Days of Biomechanics 2014, Sofia, 20.11-21.11.2014г.
BULGARIAN SOCIETY OF BIOMECHANICS
INSTITUTE OF MECHANICS, BAS
„Days of Biomechanics - 2014”
20.11-21.11.2014 г.
BOOK OF ABSTRACTS
Organizing Committee:
Stoyan Stoytchev
Svetoslav Nikolov
Rositsa Raikova
Gergana Nikolova
Study of the blood flow in the common carotid artery bifurcation
N. Antonova1, X. Dong2, I.Velcheva3, E. Kaliviotis4, P. Tosheva1
1Department of Biomechanics, Institute of Mechanics, Bulgarian Academy of Sciences, 1113 Sofia Acad. G. Bonchev str., bl. 4, Bulgaria
2School of Civil Engineering, Tianjin University, China, 300072
3Department of Neurology, University Hospital of Neurology and Psychiatry
“St. Naum”, Medical University, Sofia, Bulgaria
4Department of Engineering, University College London, London, UK
Blood flow in the carotid artery bifurcation is studied on the basis of the Navier-Stokes equations performing numerical simulations by a finite volume method and considering one wave period. Four different cases of the common carotid bifurcation were examined: without stenoses, with one, two and three stenoses. Based on geometry reconstruction a mesh generation is done. The case studies are based on different anatomies presented by the one, two or three stenoses of common carotid bifurcation vessel. The physiological geometry can be imported into a CFD solver.
The numerical results of the blood flow in the common carotid bifurcation give detail picture of the axial velocity and WSS distribution. For the case of carotid bifurcation without stenoses results for the axial velocity distribution are presented in six characteristic time points T=0 s, 0.1s 0.2s, 0.3s, 0.4s, 0.5s.
The results show that the blood flow in the carotid bifurcation is unsteady and the flow disturbances depend on the time and type of the stenoses. The pattern of the velocity and the WSS are obtained and comparison of the peak wall shear stress (WSS) is done for the four considered cases. The recirculation zone behind the bifurcation and stenosis is the area with low shear stress. The peak WSS are increasing and the maximum is being achieved earlier with increase of the number of stenoses. The dependence of the peak WSS on time reflects the changes due to the velocity of the pulse wave. Comparison of the peak wall shear stress for the four different cases (without stenoses and with 1, 2 and 3 stenoses correspondingly) reveals the peak WSS maximum value at the characteristic point of T=0.2 s for the cases with two and three stenoses. In the case of a bifurcation without or with one stenosis, the maximum WSS is achieved with a delay of 0.02 seconds compared to the other two cases. The differences in the maximal WSS value (1.8 Pa) for the cases with 1, 2 and 3 stenoses in comparison to the case without stenosis (1.5 Pa) are observed at the characteristic point of the pulse wave at T= 0.45 s.
The results could play an important role in understanding the formation, growth, rupture and prognosis of damage of the vessel wall and may be a practical tool for planning treatment and follow-up of patients after neurosurgical or endovascular interventions with 3D angiography. The results also present the potential of using numerical simulation to provide existing clinical prerequisites for diagnosis and therapeutic treatment.
Gait control of humans with assistive devices
R. Antonova, S. Karastanev, P. Kiriazov
Department of Biomechanics, Institute of Mechanics, Bulgarian Academy of Sciences,
1113 Sofia, Acad. G. Bonchev str., bl. 4, Bulgaria
Gait control is a complex process which has an intrinsic focus on planning, execution and adaptation of the whole-body movement by the CNS. An underlying assumption in our work is that the motion of healthy people is optimal with respect to speed, positioning accuracy, and energy expenditure. Motor control may become much more complicated for people having stroke, traumas or neurological diseases. Generally speaking, we need to consider complicated optimisation problems for complex neuro-musculoskeletal systems.
Patients need to restore their motor control functions and motion performance to the best possible level. Various assistive devices may be used for restoration of human movement abilities: crutches, prostheses, passive and active orthoses, robotic exoskeletons, etc. To meet the above challenges, it is very important how to properly decompose complex modelling, identification and optimisation tasks into sets of much easier-to-find satisfactory solutions. It is of primary importance to properly identify the structure of the walking dynamics for every locomotion phase and the corresponding control functions. At first, a set of variables (controlled outputs) that best characterize human dynamic performance in the locomotion task has to be defined. Second, we have to find those driving forces/torques that mostly contribute to the dynamic performance in this task.
Mathematical model for estimating of external mechanical work in step test
Z. Arakchiyski
National Sports Academy “V. Levski”, Sofia, Bulgaria
Introduction
Typically, the options for determining the physical condition are based on the use of bicycle ergometers, treadmills and a number of devices for carrying out the step tests. Interest is the development of method, which is based on a known step tests for determination of the indirect VO2 max and allow the calculation of PWC170. Results of another study, where mechanical work for steps is based on a variant of equation, proposed by the author, are reported to the 4th Congress of FIEP [1] and World Congress of Performance Analysis of Sport VІІІ [2]. The aim of this study was to develop an equation to quantify the external mechanical work in step test, enabling calculation of PWC170 using the classical Margaria Step Test, considering the rhythmicity of the test performance.
Methods
15 players from the senior team of FC "CSKA" - Sofia with bodyweight 77.5 ± 5.3 kg and height 183.3 ± 4.0 cm were studied. All test persons are loaded once by the aerobic step-test of Margaria at platform height 0.4 m. The protocol of the conducted a two-stage test is 15 steps per minute during the first 5-minute load and 25 steps per minute for the second 5-minute load. Rhythm is determined by a metronome. Heart rate (HR) was measured with a Sport Tester PE-3000. By visual assessment into protocol is noted in two categories rhythm of execution of movements during the test, which are also registered with a standard video camera for subsequent comparisons. Results were compared with these from bicycle ergometer test, carried out two days before step test. For analytical calculation of the mechanical work on Margaria step-test, one step is divided into two phases - move up and down.
Results
The results from bicycle ergometer test and step test for PWC170 form a two group. In the first group, the differences are in the range -1 – +2 %, wile in the other group is 5 – 8 % higher in step test. The significantly higher values for the second group are due to the marked unrhythmic execution of step test. This is most often in the downward movement, when the player comes down for a shorter time than is provided in the protocol. In this case is performed less muscle work in alighting from the platform, leading to less fatigue, lower values of heart rate and ultimately to a higher calculated working capacity. The introduced coefficient reduces the differences between the two tests in these cases within 3%.
Discussion/Conclusion
External work is the work performed by external forces – mainly from the ground – to move the center of mass through a displacement. The proposed model is based on several assumptions. One is that external work satisfactorily estimates the total mechanical work performed on the body. Another assumption is that the time of downward movement first single support is equally for all test steps and the center of mass motion is uniformly accelerated. This allows easily estimating the downward movement external work and gives us satisfactorily results for the purposes of this study. Finally, the relevance of estimates of mechanical work performed on the body to actual work performed by the muscles is based on presume that there is little mechanical energy storage and little muscular co-contraction during step. These latter suppositions are legitimate sources of error, but they also apply to all other non-invasive estimates of mechanical work. Given the existing methods for determining the mechanical work on step loads, this work is original and more accurate method that takes into account not only the influence of negative work, but also acceleration of the center of mass in one step.
References
[1] Pavlova, E., Uzunova, G., Arakchiyski, Z. (2007). Margaria Step Test for Estimating WC170. 4th FIEP European Congress Physical Education and Sports, 160 – 166. ISBN: 978-80-89324-00-2.
[2] Pavlova, E., Uzunova, G., Arakchiyski, Z. (2008). Comparison between PWC170 estimated by equation and Krastev’s table in step test. World Congress of Performance Analysis of Sport VІІІ, 123 – 127, ISBN: 19012880011.
A study of indomethacin release from polymersome nanoparticles solution under the presence of ethanol
R. Blagoeva1, A. Nedev1 , V. Michailova2
1Institute of Mechanics – Bulgarian Academy of Sciences, Acad. G. Bonchev Str.,
bl. 4, 1113 Sofia
2Faculty of Pharmacy – Medical University, 2 Dunav Str., 1000 Sofia
A study of indomethacin release in vitro from polymersome nanoparticles solution is presented.In vitro release was conducted in distilled water containing different ethanol content, as well as different rate of ethanol injection, using the dialysis tube method.
The recently proposed by the author’s mathematical model for drug release was validated under the obtained experimental results. It was used for establishing the effect of ethanol concentration and rate of injection in the nanoparticles solution upon drug release. Numerical simulation of indomethacin release was performed within a period of 2 days in the case of membrane presence, as well as when neglecting it.
Traffic jams on chains with a shortcut of arbitrary length
(in the framework of TASEP - a model of biological transport)
N. Zh. Bunzarova 1,2, N. C. Pesheva2 , J. G. Brankov 1,2
1 Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research,
141980 Dubna, Russia
2Institute of Mechanics, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
We report here results of our study on the appearance of traffic jams on chains with a shortcut between two simple chain segments in the framework of the Totally Asymmetric Simple Exclusion Process (TASEP) in the maximal current phase. We study this problem both numerically (by numerical simulations) and analytically within the mean-field approximation (by the effective rates approximation (ERA) method, developed in our previous study of TASEP on simple networks). The conditions for the occurrence of traffic jams are determined for arbitrary length of the shortcut. The problem presents interest on its own since the conditions for coexistence of low- and high-density phases are essentially different from those for a simple chain between two reservoirs. In the considered case of equal probability for a particle to take the main segment or the shortcut, the model displays an unexpected feature: the current through the longer shunted segment is larger than the current through the shortcut. Our findings are of interest to vehicular traffic jams on single-lane roads but they also may have relevance to biological transport processes - phenomena like crowding of molecular motors moving along twisted proto filaments.
Efficient control learning in sport and rehabilitation
D. Despotova, P. Kiriazov, G. Nikolova
Department of Biomechanics, Institute of Mechanics, Bulgarian Academy of Sciences,
1113 Sofia, Acad. G. Bonchev str., bl. 4, Bulgaria
Motivation
Normally, goal-directed voluntary movements are performed optimally as regards motion speed, positioning accuracy, and energy expenditure. The control functions (neural signals to muscles) are to be learnt and optimised with respect to these performance indices.
Method
In our study, a natural approach for efficient motor learning is proposed. Optimal control functions have a 3-step shape and a set of key parameters is found for describing them. Those are intrinsic parameters human has to learn in dynamic point-to-point motion tasks. We make corrections in the control parameters until reach the target, applying an optimal, convergent and natural learning algorithm.
Results
Our control learning approach was applied to dynamic models of human body/limbs with two, three, and six degrees of freedom. In the computer simulations, we verified that the control learning converges and the number of trials is very small. In addition, we did some real (able-bodied) experiments with rapid aiming movements of the arm and they confirm the feasibility of the proposed approach.
Discussion
The neural structures that compute the required control forces are the so-called internal models presenting a fundamental part of the voluntary motor control. We believe that the proposed approach can be used to rebuild such models (cortical reorganization) by proper training procedures.
Conclusion
Thus we have the necessary scientific basis to develop efficient rehabilitation for various movement disorders and various motion tasks in activities of daily living. The proposed concepts and algorithms could be very useful in designing also adequate control strategies for efficient motion analysis and sport performance optimization.
Key words
goal-directed movements, control optimization;
Prognosis, monitoring and prevention of the risk of postoperative infectious
I. Edissonov, S.Ranchev
Institute of Mechanic and Biomechanics. Bulgarian Academy of Science
Acad. G.Bonchev str., bl.4, 1113 Sofia, Bulgaria
In light of the current understanding of the ethnological determinants and the pathophysiological mechanisms, responsible for developing of postoperative infectious complications, the authors present an own predictive model and report their two years experience findings. The main objective of our prospective study was to establish a well – motivated parameters for early identification of an risk patient populations with a predictable response to the surgery intervention and to investigate the benefits of appropriate prevention steps. Our initial attempts to use indicators, predicting the host response to major surgical intervention and our first results has proved the here discussed complex approach beneficial in the reduction of the postoperative infectious mortality and morbidity frequencies and in the early diagnosis of the postoperative infectious complications.
Computational modeling of blood flow dynamics in brain aneurysms