Table 1.
Electrode array prototypes inserted in guinea pig cochleae in vivo.
Fig 1.
Electrode array placement in the cochlea.
(A) Diagram of a cochlea section passing through the three scala (SV, scala vestibuli; SM, scala media; ST, scala tympani) with a classification according to the placement of electrodes. From A (close to the basilar membrane) to E in a vertical orientation, and from 1 (close to the modiolus) to 5 (close to the lateral wall) in a horizontal orientation. Black circles correspond to electrode placement without hearing loss at D30, black triangles correspond to electrode placement with hearing threshold shift >40 dB at D30 without fibrosis, and light grey triangles correspond to fibrosis. (B) Macroscopic anatomy section of an electrode array in A placement, in contact with a fracture of the osseous spiral lamina (blue circle in A). (C) Macroscopic anatomy section of an electrode array in 4C placement surrounded by reaction fibrosis * (green circle in A). (D) Macroscopic anatomy section of an electrode array in 2C placement away from basilar membrane and osseous spiral lamina (red circle in A).
Fig 2.
Pre-implantation hearing (dB) according to the electrode array.
Preoperative measurement according to the animal group: 0.4R (black squares) (n = 7), 0.4 (dark grey circles) (n = 7), and 0.3 (light grey triangles) (n = 6). Before implantation, the animals in the three groups had similar hearing thresholds (dB).
Fig 3.
Hearing loss (dB) between D7 and D30 according to the electrode arrays.
Hearing threshold shift between D7 and D30 measurement according to the animal group: 0.4R (black squares) (n = 7), 0.4 (dark grey circles) (n = 7), and 0.3 (light grey triangles) (n = 6). At D30, hearing loss was unchanged compared to that at D7, and this applied to each group.
Fig 4.
Influence of electrode array geometry on hearing loss.
A: D7. B: D30. Hearing threshold shift measurement according to 0.4R (black squares) (n = 7), 0.4 (dark grey circles) (n = 7), and 0.3 (light grey triangles) (n = 6) electrode arrays, inserted at 0.25 mm/s. Values are means ± SEM. Statistical analysis was with two-way Anova (p<0.001 at D7, and p<0.05 at D30), comparison between 0.3 and 0.4R (*p<0.05, **p<0.01, ***p<0.001), comparison between 0.4 and 0.4R ($p<0.05).
Fig 5.
Array force insertions in mN (millinewtons) as function of insertion duration in a guinea pig model with three different array design.
Insertion forces remained low in the first half on the insertion and then slowly rose and reached a maximum with the three array design at the end of the insertion. In this example, a higher peak force with the 0.4R arrays (red) can be observed compared 0.4(blue) and 0.3 (green) array design.
Fig 6.
Maximal peak force measured during insertion of the three electrode array types.
Electrode array geometry influences the maximal peak of the insertion force. Values are means± SEM. One-way Anova, *p<0.05.
Fig 7.
Correlation between hearing loss (dB) at 16000 Hz on D7 and maximal peak force measured during insertion of the three types of electrode array.
0.4R (black squares) (n = 7), 0.4 (dark grey circles) (n = 7), and 0.3 (light grey triangles) (n = 6) electrode arrays. Linear regression, respectively: Y = 0.31X + 17.2, Y (mN), X (dB), n = 20, R = 0.13, slope not different from 0, p = 0.12.
Table 2.
Hearing loss (dB) at 8000 and 16000 Hz, between D7 and D0, between D30 and D0, and between D30 and D7, in the 6 guinea pigs studied for macroscopic anatomy and with poor hearing (hearing loss > 40 dB).