[Measurement of temperature and sound pressure in the inner ear during application of the argon-laser (author's transl)].

Laser stapedectomy is looked upon as an operation method which may be less harmful to the inner ear. The purpose of this study was to investigate the course of temperature behind the footplate of isolated human petrous bones while using the Argon Laser. We found that a non-linear relationship exists between the power of the Laser beam, the duration of the impulse and the sudden temperature rise during the impulse. Another, though linear, relationship exists between the energy of the beam and the permanent elevation of temperature in the perilymph during repeated shots. The observation of tiny bubbles beneath the focus on the wall of a plastic tube (which we used as a model for flow studies) led us to assume that the same may be true for the perilymph, too. The bursting of these bubbles was thought to cause a sudden rise of pressure in the inner ear. We were able to measure this Laser-generated sound pressure which reached 59 dB (A) for a beam energy of 1.0 Ws. Very low frequencies, which were not determined by this method, might very well cause damage to the inner ear structures. Finally, we proved that the results found a the isolated petrous bone which we fixed in a 37 degree waterbath can be transferred to in vito conditions: The course of the temperature was investigated in the cochlea of live Guinea pigs and shortly after death without detecting any change of the results.