[The effects of cochleostomy of hearing threshold in animal experiment].

INTRODUCTION To assess an effect of cochleostomy on hearing threshold in guinea pigs. MATERIAL AND METHODS The authors performed animal experiments using five 3-month-old guinea pigs. Before experiment hearing threshold were evaluated. Surgery involved access to the temporal bone by a post-auricular incision. After a wide opening of the bulla cochleostomy was created (10,000 turn/min, diamond bur of 0.8 mm diameter). Hearing threshold was identified on the basis of presence of wave V in auditory brainstem responses (ABR) for click and frequency-specific stimulation. Also morphology and latency changes for wave V for this stimulation was assessed. Hearing status was evaluated before, just after and 1-, 2-, and 4-weeks after surgery. For surgical procedure and ABR examination all animals were anesthetized with an intramuscular injection of ketamine (50 mg/kg) mixed with xylazine (9 mg/kg) in the supplemental doses. After surgery the animal was treated by antibioticoterapy for 3 days--Enrofloksacyna 0.3 ml subcutaneouly and analgesic--Tolfedine 0.05 mg in second day. RESULTS Four week observation of ABR morphology and hearing thresholds for click and frequency-specific stimulation of 100 dB SPL intensity showed only temporary changes confirming that cochleostomy did not affect cochlear function. CONCLUSIONS The correctly performed cochleostomy in guinea pigs did not affect persistently the cochlear function indicating that such an option of CI electrode insertion in patients is safe.