Acute hypoxia elicits prefrontal oxygenation asymmetry in young adults

Figures

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  Fig. 1. Experimental protocol of isocapnic hypoxia test. Abbreviations: PETCO2, partial pressure of end-tidal carbon dioxide; PETO2, partial pressure of end-tidal oxygen.

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  Fig. 2. Typical example of time traces of changes in (a) PETO2, PETCO2, and (b) HR, as well as normalized changes in (c) deoxy-Hb, total-Hb, oxy-Hb, and (d) StO2 in the relatively deeper layer over the frontal poles in relation to time after baseline. (a) Solid line: PETO2, dashed line: PETCO2. (c), (d) Red solid lines: oxy-Hb, deoxy-Hb, total-Hb, and StO2 over FPL; black solid lines: oxy-Hb, deoxy-Hb, total-Hb, and StO2 over FPR. Abbreviations: PETCO2, partial pressure of end-tidal carbon dioxide (Torr); PETO2, partial pressure of end-tidal oxygen (Torr); HR, heart rate (beats/min); oxy-Hb, oxygenated hemoglobin; deoxy-Hb, deoxygenated hemoglobin; total-Hb, total hemoglobin; StO2, tissue oxygen saturation; FPL, left frontal pole; FPR, right frontal pole.

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  Fig. 3. Average time traces of changes in (a) PETO2 and PETCO2, (b) HR and normalized changes in (c) deoxy-Hb, total-Hb, oxy-Hb, and (d) StO2 in the relatively deeper layer over the frontal poles in relation to time after baseline. Each symbol and error bar represents the 60-s mean and SD among n=15 subjects. Open squares: PETO2; solid squares: PETCO2; solid circles: HR; open squares: oxy-Hb, deoxy-Hb, total-Hb, and StO2 over FPL; solid squares: oxy-Hb, deoxy-Hb, total-Hb, and StO2 over FPR. Changes in PETCO2 and PETO2 were analyzed using repeated-measures ANOVA in conjunction with the Bonferroni post hoc test for multiple comparisons. ##, ### indicate significant differences from the baseline at 2 min before the onset of hypoxic air feeding at P<0.05, P<0.0001, respectively. Effects of hypoxia on changes in hemodynamics in the relatively deeper layer over the frontal poles (time) and differences in hemodynamic responses between FPL and FPR (channel; Ch) were analyzed using two-way repeated-measures ANOVA (Ch × time) in conjunction with the Bonferroni post hoc test for multiple comparisons. ##, ### indicate significant differences from the baseline at 2 min before the onset of hypoxic…

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  Fig. 4. Relationship between changes in total-Hb in the relatively deeper layer over the frontal poles [(a) FPL and (b) FPR] and changes in mean HR. Pearson’s correlation coefficient was used. Abbreviations: total-Hb, total hemoglobin; HR, heart rate; FPL, left frontal pole; FPR, right frontal pole.

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  Fig. 5. Changes in hemodynamics in the superficial layer over (a) FPL and (b) FPR in response to hypoxia. Changes in hemodynamics in the relatively deeper layer are shown for reference. Each symbol and error bar represents the 60-s mean and SD among n=15 subjects. Solid triangles: oxy-Hb and deoxy-Hb in the relatively deeper layer over FPL and FPR; open triangles: oxy-Hb and deoxy-Hb of the relatively superficial layer over FPL and FPR. Effects of hypoxia on changes in hemodynamics in the superficial layer of the forehead (time) and the difference between FPL and FPR (channel; Ch) were analyzed using two-way repeated-measures ANOVA (Ch × time) in conjunction with the Bonferroni post hoc test for multiple comparisons. # indicates significant difference from the baseline at 2 min before the onset of hypoxic air feeding at P<0.05. Abbreviations: FPL, left frontal pole; FPR, right frontal pole; oxy-Hb, oxygenated hemoglobin; deoxy-Hb, deoxygenated hemoglobin; SD, standard deviation; ANOVA, analysis of variance.