The Effects of Micro-vessel Curvature Induced Elongational Flows on Platelet Adhesion

The emerging profile of blood flow and the cross-sectional distribution of blood cells have far reaching biological consequences in various diseases and vital internal processes, such as platelet adhesion. The effects of several essential blood flow parameters, such as red blood cell free layer width, wall shear rate, and hematocrit on platelet adhesion were previously explored to great lengths in straight geometries. In the current work, the effects of channel curvature on cellular blood flow are investigated by simulating the accurate cellular movement and interaction of red blood cells and platelets in a half-arc channel for multiple wall shear rate and hematocrit values. The results show significant differences in the emerging shear rate values and distributions between the inner and outer arc of the channel curve, while the cell distributions remain predominantly uninfluenced. The simulation predictions are also compared to experimental platelet adhesion in a similar curved geometry. The inner side of the arc shows elevated platelet adhesion intensity at high wall shear rate, which correlates with increased shear rate and shear rate gradient sites in the simulation. Furthermore, since the platelet availability for binding seems uninfluenced by the curvature, these effects might influence the binding mechanics rather than the probability. The presence of elongational flows is detected in the simulations and the link to increased platelet adhesion is discussed in the experimental results.

A novel multiple subdivision-based algorithm for quantitative assessment of retinal vascular tortuosity

Vascular tortuosity as an indicator of retinal vascular morphological changes can be quantitatively analyzed and used as a biomarker for the early diagnosis of relevant disease such as diabetes. While various methods have been proposed to evaluate retinal vascular tortuosity, the main obstacle limiting their clinical application is the poor consistency compared with the experts’ evaluation. In this research, we proposed to apply a multiple subdivision-based algorithm for the vessel segment vascular tortuosity analysis combining with a learning curve function of vessel curvature inflection point number, emphasizing the human assessment nature focusing not only global but also on local vascular features. Our algorithm achieved high correlation coefficients of 0.931 for arteries and 0.925 for veins compared with clinical grading of extracted retinal vessels. For the prognostic performance against experts’ prediction in retinal fundus images from diabetic patients, the area under the receiver operating characteristic curve reached 0.968, indicating a good consistency with experts’ predication in full retinal vascular network evaluation.

Performance of the Gore VBX Balloon Expandable Endoprosthesis as Bridging Stent-Graft in Branched Endovascular Aortic Repair for Thoracoabdominal Aneurysms

Purpose Bridging stent stability is crucial for efficacy and safety of branched aortic endovascular repair (bEVAR) of thoracoabdominal aortic aneurysms (TAAAs). In this study, we assess the performance of the new Viabahn Balloon-Expandable endoprosthesis (VBX) in bEVAR. Based on our learning curve we give recommendations for a safe and effective use of the device. Materials and Methods We prospectively collected the data of patients with TAAAs undergoing bEVAR between December 2017 and December 2019. All patients with implantation of at least 1 VBX stent-graft as bridging stent were included in our single-center analysis. Demographic, comorbidity, and computed tomography angiography (CTA) data of 112 patients were retrospectively evaluated. Primary endpoint was a composite of branch-related technical success and freedom from target vessel instability. Secondary endpoints were clinical and ongoing clinical success. Results Primary endpoint: technical success was achieved in all patients (100%) with a freedom from target vessel instability of 96.3% after a median follow-up of 18 months. Overall mortality was 13.4% (n=15) and 13 patients underwent secondary interventions, 12 of them are still alive and 1 suffered from aneurysm sac expansion, consequently an ongoing clinical success of 75.9% was reached. After modification of the implantation technique during the course of the study by selecting longer stent lengths after accurate estimation of vessel curvature and expected adaptation of the flexible endoskeleton to the specific anatomical conditions, no type Ic endoleaks were observed in the last 70 cases. Conclusions The VBX stent-graft can be safely used as bridging stent for branched thoracoabdominal repair. However, learning curve should be considered to avoid type Ic endoleak and edge stenosis. Based on this experience longer landing zones and 2-step deployment of VBX are useful for successful bridging also of challenging target vessels.

How does vessel curvature influence drug release from DES and drug transport in arterial tissue?

Several computational models of transport of drugs eluted from drug-eluting stents (DES) in curved arteries were developed in order to investigate the influence of the arterial curvature and complex geometries on drug transport in the blood flow and in the arterial wall.

Modified Curvature-based Trigonometric Identities for Retinal Blood Vessel Tortuosity Measurement in Diabetic Retinopathy Fundus Images

In current clinical practice, there is no specific standard and grading system that can be used to measure the behaviour of the retinal blood vessel curvature. The retinal blood vessel curvature is measured based on clinical experiences. It is very subjective and inconsistent to describe the presence of tortuosity in fundus images. Thus, this paper aims to measure the tortuosity of retinal blood vessel using curvature-based method and investigate its relationship with diabetic retinopathy (DR) disease. The proposed tortuosity measures have been tested on 43 fundus images belonging to patients who have been diagnosed with DR disease and validated by two clinical experts from our collaborative hospital. On average, the proposed algorithm achieved 90.7% (accuracy), 98.72% (sensitivity) and 9.3% (false negative rate), that shows significant tortuosity presence in diabetic retinopathy fundus images.

A Test of Steady State Erosion Models

Here we ask the question: how well is the erosion of particle beds in vessels with curved bottoms at industrial scale flow rates represented by models of radial wall jets traversing flat surfaces using the critical shear stress for erosion from the Shields diagram? This mathematical construction has been used successfully to predict the functional forms for the extent of erosion with time using two dimensionless fitting parameters (Pease, et al., 2017). However, the direct prediction of the curves without fitting and scaling has not been tested quantitatively. Here we evaluate the radial wall jet models of Poreh, et al., (1967) and Rajaratnam (1976) and the expressions for the Shields diagram by Paphitis (2001) and Cao, Pender, and Meng (2006). The use of two models for each element accounts for uncertainty in model selection. The data selected to benchmark these models was obtained in a geometrically scaled version of an industrial scale mixing vessel with 12 jets arrayed in a double ring configuration (Meyer, et al., 2012). These particular jets were operated continuously with observations at steady-state, providing a direct comparison between the long-time erosion fronts and these proposed long-time solutions (i.e., where the applied shear stress equals the critical shear stress for erosion) without interference from transients or parameters that affect transients (e.g., the particle bed thickness). We find experimentally that the extent of the erosion depends significantly on the vessel curvature. Even so, we also find that all of these formulations significantly over predict the extent of erosion observed experimentally. A discussion of model features that may be modified to revise the theory into quantitative agreement is presented.

Modeling Jet Erosion of Particle Beds

Here we present and benchmark an analytical model to describe the radial extent of erosion of settled particle beds by radial wall jets as a function of time. The extent of erosion is an essential measure of the performance of vessels mixed by arrays of radial wall jets because portions of vessel floors not cleared of settled particles may accumulate undesirable constituents. We derive a model of the cleared radius as a function of time scaled so that fits may be described using only two free parameters. We find remarkably good agreement between experimental data and the model upon fitting. Extracted fitting parameters are shown to be reasonable. The influence of nozzle transience on erosion transience has also been evaluated. We find that nozzle transience explains the initially slower rate of erosion and decreases the final extent of erosion by one to three nozzle diameters for the cases considered. Future work remains to evaluate the dimensionless groups from conservation laws and account for vessel curvature.