authors.initials: X
authors.lastname: Soler
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Wise
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: George R
authors.initials: GR
authors.lastname: Washko
authors.affiliation: Department of Radiology and Biomedical Engineering, University of Iowa Carver College of Medicine, Iowa City.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Hoffman
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Morehouse School of Medicine, Atlanta, Georgia.
authors.forename: Marilyn G
authors.initials: MG
authors.lastname: Foreman
authors.affiliation: Division of Pulmonary, Allergy and Critical Care Medicine, University of Alabama at Birmingham2UAB Lung Health Center, University of Alabama at Birmingham3UAB Lung Imaging Core, University of Alabama at Birmingham14Veterans Affairs Medical Center, Birming.
authors.forename: Mark T
authors.initials: MT
authors.lastname: Dransfield
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D018450:Disease Progression; D004417:Dyspnea / Q000000981:diagnostic imaging / Q000208:ethnology / Q000503:physiopathology; D017079:Exercise Tolerance; D045853:Exhalation / Q000502:physiology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D001239:Inhalation / Q000502:physiology; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D001261:Pulmonary Atelectasis / Q000000981:diagnostic imaging / Q000208:ethnology / Q000401:mortality / Q000503:physiopathology*; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging / Q000401:mortality / Q000503:physiopathology*; D011788:Quality of Life; D012119:Respiration; D012907:Smoking / Q000009:adverse effects / Q000503:physiopathology*; D014057:Tomography, X-Ray Computed; D014133:Tracheal Diseases / Q000000981:diagnostic imaging / Q000503:physiopathology*
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