Postural and ambulatory changes in regional flow and skin perfusion.

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

Methods: 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.

Results: 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.

Conclusion: 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.