A THEORETICAL-STUDY OF THE THERMAL RESPONSE OF SKIN TO CRYOGEN SPRAY COOLING AND PULSED-LASER IRRADIATION - IMPLICATIONS FOR TREATMENT OF PORT-WINE STAIN BIRTHMARKS

The successful treatment of port wine stain (PWS) patients undergoing laser therapy is based on selective thermal coagulation of blood vesse ls without damaging the normal overlying epidermis. Cryogen spray cool ing of skin may offer an effective method for minimizing epidermal the rmal injury. Inasmuch as the density of melanosomes and depth of PWS b lood vessels can vary considerably, an optimum cooling strategy is req uired on an individual patient basis. We present a theoretical study o f the thermal response of various pigmented PWS lesions to spray cooli ng in conjunction with flashlamp-pumped pulsed dye laser irradiation ( 585 nm). Results of our model indicate that precooling of skin using t etrafluoroethane as the cryogen spray is sufficient to eliminate epide rmal thermal injury when using incident fluences less than 10 J cm(-2) and 8 J cm(-2) on patients with intermediate and high epidermal melan in content, respectively. Cryogens that have lower boiling points than tetrafluoroethane may allow successful treatment when using fluences equal to or greater than those indicated.