Influence of Intracochlear Air on Experimental Pressure Measurements

Abstract

Introduction: 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. Objective: 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. Materials and Methods: 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. Results: 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) (p < 0.0044, ANOVA). Besides this, in the last condition with 50% fluid, a plateau was formed when the fiber optic reached the air portion. Conclusion: 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).