Maximal respiratory exchange ratio during treadmill cardiopulmonary exercise testing in adults based on age, sex, and body mass index.

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Dourado, Victor Zuniga; Federal University of São Paulo (UNIFESP), Santos, São Paulo, Brazil
Matheus, Agatha Caveda;Barbosa, Alan Carlos Brisola;Simões, Maria do Socorro Morais Pereira; et al

Heart & lung : the journal of critical care,2025 Oct 17

  • Background: Chronotropic and biomechanical limitations, and elevated O2/workload ratio during cardiopulmonary exercise testing (CPET), often constrain the ability to reach a maximal rate of gas exchange (RER) > 1.00 in obese subjects. We hypothesize that RER during CPET differs significantly by body mass index (BMI), necessitating BMI- Age- and Sex-specific values to assess maximal effort.
  • Objectives: To establish RER reference values in adults undergoing treadmill CPET based on age, sex, and BMI.
  • Methods: We analyzed 1612 treadmill ramp CPETs in adults (893 women) with obesity (n=772; mean age 42±13 years, weight 104±20 kg, and BMI 37±5 kg/m²) and without (n=840; mean age 39±14 years, weight 69±12 kg, and BMI 24±2 kg/m²). We excluded CPETs with operational problems and with spirometric and/or ECG abnormalities. We generated sex-, age- (<33, 34-46, >46 years), and BMI-specific (<30, ≥30 kg/m 2 ) RER values. We fit a multiple regression to explore determinants of RER. We also derived an obesity-specific estimation of maximum heart rate (HRmax).
  • Results: Participants were 442 normal-weight (BMI<25 kg/m 2 ), 398 overweighted (BMI=25-29.99 kg/m 2 ), 295 class-1 obese (BMI=30-34.99 kg/m 2 ), 247 class-2 obese (BMI=35-39.99 kg/m 2 ), and 230 class-3 obese (BMI≥40 kg/m 2 ). We set p<0.05 as the significance threshold for all statistical tests. Age, sex, and BMI significantly determined RER (R 2 = 0.195). We found sub-1.0 RER, notably in obese and older females. The HR bpm equation was 195.2-(0.796 x age years ).
  • Conclusion: Fixed values of RER may inadequately reflect maximal effort, particularly in obese, older, and unfit individuals. These findings have direct implications for accurately assessing cardiorespiratory fitness in individuals with obesity.