Clinical utility of the oxygen uptake efficiency slope in cystic fibrosis patients

The present study investigated the validity and the reliability of the oxygen uptake efficiency slope (OUES) as a determinant of exercise tolerance in adults with cystic fibrosis (CF).

31 CF patients and 34 healthy controls performed a maximal incremental cycle test with respiratory gas-exchange measurements. OUES was calculated from data taken from different percentages of the entire exercise duration, including 80% (OUES(80)) and 100% (OUES(100)). Peak oxygen uptake (VO(2peak)) and gas exchange threshold (GET) were also determined. The agreement between submaximal parameters and VO(2peak) was assessed using Bland Altman plots. Test retest reliability was evaluated in CF patients using absolute (SEM) and relative indices (ICC).

On the contrary to the GET, which was undetectable in 16% of the CF patients, the OUES was easily determined in all patients. Among all the submaximal variables, OUES(80) had the best reliability (ICC=0.94, SEM=7.3%) and agreement with VO(2peak) (r(2)=0.83, P<0.01; limits of agreement: ±365mL min(-1)) and did not differ from OUES(100).

OUES(80) is a reliable and more useful submaximal parameter than the GET and may find use in the interpretation of exercise studies in CF patients who are unable to perform maximal exercise.