Human cochlear hydrodynamics: A high-resolution μCT-based finite element study

Abstract

Measurements of perilymph hydrodynamics in the human cochlea are scarce, being mostly limited to the fluid pressure at the basal or apical turn of the scalae vestibuli and tympani. Indeed, measurements of fluid pressure or volumetric flow rate have only been reported in animal models. In this study we imaged the human ear at 6.7 and 3-μm resolution using μCT scanning to produce highly accurate 3D models of the entire ear and particularly the cochlea scalae. We used a contrast agent to better distinguish soft from hard tissues, including the auditory canal, tympanic membrane, malleus, incus, stapes, ligaments, oval and round window, scalae vestibule and tympani. Using a Computational Fluid Dynamics (CFD) approach and this anatomically correct 3D model of the human cochlea, we examined the pressure and perilymph flow velocity as a function of location, time and frequency within the auditory range. Perimeter, surface, hydraulic diameter, Womersley and Reynolds numbers were computed every 45 degrees of rotation around the central axis of the cochlear spiral. CFD results showed both spatial and temporal pressure gradients along the cochlea. Small Reynolds number and large Womersley values indicate that the perilymph fluid flow at auditory frequencies is laminar and its velocity profile is plug-like. The pressure was found 102–106° out of phase with the fluid flow velocity at the scalae vestibule and tympani, respectively. The average flow velocity was found in the sub-μm/s to nm/s range at 20–100 Hz, and below the nm/s range at 1–20 kHz.

Theoretical Evaluation and Experimental Validation of Localized Therapeutic Hypothermia Application to Preserve Residual Hearing After Cochlear Implantation

“…In the present study, we did not model the movement of the inner ear fluids or blood perfusion within the cochlea. Several studies have confirmed the presence of local and temporal pressure gradients that may be important factors contributing to heat transfer (De Paolis et al 2017; Olson 1999; Salt et al 2001; Salt et al 1986). The present model also does not take into account differences in soft and hard tissues in the human ear and may benefit from higher resolution, micro-computer tomography (CT) geometric model (De Paolis et al 2017; Manoussaki and Chadwick 2000).…”

“…Several studies have confirmed the presence of local and temporal pressure gradients that may be important factors contributing to heat transfer (De Paolis et al 2017; Olson 1999; Salt et al 2001; Salt et al 1986). The present model also does not take into account differences in soft and hard tissues in the human ear and may benefit from higher resolution, micro-computer tomography (CT) geometric model (De Paolis et al 2017; Manoussaki and Chadwick 2000). Finally, based upon our previously published experiments in the rat model of cochlear implantation (Tamames et al 2016), we developed the hypothermia protocol to incorporate rewarming the cochleae to baseline temperature.…”

“…Following these studies, we utilized Pennes bio-heat equation and finite element analysis to simulate the temperature distribution in the cochlea during therapeutic hypothermia. Studies of heat distribution in the cochlea during infrared stimulation utilized simplified geometries to effectively identify an increase of the cochlear temperature (De Paolis et al 2017; Liljemalm et al 2013; Manoussaki et al 2000; Zhang et al 2015). The present study produced a novel numerical analysis model that instead used true 3D inner ear organ and temporal bone geometries derived from MRI and CT scans.…”

Advances and challenges in adeno-associated viral inner-ear gene therapy for sensorineural hearing loss

“…The risk of perilymph leakage can be mitigated by plugging fascia to RWM perforations, but the outcome is unpredictable. 104 , 105 Another unwanted effect observed in intra-cochlear administration is restricted viral distribution secondary to the low flow rate of cochlear fluid in adult mice. After RWM injection, a high local concentration of viral vectors was found with an efficiency gradient from base to apex due to slow distribution and subsequently, poor transduction leading to a high therapeutic concentration in the basal area but sub-therapeutic in the apical area.…”

Segmentation and reconstruction of the 3D geometry of the middle and inner ear

“…Optimal designed ossicular prosthesis and cochlear implant electrodes, as well as their precise insertion are possible thanks to the development of computer-aided engineering (CAE) and computer-aided surgery (CAS): design of the ossicular prosthesis and cochlear implant electrodes is greatly simplified by computer-aided design (CAD) [4,5]; afterwards verification and optimization of them are achieved by finite element method (FEM) [6,7,10]; due to the complexity and small scale of the structure of the middle and the inner ear, CAS is usually applied in preoperative surgery planning and navigation during the surgery [8,9].…”