A simulation model for the study of EMG signals in normal and pathological conditions

The aim of this work is the study of the influence of the MUAP morphology on the compound EMG signal, by means of a simulation model. The simulated EMG is obtained as the sum of the number of MUs chosen on the basis of considerations concerning the muscle fibre dimension, the concentric needle electrode uptake area and the conduction volume. Myopathic, initial neurogenic and chronic neurogenic conditions have been simulated together with the normal case, adopting typical MUAPs. The interspike interval (ISI) has been simulated by means of a stochastic variable. Both time and frequency domain analyses have been performed on the simulated EMG. The results of time domain analysis are in very good agreement with experimental findings in the case of myopathies. The results of frequency domain analysis are in good agreement with experimental findings in the case of chronic neurogenic pathologies. The clinical difficulty encountered in discriminating some myopathic patterns from neurogenic ones can be well understood with the aid of the simulated signal. Since the presence of large potentials influences the value of the skewness of the spectrum, use of this parameter should be recommended in following the progress of neurogenic cases.