Laser surgery of port wine stains using local vacuum pressure: Changes in skin morphology and optical properties (part I)

Background and Objectives: In a recent case study, the use of a suction device to aid in port wine stain (PWS) laser treatments showed favorable results. It is our objective to further understand the mechanisms of vacuum-assisted laser therapy by analyzing the mechanical and optical changes of the skin and musculoskeletal tissues during the application of mild vacuum pressure from a suction cup. Study Design/Materials and Methods: A mathematical model of tissue deformation was used to determine the changes in tissue morphology that affect the underlying laser-tissue interactions, such as epidermal stretching and thinning, blood vessel dilation, and change in blood vessel depth. Video imaging experiments were used to verify the bulk tissue deformation and skin surface stretching computed by the mathematical model. Additionally, visible reflectance spectroscopy was used to determine the changes in the optical characteristics of tissue, including blood vessel dilation and epidermal absorption coefficient. Results: At a vacuum pressure of 50 kP(a), the epidermis at the center of the suction cup was measured to stretch 4% and was calculated to be thinned approximately 6%. Blood vessels embedded in the dermis were measured to dilate up to two times their original size. However, these vessels were calculated to be displaced toward the skin surface by a very small amount, approximately 1-3 mu m. The absorption coefficient of the epidermis was also measured to be reduced significantly by approximately 25% at a wavelength of 585 nm. Conclusions: Mild vacuum pressure applied to the skin surface causes considerable changes in the morphology and optical properties of the tissue. These changes may be used for more efficient photothermolysis of small PWS blood vessels.