M. Lokietek, A. Marionneau, S. Lecoq, S. Henni, M. Houle and P. Abraham

Respir Physiol Neurobiol 2026 Vol. 343 Pages 104573

BACKGROUND AND OBJECTIVE: 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 (PETO(2)) and transcutaneous oxygen pressure (PtcO(2)) 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-tcDO(2)) and oxygen uptake (VO(2)) in apparently healthy individuals. METHODS: This retrospective study analyzed medical records (n = 68) from incremental CPETs performed with PtcO(2) monitoring. Breath‑by‑breath PETO(2) and VO(2) data from CPET tests were also extracted. The relationship between ET‑tcDO(2) and VO(2) was then characterized using functional data analysis (FDA) and polynomial regression models of increasing degree.
RESULTS: FDA demonstrated high modeling accuracy (adjusted R(2) = 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 R(2) = 0.48). At the individual level, most responses followed a polynomial of the third degree, with 75% of participants exhibiting an adjusted R(2) above 0.7.
CONCLUSION: Continuous PtcO(2) monitoring enables detailed characterization of exercise-induced alveolar-arterial gas exchange in apparently healthy individuals. ET-tcDO(2) follows a polynomial of the third-degree during CPET. The combined use of PETO(2) and PtcO(2) may offer a simple, non-invasive approach for assessing alveolar-arterial gas exchange in routine clinical practice that should be further investigated.