title: Distribution of emphysema in heavy smokers: impact on pulmonary function.
abstract: OBJECTIVE
  To investigate impact of distribution of computed tomography (CT) emphysema on severity of airflow limitation and gas exchange impairment in current and former heavy smokers participating in a lung cancer screening trial.
  
  
  METHODS
  In total 875 current and former heavy smokers underwent baseline low-dose CT (30 mAs) in our center and spirometry and diffusion capacity testing on the same day as part of the Dutch-Belgian Lung Cancer Screening Trial (NELSON). Emphysema was quantified for 872 subjects as the number of voxels with an apparent lowered X-ray attenuation coefficient. Voxels attenuated <-950 HU were categorized as representing severe emphysema (ES950), while voxels attenuated between -910 HU and -950 HU represented moderate emphysema (ES910). Impact of distribution on severity of pulmonary function impairment was investigated with logistic regression, adjusted for total amount of emphysema.
  
  
  RESULTS
  For ES910 an apical distribution was associated with more airflow obstruction and gas exchange impairment than a basal distribution (both p<0.01). The FEV(1)/FVC ratio was 1.6% (95% CI 0.42% to 2.8%) lower for apical predominance than for basal predominance, for Tlco/V(A) the difference was 0.12% (95% CI 0.076-0.15%). Distribution of ES950 had no impact on FEV(1)/FVC ratio, while an apical distribution was associated with a 0.076% (95% CI 0.038-0.11%) lower Tlco/V(A) (p<0.001).
  
  
  CONCLUSIONS
  In a heavy smoking population, an apical distribution is associated with more severe gas exchange impairment than a basal distribution; for moderate emphysema it is also associated with a lower FEV(1)/FVC ratio. However, differences are small, and likely clinically irrelevant.
authors.affiliation: Department of Radiology, University Medical Center, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands. h.gietema@umcutrecht.nl
authors.forename: Hester A
authors.initials: HA
authors.lastname: Gietema
authors.forename: Pieter
authors.initials: P
authors.lastname: Zanen
authors.forename: Arnold
authors.initials: A
authors.lastname: Schilham
authors.forename: Bram
authors.initials: B
authors.lastname: van Ginneken
authors.forename: Rob J
authors.initials: RJ
authors.lastname: van Klaveren
authors.forename: Mathias
authors.initials: M
authors.lastname: Prokop
authors.forename: Jan Willem J
authors.initials: JW
authors.lastname: Lammers
mesh_terms: D000368:Aged; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D016015:Logistic Models; D008175:Lung Neoplasms / Q000000981:diagnostic imaging; D008297:Male; D008403:Mass Screening; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging / Q000503:physiopathology*; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging / Q000503:physiopathology*; D012907:Smoking / Q000009:adverse effects / Q000503:physiopathology*; D013147:Spirometry; D014057:Tomography, X-Ray Computed; D014797:Vital Capacity / Q000502:physiology*