Damian Obidowski

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.

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.

Comparison of Numerical Simulations and Ultrasonography Measurements of the Blood Flow through Vertebral Arteries

Vertebral arteries are a system of two blood vessels through which blood is carried to the rear region of the brain. This region of the human body has to be very well supplied with blood. Blood is delivered to the brain through carotid arteries as well. Due to their position and shape, vertebral arteries are a special kind of blood vessels. They have their origin at a various distance from the aortic ostium, can branch off at different angles, and have various lengths, inner diameters and spatial shapes. The above-mentioned variations are connected with inter-patient differences in the human anatomy. In the upper part of vertebral arteries, there is a marked arch curvature, owing to which turning the head is not followed by obliteration of these vessels. Contrary to other arteries, vertebral arteries join at their ends to form one vessel, a comparatively large basilar artery. This junction can be characterized by a varied geometry as well. For individual geometrical configurations of the vertebral artery system, there are also differences in the diameter of the left and right artery. All the abovementioned differences result from a unique individual anatomical structure and do not follow from any pathology (Daseler & Anson 1959; Jozwik & Obidowski 2008; Jozwik & Obidowski 2010). Some symptoms occurring in patients may suggest that the cause of an ailment lies in an incorrect blood supply to the rear region of the brain, and thus in an incorrect blood flow through vertebral arteries. The direct cause of such a phenomenon can result from arterial occlusion. The ultrasonography is employed to check the flow correctness. It is rather difficult to conduct this imaging procedure, but if it is performed by an experienced specialist, then the results obtained can be considered reliable. It happens, however, that the measured values of the maximum and minimum velocity in the left and right artery, which characterize the blood flow, differ significantly. Hence, the diagnosis of arteriosclerosis in these vessels is well based. It can be an indication for a surgical procedure (Mysior 2006). A significantly large percentage of cases diagnosed in such a way are not related to changes in the artery structure, and thus surgery would be irrelevant. If a structure and a shape of vertebral arteries, their individual variations are considered, then differences in the blood flow and a lack of relation between these differences and artery diameters can result from flow phenomena only.

A differential planetary gear for regulation drive design and selected tests

Radial fans with efficiency regulation during their work using variational geometry of the rotor have not been used in industries until now, despite the fact that this is the most economically effective regulation method. One of the causes for this was the lack of a convenient method of transferring drive to moving blades of the fan. This paper presents an innovative method of transferring drive on the blades using a differential planetary gear. The construction is described, and a strength calculation methodology and tests confirming correctness of work are shown as well. The presented solution can become a new standard in the construction of energy fans.

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.

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.