title: COPD phenotype description using principal components analysis.
abstract: BACKGROUND
  Airway inflammation in COPD can be measured using biomarkers such as induced sputum and Fe(NO). This study set out to explore the heterogeneity of COPD using biomarkers of airway and systemic inflammation and pulmonary function by principal components analysis (PCA).
  
  
  METHODS
  In 127 COPD patients (mean FEV1 61%), pulmonary function, Fe(NO), plasma CRP and TNF-alpha, sputum differential cell counts and sputum IL8 (pg/ml) were measured. Principal components analysis as well as multivariate analysis was performed.
  
  
  RESULTS
  PCA identified four main components (% variance): (1) sputum neutrophil cell count and supernatant IL8 and plasma TNF-alpha (20.2%), (2) Sputum eosinophils % and Fe(NO) (18.2%), (3) Bronchodilator reversibility, FEV1 and IC (15.1%) and (4) CRP (11.4%). These results were confirmed by linear regression multivariate analyses which showed strong associations between the variables within components 1 and 2.
  
  
  CONCLUSIONS
  COPD is a multi dimensional disease. Unrelated components of disease were identified, including neutrophilic airway inflammation which was associated with systemic inflammation, and sputum eosinophils which were related to increased Fe(NO). We confirm dissociation between airway inflammation and lung function in this cohort of patients.
authors.affiliation: University of Manchester, North West Lung Research Centre, University Hospital of South Manchester Foundation Trust, Manchester, UK. keyaroy2003@yahoo.co.uk
authors.forename: Kay
authors.initials: K
authors.lastname: Roy
authors.forename: Jacky
authors.initials: J
authors.lastname: Smith
authors.forename: Umme
authors.initials: U
authors.lastname: Kolsum
authors.forename: Zöe
authors.initials: Z
authors.lastname: Borrill
authors.forename: Jørgen
authors.initials: J
authors.lastname: Vestbo
authors.forename: Dave
authors.initials: D
authors.lastname: Singh
mesh_terms: D000368:Aged; D015992:Body Mass Index; D002097:C-Reactive Protein / Q000378:metabolism; D004804:Eosinophils / Q000473:pathology; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D007249:Inflammation / Q000235:genetics / Q000503:physiopathology; D016209:Interleukin-8 / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010641:Phenotype; D029424:Pulmonary Disease, Chronic Obstructive / Q000097:blood / Q000235:genetics* / Q000503:physiopathology; D012907:Smoking / Q000453:epidemiology; D013183:Sputum / Q000378:metabolism / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000097:blood
chemical_list: D016209:Interleukin-8; D014409:Tumor Necrosis Factor-alpha; D002097:C-Reactive Protein