The end-tidal to transcutaneous oxygen pressure gradient follows a third-degree polynomial relationship with oxygen uptake during exercise, decreasing until VO2=1.26 L/min before increasing.
What statistical model best characterizes the relationship between the end-tidal to transcutaneous oxygen pressure gradient and oxygen uptake during cardiopulmonary exercise testing in healthy individuals?
The end-tidal to transcutaneous oxygen pressure gradient follows a third-degree polynomial relationship with oxygen uptake during CPET, suggesting a potential non-invasive method to assess alveolar-arterial gas exchange.
During cardiopulmonary exercise testing (CPET), the alveolar–arterial oxygen gradient varies with exercise intensity, but direct assessment is limited by the invasiveness of arterial sampling. End-tidal oxygen pressure (PETO₂) and transcutaneous oxygen pressure (PtcO₂) may provide non-invasive estimates of alveolar and arterial oxygen pressures. This study aimed to identify the statistical model that best characterize the relationship between the end-tidal to transcutaneous oxygen pressure gradient (ET-tcDO₂) and oxygen uptake (VO₂) in apparently healthy individuals. This retrospective study analyzed medical records (n=68) from incremental CPETs performed with PtcO₂ monitoring. Breath‑by‑breath PETO₂ and VO₂ data from CPET tests were also extracted. The relationship between ET‑tcDO₂ and VO₂ was then characterized using functional data analysis (FDA) and polynomial regression models of increasing degree. FDA demonstrated high modeling accuracy (adjusted R² = 0.96). ET-tcDO2 decreased at onset of exercise, until VO2=1.26 L/min, and then increased until maximal exercise. Among polynomial regression models, the polynomial of the third degree best described this relationship (adjusted R² = 0.48). At the individual level, most responses followed a polynomial of the third degree, with 75% of participants exhibiting an adjusted R² above 0.7. Continuous PtcO₂ monitoring enables detailed characterization of exercise-induced alveolar–arterial gas exchange in healthy individuals. ET-tcDO₂ follows a polynomial of the third-degree during CPET. The combined use of PETO₂ and PtcO₂ may offer a simple, non-invasive approach for assessing alveolar–arterial gas exchange in routine clinical practice that should be further investigated.
Lokietek et al. (2026) studied this question. The end-tidal to transcutaneous oxygen pressure gradient follows a third-degree polynomial relationship with oxygen uptake during exercise, decreasing until VO2=1.26 L/min before increasing.