[Functional effect of the argon laser on the hearing organ of the guinea pig].

While numerous histological findings point towards a possible destruction of inner-ear structures by the Argon-Laser we still miss a satisfactory statement concerning functional impact of stapedectomy or stapedotomy using laser beams. To investigate this we irradiated the promontorium of each of 10 guinea-pigs with laser powers between 0.6 W and 2.2 W ten times for 0.5 s. Then, and on the first, fifth and tenth postoperative day we recorded the brainstem potential evoked by bone-conducted clicks. We found that after the application of laser power up to 1.2 W a reversible threshold shift of up to 20 dB took place. Above powers of 1.2 W a permanent threshold shift was found (Fig. 1). Before sacrificing the animals we recorded the course of temperature in the perilymph during laser irradiation (Fig. 2 and 3). In order to set application limits of power within we consider laser impact functionally critical we compared the temperature increment during single shots and permanent elevation of the temperature above body temperature with values we have found earlier at the human petrous bone (Fig. 2 and 3). This led us to the conclusion that the temperature increment during the shot might be the limiting factor as far as the deterioration of inner-ear function is concerned. This may very well coincide with our hypothesis (Thoma and coworkers, 1981) that the vaporization of endocochlear fluid during the shot is a possible cause of cochlear malfunction after stapedectomy by laser.