Filling and emptying of the low-pressure blood vessels of the human forearm.

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Abstract
Forearm volume (FV) was measured in a plethysmograph pressurized to 20 mm Hg, and venous pressure (VP) was observed in 1 or 2 veins while a congesting cuff was inflated and deflated at controlled rates. With sudden inflations, pressure rose at different rates in different veins. This evidence of uneven venous filling could be exaggerated by selectively increasing blood flow to skin (body heating) and is attributed to differences in blood flow to different parts of the forearm, interference with pressure equalization by the valves. When VP was kept at plateau levels, swelling occurred at rates directly related to the speed of ascent to the plateau. The delayed swelling is attributed to some combination of capillary filtration, stress relaxation, and recruitment of capacity vessels due to irregular filling. With nonuniform venous filling, distensibility cannot be determined by relating [DELTA]FV to [DELTA]VP in a single vein. Uniform pressure changes may be achieved, at least in superficial veins, by inflating the cuff very slowly (<0.25 mm Hg/sec) or by deflating it at I mm Hg/sec, after filling the veins uniformly.