Smooth muscle model for functional electrical stimulation applications : Simulation of realistic bladder behavior under FES

In this paper, we present a smooth muscle model which enables simulation of functional electrical stimulation (FES) induced contraction. The major novelty of this new version of our model is that it includes muscle cell calcium dynamics. We establish the relationship between calcium concentration and electrical potential of the membrane cell. Calcium concentration drives the microscopic mechanics of the muscle inducing contraction. We also refined the mechanical model: smooth muscles have slower dynamics than striated ones, it is therefore possible to neglect the second order terms in the differential equations. Validation of the model is achieved through the simulation of a well known example: the bladder electrical stimulation with a Finetech / Brindley implant. The obtained results are compared qualitatively with the experimental data available in the literature and show good consistency both in shape and time course. In order to obtain quantitative simulations, we need to perform the identification of the model through in-vivo testing on animals. Once this validation step is done, it will be possible to apply our methodology to human bladder neural stimulation.