Reflection spectroscopy of analgesized skin

Analgesized skin, when subjected to heat stimuli, responds by increasing sk in perfusion. This response does not originate from increased perfusion in superficial capillaries, but rather in the deeper lying vessels. The aim of this study was to assess changes in blood chromophore content, measured by reflection spectroscopy, in relation to the perfusion increase, especially regarding the chromophores oxyhemoglobin and deoxyhemoglobin. Eleven norma l subjects were treated with analgesic cream (EMLA) and placebo for 20, 40, 60, 120, and 180 min. Individual reactions to local heating were classifie d as responses if the change in reflection data or the change in perfusion, as measured by laser Doppler blood flowmetry, exceeded 2 standard deviatio ns of normal variation. The increase in blood perfusion. or in blood conten t gave rise to an increased absorption, interpreted as an increase due main ly to the chromophore oxyhemoglobin. The number of responses increased with increased treatment time for EMLA-treated areas. In general, there was a g ood agreement between both methods; 44 of 55 classifications coincided for the two methods used. In conclusion, analgesized forearm skin, which had be en exposed to local heating, responded with an elevated perfusion consistin g of oxygenated blood. This strengthens the hypothesis that the flow increa se occurs through dilatation of larger deeper lying skin vessels and not in the capillaries. (C) 2001 Academic Press.