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Vascular access is a lifeline for hemodialysis patients. Its lifetime is affected by many hemodynamic factors such as pressure, flow regime and wall shear stress. During hemodialysis, changes in hemodynamic parameters occur due to the flow from needles inserted into the vascular system. Primarily, there is a change in shear stress that affects the vascular wall. Pathological effects of high or low WSS are known. The effect of jet from a venous needle on hemodynamics parameters was studied, but the influence of the arterial needle on hemodynamics parameters is not sufficiently studied. To understand its possible effects, we performed in vivo and in vitro studies. Methods. In vivo experiment: The existence of flow reversal around the suction needle was visualized in a group of 12 randomly selected patients using ultrasound velocity profiling (Doppler ultrasonography) during hemodialysis. In vitro experiment: The flow field was measured using the stereo particle image velocimetry method (stereo PIV). Two regimes were studied. In the first regime, the fluid in the extracorporeal circuit was pumped by a peristaltic pump. In the second regime, the continuous pump was used in the extracorporeal circuit. The conditions were set to resemble those in vascular access during a hemodialysis session. Flow volume was set to 600 mL/min for vascular access and 200 mL/min for the extracorporeal circuit. Results. The main finding of this study was that the wall in the region of the arterial needle was stressed by backflow through the arterial needle. Since this was a variable, low-shear stress loading, it was one of the risk factors for the development of stenosis. Cyclic flow reversal was apparent in all of the included hemodialysis patients. The stereo PIV in vitro experiment revealed the oscillating character of wall shear stress (WSS) inside the model. High shear stress was documented upstream of the injection point of the arterial needle. An area of very low WSS was detected right behind the injection point during a pulse of the peristaltic pump. The minimal and maximal values of the WSS during a pulse of the peristaltic pump in the observed area were −0.7 Pa and 6 Pa, respectively. The distribution of wall shear stress with the continual pump used in the extracorporeal circuit was similar to the distribution during a pulse of the peristaltic one. However, the WSS values were continual, the WSS did not oscillate. WSS ranged between 4.8 Pa and 1.0 Pa.

In our work, we focused on measuring the performance characteristics of a test hydrogen fuel cell with an open cathode. The aim of the work was to verify the effect of the mass flow through the fuel cell on the power output as a function of the current density and voltage on the fuel cell. A test bench capable of testing fuel cells up to 2000 W was used to measure the power characteristics. The test fuel cell was composed of three cells and its total membrane area was 100 cm2. A PIV measurement system was used to measure the mass flow. The mass flow measurement was performed at the inlet of the fuel cell. The measurements included the determination of the inlet temperature distribution using a thermal imaging camera. The presented measurements were performed for two configurations with original and optimized diffuser at the inlet of the fans. Finally, the effect of mass flow and overall thermal management on the fuel cell performance is discussed, including the effect of the newly designed diffuser.

Measurement of velocity fields by PIV method is often limited by the scale of the measured model. This is doubly true for the stereo PIV method. Problems of measurement in small (but still macroscopic) scales are associated with optical distortions in the optical path of the camera. Additionally, there is a calibration problem for stereo PIV. Therefore, this paper is devoted to the description of PIV methodology for measurement in small geometrical scales. The idealized transparent model of hemodialysis vascular access was used in this paper. This model had realistic vascular access dimensions (6 mm in diameter). A special working blood-mimicking fluid (BMF) was mixed with a refractive index matching that of the model. The refraction and distortion of light passing through the interface between the model and the fluid was so small, that it was possible to calibrate the stereo PIV outside the measured model. The accuracy of this calibration is discussed and verified by measuring the velocity field on a straight section of the vascular access model for laminar flow.

The aim of present work is focused on determining accuracy of the measurement using the Particle Image Velocimetry based on an analysis of synthetic Uniform flow test and Couette flow test. We focused on testing the Standard Cross Correlation algorithm and interdependence between the several metrics based on the ratio signal and noise peak and the measurement accuracy at each point. This work is describing the influence of the new corrected metric that is corrected by a displacement measured in the last iteration, detected mean density of the particles and the velocity gradient. Newly proposed method of calculating the metric, Lost of Particle Ratio, is based on the determination of the magnitudes of two correlation peaks. In this work there is defined and compared another metric based on the result of synthetics data test which is based on determination of main parameters as number of particles, gradient in interrogation area and displacement of particles calculated in the last step of correlation. For all presented metrics the relationship is between the metrics and the accuracy.

The aim of this paper was to test a newly designed algorithm for more accurate calculation of the image displacement of seeding particles when taking measurement using the Particle Image Velocimetry method. The proposed algorithm is based on modification of a classical iterative approach using a three-point subpixel interpolation and method using relative deformation of individual areas for accurate detection of signal peak position. The first part briefly describes the tested algorithm together with the results of the performed synthetic tests. The other part describes the measurement setup and the overall layout of the experiment. Subsequently, a comparison of results of the classical iterative scheme and our designed algorithm is carried out. The conclusion discusses the benefits of the tested algorithm, its advantages and disadvantages.

Vascular stenosis is often described only by its percentage in both clinical and scientific praxis. Previous studies gave inconclusive results regarding the effect of stenosis eccentricity on its hemodynamic effect. The aim of this experimental study was to investigate and quantify the effect of stenosis severity and eccentricity on the pressure drop. A combination of pressure and flow measurements by Particle Imaging Velocimetry (PIV) method was used. Models of the same stenosis significance but with different levels of eccentricity were studied in vitro by PIV. This study has shown that stenosis asymmetry is associated with more profound pressure drop and flow volume decrease. On the contrary, pressure drop and flow volume decrease were not further significantly influenced by the level of asymmetry. Hemodynamic changes associated with stenosis eccentricity must be taken into account in both clinical and scientific studies.

The paper describes the flow measurement in an aneurysm model by PIV (Particle Image Velocimetry) and PLIF (Planar Laser Induced Fluorescence) method. The velocity field and the concentration were determined for four steady and one unsteady flow regimes.The area of the main flow and the area of liquid circulation in the region of the bulge were defined on the basis of velocity field measurement. Mean concentration of dye was evaluated in three areas: the entry to the model, the bulge of aneurysm and the outlet of the model. Concentration in course of time and residence time of dye are discussed on the dependance of unsteady flow.

A stenosis is a narrowing in a tubular organ. In medicine, vessel stenosis poses health risk for people. In the last work, experimental investigation of pressure loss coefficient for varying stenosis eccentricity and shape for steady flow were performed. In this work, experimental investigation of pressure loss for varying stenosis eccentricity and shape under periodic flow were performed. Four models of different geometry were studied, two models are axisymmetric stenoses and two models are eccentric stenoses. All models were stenosis of 75% area reduction. The periodic flow, generated by a controllable pump, has sinus shape in an inlet. The measuring range of medium Reynolds number was from 500 to 1500, range of ratio between an amplitude and medium flow rate was from 0.2 to 0.6 and range of frequency was from 0.2 to 1 Hz. The pressure loss for each conditions was quantified by mean value, amplitude and phase shift against flow rate.

The paper deals with the experimental findings of pressure losses across a pair of stenoses depending on their distance. Pressure loss coefficient of one of stenosis was determined. Pressure loss coefficient of double stenosis was determined afterwards for different distances of stenoses. The paper shows region where stenoses are affected and where are not. Overall loss coefficient is lower than the sum of two coefficients of one stenosis in region where stenoses are affected. Pressure loss coefficient of double stenosis is equal to the sum of two stenosis, in case of its longer distance.

A stenosis is a narrowing in a tubular organ or structure. In medicine, vessel stenosis poses health risks for people. In this work, experimental investigations of pressure loss coefficient for varying stenosis eccentricity and shape were performed. Five models of different geometry were studied; all models were stenosis of 75 % area reduction. The flow conditions approximate physiological flow. The measuring range of Reynolds number was from 130 to 2730, measured values of pressure loss coefficient were from 12 to 20. The steady experimental results indicated that static pressure loss coefficient is affected by the shape of stenosis, but it was affected more significantly by the eccentricity. Visualization experiments have been performed in Polycarbonate models.

Stenosis is the most frequent vascular access complication and is responsible for access thrombosis and thus long-term patency limitation. Regular arteriovenous graft (AVG) examination by ultrasonography and preemptive balloon angioplasty prolong AVG cumulative patency according to some, but by far not all trials. This was why the routine use of ultrasound surveillance is not recommended recently.In this review we show huge differences in the definition of stenosis significance among the trials and other probable factors, which may have caused the contradiction of the results. Without precise definition of stenosis significance, many AVGs have been undergoing unnecessary balloon interventions with high morbidity, high cost and low benefit.

Influenza A virus is an important cause of acute respiratory infections (ARI). Clinical manifestations of ARI vary from mild or moderate to life-threatening conditions requiring intensive care. Given the segmented genome, a large natural reservoir of other influenza virus subtypes, and antibody selection pressure in the population, the virus is variable and genetically unstable. The phylogenetic analysis and genotyping of A/H3N2 influenza viruses isolated from patients hospitalised with influenza-like illness symptoms in the Na Bulovce Hospital in the season 2011/2012 support the assumption that the pathogenicity is a polygenic trait modifiable by the host health status and seems not to be unambiguously associated with any specific mutations.

Es wurde die Oxydation des N,N,N',N'-Tetramethylbenzidins und Malachitgrüns mit dem Diphosphatkomplex des dreiwertigen Mangans untersucht. Wie festgestellt wurde, entsteht in beiden Fällen Diphenochinon-(4,4')-bis-dimethylimin, das einer witeren Oxydation nicht unterliegt. Diese Reaktion kann zur indirekten Bestimmung beider Substanzen, die auf deren Oxydation mit Reagensüberschuß und auf der Absorbanzmessung beruht, herangezogen werden, wobei die Absorbanzmessung dem entstehenden Diphenochinon-(4,4')-bis-dimethylimin entspricht. Es wurden die Korrektheit und Reproduzierbarkeit dieser Methode bei der Bestimmung des Malachitgrüngehaltes in der praktischen Probe bestätigt.

The paper presents results of experimental investigation of steady flow in the region of common carotid artery (CCA). The CCA bifurcates into two branches: into internal carotid artery (ICA) and external carotid artery (ECA). ICA, that supplies blood to the brain is enlarged. This region is referred as the carotid sinus. In the present study, three models of the carotid artery bifurcation have been manufactured. The models vary in geometry of the carotid sinus. Their effect on fluid flow has been investigated under steady flow condition, utilizing Particle Image Velocimetry (PIV) and flow visualization. The flow conditions approximate physiological flow. The measuring range of Reynolds number was from 400 to 1300. Experimental results indicated the effect of carotid sinus geometry on the main flow in common carotid artery.