title: Factor analysis in predominantly severe COPD: identification of disease heterogeneity by easily measurable characteristics.
abstract: BACKGROUND
  The clinical and demographic variables defining the heterogeneity of chronic obstructive pulmonary disease (COPD) are unclear. A post-hoc analysis of five randomised studies in patients with a history of previous exacerbations examined the clinical and demographic characteristics describing moderate-to-very-severe COPD.
  
  
  METHODS
  Factor analysis was performed on all continuous baseline demographic and clinical data, without variable selection. Analyses were based on the full cohort and on stratifications by pack-years smoked, smoking status, gender, and comorbidities; patient exacerbation history was analysed in two of the five studies.
  
  
  RESULTS
  6162 COPD patients were evaluated (70% male; 40% current smokers; mean pre-bronchodilator forced expiratory volume in 1 s [FEV1] 35.2% predicted). Baseline clinical and demographic variables loaded differentially on six factors with minimal overlap, explaining 60.4% of the heterogeneity: 1) symptoms (cough, dyspnoea, sleep disturbance), health status, reliever use; 2) pre-bronchodilator FEV1, FEV1/forced vital capacity, morning peak expiratory flow (PEF), body mass index (BMI); 3) blood pressure; 4) age, months since first COPD symptoms; 5) PEF variability; 6) pulse, FEV1 reversibility. Most factors loaded similarly in stratified and exacerbation analyses. BMI loaded with reversibility in females, and with age and months since first COPD symptoms in ex-smokers. Exacerbations loaded to factor 6.
  
  
  CONCLUSIONS
  Readily available data can explain ≈ 60% of COPD heterogeneity in a large dataset of predominantly severe COPD patients. Factors were robust over determinants of disease outcome; gender, smoking status, pack-years smoked, and comorbidities. The main factors were largely unchanged by adding exacerbations. Only BMI loaded to other factors.
authors: University of Groningen, University Medical Center Groningen, Department of Pulmonary Medicine and Tuberculosis, GRIAC Research Institute, AA11, Hanzeplein, PO Box 30001, 9700 RB Groningen, The Netherlands. Electronic address: d.s.postma@umcg.nl.
authors: Dirkje S
authors: DS
authors: Postma
authors: Antonio R
authors: AR
authors: Anzueto
authors: Christine
authors: C
authors: Jenkins
authors: Barry J
authors: BJ
authors: Make
authors: Thomas
authors: T
authors: Similowski
authors: Ollie
authors: O
authors: Östlund
authors: Göran S
authors: GS
authors: Eriksson
authors: Peter M
authors: PM
authors: Calverley
mesh_terms: D000208:Acute Disease; D015992:Body Mass Index; D001993:Bronchodilator Agents / Q000627:therapeutic use; D005163:Factor Analysis, Statistical; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010366:Peak Expiratory Flow Rate / Q000502:physiology; D029424:Pulmonary Disease, Chronic Obstructive / Q000188:drug therapy / Q000503:physiopathology*; D016032:Randomized Controlled Trials as Topic; D012737:Sex Factors; D012907:Smoking / Q000503:physiopathology; D014797:Vital Capacity / Q000502:physiology
chemical_list: D001993:Bronchodilator Agents
keywords: Chronic obstructive pulmonary disease; Exacerbations; Factor analysis; Heterogeneity