Influence of Nd-YAG laser on cochlear function: experimental study

Abstract

Idea: One of the main problems of using lasers in middle ear surgery is the prevention of damage to the cochlear and vestibular receptor cells. So it is very important to learn the threshold of safe laser energy regarding the inner ear function. This is possible only under experimental terms. Method: We have studied the influence of laser irradiation on the function of inner ear receptors using short latence evoked auditory brain stem potential in rabbit models. After being registered, the initial potentials of laser irradiation were applied to the medial wall of the tympanic cavity in one ear. The other ear served as control. To evaluate the laser energy reaching the inner ear receptors of animals, we measured the thickness of the rabbit's bone medial wall of tympanic cavity. Results: It was found that the threshold of auditory inhibitory activity of the Nd-YAG laser was 7–8 W during 0.4–0.6 s, through fiber with a diameter of 600 μ. The thickness of the rabbit's bone medial wall of tympanic cavity was about 0.2 mm. Conclusion: Taking into consideration the difference in bone wall thickness in rabbit and in man and using the coefficients of laser transparency of bone tissue, which had been established by us earlier, we consider a power of 14–18 W during 0.4–0.6 s through a fiber 600 μ in diameter might be critical during manipulations in the human middle ear.