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CLINICAL STUDIES: EXERCISE

Oxygen uptake efficiency slope: an index of exercise performance and cardiopulmonary reserve requiring only submaximal exercise

Milton Hollenberg, MD^* and Ira B. Tager, MD, MPH

^* Department of Medicine, University of California, San Francisco and the Department of Veterans Affairs Medical Center, San Francisco, California, USA
Division of Public Health Biology and Epidemiology, School of Public Health, University of California, Berkeley, Berkeley, California, USA. %

Manuscript received September 10, 1999; revised manuscript received January 17, 2000, accepted March 2, 2000.

Reprint requests and correspondence: Dr. Milton Hollenberg, Veterans Affairs Medical Center, 111C3, 4150 Clement Street, San Francisco, California 94121
hollenberg.milton{at}sanfrancisco.va.gov

OBJECTIVES

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.

BACKGROUND

Maximal oxygen uptake (O_{2 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 O_{2 max} and more appropriate than the commonly used peak oxygen consumption (O_{2 peak}).

METHODS

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.

RESULTS

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 1.10. On serial tests the OUES was less variable than exercise duration or O_{2 peak}. It correlated strongly with O_{2 max}, 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.

CONCLUSIONS

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.

Abbreviations and Acronyms   BSA = body surface area   CHF = congestive heart failure   ECG = electrocardiogram   FEV1 = forced expiratory volume in 1 s   OUES = Oxygen Uptake Efficiency Slope   RER = respiratory exchange ratio   CO2 = carbon dioxide production   E = minute ventilation   O2 = oxygen consumption   O2 max = maximal oxygen uptake   O2 peak = peak oxygen consumption

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