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

BackgroundThe 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).Methods31 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% (OUES80) and 100% (OUES100). Peak oxygen uptake (VO2peak) and gas exchange threshold (GET) were also determined. The agreement between submaximal parameters and VO2peak was assessed using Bland Altman plots. Test retest reliability was evaluated in CF patients using absolute (SEM) and relative indices (ICC).ResultsOn 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, OUES80 had the best reliability (ICC = 0.94, SEM = 7.3%) and agreement with VO2peak (r2 = 0.83, P < 0.01; limits of agreement: ± 365 mL min− 1) and did not differ from OUES100.ConclusionsOUES80 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.