Air embolism and veins is greater than atmospheric pressure, an air embolus does not often happen when a blood vessel is injured. In the veins above the heart, such as in the head and neck, the venous pressure may be less than atmospheric and an injury may let air in. This is one reason why surgeons must be particularly careful when operating on the brain, and why the head of the bed is tilted down when inserting or removing a central venous catheter from the jugular or subclavian veins. When air enters the veins, it travels to the right side of the
Ultrasonography of chronic venous insufficiency of the legs and show valvular function: Normal blood flow is anterograde (going to the heart), and from superficial to deep veins via perforator veins. However, there are two exceptions: firstly, the great saphenous vein (GSV) collaterals, (the veins that run parallel), drain the abdominal wall and have a flow from top to bottom so that when an examiner tests the sapheno-femoral junction, a false positive diagnosis might be made; secondly, in the flow from the sole of the foot venous network around 10% drains to the dorsal venous arch of the foot, going therefore against the norm, from deep to superficial veins.