title: Grading the severity of obstruction in mixed obstructive-restrictive lung disease.
abstract: BACKGROUND
  The severity of obstructive pulmonary disease is determined by the FEV(1) % predicted based on the American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines. In patients with coexisting restrictive lung disease, the decrease in FEV(1) can overestimate the degree of obstruction. We hypothesize that adjusting the FEV(1) for the decrease in total lung capacity (TLC) results in a more appropriate grading of the severity of obstruction.
  
  
  METHODS
  We examined a large pulmonary function test database and identified patients with both restrictive (TLC < 80% predicted) and obstructive (FEV(1)/FVC < the lower limit of normal) lung disease. FEV(1) % predicted was adjusted for the degree of restriction by dividing it by TLC % predicted. We compared the distribution of severity grading between adjusted and unadjusted values according to ATS/ERS criteria and determined how the distribution of severity would change based on asthma and COPD guidelines.
  
  
  RESULTS
  We identified 199 patients with coexisting restrictive and obstructive lung disease. By ATS/ERS grading, the unadjusted data categorized 76% of patients as having severe or very severe obstruction and 11% as having mild or moderate obstruction. The adjusted data classified 33% with severe or very severe obstruction and 44% with mild or moderate obstruction. Of the corrected values, 83% resulted in a change to less severe obstruction by ATS/ERS guidelines, and 44% and 70% of patients, respectively, would be reclassified as having less severe obstruction by current asthma and COPD guidelines.
  
  
  CONCLUSIONS
  This method results in a more appropriate distribution of severity of obstruction, which should lead to more accurate treatment of obstruction in these patients.
authors.affiliation: Department of Medicine, University of Vermont College of Medicine, Burlington, VT.
authors.forename: Zechariah S
authors.initials: ZS
authors.lastname: Gardner
authors.affiliation: St. Louis University Hospital, St. Louis, MO.
authors.forename: Gregg L
authors.initials: GL
authors.lastname: Ruppel
authors.affiliation: Division of Pulmonary and Critical Care Medicine, University of Vermont College of Medicine, Burlington, VT. Electronic address: david.kaminsky@uvm.edu.
authors.forename: David A
authors.initials: DA
authors.lastname: Kaminsky
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008173:Lung Diseases, Obstructive / Q000145:classification / Q000453:epidemiology / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D017410:Practice Guidelines as Topic; D012720:Severity of Illness Index; D014109:Total Lung Capacity