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

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/spl deg/C); and (2) spray cooling with a freon substitute cryogen [tetrafluoroethane; boiling point /spl ap/-26/spl deg/C at 1 atmospheric pressure (atm)]. Measurements utilizing infrared radiometry show surface temperature reductions from 30/spl deg/C to 14-19/spl deg/C are obtained within approximately is in response to sapphire contact cooling. Surface temperature reductions to values between 5/spl deg/C and -9/spl deg/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 /spl mu/m 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.