Global and detailed features of motor unit potential in myogenic and neurogenic disorders

Motor unit action potential (MUAP) may be characterized by two complementar y features: global and detailed. The global feature is represented by the e nvelope of the curve while the detailed feature describes the fluctuations around the envelope. The global feature represents the magnitude of the sig nal and is related to the number of fibers contributing to the MUAP. The de tailed feature indicates the single fiber potential's synchronization. The global feature is characterized by amplitude and duration and may be quanti fied by the following indexes: area/amplitude or size index, which is inter preted as the potential "thickness". The detailed feature is characterized by the number of phases and turns. The irregularity coefficient, which is r elated to the "length" of the curve, combines the number of phases and turn s with their amplitudes. The aim of this study was to analyze the relations hip between the global and detailed features of MUAPs in various neuromuscu lar disorders. In neurogenic cases, with the exeption of the correlation be tween the duration and number of turns (r=0.58), no correlation between any other parameters related to global and detailed features were significant (r less than or equal to 0.4). In myogenic cases, a significant correlation between the irregularity coefficient and duration (r=0.71), irregularity c oefficient and area/amplitude (r=0.54) rather than that between the irregul arity coefficient and area (r=0.32), has been found. The correlations betwe en parameters were more significant in more chronic processes. (C) 1999 IPE M. Published by Elsevier Science Ltd. All rights reserved.