Influence of Intracochlear Air on Experimental Pressure Measurements

<b><i>Introduction:</i></b> Intracochlear pressure changes have been assumed to play a central role in hearing preservation during cochlear implantation. The pressure in different settings has been evaluated (temporal bones vs. cochlea models) and was found to have advantages and disadvantages. Experimentally, problems have been discussed to influence the results substantially. <b><i>Objective:</i></b> The aim of the present study was to evaluate the effect of intracochlear air on the measurements in a cochlea model by using a fiber optic pressure sensor. <b><i>Materials and Methods:</i></b> The experiments were performed in an uncurled 3D printed full cochlea model. A microfiber-optic pressure sensor was inserted, and intracochlear pressures were evaluated under 3 conditions: (1) cochlea model filled to 100% with fluid, (2) cochlea model filled with air, and (3) cochlea model filled to approximately 50% with fluid. Since the cochlea model is transparent, a direct visualization of air under the microscope was possible when performing the insertions. <b><i>Results:</i></b> In the first condition, the mean intracochlear pressure at the end of the insertion was 0.044 psi (SD 0.012, 95% CI). In the second setting, the results were similar. In the last scenario, with 50% filling, the mean intracochlear pressure was statistically significantly different with a mean value of 0.074 psi (SD 0.013, 95% CI) (<i>p</i> &#x3c; 0.0044, ANOVA). Besides this, in the last condition with 50% fluid, a plateau was formed when the fiber optic reached the air portion. <b><i>Conclusion:</i></b> The results obtained in a 3D printed full cochlea model show the importance of a direct evaluation of air inside the experimental setting. The exclusion of intracochlear air should be an important factor for the choice of the model for intracochlear pressure measurement (temporal bone vs. cochlea model).

Minimizing Intracochlear Pressure: Influence of the Insertion Sheath

Objective: Atraumatic cochlear implantation (CI) and insertion of the electrode in particular are major goals of recent CI surgery. Perimodiolar electrode arrays need a stylet or exosheath for insertion. The sheath can influence the intracochlear pressure changes during insertion of the electrode. The aim of this study was to modify the insertion sheath to optimize intracochlear pressure changes. Methods: In an artifical cochlear model, 7 different modified insertion sheaths were used. The intracochlear pressure was measured with a micro-optical sensor in the apical part of the model cochlea. Results: Significant lower intracochlear pressure changes were observed when the apical part of the insertion sheath was either shortened or tapered. Modification of the stopper does influence the intracochlear pressure significantly. Conclusion: Modification of the insertion sheath leads to lower intracochlear pressure gain. The differences and impact on intracochlear pressure changes found in this study underline the importance of even subtle modifications of the electrode insertion technique.

Effect of Underwater Insertion on Intracochlear Pressure

Background: The importance of intracochlear pressure during cochlear electrode insertion for the preservation of residual hearing has been widely discussed. Various aspects of pre-insertional, intra-insertional, and post-insertional relevant conditions affect intracochlear pressure. The fluid situation at the round window during electrode insertion has been shown to be an influential factor.Aims/Objectives: The aim of the study was to compare various insertion techniques in terms of the fluid situation at the round window.Material and Methods: We performed insertion of cochlear implant electrodes in a curled artificial cochlear model. We placed and fixed the pressure sensor at the tip of the cochlea. In parallel to the insertions, we evaluated the maximum amplitude of intracochlear pressure under four different fluid conditions at the round window: (1) hyaluronic acid; (2) moisturized electrode, dry middle ear; (3) middle ear filled with fluid (underwater); and (4) moisturized electrode, wet middle ear, indirectly inserted.Results: We observed that the insertional intracochlear pressure is dependent on the fluid situation in front of the round window. The lowest amplitude changes were observed for the moisturized electrode indirectly inserted in a wet middle ear (0.13 mmHg ± 0.07), and the highest values were observed for insertion through hyaluronic acid in front of the round window (0.64 mmHg ± 0.31).Conclusions: The fluid state in front of the round window influences the intracochlear pressure value during cochlear implant electrode insertion in our model. Indirect insertion of a moisturized electrode through a wet middle ear experimentally generated the lowest pressure values. Hyaluronic acid in front of the round window leads to high intracochlear pressure in our non-validated artificial model.