Maximal Aerobic Capacity and the Oxygen Uptake Efficiency Slope as Predictors of Large Artery Stiffness in Apparently Healthy Subjects

Initial evidence indicates large artery stiffness may be an important marker of cardiovascular health. Several investigations have shown subjects with increased arterial stiffness are at a higher risk for adverse events.1-6 Moreover, several easily obtained variables have demonstrated a significant relationship with arterial stiffness, allowing for its prediction by regression analysis.7-10 Of these variables, age, resting systolic blood pressure (SBP), and maximal aerobic capacity (VO2max) appear to be some of the more relevant predictors of arterial stiffness. While the measurement of age and SBP are simple and straightforward, several measurements may be used to express aerobic fitness. Although VO2max is the most widely accepted marker of aerobic hfitness11, other measures obtained from exercise testing have recently been proposed as potential surrogates for this long established gold standard. The oxygen uptake efficiency slope (OUES) is 1 such measure that has recently gained considerable attention.12 The OUES, derived from the linear relationship between oxygen uptake (y-axis) and the logarithmic transformation of minute ventilation (x-axis), has been postulated to reflect the integrated function and health of the pulmonary, cardiovascular and skeletal muscle systems during aerobic exercise. Previous studies have demonstrated the OUES 1) to be strongly correlated with VO2max 13,14; 2) to reflect varying degrees of cardiovascular health/disease severity15; and 3) to possess prognostic value16. The OUES is purported to be independent of subject effort and can be obtained during submaximal exercise, both of which are potential advantages over VO2max. The fact that the OUES can be obtained submaximally may prove to be advantageous from a staffing, and therefore economical standpoint, given direct supervision is less of a necessity, even in populations at higher risk for or diagnosed with cardiovascular disease. Moreover, a submaximal test is more comfortable for the patient and removes requirements to put forth a maximal effort in order to obtain a valid measure of aerobic capacity. In the present practice of cardiopulmonary exercise testing, VO2max continues to be the most frequently assessed variable in the assessment of individual overall cardiovascular health and risk for future adverse events. Given the strong correlation between VO2max and the OUES, this latter variable may also prove to be clinically relevant. This may be particularly advantageous given the OUES can be derived from submaximal testing, creating a more favorable staffing and budgetary scenario for cardiopulmonary exercise laboratories. To our knowledge, there is an overall lack of research examining the ability of OUES to reflect varying degrees of cardiovascular health. More specific to the present study, unlike VO2max, we are unaware of any previous investigation that has examined the relationship between OUES and arterial stiffness, the latter potentially being an important marker of cardiovascular health with prognostic implications. The purpose of the present investigation is to therefore assess this relationship and determine if the OUES is a viable surrogate for VO2max in a multivariate regression analysis developed to estimate large artery stiffness.