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 (VO_2peak), 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 VO_2peak (r = 0.646), the ventilatory threshold (r = 0.548) and OUES (r = 0.589). OUES correlated strongly with VO_2peak (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.