Background and Objective Pulsed dye laser (PDL) is a commonly used treatment for Port Wine Stain birthmarks (PWS). However, deeper components of PWS are often resistant to PDL. Deeper penetrating lasers, including the long pulsed Neodymium:Yttrium Aluminum Garnet (Nd:YAG) laser have been used, but carry greater risk. This study evaluates the distinct blood vessel thermal responses to visible (595 nm) and near infrared (1,064 nm) lasers using animal and numerical models. Study Design/Materials and Methods Blood vessels in the rodent dorsal skin chamber (DSC) were irradiated by a 595 nm PDL and a long-pulsed 1,064 nm Nd:YAG laser. Laser-induced immediate and 1-hour post-structural and functional changes in the vessels were documented. Numerical simulations were conducted using a 1,000 μm depth SD mouse skin fold to simulate experimental conditions. Results PDL irradiation produced immediate blood vessel hemorrhage. Modeling indicated this occurs due to preferential heating of the superior parts of large blood vessels. Nd:YAG irradiation resulted in blood vessel constriction; modeling indicated more uniform heating of vessel walls. Conclusion PDL and Nd:YAG lasers result in distinct tissue responses. This supports different observable clinical treatment end points when using these devices. Vessel constriction associated with the Nd:YAG may be more difficult to observe and is one reason this device may carry greater risk. Lasers Surg. Med. 46:479–487, 2014.

The authors have indicated no significant interest with commercial supporters.A blative laser resurfacing is an effective treatment modality for rejuvenation and skin tightening. In the 1980s, the high-energy short-pulsed carbon dioxide (CO 2 ) laser was the first laser used for ablative resurfacing; however, its extensive collateral thermal damage was associated by a relatively high risk for adverse events and downtime. 1,2 The advent of the 2,940-nm erbium:yttrium aluminum garnet (Er:YAG) laser introduced an alternative device for ablative laser resurfacing with the ability to improve the appearance of skin with faster healing, less persistent erythema, and less delayed-onset permanent hypopigmentation.Like its CO 2 predecessor, the Er:YAG laser targets both intracellular and extracellular water as its chromophore. With a wavelength more closely corresponding to the absorptive peak of water (3,000 nm), its energy more efficiently vaporizes water-containing tissue, minimizing collateral thermal damage. 2,3 Superficial epidermal vaporization induces expression of keratin 16 (KRT16), a maker for epidermal injury, and also a rapid transient increase in keratinocyte proliferation, as indicated by staining for Ki67. However, with this simple superficial injury, the epidermal basal layer remains unaffected, and immunostaining for laminin gamma-2 confirms this integrity.Of interest, intra-epidermal injury alone can drive dermal extracellular matrix changes and remodeling. 4 This wound-healing response is evidenced by a marked increase in the inflammatory cytokines interleukin (IL)-1 beta and IL-8, a potent chemoattractant for polymorphonuclear leukocytes. The subsequent neutrophil infiltration extends from the dermis into the epidermis.The inflammatory phase is followed by remodeling of the dermal extracellular matrix and is driven by the activator protein 1 transcription factor complex, which regulates transcription of several important cytokines and metalloproteinases (MMPs). Metalloproteinase-1 initiates cleavage of collagen fibrils; MMP-3 and MMP-9 further degrade cleaved collagen. These factors are substantially elevated in both the epidermis and dermis.Fibroblasts throughout the mid to upper dermis increase production of Type I and Type III collagens. 4 It has been hypothesized that relatively low and controlled concentrations of reactive oxygen species stimulate signal transduction processes for transcription factor activation, gene expression, muscle contraction, and fibroblast growth, thus playing a role in collagen and extracellular matrix formation. 5 Nevertheless, Er:YAG laser resurfacing involves a highly organized cascade of molecular events that stimulate wound healing and dermal matrix remodeling. *All the authors are affiliated with the