Venous Volume and Venous Blood Flow Velocity

Depending on the exerted pressure and the body position, external compression is able to narrow or to occlude superficial and deep leg veins.14

In the supine position an external pressure of 1015 mm Hg is enough to decrease the venous diameter. The resulting increase of blood flow velocity as clearly shown by measuring the circulation time with isotopes15 is the rationale for recommending light compression stockings for thromboprophylaxis in bedridden patients.

Venous volume can be assessed using air-plethysmogra-phy (APG) that shows a significantly more pronounced reduction by inelastic than by elastic compression, even when the resting pressure is the same.4

In the upright position elastic stockings will have only a minor effect on decreasing the diameter of the leg veins.16 However, a very small decrease of venous diameter will result in an overproportional decrease of the local blood volume as demonstrated by several plethysmographic studies.4,12

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