title: [Six-minute-walk test and maximum exercise test in cycloergometer in chronic obstructive pulmonary disease. Are the physiological demands equivalent?].
abstract: OBJECTIVE
  The physiological load imposed by the six minute walk test (SMWT) in chronic obstructive pulmonary disease (COPD) patients come from small studies where the influence of disease severity has not been assessed. The aim of the present study was to compare the SMWT with an incremental cardiopulmonary exercise test (CPET) in patients classified by disease severity according to FEV(1) (cutoff 50% predicted).
  
  
  METHODS
  Eighty-one COPD patients (53 with FEV(1) > or =50%) performed both tests on two consecutive days. Oxygen consumption (VO(2)), carbon dioxide production (VCO(2)), minute ventilation (V(E)), heart rate (HR) and pulse oximetry (SpO(2)) were measured during SMWT and CPET using portable equipment. Dyspnea and leg fatigue were measured with the Borg scale.
  
  
  RESULTS
  In both groups, walking speed was constant during the SMWT and VO(2) showed a plateau after the 3rd minute. When comparing SMWT (6th min) and peak CPET, patients with FEV(1) > or =50% showed a greater VO(2), but lower values of VCO(2),V(E), HR, dyspnea, leg fatigue, and SpO(2) during walking. In contrast, in those with FEV(1) <50% predicted values were similar. Distance walked during the SMWT strongly correlated with VO(2) at peak CPET (r=0.78; P=0.0001).
  
  
  CONCLUSIONS
  The SMWT is a constant load exercise in COPD patients, regardless of disease severity. It imposes high metabolic, ventilatory and cardiovascular requirements, which were closer to those of CPET in severe COPD. These findings may explain the close correlation between distance walked and peak CPET VO(2).
authors.affiliation: Departamento de Enfermedades Respiratorias, Pontificia Universidad Católica de Chile, Santiago, Chile. odiazp@vtr.net
authors.forename: Orlando
authors.initials: O
authors.lastname: Díaz
authors.forename: Arturo
authors.initials: A
authors.lastname: Morales
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Osses
authors.forename: Julieta
authors.initials: J
authors.lastname: Klaassen
authors.forename: Carmen
authors.initials: C
authors.lastname: Lisboa
authors.forename: Fernando
authors.initials: F
authors.lastname: Saldías
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D013997:Time Factors; D016138:Walking