Numerical flow experiment for assessing predictors for cerebrovascular accidents in patients with PHACES syndrome.

There is an increased risk of cerebrovascular accidents (CVA) in individuals with PHACES, yet the precise causes are not well understood. In this analysis, we aimed to examine the role of arteriopathy in PHACES syndrome as a potential contributor to CVA. We analyzed clinical and radiological data from 282 patients with suspected PHACES syndrome. We analyzed clinical features, including the presence of infantile hemangioma and radiological features based on magnetic resonance angiography or computed tomography angiography, in individuals with PHACES syndrome according to the Garzon criteria. To analyze intravascular blood flow, we conducted a simulation based on the Fluid-Structure Interaction (FSI) method, utilizing radiological data. The collected data underwent statistical analysis. Twenty patients with PHACES syndrome were included. CVAs were noted in 6 cases. Hypoplasia (p = 0.03), severe tortuosity (p < 0.01), absence of at least one main cerebral artery (p < 0.01), and presence of persistent arteries (p = 0.01) were associated with CVAs, with severe tortuosity being the strongest predictor. The in-silico analysis showed that the combination of hypoplasia and severe tortuosity resulted in a strongly thrombogenic environment. Severe tortuosity, combined with hypoplasia, is sufficient to create a hemodynamic environment conducive to thrombus formation and should be considered high-risk for cerebrovascular accidents (CVAs) in PHACES patients.

A two-stage model of an arteriovenous fistula maturation process.

PURPOSE: An arteriovenous fistula has been a widely accepted vascular access for hemodialysis, however, a fistula maturation process is still not fully understood. In the short period of time, right after vein and artery shunting, the physical and biological changes take place mainly in the venous wall. A two-stage modeling method of arteriovenous fistula maturation process was proposed and presented. METHODS: The first stage of the maturation was modeled with two-way coupled fluid structure interaction computer simulations. Whereas for the second, biological stage, a model was based on the change in the elasticity of the venous wall due to wall shear stress (WSS) modifications. RESULTS: The relation between stress and radial and circumferential strain, based on Lame's theory, makes possible to introduce a mathematical model defining modulus of elasticity, averaged WSS, and venous diameter as time functions. The presented model enables one to predict changes in the monitored parameters in the arteriovenous fistula taking place in the time longer than 90 days. CONCLUSIONS: We found that probably the majority of fistulas can be assessed to be mature too early, when the adequate blood flow rate is achieved but mean WSS still remains at the non-physiological level (>10 Pa).

Inhaled drug airflow patterns and particles deposition in the paediatric respiratory tract.

PURPOSE: The effectiveness of inhaled drugs is strictly related to areas reachable by drug particles. Unless particles reach the desired part of the bronchial tree, their influence might not meet the expectations. Consequently, the disease progress might not be stopped or even slowed down. Therefore, the primary objective of this research was to analyze the airflow patterns and particle deposition of a standard inhaled drug using computational fluid dynamics. METHODS: The study was devoted to the analysis of the particle diameter influence on their deposition areas within the entire respiratory tract. Two patient-specific respiratory tract models, for 6 and 12-year-old patients, were reconstructed based on the computed tomography examinations. Numerical analyses were carried out as stationary ones with the constant inflow of the particles of various diameters (within the range of 1-50 µm). It was proven that depending on the particle size, their deposition within the respiratory tract varies significantly. RESULTS: The vast majority of the particles with diameters over 20 µm is gathered on the walls of the throat, whereas particles of diameters 5-15 µm are accumulated mainly on the trachea walls, leaving the alveoli insufficiently supplied with the drug particles. CONCLUSIONS: The inhaled drug size cannot be treated as negligible factor during the drug spraying. An improper distribution of the particles might not inhibit the symptoms of the asthma. Numerical simulations may improve drugs selection and visualize their distribution along the airways, which might accelerate asthma treatment personalization.

Methods for determination of stagnation in pneumatic ventricular assist devices.

BACKGROUND: A pneumatic paediatric ventricular assist device developed at the Foundation of Cardiac Surgery Development, Zabrze, equipped with valves based on J. Moll's design, with later modifications introduced at the Institute of Turbomachinery, Lodz University of Technology, was tested numerically and experimentally. The main aim of those investigations was to detect stagnation zones within the ventricular assist device and indicate advantages and limitations of both approaches. METHODS: In the numerical transient test, a motion of the diaphragm and discs was simulated. Two different methods were used to illustrate stagnation zones in the ventricular assist device. The flow pattern inside the chamber was represented by velocity contours and vectors to validate the results using images obtained in the laser particle image velocimetry experiment. RESULTS: The experimental light-based method implied problems with proper illumination of regions in the wall vicinity. High-resolution flow data and other important parameters as stagnation regions or flow patterns in regions not accessible for light in the particle image velocimetry method are derived in the numerical solution. However, computations of a single case are much more time-consuming if compared to a single experiment conducted on a well-calibrated stand. CONCLUSION: The resulting main vortexes in the central part of the pump chamber and the velocity magnitudes are correlated in both methods, which are complementary and when used together offer better insight into the flow structure inside the ventricular assist device and enable a deeper analysis of the results.

Experimental investigations of the aerated polymethylmethacrylate-based vertebral cement flow in capillaries.

INTRODUCTION: A constant growth in the population suffering from osteoporotic vertebral weakening is observed. As a result, vertebroplasty procedures become more and more common. Unfortunately, they may be associated with several complications occurring during bone cement injection, including its leakage or overheating of tissues. Despite several experimental studies, there is a lack of data related to random aeration of the bone cement. Therefore, the main objective of the following investigations was to emphasize that random aeration of the bone cement, and, consequently, a compressibility factor, could not be treated as a negligible factor during the vertebroplasty procedure and had to be taken into account in the development of the mathematical model. MATERIALS AND METHODS: A special test rig to reproduce the vertebroplasty procedure was designed and built. The authors conducted numerous experiments on polymethylmethacrylate-based bone cement flows, analyzing different flow conditions, such as volume flow rate and flow channel diameter. Time periods of the flow front between characteristic sections and pressures (differential and gauge) were measured. RESULTS: All investigations revealed that bone cements mixed in special mixing kits were characterized by a random level of aeration which led to varied flow parameters. Comparing the experimental results with the theoretical values of the continuity equation, the highest difference in the flow duration reached 140%. DISCUSSION: It has been proven that the aeration of the bone cement alters the flow dynamics. Therefore, much more data are required for statistical analysis to validate a mathematical model of the bone cement flow.

Particle image velocimetry tests on pediatric 45-cc and 30-cc ventricle assist devices: effects of heart rate on VAD operation.

BACKGROUND: This study investigated flow analysis inside pediatric ventricle assist devices (VADs) designed and manufactured at the Foundation for Cardiac Surgery Development (FRK), Zabrze, Poland. The main goal of the experiment was to define the minimal heart rate admissible in clinical practice. METHODS: The flow was directed by mechanical, single-disc valves developed at the Lodz University of Technology, Institute of Turbomachinery in Lodz, Poland. VAD operation conditions under different heart rates were analyzed. Measurements were performed on Religa PED pediatric VADs (45 cm3 and 30 cm3) with a particle image velocimetry (PIV) system. RESULTS: Due to the PIV method used, the measurements were made without interference of the measuring system onto the flow structure in the investigated channel, as the measurement procedure is noninvasive. During the investigations conducted in different measurement planes, the majority of the flow volume in the chamber was observable. CONCLUSIONS: The measurements at different heart rates demonstrated a significant influence of this parameter on the flow nature in the heart ventricle. Additionally, it was found that the heart rate affected the operation of heart valves in the VAD.

Numerical investigations of the unsteady blood flow in the end-to-side arteriovenous fistula for hemodialysis.

PURPOSE: The aim of this study was to investigate the blood flow in the end-to-side arteriovenous (a-v) fistula, taking into account its pulsating nature and the patient-specific geometry of blood vessels. Computational Fluid Dynamics (CFD) methods were used for this analysis. METHODS: DICOM images of the fistula, obtained from the angio-computed tomography, were a source of the data applied to develop a 3D geometrical model of the fistula. The model was meshed, then the ANSYS CFX v. 15.0 code was used to perform simulations of the flow in the vessels under analysis. Mesh independence tests were conducted. The non-Newtonian rheological model of blood and the Shear Stress Transport model of turbulence were employed. Blood vessel walls were assumed to be rigid. RESULTS: Flow patterns, velocity fields, the volume flow rate, the wall shear stress (WSS) propagation on particular blood vessel walls were shown versus time. The maximal value of the blood velocity was identified in the anastomosis - the place where the artery is connected to the vein. The flow rate was calculated for all veins receiving blood. CONCLUSIONS: The blood flow in the geometrically complicated a-v fistula was simulated. The values and oscillations of the WSS are the largest in the anastomosis, much lower in the artery and the lowest in the cephalic vein. A strong influence of the mesh on the results concerning the maximal and area-averaged WSS was shown. The relation between simulations of the pulsating and stationary flow under time-averaged flow conditions was presented.

Simulations of the blood flow in the arterio-venous fistula for haemodialysis.

The Ciminio-Brescia arterio-venous fistula is a preferred vascular access for haemodialysis, but it is often associated with the development of vascular complications, due to changes in hemodynamic conditions. Computational fluid dynamics methods were involved to carry out seven simulations of the blood flow through the fistula for the patient specific (geometrical) case and various boundary conditions. The geometrical data, obtained from the angio-computed tomography, were used to create a 3-dimensional CAD model of the fistula. The blood flow patterns, blood velocity and the wall shear stress, thought to play a key role in the development of typical complications (stenoses, thromboses, aneurysms, etc.), have been analyzed in this study. The blood flow is reversed locally downstream the anastomosis (where the artery is connected to the vein) and downstream the stenosis in the cannulated vein. Blood velocity reaches abnormal value in the anastomosis during the systolic phase of the cardiac cycle (2.66 m/s). The wall shear stress changes in this place during a single cycle of the heart operation from 27.9 to 71.3 Pa (average 41.5 Pa). The results are compared with data found in the literature.

Numerical simulations of the blood flow in the patient-specific arterial cerebral circle region.

The Cerebral Circle Region, also known as the Circle of Willis (CoW), is a loop of arteries that form arterial connections between supply arteries to distribute blood throughout the cerebral mass. Among the population, only 25% to 50% have a complete system of arteries forming the CoW. 3D time-varying simulations for three different patient-specific artery anatomies of CoW were performed in order to gain a better insight into the phenomena existing in the cerebral blood flow. The models reconstructed on the basis of computer tomography images start from the aorta and include the largest arteries that supply the CoW and the arteries of CoW. Velocity values measured during the ultrasound examination have been compared with the results of simulations. It is shown that the flow in the right anterior artery in some cases may be supplied from the left internal carotid artery via the anterior communicating artery. The investigations conducted show that the computational fluid dynamic tool, which provides high resolution in both time and space domains, can be used to support physicians in diagnosing patients of different ages and various anatomical arterial structures.

Numerical simulations of the blood flow through vertebral arteries.

Vertebral arteries are two arteries whose structure and location in human body result in development of special flow conditions. For some of the arteries, one can observe a significant difference between flow rates in the left and the right arteries during ultrasonography diagnosis. Usually the reason of such a difference was connected with pathology of the artery in which a smaller flow rate was detected. Simulations of the flow through the selected type of the vertebral artery geometry for twenty five cases of artery diameters have been carried out. The main aim of the presented experiment was to visualize the flow in the region of vertebral arteries junction in the origin of the basilar artery. It is extremely difficult to examine this part of human circulation system, thus numerical experiments may be helpful in understanding the phenomena occurring when two relatively large arteries join together to form one vessel. The obtained results have shown that an individual configuration and diameters of particular arteries can exert an influence on the flow in them and affect a significant difference between flow rates for vertebral arteries. It has been assumed in the investigations that modelled arteries were absolutely normal, without any pathology. In the numerical experiment, the non-Newtonian model of blood was employed.