Modelling the Action of Caloric Stimulation of the Vestibule: IV. the Global Mechanical Model

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Abstract
Caloric stimulation acts on the bio-accelerometer (the semi-circular canal), as on engineered ones, through second order type multiple pathways. Three temperature induced peripheral actions have been described in our previous reports. The hydrostatic mechanism induces in the endolymph a gravity dependent transcupular stationary pressure difference. The differential expansion of the membranous duct and its content creates a local volume variation, while the modification of the transmembranous exchanges causes a local pressure variation. These two last mechanisms are gravity independent. They depend on parameters of the membrane, and induce a transcupular transient pressure difference and a stationary variation of the inflating pressure. It seems reasonable to assume the independency of these three mechanisms. If this assumption is true, than the global effect of caloric stimulation should be the sum of the effects of the three partial mechanisms. It is shown here that, for the physical model, this assumption holds. For humans, in the more general frame of the caloric vestibulo-ocular reflex experiments reported in the first paper, qualitatively and quantitatively this assumption holds, too. The model predicts a percentage of gravidity dependent effects of about 75%. It is shown that the reported human experiments lead to compatible estimates of this percentage. For humans in the earth gravity field, enduring the caloric stimulation it is not necessary to include neither otolithic interactions, nor significant modifications of the mecano-neural transduction, in the limits of precision of today's experimentation.

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