Long-term stability of the oxygen pulse curve during maximal exercise

INTRODUCTION: Exercise oxygen pulse (O-2 pulse), a surrogate for stroke volume and arteriovenous oxygen difference, has emerged as an important variable obtained during cardiopulmonary exercise testing. OBJECTIVES: We hypothesized that the O-2 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 O-2 pulse was calculated by dividing its absolute value by body weight. Subjects were classified into quintiles of relative O-2 pulse. Cardiopulmonary exercise testing results and the O-2 pulse curve pattern, expressed by its slope and intercept, were compared among quintiles of relative O-2 pulse at both cardiopulmonary exercise testings. RESULTS: After excluding the first minute of CPX (rest-exercise transition), the relative O-2 pulse curve exhibited a linear increase, as demonstrated by high coefficients of determination (R-2 from 0.75 to 0.90; p<0.05 for all quintiles). Even though maximum oxygen uptake and relative O-2 pulse were significantly higher in the second cardiopulmonary exercise testing for each quintile of relative O-2 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 5(th) quintile). CONCLUSION: Excluding the rest-exercise transition, the relative O-2 pulse exhibited a stable linear increase throughout maximal exercise in adults that were retested under same clinical conditions.