title: Creation of a model comparing 6-minute walk test to metabolic equivalent in evaluating treatment effects in pulmonary arterial hypertension.
abstract: BACKGROUND
  The 6-minute walk test (6MWT) is the current standard to assess exercise capacity in pulmonary arterial hypertension (PAH). We compared the Naughton-Balke treadmill test reported in exercise metabolic equivalents (METs) with the 6MWT to evaluate whether MET could be a useful tool to assess exercise capacity.
  
  
  METHODS
  Serial 6MWTs followed by Naughton-Balke treadmill tests were performed in 47 PAH patients initiating a change in PAH therapy at baseline (i.e., Time 0) and Weeks 6, 12, 24 and 48; New York Heart Association (NYHA) functional class (FC) was also assessed. Hemodynamics data were recorded at baseline and Weeks 12 and 48. Treadmill time was converted to MET. Generalized estimating equation models, receiver-operating characteristic curves and fixed-effect linear models were utilized to create a model comparing 6MWT to MET.
  
  
  RESULTS
  MET correlated with 6MWT (r = 0.62). Piecewise linear function described the relationship between 6MWT and MET. 6MWT and MET were both associated with FC (p < 0.001) with similar ability to discriminate FC. Changes in hemodynamics in response to a change in PAH therapy correlated with changes in both 6MWT and MET. In less sick patients (i.e., FC II), the changes in 6MWT were less pronounced than with MET.
  
  
  CONCLUSIONS
  MET appears to be a reliable measure of exercise capacity in PAH, and correlates with 6MWT. MET can be used in clinical assessment and is helpful in demonstrating improvements in exercise capacity in less sick patients.
authors.affiliation: Section of Cardiology, Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA. mgomberg@medicine.bsd.uchicago.edu
authors.forename: Mardi
authors.initials: M
authors.lastname: Gomberg-Maitland
authors.forename: Dezheng
authors.initials: D
authors.lastname: Huo
authors.forename: Raymond L
authors.initials: RL
authors.lastname: Benza
authors.forename: Vallerie V
authors.initials: VV
authors.lastname: McLaughlin
authors.forename: Victor F
authors.initials: VF
authors.lastname: Tapson
authors.forename: Robyn J
authors.initials: RJ
authors.lastname: Barst
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D002648:Child; D023381:Endpoint Determination; D004734:Energy Metabolism / Q000502:physiology; D005080:Exercise Test / Q000379:methods*; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006801:Humans; D006976:Hypertension, Pulmonary / Q000503:physiopathology* / Q000628:therapy; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D010101:Oxygen Consumption / Q000502:physiology; D011446:Prospective Studies; D015203:Reproducibility of Results; D016138:Walking / Q000502:physiology*