A COMPARATIVE-STUDY OF HUMAN SKIN THERMAL RESPONSE TO SAPPHIRE CONTACT AND CRYOGEN SPRAY COOLING

Surface cooling, in conjunction with various thermally mediated therap eutic procedures, can provide a means to protect superficial tissues f rom injury while achieving destruction of deeper targeted structures. We have investigated the thermal response of irt-vivo human skin to: 1 ) contact cooling with a sapphire window (6-12 degrees C); and 2) spra y cooling with a freon substitute cryogen [tetrafluoroethane; boiling point approximate to -26 degrees C at 1 atmospheric pressure (atm)]. M easurements utilizing infrared radiometry show surface temperature red uctions from 30 degrees C to 14-19 degrees C are obtained within appro ximately is in response to sapphire contact cooling. Surface temperatu re reductions to values between 5 degrees C and -9 degrees C are obtai ned in response to 20-100-ms cryogen spurts. Computational results, ba sed on fitting the measured radiometric surface temperature to estimat e heat transfer parameters, show: 1) temperature reductions remain loc alized to approximately 200 mu m of superficial tissue; and 2) values of heat flux and total energy removed per unit skin surface area at le ast doubled when using cryogen spray cooling.