We sought to evaluate, in adults, the efficacy of the Oxygen Uptake Efficiency Slope
(OUES), an index of cardiopulmonary functional reserve that can be based upon a submaximal
exercise effort.
Maximal oxygen uptake (VO2,max), the most reliable measure of exercise capacity, is
seldom attained in standard exercise testing. The OUES, which relates oxygen uptake
to total ventilation during exercise, was proposed by Baba and coworkers (7) in a
study of pediatric cardiac patients. They felt this submaximal index of cardiopulmonary
reserve might be more practical than VO2max and more appropriate than the commonly
used peak oxygen consumption (VO2 peak).
Treadmill exercise tests with simultaneous respiratory gas measurement were performed
in 998 older subjects free of clinically recognized cardiovascular disease and 12
male patients with congestive heart failure. During incremental exercise, oxygen uptake
was plotted against the logarithm of total ventilation, and the OUES was determined.
The OUES, when calculated only from the first 75% of the exercise test, differed by
1.9% from the OUES calculated from 100% of exercise time in subjects with a peak respiratory
exchange rate > or =1.10. On serial tests the OUES was less variable than exercise
duration or VO2 peak. It correlated strongly with VO2max, with forced expiratory volume
in 1 s and negatively with a history of current smoking. The OUES declined linearly
with age in both women and men. A small sample of patients with congestive heart failure
had OUES values much lower than those of older subjects without cardiovascular disease.
The OUES is an objective, reproducible measure of cardiopulmonary reserve that does
not require a maximal exercise effort. It integrates cardiovascular, musculoskeletal
and respiratory function into a single index that is largely influenced by pulmonary
dead space ventilation and exercise-induced lactic acidosis.