1. A system for diagnosing and preventing, deep vein thrombosis in a body limb, comprising: a compression system for applying external pressure to a body limb; and a venous phasic flow monitoring system to monitor a venous phasic flow in a body limb; said venous phasic flow monitoring system determining a presence of deep vein thrombosis in the body limb by detecting a change in a volume of the body limb.