Er:YAG laser skin resurfacing using repetitive long-pulse exposure and cryogen spray cooling: I. Histological study

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Abstract
Background and Objective To evaluate histologically the characteristics of repetitive Er:YAG laser exposure of skin in combination with cryogen spray cooling (CSC), and its potential as a method of laser skin resurfacing. Study Design/Materials and Methods Rat skin was irradiated in vivo with sequences of 10 Er:YAG laser pulses (repetition rate 20 Hz, pulse duration 150 or 550 μs, single‐pulse fluence 1.3–5.2 J/cm2). In some examples, CSC was applied to reduce epidermal injury. Histologic evaluation was performed 1 hour, 1 day, 5 days, and 4 weeks post‐irradiation. Results A sequence of ten 550‐μs pulses with fluences around 2 J/cm2 resulted in acute dermal collagen coagulation to a depth of approximately 250 μm, without complete epidermal ablation. CSC improved epidermal preservation, but also diminished the coagulation depth. Four weeks after irradiation, neo‐collagen formation was observed to depths in excess of 100 μm. Conclusions Dermal collagen coagulation and neo‐collagen formation to depths similar to those observed after CO2 laser resurfacing can be achieved without complete ablation of the epidermis by rapidly stacking long Er:YAG laser pulses. Application of CSC does not offer significant epidermal protection for a given dermal coagulation depth. Lasers Surg. Med. 28:121–130, 2001.