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LINUX Cluster Project

Num. Simulation der Strömungs- und Festkörpermechanik


Institution

  • Name: Lehrstuhl für Numerische Mechanik
  • Address: Boltzmannstraße 15, 85748 Garching
  • Project Proposal Date: 2018-10-31 17:34:46

Abstract:

1.Recent years have seen a strong trend towards modeling and simulation in biomedical engineering, biomechanics, biofluids, and mechanobiology. Due to its significance, hemo- dynamics is one area of enforced activity in this respect, but despite all efforts undertaken so far, a number of very important questions that could lead to a real medical impact still remain open. This proposal aims at such questions and wants to enhance rough magnetic resonance imaging data by detailed simulations of the interaction between blood flow and arterial wall in order to compute quantities such as internal and superficial vessel wall stress and thus to obtain early indicators of disease. In the cardiovascular system the continuous interaction between blood flow and the arterial wall plays a crucial role. Plaque or aneurysm rupture occurs when hemodynamic blood pressure and thus internal plaque stress exceed a threshold that cannot be compensated by vessel wall deformation. Diseases such as atherosclerosis significantly change the vessel wall composition by incorporation of lipids, smooth muscle cells, and extracellular ma- trix, thereby locally changing the material properties. Magnetic resonance imaging (MRI) may help elucidating the interplay between blood flow and vessel wall stability by pro- viding patient-specific data on regional blood flow, vessel wall geometry, and vessel wall deformability, but the resolution of these data, in particular of the vessel wall composition, is limited. Refined mathematical models of the blood flow wall interaction in combina- tion with efficient and robust numerical simulation methods, on the other hand, have the potential to enhance these patient-specific MRI data so that changes in wall composition and stress peaks can be identified at early stages. In this way, a real medical impact is achievable. Ingredients needed for such an approach are the best of medical imaging, arterial wall modeling and the most efficient, robust and reliable computational methods for fluid- structure interaction. With respect to the latter, we concentrate on partitioned methods and their stable and efficient realization as combined iterative processes that consist of up to three different iteration levels. To meet the overall goal, we will build on a sound basis of expertise in all these areas, and we will create a multidisciplinary thematic research group that works in joint and synergistic ways. 2.The acute respiratory distress syndrome is a large contributor to high mortality rates of patients in intensive care units. It is characterized by a number of factors including overstretching of alveolar tissue. In the past, studies have shown, that with a change in the ventilation protocol the mortality rate can be significantly reduced. Unfortunately these trials are very time and money consuming and limited due to ethical constraints. Therefore computer simulations of the lung mechanics are suggested as an interesting alternative in order to develop improved - and maybe even patient specific - ventilation protocols. Furthermore, comprehensive computational lung models can be also utilized in many other fields. However, to understand the reason, why lungs still become damaged or inflamed during mechanical ventilation, is a key question sought by the medical community. The answer to this questions would aid the development of new and better protective ventilation systems. During VILI the parchymal lung tissue is overstretched, which causes inflammatory reactions. This over stretching occurs very locally at the alveolar level. For this reason we want to mechanically investigate the deformations in the alveolar tissue. A key point in this study is to understand the relationship between local and global deformations ie. what local strains occur in the wall as a result of global deformation. Alternative experimental methods have major drawbacks as the deformation state can only be determined two dimensionally or for a cluster of alveoli. The present work represents the first of its kind performing a simulation on a realistic three dimensional geometry. The advantage of the simulation is that we can get three dimensional information. Hence it is expected that the results here provide detail insight into the local structural behavior of alveoli. For our geometries we are utilizing µCT scans of living rat lung slices. These scans have a resolution of higher than 1.4 µm. A parenchyma cube (300 µm x 300 µm x 300 µm) is segmented with Amira(Mercury) and meshed with tetrahedral elements utilizing Harpoon (Shark). The geometries have around 5 million degrees of freedom. Preliminary simulations of a uniaxial stretched cube have shown that a global deformation of 10% already induces strains of up to 40% in the alveolar walls. Consequently, resolving the realistic alveolar morphology is crucial when investigating local over stretching of lung tissue in the case of VILI.