Analysis of crosstalk signals in a cylindrical layered volume conductor – Influence of the anatomy, detection system and physical properties of the tissues

A comparison of the ability of different spatial filters to reduce the amount of crosstalk in a surface electromyography (sEMG) measurement was conducted. It focused on the influence of different properties of the muscle anatomy and detection system used on the amount of crosstalk present in the measurements. An analytical model was developed which enabled the simulation of single fibre action potentials (SFAPs). These fibres were grouped together in motor units (MUs). Each MU has characteristics which, along with the SFAPs, are used to obtain the motor unit action potential (MUAP). A summation of the MUAPs from all the MUs in a muscle leads to the electromyogram (EMG) signal generated by the muscle. This is the first model which simulates a complete muscle for crosstalk investigation. Previous studies were done for single fibres (Farina&Rainoldi 1999; Farina et al. 2002e; Farina et al. 2004a) or MUs (Dimitrova et al. 2002; Dimitrov et al. 2003; Winter et al. 1994). Lowery et al. simulated a complete muscle, but only investigated one spatial filter (Lowery et al. 2003a). This model is thus the first of its kind. EMG signals were generated for limbs with different anatomical properties and recorded with various detection systems. The parameters used for comparison of the recorded signals are the average rectified value (ARV) and mean frequency (MNF), which describe the amplitude and frequency components of an EMG signal, respectively. These parameters were computed for each EMG signal and interpreted to make recommendations on which detection system results in the best crosstalk rejection for a specific experimental set-up. The conclusion is that crosstalk selectivity in an sEMG measurement is decreased by increasing the thickness of the fat layer, increasing the skin conductivity, decreasing the fibre length, increasing the interelectrode distance of the detection system, placing the detection electrodes directly above the end-plate area or an increased state of muscle contraction. Varying the contraction force strength or placing the detection electrodes directly above the tendon area has no influence on the crosstalk selectivity. For most of the conditions investigated, the normal double differential (NDD) detection system results in the best crosstalk reduction. The only exceptions are a set-up with poor skin conductivity where NDD and double differential (DD) performed comparably, and the two simulations in which the muscle length is varied, where the DD filter performed best. Previous studies have found DD to be more selective for crosstalk rejection than NDD (Dimitrov et al. 2003; Farina et al. 2002a; Van Vlugt&Van Dijk 2000). Possible reasons for the contradictory results are the high value of skin conductivity currently used or influences of the muscle geometry.Dissertation (MEng(Bio-Engineering))--University of Pretoria, 2007.Electrical, Electronic and Computer Engineeringunrestricte

Two-dimensional generator function for the vectorcardiogram for use in volume conduction models of the thorax

An electrocardiogram (ECG) measures the electrical activity of the heart on the surface of the skin. Volume conduction models of the thorax can be designed to simulate such measurements. However, to drive such simulations a generator function is required to describe the electrical activity of the heart. Although such simulations, varying in complexity, are discussed in literature, there is a need for a simplified, though comprehensive approach that can be used as a concise introduction to this topic, or for cases where one is primarily interested in first-order approximations of this problem. In this article an overview of the vector interpretation of the ECG, also known as a vectorcardiogram (VCG), is presented in the two-dimensional frontal plane of a human. The derivation of the equivalent electric dipole (i.e. the cardiac vector) from the VCG, which can be used as a current-source generator function for volume conduction model simulating the ECG, is discussed. A procedure for implementing such a volume conduction model with the finite element technique, using this simplified two-dimensional generator function, is discussed and the results are presented. The general features observed in recorded ECG leads agree with those predicted by this simple model. AFRIKAANS: 'n Elektrokardiogram (EKG) meet die elektriese aktiwiteit van die hart op die veloppervlak. Volumegeleidingsmodelle van die toraks kan ontwerp word om hierdie metings te simuleer. 'n Generatorfunksie, wat die elektriese aktiwiteit van die hart beskryf, word benodig om hierdie simulasies aan te dryf. Hoewel soortgelyke simulasies van variërende kompleksiteit in die literatuur bespreek word, is daar 'n behoefte aan 'n vereenvoudigde, dog omvattende benadering wat kan dien as inleiding tot die onderwerp of vir gevalle waar 'n eerste-orde-benadering tot die probleem voldoende is. In hierdie artikel word 'n oorsig gegee oor die vektorinterpretasie van die EKG, ook bekend as 'n vektorkardiogram (VKG), in die tweedimensionele menslike frontale vlak. Die afleiding van die ekwivalente elektriese dipool (met ander woorde die kardiale vektor) vanaf die VKG, wat gebruik kan word as 'n stroombron-generatorfunksie vir volumegeleidingsmodelle wat die EKG simuleer, word bespreek. 'n Prosedure om so 'n volumegeleidingsmodel met die eindige-element-tegniek te implementeer en die vereenvoudigde tweedimensionele generatorfunksie te gebruik, sowel as die resultate daarvan, word bespreek. Die algemene kenmerke van gemete EKG-afleidings stem ooreen met dié wat deur die eenvoudige model voorspel word