Microscopic and macroscopic volume conduction in skeletal muscle tissue, applied to simulation of single-fibre action potentials

Abstract

~ ~i i !i i ĩi !ĩ!(i !i i ĩĩ ~ pic volur)om eering Division, PO muscle ffi lcroscop source,, ' of singh 7branes l rose cal homc ted fibre ivity to var Pt Within a, ;11 as the ] "onduction 7e radial d, est foJ th~ to an activ tential, Skeletal 1 Introduction IN HOMOGENEOUS volume conductor models of skeletal muscle tissue (used for example by ROSENFALCK, 1969; NANDEDKAR and ST~,LB~RG, 1983) the tissue has no structure. It is considered as a bulk material with anisotropic conductivities tr= (in the longitudinal fibre direction) and a, (radial). Usually, az and a, are taken real-valued. ALBERS et al. (1986) introduced a microscopic, frequency-dependent volume conductor model to study the relationship between SFAP and tissue structure. This network model accounted explicitly for the fibrous structure of skeletal muscle tissue. It was used for the calculation of the transfer function between a moving current source and the resulting extracellular potential (ALBERS et al., 1988). It was shown that, close to the source, the transfer function is significantly different from the transfer function calculated with a homogeneous, frequency-independent volume conductor model. This is a direct effect of the fibrous structure of the tissue in the inhomogeneous, capacitive model. In the

Modelling Fibrillation Potentials—Analysis of Time Parameters in the Muscle Intracellular Action Potential

“…Neglecting some side effects (the frequency-dependence of some volume conduction parameters [17]- [18] or the distortion of the electric field introduced by the recording electrode [8]), we can assume that the amplitude of a SFAP is lower as the radial distance increases. In contrast, duration parameters of the SFAP main spike (i.e.…”

The bioelectrical source in computing single muscle fiber action potentials

“…Close to the active fiber, the frequency-dependent behavior of the muscle fiber membranes has to be taken into account. Microscopic, frequency-dependent volume conduction parameters in skeletal muscle tissue can be introduced in an electrical network model (7,8). Such a network model has been used to calculate SFAPs (7)(8)(9)14), and its results (9,14) have been related to experimental results ( 15,16).…”

“…Several attempts have been made to explain the discrepancies between experimental and simulation results by volume conduction effects. Attention was paid to (a) sensitivity to changes in the network parameters (8), (b) capacitive properties of the T-tubular system (7), (c) frequency-dependent properties of the outer medium surrounding the core network part of the model ( 9), (d) muscle boundary ( 14), and (e) the presence of inhomogeneities (not yet published). However, no apparently improving effect was found either on the duration or on the shape of the computed SFAPs.…”

Sensitivity of the amplitude of the single muscle fibre action potential to microscopic volume conduction parameters

“…Owing to the larger volume of intracellular space at larger distances the intracellular properties play a more dominant role. Single-fibre action potentials (SFAPs) simulated with this microscopic model differed significantly from results obtained with a homogeneous volume conductor model within a range of 300 #In from the excited muscle fibre (ALBERS et al, 1988b).…”

“…This latter dependence is almost in accordance with the simulation results of NANDEDKAR and ST/~LBERG (1983) in a homogeneous, noncapacitive, anisotropic volume conductor model, They obtained an inversely proportional dependence of SFAP amplitudes with conduction velocity. One should expect such an accordance because for smaller capacitances, faster sources and larger radial distances our microscopic nonhomogeneous capacitive model can be substituted more and more satisfactorily by the macroscopic, homogeneous and noncapacitive approach (ALBERS et al, 1986;1988a;1988b).…”