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.