title: Characterizing functional lung heterogeneity in COPD using reference equations for CT scan-measured lobar volumes.
abstract: BACKGROUND
  CT scanning is increasingly used to characterize COPD. Although it is possible to obtain CT scan-measured lung lobe volumes, normal ranges remain unknown. Using COPDGene data, we developed reference equations for lobar volumes at maximal inflation (total lung capacity [TLC]) and relaxed exhalation (approximating functional residual capacity [FRC]).
  
  
  METHODS
  Linear regression was used to develop race-specific (non-Hispanic white [NHW], African American) reference equations for lobar volumes. Covariates included height and sex. Models were developed in a derivation cohort of 469 subjects with normal pulmonary function and validated in 546 similar subjects. These cohorts were combined to produce final prediction equations, which were applied to 2,191 subjects with old GOLD (Global Initiative for Chronic Obstructive Lung Disease) stage II to IV COPD.
  
  
  RESULTS
  In the derivation cohort, women had smaller lobar volumes than men. Height positively correlated with lobar volumes. Adjusting for height, NHWs had larger total lung and lobar volumes at TLC than African Americans; at FRC, NHWs only had larger lower lobes. Age and weight had no effect on lobar volumes at TLC but had small effects at FRC. In subjects with COPD at TLC, upper lobes exceeded 100% of predicted values in GOLD II disease; lower lobes were only inflated to this degree in subjects with GOLD IV disease. At FRC, gas trapping was severe irrespective of disease severity and appeared uniform across the lobes.
  
  
  CONCLUSIONS
  Reference equations for lobar volumes may be useful in assessing regional lung dysfunction and how it changes in response to pharmacologic therapies and surgical or endoscopic lung volume reduction.
authors.affiliation: Pulmonary and Critical Care Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA. Electronic address: ccome@partners.org.
authors.forename: Carolyn E
authors.initials: CE
authors.lastname: Come
authors.affiliation: Pulmonary and Critical Care Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Alejandro A
authors.initials: AA
authors.lastname: Diaz
authors.affiliation: Division of Biostatistics and Bioinformatics, National Jewish Health, Department of Biostatistics and Informatics, Colorado School of Public Health, Denver, CO.
authors.forename: Douglas
authors.initials: D
authors.lastname: Curran-Everett
authors.affiliation: Pulmonary and Critical Care Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Nivedita
authors.initials: N
authors.lastname: Muralidhar
authors.affiliation: Pulmonary and Critical Care Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA; Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Craig P
authors.initials: CP
authors.lastname: Hersh
authors.affiliation: Division of Radiology, National Jewish Health, University of Colorado School of Medicine, Denver, CO.
authors.forename: Jordan A
authors.initials: JA
authors.lastname: Zach
authors.affiliation: Division of Radiology, National Jewish Health, University of Colorado School of Medicine, Denver, CO.
authors.forename: Joyce
authors.initials: J
authors.lastname: Schroeder
authors.affiliation: Division of Radiology, National Jewish Health, University of Colorado School of Medicine, Denver, CO.
authors.forename: David A
authors.initials: DA
authors.lastname: Lynch
authors.affiliation: Pulmonary and Critical Care Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Bartolome
authors.initials: B
authors.lastname: Celli
authors.affiliation: Pulmonary and Critical Care Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: George R
authors.initials: GR
authors.lastname: Washko
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D016014:Linear Models; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011857:Radiographic Image Interpretation, Computer-Assisted; D012016:Reference Values; D012129:Respiratory Function Tests; D012720:Severity of Illness Index; D014057:Tomography, X-Ray Computed