Abstract Body (Do not enter title and authors here): Backgrounds: In cardiopulmonary exercise testing (CPET), a peak respiratory exchange ratio (pRER) is used as a marker of effort adequacy for determining peak VO₂ (VO_2peak), a vital sign in clinical decision-making processes. The cut-off point of pRER in healthy volunteers varies from 1.0 to 1.20 among studies. The aim of this study was to search whether there is such a specific point of pRER on determining VO_2peak.
Methods: From cross-sectionally accumulated 21,490 CPET records by a cycle ergometer, 1,165 healthy participants, aged 11 to 86 years (760 males and 405 females) were selected. Age dependency and sex difference of pRER were assessed in males and females. We expected that there may be an inflection point in a relation between pRER and VO_2peak. Then, the data were split consecutively into classes of pRER in 50 to 73 subjects each, where VO_2peak was the dependent variable and classes of pRER were the independent variable.
Results: Sex differences in body weight, height, body mass index, VO_2peak, work rate and systolic blood pressure were significant, but not in pRER. An age-dependent decrease rate of pRER for males and females was statistically significant but this decreased rate was less than 0.01 RER in every 10 years, which support to handle pRER data including both females and males. The number of pRER classes was 21 (55 ± 9 subjects in each class), where two linear regression lines were visually confirmed between VO_2peak (range: 12.8 – 59.4 mL/kg/min) and pRER (range: 0.084 – 1.50), and the slope becomes less than one third gentler above 1.12 on pRER.
Conclusions: An inflection point of a relation between VO_2peak and pRER indicates a unique cut off point of acceptable peak exercise where the relation above 1.12 pRER may represent a limit of O₂ uptake during CPET in healthy subjects.