ORIGINAL ARTICLE Oxygen uptake efficiency plateau: physiology and reference values Xing-Guo Sun • James E. Hansen • William W. Stringer Received: 4 January 2011 / Accepted: 27 May 2011 / Published online: 22 June 2011 Ó Springer-Verlag 2011 Abstract The relationship of oxygen uptake ð _ V O 2 Þ to ventilation ð _ V EÞ, i.e., oxygen uptake efficiency (OUE) is known to differ between normal subjects and patients with congestive heart failure. However, only the oxygen uptake efficiency slope (OUES, i.e., slope of _ V O 2 = log _ V E) has previously been reported. To understand the physiology and to improve the usefulness of OUE in assessing car- diovascular function, we analyzed the complete response pattern of OUE during entire incremental exercise tests and ascertained effect of age, body size, gender, fitness, and ergometer type on exercise OUE to generate reference values in normal healthy subjects. We investigated the effect of age, gender, and fitness on OUE using incremental cardiopulmonary exercise in 474 healthy subjects, age 17– 78 years, of which 57 were highly fit. The final methods of OUE analysis were: (1) OUE plateau at the highest values (OUEP), (2) OUE at anaerobic threshold (OUE@AT), and (3) OUES using the entire exercise period. The OUEP and OUE@AT were similar, highly reproducible, less variable than the OUES (p \ 0.0001), and unaffected by the study sites or types of ergometry. The resultant prediction equations from 417 normal subjects for men were OUEP (mL/L) = 42.18 - 0.189 9 years ? 0.036 9 cm and OUES [L/min/log(L/min)] =-0.610 - 0.032 9 years ? 0.023 9 cm ? 0.008 9 kg. For women, OUEP (mL/L) = 39.16 - 0.189 9 years ? 0.036 9 cm and OUES [L/min/log(L/min)] =-1.178 - 0.032 9 years ? 0.023 9 cm ? 0.008 9 kg. OUE@AT was similar to OUEP. Extreme fitness has a minimal effect on OUEP. OUEP is advantageous, since it measures maximal oxygen extrac- tion from ventilated air but does not require high intensity exercise. The OUEP is a non-invasive parameter dependent only on age, gender, height, and cardiovascular health. Keywords Oxygen uptake efficiency plateau  Cardiopulmonary exercise testing  Cardiovascular health  Normal values  Physiology Introduction Extracting O 2 from the atmosphere and transporting it for use by metabolizing organs, i.e., oxygen uptake ( _ V O 2 , STPD) is a high priority for the cardiovascular and respi- ratory systems. From the Fick principle, _ V O 2 is the product of cardiac output and arterial-mixed venous blood oxygen content difference (Stringer et al. 1997; Sun et al. 2000; Wasserman 2002; Wasserman et al. 2005). In normal subjects and in patients with cardiovascular diseases, the predominant limitations during usual activities or during a cardiopulmonary exercise test (CPET) are not likely hyp- oxemia, anemia, or inadequate ventilation ( _ V E, BTPS). Limitation is more likely due to inability to adequately increase cardiac output, improve distribution of lung blood flow to facilitate oxygen extraction from lung gases, or improve distribution of systemic blood flow and peripheral oxygen extraction. Thus, the response during exercise of Communicated by Susan A. Ward. The partial data have been reported as a Poster presentation at American Physiology Society (APS)/Experimental Biology (EB) in April 2010. X.-G. Sun (&)  J. E. Hansen  W. W. Stringer Department of Medicine, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, St. John’s Cardiovascular Research Center, 1124 West Carson Street, Torrance, CA 90509-2910, USA e-mail: xgsun@labiomed.org; xingguosun@yahoo.com 123 Eur J Appl Physiol (2012) 112:919–928 DOI 10.1007/s00421-011-2030-0