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Blood flow velocity for the internal carotid arteries (●), vertebral arteries (▲), and internal jugular veins (■) at various head-down tilt angles. Measurements were taken at baseline (0°) and after 4.5-h head-down tilt with phase-contrast MRI. Values are means ± SE. *P < 0.05. **P < 0.01. ***P < 0.001.
