title: How Common Is Airflow Limitation in Patients With Emphysema on CT Scan of the Chest?
abstract: BACKGROUND
  COPD has traditionally been defined by the presence of irreversible airflow limitation on spirometry using either the GOLD (Global Initiative for Chronic Obstructive Lung Disease) or American Thoracic Society/European Respiratory Society criteria (lower limit of normal [LLN]). We have observed that some patients with clinical COPD and emphysema on chest CT scan have no obstruction on spirometry. The purpose of this study was to assess the prevalence of obstruction by GOLD and LLN criteria in patients with emphysema on CT scan and determine which radiographic criteria were associated with a clinical diagnosis of COPD.
  
  
  METHODS
  We retrospectively analyzed the clinical records and spirometry of all patients who had radiographically defined emphysema on chest CT scans completed at the University of Vermont in 2011. We compared spirometric criteria and CT scan factors with the presence of clinical COPD based on chart review.
  
  
  RESULTS
  We identified 274 patients with CT scan-defined emphysema. GOLD criteria detected obstruction in 228 patients (83%), and LLN detected obstruction in 206 patients (75%). However, GOLD failed to correctly identify 19 patients (6.9%) and LLN failed to identify 38 patients (13.9%) (average 10.4%) who had radiographic emphysema and a clinical diagnosis of COPD. Obese patients had a lower prevalence of obstruction whether classified by LLN or GOLD. Among patients with spirometric obstruction, there were greater degrees of emphysema and more severely increased airway wall thickness. Factors that were independently associated with clinical COPD were lower FVC % predicted, lower FEV1/FVC ratio, and increasing airway wall thickness.
  
  
  CONCLUSIONS
  Spirometry missed 10.4% of patients with clinical COPD who have significant emphysema on chest CT scan.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Burlington, VT.
authors.forename: Sanjiva M
authors.initials: SM
authors.lastname: Lutchmedial
authors.affiliation: University of Vermont College of Medicine, Burlington, VT.
authors.forename: Whitney G
authors.initials: WG
authors.lastname: Creed
authors.affiliation: Department of Radiology, Burlington, VT.
authors.forename: Alastair J
authors.initials: AJ
authors.lastname: Moore
authors.affiliation: Division of Thoracic Radiology, Burlington, VT.
authors.forename: Ryan R
authors.initials: RR
authors.lastname: Walsh
authors.affiliation: Division of Thoracic Radiology, Burlington, VT.
authors.forename: George E
authors.initials: GE
authors.lastname: Gentchos
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Burlington, VT. Electronic address: david.kaminsky@uvm.edu.
authors.forename: David A
authors.initials: DA
authors.lastname: Kaminsky
mesh_terms: D000368:Aged; D000403:Airway Resistance / Q000502:physiology; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology; D011237:Predictive Value of Tests; D015995:Prevalence; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000503:physiopathology*; D012189:Retrospective Studies; D012307:Risk Factors; D013147:Spirometry; D014057:Tomography, X-Ray Computed; D014797:Vital Capacity / Q000502:physiology