Abstract P345: Is a Fixed Value of the Rate of Gas Exchange Appropriate to Indicate the Maximum Effort of Obese and Nonobese Adults Undergoing a Treadmill Cardiopulmonary Exercise Test?

Abstract

Introduction: Obese individuals present a higher O2 uptake/workload during a treadmill cardiopulmonary exercise test (CPET) in addition to chronotropic and biomechanical impairment, which preclude them, many times, from reaching a maximal rate of gas exchange (Rmax) > 1.0. Therefore, it is necessary to develop reference values for Rmax for a treadmill CPET according to age, sex, and a wide range of body mass index (BMI). Objectives: To establish reference values for Rmax for a treadmill CPET according to age, sex, and BMI. Methods: We re-examined 1,612 treadmill ramp CPETs of adults (893 women), of which 772 were obese (BMI ≥ 30 kg/m 2 ). We excluded tests of nonobese participants with HRmax < 85% of predicted, of any participant with a rate of perceived exertion in the BORG scale < 4 (intense), and of those that we had operational problems during the test. We produced a Rmax percentile table according to sex, age (< 33, 34 to 46, and > 46 years), and BMI (< 30 and ≥ 30 kg/m 2 ). We fit stepwise multiple regressions to investigate the influence of age, sex, BMI, and cardiovascular risk on Rmax. We also presented an obesity-specific equation to estimate maximum heart rate (HRmax). Results: We evaluated 442 eutrophic participants (BMI < 25 kg/m 2 ), 398 were overweighted (BMI = 25 - 29.99 kg/m 2 ), 295 had class 1 obesity (BMI = 30 - 34.99 kg/m 2 ), 247 had class 2 obesity (BMI = 35 - 39.99 kg/m 2 ) and 230 had class 3 obesity (BMI ≥ 40 kg/m 2 ). Age, sex, and BMI were the main determinants of Rmax (R 2 = 0.195). The table with percentiles confirmed that the lower limits of Rmax did not reach 1.0, especially in older, obese, and female participants (Table 1). In the obese participants, we could predict HRmax as 195.2 - (0.796 x age). Conclusions: The Rmax values in a treadmill CPET should be chosen considering attributes such as age, sex, and BMI. Our results suggest that fixed values of Rmax are not appropriate to indicate maximum effort, especially in people with low cardiorespiratory fitness.