title: Long-term stability of the oxygen pulse curve during maximal exercise.
abstract: BACKGROUND
  Exercise oxygen pulse (O₂ pulse), a surrogate for stroke volume and arteriovenous oxygen difference, has emerged as an important variable obtained during cardiopulmonary exercise testing.
  
  
  OBJECTIVE
  We hypothesized that the O₂ pulse curve pattern response to a maximal cycling ramp protocol exhibits a stable linear pattern in subjects reevaluated under the same clinical conditions.
  
  
  METHODS
  We retrospectively studied 100 adults (80 males), mean age at baseline of 59 + 12 years, who performed two cardiopulmonary exercise testings (median interval was 15 months), for clinical and/or exercise prescription reasons. The relative O₂ pulse was calculated by dividing its absolute value by body weight. Subjects were classified into quintiles of relative O₂ pulse. Cardiopulmonary exercise testing results and the O₂ pulse curve pattern, expressed by its slope and intercept, were compared among quintiles of relative O₂ pulse at both cardiopulmonary exercise testings.
  
  
  RESULTS
  After excluding the first minute of CPX (rest-exercise transition), the relative O₂ pulse curve exhibited a linear increase, as demonstrated by high coefficients of determination (R² from 0.75 to 0.90; p < 0.05 for all quintiles). Even though maximum oxygen uptake and relative O₂ pulse were significantly higher in the second cardiopulmonary exercise testing for each quintile of relative O₂ pulse (p < 0.05 for all comparisons), no differences were found when slopes and intercepts were compared between the first and second cardiopulmonary exercise testings (p > 0.05 for all comparisons; except for intercept in the 5th quintile).
  
  
  CONCLUSIONS
  Excluding the rest-exercise transition, the relative O₂ pulse exhibited a stable linear increase throughout maximal exercise in adults that were retested under same clinical conditions.
authors.affiliation: Gama Filho University, Rio de Janeiro, Rio de Janeiro, Brazil. ricardobrandaorj@gmail.com
authors.forename: Ricardo Brandão
authors.initials: RB
authors.lastname: Oliveira
authors.forename: Jonathan
authors.initials: J
authors.lastname: Myers
authors.forename: Claudio Gil Soares de
authors.initials: CG
authors.lastname: Araújo
mesh_terms: D000704:Analysis of Variance; D001835:Body Weight / Q000502:physiology*; D005080:Exercise Test / Q000379:methods*; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology*; D012189:Retrospective Studies