Association between oxygen uptake efficiency slope (OUES), an effort-independent measure of cardiorespiratory fitness (VO2max), and robust/pre-frail status in an elderly Chinese population
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Peak oxygen uptake or consumption (VO2max) is a measure of cardiorespiratory fitness that provides prognostic
information in heart failure patients being considered for transplant, and is also widely used in exercise capacity
testing. However, accurate determination of threshold capacity is effort-dependent, and poses challenges when
assessing older adults. Previous studies have shown that calculating the oxygen uptake efficiency slope (OUES)
through the use of multiple VO2 data points at different exercise levels in conjunction with minute ventilation
(VE) can inform exercise capacity independent of effort and may be superior to VO2max. We hypothesise that
OUES in this physiological context can distinguish robust versus pre-frail older adults.

To compare VO2max with OUES in a community-dwelling older adult population able to freely ambulate.

This study included subjects in the Mr & Ms Os Cohort with a complete set of cardiopulmonary exercise testing
(CPET) data. OUES (‘a’) was calculated using the following equation: VO2 = a · log(VE) + b. A 4-point frailty
scale was used to classify robust/pre-frail status, and 1 point was assigned for each positive criterion: i) very little
or no energy, ii) difficulty in climbing up 10 steps of stairs, iii) inability to walk 100 yards, and iv) presence of 3 or
more predefined co-morbidities. A score of zero (0) was considered ‘robust’, and 1 to 2 points indicated pre-frailty.
Four primary measures were used to assess cardiorespiratory fitness against robust/pre-frail status: VO2max,
VO2max/kg (or VO2max indexed to body weight in kilograms), OUES, and OUES/kg. Student’s t test was used
for comparing means between two groups. The study was approved by the institutional ethics review committeee
and adhered to the Declaration of Helsinki.

The study included 550 subjects (457 males and 93 females) with a mean age of 76.7 y ± 5.34. The ratios (or
relative proportions) of robust:pre-frail individuals in the male and female subject groups were 3.57 (78.12% vs.
21.88%) and 1.74 (63.44% vs. 36.56%), respectively. The robust group outperformed the pre-frail group in all four
measures. Among these, VO2max/kg most strongly differentiated robust/pre-frail status in male (22.6 vs. 19.6, P =
7.32 x 10e–12) and female (20.4 vs. 17.4, P = 2.59 x 10e–5) subjects. OUES did not significantly differentiate
robust/pre-frail status in male subjects (1769.9 vs. 1709.9, P = 0.11), and only modestly in female subjects (1486.8
vs.1259.0, P = 0.001). VO2max and OUES/kg also differentiated robust/pre-frail status to varying extents in both
sexes (range, P = 0.0067 to 7.85 x 10e–7).

In the manner in which older Chinese adults have been stratified by robust/pre-frail status as used in this study,
VO2max/kg (or indexed VO2max) was the most strongly significant metric for differentiating robust versus prefrail
individuals compared with VO2max, OUES or OUES/kg.
All Author(s) ListErik Fung, Leong Ting Lui, Forrest Yau, Jason Leung, Jean Woo
Name of ConferenceHeart Failure 2018 & World Congress on Acute Heart Failure
Start Date of Conference26/05/2018
End Date of Conference29/05/2018
Place of ConferenceVienna
Country/Region of ConferenceAustria
Proceedings TitleEuropean Journal of Heart Failure
Volume Number20
Issue NumberSupp 1
Pages528 - 529
LanguagesEnglish-United Kingdom

Last updated on 2021-20-01 at 02:01