Vortical flow in the utricle and the ampulla: a computational study on the fluid dynamics of the vestibular system
ABSTRACT We present a computational study of the fluid dynamics in healthy semicircular canals (SCCs) and the utricle. The SCCs are the primary sensors for angular velocity and are located in the vestibular part of the inner ear. The SCCs are connected to the utricle that hosts the utricular macula, a sensor for linear acceleration. The transduction of angular motion is triggered by the motion of a fluid called endolymph and by the interaction of this fluid with the sensory structures of the SCC. In our computations, we observe a vortical flow in the utricle and in the ampulla (the enlarged terminal part of the SCCs) which can lead to flow velocities in the utricle that are even higher than those in the SCCs. This is a fundamentally new result which is in contrast to the common belief that the fluid velocities in the utricle are negligible from a physiological point of view. Moreover, we show that the wall shear stresses in the utricle and the ampulla are maximized at the positions of the sensory epithelia. Possible physiological and clinical implications are discussed.
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ABSTRACT: In patients with Ménière's disease (MD), caloric testing can show, depending on the stage and activity of the disease, a variety of results. Between attacks, many, or perhaps even most, patients with unilateral early or mild MD have normal caloric tests; late MD can show abnormalities ranging from mild to severe unilateral canal paresis with or without directional preponderance. The explanation of canal paresis in MD is not clear. The most obvious explanation, severe loss of lateral canal hair cells, is not likely to be correct because hair cell loss will not explain the fluctuating canal paresis to caloric stimulation. In contrast, the published evidence is that rotational testing of semicircular canal function in MD patients typically shows little reduction in function and even enhancement of vestibulo-ocular reflex gain, at least in the early stages of the disease. Here, we offer a novel explanation for this dissociation. We propose that hydropic expansion of the lateral canal membranous labyrinth permits convective recirculation within the duct that allows dissipation of the hydrostatic force that would normally cause cupular displacement and nystagmus in the caloric test. © 2015 New York Academy of Sciences.Annals of the New York Academy of Sciences 02/2015; 1343(1). DOI:10.1111/nyas.12687 · 4.31 Impact Factor
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ABSTRACT: The method of fundamental solutions (MFS) is a meshless method for the solution of boundary value problems and has recently been proposed as a simple and efficient method for the solution of Stokes flow problems. The MFS approximates the solution by an expansion of fundamental solutions whose singularities are located outside the flow domain. Typically, the source points (i.e. the singularities of the fundamental solutions) are confined to a smooth source layer embracing the flow domain. This monolayer implementation of the MFS (monolayer MFS) depends strongly on the location of the user-defined source points: On the one hand, increasing the distance of the source points from the boundary tends to increase the convergence rate. On the other hand, this may limit the achievable accuracy. This often results in an unfavorable compromise between the convergence rate and the achievable accuracy of the MFS. The idea behind the present work is that a multilayer implementation of the MFS (multilayer MFS) can improve the robustness of the MFS by efficiently resolving different scales of the solution by source layers at different distances from the boundary. We propose a block greedy-QR algorithm (BGQRa) which exploits this property in a multilevel fashion. The proposed multilayer MFS is much more robust than the monolayer MFS and can compute Stokes flows on general two-and three-dimensional domains. It converges rapidly and yields high levels of accuracy by combining the properties of distant and close source points. The block algorithm alleviates the overhead of multiple source layers and allows the multilayer MFS to outperform the monolayer MFS. (C) 2012 Elsevier Inc. All rights reserved.Journal of Computational Physics 07/2012; 231(18-18):6139-6158. DOI:10.1016/j.jcp.2012.05.023 · 2.49 Impact Factor
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ABSTRACT: In this paper, we study the Posterior Semicircular Canal of the Peripheral Vestibular system containing moving Otoconia (Calcium Carbonate crystals) which leads to the condition of Benign Paroxysmal Positional Vertigo (BPPV). Using the governing equations of the affected semicircular canal we develop a novel MEMS device to mimic the pathophysiological condition wherein the kinocilia structure is modeled using PZT-2 micro-cantilever placed at various positions in the device to sense the position of the otoconia. The deflection produces a voltage of 0.416 mV indicating the proximity of the particles. Using this information we describe a functional block of this device that aids in treating BPPV via an audio assisted Canalith Repositioning Procedure (CRP).2013 8th IEEE International Conference on Nano/Micro Engineered and Molecular Systems (NEMS); 04/2013