Effects of detection system parameters on cross-correlations between MUAPs generated from parallel and inclined muscle fibres

Abstract

The aim of this study was to investigate the effects of inter-electrode distance (IED), electrode radius (ER) and electrodes configurations on cross-correlation coefficient (CC) between motor unit action potentials (MUAPs) generated in a motor unit (MU) of parallel fibres and in a MU of inclined fibres with respect to the detection system. The fibres inclination angle (FIA) varied from 0° to 180° by a step of 5°. Six spatial filters (the longitudinal single differential (LSD), longitudinal double differential (LDD), bi-transversal double differential (BiTDD), normal double differential (NDD), an inverse binomial filter of order two (IB2) and maximum kurtosis filter (MKF)), three values of IED and three values of ER were considered. A cylindrical multilayer volume conductor constituted by bone, muscle, fat and skin layers was used to simulate the MUAPs. The cross-correlation coefficient analysis showed that with the increase of the FIA, the pairs of MUAPs detected by the IB2 system were more correlated than those detected by the five other systems. For each FIA, the findings also showed that the MUAPs pairs detected by BiTDD, NDD, IB2 and MKF systems were more correlated with smaller IEDs than with larger ones, while inverse results were found with the LSD and LDD systems. In addition, the pairs of MUAPs detected by the LDD, BiTDD, IB2 and MKF systems were more correlated with large ERs than with smaller ones. However, inverse results were found with the LSD and NDD systems.

Ability of spatial filters to distinguish between two MUAPs generated from MUs with different locations, sizes and fibers pennation

“…The common point between this work [22] and the work in our hands lies in the behaviours of the spatial filters according to the pennation of the fibres. As first limitation of the results revealed in [22], the effects of the location and size of the two MUs on the correlation coefficient between the MUAPs generated by the two MUs were not taken into account. The second limitation of the results shown in [22] is that the ability to distinguish between MUAPs generated from two MUs was not also addressed.…”

“…Figure 3. Arrangement of the electrodes configured in the seven investigated filters with respect to the fibres orientation [4,22]. Reproduced with permission of authors from [22].…”

“…The MUAP amplitude decreases are important with the anisotropic one dimensional (1D) filters and are not significant in the case of the almost two dimensional (2D) filters (NDD and IB2 filters). This result was due to the arrangement of the electrodes configured in each filter with respect to the fibres direction and to the weights given to them (this is due to the fact that the 1D filters are highly anisotropic and the 2D filters are almost isotropic) [21,22].…”

“…In a recent work [22], the effects of detection system parameters (inter-electrode distances, electrodes shape and size) on the cross-correlation coefficients of MUAPs generated from MUs of parallel and inclined muscle fibres has been investigated. The common point between this work [22] and the work in our hands lies in the behaviours of the spatial filters according to the pennation of the fibres.…”

“…In a recent work [22], the effects of detection system parameters (inter-electrode distances, electrodes shape and size) on the cross-correlation coefficients of MUAPs generated from MUs of parallel and inclined muscle fibres has been investigated. The common point between this work [22] and the work in our hands lies in the behaviours of the spatial filters according to the pennation of the fibres. As first limitation of the results revealed in [22], the effects of the location and size of the two MUs on the correlation coefficient between the MUAPs generated by the two MUs were not taken into account.…”