Venous emptying mediates a transient vasodilation in the human forearm

Venous emptying mediates a transient vasodilation in the human forearm. Am J Physiol Heart Circ Physiol 279: H1007-H1014, 2000.--We tested the hypothesis that venous emptying serves as a stimulus for vasodilation in the human forearm. We compared the forearm blood flow (FBF; pulsed Doppler mean blood velocity and echo Doppler brachial artery diameter) response to temporary elevation of a resting forearm from below to above heart level when venous volume was allowed to drain versus when venous drainage was prevented by inflation of an upper arm cuff to ~30 mmHg. Arm elevation resulted in a rapid reduction in venous volume and pressure. Cuff inflation just before elevation effectively prevented these changes. FBF was briefly reduced by ~16% following arm elevation. A transient (86%) increase in blood flow began by ~5 s of arm elevation and peaked by 8 s, indicating a vasodilation. This response was completely abolished by preventing venous emptying. Arterial inflow below heart level was markedly elevated by 343% following brief (4 s) forearm elevation. This hyperemia was minor when venous emptying during forearm elevation had been prevented. We conclude that venous emptying serves as a stimulus for a transient (within 10 s) vasodilation in vivo. This vasodilation can substantially elevate arterial inflow. blood flow; vein; doppler ultrasound; venoarteriolar reflex