For cochlear implant training and robotic cochlear implant experiments, the design method of scalable scala tympani model was proposed. The mathematical model of the cochlea was used as the central curve of scala tympani channel. Referring to the clinical anatomy data, the contour of the scala tympani cross-section was approximated as an ellipse. The profile was placed along the central curve, and the angle was adjusted to determine the position and orientation of the profile in three dimensions such that the central curve passes through its center. The data was imported into Matlab to generate a three-dimensional mathematical model of scala tympani, which can be expanded by setting different scale factors. The virtual scala tympani model was generated in SolidWorks, and the 2:1 fully transparent scala tympani model were fabricated by 3D printing to replace the specimen for experiment.
Cochlea/surgery* ; Cochlear Implantation ; Cochlear Implants ; Robotics ; Scala Tympani/surgery*

OBJECTIVES: To investigate the electric-acoustic interactions within the inferior colliculus of guinea pigs and to observe how central masking appears in invasive neural recordings of the inferior colliculus (IC). METHODS: A platinum-iridium wire was inserted to scala tympani through cochleostomy with a depth no greater than 1 mm for intracochlear stimulation of electric pulse train. A 5 mm 100 microm, single-shank, thin-film, penetrating recording probe was inserted perpendicularly to the surface of the IC in the coronal plane at an angle of 30-40degrees off the parasagittal plane with a depth of 2.0-2.5 mm. The peripheral and central masking effects were compared using electric pulse trains to the left ear and acoustic noise to the left ear (ipsilateral) and to the right ear (contralateral). Binaural acoustic stimuli were presented with different time delays and compared with combined electric and acoustic stimuli. The averaged evoked potentials and total spike numbers were measured using thin-film electrodes inserted into the central nucleus of the IC. RESULTS: Ipsilateral noise had more obvious effects on the electric response than did contralateral noise. Contralateral noise decreased slightly the response amplitude to the electric pulse train stimuli. Immediately after the onset of acoustic noise, the response pattern changed transiently with shorter response intervals. The effects of contralateral noise were evident at the beginning of the continuous noise. The total spike number decreased when the binaural stimuli reached the IC most simultaneously. CONCLUSION: These results suggest that central masking is quite different from peripheral masking and occurs within the binaural auditory system, and this study showed that the effect of masking could be observed in the IC recording. These effects are more evident and consistent with the psychophysical data from spike number analyses than with the previously reported gross potential data.
Acoustics ; Animals ; Ear ; Electrodes ; Evoked Potentials ; Guinea ; Guinea Pigs ; Inferior Colliculi ; Masks ; Noise ; Scala Tympani

BACKGROUNDS AND OBJECTIVES: We developed a method of intraotic treatment using gentamicin (GM) in chinchillas. MATERIALS AND METHOD: An osmotic pump, connected near the round window by a Teflon tube (0.13mm ID X 0.18mm OD) through an opening in the scala tympani, continuously perfused 12microliter of GM per day for a week. In the three experimental groups (n=12), each animal was treated with a total dose of 0.1mg of GM for a week. Animals in the control group (n=4) were immediately sacrificed after perfusion with saline for a week. RESULTS: In the control group, there was no damage in any of the hair cells. In the treatment group, the hair cells were more severely damaged at 4 weeks than at 1 week. The outer hair cells were more sensitive to GM than the inner hair cells. Among the outer hair cells, the first rows were damaged first. The basal part of cochlea was damaged earlier than the apical. The ototoxic effect continued even after perfusion had ceased. CONCLUSIONS: This pump system limits drug distribution to the target tissue, minimizing systemic side effects while permitting precise control of delivery rate, volume, concentration and duration.
Animals ; Chinchilla* ; Cochlea ; Gentamicins* ; Hair ; Microscopy, Electron, Scanning ; Perfusion ; Polytetrafluoroethylene ; Scala Tympani

OBJECTIVES: Lidocaine is one of the therapeutic trials to treat tinnitus. However, the exact mechanism of the effect of lidocaine remains unclear. The aim of this study was to elucidate the action site of lidocaine in the cochlea by measuring compound action potential (CAP) and transient evoked otoacoustic emission (TEOAE) amplitude in guinea pigs. METHOD: Artificial perilymph was perfused into the scala tympani of the guinea pig cochlea in the control group, and lidocaine diluted with artificial perilymph was perfused into the scala tympani of the experimental groups. Electrocochleogram (ECoG) and TEOAE were measured in each groups both before and after lidocaine perfusion. RESULTS: Artificial perilymph perfused to the scala tympani of the guinea pig cochleae did not affect either the CAP threshold or the TEOAE response. But, lidocaine perfused into the scala tympani of the guinea pig cochleae produced a dose-dependent increase in CAP threshold, but did not affect TEOAE response. CONCLUSION: This study revealed that lidocaine perfused into the scala tympani of the guinea pig cochlea affects the CAPthreshold but not the TEOAE amplitude and reproducibility. It means that the locally perfused lidocaine affects the cochlear nerve greater than the outer hair cells.
Action Potentials ; Animals ; Cochlea* ; Cochlear Nerve ; Guinea Pigs* ; Guinea* ; Hair ; Lidocaine* ; Perfusion ; Perilymph ; Scala Tympani ; Tinnitus

BACKGROUND AND OBJECTIVES: The goal of this study was to examine insertion depth, intracochlear position and insertion trauma with the stimulation electrode of the Nurobiosys cochlear implant. SUBJECTS AND METHOD: Four electrodes were implanted in fresh temporal bones of the human cadavers using realistic surgical procedures. Plain film X-ray images were taken from the electrode inserted in the specimens to estimate the insertion depth. After the electrode implantation, all human temporal bones were trimmed to extract the cochleae. The extracted cochleae from the temporal bone were immersed in acrylic resin to fix the position of electrode placed in the scala tympani. The resin treated cochleae were cut in radial section and polished. All crosssections were imaged with a microscope to assess the trauma by the electrode implantation. RESULTS: The mean insertion depth was about 300degrees with the cochlea angle. The insertion trauma was observed in one section of a temporal bone. The mean distance from electrode to modiolus was about 0.75 millimeter. CONCLUSION: The incidence, severity of trauma and insertion depth of the studied electrode showed similar results with that of other straight type electrode in literature.
Cadaver ; Cochlea ; Cochlear Implants ; Electrodes ; Humans ; Incidence ; Scala Tympani ; Temporal Bone

Labyrinthitis ossificans (LO) is a pathologic formation of fibrosis and new bone within the lumen of the otic capsule. The LO is a challenging issue in cochlear implantation since obliteration and obstruction of the cochlea make electrode insertion through scala tympani (classic route) difficult. Moreover, tympanomastoidectomy for resolution of chronic otitis media is also simultaneously considered for tympanogenic LO with severe to profound hearing loss because ossification could progress in case of staged or delayed implantation after initial tympanomastoidectomy. We report a patient with tympanogenic LO, who received subtotal petrosectomy with simultaneous cochlear implantation via scala vestibuli instead of the scala tympani for hearing rehabilitation.
Cochlea ; Cochlear Implantation* ; Cochlear Implants* ; Ear, Inner* ; Electrodes ; Fibrosis ; Hearing ; Hearing Loss ; Humans ; Labyrinthitis* ; Otitis Media ; Rehabilitation ; Scala Tympani ; Scala Vestibuli*

OBJECTIVES: The aims of this study were to investigate the feasibility of isosorbide delivery into perilymph through the round window membrane (RWM), and to compare the intracochlear isosorbide concentration in perilymph after oral administration (PO) versus that after round window perfusion (RWP). METHODS: Sixteen male guinea pigs (32 ears) were used. Isosorbide, an osmotic diuretic, was administered via RWP or PO. First, to investigate the optimal perfusion time, perilymph sampling of scala tympani from the RWM was performed after RWP for 15, 30, or 60 minutes. Second, to compare the drug concentration after RWP versus that after PO, perilymph was aspirated at 3 and 6 hours after administration. Intracochlear concentration of isosorbide was analyzed by high-performance liquid chromatography coupled to refractive index detection. RESULTS: Isosorbide passed through the RWM into perilymph after RWP. After RWP for 15, 30, and 60 minutes, mean isosorbide concentrations in perilymph were 116.27+/-44.65, 245.48+/-112.84, and 279.78+/-186.32 mM, respectively. The intracochlear concentration after RWP for 30 minutes was higher than that after RWP for 15 minutes (P=0.043). At 3 and 6 hours after PO, isosorbide concentrations in perilymph were 28.88+/-4.69 and 12.67+/-2.28 mM, respectively. In contrast, the corresponding concentrations after RWP were 117.91+/-17.70 and 75.03+/-14.82 mM at 3 and 6 hours, respectively. Isosorbide concentrations in perilymph following RWP were significantly higher than those following PO at both 3 and 6 hours (P=0.025 and P=0.034, respectively). CONCLUSION: Isosorbide can rapidly pass through the RWM after RWP in guinea pigs, and 30 minutes of perfusion is considered to be appropriate. In addition, over a 6-hour period, RWP can deliver higher concentrations of isosorbide into perilymph than those achieved with PO.
Administration, Oral* ; Animals ; Chromatography, Liquid ; Diuretics, Osmotic ; Guinea Pigs* ; Humans ; Isosorbide* ; Male ; Membranes ; Meniere Disease ; Perfusion* ; Perilymph* ; Refractometry ; Scala Tympani

OBJECTIVE: To compare the impedance between the modiolus and the inner wall of scala tympani with that between the modiolus and the outer wall of scala tympani. METHOD: The impedances between the modiolus and the inner wall of scala tympani and the impedance between the modiolus and the outer wall of scala tympani were measured, calculated and compared under different stimulating rates 0.1, 1.0, 10.0 kHz. RESULT: The impedance between the modiolus and the inner wall of scala tympani is less than that between the modiolus and the outer wall of scala tympani (P < 0.05). CONCLUSION To effectively stimulate the residual neurons in the spiral ganglion, the electrodes should be kept close to the inner wall of scale tympani.
Adult ; Cochlea ; physiology ; Cochlear Implants ; Electric Impedance ; Electrodes ; Humans ; Scala Tympani ; physiology ; Spiral Ganglion ; Temporal Bone ; physiology

OBJECTIVETo investigate the related parameters of the temporal bone structure for determining the position of implanting electrode into the scala tympani in cochlear implantation surgery through the facial recess and epitympanum approach.

METHODSIn a surgical simulation experiment, 20 human temporal bones were studied and measured to determine the related parameters of the temporal bone structure.

RESULTSThe distance 5.91∓0.29 mm between the short process of the incus and the round window niche, 2.11∓0.18 mm between the stapes and the round window niche, 6.70∓0.19 mm between the facial nerve in the perpendicular paragraph and the round window niche, 2.22∓0.21 mm from the pyramidal eminence to the round window, and 2.16∓0.14 mm between the stapes and the round window. The minimal distance between the implanting electrode and the vestibular window was 2.12∓0.19 mm. The distance between the cochleariform process and the round window niche was 3.79∓0.17 mm. The position of the cochlear electrode array insertion into the second cochlear turn was 2.25∓0.13 mm under the stapes. The location of the cochlear electrode array insertion into the second cochlear turn was 2.28∓0.20 mm inferior to the pyramidal eminence.

CONCLUSIONThese parameters provide a reference value to determine the different positions of cochlear electrode array insertion into the scale tympani in different patients.

Adult ; Cochlea ; anatomy & histology ; surgery ; Cochlear Implantation ; Cochlear Implants ; Ear, Middle ; anatomy & histology ; surgery ; Female ; Humans ; Male ; Round Window, Ear ; anatomy & histology ; surgery ; Scala Tympani ; anatomy & histology ; surgery

BACKGROUND AND OBJECTIVES: Neural response telemetry (NRT) has been used as one of the most useful tools to measure neural responses ranging from spiral ganglion cells to electrical stimulation via the Nucleus 24 cochlear implant. The purpose of this study was to assess and analyze the result of NRT measured intraopertively and apply the result in postoperative mapping. SUBJECTS AND METHOD: The NRT test was administered to 72 patients (49 children and 23 adults) with the Nucleus 24 cochlear implant. After inserting of the electrode array into the scala tympani, an impedance test was administered to check the integrity of each inserted electrode. In cases of partial insertion, the electrodes outside the cochlear were excluded along with those proven to be short circuited. The electrically evoked action potential (EAP) was recorded using version 3.0 of NRT software. One intra-cochlear electrode (electrode 2, 4, 6, 8, 10, 12, 14, 16) with MP1 as reference was chosen for the stimulating pair. The recording electrode was located 3 electrodes away apically from the stimulating intracochlear electrode and referenced to MP2. The amplifier gain and sampling delay were optimized for each subject using electrode 4 and these same parameters were used throughout the test. RESULTS: Out of 72 implantees, 56 patients (78%) were observed to produce reliable responses: 16 (70%) of 23 adults and 40 (82%) of 49 children responded. The patients who failed to produce NRT response had higher T levels than patients who had NRT response. CONCLUSION: Eighty percent of the implantees without any inner ear anomaly showed reliable response to intraopertive NRT measurement. The intra-operarative NRT data may be used to predict electrical stimulation levels in programming.
Action Potentials ; Adult ; Child ; Cochlear Implantation ; Cochlear Implants* ; Ear, Inner ; Electric Impedance ; Electric Stimulation ; Electrodes ; Humans ; Scala Tympani ; Spiral Ganglion ; Telemetry*