title: Current Smoking Status Is Associated With Lower Quantitative CT Measures of Emphysema and Gas Trapping.
abstract: OBJECTIVE
  The purposes of this study were to evaluate the effect of smoking status on quantitative computed tomography CT measures of low-attenuation areas (LAAs) on inspiratory and expiratory CT and to provide a method of adjusting for this effect.
  
  
  METHODS
  A total of 6762 current and former smokers underwent spirometry and volumetric inspiratory and expiratory CT. Quantitative CT analysis was completed using open-source 3D Slicer software. LAAs were defined as lung voxels with attenuation values ≤-950 Hounsfield units (HU) on inspiratory CT and ≤-856 HU on expiratory CT and were expressed as percentage of CT lung volume (%LAAI-950 and %LAAE-856). Multiple linear regression was used to determine the effect of smoking status on %LAAI-950 and %LAAE-856 while controlling for demographic variables, spirometric lung function, and smoking history, as well as total lung capacity (%LAAI-950) or functional residual capacity (%LAAE-856). Quantile normalization was used to align the %LAAI-950 distributions for current and former smokers.
  
  
  RESULTS
  Mean %LAAI-950 was 4.2±7.1 in current smokers and 7.7±9.7 in former smokers (P<0.001). After adjusting for confounders, %LAAI-950 was 3.5 percentage points lower and %LAAE-856 was 6.0 percentage points lower in current smokers than in former smokers (P<0.001). After quantile normalization, smoking status was an insignificant variable in the inspiratory regression model, with %LAAI-950 being 0.27 percentage points higher in current smokers (P=0.13).
  
  
  CONCLUSIONS
  After adjusting for patient demographics and lung function, current smokers display significantly lower %LAAI-950 and %LAAE-856 than do former smokers. Potential methods for adjusting for this effect would include adding a fixed value (eg, 3.5%) to the calculated percentage of emphysema in current smokers, or quantile normalization.
authors.affiliation: Divisions of *Radiology †Biostatistics and Bioinformatics, National Jewish Health, Denver ∥Department of Epidemiology, University of Colorado, Anschutz Medical Campus, Aurora, CO ‡Department of Radiology, Soonchunhyang University Hospital, Cheonan, Korea §Department of Radiology, St. Marianna University School of Medicine Kawasaki, Japan.
authors.forename: Jordan A
authors.initials: JA
authors.lastname: Zach
authors.forename: Andre
authors.initials: A
authors.lastname: Williams
authors.forename: Sung-Shiick
authors.initials: SS
authors.lastname: Jou
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Yagihashi
authors.forename: Douglas
authors.initials: D
authors.lastname: Everett
authors.forename: John E
authors.initials: JE
authors.lastname: Hokanson
authors.forename: Douglas
authors.initials: D
authors.lastname: Stinson
authors.forename: David A
authors.initials: DA
authors.lastname: Lynch
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D012119:Respiration; D012129:Respiratory Function Tests / Q000706:statistics & numerical data; D012907:Smoking / Q000453:epidemiology*; D013147:Spirometry; D014057:Tomography, X-Ray Computed; D014481:United States / Q000453:epidemiology