Decomposition of EMG Signals

Interpretation of the electromyogram (EMG) is an important part of the clinical neurophysiological evaluation of patients with suspected neuromuscular disorders. The recent advent of computerized electrodiagnostic equipment is making quantitative analysis of EMG signals more practical, with the expectation that this will lead to greater objectivity and increased diagnostic sensitivity.

We have developed a computerized method for analyzing clinical EMG signals known as Automatic Decomposition Electromyography (ADEMG). The ADEMG method analyzes clinical EMG signals by decomposing them into their component motor-unit action potentials (MUAPs) and their firing rates. It is designed to be a convenient adjunct to the conventional needle EMG examination, analyzing EMG signals that are recorded during constant isometric contractions using a standard concentric or monopolar needle electrode and a conventional electromyograph. The analysis involves identifying the MUAPs, averaging them from the EMG signal, and measuring their amplitudes, durations, numbers of turns, and firing rates. ADEMG can analyze EMG signals recorded at up to 30% MVC and containing up to 15 simultaneously active MUAPs. A version of ADEMG is commercially available for the Nicolet Viking electromyograph.

More recently, We have developed an interactive computer program for decomposing EMG signals. Using this program, it is possible to fully identify MU discharge patterns and accurately measure MUAP waveforms.

References

McGill KC, Cummins KL, Dorfman LJ. Automatic decomposition of the clinical electromyogram. IEEE Trans Biomed Eng, BME-32: 470-477, 1985.

McGill KC, Dorfman LJ. Automatic decomposition electromyography: validation and normative data in brachial biceps. Electroenceph Clin Neurophysiol, 61: 453-461, 1985.

Howard JE, McGill KC, Dorfman LJ. Properties of motor unit action potentials recorded with concentric and monopolar needle electrodes: ADEMG analysis. Muscle and Nerve, 11: 1051-1055, 1988.

Howard JE, Dorfman LJ, McGill KC. Age effects on properties of motor unit action potentials: ADEMG analysis. Ann Neurol, 24: 207-213, 1988.

Dorfman LJ, Howard JE, McGill KC. Influence of contractile force on properties of motor unit action potentials: ADEMG analysis. J Neurol Sci, 86: 125-136, 1988.

Dorfman LJ, Howard JE, McGill KC. Motor unit firing rates and firing variability in the detection of neuromuscular disorders. Electroenceph Clin Neurophysiol, 73: 215-224, 1989.

McGill KC, Lateva ZC. Accurate estimation of motor-unit action potential waveforms and discharge patterns. 11th Intl Congr Electromyogr Clin Neurophysiol, Prague, Czech Republic, 1999. Abstract