Laser pulse impact on rat mesenteric blood vessels in relation to laser treatment of port wine stain

Background and Objective: To study the impact of laser pulses on animal mic rovasculature as a model for laser treatment of port wine stains. Study Design/Materials and Methods: Rat mesenteric blood vessels were irrad iated with a laser pulse (585 nm, 0.2-0.6 ms pulse duration, 0.5-30 J/cm(2) radiant exposure). Video microscopy was used to assess vessel dilation, fo rmation of intravascular thrombi, bubble formation, and vessel rupture. Cha nges in reflection during a laser pulse were measured by simultaneously rec ording the temporal behavior of the incident and reflected signals. Results: A threshold radiant exposure of approximately 3 J/cm(2) was found for changes in optical properties of blood in vivo, confirming previous in vitro results. Often, laser exposure induced a significant increase in vess el diameter, up to three times the initial diameter for venules and four ti mes for arterioles, within 200 ms after laser exposure. Arterioles were mor e likely to dilate than venules. Sometimes, immediately after the pulse, ro und structures, interpreted as being gas bubbles, were seen within the vess el lumen. Conclusions: A variety of phenomena can occur when blood vessels of sizes c omparable to those in port wine stains are irradiated with laser pulses as used in port wine stain treatment. Thrombus formation and vessel rupture ha ve been described before from histological sections of laser-irradiated por t wine stains. However, vessel dilation and formation of non-transient gas bubbles as found in this study have not been described before. (C) 2001 Wil ey-Liss, Inc.