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Simulation of sensory nerve action potentials
$243 tion, area, excitability, etc.). Furthermore, by comparing the M-response area with the averaged area of different recurrent responses of single motor units, it is possible to calculate an index (M-R) which is a useful parameter in pathological conditions. The F-response is obtained by surface electrodes placed in belly-tendon positions. As soon as the operator has obtained the maximal M-response, he must define the window-time of the analysis by placing the markers on the base line of the display with a cursor. From this moment the acquisition starts and the signal is accepted by the computer and displayed provided that the amplitude is more than a predetermined threshold value. The following potentials are compared with the previous ones, by a point-to-point subtraction. Single motor unit potentials are defined on the basis of the criteria of identical configuration and variability in latency less than 100 msec. Some clinical applications are reported.
DPP4.03 CONCENTRIC NEEDLE EMG IN REINNERVATING AND DENERVATING M O T O R UNITS.
records single fibre activity, the other one, opposite to the SF surface, has a normal surface area and is designed to record normal motor unit action potentials (MUAPs). There are two aspects to the MUAP analysis method with this needle, distinguishing it from conventional methods. 1) The leading-off area is the same, but the position of the surface with respect to the needle shaft is different. Experiments were carried out using an electrode equipped with both a conventional concentric recording surface at the tip and a surface at the side of the needle. In the deltoid muscle of healthy volunteers we searched for recordings from the same motor unit with both electrode surfaces. From the side surface MUAPs were recorded which had on the average 50% higher amplitudes. The spike durations were about 10% less, as compared with the tip surface. The slower MUAP components (total duration, slow wave amplitude) were not different. 2) The wave shapes of averaged MUAPs probably depend on choosing a single fibre or the MUAP recording itself for triggering. This was confirmed by computer analysis. Here as well the MUAP amplitudes were most affected. Explanations for these results are given.
S.D. Nandedkar, D.B. Sanders and E.V. Stalberg (Durham, NC, USA) We have used computer models to simulate motor units (MUs) and electromyographic motor unit action potentials (MUAPs). Six normal MUs were simulated, each containing 50 muscle fibers. To simulate reinnervation the number of fibers in the MU was increased sequentially to 75, 100, 150 and 200. The amplitude, area, duration and polyphasia of the simulated concentric needle EMG MUAPs increased in the simulated reinnervated MUs. Increased polyphasia was the earliest abnormality seen. The mean MUAP amplitude increased by only 50% even when the number of muscle fibers was increased to 200. The MUAP area and duration increased more than the amplitude. To simulate denervation of previously reinnervated MUs, the number of fibers of the previously reinnervated MUs was reduced to 50 by random deletion. MUAP amplitude, area and duration decreased in parallel with the loss of muscle fibers but the MUAPs were more polyphasic and the MUAP amplitude varied more than in a population of normal MUs having the same number of fibers.
DPP4.04 T H E DEPENDENCE OF M O T O R UNIT POTENTIALS ON ELECTRODE C O N S T R U C T I O N AND METHO D S OF DATA ANALYSIS. D. Stegeman, H. Vingerhoets, P. Hofman and S. Notermans (Nijmegen, The Netherlands) Special EMG electrodes have been constructed for various purposes. The two channel electrode of Falck (Falck 1983, thesis, Univ. of Turku, Finland) is an example. One surface
DPP4.05 SIMULATION OF SENSORY NERVE ACTION POTENTIALS.
D. Nielsen and A. Rosenfalck (Aalborg, Denmark) Changes in the shape of the sensory nerve action potential may contain more information than is obtained by measurement of the parameters used clinically to quantify nerve injuries. The standard parameters are: the maximal and minimal conduction velocities and the maximal amplitude of the sensory nerve action potential. A model assuming alinear superposition of temporally dispersed single fiber potentials (Rosenfalck and Ottosen, 1982) was used to estimate changes in the shape and in the standard parameters. The assumption that the nerve fibres were differently affected was modelled by adding 1-2 msec superimposed by 10% stochastic noise to the latencies of the individual nerve fibres potentials. Changes in shape were significant when about 40% of the nerve fibres were assumed to be damaged, focally or scattered, while changes in maximal conduction velocity and amplitude remained within the range of normal controls. To simulate a split-up potential with a considerable reduction in amplitude similar to that recorded in many localized nerve lesions (Buchthal, Rosenfalck, Trojaborg, 1974), the model required that some of the fibre groups were delayed more than other groups.
DPP4.03 CONCENTRIC NEEDLE EMG IN REINNERVATING AND DENERVATING M O T O R UNITS.
records single fibre activity, the other one, opposite to the SF surface, has a normal surface area and is designed to record normal motor unit action potentials (MUAPs). There are two aspects to the MUAP analysis method with this needle, distinguishing it from conventional methods. 1) The leading-off area is the same, but the position of the surface with respect to the needle shaft is different. Experiments were carried out using an electrode equipped with both a conventional concentric recording surface at the tip and a surface at the side of the needle. In the deltoid muscle of healthy volunteers we searched for recordings from the same motor unit with both electrode surfaces. From the side surface MUAPs were recorded which had on the average 50% higher amplitudes. The spike durations were about 10% less, as compared with the tip surface. The slower MUAP components (total duration, slow wave amplitude) were not different. 2) The wave shapes of averaged MUAPs probably depend on choosing a single fibre or the MUAP recording itself for triggering. This was confirmed by computer analysis. Here as well the MUAP amplitudes were most affected. Explanations for these results are given.
S.D. Nandedkar, D.B. Sanders and E.V. Stalberg (Durham, NC, USA) We have used computer models to simulate motor units (MUs) and electromyographic motor unit action potentials (MUAPs). Six normal MUs were simulated, each containing 50 muscle fibers. To simulate reinnervation the number of fibers in the MU was increased sequentially to 75, 100, 150 and 200. The amplitude, area, duration and polyphasia of the simulated concentric needle EMG MUAPs increased in the simulated reinnervated MUs. Increased polyphasia was the earliest abnormality seen. The mean MUAP amplitude increased by only 50% even when the number of muscle fibers was increased to 200. The MUAP area and duration increased more than the amplitude. To simulate denervation of previously reinnervated MUs, the number of fibers of the previously reinnervated MUs was reduced to 50 by random deletion. MUAP amplitude, area and duration decreased in parallel with the loss of muscle fibers but the MUAPs were more polyphasic and the MUAP amplitude varied more than in a population of normal MUs having the same number of fibers.
DPP4.04 T H E DEPENDENCE OF M O T O R UNIT POTENTIALS ON ELECTRODE C O N S T R U C T I O N AND METHO D S OF DATA ANALYSIS. D. Stegeman, H. Vingerhoets, P. Hofman and S. Notermans (Nijmegen, The Netherlands) Special EMG electrodes have been constructed for various purposes. The two channel electrode of Falck (Falck 1983, thesis, Univ. of Turku, Finland) is an example. One surface
DPP4.05 SIMULATION OF SENSORY NERVE ACTION POTENTIALS.
D. Nielsen and A. Rosenfalck (Aalborg, Denmark) Changes in the shape of the sensory nerve action potential may contain more information than is obtained by measurement of the parameters used clinically to quantify nerve injuries. The standard parameters are: the maximal and minimal conduction velocities and the maximal amplitude of the sensory nerve action potential. A model assuming alinear superposition of temporally dispersed single fiber potentials (Rosenfalck and Ottosen, 1982) was used to estimate changes in the shape and in the standard parameters. The assumption that the nerve fibres were differently affected was modelled by adding 1-2 msec superimposed by 10% stochastic noise to the latencies of the individual nerve fibres potentials. Changes in shape were significant when about 40% of the nerve fibres were assumed to be damaged, focally or scattered, while changes in maximal conduction velocity and amplitude remained within the range of normal controls. To simulate a split-up potential with a considerable reduction in amplitude similar to that recorded in many localized nerve lesions (Buchthal, Rosenfalck, Trojaborg, 1974), the model required that some of the fibre groups were delayed more than other groups.