FINITE ELEMENT MODELING OF A TRANSIENT FUNCTIONAL ELECTRICAL STIMULATION

Distribution of three-dimensional current and potential is very important for precise stimulation in functional electrical stimulation. Static models describe the effect of an amplitude change of the stimulation, but the result is the same for different pulse duration. We present the finite element model of a transient electrical stimulation on the upper arm. A standard Galerkin procedure was derived in order to obtain discrete finite element equations. Different tissue properties are defined by their conductive and dielectric properties. It is aimed to show that FE modeling of stimulation can give the spatial-temporal location and amplitude of the current to be dynamically configured. Two cases were modeled with the same geometry but with different input of the current pulse, electrode size, positions and tissue properties. The first model case was compared with experimental and numerical results form the literature. The second one was fitted to our own experimental investigations on a few volunteers. The fitting was performed on tissue parameters. Both cases have shown a strong effects of transient conditions and relative permittivity of the skin on the solutions. Our observation showed that dielectric tissue properties (permittivity) cannot be neglected and that the static approach in the electrical stimulation is not appropriate. Hence, the therapeutic strategy should take into account these effects during the functional electrical stimulation.