Effects of markedly increased intravascular pressure on the volume-flow characteristics in venous vessels of human limbs

The purpose was to study the effects of markedly increased local intravascular pressures on the flow characteristics in human limb veins. The subject was either seated inside a pressure chamber with one arm slipped through a hole in the chamber door (n=7) or positioned supine with a lower leg protruding to the outside (n=15). By increasing chamber pressure, transmural pressure in the vessels of the test limb was increased up to +150 mmHg for the arm and +240 mmHg for the leg. Flow profile and vessel diameter were measured with ultrasonographic/ Doppler techniques. The arm vessels were studied before and during blocking of the blood flow through the hand (BBF). Antegrade, pulsatile, arterial like flow profiles were observed at high distending pressures in the brachial and radial veins in all subjects and in ~50% of the subjects in the cephalic and posterior tibial veins. In five of seven subjects blood flow in the brachial vein remained pulsatile even during BBF. That pulsatile volume-flow characteristics was observed in all veins may suggest that markedly elevated intravascular pressures, induce considerable arteriovenous shunting, presumably via arteriovenous anastomoses (AVAs). That a pulsatile venous flow was present in the brachial vein also during BBF may suggest that significant AVAs exist not only in the hand but also in the forearm.