Sympathetic skin vasoconstriction - further evaluation using laser Dopplertechniques

The aim of this study was to quantify the reflex sympathetic vasoconstricti on in skin at different depths. Twenty healthy subjects were studied. Finge r skin blood flow was measured using laser Doppler perfusion imaging (LDPI) and laser Doppler perfusion monitoring (LDPM). In LDPM, a probe with fibre s separated 0.25 mm (deep) and 0.14 mm (superficial) from the illuminating fibre was used. Local heating (40 degreesC) was achieved with a Peltier ele ment, and reflex vasoconstriction induced by immersion of the contra-latera l hand and forearm for 3 min in water at 15 degreesC. The change in skin bl ood flow was measured and a vasoconstriction index (VAC: cooling/before coo ling) calculated. VAC indices of LDPI, LDPM-0.25 and LDPM-0.14 were 0.60, 0 .59 and 0.60, respectively. The two components of the LDPM perfusion value, blood cell velocity and concentration, were studied separately. Their cont ributions in LDPM-0.25 were roughly the same, whereas the velocity componen t dominated in LDPM-0.14, although their relative responses in the two chan nels were similar. We conclude that sympathetic skin vasoconstriction does not significantly differ in two compartments, as probed with fibres separat ed by 0.25 and 0.14 mm. Blood cell velocity is influenced in a proportional way, as is concentration.