Oxygen uptake efficiency slope: a reliable surrogate parameter for exercise capacity in healthy and cardiac children?

Objectives: Cardiopulmonary exercise test (CPET) provides accurate evaluation of physical capacity and disease severity in children with congenital heart disease (CHD). However, full participation to obtain optimal measure of VO_2max may be difficult. As an alternative, the oxygen uptake efficiency slope (OUES) is a reproducible and reliable parameter measured during CPET, which does not require a maximal exercise to be interpretable. This study aimed to evaluate the OUES of a large cohort of children with CHD, in comparison with healthy controls. We also intended to identify, in this specific population, the clinical and CPET variables associated with the OUES.

Methods: This cross-sectional study was carried out between November 2010 and September 2015 in two tertiary care paediatric and congenital cardiology centres.

Results: 709 children were included (407 CHD and 302 healthy controls). The association of clinical characteristics with weight-normalised OUES (OUES_kg) was studied using a multivariable analysis. The mean OUES_kg was significantly lower in CHD than in healthy controls (38.6±8.5 and 43.9±8.5; p<0.001, respectively), especially in the most severe CHD. The OUES_kg correlated with VO_2max (r=0.85, p<0.001), with cut-off values for normal exercise capacity of 38.4 in boys and 31.0 in girls. The decrease of OUES_kg was associated with increased age, increased Body Mass Index, number of cardiac catheter or surgical procedures, female gender and decreased forced vital capacity (Z-score).

Conclusion: The OUES is significantly impaired in children with CHD and strongly correlates with VO_2max. The OUES has the same clinical determinants as VO_2max and therefore may be of interest in submaximal exercise.

Trial registration number: NCT01202916.