Influence of tissue inhomogeneities on noninvasive muscle fiber conduction velocity measurements-investigated by physical and numerical modeling

The hypothesis that the observed fluctuations in propagation velocity are caused by electrically inhomogeneous tissue, regions of different electrical conductivity which are located between the excited muscle fibers and the recording electrodes and which cause a deformation of the extracellular electric current field, was examined. The investigation was performed by means of a physical model as well as by finite element model calculations. In both models single, simple shaped (cylindrical) inhomogeneity regions with a conductivity of 0.1 to 10 times that of the surrounding medium and diameters ranging between 1.6 and 2.7 mm were placed between excitation sources and recording site. The results indicate that the observed conduction velocity fluctuations of up to some 10% can be attributed to inhomogeneity effects of the tissue conductivity.