Evaluation Of Motor Unit Number Index(MUNIX) Based On High-Density Surface Electromyography Signals

Motor unit number index(MUNIX)is a sensitive biomarker for monitoring the status of innervation in patients with neurodegenerative diseases.It has the advantages of simple operation,non-invasive and good tolerance to subjects.Satisfactory repeatability is essential to the interpretation of the MUNIX results.In this study,the influence of the number and the placement of channels on the repeatability of MUNIX was investigated by using the high-density surface electromyography(HD-s EMG)signals of 128 channels.The main works are as follows:On the basis of thorough analysis of the current research status of estimation methods for motor units at home and abroad,the research direction was established to improve the repeatability of MUNIX methods under different conditions.The generation mechanism of EMG signals was understood.Meanwhile,the compound muscle action potential(CMAP)signals under electrical stimulation and surface interference pattern(SIP)signals under different percent of maximum voluntary contraction levels were collected by high-density surface EMG electrodes.According to the characteristics of CMAP signals and surface interference pattern signals,various interferences of EMG signal were analyzed.The original EMG data were denoised respectively,including band pass,notch filter and baseline drift removal.The artifact of CMAP signal was eliminated,which ensured the accuracy and validity of the data used in MUNIX calculation.Based on the spatial plasticity characteristics of high-density EMG signals,EMG information of various spatial states were obtained and the weighted amplitude of CMAP is introduced to select different channels and corresponding weights.The single-channel MUNIX and multi-channel weighted average MUNIX were defined and compared,which enabled the calculation of the weighted MUNIX values including different channels.Coefficient of variation was selected to define the repeatability of MUNIX.The significance analysis of intra-trial/inter-trial coefficient of variation was analyzed by using the bilateral t-test.By referring to the CMAP and the regional distribution of the innervation area,the repeatability with different channel numbers included and different positions on the muscle surface was compared.The results showed that increasing the number of channels or selecting channels near the innervation zone significantly increased the repeatability of MUNIX.In this paper,an MUNIX repeatability improvement algorithm based on weighted CMAP value was proposed.Also,the two potential reasons affecting MUNIX variability,channel number and channel location,were discussed.It provides a new perspective way to improve the repeatability of MUNIX by using high-density surface electromyography signals.The proposed multi-channel weighted MUNIX method can be used as a reliable tool to evaluate neurodegeneration.