Experimental Study Of REZ-1 Cochlear Implant In Human Adult Temporal Bone Specimens

OBJECTIVES To study the number of electrode rings that can be inserted into the cochlea, the implantation processes, the location of each REZ-1 electrode ring in the cochlea and the position change of electrodes after implantation mode change.MATERIALS AND METHODS In 12 human adult temperal bone specimens, scala vestibulae roves were removed and electrodes were implanted under Zeiss microscope. The number of electrodes that can be inserted into each cochlea was counted; the implantation processes and position of each electrode were observed and recorded. The angle that each electrode ring coiled the modiolus and the distance between each electrode ring and the modiolus were measured. Linear and curve regressions were evaluated by Spss 11.5 according to the ordinal number of each electrode ring from the site of cochleostomy. The angle that each electrode ring coiled the modiolus and the distance between each electrode ring and the modiolus were measured after withdrawal of one electrode ring.RESULTS The number of electrode rings that can be inserted into each cochlea was from 22 to 27 in the 12 specimens. Almost all the electrode rings in the cochlea were close to the outer wall of scala tympani. No perforation basal membrane and bone fracture was seen. The angle that each electrode ring coiled the modiolus and the ordinal number of each electrode ring in the cochlea were in accordance with quadratic function (F=11393.8, p<0.001). The distance between each electrode ring and the modiolus was in accordance with logistic function for the first nine electrodes (F=1001.44, p<0.001 =, or with linear function for the other electrodes (F=1602.06, p <0.001 =. After one electrode withdrawal, the distance between each electrode from No. 10 to No. 16 and the modiolus reduced significantly (paired t test, p<0.05).CONCLUSIONS The insertion depth of REZ-1 cochlear implantation was enough. Almost all the electrode rings in the scala tympani were close to the outer wall of scala tympani. No perforation of basal membrane and bone fracture in the cochlea were seen for REZ-1 cochlear implantation. The angle of each electrode ring that coiled the modoilus and the distance between each electrode ring and the modiolus can be calculated by the ordinal number of each electrode ring in the cochlea by the function. After withdrawal of one electrode ring, the distance between some electrode ring and the modiolus reduced.Part II Radiological Study of REZ-1 Electrodes In Human Adult Temporal Bone SpecimensOBJECITVES To find the accurate site of cochleostomy in cochlear view in order to count the ordinal number of each REZ-1 electrode ring in the cochlea and help to calculate the angle that each electrode ring coils the modiolus. To evaluate 3D spiral CT scan and multiple plate reconstruction for the judgments of the position of each electrode ring and insertion depth after REZ-1 cochlear implantation. MATERIALS AND METHODS After REZ-1 electrodes were implanted in 12 human adult temporal bone specimens, cochleostomy site was labeled by a pinhead and cochlear view was selected for the radiograph. In the cochlear view, the first reference line through the apex of the superior semicircular canal and the midpoint of the vestibules, the second reference line parallel the first was the tangent to the outer edge of the vestibule. The number of electrode rings on the cochlear side of the second reference line was counted and compared to the number of electrode rings counted by the pinhead label. After REZ-1 electrodes were implanted in 5 human adult temporal bone specimens, 3D spiral CT scan was taken for each specimen. Multiple plate reconstruction was manipulated to display the electrodes clearly.RUSULTS The number counted in the same specimen through the two methods was the same. Each REZ-1 electrode could not be identified on the spiral CT scan and multiple plate reconstruction. The width of each REZ-1 electrode increased at leasttwice. The insertion depth evaluated by 3D spiral CT multiple plate reconstruction was in accordance with that of cochlear view. 3D spiral CT multiple plate reconstruction showed that most of the electrodes in the cochlea were close to the outer wall of scala tympani.CONCLUSIONS Each REZ-1 electrode could not be identified on the 3D spiral CT scan and multiple plate reconstruction. But the insertion depth and position of electrodes in the scala tympani could be displayed by the the 3D spiral CT scan and multiple plate reconstruction.Part III Impedance Study of REZ-1 Electrodes In Human Adult Temporal Bone SpecimensOBJECTIVES To study the relationship between the impedance of paired electrodes and distance of the paired electrodes, the relationship between the impedance of paired electrodes and the position of the paired electrodes. To study the effects of less perilymph on the impedance between the electrode and modiolus. To study the effects of position of intracochlear electrode on the electrode-modiolus impedance.MATERIALS AND METHODS REZ-1 electrodes were implanted in 6 fresh human adult temporal bone specimens. Alternating electrical source was used. A 1K ohm pure resistance was in series with the paired electrodes. The voltage of the pure resistance and the voltage of the electrodes and the pure resistance were recorded. Thus, the impedance of paired electrodes could be calculated. The apex electrode was paired with the other electrode, and the impedance was calculated for each pair. All the impedance of neighboring paired electrodes and paired electrodes with one electrode apart were calculated. The stimulating rates of signals were 2Hz, 10Hz, 100Hz, 1KHz, 10KHz, respectively. The electrode-modiolus impedance was measured, calculated and compared when the perilymph was enough or dried up. The electrode-modiolus impedance was measured, calculated and compared when the electrode was close tothe outer wall or the inner wall of scala tympani. The stimulating rates selected was 100Hz, 1KHz, 10KHz.RESULTS The impedance of paired electrodes increased as the distance between the paired electrodes increased. The impedance of neighboring electrodes increased, as the electrodes were closer to the apical turn of the cochlea (liner regression, F=198.97, p<0.001). The impedance of paired electrodes separated by one electrode increased, as the electrodes were closer to the apical turn of the cochlea (liner regression, F=126.35, p<0.001). The electrode-modiolus impedance decreased significantly when the electrode was moved from close to the outer wall of scala tympani to close to the inner wall of scala tympani (paired t test, p<0.05). The electrode-modiolus impedance increased significantly when the perilymph dried up compared to that when the perilymph was plentiful (paired t test, p<0.001).CONCLUSIONS The impedance of paired electrodes increased as the distance between the paired electrodes increased. The impedance of neighboring electrodes increased, as the electrodes were closer to the apical turn of the cochlea. The impedance of paired electrodes separated by one electrode increased, as the paired electrodes were closer to the apical turn of the cochlea. The electrode-modiolus impedance decreased when the electrode was moved from the outer wall of scala tympani to the inner wall of scala tympani. The electrode-modiolus impedance increased when the perilymph dried up.