A kind of emulsified oil enhances vasodilatation effect of CO₂ in human skin during hot water bathing at 100 ppm

Abstract

It has been previously demonstrated that the carbon dioxide (CO₂) bathing at 100 ppm could affect thermoregulation through the cutaneous vasodilatation caused by CO₂. The purpose of this study was to investigate the modifying effect of emulsified oil on cutaneous blood flow during CO₂ bathing in humans. Seven healthy young adult men participated in this study. Experimental CO₂ water at 100 ppm was obtained by dissolving the mixture of NaHCO₃ and succinic acid in tap water. After resting for 20 min in the room at 25^oC and 50% RH, the subject was immersed up to the shoulder level for 10 min in experimental bath water at 40^oC in which the emulsified oil (fatty acid esters and nonionic surfactants) was dissolved with a concentration of 10 ppm. Tympanic temperature, cutaneous blood flow on the chest and the forearm (as an immersed area) were recorded continuously. Our main finding was that cutaneous blood flow in the immersed area was significantly greater in the experiments where the emulsified oil was added as compared with the control experiment where the emulsified oil was not added. It was suggested that in 100 ppm CO₂ bathing emulsified oil could enhance the cutaneous vasodilatation induced by CO₂ in human skin. However, the underlying mechanisms remain to be examined. [J Physiol Sci. 2008;58 Suppl:S102]