TY - GEN A1 - Birkenmaier, Clemens A1 - Krenkel, Lars A1 - Lehle, Karla T1 - Linking flow conditions in membrane oxygenators to arrangements of multimeric von-Willebrand-factor as indication for coagulation T2 - World Congress of Biomechanics 2018, Convention Centre Dublin, 8.-12. Juli 2018 N2 - Introduction Shear induced multimerisation of von-Willebrand-factor (vWF) is supposed to play an important role in coagulation inside extracorporeal membrane oxygenators. However, there is no proof that links observed vWF structures to computed or measured flow conditions. Methods The structures of multimeric vWF fibers, observed in clinically used membrane oxygenators is examined using immunofluorescence microscopy (IFM) using Carstairs’ staining method (positive ethics committee vote). The flow around the membrane fibres inside the oxygenator is investigated in terms of shear rate, wall shear velocity and streamlines by using CFD (RANS, Carreau-Yasuda viscosity, geometry remodelled after high-resolution µCT-scans). By interpreting the histological and numerical results in this common context, indications for shear induced coagulation mechanisms can be identified. Results The fibre structures of multimeric vWF build regular but not exactly symmetric formations around the contact face (CF) between the crosswise stacked oxygenator fibres (OF), see fig.1B, vWF marked red. Annular around the CF arranged, cells are likely to be found, see fig.1B, nuclei marked blue. The computed streamlines around the OF show attached flow around the circular fibres. However, the irregular arrangement of real OF produce considerable cross flow between the interconnected neighbouring channels, in contrast to previous 2D-simulations. Thus, the CF are washed around closely by blood, also from neighbouring channels. The wall shear velocity streamlines form regular, slightly asymmetric shapes around the contact faces. The occurring maximum shear rates are in the range of 1,000 1/s. Discussion The shapes of vWF structures found in clinically used oxygenators match the computational results in terms of wall shear velocity and streamlines well. The accumulation of cells close to the CF can also be explained by fluid mechanics, as there are small shear gradients and slow velocities. However, occurring shear rates between OFs are too low to trigger multimerisation of vWF. That raises the question where in the circuit the actual activation of vWF is started and how, at least partly chained, vWF multimeres are attracted towards the OF surface. A next step will be the investigation of the actual shear rate triggered (or mediated) multimerisation of vWF. Towards this end, microfluidic experiments with shear triggered coagulation will be performed. Also of big interest is the computation of the flow situation in the oxygenator in proximity to chaining threads, which have been ignored in computations so far. However, first a realistic representation of the effective viscosity in computations is needed, which is not available yet. Y1 - 2018 ER - TY - JOUR A1 - Schmitz, Paul A1 - Neumann, Christoph Cornelius A1 - Neumann, Carsten A1 - Nerlich, Michael A1 - Dendorfer, Sebastian T1 - Biomechanical analysis of iliac crest loading following cortico-cancellous bone harvesting JF - Journal of Orthopaedic Surgery and Research N2 - Background Iliac crest bone harvesting is a frequently performed surgical procedure widely used to treat bone defects. The objective of this study is to assess the biomechanical quantities related to risk for pelvic fracture after harvesting an autologous bone graft at the anterior iliac crest. Methods Finite element models with a simulated harvest site (sized 15 × 20 mm, 15 × 35 mm, 30 × 20 mm and 30 × 35 mm) in the iliac wing are created. The relevant loading case is when the ipsilateral leg is lifted off the ground. Musculoskeletal analysis is utilized to compute the muscle and joint forces involved in this motion. These forces are used as boundary conditions for the finite element analyses. Bone tissue stress is analyzed. Results Critical stress peaks are located between the anterior superior iliac spine (ASIS) and the anterior edge of the harvest site. Irrespective of the graft size, the iliac wing does not show any significant stress peaks with the harvest site being 20 to 25 mm posterior to the ASIS. The harvest area itself inhibits the distribution of the forces applied on the ASIS to extend to the posterior iliac wing. This leads to a lack of stress posterior to the harvest site. A balanced stress distribution with no stress peaks appears when the bone graft is taken below the iliac crest. Conclusion A harvest site located at least 20 to 25 mm posterior to the ASIS should be preferred to minimize the risk of iliac fatigue fracture. KW - Bone harvesting KW - Autologous bone graft KW - Iliac crest KW - Fatigue fracture KW - Pelvis KW - ASIS KW - FEA KW - Biomechanical investigation KW - Beckenkammknochen KW - Knochenentnahme KW - Spongiosa KW - Biomechanische Analyse Y1 - 2018 U6 - https://doi.org/10.1186/s13018-018-0822-1 VL - 13 IS - 108 SP - 1 EP - 8 PB - Springer Nature ER - TY - JOUR A1 - Benditz, Achim A1 - Auer, Simon A1 - Spörrer, J.F. A1 - Wolkerstorfer, S. A1 - Grifka, Joachim A1 - Süß, Franz A1 - Dendorfer, Sebastian T1 - Regarding loads after spinal fusion, every level should be seen separately: a musculoskeletal analysis JF - European Spine Journal N2 - The number of spinal fusion surgeries is steadily increasing and biomechanical consequences are still in debate. The aim of this study is to provide biomechanical insights into the sagittal balance of the spine and to compare spinal load before and after spinal fusion. METHOD: The joint reaction forces of 52 patients were analyzed in proximo-distal and antero-posterior direction from the levels T12-L1 to L5-S1 using musculoskeletal simulations. RESULTS: In 104 simulations, pre-surgical forces were equal to post-surgical. The levels L4-L5 and T12-L1, however, showed increased spinal forces compression forces with higher sagittal displacement. Improved restauration of sagittal balance was accompanied by lower spinal load. AP shear stress, interestingly decreased with sagittal imbalance. CONCLUSION: Imbalanced spines have a risk of increased compression forces at Th12-L1. L4-L5 always has increased spinal loads. These slides can be retrieved under Electronic Supplementary Material. KW - AnyBody Modeling System KW - Musculoskeletal analysis KW - Sagittal balance KW - Spinal fusion KW - Spine biomechanics KW - Biomechanische Analyse KW - Wirbelsäulenversteifung KW - Vergleichende Anatomie Y1 - 2018 U6 - https://doi.org/10.1007/s00586-018-5476-5 VL - 27 IS - 8 SP - 1905 EP - 1910 PB - Springer-Verlag ER - TY - JOUR A1 - Philipp, Alois A1 - de Somer, Filip A1 - Foltan, Maik A1 - Bredthauer, Andre A1 - Krenkel, Lars A1 - Zeman, Florian A1 - Lehle, Karla T1 - Life span of different extracorporeal membrane systems for severe respiratory failure in the clinical practice JF - PLOS ONE N2 - Over the past decade, veno-venous extracorporeal membrane oxygenation (vvECMO) has been increasingly utilized in respiratory failure in patients. This study presents our institution´s experience focusing on the life span of ECMO systems reflecting the performance of a particular system. A retrospective review of our ECMO database identified 461 adult patients undergoing vvECMO (2010-2017). Patients that required more than one system and survived the first exchange >24 hours (n = 139) were included. Life span until the first exchange and exchange criteria were analyzed for all systems (PLS, Cardiohelp HLS-set, both Maquet Cardiopulmonary, Rastatt, Germany; Deltastream/Hilite7000LT, iLA-activve, Xenios/NovaLung, Heilbronn, Germany; ECC.O5, LivaNova, Mirandola, Italy). At our ECMO center, the frequency of a system exchange was 30%. The median (IQR) life span was 9 (6-12) days. There was no difference regarding the different systems (p = 0.145 and p = 0.108, respectively). However, the Deltastream systems were exchanged more frequently due to elective technical complications (e. g. worsened gas transfer, development of coagulation disorder, increased bleedings complications) compared to the other exchanged systems (p = 0.013). In summary, the used ECMO systems are safe and effective for acute respiratory failure. There is no evidence for the usage of a specific system. Only the increased predictability of an imminent exchange preferred the usage of a Deltastream system. However, the decision to use a particular system should not depend solely on the possible criteria for an exchange. KW - Equipment Failure Analysis/statistics & numerical data KW - Extracorporeal Membrane Oxygenation/instrumentation KW - Membrane/classification/standards/statistics & numerical data KW - Primary Health Care/statistics & numerical data KW - Respiratory Distress Syndrome/therapy KW - Retrospective Studies KW - Severity of Illness Index KW - Time factors KW - MULTIDETECTOR COMPUTED-TOMOGRAPHY KW - THROMBOTIC DEPOSITS KW - ECMO SYSTEMS KW - Flow KW - OXYGENATION Y1 - 2018 U6 - https://doi.org/10.1371/journal.pone.0198392 VL - 13 IS - 6 SP - 1 EP - 10 PB - PLOS ER - TY - JOUR A1 - Raptis, Georgios T1 - Technischer Datenschutz in der telemedizinischen Versorgung JF - Der Krankenhaus-JUSTITIAR N2 - Die fortschreitende Digitalisierung des Gesundheitswesens ebnet auch den Weg einer stärkeren Verbreitung der telemedizinischen Versorgung in Deutschland. Die Politik erleichtert diesen Weg, z.B. mit dem eHealth-Gesetz oder mit der Lockerung des "Fernbehandlungsverbots" durch den Deutschen Ärztetag. Dabei wird schon aus der Definition (siehe z.B. die unten stehende Definition der AG Telemedizin) klar, dass Telemedizin keine neue medizinische Disziplin begründet. Bei Telemedizin handelt es sich nur um ein technisches Werkzeug in Kombination mit geeigneten klinischen Prozessen, damit bestehende medizinische Expertise unter Einsatz von Informations- und Kommunikationstechnologien räumliche Entfernungen oder einen zeitlichen Versatz überbrücken kann. Patientinnen und Patienten können also behandelt werden, auch wenn sie vom Arzt räumlich entfernt sind. KW - Telemedizin KW - Datenschutz Y1 - 2018 VL - 7 IS - 4 SP - 105 EP - 107 ER - TY - GEN A1 - Birkenmaier, Clemens A1 - Krenkel, Lars T1 - Towards a realistic model of blood viscosity and coagulation in membrane oxygenators T2 - 6th European Conference on Computational Mechanics (Solids, Structures and Coupled Problems) - ECCM 6; 7th European Conference on Computational Fluid Dynamics - ECFD 7 : Glasgow, Scotland, UK, June 11-15, 2018 N2 - Modelling blood flow an shear induced coagulation in membraene oxygenators (MO) is challenging. The relevant geometry of oxygenator fibers (OF) and chaining threads is complex and spans several length scales. In relevant scales and regimes blood shows several significant non-Newtonian effects. Existing models are only capable of accounting for some, but not all relevant effects. Additionally, coagulation processes are influencing fluid properties and geometry significantly. Due to the enormous size of the discretised geometries highly detailed viscosity and coagulation properties of blodd flow in MOs. First step is to find a gemoetry dependent viscosity representation on basis of parametric micro channel experiments with anti-coagulated blood. Next step is a statistic coagulation model, based on micro channel experiments with human (re-calcified citrated) whole blood an evaluation of clinically used osygenators. Since shear rate dependent (i.e. viscosity dependet) coagulation in return influences the viscosity, a combined model with suitable implementation in a RANS framework is necessary. Towards this end, micro channel experiments with new and used single OFs triggering coagulation are performed. Structures of multimeric von Willebrand fibers (vWF), as indicator for shear induced coagulation, are compared to computed and measured flow conditions, using immunofluorescence microscopy, RANS-computations and µPIV, respectively. Preliminary examinations in clinically used MOs show good agreement between occurring structures of vWF, cell depositions and computed flow patterns (geometry form µCT-Scans). However, computed shear rates might be to low to actually trigger activation of vWF. The complex geometry of MOs results in huge meshes, which makes RANS with statistical modelling of viscosity and coagulation a reasonable approach. Towards this end, experimental data on micro channel level with evaluation on real application level is crucial. Especially regarding clotting processes, micro fluidic experiments are powerful research tool. KW - Blood Viscosity KW - Shear Raed Induced Coagulation KW - Membrane Oxygenator Y1 - 2018 ER - TY - CHAP A1 - Birkenmaier, Clemens A1 - Steiger, Tamara A1 - Philipp, Alois A1 - Lehle, Karla A1 - Krenkel, Lars T1 - Flow-induced accumulations of von Willebrand factor inside oxygenators during extracorporeal life support therapy T2 - Proceedings of 12th International Conference BIOMDLORE 2018, June 28–30, 2018, Białystok, Poland N2 - BACKGROUND: Shear-induced conformational changes of von Willebrand factor (vWF) may be responsible for coagulation disorder and clot formation inside membrane oxygenators (MOs) during extracorporeal membrane oxygenation (ECMO) therapy. OBJECTIVE: The aim was to identify vWF structures inside clinically used MOs and employ computational fluid dynamics to verify the corresponding flow conditions. METHODS: Samples from gas exchange membranes (GEM) from MOs were analysed for accumulations of vWF and P-selectin-positive platelets using immunofluorescence techniques. Streamlines and shear rates of the flow around GEMs were computed using a laminar steady Reynolds-Averaged-Navier-Stokes approach. RESULTS: Most samples were colonized with equally distributed leukocytes, integrated in thin cobweb-like vWF-structures. Only 25 % of the samples showed extended accumulations of vWF. Computed streamlines showed considerable cross flow between interconnected neighbouring channels. Stagnation points were non-symmetric and contact faces were washed around closely. The occurring maximum shear rates ranged from 2,500 to 3,000 1/s. CONCLUSIONS: If pronounced vWF structures are present, shape and extent match the flow computations well. Computed shear rates bear a critical degree of uncertainty due to the improper viscosity model. If flow conditions inside the MO were sufficient to affect vWF, a more consistent distribution of vWF across the samples should be present. KW - Blood Viscosity KW - Shear Rate Induced Coagulation KW - Hemodynamics KW - Membrane Oxygenator KW - von Willebrand factor Y1 - 2018 SN - 978-1-5386-2396-1 U6 - https://doi.org/10.1109/BIOMDLORE.2018.8467205 PB - IEEE CY - Piscataway, NJ ER - TY - GEN A1 - Wiesent, Lisa A1 - Hupke, Constantin A1 - Balk, Christian A1 - Schultheiss, Ulrich A1 - Schratzenstaller, Thomas T1 - Optimization of the cardiovascular stent design towards improved expansion behaviour and radial stiffness properties T2 - Biomedizinische Technik N2 - - Development of a FEA Tool for a realistic stent simulation - investigation on minor modification on the stent design on the expansion behaviour - analysis of three stent designs: classical stent design with pronounced dogbone effect, two modified stent design (non-dogbone-design) KW - Kardiovaskuläres System KW - Stent Y1 - 2018 U6 - https://doi.org/10.1515/bmt-2018-6031 VL - 63 IS - s1 ER - TY - GEN A1 - Geith, Markus A. A1 - Swidergal, Krzysztof A1 - Schratzenstaller, Thomas A1 - Holzapfel, Gerhard A. A1 - Wagner, Marcus T1 - Numerical analysis of stent delivery systems during pre- and intraoperative processes T2 - 15. Deutsches LS-DYNA Forum, 15.-17.10.2018, Bamberg Y1 - 2018 UR - https://www.researchgate.net/publication/335260823_Numerical_analysis_of_stent_delivery_systems_during_pre-_and_intraoperative_processes ER - TY - CHAP A1 - Gross, Simon A1 - Verkerke, Gijsbertus Jacob A1 - Dendorfer, Sebastian T1 - Combined Experimental and Numerical Approach to Investigate Changes in Muscle Recruitment Pattern of the Back Muscles during Exhausting Exercise T2 - World Congress Biomechanics Dublin, 2018 N2 - In recent years, musculoskeletal computation has become a widely used tool to investigate joint and muscle forces within the human body. However, the issue of muscle fatigue is not considered adequately in most models and is a challenging task. One aspect that needs to be examined is the interaction of muscles during an exhausting task. Therefore, an experimental study was designed to analyze the changes of back muscle recruitment pattern during such exercises. In this study 38 subjects (27 male, 11 female, height = 177±8.5 cm, weight = 74.0±13.6 kg) participated. Each subject had to perform three static and three dynamic exhausting exercises where the back muscles were loaded with subject specific forces using a dynamometer adapter especially designed for the trunk muscles. To collect the muscle activity, twelve surface electromyography sensors were applied on the back, and four on the abdominal muscles. Muscle activity and fatigue were analyzed by calculating the maximum voluntary contraction normalized signal and the median frequency. At first the fatigue of m. erector spinae and m. multifidi was analyzed, since these muscles carry the main load during the exercises. Subsequently the activity of the m. trapezius, m. rectus abdominis and m. obliquus externus were investigated to determine recruitment patterns. To gain more detailed information of these patterns a numerical model was built using the AnyBody Modeling System™. Analyzing the measurements, we can observe an increasing muscle activity during isokinetic exercises while the force is constant. Since the activity in the simulation is defined as the current force output divided by the strength of the muscle, the strength parameter was scaled down based on the measured data, assuming a linear force – activity correlation, and using a numerical algorithm considering the influence of cross talk. The results show, that changes in recruitment pattern can be divided into three major subgroups. Prior to total exhaustion, some of the subjects show additional activation of muscles in the trapezius region, while other subjects show an additional activation of abdominal muscles, increasing the intra-abdominal pressure which supports the spine. In the third group an activation in both regions can be observed. The numerical simulations show an increasing activity of abdominal muscles as well as muscles in the upper back. Especially the m. latissimus dorsi shows a significantly higher activity. The results lead to the conclusion that prior to total exhaustion, additional muscles are recruited to support the main muscles. It was shown that abdominal muscles are activated to support back muscles by pressurizing the trunk cavity to delay total exhaustion as long as possible. In conclusion, the results show that changes in muscle recruitment pattern need to be considered when introducing muscle fatigue to musculoskeletal models. Y1 - 2018 ER -