Cognitive fatigue due to exercise under normobaric hypoxia is related to hypoxemia during exercise

Figures

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  Figure 1. (A) A typical example of the percutaneous arterial oxygen saturation (SpO2) during exercise. Immediately before exercise, the inhaled hypoxic gas was switched from hypoxia (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{F}}_\text{IO}}_{_{2}}$$\end{document}FIO2= 0.135; blue background) to a milder hypoxic gas (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{F}}_\text{IO}}_{_{2}}$$\end{document}FIO2= 0.161 ± 0.018; orange background), which was adjusted so that SpO2 during exercise remained at the resting level in the ME condition (red). Immediately after the end of the exercise, the inhaled hypoxic gas was again returned to hypoxia (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs}…

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  Figure 2. (A) Comparison of the reaction time (RT) between the incongruent and neutral conditions. The incongruent condition exhibits a significantly slower RT than the neutral condition (***P < 0.001). (B) Comparison of the error rate between the incongruent and neutral conditions. Significant Stroop interference effects are observed (**P < 0.005). (C) The mean difference of the RT in incongruent and neutral trials indicates Stroop interference for each condition. (D) Stroop interference (RT) differences between post- and pre-sessions for each condition. Stroop interference differences are significantly more positive in the hypoxic exercise (HE) condition than in the milder hypoxic exercise (ME) condition (*P < 0.05). Error bars indicate the standard error.

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  Figure 3. The spatial profiles of functional near-infrared spectroscopy channels and region of interest segmentation used in the current study; they were introduced in previous studies46,50. Channel numbers and FT7 and FT8 in the international 10–20 electroencephalography standard positions are denoted above the corresponding locations. The channels enclosed by the black broken lines were defined as the l-DLPFC, and their data were integrated for further analyses.

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  Figure 4. (A) Stroop interference differences between post- and pre-sessions for oxygenated hemoglobin (oxy-Hb) signal contrasts in both conditions. (B) Oxy-Hb signal differences for the hypoxic exercise (HE) condition are significantly lower than those for the milder hypoxic exercise (ME) condition (P < 0.05). Error bars indicate the standard error.

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  Figure 5. (A) The two conditions, breathing a moderately hypoxic gas (hypoxic exercise [HE]) and breathing a milder hypoxic gas, during which oxygen was added to the moderately hypoxic gas to maintain the oxygen saturation (SpO2) level during milder hypoxic exercise (ME). Cortical hemodynamic changes were monitored with functional near-infrared spectroscopy (fNIRS) while participants performed the Stroop task. HR, heart rate. (B) In both conditions, the exercise and color-word Stroop task (CWST) were performed on a recumbent cycle ergometer. Hypoxic gas (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{F}}_\text{IO}}_{_{2}}$$\end{document}FIO2 = 0.135) stored in a Douglas bag was inhaled through a mask. (C) In the ME condition, SpO2 was adjusted during exercise by adding oxygen gas with humidity to prevent the participant’s throat from drying out to the hose connecting the Douglas bag to the mask.