Oxygen dissociation curve inflection point during incremental exercise: a trigger for the Bohr effect

Figures

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  Fig. 1. Fig. 4B from Stringer et al. (1994) [48], adapted with permission, showing group mean femoral vein O2Hb saturation vs. PO2 during 6-min constant work rate exercise at an intensity of GET \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{\text V}\text{O}_2$$\end{document}V˙O2 plus 75% of the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{\text V}\text{O}_2$$\end{document}V˙O2 difference between GET and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{\text V}\text{O}_2$$\end{document}V˙O2max. Blood was sampled at rest, every 5 s during the first 120 s of exercise (using a computer-driven anaerobic collector with time correction for…

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  Fig. 2. Redrawn Fig. 1A,D,C,B from Stringer et al. 1994 with permission [48] showing group mean femoral vein PO2, PCO2, pH, and O2Hb saturation (n = 12) from the incremental exercise testing as functions of %\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{\text V}\text{O}_2$$\end{document}V˙O2max. Blood was sampled at rest, unloaded cycling, and each minute during increasing work rate exercise. Arrows mark the gas exchange threshold (GET = 64% \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{\text V}\text{O}_2$$\end{document}V˙O2max). Gray shading shows 95% confidence intervals, and dashed lines indicate 95% prediction intervals

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  Fig. 3. A Recreated Fig. 4B from Stringer et al. 1994 incremental exercise test data (herein Fig. 1) [48]. Blue dots show O2Hb saturation vs. PO2 for n = 12 mean samples from five participants. Gray lines are the O2Hb dissociation curves calculated using the Dash et al. 2016 model with each sample’s PO2, PCO2, pH, [2,3-DPG] = 0.0029 M, Hct = 0.45, and Hb = 0.00528 M (Fig. 2) and a temperature increase from 37.0 to 38.0 °C, while the blue curve represents the in vivo O2Hb dissociation curve based on the fitted values of Fig. 2. Black dots at 50% O2Hb saturation indicate the P50 for each curve, and those around 36% mark the inflection points. CO2Hb (orange) and HbNH3+ (green) in vivo dissociation curves are plotted with the dashed gray line marking the intersection’s alignment with sample 4 passing its in vitro ODC inflection point. B Bland–Altman plot comparing the O2Hb saturation measured by Stringer et al. with the simulated ones shown in Panel A. C, D The same analyses as in panels A, B but with 37.0 °C fixed and [2,3-DPG] set to 0.00350 M

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  Fig. 4. Illustration of the progression of O2Hb (blue), CO2Hb (orange), and HbNH3+ (green) across the n = 12 samples, highlighting shifts in the in vitro curves and the corresponding development of the in vivo curves. Each panel presents the current sample’s data point along with its in vitro ODC, CDC, and HDC (light-colored), all previous samples’ in vitro curves (gray), and the trace of the in vivo curves as they develop from earlier data points to the present (dark-colored)

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  Fig. 5. The chemical species the Dash et al. 2016 model returns for the n = 12 samples of Stringer et al. 1994 and their fitted values (solid lines) as functions of %\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{\text V}\text{O}_2$$\end{document}V˙O2max (Fig. 2), identifying the behavior of the equilibria of Eqs. (1) to (6). Note: The physiological parameters in the Dash et al. model vary as in the experiments of Stringer et al. (Fig. 2), capturing natural interactions among variables within the system