Laser Surgery of Port Wine Stains Using Local Vaccum Pressure: Changes in Calculated Energy Deposition (Part II)

Background and Objectives: Application of local vacuum pressure to human skin during laser irradiation results in less absorption in the epidermis and more light delivered to targeted vessels with an increased blood volume. The objective of the present numerical study is to assess the effect of applying local vacuum pressure on the temperatures of the epidermis and small vessels during port wine stain (PWS) laser treatment. Study Design/ Materials and Methods: Mathematical models of light deposition and heat diffusion are used to compute absorbed energy and temperature distributions of skin and blood vessels with different diameters (10–60 mm) at variousdepths (200–800mm)exposed to laser irradiation under atmospheric and vacuum pressures. Results: Under 50 kPa (15 in Hg) vacuum pressure, peak temperatures at the inner walls of small diameter vessels (10–30 mm) located 200–300 mmbelow the skin surface are 108C higher than those under atmospheric pressure, and peak temperatures in the epidermis of patients with skin phototype II are 58C lower. In patients with darker skin phototype (IV), the peak temperature at the inner wall of a 10 mm diameter vessel located 200 mm below the skin surface is 58C higher than that under atmospheric pressure, and the peak temperature in the epidermis is 108C lower. Conclusions: Additional energy deposition in a larger blood volume permits higher temperatures to be achieved at vessel walls in response to laser irradiation. While more energy is deposited in every vessel, temperature gains in small diameter vessels (10–30 mm) are greater, increasing the likelihood of irreversible thermal damage to such vessels. In addition, temperatures in the epidermis decrease because less energy is absorbed therein due to reduced epidermal thickness and concentration of melanin per unit area. Lasers Surg. Med. 39:118–127, 2007. 2007 Wiley-Liss, Inc.