Pro fyziologické proudění vzduchu nosní dutinou a bezproblémové nosní dýchání je důležitý nízký odpor a převážně laminární charakter proudění s minimem turbulencí. Patologické stavy (např. deviace/perforace nosní přepážky) způsobují zvýraznění turbulencí s nárůstem nosního odporu, který je pacienty vnímán jako nosní neprůchodnost. Nosní neprůchodnost negativně ovlivňuje každodenní aktivity pacientů a zhoršuje kvalitu života. Ke studiu nosní aerodynamiky jsou využívány mechanické či kadaverózní modely nosu, nebo je proudění vzduchu nosem studováno pomocí počítačového modelování tzv. CFD (computational fluid dynamics). CFD je v současnosti dominantní metodou ke studiu nosního proudění, využívá vytvoření 3D počítačového modelu nosní dutiny dle CT vyšetření. Narůstající znalosti nosního proudění mají potenciál využití v klinické praxi, především v rinochirurgii - přesnější zacílení operační léčby pacientů s nosní neprůchodností a hodnocení efektivity operací.

The physiological nasal airflow with low resistance and low level of turbulences is necessary for normal nasal breathing. Pathological conditions (e.g. septal deviation/perforation) cause elevation of nasal resistance that patients feel like nasal obstruction. The nasal obstruction worsens quality of life. There are some possibilities how to simulate and study nasal airflow - mechanic models or computational fluid dynamics (CFD). Nowadays, CFD is dominant method for simulating nasal airflow. There is a potential to apply aerodynamic information to clinical rhinology and rhinosurgery.

• Klíčová slova
• proudění vzduchu nosem, laminární proudění, turbulentní proudění,
• MeSH
• konvekce * MeSH
• lidé MeSH
• nos * fyziologie   patologie   MeSH
• perforace nosní přepážky patofyziologie   MeSH
• počítačová simulace MeSH
• pohyb vzduchu MeSH
• získané deformity nosu patofyziologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• práce podpořená grantem MeSH
• přehledy MeSH

Úvod: Charakter nosního proudění je zásadní pro bezproblémové nosní dýchání, stejně jako může být patofyziologickým podkladem symptomů nosních onemocnění (nosní neprůchodnost, sekrece, tvorba krust aj.). Je obtížné definovat jeden fyziologický charakter proudění, protože subjektivní potíže nemocných často nejsou v korelaci s objektivním nálezem. Pozornost je proto věnována studiu nosní aerodynamiky, pro které je v současnosti nejvíce využíváno počítačové modelování proudění, tzv. computational fluid dynamics (CFD). Metodika: Pro simulaci nosního proudění byl ve spolupráci s Vysokou školou báňskou (VŠB) vytvořen 3D model dle CT vyšetření nosní dutiny pacientky, která neměla potíže s nosním dýcháním ("fyziologická" nosní dutina). Výsledky: Dle získaných výsledků se liší proudění vzduchu v pravé a levé nosní dutině. Hlavní proud vzduchu lze pozorovat jak v dolním a dolní části společného průduchu, tak i ve středním a střední části společného průduchu. První výsledky se shodují se studiemi uvádějícími značné rozdíly v nosní aerodynamice mezi zdravými jedinci. Závěr: Počítačové modelování proudění vzduchu má potenciál být využíváno v klinické praxi, především ve funkční rinochirurgii.

Introduction: The pattern of the nasal airflow is crucial for normal nasal breathing as well as it can be a pathophysiological underlay of nasal symptoms (nasal obstruction, crusting etc). It is difficult to define one physiological airflow pattern because subjective symptoms of patients do not correlate with objective findings quite often. Nowadays, the computational fluid dynamics (CFD) is dominant way how to simulate and study nasal airflow. Methods: For nasal airflow simulation 3D model of nasal cavity was created according to CT scans of nasal cavity (patient had no problems with nasal breathing). The 3D model was created with the cooperation with Technical University of Ostrava. Results: Our first experience with CFD showed that there is a different airflow pattern between right and left nasal cavity. Major part of airflow was detected in inferior and inferior part of common meatus and also in the middle and in the middle part of common nasal meatus. These results support studies that declare differences in nasal aerodynamics among healthy adults. Conclusion: CFD has a potential to be used in clinical practice especially in functional rhinosurgery.

• Klíčová slova
• nosní proudění,
• MeSH
• konvekce MeSH
• lidé MeSH
• nos * fyziologie   MeSH
• počítačová simulace * MeSH
• zobrazování trojrozměrné MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• práce podpořená grantem MeSH

Numerous models of human lungs with various levels of idealization have been reported in the literature; consequently, results acquired using these models are difficult to compare to in vivo measurements. We have developed a set of model components based on realistic geometries, which permits the analysis of the effects of subsequent model simplification. A realistic digital upper airway geometry except for the lack of an oral cavity has been created which proved suitable both for computational fluid dynamics (CFD) simulations and for the fabrication of physical models. Subsequently, an oral cavity was added to the tracheobronchial geometry. The airway geometry including the oral cavity was adjusted to enable fabrication of a semi-realistic model. Five physical models were created based on these three digital geometries. Two optically transparent models, one with and one without the oral cavity, were constructed for flow velocity measurements, two realistic segmented models, one with and one without the oral cavity, were constructed for particle deposition measurements, and a semi-realistic model with glass cylindrical airways was developed for optical measurements of flow velocity and in situ particle size measurements. One-dimensional phase doppler anemometry measurements were made and compared to the CFD calculations for this model and good agreement was obtained.

• MeSH
• biologické modely MeSH
• lidé MeSH
• mechanika dýchání fyziologie   MeSH
• plíce fyziologie   MeSH
• počítačová simulace MeSH
• ústa fyziologie   MeSH
• výměna plynů v plicích fyziologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

In this article, the results of numerical simulations using computational fluid dynamics (CFD) and a comparison with experiments performed with phase Doppler anemometry are presented. The simulations and experiments were conducted in a realistic model of the human airways, which comprised the throat, trachea and tracheobronchial tree up to the fourth generation. A full inspiration/expiration breathing cycle was used with tidal volumes 0.5 and 1 L, which correspond to a sedentary regime and deep breath, respectively. The length of the entire breathing cycle was 4 s, with inspiration and expiration each lasting 2 s. As a boundary condition for the CFD simulations, experimentally obtained flow rate distribution in 10 terminal airways was used with zero pressure resistance at the throat inlet. CCM+ CFD code (Adapco) was used with an SST k-ω low-Reynolds Number RANS model. The total number of polyhedral control volumes was 2.6 million with a time step of 0.001 s. Comparisons were made at several points in eight cross sections selected according to experiments in the trachea and the left and right bronchi. The results agree well with experiments involving the oscillation (temporal relocation) of flow structures in the majority of the cross sections and individual local positions. Velocity field simulation in several cross sections shows a very unstable flow field, which originates in the tracheal laryngeal jet and propagates far downstream with the formation of separation zones in both left and right airways. The RANS simulation agrees with the experiments in almost all the cross sections and shows unstable local flow structures and a quantitatively acceptable solution for the time-averaged flow field.

• MeSH
• biologické modely * MeSH
• biomechanika MeSH
• bronchy fyziologie   MeSH
• časové faktory MeSH
• dýchání * MeSH
• lidé MeSH
• numerická analýza pomocí počítače * MeSH
• plicní ventilace fyziologie   MeSH
• trachea fyziologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• srovnávací studie MeSH

Roste počet jedinců s náhodně diagnostikovanou mozkovou výdutí, jejíž prasknutí vede k nejtěžší formě cévní mozkové příhody. Metoda počítačového modelování hemodynamiky se snaží popsat patofyziologii a riziko ruptury mozkové výdutě. V našem projektu chceme využít modely hemodynamiky kalkulované na základě neinvazivních radiodiagnostických metod a pomocí vlastního algoritmu vyvinutého v Matematickém ústavu Univerzity Karlovy. Hlavním cílem projektu je u pacientů operovaných pro mozkovou výduť, prasklou i neprasklou, popsat parametry hemodynamiky a tyto korelovat s histologickými změnami cévní stěny vaku aneuryzmatu. Dalším cílem je u skupiny sledovaných neprasklých aneuryzmat, která jsou vedena v multicentrické databázi sdílené několika neurochirurgickými pracovišti v ČR, popsat vývoj hemodynamických parametrů v čase a porovnat s výsledky hemodynamiky prasklých aneuryzmat. Projekt pomáhá vytvářet multioborovou platformu s mezinárodní spoluprácí pro výzkum hemodynamiky mozkových aneuryzmat.; The number of patients incidentally diagnosed for a brain aneurysm, the rupture of which may lead to the most severe type of stroke, is increasing. Modelling hemodynamics in brain aneurysms tries to describe pathophysiology and the risk of rupture of intracranial aneurysms. In our project we will assess models of hemodynamics based non-invasive radiodiagnostic methods and an in-house mathematical algorithm developed at the Mathematical Institute of the Charles University. The main goal of the project is to correlate parameters of hemodynamics with histological changes of the blood vessels wall of the aneurysm sac in patients operated for ruptured as well as unruptured intracranial aneurysms. Another goal of the project is to evaluate hemodynamics in followed unruptured aneurysms from our multicenter database shared among several neurosurgical centers in the Czech Republic and compare with hemodynamic parameters in ruptured aneurysms. The project will help building a multi-modal platform for studying CFD in brain aneurysms with international cooperation.

• MeSH
• cévy patologie   MeSH
• hemodynamika MeSH
• intrakraniální aneurysma komplikace   patofyziologie   MeSH
• lidé MeSH
• počítačová simulace MeSH
• prasklé aneurysma etiologie   patofyziologie   patologie   MeSH
• rizikové faktory kardiovaskulárních chorob MeSH
• Check Tag
• lidé MeSH

• Konspekt
• Patologie. Klinická medicína
• NLK Obory
• neurologie
• angiologie
• NLK Publikační typ
• závěrečné zprávy o řešení grantu AZV MZ ČR

A microfluidic cell capture device was designed, fabricated, evaluated by numerical simulations and validated experimentally. The cell capture device was designed with a minimal footprint compartment comprising internal micropillars with the goal to obtain a compact, integrated bioanalytical system. The design of the device was accomplished by computational fluid dynamics (CFD) simulations. Various microdevice designs were rapidly prototyped in poly-dimethylsiloxane using conventional soft lithograpy technique applying micropatterned SU-8 epoxy based negative photoresist as moulding replica. The numerically modeled flow characteristics of the cell capture device were experimentally validated by tracing and microscopic recording the flow trajectories using yeast cells. Finally, we give some perspectives on how CFD modeling can be used in the early stage of microfluidics-based cell capture device development.

• MeSH
• design vybavení MeSH
• hydrodynamika MeSH
• mikrofluidika přístrojové vybavení   MeSH
• Saccharomyces cerevisiae chemie   MeSH
• výpočetní biologie přístrojové vybavení   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Passage of nasal airflow during breathing is crucial in achieving accurate diagnosis and optimal therapy for patients with nasal disorders. Computational fluid dynamics (CFD) is the dominant method for simulating and studying airflow. The present study aimed to create a CFD nasal airflow model to determine the major routes of airflow through the nasal cavity and thus help with individualization of surgical treatment of nasal disorders. The three-dimensional nasal cavity model was based on computed tomography scans of the nasal cavity of an adult patient without nasal breathing problems. The model showed the main routes of airflow in the inferior meatus and inferior part of the common meatus, but also surprisingly in the middle meatus and in the middle part of the common nasal meatus. It indicates that the lower meatus and the lower part of the common meatus should not be the only consideration in case of surgery for nasal obstruction in our patient. CFD surgical planning could enable individualized precise surgical treatment of nasal disorders. It could be beneficial mainly in challenging cases such as patients with persistent nasal obstruction after surgery, patients with empty nose syndrome, and patients with a significant discrepancy between the clinical findings and subjective complaints.

• Publikační typ
• časopisecké články MeSH

The aeroacoustic mechanisms in human voice production are complex coupled processes that are still not fully understood. In this article, a hybrid numerical approach to analyzing sound generation in human voice production is presented. First, the fluid flow problem is solved using a parallel finite-volume computational fluid dynamics (CFD) solver on a fine computational mesh covering the larynx. The CFD simulations are run for four geometrical configurations: both with and without false vocal folds, and with fixed convergent or convergent-divergent motion of the medial vocal fold surface. Then the aeroacoustic sources and propagation of sound waves are calculated using Lighthill's analogy or acoustic perturbation equations on a coarse mesh covering the larynx, vocal tract, and radiation region near the mouth. Aeroacoustic sound sources are investigated in the time and frequency domains to determine their precise origin and correlation with the flow field. The problem of acoustic wave propagation from the larynx and vocal tract into the free field is solved using the finite-element method. Two different vocal-tract shapes are considered and modeled according to MRI vocal-tract data of the vowels /i/ and /u/. The spectra of the radiated sound evaluated from acoustic simulations show good agreement with formant frequencies known from human subjects.

• MeSH
• akustika * MeSH
• hlas * MeSH
• hlasové řasy fyziologie   MeSH
• larynx fyziologie   MeSH
• lidé MeSH
• vzduch * MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

OBJECTIVE: The accuracy of phase-contrast magnetic resonance imaging (PC-MRI) measurement is investigated using a computational fluid dynamics (CFD) model with the objective to determine the magnitude of the flow underestimation due to turbulence behind a narrowed valve in a phantom experiment. MATERIALS AND METHODS: An acrylic stationary flow phantom is used with three insertable plates mimicking aortic valvular stenoses of varying degrees. Positive and negative horizontal fluxes are measured at equidistant slices using standard PC-MRI sequences by 1.5T and 3T systems. The CFD model is based on the 3D lattice Boltzmann method (LBM). The experimental and simulated data are compared using the Bland-Altman-derived limits of agreement. Based on the LBM results, the turbulence is quantified and confronted with the level of flow underestimation. RESULTS: LBM gives comparable results to PC-MRI for valves up to moderate stenosis on both field strengths. The flow magnitude through a severely stenotic valve was underestimated due to signal void in the regions of turbulent flow behind the valve, consistently with the level of quantified turbulence intensity. DISCUSSION: Flow measured by PC-MRI is affected by noise and turbulence. LBM can simulate turbulent flow efficiently and accurately, it has therefore the potential to improve clinical interpretation of PC-MRI.

• MeSH
• aortální chlopeň * MeSH
• aortální stenóza * MeSH
• fantomy radiodiagnostické MeSH
• lidé MeSH
• magnetická rezonanční tomografie MeSH
• rychlost toku krve MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH

BACKGROUND: Understanding the risk factors leading to intracranial aneurysm (IA) rupture have still not been fully clarified. They are vital for proper medical guidance of patients harboring unruptured IAs. Clarifying the hemodynamics associated with the point of rupture could help could provide useful information about some of the risk factors. Thus far, few studies have studied this issue with often diverging conclusions. METHODS: We identified a point of rupture in patients operated for an IAs during surgery, using a combination of preoperative computed tomography (CT) and computed tomography angiography (CTA). Hemodynamic parameters were calculated both for the aneurysm sac as a whole and the point of rupture. In two cases, the results of CFD were compared with those of the experiment using particle image velocimetry (PIV). RESULTS: We were able to identify 6 aneurysms with a well-demarcated point of rupture. In four aneurysms, the rupture point was near the vortex with low wall shear stress (WSS) and high oscillatory shear index (OSI). In one case, the rupture point was in the flow jet with high WSS. In the last case, the rupture point was in the significant bleb and no specific hemodynamic parameters were found. The CFD results were verified in the PIV part of the study. CONCLUSION: Our study shows that different hemodynamic scenarios are associated with the site of IA rupture. The numerical simulations were confirmed by laboratory models. This study further supports the hypothesis that various pathological pathways may lead to aneurysm wall damage resulting in its rupture.

• Publikační typ
• časopisecké články MeSH