Rudolf Huebner

Blood flow in hemodialysis catheters: a numerical simulation and microscopic analysis of in vivo-formed fibrin.

Although catheters with side holes allow high flow rate during hemodialysis, they also induce flow disturbances and create a critical hemodynamic environment that can favor fibrin deposition and thrombus formation. This study compared the blood flow and analyzed the influence of shear stress and shear rate in fibrin deposition and thrombus formation in nontunneled hemodialysis catheters with unobstructed side holes (unobstructed device) or with some side holes obstructed by blood thrombi (obstructed device). Computational fluid dynamics (CFD) was performed to simulate realistic blood flow under laminar and turbulent conditions. The results from the numerical simulations were compared with the fibrin distribution and thrombus architecture data obtained from scanning electron microscopy (SEM) and two photons laser scanning microscopy (TPLSM) on human thrombus formed in catheters removed from patients. CFD showed that regions of flow eddies and separation were mainly found in the venous holes region. TPLSM characterization of thrombi and fibrin structure in patient samples showed fibrin formations in accordance with simulated flux dynamics. Under laminar flow conditions, the wall shear stress close to border holes increased from 87.3±0.2 Pa in the unobstructed device to 176.2±0.5 Pa in the obstructed one. Under turbulent flow conditions, the shear stress increased by 47% when comparing the obstructed to the unobstructed catheter. The shear rates were generally higher than 5000/s and therefore sufficient to induce fibrin deposition. This findings were supported by SEM data documenting a preferential fibrin arrangement on side hole walls.

Hemodialysis catheter thrombi: visualization and quantification of microstructures and cellular composition

Purpose Despite the increasing use of central venous catheters (CVC) for hemodialysis in clinical practice, the role of CVC in thrombus development is poorly understood. This work aims at defining new methods and protocols for assessing the micromorphology and composition of thrombi formed into tunneled and non-tunneled hemodialysis CVC removed from patients. Methods Twenty-nine CVCs were collected and the microscopic features of intra-luminal thrombi were quantified by scanning electron microscopy (SEM) and visualized by two photon laser scanning microscopy (TPLSM). Results SEM quantification showed that fibrin was the most abundant structure in CVC thrombi. Specifically, the median micromorphologic composition of the surface layer resulted in: 42.6% of fibrin plaque, 16.3% of fibrin network, 0.4% of fibrin fibers, 9.3% of platelets, 10.3% of erythrocytes and 1.7% of white blood cells. TPLSM showed that sub-surface layers were instead composed by smaller amounts of fibrin and platelets and higher amounts of blood cells. Conclusions Integration of SEM and TPLSM was found to be an excellent tool for characterizing thrombi in hemodialysis CVC removed from patients. Protocols and techniques presented here may be useful in the development and testing of new strategies for limiting thrombus formation on vascular access because of CVC.

Vibration measurement on artificial heart valve by laser Doppler vibrometry

The use of artificial heart valves is more and more diffused in the medical practice in particular in Europe and US where the average age of the people is continuously increasing. In the engineering point of view they present several problems that can be faced by a deep knowledge of the behaviour in operative conditions. Such problems are mainly related to the compatibility with the patient body and the reliability of the valve itself, and both are related to the possibility of a continuative and extended application in real cases. The compatibility is mainly related to the material choice and to the fluid-dynamic behaviour. The reliability can be basically improved by a smart and simplified design of each component, which imposes a really intensive evaluation of the response to operative inputs. Fatigue is one of the most important effects related to reliability. A mechanical valve is subjected to fluid-dynamics forces and repeatable shocks. due the impact on the constraints, which create dangerous vibrations. The analysis of such vibrations by SLDV[1][2] in both free and operative conditions is the main task of the present work. In this paper an experimental and numerical analysis of the vibrational behaviour of a mono-leaflet valve was performed in order to extract useful information on the optimised design. An in vitro test, simulating operative conditions, was performed in order to verify the real behaviour of the valve.

Determination of a quantitative parameter to evaluate swimming technique based on the maximal tethered swimming test

Abstract The aim of this study was to propose a new force parameter, associated with swimmers’ technique and performance. Twelve swimmers performed five repetitions of 25 m sprint crawl and a tethered swimming test with maximal effort. The parameters calculated were: the mean swimming velocity for crawl sprint, the mean propulsive force of the tethered swimming test as well as an oscillation parameter calculated from force fluctuation. The oscillation parameter evaluates the force variation around the mean force during the tethered test as a measure of swimming technique. Two parameters showed significant correlations with swimming velocity: the mean force during the tethered swimming (r = 0.85) and the product of the mean force square root and the oscillation (r = 0.86). However, the intercept coefficient was significantly different from zero only for the mean force, suggesting that although the correlation coefficient of the parameters was similar, part of the mean velocity magnitude that was not associated with the mean force was associated with the product of the mean force square root and the oscillation. Thus, force fluctuation during tethered swimming can be used as a quantitative index of swimmers’ technique.

Quantification of fibrin in blood thrombi formed in hemodialysis central venous catheters: a pilot study on 43 CVCs.

Purpose Fibrin deposition and thrombotic occlusion represent a serious cause of access dysfunction in hemodialysis central venous catheters (CVCs). The aim of this work was to define and apply a method for imaging and quantifying fibrin in thrombi formed into the side holes of CVCs. Methods Forty-three CVCs removed from a cohort of dialyzed patients were analyzed in this pilot study. Hematoxylin and eosin and a modified Carstairs staining were applied on permanent thrombus sections. Fluorescence microscopy and image analysis were performed to quantify the fibrin amount. Results Highly fluorescent areas were invariably associated with fibrin by Carstairs method. The deposition of concentric layers of fibrin and erythrocytes was easily identified by fluorescence microscopy, showing growth features of the thrombus. Fibrin amount in diabetic patients was significantly higher than that in nondiabetic patients with median (interquartile range) values of 51% (47-68%) and 44% (30-54%), respectively (p=0.032). No significant difference in fibrin content was found by grouping data according to catheter type, permanence time, insertion site and dialysis vintage. Higher variability in fibrin values was found in thrombi from CVCs removed after 1-15 days compared with 16-60 days. A trend of an increase in fibrin amount in thrombi was noted according to blood platelet count at CVC insertion. Conclusions The analytical method presented here proved to be a rapid and effective way for quantifying fibrin content in thrombi formed on CVCs with potential application in future clinical studies.

Numerical Analysis of the Piston Crown Geometry Influence on the Tumble and Squish in a Single Cylinder Engine

The objective of this paper is to simulate the air flow (cold run) inside a single cylinder research engine for different geometries of the piston crown and investigate the influence of them on the Tumble coefficient and Squish. The study was conducted through the software star-CD, with the module esice (Expert System – Internal Combustion Engine) and simulations of the air flow with the flat piston were carried out at the first time. Once the simulation methodology was created according to its correlation with the experimental results, the geometry of the piston crown is changed and other numerical simulations are performed. Thereby, with the comparison between the obtained results for different geometries, the air flow inside the combustion chamber can be characterized, and the effects of the geometry changing on the Tumble coefficient, Squish and other flow parameters verified.

Numerical Modeling of Flow into Primary Dedusting System of a 130t Converter

In this work an analysis of gases’ behavior into primary dedusting system of basic oxygen furnace (BOF) converter was developed. The methodology involves Computational Fluid Dynamics (CFD) to simulate velocity, temperature of gases in combustion for multi-phases systems including solid particles. The influence of the air in the flow, analysis of temperature and gas along the dedusting system and the influence in cooling pipes was investigated. Numerical data were validated with real values of the process. The next step was the implementation of changes in the geometry of the ducts in order to find a more stable situation for the equipment. The best result was obtained by increasing the diameter and smoothing the geometries in curves.

Development of esthetic prosthesis for a patient with severe stigmatizing facial lesions due to cancer: a pilot study

PurposeSevere physical facial deformities due to surgical interventions can have significant psychosocial consequences to patient’s relationships with friends and family and thus, has a considerable impact on their quality of life. We have developed a 3D prosthesis for a 56-year-old woman diagnosed with epidermoid carcinoma at the right hemiface, to improve her quality of life.MethodsThe patient started radiotherapy with modulated intensity. To deal with the advance of the process, a maxilectomy of supra structure with modified radical cervical emptying on the right hemiface was performed. Reconstruction of areas surgically affected by the displacement of islands of skin and muscle (flaps) from healthy regions was initiated. Although the procedure occurred without intercurrences, the patient developed necrosis and loss of the myocutaneous flap. After the removal of the flap, the esthetic result of the treatment was evident causing exposure of subcutaneous and granulation tissues.ResultsA computational model was used to develop a 3D structure of the affected area and then used to construct the prosthesis. The prosthesis was applied over the affected area, and the patient was able see her face on the mirror for the first time in years. The patient was grateful and hopeful.ConclusionWe have found that the application of this new technology greatly improves the social interaction of patients with deformities due to surgical interventions.

Indirect sinusoidal vibrations induces an acute increase in explosive strength

The purpose of this study was to examine the acute effect of indirect vibration on neuromuscular responses and fatigue resistance (electromyographic activity - EMG and force) during isometric exercise. Nineteen healthy men (age=22.4±2.7years; body mass=76.4±12.9kg, height=175±6.7cm) performed isometric elbow flexion exercises in three experimental treatments: only isometric exercise (control - CON); isometric exercise with the addition of sinusoidal vibrations (SVE1; frequency=20Hz, displacement=3.55±0.54mm); and isometric exercise with the addition of sinusoidal vibrations with frequency variation (SVE2; frequency=20±3Hz, displacement=3.6±0.8mm). The peak of the rate of EMG rise (RER) and the root mean square of biceps brachii during the first 200ms (RMS200bic) were significantly higher in SVE1 (RMS200bic, 25.57±11.70%MVC; RER, 266.91±130.16%MVCs-1) than CON (RMS200bic, 19.31±8.19%MVC; RER, 169.15±65.98%MVCs-1). Regarding force, in SVE1, compared to CON, significant increases were observed in peak of rate of force development (CON, 643.96±192.57N/s; SVE1, 845.54±292.84N/s), rate of force development in the first 200ms (CON, 382.92±138,63N/s; SVE1, 501.09±147.46N/s), and impulse in 200ms (CON, 8.56±3.56Ns; SVE1, 11.67±4.45Ns). The addition of indirect sinusoidal vibrations during exercise induced increases in the rate of force development (explosive strength), without affecting the peak force (maximal strength) and the ability to sustain strength production.

Computational Fluid Dynamics Simulation of Steel Bars Cooling by Free Convection and Thermal Radiation

In this article, the pilling process of hot steel bars is analyzed. During the loading three bars are placed over a wood surface, after those other three are placed over the previous for two times with 5 minutes intervals between them.They are all subject to a slow cooling by thermal radiation and free convection.A Computational Fluid Dynamics (CFD) model to predict the temperature profile of them is developed. Comparison between the CFD simulation results and experimental data yielded an average difference in the bars temperature between -0.3oC and 3.5oC.