[Transformation of hemoglobulin into methemoglobulin during heating of blood: its role in the treatment of vascular lesions using an Nd: YAG (1.06 m) laser treatment of vascular lesions].

Clinical modifications are usually observed during the irradiation of a blood vessel with a laser. These modifications are due to the heating of the blood. Photothermal modifications of oxy-hemoglobin (Hb-O(2)) and des-oxyhemoglobin (Hb) induce formation of met-hemoglobin (Met-Hb), not normally present in healthy human blood. In the near-infrared, the optical absorption of Met-Hb is 3 to 4 times higher that the other chemical constituents of blood. Consequently, after the conformational change of the molecule of heme, the near-infrared (1.06 microm) absorption is considerably enhanced. In order to improve the Nd: YAG laser treatment of vascular lesions, using a non uniform pulse sequence appears to be a much better and safer solution than using a single pulse. The non uniform pulse sequence consists of 3 pulses. The first one induces the optical modification of the blood. After a few hundreds of milliseconds, a 2(nd) and a 3(rd), carrying an energy 3 to 4 times lower than the 1(st) one, are applied. These two pulses maintained a constant temperature inside the vessel. In order to achieve the complete destruction of the vessel, the total duration of the non uniform pulse sequence is similar to the thermal relaxation time of the blood vessel. In conclusion; a better knowledge of the laser tissue interaction process can lead to a better use of a laser. In this particular case, the efficiency of the Nd: YAG laser treatment of vascular lesions can be considerably improved while preserving non-targeted structures.