Response profiles of oxygen uptake efficiency during exercise in healthy children

Background: Oxygen uptake efficiency (OUE), the relation between oxygen uptake (VO2) and minute ventilation (VE), differs between healthy children and children with heart disease. This study aimed to investigate the normal response profiles of OUE during a progressive cardiopulmonary exercise test. Design: Cross-sectional. Methods: Healthy children between eight and 19 years of age (114 boys and 100 girls, mean +/- SD age 12.7 +/- 2.8 years) performed a maximal cardiopulmonary exercise test. Peak VO2 (VO2peak), ventilatory threshold and peak VE were determined. OUE was determined by the OUE plateau (OUEP), OUE at the ventilatory threshold (OUE@VT) and OUE slope (OUES). Results: OUEP (42.4 +/- 4.6) and OUE@VT (41.9 +/- 4.7) were similar and less variable than OUES (2138 +/- 703). OUEP correlated strongly with OUE@VT (r=0.974); however, OUEP was weak-to-moderately correlated with VO2peak (r=0.646), the ventilatory threshold (r=0.548) and OUES (r=0.589). OUES correlated strongly with VO2peak (r=0.948) and the ventilatory threshold (r=0.856). Reference centiles for OUEP show an almost linear increase from about 37 in eight-year olds to about 47 in 18-year olds, with no sex-difference. OUES increased from about 1400 in eight-year-old boys to approximately 3500 in 18-year-old boys. OUES increased from roughly 1250 in eight-year-old girls to about 2650 in 18-year-old girls. Conclusions: This study provides sex- and age-related normative values for both OUEP and OUES, which facilitates the interpretation of OUE in children. OUEP and OUES are objective and non-invasive cardiopulmonary exercise test parameters which do not require a maximal effort and might be indicative of cardiorespiratory function during exercise.