Quantification of sympathetic vascular responses in skin by laser Doppler flowmetry

An improved physiological test of focal sympathetic nervous function using a laser Doppler flowmeter is presented. The test evaluates rapid reflex changes in skin blood flow at the finger tip where there are abundant arteriovenous anastomoses with dense sympathetic innervation. Indirect body heating was employed in all subjects to induce central vasodilation and to obtain stable comparable finger tip blood flows prior to stimulus. The reflex vasoconstriction which occurs following inspiratory gasp and contralateral hand cold challenge was quantified and its reproducibility investigated on three separate occasions in 20 young subjects. The variability in responses both within and between young subjects was small. The test was applied to 10 diabetic patients with autonomic neuropathy and to 10 age-matched control subjects. Vasoconstrictor reflexes were significantly lower in the diabetic group (p less than 0.005) with responses lower than 2 SD from the mean for age-matched controls. In conclusion, the test provides an assessment of focal autonomic damage which can be applied to other regions of the body rich in arteriovenous anastomoses and may have application in clinical studies investigating autonomic activity.