title: Would an endosteal CI-electrode make sense? Comparison of the auditory nerve excitability from different stimulation sites using ESRT measurements and mathematical models.
abstract: Regarding potential endosteal cochlear implant electrodes, the primary goal of this paper is to compare different intra- and extra-cochlear stimulation sites in terms of current strengths needed for stimulating the auditory nerve. Our study was performed during routine cochlear implantation using needle electrodes for electric stimulation and by visually recording electrically elicited stapedius reflexes (ESRT) as a measure for the stimulus transfer. Of course this rather simple setup only allows rough estimations, which, however, may provide further arguments whether or not to proceed with the concept of an endosteal electrode. In addition, a mathematical model is being developed. In a pilot study, intra-operative electric stimuli were applied via a needle electrode commonly used for the promontory stimulation test. Thus, stapedius reflex thresholds (ESRTs), electrically elicited via the needle from different points inside and outside the cochlea served as indicators for the suitability of different electrode positions towards the modiolus. Tests were performed on 11 CI-recipients. In addition, the extension of electrical fields from different stimulation sites is simulated in a mathematical cochlea model. In most patients ESRT measurements could be performed and evaluated. Thus an "endosteal" stimulation seems possible, although the current intensities must be higher than at intraluminal stimulation sites. Moreover, our model calculations confirm that the extension of electric fields is less favourable with increasing distance from the electrode to the ganglion nerve cells. In terms of hearing, the concept of an endosteal electrode should only be promoted, if its superiority for hearing preservation can be proven, e.g. in animal experiments. However, for other indications like the electric suppression of tinnitus, further research seems advisable.
  
  
  METHODS
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authors: Department of Otorhinolaryngology, Head and Neck Surgery, University of Rostock, Doberaner Strasse, 137-139, 18057, Rostock, Germany, hans-wilhelm.pau@med.uni-rostock.de.
authors: Hans Wilhelm
authors: HW
authors: Pau
authors: Annekathrin
authors: A
authors: Grünbaum
authors: Karsten
authors: K
authors: Ehrt
authors: Rüdiger
authors: R
authors: Dahl
authors: Tino
authors: T
authors: Just
authors: Ursula
authors: U
authors: van Rienen
mesh_terms: D003054:Cochlear Implants; D003056:Cochlear Nerve / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods*; D004567:Electrodes, Implanted; D006801:Humans; D008959:Models, Neurological; D009119:Muscle Contraction / Q000502:physiology; D011474:Prosthesis Design; D012018:Reflex / Q000502:physiology*; D013198:Stapedius / Q000502:physiology*
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