Postural and ambulatory changes in regional flow and skin perfusion

Studies of orthostatic changes in cutaneous micro-perfusion have yielded conflicting results, likely from imprecision of legacy equipment.

Postural flow changes in the femoral vessels and cervical carotids were measured in healthy normal adults using duplex equipment. Nutrient skin flow was measured using Hyperspectral imager (OxyVu-2™), a newer non-touch measurement technology.

There are regional variations in cutaneous capillary density, sparse in the abdomen but richer in the forehead and ankle. Orthostatic microvascular congestion displays regional variations reflective of the non-linear pressure-volume relationship in thin walled vessels. There is profound cutaneous deoxygenation (≈40% reduction) in the lower body starting at the level of the umbilicus and involving all levels below, in the erect posture; upper body is unaffected. Quantitative regional flow is preserved however, with an increase in pulse rate despite a velocity decrease in the femoral vessels. Increasing the arterio-venous gradient by calf-emptying maneuvers resulted in little improvement in cutaneous oxygenation unable to overcome the powerful orthostatic vasoconstriction.

There is intense orthostatic vasoconstriction and cutaneous deoxygenation of the lower limbs to a degree not previously suspected. This powerful mechanism may be relevant to an understanding of dysvascular syndromes, particularly those with strong orthostatic features.