Electrical impedance in bovine skeletal muscle as a model for the study of neuromuscular disease.

Electrical impedance myography (EIM) consists of a set of bioimpedance methods configured for neuromuscular disease assessment, in which high-frequency electrical current is applied to a limb and the consequent surface voltage pattern over a muscle is evaluated. Prior human work has shown that the EIM parameters of resistance, reactance and phase change in different neuromuscular disease states including neurogenic and myopathic conditions. These parameters are also sensitive to the angle at which current is applied and measured relative to muscle fiber direction, a characteristic known as anisotropy. In order to obtain insights into the impedance characteristics of mammalian skeletal muscle without the confounding effects of an overlying skin-fat layer, bone and irregular muscle shape, we performed EIM on three 'nearly ideal' round 16 cm diameter, 1 cm equal thickness pieces of bovine rectus abdominis muscle. Using a standardized tetrapolar electrode array with 50 kHz electrical current, we identified strong anisotropy in the measured reactance and phase, with weaker anisotropy identified for resistance. We also found that increasing amounts of muscle maceration, a rough model of myopathic or traumatic muscle fiber injury, reduced phase and muscle anisotropy when current was injected perpendicular to the muscle fibers. These findings support that EIM parameters, including muscle anisotropy, are likely to be sensitive to the pathological changes that occur in neuromuscular disease states.