Contribution of Laser-Induced Gas-Vapor-Liquid Dynamics to the Mechanism of Endovenous Laser Ablation

Abstract

The aim of the investigation is to ground experimentally the mechanism of endovenous laser ablation (EVLA), based on laser-induced convective heat transfer from the blood to the vein walls due to its boiling as a dominating process in a complicated mechanism of heat exchange occurring in endovasal laser manipulations.Materials and Methods. In experimental modeling of EVLA, fragments of varicose trunks of great suphenous veins, removed by combined phlebectomy, have been used. Laser radiation with 970 nm wavelength and 6 and 7 W power was delivered into the vein through a quartz optical fiber with a flat preblackened (initiated) tip. Pullback velocity was 0.5 mm/s. The surface temperature of the vein was measured during laser radiation using FLIR A600 (Sweden) infrared camera. Denaturation of collagen in the vein wall caused by laser impact was determined by differential scanning calorimetry.Results. Recording the surface temperature dynamics of vein with infrared camera allowed visualization of spot heating of the vein wall by the fluid surrounding the gas-steam bubbles. Temperature saturation in the dynamics of heating the media under study has been established to exist, being one of the characteristic features of the first-order phase transition. The degree of collagen denaturation in the venous wall specimens at 6 and 7 W amounted to 87±5 and 97±3%, respectively.Conclusion. Bubble boiling of blood in the veins, providing fast and efficient heat transfer from the heated tip of the quartz optical fiber to the vein walls, has been experimentally confirmed. For successful performing of the EVLA, the fiber traction must be started at the moment of blood boiling; at lower laser powers the fiber must be held for a longer period. In clinical EVLA procedures less powerful and safer laser devices can be used, reducing the risk of post-treatment complications.

Thermography of Whole Blood during Laser Heating through Bare Fiber

“…The formation of coagulate is the most important factor influencing the result of laser exposure to blood. As the temperature rises, the formation of vapor-gas bubbles [5], decomposition and oxidation of the organic components of biological tissues, and carbonization are observed [6][7][8]. A review of mechanisms and modeling outcomes under endovenous laser treatment is presented in Ref.…”