Enhanced cardiac vagal activity and mood after low-dose hypoxic gas inhalation in healthy young adults

Figures

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  Fig. 1. Overall experimental design and depiction of segments, consisting of normobaric normoxic (NN) and normobaric hypoxic (NH) conditions. Gray-colored segments indicate periods of hypoxia in normobaric hypoxia condition.

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  Fig. 2. Fluctuation of SpO2 (A), heart rate (B) and HRV indices (C-F) during the entire experiment for both conditions. NH, normobaric hypoxia; NN, normobaric normoxia; SpO2, saturation of percutaneous oxygen; HR, heart rate; SI, Baevsky stress index. The dashed gray line represents the mean Pre value of the NH condition. The gray colored box represents a 10-minute Hypoxia1–2 session for both conditions. *p < 0.05, **p < 0.01, and ***p < 0.001 between two groups; ap < 0.05, aap < 0.01, and aaap < 0.001 compared to Pre-session.

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  Fig. 3. Changes in pleasure levels before, during, and after hypoxia and their results for repeated measures relationship with lnRMSSD and SI. Fig. A: gray box represents the 10-minute Hypoxia1–2 session for both conditions. NH, normobaric hypoxia; NN, normobaric normoxia. **p < 0.01, ***p < 0.001 between two groups; ap < 0.05, aaap < 0.001 compared to Pre-session. Fig. B,C: scatter plots show individual data points (N = 294), with each point representing a participant’s measurement across all conditions and sessions. Each participant’s data depicted in a consistent color. The line in the scatter plot represents the linear regression for each participant. SI, Baevsky stress index. *p < 0.05,***p < 0.001.

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  Fig. 4. Schematic illustration of hypoxic dose-dependent vagal response. The left graph illustrates the hormetic stress response in CVA following acute hypoxia, with the vertical double-headed arrow indicating the extent of rebound in CVA (ΔCVA = lnRMSSDPost1 – lnRMSSDpre). The plots displayed in the right graph represent FIO2 levels of 9.6 %, 13.5 %, 16.0 %, and sea level, respectively, arranged in non-equidistant intervals. Data of 13.5 % and 20.9 % were plotted based on the main results [Fig. 2], and data of 9.6 % and 16.0 % were drawn based on the supplemental experiment [Fig. S1, S2]. Data are presented as the mean, with the gray bands indicating 95% confidence intervals. Note that all three conditions were conducted with different sample sizes. FIO2, fraction of inspired oxygen.