Suspensory Tethers and Critical Point Membrane Displacement in Endolymphatic Hydrops

Abstract

Introduction Grossly displaced membranes are characteristic of endolymphatic hydrops. The process whereby physiological membrane displacement becomes pathological may be mediated by stress, but the membrane biomechanics underlying this transition are unclear. Objective This study seeks to determine the role of suspensory tethers during pressure-induced membrane displacement in the generation of the membranous lesions seen in this disease entity using a biomechanical model approach. Methods The location of membrane suspensory tethers was identified histologically. The influence of tethers on model membrane configuration during displacement was assessed graphically. The relationship of membrane configuration during displacement to curvature radius was quantified trigonometrically. The relationship of curvature radius to stress susceptibility was determined mathematically. The net effect of suspensory tethers on membrane stress levels for various degrees of membrane distention and displacement was then calculated numerically. Results In the inferior labyrinth, suspensory tethers are found to occur on the membranes' boundaries. Such tethering is found to impose a biphasic effect on membrane curvature with increasing degrees of displacement. As a consequence, tensile stress susceptibility is found to decline with initial membrane displacement to a critical point nadir beyond which stress then increases monotonically. No such effect was found for the superior labyrinth. Conclusion Boundary tethers in the inferior labyrinth are associated with significant tensile stress reductions until a critical point of membrane displacement is reached. Displacements short of the critical point may be physiological and even reversible, whereas such displacements beyond the critical point are apt to be overtly hydropic and irreversible.

First evidence of the link between internal and external structure of the human inner ear otolith system using 3D morphometric modeling

“…While the walls of the membranous labyrinth are often modelled as rigid 44 – 46 , more recent biomechanical models indicate the importance of membrane dynamics in the ear. For example, thickly-walled utriculo-canal morphology 47 , 48 and supporting trabecular meshwork in the perilymphatic space 49 contribute to reduced stress proclivities in the mammalian pars superior. In addition, we now know more about tendencies for membrane displacement in the pars inferior, particularly in cases of differential fluid pressures 49 – 51 .…”

“…For example, thickly-walled utriculo-canal morphology 47 , 48 and supporting trabecular meshwork in the perilymphatic space 49 contribute to reduced stress proclivities in the mammalian pars superior. In addition, we now know more about tendencies for membrane displacement in the pars inferior, particularly in cases of differential fluid pressures 49 – 51 . These morphological changes to the membranous labyrinth, along with others such as those acquired during aging 52 or vestibular endolymphatic hydrops 53 can alter flow dynamics (as observed in models of the utricle 44 ) leading to differential vestibular transduction.…”