**2. Material and methods**

Spontaneous activity was recorded with concentric needle electrodes (DISA 13L58) and a 4 channel Disa 1500 EMG machine interfaced with a 4-channel Teac R 61 D cassette recorder. Amplification was set at 50 µV/div, and high-pass and low-pass filters at 20 and 2000 Hz, respectively. 94 sequences of spontaneous activity were divided into the following categories by audiovisual analysis: random fibrillations, slightly irregular fibrillations with occasional pauses, regular fibrillations (Partanen & Danner 1982), "myokymic" fibrillations, and end plate spikes (Partanen 1999). 10- or 20-second samples of the given sequences were digitized (sampling frequency 10 kHz) and analyzed in a Hewlett Packard 340 computer for interpo‐ tential intervals and wave forms.

for the analysis. This was possible because these fibrillation sequences were persistent with the same firing pattern. Also a sequence of rhythmic fibrillation potentials had to proceed several seconds in order to be accepted. Rhythmic fibrillations were usually elicited by needle insertion and they showed a gradual shift of interpotential intervals during the recording time (Conrad et al. 1972). A short-lasting burst of insertion activity was not accepted. Slightly irregular fibrillations with pauses did not show a gradual shift in the basal interval, nor were

Different Types of Fibrillation Potentials in Human Needle EMG

http://dx.doi.org/10.5772/55352

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**Figure 1.** A regular sequence of fibrillation potentials. Interruptions in line indicate interruptions in recording. On the vertical axis is the interpotential interval of fibrillation potentials. On the horizontal axis is the number of successive

**Figure 2.** Randomly occurring fibrillations 33 days after muscle biopsy. Vertical axis is the interpotential interval. Hori‐ zontal axis is the number of successive intervals; there are 10 intervals per division. From Partanen, J.V. & Danner, R.

intervals. There are 20 intervals per division. From Partanen, J.V. & Danner, R. (1982), Author´s own work.

they affected by needle insertion.

(1982), Author´s own work.

"Myokymic" discharges of partially denervated muscles usually exhibited short sequences and they were found to be either "fibrillation-like" or "motor unit potential-like". These sequences were occasionally studied with another EMG needle inserted a few millimeters from the primary electrode in parallel with the muscle fibres. In "fibrillation-like" myokymic discharges it was difficult to find a synchronous discharge of the same muscle fibre in the second EMG channel whereas in "motor unit potential-like" sequences a synchronous discharge was readily observed indicating a sum potential of several muscle fibres of the motor unit. In such a case the sequence was omitted.

The raw EMG data were processed with an automatic analysis system (Partanen 1999). The rise rate, computed using a simple "low pass differentiator" (Usui & Admiror 1982) with a user definable threshold level was applied for potential recognition. Each potential recognized as belonging to the given sequence was marked with a cursor. Thereafter the sequence was checked visually on a large screen, potential by potential in order to correct possible misclas‐ sifications of the automatic program. In case of uncertainty, caused, for example, by superim‐ position of potentials the data were discarded and a new sample of the given sequence was taken from the tape and the procedure was repeated.

Subsequently the analysis program computed the number of intervals, mean, standard deviation, median, minimum, maximum, and interval range of the intervals, as well as the amplitude, and the spike duration of the averaged potential. The initial positive deflection of the potential could also be measured. In order to assess the regularity of firing, also the mean consecutive difference (MCD) (Stålberg et al. 1971) and the average proportional consecutive interval difference (APCID) (Conrad et al. 1972) were calculated.

The different potential categories were analyzed using Student´s unpaired t-test.
