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.

Numerical simulation of the role of the utriculo-endolymphatic valve in the rotation-sensing capabilities of semicircular canals

“…All vortices are in the opposite direction to head angular acceleration due to the inertia. The endolymphatic flow regime is consistent with the prediction by Boselli et al (2012). In addition, the velocity profiles can be proved to be a parabolic shape (Fig.…”

“…All of them found that the responses are positively correlated to stimulation. Simultaneously, mathematical models were introduced, and endolymph and cupular responses to head rotation were explored (Boselli et al, 2012;Damiano and Rabbitt, 1996;Lasker et al, 2008;Oman et al, 1987;Rabbitt et al, 2009;Van Buskirk et al, 1976;Van Egmond et al, 1949). However, the SCCs were usually represented as the torsion pendulum in above mathematical models.…”

A multilayer method of fundamental solutions for Stokes flow problems

“…Changing the center of rotation changes the linear acceleration of the system. Linear acceleration, however, does not lead to any flow in the canal [47], such that the total flow u þ u p is independent from the center of rotation. Later, we will exploit this property to validate our computation.…”

“…The total flow which is obtained by adding the particular solution u p ¼ Cr 3 e h to u models the Stokes flow in a semicircular canal of the inner ear induced by an angular acceleration of 120 =s 2 where the center of rotation is at the origin [47,22]. Changing the center of rotation changes the linear acceleration of the system.…”

“…As a part of these efforts, we also computed the flow in a three-dimensional version of the semicircular canal in Fig. 2 [47]. There, we used about 8000 collocation points and offered to the BGQRa four layers with 5459 source points on each layer.…”