How to get ulcers from it?

No inflow: Venous stasis is caused by valve problems that allow blood from deep high-pressure veins to enter low-pressure veins just under the skin. These veins enlarge, letting fluid through the walls (swelling), letting blood through (discoloration) and finally having so much back pressure that nutritious arterial blood cannot enter an area of the skin resulting in ulcers. It is treated by laser ablation.