Configuration of normal and abnormal non-volitional single muscle fiber discharges

Objective: This investigation utilizes a single muscle fiber simulation to compare and contrast single muscle fiber waveform configurations arising from innervated and denervated tissue taking into account possible tissue-electrode interactions. Methods: Intracellular action potentials (IAPs) from innervated and denervated muscle tissue are simulated. The extracellular waveform configurations as recorded from the fiber's midpoint (endplate in innervated tissue), halfway between the midpoint and fiber termination, as well as fiber termination for both innervated and denervated single muscle fibers are examined. Further, two types of muscle fiber terminations are assessed: (1) sealed end effect; and (2) compressed end effect. Results: Irrespective of different types of IAPs, recordings from the fibers' middle, halfway between the midpoint and termination, as well as from the sealed end, revealed similar configurations. However, for the innervated fiber's compressed termination, a monophasic positive waveform was derived while the denervated fiber's compressed termination generated a prototypical positive sharp wave. Conclusions: It is hypothesized that the needle electrode can no longer be considered a passive recording device but may interact with the fiber so as to generate a sealed end or compressed end effect. Depending upon the type of needle-fiber interaction and the electrode's location with respect to the IAP's generation site, a limited number of potentials with specific configurations will be recorded for both innervated and denervated tissue. Further, depending upon the type of needle-tissue interaction, innervated muscle fibers can generate non-volitional waveforms with configurations similar to those recorded from denervated tissue. It is no longer sufficient to merely consider waveform configuration when attempting to define positive sharp waves and fibrillation potentials, but it is important now also to consider firing rate and rhythm. Copyright (C) 2000 Elsevier Science Ireland Ltd.