title: Preservation of auditory brainstem response thresholds after cochleostomy and titanium microactuator implantation in the lateral wall of cat scala tympani.
abstract: OBJECTIVE
  The safety of implanting a titanium microactuator into the lateral wall of cat scala tympani was assessed by comparing preoperative and postoperative auditory brainstem response (ABR) thresholds for 1 to 3 months.
  
  
  BACKGROUND
  The safety of directly stimulating cochlear perilymph with an implantable hearing system requires maintaining preoperative hearing levels. This cat study is an essential step in the development of the next generation of fully implantable hearing devices for humans.
  
  
  METHODS
  Following GLP surgical standards, a 1-mm cochleostomy was drilled into the lateral wall of the scala tympani, and a nonfunctioning titanium anchor/microactuator assembly was inserted in 8 cats. The scala media was damaged in the 1 cat. ABR thresholds with click and 4- and 8-kHz stimuli were measured preoperatively and compared with postoperative thresholds at 1, 2, and 3 months. Nonimplanted ear thresholds were also measured to establish statistical significance for threshold shifts (>28.4 dB). Two audiologists independently interpreted thresholds.
  
  
  RESULTS
  Postoperatively, 7 cats implanted in the scala tympani demonstrated no significant ABR threshold shift for click stimulus; one shifted ABR thresholds to 4- and 8-kHz stimuli. The eighth cat, with surgical damage to the scala media, maintained stable click threshold but had a significant shift to 4- and 8-kHz stimuli.
  
  
  CONCLUSIONS
  This cat study provides no evidence of worsening hearing thresholds after fenestration of the scala tympani and insertion of a titanium anchor/microactuator, provided there is no surgical trauma to the scala media and the implanted device is securely anchored in the cochleostomy. These 2 issues have been resolved in the development of a fully implantable hearing system for humans. The long-term hearing stability (combined with histologic studies) reaffirm that the microactuator is well tolerated by the cat cochlea.
authors.affiliation: *OtoKinetics Inc., Salt Lake City, Utah; †Queen City ENT Associates-Cincinnati, Ohio; ‡Salus University-Elkins Park, Pennsylvania; §Battelle Memorial Institute-Columbus; and ∥Cincinnati Children's Medical Hospital-Cincinnati, Ohio, U.S.A.
authors.forename: S George
authors.initials: SG
authors.lastname: Lesinski
authors.forename: Jessica
authors.initials: J
authors.lastname: Prewitt
authors.forename: Victor
authors.initials: V
authors.lastname: Bray
authors.forename: Radhika
authors.initials: R
authors.lastname: Aravamudhan
authors.forename: Oscar A
authors.initials: OA
authors.lastname: Bermeo Blanco
authors.forename: Brenda L
authors.initials: BL
authors.lastname: Farmer-Fedor
authors.forename: Jonette A
authors.initials: JA
authors.lastname: Ward
mesh_terms: D000161:Acoustic Stimulation; D000758:Anesthesia; D000818:Animals; D001309:Auditory Threshold; D002415:Cats; D003051:Cochlea / Q000601:surgery*; D019929:Cochlear Implantation; D003054:Cochlear Implants; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D007839:Functional Laterality / Q000502:physiology; D008297:Male; D013506:Otologic Surgical Procedures; D012533:Scala Tympani / Q000601:surgery*; D014025:Titanium
chemical_list: D014025:Titanium