Biomechanical Analysis of Angular Motion in Association with Bilateral Semicircular Canal Function.

The aim of this study was to characterize cupular deformation by calculating the degree of cupular expansion and cupular deflection using a finite element model of bilateral human semicircular canals (SCCs). The results showed that cupular deflection responses were consistent with Ewald's II law, whereas each pair of bilateral cupulae simultaneously expanded or compressed to the same degree. In addition, both the degree of cupular expansion and cupular deflection can be expressed as the solution of forced oscillation during head sinusoidal rotation, and the amplitude of cupular expansion was approximately two times greater than that of cupular deflection. Regarding the amplitude frequency and phase frequency characteristics, the amplitude ratios among the horizontal SCC, the anterior SCC, and the posterior SCC cupular expansion was constant at 1:0.82:1.62, and the phase differences among them were constant at 0 or 180° at the frequencies of 0.5-6 Hz. However, both the amplitude ratio and the phase differences of the cupular deflection increased nonlinearly with the increase of frequency and tended to be constant at the frequency band between 2 and 6 Hz. The results indicate that the responses of cupular expansion might only be related to the mass and rigidity of three cupulae and the endolymph, but the responses of cupular deflection are related to the mass, rigidity, or damping of them, and these physical properties would be affected by vestibular dysfunction. Therefore, both the degree of cupular expansion and cupular deflection should be considered important mechanical variables for induced neural signals as these variables provide a better understanding of the SCCs system's role in the vestibulo-ocular reflex during the clinical rotating chair test and the vestibular autorotation test. Such a numerical model can be further built to provide a useful theoretical approach for exploring the biomechanical nature underlying vestibular dysfunction.