Pathophysiology of chronic limb ischemia.

Chronic ischemia of the lower extremities is an everyday problem in vascular surgery clinics. In Germany, approximately 3% of all hospitalizations are due to peripheral artery disease (PAD), with critical limb ischemia (CLI) in particular showing a rapid increase. The consequences of chronic undersupply range from reduced walking distance to loss of limbs. At the beginning there are stress factors, such as hyperlipidemia (LDL), free radicals, arterial hypertension, infections or subclinical inflammation that interfere with endothelial homeostasis and cause endothelial dysfunction with increased permeability. Cells of the immune system are attracted and migrate into the vascular wall, where they lead to the degradation of matrix components and destabilization of the plaque. By changing the phenotype of smooth muscle cells and macrophages towards osteoclast-like cells, bone-like hardening of the vessel wall takes place. Above a vessel wall thickness of approximately 100 µm, hypoxia-induced factor (HIF-1α) is intensified by the lack of oxygen, which leads to an increase in growth factors, such as vascular endothelial growth factor (VEGF). This promotes angiogenesis, but it is not sufficient to compensate for a stenosed artery. Arteriogenesis refers to the growth of existing collateral vessels. The driving forces are the pressure gradient before and after the stenosis and the shear forces acting on the vessel walls. In the case of progressive stenosis, the compensatory capacities can be overtaxed and a manifest hypoxia in the tissue with regression of the obtained vascular structures and tissue atrophy occurs.