Colonization of in-dwelling catheters by microbial biofilms is a major concern in patient health eventually leading to catheter-related blood stream infections. Biofilms are less susceptible to ...standard antibiotic therapies that are effective against planktonic bacteria. Standard procedure for the detection of microorganisms on the catheter tip is culture. However, viable but non-culturable cells (VBNCs) may be missed. The aim of this study was to evaluate the use of fluorescence in situ hybridization (FISH) as an indicator to visualize and quantify the effect of the antibiotics daptomycin and vancomycin on biofilms in situ. We established an in vitro catheter biofilm model of Staphylococcus epidermidis biofilms on polyurethane catheters. Biofilm activity was measured by FISH and correlated to colony forming units (CFU) data. Digital image analysis was used for quantification of total biofilm mass and the area of the FISH positive biofilm cells. FISH showed a pronounced effect of both antibiotics on the biofilms, with daptomycin having a significantly stronger effect in terms of both reduction of biofilm mass and number of FISH-positive cells. This supports the anti-biofilm capacity of daptomycin. Interestingly, neither antibiotic was able to eradicate all of the FISH-positive cells. In summary, FISH succeeded in visualization, quantification, and localization of antibiotic activity on biofilms. This technique adds a new tool to the arsenal of test systems for anti-biofilm compounds. FISH is a valuable complementary technique to CFU since it can be highly standardized and provides information on biofilm architecture and quantity and localization of survivor cells.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Aortic coarctation (CoA) accounting for 3–11% of congenital heart disease can be successfully treated. Long-term results, however, have revealed decreased life expectancy associated with abnormal ...hemodynamics. Accordingly, an assessment of hemodynamics is the key factor in treatment decisions and successful long-term results. In this study, 3D angiography whole heart (3DWH) and 4D phase-contrast magnetic resonance imaging (MRI) data were acquired. Geometries of the thoracic aorta with CoAs were reconstructed using ZIB-Amira software. X-ray angiograms were used to evaluate the post-treatment geometry. Computational fluid dynamics models in three patients were created to simulate pre- and post-treatment situations using the FLUENT program. The aim of the study was to investigate the impact of the inlet velocity profile (plug vs. MRI-based) with a focus on the peak systole pressure gradient and wall shear stress (WSS). Results show that helical flow at the aorta inlet can significantly affect the assessment of pressure drop and WSS. Simplified plug inlet velocity profiles significantly (
p
< 0.05) overestimate the pressure drop in pre- and post-treatment geometries and significantly (
p
< 0.05) underestimate surface-averaged WSS. We conclude that the use of the physiologically correct but time-expensive 4D MRI-based
in vivo
velocity profile in CFD studies may be an important step towards a patient-specific analysis of CoA hemodynamics.
Haemodynamics and morphology play an important role in the genesis, growth and rupture of cerebral aneurysms. The goal of this study was to generate and analyse statistical wall shear stress (WSS) ...distributions and shapes in middle cerebral artery (MCA) saccular aneurysms. Unsteady flow was simulated in seven ruptured and 15 unruptured MCA aneurysms. In order to compare these results, all geometries must be brought in a uniform coordinate system. For this, aneurysms with corresponding WSS data were transformed into a uniform spherical shape; then, all geometries were uniformly aligned in three-dimensional space. Subsequently, we compared statistical WSS maps and surfaces of ruptured and unruptured aneurysms. No significant (p > 0.05) differences exist between ruptured and unruptured aneurysms regarding radius and mean WSS. In unruptured aneurysms, statistical WSS map relates regions with high (greater than 3 Pa) WSS to the neck region. In ruptured aneurysms, additional areas with high WSS contiguous to regions of low (less than 1 Pa) WSS are found in the dome region. In ruptured aneurysms, we found significantly lower WSS. The averaged aneurysm surface of unruptured aneurysms is round shaped, whereas the averaged surface of ruptured cases is multi-lobular. Our results confirm the hypothesis of low WSS and irregular shape as the essential rupture risk parameters.
Investigations of ventricular flow patterns during mechanical circulatory support are limited to
in vitro
flow models or
in silico
simulations, which cannot fully replicate the complex anatomy and ...contraction of the heart. Therefore, the feasibility of using echocardiographic particle image velocimetry (Echo-PIV) was evaluated in an isolated working heart setup. Porcine hearts were connected to an isolated, working heart setup and a left ventricular assist device (LVAD) was implanted. During different levels of LVAD support (unsupported, partial support, full support), microbubbles were injected and echocardiographic images were acquired. Iterative PIV algorithms were applied to calculate flow fields. The isolated heart setup allowed different hemodynamic situations. In the unsupported heart, diastolic intra-ventricular blood flow was redirected at the heart’s apex towards the left ventricular outflow tract (LVOT). With increasing pump speed, large vortex formation was suppressed, and blood flow from the mitral valve directly entered the pump cannula. The maximum velocities in the LVOT were significantly reduced with increasing support. For the first time, cardiac blood flow patterns during LVAD support were visualized and quantified in an
ex vivo
model using Echo-PIV. The results reveal potential regions of stagnation in the LVOT and, in future the methods might be also used in clinical routine to evaluate intraventricular flow fields during LVAD support.
Pressure drop associated with coarctation of the aorta (CoA) can be successfully treated surgically or by stent placement. However, a decreased life expectancy associated with altered aortic ...hemodynamics was found in long-term studies. Image-based computational fluid dynamics (CFD) is intended to support particular diagnoses, to help in choosing between treatment options, and to improve performance of treatment procedures. This study aimed to prove the ability of CFD to improve aortic hemodynamics in CoA patients. In 13 patients (6 males, 7 females; mean age 25 ± 14 years), we compared pre- and post-treatment peak systole hemodynamics pressure drops and wall shear stress (WSS) vs. virtual treatment as proposed by biomedical engineers. Anatomy and flow data for CFD were based on MRI and angiography. Segmentation, geometry reconstruction and virtual treatment geometry were performed using the software ZIBAmira, whereas peak systole flow conditions were simulated with the software ANSYS
®
Fluent
®
. Virtual treatment significantly reduced pressure drop compared to post-treatment values by a mean of 2.8 ± 3.15 mmHg, which significantly reduced mean WSS by 3.8 Pa. Thus, CFD has the potential to improve post-treatment hemodynamics associated with poor long-term prognosis of patients with coarctation of the aorta. MRI-based CFD has a huge potential to allow the slight reduction of post-treatment pressure drop, which causes significant improvement (reduction) of the WSS at the stenosis segment.
Abstract Background Local wall shear stress (WSS) has an impact on local remodelling of the vessel wall. WSS in turn strongly depends on local geometry. Our aim was to characterize patterns of local ...wall shear stress associated with distinct types of remodelling in coronary arteries. Vessel size and flow rates are different between patients, however. To compare distribution patterns of WSS in analogy to fluid-dynamic modelling, non-dimensional WSS/area functions are calculated. Methods Right coronary arteries from seven controls, five patients with coronary artery disease (CAD) and five patients with aneurysmatic CAD (AnCAD) were analyzed. Flow simulations were performed in three-dimensionally reconstructed coronary vessels from biplane angiographic projections. Local WSS was normalized as percentage of maximum value in a histogram (100 classes) and corresponding area was expressed as percentage of total area. Results The normalized WSS distribution was characterized by a single peak with a large lower tie in controls, a loss of the single peak and a stochastic distribution in AnCAD and a narrowing of the lower tie in CAD. Correct classification of 16/17 coronary arteries was feasible by Fisher's discriminant functions based on median WSS, mean diameter, percentage of area with WSS ≤ 0.4 Pa and with WSS ≥ 15 Pa. Conclusion Normalized WSS distribution might be an efficient tool in comparing wall shear stress between different patient groups. Whether normalized WSS distribution curves are apt to grade severity of disease remains to be investigated.
Objectives: Hypertension is a common condition that greatly increases the risk of developing cardiovascular disease. Non-invasive blood pressure measurements are the most important tool for the ...timely detection of hypertension. Current standard methods rely on the use of an upper arm cuff. However, these devices cannot be used for patients with amputated or malformed upper extremities. To address this problem, an alternative method of determining blood pressure at the cheek has been developed. Methods: A photoplethysmogram (PPG) of the facial artery is measured via a mouthpiece to detect blood volume changes. The photodiodes are located in the oral cavity and the pressure pad with photodetectors is located on the outside of the cheek. During the measurement, the pressure pad is inflated to 200 mmHg to ensure the collapse of the artery, and then slowly deflated. The pressure in the pressure pad correlates with the systolic blood pressure during the deflation phase. The transmission of light through the facial artery correlates with the blood volume inside the artery and is recorded in parallel. The systolic blood pressure is determined by means of an algorithm that iteratively calculates sigmoid fits. The resulting systolic pressure is fed to a pre-trained neural network. A cuffed oscillometric device served as the reference method. Results: A dataset comprised of 52 measurements was used for the evaluation of the method. The average error of the proposed method is 4.06 mmHg with a standard deviation of 3.75 mmHg. The systolic blood pressure of the subjects ranges from 100 – 150 mmHg. Conclusions: Although the accuracy is within the normative requirement of 5 ± 8 mmHg, the significance of the results cannot be shown due to the lack of data set size.
Objectives: The broad use of rotary blood pumps is limited by its induced blood damage, which leads to a high number of adverse events. Most of the blood damage is generated in the gap between the ...rotor blades and the housing wall, the area with the highest stress load and very short exposure times. The damage is caused by both shear and normal forces on the blood components. The objective is to investigate the blood damage in this region by examining different gap geometries. The focus is the damage caused by high dynamic normal stresses and the comparison with the blood damage models. Methods: To measure the influence of highly dynamic normal and shear stresses on hemolysis, this study performed experiments with human whole blood in three different shaped microchannels representing three flow scenarios. The test setup allows a high number of stress loads with low hemolysis beside the microchannels. For the level and duration of the applied stress loads, parameters of typical critical areas of rotational blood pumps were used as a basis. In addition, flow simulations were performed to capture the flow fields and various stress-based hemolysis models were applied to estimate the hemolysis. Results: We measured hemolysis in the physiological range for unphysiological shear stresses up to 2000 Pa, normal stresses up to 1176 Pa with exposure times in the range of milliseconds and up to 1200 stress load repetitions. The hemolysis was independent of the geometry of the microchannel and of the same order of magnitude as the reference channel. The applied models estimated higher hemolysis levels and significant differences between the microchannels. Conclusions: The results suggest that short-term, highly dynamic stresses play a smaller role in hemolysis than assumed by the applied stress-based models.
Flow fields are one of the key factors associated with the life threatening formation of thrombi in artificial organs. Therefore, knowledge of flow field is crucial for the design and optimization of ...a long-term blood pump performance. The blood chamber flow of a novel counterpulsation heart assist device (CPD) has been investigated using laser Doppler velocimetry (LDV), particle image velocimetry (PIV), and near-wall PIV (wall-PIV). The wall-PIV is an in-house developed technique assessing wall shear rates (WSR). These experimental techniques analyzed complex transient three-dimensional (3D) flow fields including major and secondary structures during the whole CPD cycle (ejection, filling, and hold time). PIV measurements in the central plane investigated an evolution (development and destruction) of the blood chamber fully filling vortex as the major CPD flow structure. The wall-PIV measurements identified areas of blood stagnation (vortex center and jet impingements) and quantified WSR at the front housing. Maximal mean WSR of 2,045 ± 605 s
−1
were found at the end of the filling. The LDV, which identified helical flow structure at the outer region of the pump, was used to complete 3D flow analysis and to combine PIV and wall-PIV results. The results suggest good washing behavior of the CPD regarding thrombus formation.
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