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A comparative study of human skin thermal response to sapphire contact and cryogen spray cooling

Published Web Location Commons 'BY' version 4.0 license

Surface cooling, in conjunction with various thermally mediated therapeutic procedures, can provide a means to protect superficial tissues from injury while achieving destruction of deeper targeted structures. We have investigated the thermal response of in-vivo human skin to: 1) contact cooling with a sapphire window (6-12 degrees C); and 2) spray cooling with a freon substitute cryogen [tetrafluoroethane; boiling point approximately -26 degrees C at 1 atmospheric pressure (atm)]. Measurements utilizing infrared radiometry show surface temperature reductions from 30 degrees C to 14-19 degrees C are obtained within approximately 1 s in response to sapphire contact cooling. Surface temperature reductions to values between 5 degrees C and -9 degrees C are obtained in response to 20-100-ms cryogen spurts. Computational results, based on fitting the measured radiometric surface temperature to estimate heat transfer parameters, show: 1) temperature reductions remain localized to approximately 200 microns of superficial tissue; and 2) values of heat flux and total energy removed per unit skin surface area at least doubled when using cryogen spray cooling.

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