The oxygen uptake efficiency slope is not a valid surrogate of aerobic fitness in cystic fibrosis.

Williams CA, Tomlinson OW, Chubbock LV, Stevens D, Saynor
ZL, Oades PJ, Barker AR

Pediatr Pulmonol. 2018 Jan;53(1):36-42. doi: 10.1002/ppul.23896. Epub 2017 Oct

BACKGROUND: Maximal cardiopulmonary exercise testing is recommended on an annual
basis for children with cystic fibrosis (CF), due to clinically useful prognostic
information provided by maximal oxygen uptake (V̇ O2max ). However, not all
patients are able, or willing, to reach V̇O2max , and therefore submaximal
alternatives are required. This study explored the validity of the oxygen uptake
efficiency slope (OUES) as a submaximal measure of V̇O2max in children and
adolescents with CF.
METHODS: Data were collated from 72 cardiopulmonary exercise tests (36 CF, 36
controls), with OUES determined relative to maximal and submaximal parameters of
exercise intensity, time, and individual metabolic thresholds. Pearson’s
correlation coefficients, independent t-tests, and factorial ANOVAs were used to
determine validity.
RESULTS: Significant (P < 0.05) correlations with V̇O2max were observed for most
expressions of OUES, but were consistently weaker in CF (r = 0.30-0.47) when
compared to CON (r = 0.58-0.89). Mean differences for all OUES parameters between
groups were not significant (P > 0.05). When split by V̇O2max tertiles, minimal
significant differences were found between, and within, groups for OUES,
indicating poor discrimination of V̇O2max .
CONCLUSIONS: The OUES is not a valid (sub) maximal measure of V̇O2max in children
and adolescents with mild-to-moderate CF. Clinicians should continue to use
maximal markers (ie, V̇O2max ) of exercise capacity.