Laser-induced thermal injury to dermal blood vessels: Analysis of wavelength (585 nm vs. 595 nm), cryogen spray cooling, and wound healing effects

Background and Objectives: Successful laser treatment of cutaneous hyper-vascular lesions requires appropriate laser irradiation parameters for selective photothermolysis of ectatic dermal blood vessels as well as appropriate cooling parameters for epidermal protection based on an individual patient basis. Using the rabbit ear as an in vivo model for dermal vasculature, we investigated the influences of laser wavelength (585 nm vs. 595 run) and cryogen spray cooling with various spurt durations on the laser-induced thermal injury to dermal blood vessels. Wound healing response was also evaluated in 2 hours and 4 days. Study Design/Materials and Methods: Flashlamp-pumped pulsed dye laser ScleroPlus (TM) (operated at the wavelength of 585 or 595 nm) was used for the comparison between the influences of two wavelengths (585 nm vs. 595 nm). R134-a cryogen spurts with the durations from 50 to 300 milliseconds were sprayed onto the sites to be irradiated and terminated 20 milliseconds before the onset of the laser pulses. In vivo rabbit ear was used as the model for cutaneous hyper-vascular lesions. Totally 10 New Zealand Albino white rabbits were experimented and in each rabbit ear six to seven sites were irradiated. Five animals were sacrificed 2 hours after the irradiation, and the remaining five sacrificed 4 days after the irradiation. Thermal injury to the blood vessel was assessed by hematoxylin and eosin stained histological sections and confirmed by an apoptosis assay. Results: When the radiant exposures were above 10 J/cm(2), 595 nm wavelength induced equivalent or more severe thermal injury to dermal blood vessels than 585 nm. Cryogen spray cooling with the spurt durations above 100 milliseconds resulted in increased depth of the most superficial thermal injury to dermal blood vessels than without cooling, indicating that superficial blood vessels were non-specifically cooled by the cryogen spurts applied at these parameters. Laser-induced thermal injury was significantly healed in the rabbit ear vasculature at 4 days post irradiation. Conclusions: Given sufficient radiant exposure, 595 nm wavelength can induce equivalent or more severe vascular injury compared with 585 mn. Cryogen spray cooling with the spurt durations above 100 ms may impair the photocoagulation of superficial blood vessels. Irreversible thermal injury to blood vessel can be achieved only when the basement membrane of blood vessel wall is irreversibly damaged..