Physiologically realistic results are the aim of every blood flow simulation. This is not different in aorto-coronary bypasses where the properties of the coronary circulation may significantly affect the relevance of the performed simulations. By considering three patient-specific bypass geometries, the present article focuses on two aspects of the coronary blood flow - its phasic flow pattern and its behaviour affected by blood rheology. For the phasic flow property, a multiscale modelling approach is chosen as a means to assess the ability of five different types of coronary boundary conditions (mean arterial pressure, Windkessel model and three lumped parameter models) to attain realistic coronary haemodynamics. From the analysed variants of boundary conditions, the best option in terms of physiological characteristics and its potential for use in patient-based simulations, is utilised to account for the effect of shear-dependent viscosity on the resulting haemodynamics and wall shear stress stimulation. Aside from the Newtonian model, the blood rheology is approximated by two non-Newtonian models in order to determine whether the choice of a viscosity model is important in simulations involving coronary circulation. A comprehensive analysis of obtained results demonstrated notable superiority of all lumped parameter models, especially in comparison to the constant outlet pressure, which regardless of bypass type gave overestimated and physiologically misleading results. In terms of rheology, it was noted that blood in undamaged coronary arteries behaves as a Newtonian fluid, whereas in vessels with atypical lumen geometry, such as that of anastomosis or stenosis, its shear-thinning behaviour should not be ignored.
BACKGROUND: In clinical medicine, little is known about the use of allografts for portal vein (PV) reconstruction after pancreaticoduodenectomy (PD). Portal and caval systems are physiologically different, therefore the properties of allografts from caval and portal systems were studied here in a pig model. MATERIALS AND METHODS: PD with PV reconstruction with allogeneic venous graft from PV or inferior vena cava (IVC) was performed in 26 pigs. Biochemical analysis and ultrasonography measurements were performed during a 4-week monitoring period. Computer simulations were used to evaluate haemodynamics in reconstructed PV and explanted allografts were histologically examined. RESULTS: The native PV and IVC grafts varied in histological structure but were able to adapt morphologically after transplantation. Computer simulation suggested PV grafts to be more susceptible to thrombosis development. Thrombosis of reconstructed PV occurred in four out of five cases in PV group. CONCLUSION: This study supports the use of allografts from caval system for PV reconstruction in clinical medicine when needed.
- MeSH
- alografty MeSH
- anastomóza chirurgická metody MeSH
- hemodynamika MeSH
- léčba šetřící orgány MeSH
- mrtvola MeSH
- odběr tkání a orgánů MeSH
- pankreatoduodenektomie * MeSH
- počítačová simulace * MeSH
- pooperační komplikace etiologie MeSH
- prasata MeSH
- pylorus MeSH
- regionální krevní průtok MeSH
- ultrasonografie MeSH
- velikost orgánu MeSH
- vena cava inferior anatomie a histologie diagnostické zobrazování fyziologie transplantace MeSH
- vena portae anatomie a histologie diagnostické zobrazování fyziologie chirurgie MeSH
- zákroky plastické chirurgie metody MeSH
- žilní trombóza etiologie MeSH
- zvířata MeSH
- Check Tag
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- srovnávací studie MeSH
The paper deals with modeling the liver perfusion intended to improve quantitative analysis of the tissue scans provided by the contrast-enhanced computed tomography (CT). For this purpose, we developed a model of dynamic transport of the contrast fluid through the hierarchies of the perfusion trees. Conceptually, computed time-space distributions of the so-called tissue density can be compared with the measured data obtained from CT; such a modeling feedback can be used for model parameter identification. The blood flow is characterized at several scales for which different models are used. Flows in upper hierarchies represented by larger branching vessels are described using simple 1D models based on the Bernoulli equation extended by correction terms to respect the local pressure losses. To describe flows in smaller vessels and in the tissue parenchyma, we propose a 3D continuum model of porous medium defined in terms of hierarchically matched compartments characterized by hydraulic permeabilities. The 1D models corresponding to the portal and hepatic veins are coupled with the 3D model through point sources, or sinks. The contrast fluid saturation is governed by transport equations adapted for the 1D and 3D flow models. The complex perfusion model has been implemented using the finite element and finite volume methods. We report numerical examples computed for anatomically relevant geometries of the liver organ and of the principal vascular trees. The simulated tissue density corresponding to the CT examination output reflects a pathology modeled as a localized permeability deficiency.
- MeSH
- analýza metodou konečných prvků MeSH
- biologické modely MeSH
- jaterní oběh * fyziologie MeSH
- játra krevní zásobení diagnostické zobrazování MeSH
- kontrastní látky farmakokinetika MeSH
- lidé MeSH
- matematické pojmy MeSH
- počítačová rentgenová tomografie statistika a číselné údaje MeSH
- počítačová simulace MeSH
- poréznost MeSH
- vylepšení rentgenového snímku metody MeSH
- zobrazování trojrozměrné statistika a číselné údaje MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
1st edition 541 stran : ilustrace (převážně barevné), portréty, tabulky ; 24 cm
- Konspekt
- Ortopedie. Chirurgie. Oftalmologie
- NLK Obory
- chirurgie
- experimentální medicína
- NLK Publikační typ
- kolektivní monografie
