Venous emptying mediates a transient vasodilation in the human forearm

We tested the hypothesis that venous emptying serves as a stimulus for vaso dilation in the human forearm. We compared the forearm blood flow (FBF; pul sed Doppler mean blood velocity and echo Doppler brachial artery diameter) response to temporary elevation of a resting forearm from below to above he art level when venous volume was allowed to drain versus when venous draina ge was prevented by inflation of an upper arm cuff to similar to 30 mmHg. A rm elevation resulted in a rapid reduction in venous volume and pressure. C uff inflation just before elevation effectively prevented these changes. FB F was briefly reduced by similar to 16% following arm elevation. A transien t (86%) increase in blood flow began by similar to 5 s of arm elevation and peaked by 8 s, indicating a vasodilation. This response was completely abo lished by preventing venous emptying. Arterial inflow below heart level was markedly elevated by 343% following brief (4 s) forearm elevation. This hy peremia was minor when venous emptying during forearm elevation had been pr evented. We conclude that venous emptying serves as a stimulus for a transi ent (within 10 s) vasodilation in vivo. This vasodilation can substantially elevate arterial inflow.