Modelling the action of caloric stimulation of the vestibule. II. The mechanical model of the semi-circular canal considered as an inflatable structure.

In order to explain the mechanical effects that arise when a semi-circular canal is thermally stimulated in the horizontal position (i.e. in the absence of gravity effects) a physical model was used. The duct (corresponding to the canal) is deformable, the pressure transducer (corresponding to the ampulla) is not deformable. There is no thermal similarity but a dynamical similarity has been respected, so the mechanical phenomena occurring in the semi-circular canal and in the model are identical. The time scale is close to one. The physical model showed that the relative volume variations (fluid/duct) due to caloric stimulation lead to a pressure variation measured by the pressure transducer at the place of the ampulla and the cupula. The time history and the value of this pressure depend on the mechanical and thermal properties of the duct and the fluid. The qualitative responses of the physical model and of the vestibulo-ocular reflex after caloric stimulation were coherent. A numerical model simulating the same mechanisms yielded a quantitative estimation of the transcupular pressure arising in a horizontal semi-circular canal (i.e. without gravity dependent effects) during caloric stimulation. The physical model and the numerical simulation take no account of the inflating pressure variation.