The laser, a light amplification device by stimulated radiation emission, is a device capable of transforming other energies into electromagnetic radiation by emitting
light beams of different wavelengths. These are devices that amplify the light and produce coherent beams of light whose frequency ranges from infrared to X-rays. Depending on the medium used, lasers are often referred to as solid state, gas, semiconductors or liquids.
The stimulated emission, the process on which the Laser is based, was described by A. Einstein in 1917, but it is not until the 1960s, when the first laser process was observed in a ruby crystal and its first application in the field of Medicine, will be the removal of a tumor in the retina. The pioneers in applying the laser in Urology were Parsons in 1968 in Penile Carcinoma, Mulvaney and Beck in 1968 in the lithofragmentation of bladder stones with ruby laser and Watson and Dretler in 1984 with pulsed dye laser (coumarin green) in lithofragmentation of ureteral lithiasis.
Uses of the laser in Urology
The possible uses of the laser are almost unlimited, becoming a very valuable tool in biomedical sciences, thanks to the various effects (photovaporization, photodisruption, photocoagulation or photo stimulation) that it causes when interacting with tissues. For this reason, today, the use of lasers in the field of Urology offers us a wide range of possibilities, ranging from deobstructive surgery such as fragmentation of a stone or resection and ablation of prostate tissue to reconstructive surgery such as it is the welding of tissues in the vasovasostomy or the repair of a urethral stricture.
Mechanism of action of the laser
When we apply a laser on an organic tissue, it interacts with the cells of that tissue, causing the following effects11-16:
• Photodisruption: giving rise to the cellular burst due to the high temperature (from 37º to 2000º) that the cell acquires as a result of the great release of energy. This effect is used for the destruction of malignant cells and high power lasers (Neodymium or CO2) are required.
• Photovaporization: the evaporation of water from the cell with which the laser interacts, can increase the tissue temperature from 37º to 400º (CO2 laser).
• Photocoagulation: the interaction of the laser with the cell causes changes in the tertiary and quaternary structure of cellular proteins, raising the temperature from 37º to 65º and consequently causing photocoagulation of the blood (Argon laser and Green laser).
• Photoreradiation: the interaction of the laser with the tissue causes a very slight rise in temperature, in 1-2 degrees and this effect of local heat, would act accelerating the physiological processes (soft or low power lasers).
• Photo-stimulation or photochemistry: the most fascinating but at the same time unknown effect for which several hypotheses have been proposed: existence of a bioplasma as a second body in all living beings, which would have semiconductor properties and would be the recipient of eutrophic messages. Another hypothesis proposes that the laser reduces the negative charge on the cell membrane, altering its permeability and consequently favoring the exchange of some ions. Therefore, after the administration of a photosensitizing substance, the malignant cells can in turn retain said substances, favoring the action of lasers that have affinity (for example, porphyrins and protoporphyrins). The result is a photochemical reaction that would release free radicals at the intracellular level causing cell death. This effect has been used photodynamic therapy of skin tumors and for the diagnosis of carcinoma in situ of the bladder.
• Photoacoustic or mechanical: it is based on the conversion of the energy of different types of lasers into shock waves that underlie lithotripsy.
Lasers used in urology
Currently, different types of lasers are based on different criteria, but not all of them have applicability in the usual urological practice. Thus, within all of them we can highlight: Ruby Laser, CO2 Laser, Neodimium Laser: Yttrium-Aluminum-Garnet, KTP Laser or Green Laser, Dye Laser, Alexandrite Laser, Semiconductor Diode Laser, Holmium Laser, Nitrogen Laser, Erbium Laser, Thulium laser.
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