Browsing by Author "Heidlauf, Thomas"

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    Chemo-electro-mechanical modelling of the neuromuscular system
    (2015) Heidlauf, Thomas; Röhrle, Oliver (Prof., PhD)
    Body movement is the result of cascades of complex chemical, electrical, and mechanical processes taking place at different length and time scales. This thesis deals with the biophysical modelling of these processes. In detail, the generation of electrical signals in spinal motor neurons is investigated based on the Hodgkin-Huxley formalism. Next, the complex signaling pathway leading from electrical excitation to contraction and force generation of the muscle fibres is modelled. Based on a structural model of the muscle and the bidomain equations, a method is proposed to predict electromyographic signals, which are frequently recorded in the clinic and result from the propagation of electrical signals along the muscle fibres to induce the contraction. Extending this model by a continuum-mechanical approach, a multiscale model of the neuromuscular system is obtained that considers chemical, electrical, and mechanical properties and allows to predict force generation, muscle deformation, and the EMG signal during fixed-length and non-isometric contractions. The proposed framework can potentially be used as an in-silico laboratory to investigate changes in the behaviour resulting from pathological conditions or drug treatment.
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    Modeling the chemoelectromechanical behavior of skeletal muscle using the parallel open-source software library OpenCMISS
    (2013) Heidlauf, Thomas; Röhrle, Oliver
    An extensible, flexible, multiscale and multiphysics model for non-isometric skeletal muscle behavior is presented. The skeletal muscle chemoelectromechanical model is based on a bottom-up approach modeling the entire excitation-contraction pathway by strongly coupling a detailed biophysical model of a half-sarcomere to the propagation of action potentials along skeletal muscle fibers, and linking cellular parameters to a transversely isotropic continuum-mechanical constitutive equation describing the overall mechanical behavior of skeletal muscle tissue. Since the multiscale model exhibits separable time scales, a special emphasis is placed on employing computationally efficient staggered solution schemes. Further, the implementation builds on the open-source software library OpenCMISS and uses state-ofthe-art parallelization techniques taking advantage of the unique anatomical fiber architecture of skeletal muscles. OpenCMISS utilizes standardized data structures for geometrical aspects (FieldML) and cellular models (CellML). Both standards are designed to allow for a maximum on flexibility, reproducibility, and extensibility. The results demonstrate the model´s capability of simulating different aspects of non-isometric muscle contraction and to efficiently simulate the chemoelectromechanical behavior in complex skeletal muscles such as the tibialis anterior muscle.
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    A multiscale chemo-electro-mechanical skeletal muscle model to analyze muscle contraction and force generation for different muscle fiber arrangements
    (2014) Heidlauf, Thomas; Röhrle, Oliver
    The presented chemo-electro-mechanical skeletal muscle model relies on a continuum-mechanical formulation describing the muscle's deformation and force generation on the macroscopic muscle level. Unlike other three-dimensional models, the description of the activation-induced behavior of the mechanical model is entirely based on chemo-electro-mechanical principles on the microscopic sarcomere level. Yet, the multiscale model reproduces key characteristics of skeletal muscles such as experimental force-length and force-velocity data on the macroscopic whole muscle level. The paper presents the methodological approaches required to obtain such a multiscale model, and demonstrates the feasibility of using such a model to analyze differences in the mechanical behavior of parallel-fibered muscles, in which the muscle fibers either span the entire length of the fascicles or terminate intrafascicularly. The presented results reveal that muscles, in which the fibers span the entire length of the fascicles, show lower peak forces, more dispersed twitches and fusion of twitches at lower stimulation frequencies. In detail, the model predicted twitch rise times of 38.2 ms and 17.2 ms for a 12 cm long muscle, in which the fibers span the entire length of the fascicles and with twelve fiber compartments in series, respectively. Further, the twelve-compartment model predicted peak twitch forces that were 19 % higher than in the single-compartment model. The analysis of sarcomere lengths during fixed-end single twitch contractions at optimal length predicts rather small sarcomere length changes. The observed lengths range from 75 to 111 % of the optimal sarcomere length, which corresponds to a region with maximum filament overlap. This result suggests that stability issues resulting from activation-induced stretches of non-activated sarcomeres are unlikely in muscles with passive forces appearing at short muscle length.
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