| Objective:Establish the tree shrew model of perilymph fistula and lateral semicircular canal dehiscence in order to figure out the advantage of shrew model and reveal the auditory characteristics of pre-operation and post-operation of tree shrew by use electrocochleography. All this work provide the dates about the electrophysiology of the tree shrew and helped for the further diagnosis of perilymph fistula and lateral semicircular canal dehiscence. This research also make the foundation of the future observation of morphology and chronic trial.Methods:The tree shrews with positive Preyer’s reflex, the external auditory canal patency otoscopy, tympanic membrane integrity, middle ear without infection were under anesthesia by testing click evoked ABR using a Tucker-Davis Technologies System. After hearing was re-assessed, the abnormal tree shrew were got rid of and we chose twenty healthy tree shrews to enter the test. The twenty tree shrews were randomly divided into two group. Group A were used to establish the perilymph fistula model, Group B were used to establish the lateral semicircular canal dehiscence model. The two group were tested the hearing function by electrocochleogram post-operation15min,1-3H,24H,48H. Observed the change of hearing function in different time after the operation.Results:(1) Tree shrew’s auditory bubble which was thin as paper located in superficial,and the structure of its ear was visible and easy to operate. The auditory bubble was also easy to open up and the round window was easy to expose, we could see the whole structure of the round window under the microscope. The position of lateral semicircular canal was also superficial and easy to operate.(2) The tree shrew SP-AP of pre-operation which was click-evoked showed that:in the time of pre-operation, the AP was a nonlinear distribution, its amplitudes increased as the click level was increased from35to90dB SPL, at the90dB SPL the amplitude reached the peak104.68±17.08μv. But the latencies was a linear distribution, at100dB SPL its shortest latencies was1.09±0.06ms. SP just appeared at a high level intensity about50to100dB SPL, its amplitude and latencies was a linear distribution, amplitudes increased and latencies decreased as the click level was increased from50to100dB SPL AP response reaction threshold shift was40.50±2.34dB SPL and the SP was56.25±6.66dB SPL (n=20) in the tree shrews of pre-operation.(3) After operation15min, the AP of A,B group kept the nonlinear distribution characteristic.(4) After operation1-3H, the AP of A,B group lost the nonlinear distribution characteristic, the hearing loss was the most serious.(5) After operation24H, the AP of A group regained the nonlinear distribution characteristic. In group A, there is-SP appeared in post-operation24H, the rate of SP/AP was0.36±0.03.(6) After operation48H, the AP of A group still kept the nonlinear distribution characteristic. At this moment, the-SP was disappeared. In group B, it still didn’t recover the nonlinear distribution characteristic.Conclusion:(1)The tree shrews as animal model have a lot of advantages compared to other animal models such as guinea pigs, rats in anatomy and we held the tree shrews were more similar with human, which make the results of the experiment were more useful than other animals. The round window of tree shrew can be expose directly and the lateral semicircular canal was superficial. This research successfully established the animal model of perilymph fistula and lateral semicircular canal dehiscence and we got some dates of electrophysiology which supply some useful proof for the diagnosis in clinic work and also lay the foundation of the observation of morphology and future chronic model.(2) We can conclude that temporary perilymph fistula have a little effect on the hearing function due to the group A of15min which may give the evidence for the security of the operation which make perilymph discharged for short time.(3) The perilymph fistula group suffered from the hearing loss most serious in the1-3H group. The24H group began to recover and at48H the hearing function reached the optimal which proved that in this group, the destroy of some parts of out hear cell was reversible. The hearing function of lateral semicircular canal dehiscence group was more serious than perilymph fistula group which proved that the endolymph fistula can make the irreversible trauma to the structure of inner ear. These patients whose hearing was continuous loss we should pay attention to the endolymph fistula and the operation should be done as soon as possible, or the patient will suffer from the bad prognosis. |
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