Capillary recruitment and pain relief on leg dependency in patients with severe lower limb ischemia

Patients suffering from severe lower limb ischemia may experience pain relief on leg dependency despite the fact that dependency normally results in arteriolar vasoconstriction. To clarify this possible paradox, skin microcirculation of the limb was investigated in 75 patients with different stages of lower limb ischemia and in 12 asymptomatic subjects.

Using nailfold capillary video microscopy, red blood cell-perfused capillary density and diameter and red blood cell velocity were assessed in supine and sitting positions. Capillary density increased by changing from the supine to the sitting position, especially in patients with limb-threatening ischemia (showing a 4.5-fold increase versus a 1.5-fold increase in asymptomatic subjects). In subjects without or with mild ischemia, capillary perfusion was two to four times lower in the sitting than in the supine position. In patients with limb-threatening ischemia, perfusion was strongly reduced, being slightly higher in the sitting position. Patients with relief of pain while sitting did not always have a higher capillary perfusion but did have a higher capillary density in the sitting position.

The arteriolar postural vasoconstrictive mechanism at the nutritive level is still intact in subjects without or with mild ischemia but not in patients with severe ischemia. Capillary recruitment rather than disturbed arteriolar vasoconstriction could explain why patients with severe leg ischemia prefer leg dependency.