Identification of components from distant fibers in a recorded single muscle fiber potential (SFP) - a new approach to the SFP criteria.

OBJECTIVES: The aim of our study was to verify the effectiveness of single fiber potential (SFP) criteria in cases when the potential recorded using single fiber electrode (SFE) or concentric needle electrode (CNE) is contaminated by distant fibers.

METHODS: Morphological counterparts of SFP were studied using computer simulations. In this study, we examined triphasic potentials using a model of a linear source of SFP. The criteria defining SFP in the case of SFP contaminated by distant fibers were analyzed, and the effect of second fiber contamination on jitter and fiber diameter determination evaluated.

RESULTS: We found that SFP criteria prevent detection of SFP from fibers smaller than about 30μm in diameter, but do not prevent classification of a potential as an SFP even though it is formed by two or more fibers. This suggests that the presently used criteria may lead to incorrect interpretation of SFP potentials. SFPs contaminated by fibers of diameters differing by a few percent fulfill the criteria but a negative peak may be shifted in time and therefore impact jitter and diameter measurements. This contamination generally tends to decrease both the jitter and the determined diameter. A new approach to the identification of SFP is presented, determining fiber diameter and distance from the electrode to enable maximum sensitivity to potential contamination by the effect of a second fiber.

CONCLUSION: A new parameter characterizing SFP shape changes is introduced. This parameter is used in the method by which additional fibers affecting the SFP may be detected.