Influence of blood supply, thermal and mechanical traumata on hearing function in an animal model

Abstract

Even with modern neurosurgical techniques preservation of functional hearing in acoustic neurinoma surgery is still impossible in a large number of cases. Due to the necessity of averaging the brainstem auditory evoked potentials (BAEP) this monitoring is not a real time measurement. Therefore the surgeon cannot be sure which manipulation during the tumour dissection has caused the loss of the BAEPs. The direct monitoring of the cochlear nerve (CNAP) may warn the surgeon earlier. But it is not able to explain, which manipulation has caused the worsening of the potentials. A loss of the waves after coagulation of a vessel next to the cochlear nerve may be the result of the heat or of the disturbance of the blood supply. Potentially harmful to cochlear nerve function may be the interruption of inner ear blood supply, thermal or mechanical traumata. Experimental studies are rare to nonexistent. We therefore tested selectively each trauma for its influence on the BAEPs in an animal model. In New Zealand rabbits a lateral craniectomy of the posterior fossa was performed. Care was taken not to retract the cerebellum or to open the inner ear system, because both factors might disturb the BAEPs. Each step of the operation was followed by BAEP recording. After reaching the internal auditory canal, the cerebellopontine angle of 6 animals was exposed to heated water with definitive increasing temperature. The BAEPs did not react significantly until 71 degrees C was reached and protein coagulation started. In the second group, the internal auditory artery of 6 rabbits was compressed with a microdissector for 3 minutes. Subsequently the BAEPs disappeared in all animals. In the last group a constant pressure of 10 g was applied to 6 cochlear nerves for 1 minute consistently causing the loss of the BAEPs. The results are statistically significant (p = 0.03). We therefore concluded that the blood supply of the inner ear is of the upmost importance for cochlear nerve function. Mechanical manipulation should be minimized whereas thermal traumatization of the nerve is only critical when the nerve itself is coagulated.

Normative Auditory Brainstem Response Data for Hearing Threshold in the Rabbit

“…The curve form obtained in the authors' own investigations corresponded, in terms of the number of waves (I-V), to those described in the literature [Borg and Engström, 1983;Martin et al, 1983;Pierelli et al, 1986;Hülse and Keilmann, 1991;Romani et al, 1991;Braun and Richter, 1996]. With regard to amplitude characteristics, our findings resembled those of Braun and Richter [1996]. The appearance of the potentials evoked via BC corresponded, in terms of the number of waves and the amplitude, to the results reported by Gjuric et al [1991].…”

“…The anesthetics used in this study had already been employed in earlier investigations deriving FAEP in humans and different animal species [Braun and Richter, 1996;Jacobi, 1997] and did not show any influence on the latencies.…”

“…In their investigations, Martin et al [1983] and Osborne et al [1995] found the V wave to be the most distinct so that they employed it for threshold determination. The differences are chiefly attributable to the methodology used, especially as no standardized procedures for auditory diagnostics exist in veterinary medicine [Braun and Richter, 1996].…”

“…Normative ABR Data for Hearing Threshold in the Rabbit Audiol Neurotol 2006;11:310-317 311 ström [1983]; Martin et al [1983]; Peirelli et al [1986]; Hülse et al [1988]; Romani et al [1991]; Braun and Richter [1996], Mika and Maurer [1983], and Morizono and Paparella [1978] found that brainstem auditory evoked potentials (BAEP) recording revealed only four constant waves. Mika and Maurer [1983] reported obtaining four distinct waves on recording BAEP, with wave V discernible merely in a few cases, and even then only indistinctly.…”

Functional Outcomes of Heparin-Binding Epidermal Growth Factor-Like Growth Factor for Regeneration of Chronic Tympanic Membrane Perforations in Mice

“…29,30 The core facility at our institution provides a regulated environment with the ability to standardize electrode configuration, both the stimulation and recording parameters, and the ability to calibrate the acoustic stimulus. Despite this standardized environment within the single institution, it is possible to have varied thresholds between institutions and between species of mice and so the internal controls are valuable.…”