Relationship between cerebral arterial inflow and venous outflow during dynamic supine exercise

The regulation of cerebral venous outflow during exercise has not been studied systematically. To identify relations between cerebral arterial inflow and venous outflow, we assessed the blood flow (BF) of the cerebral arteries (internal carotid artery: ICA and vertebral artery: VA) and veins (internal jugular vein: IJV and vertebral vein: VV) during dynamic exercise using ultrasonography. Nine subjects performed a cycling exercise in supine position at a light and moderate workload. Similar to the ICA BF, the IJV BF increased from baseline during light exercise (P < 0.05). However, the IJV BF decreased below baseline levels during moderate exercise, whereas the ICA BF returned near resting levels. In contrast, BF of the VA and VV increased with the workload (P < 0.05). The change in the ICA or VA BF from baseline to exercise was significantly correlated with the change in the IJV (r = 0.73, P = 0.001) or VV BF (r = 0.52, P = 0.028), respectively. These findings suggest that dynamic supine exercise modifies the cerebral venous outflow, and there is coupling between regulations of arterial inflow and venous outflow in both anterior and posterior cerebral circulation. However, it remains unclear whether changes in cerebral venous outflow influence on the regulation of cerebral arterial inflow during exercise.