Computer simulation of field distribution and excitation of denervated muscle fibers caused by surface electrodes

In the course of this study, 2 submodels have been developed and combined, the 2-D finite element modeling of the electrical potential distribution in the human thigh and a Hodgkin and Huxley (HH) type model to calculate fibe r excitation and action potential propagation. To determine the excitation of the target muscle fiber with the help of the activating function, the fi ber's orientation within the muscle has to be known. The electric field alo ng the fiber has to be calculated as a function of the applied electric cur rent and the potential at the electrodes, respectively. The excitement of t he muscle fibers varies across a wide range depending on the active and pas sive membrane parameters and the intracellular and extracellular mediums. P ersisting denervation leads to a decay of muscle cells, and a partial subst itution by fibroblasts occurs. The electrical activation of these tissues i s more difficult, and biphasic stimulation pulses up to 200 ms in duration and 60-100 V in amplitude are needed to cause a contraction of the denervat ed muscle. An example shows the field distribution and the simulated activi ty in one representative muscle fiber of a well trained m. rectus femoris.