On changing posture from a supine position to standing, the microvasculature of the lower limbs vaso-constricts. This is the veno-arteriolar reflex (VAR) and the associated change in blood flow can be assessed by laser Doppler. The VAR is a mechanism that protects the delicate microvasculature of the lower limbs from damage due to excess hydrostatic blood pressure. The impairment of the VAR is seen in diabetes and more recently in primary biliary cirrhosis.
Although monitoring can be used, imaging will provide multiple LD flux measurements that can be averaged. The VAR index is Flux average in the dependent position / Flux average in the supine position x 100%. Observed values for VAR: normal healthy = 18%; diabetic without neuropathy = 29%; diabetic with neuropathy = 54%.
Rapid laser Doppler blood flow imaging
moorLDLS2 - Rapid laser Doppler blood flow imaging
MS3B - Mobile Stand