Turbulent Blood Flow Research Articles

Role of local hemodynamic abnormalities at pathologic tortuosity of the carotid arteries in development of vascular cerebral insufficiency

Turbulence in blood flow in patients with pathological tortuosity of the internal carotid artery at a rate in excess of 1 m/s (Re > 1140), the occurrence of wall surface vortices and increase of blood flow rate by reducing the hydraulic diameter of the arteries result in the increased hemodynamic resistance of the vasculature and the brain hypoperfusion. Variety of forms and the complexity of the geometric configuration of arteries in their pathological tortuosity require an individual approach in determining the indications for surgical treatment and the choice of method of operation. The paper describes the objective biomechanical criteria based on instrumental clinical studies of hemodynamic disturbances and determining the pressure gradient in the areas of changing the geometry of blood vessels. The integrated use of anatomic and hemodynamic parameters allows us to estimate the energy losses and pressure gradients in pathological tortuosity of the internal carotid arteries in any geometric configuration. The extension of the proximal portion of the artery with respect to the pathological curvature was found which caused by the fact that the diameter of the mouth of the carotid artery with unilateral pathological tortuosity exceeds diameter of the mouth on the contralateral side. It was showed the occurrence of parietal swirl flow corresponds to a rate of 1.2 m/s and the total turbulence – at a speed of 1.4 m/s in the arteries with diameter of 4 mm. Flow rate at which a swirl flow is 0.8 m/s and a turbulent blood flow is recorded at a rate of 1 m/s by increasing the diameter of the carotid artery to 6 mm.

Cranial Accelerometry Can Detect Cerebral Vasospasm Caused by Subarachnoid Hemorrhage.

We previously reported the presence of a cranial "bruit" in patients with cerebral vasospasm by signal processing cranial accelerometry signals time locked to the cardiac cycle. This shift to higher frequencies is likely related to the turbulence of blood flow produced by vascular narrowing. We sought to build a more quantitative model to predict cerebral vasospasm then test the accuracy of this technique to detect cerebral vasospasm in a prospective blinded study. Skull accelerometry was performed using an array of 6 highly sensitive accelerometers placed in contact with the scalp. Paired transcranial Doppler (TCD) recordings and accelerometry epochs were obtained in consecutive patients with subarachnoid hemorrhage undergoing TCD recordings for surveillance of cerebral vasospasm. The energy of rectified acceleration measurements within systolic and diastolic bands of the cardiac cycle were measured and correlated with TCD-defined spasm. This model was then tested prospectively in a blinded consecutive sample of subarachnoid hemorrhage patients to determine accuracy of the technique. We developed a model predicting cerebral vasospasm from analysis of 14 unblinded subjects with varying degrees of cerebral vasospasm as detected by TCD. We then recorded from 58 subjects obtaining 125-paired recordings of accelerometry and TCD to test this model in a blinded analysis. Accelerometry detection of any spasm versus non-spasm correlated with TCD-defined vasospasm (P<0.001). The model was 81% sensitive for detecting any cerebral vasospasm in patients, while the negative predictive value was 61%. Highly sensitive skull accelerometry can detect cerebral vasospasm with clinically meaningful accuracy. This tool holds promise in the ICU environment to detect as well as reject cerebral vasospasm as the cause of neurological deficits in subarachnoid hemorrhage.

Prediction of adherent placenta in pregnancy with placenta previa using ultrasonography and magnetic resonance imaging

ObjectiveAdherent placenta is a life-threatening condition in pregnancy, and is often complicated by placenta previa. The aim of this prospective study was to determine prenatal imaging findings that predict the presence of adherent placenta in pregnancies with placenta previa. Study designThe study included 58 consecutive pregnant women with placenta previa who underwent both ultrasonography and magnetic resonance imaging prenatally. Ultrasonographic findings of anterior placental location, grade 2 or higher placental lacunae (PL≥G2), loss of retroplacental hypoechoic clear zone (LCZ) and the presence of turbulent blood flow in the arteries were evaluated, in addition to MRI findings. Forty-three women underwent cesarean section alone; 15 women with adherent placenta underwent cesarean section followed by hysterectomy with pathological examination. To determine imaging findings that predict adherent placenta, univariate and multivariate logistic regression analyses were performed. ResultsUnivariate logistic regression analyses demonstrated that anterior placental location, PL≥G2, LCZ, and MRI were associated with the presence of adherent placenta. Multivariate analyses revealed that LCZ (p<0.01, odds ratio 15.6, 95%CI 2.1–114.6) was a single significant predictor of adherent placenta in women with placenta previa. ConclusionThis prospective study demonstrated for the first time that US findings, especially LCZ, might be useful for identifying patients at high risk for adherent placenta among pregnant women with placenta previa.

Phase contrast flow imaging in Cardiac Magnetic Resonance (CMR): Imaging turbulent blood flow

Phase contrast flow imaging in Cardiac Magnetic Resonance (CMR): Imaging turbulent blood flow

Comparison of the strain field of abdominal aortic aneurysm measured by magnetic resonance imaging and stereovision: A feasibility study for prediction of the risk of rupture of aortic abdominal aneurysm

The prediction of the risk of rupture of abdominal aortic aneurysm (AAA) is a complex problem. Currently the criteria to predict rupture of abdominal aortic aneurysms are aneurysm diameter and growth rates. It is generally believed that study of the wall strain distribution could be helpful to find a better decision criterion for surgery of aortic aneurysms before their rupture. The wall strain distribution depends on many biological and biomechanical factors such as elastic properties of the aorta, turbulent blood flow, anatomy of the aorta, presence of thrombus or not and so on. Recently, numerical simulations to estimate rupture-potential have received many attentions. However, none of the medical imaging tools for screening and monitoring of AAAs were studied in terms of mechanical behavior and experimentally to demonstrate their capability to measure relevant variables. The aim of this study was to develop a metrological approach for deployment testing of the ability of techniques for measuring local in-vitro deformations based on comparison of stereovision and MRI. In this paper, we present the implementation approach and results of the study based on cylindrical phantoms with or without AAA representing, respectively, healthy and unhealthy artery. Through this study, an experimental device was developed for the behavior study of AAA during a cardiac cycle. The results show that the stereovision techniques used in laboratory is well suited and is qualitatively and quantitatively equivalent with MRI measurements.

Numerical Study of Turbulent Pulsatile Blood Flow through Stenosed Artery Using Fluid-Solid Interaction.

The turbulent pulsatile blood flow through stenosed arteries considering the elastic property of the wall is investigated numerically. During the numerical model validation both standard k-ε model and RNG K-ε model are used. Compared with the RNG K-ε model, the standard K-ε model shows better agreement with previous experimental results and is better able to show the reverse flow region. Also, compared with experimental data, the results show that, up to 70% stenosis, the flow is laminar and for 80% stenosis the flow becomes turbulent. Assuming laminar or turbulent flow and also rigid or elastic walls, the results are compared with each other. The investigation of time-averaged shear stress and the oscillatory shear index for 80% stenosis show that assuming laminar flow will cause more error than assuming a rigid wall. The results also show that, in turbulent flow compared with laminar flow, the importance of assuming a flexible artery wall is more than assuming a rigid artery wall.

Intracranial Lesions with Low Signal Intensity on T2-weighted MR Images - Review of Pathologies.

SummaryIn this article we presented intracranial pathological substances and lesions with low signal intensity on T2-weighted images. Eight groups of substances were discussed i.e. 1. Gadolinium-based contrast materials, 2. hemoglobin degradation products 3. melanin, 4. mucous- or protein-containing lesions, 5. highly cellular lesions, 6. lesions containing mineral substances such as: calcium, copper and iron, 7. turbulent and rapid blood or CSF flow 8. air-containing spaces. Appropriate interpretation of signal intensity as well as analysis of lesion location and clinical symptoms enable a correct choice of a further diagnostic algorithm or, in many cases, final diagnosis based exclusively on an MRI examination.

"To-and-fro" waveform in the diagnosis of arterial pseudoaneurysms.

Medical ultrasound imaging with Doppler plays an essential role in the diagnosis of vascular disease. This study intended to review the clinical use of "to-and-fro" waveform at duplex Doppler ultrasonography (DDU) in the diagnosis of pseudoaneurysms in the arterial vessels of upper and lower extremities, abdominal aorta, carotid and vertebral arteries as well as to review our personal experiences of "to-and-fro" waveform at DDU also. After receiving institutional review board approval, an inclusive literature review was carried out in order to review the scientific foundation of "to-and-fro" waveform at DDU and its clinical use in the diagnosis of pseudoaneurysms in various arterial vessels. Articles published in the English language between 2000 and 2013 were evaluated in this review study. Pseudoaneurysms in arterial vessels of the upper and lower extremities, abdominal aorta, carotid and vertebral arteries characterized by an extraluminal pattern of blood flow, which shows variable echogenicity, interval complexity, and "to-and-fro" flow pattern on color Doppler ultrasonography. In these arterial vessels, Duplex ultrasonography can demonstrate the degree of clotting, pseudoaneurysm communication, the blood flow patterns and velocities. Spectral Doppler applied to pseudoaneurysms lumen revealed systolic and diastolic turbulent blood flow with traditional "to-and-fro" waveform in the communicating channel. Accurate diagnosis of pseudoaneurysm by spectral Doppler is based on the documentation of the "to-and-fro" waveform. The size of pseudoaneurysm determines the appropriate treatment approach as surgical or conservative.

Grey-scale and colour Doppler ultrasound versus magnetic resonance imaging for the prenatal diagnosis of placenta accreta

Objective: To assess the effectiveness of grey-scale and colour Doppler ultrasound (US) versus magnetic resonance imaging (MRI) for the prenatal diagnosis of placenta accreta.Methods: A prospective observational study including a total of 74 patients with placenta previa and previous uterine scar (n = 74). Grey-scale and colour Doppler US was done followed by MRI by different observers to diagnose adherent placenta. Test validity of US and MRI were calculated. Maternal morbidity and mortality were also assessed.Results: A total of 53 patients confirmed to have placenta accreta at operation. The overall sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of US was 94.34, 91.67, 96.15 and 88% compared to 96.08, 87.50, 94.23 and 91.3% for MRI, respectively. The most relevant US sign was turbulent blood flow by colour Doppler, while dark intra-placental band was the most sensitive MRI sign. Venous thromboembolism (1.3%), bladder injury (29.7%), ureteric injury (18.9%), postoperative fever (10.8%), admission to ICU (50%) and re-operation (31.1%).Conclusion: Placenta accreta can be successfully diagnosed by grey-scale and colour Doppler US. MRI would be more likely suggested for either posteriorly or laterally situated placenta previa in order to exclude placental invasion.

New Insights into the Prothrombotic State of Heparin-Induced Thrombocytopenia (HIT) Using a Novel Microfluidic System: The Endothelial Lining and “Rolling Barrage” of Activation

The most feared feature of HIT is antibody-mediated thrombosis. We have shown that this prothrombotic state is related to binding of platelet factor 4 (PF4), a chemokine densely packaged into platelet alpha-granules, to surface glycosaminoglycans (GAGs) expressed on hematopoietic and vascular cells. PF4/GAG surface complexes are recognized by HIT antibodies, activating the targeted cells. Unlike platelets that express only low-affinity chondroitin sulfate surface GAGs, endothelial cells (EC) express a glycocalyx enriched in heparan sulfate, which has higher affinity for PF4, potentially increasing their propensity to become a target for immune injury leading to thrombosis. We examined the details of the development of in situ thrombi using the cremaster arteriole laser injury model beginning with transgenic mice expressing only human PF4 (hPF4+), but lacking FcγRIIA. These mice do not develop thrombocytopenia or thrombosis when injected with the HIT-like monoclonal antibody KKO or IgGs isolated from patients with HIT. In these mice, antigenic PF4/GAG complexes were recognized by KKO at sites of vascular injury even in the absence of infused heparin. In fact, infusion of sufficient heparin dissociated PF4 from sites of injury, consistent with its higher affinity for PF4 than cell surface GAGs. This suggests that antigenic PF4/GAG complexes normally develop intravascularly whenever thrombus formation occurs, yet these complexes do not typically initiate antibody-mediated thrombosis. Real-time confocal imaging of injured vessels revealed that PF4 first bound almost exclusively to the peri-injury endothelium. This was especially evident immediately upstream of the thrombus where turbulent blood flow may lead to platelet degranulation and subsequent adherence of the released PF4 to the glycocalyx. Beginning approximately two minutes post-injury, binding of KKO, presumably to PF4/GAG complexes on platelets, is seen at the interface between the shell and core of the thrombus. We then repeated these same studies in hPF4+/FcγRIIA+ mice, where infused KKO or HIT IgGs leads to significant thrombocytopenia and widespread development of thrombi as in HIT. Similar adherence of PF4 to the peri-injury EC and then to the core/shell interface of the thrombus as seen in the hPF4+ mice, but the changes were more extensive in hPF4+/FcγRIIA+ mice after KKO infusion and often lead to vascular occlusion. To further define the basis of the prothrombotic state in HIT and to extend our studies to a human system, we examined thrombus formation in HIT in a novel microfluidic system in which vascular injury was induced in an upstream portion of a human umbilical vein EC-lined channel by reactive oxygen species generated through excitation of infused hematoporphyrin by blue light (490 nm). Following infusion of human blood, platelets accumulated and released PF4, which bound the injured endothelium, while the downstream endothelium remained quiescent. Addition of KKO to the infused whole blood lead to a HIT-like state with marked increase in platelet adhesion and binding of PF4 to the injured endothelium, but binding of PF4 now spread downstream of the boundary between injured and uninjured endothelium. This was followed by downstream platelet adhesion and often occlusion of the channel. We proposed that this spread in EC injury was a result of a “rolling barrage” of PF4 released from platelets binding to the injured patch of EC complexing to the downstream glycocalyx on the non-injured endothelium followed by KKO binding and subsequent endothelial activation. The newly activated ECs bound additional platelets and the process repeats, rolling downstream and extending thrombus growth. Thus, these studies provide important new insights into the local sequence of events that propagate clots in HIT: Targeting of the endothelial glycocalyx by HIT antibodies is a major contributor to the prothrombotic state. Platelets adherent to the site of original injury release PF4, which then binds to downstream EC glycocalyx and initiates repetitive cycles of PF4 binding, EC activation and platelet adherence, and further release of PF4 that propagates growth of thrombi to previously uninvolved vasculature. DisclosuresNo relevant conflicts of interest to declare.

Vascular theory of the formation of Randall plaques.

The relationship between calcium-based calculi and Randall plaques is well documented, but the role these plaques play in the early process of urinary stone formation remains unknown. The vascular hypothesis of Randall plaque formation has been proposed, and recent works support this concept. The renal papilla's vascular environment is subject to relative hypoxia, hyperosmolar surroundings, and turbulent blood flow. These factors together create an environment prone to vascular injury and may potentiate Randall plaque precipitation. Recent data support the similarity between the vascular calcification process itself and urinary stone formation. Furthermore, epidemiological studies have suggested an association between urinary stones, adverse cardiovascular events, and vascular calcification risk factors. The concept that an initial vascular insult precipitates a Randall plaque and subsequent urolithiasis is compelling and represents an area in need of continued research. This may lead to future novel treatment approaches to urolithiasis.

Molecular Communication Noise and Capacity Analysis for Particulate Drug Delivery Systems

Particulate Drug Delivery Systems (PDDS) are ther- apeutic methods that use nanoparticles to achieve their healing effects at the exact time, concentration level of drug nanoparti- cles, and location in the body, while minimizing the effects on other healthy locations. The Molecular Communication (MC) paradigm, where the transmitted message is the drug injection process, the channel is the cardiovascular system, and the received message is the drug reception process, has been investigated as a tool to study nanoscale biological and medical systems in recent years. In this paper, the various noise effects that cause uncertainty in the cardiovascular system are analyzed, modeled, and evaluated from the information theory perspective. Analytical MC noises are presented to include all end-to-end noise effects, from the drug injection, to the absorption of drug nanoparticles by the diseased cells, in the presence of a time-varying and turbulent blood flow. The PDDS capacity is derived analytically including all these noise effects and the constraints on the drug injection. The proposed MC noise is validated by using the kinetic Monte-Carlo simulation technique. Analytical expressions of the noise and the capacity are derived, and MC is presented as a framework for the optimization of particulate drug delivery systems (PDDS). Index Terms—Drug delivery systems, nanonetworks, molecu- lar communication, time-varying channels, communication chan- nels, intra-body communication, noise modeling, capacity, kinetic Monte-Carlo.

Navigating the 7 cs of certified practice.

Navigating the 7 cs of certified practice.

Theory to predict shear stress on cells in turbulent blood flow.

Shear stress on blood cells and platelets transported in a turbulent flow dictates the fate and biological activity of these cells. We present a theoretical link between energy dissipation in turbulent flows to the shear stress that cells experience and show that for the case of physiological turbulent blood flow: (a) the Newtonian assumption is valid, (b) turbulent eddies are universal for the most complex of blood flow problems, and (c) shear stress distribution on turbulent blood flows is possibly universal. Further we resolve a long standing inconsistency in hemolysis between laminar and turbulent flow using the theoretical framework. This work demonstrates that energy dissipation as opposed to bulk shear stress in laminar or turbulent blood flow dictates local mechanical environment of blood cells and platelets universally.

Investigation of the mechanism of soft tissue conduction explains several perplexing auditory phenomena.

Soft tissue conduction (STC) is a recently expounded mode of auditory stimulation in which the clinical bone vibrator delivers auditory frequency vibratory stimuli to skin sites on the head, neck, and thorax. Investigation of the mechanism of STC stimulation has served as a platform for the elucidation of the mechanics of cochlear activation, in general, and to a better understanding of several perplexing auditory phenomena. This review demonstrates that it is likely that the cochlear hair cells can be directly activated at low sound intensities by the fluid pressures initiated in the cochlea; that the fetus in utero, completely enveloped in amniotic fluid, hears by STC; that a speaker hears his/her own voice by air conduction and by STC; and that pulsatile tinnitus is likely due to pulsatile turbulent blood flow producing fluid pressures that reach the cochlea through the soft tissues.

What is the best imaging modality in evaluating patients with unilateral pulsatile tinnitus?

What is the best imaging modality in evaluating patients with unilateral pulsatile tinnitus?

Abstract 13: Suppression of Atherosclerosis by CD39

Atherosclerotic plaque rupture and thrombosis remains the leading cause of death in the United States. We investigated the role of CD39, a potent ecto-enzymatic regulator of platelet activation and leukocyte trafficking, in atherosclerosis. We generated mice deficient in CD39 on a hyperlipidemic, apoE -/- background and noted a two-fold higher plaque burden in when compared to apoE -/- controls ( P =0.003). We noted higher levels of circulating markers of platelet activation, soluble P-selectin (39%) and RANTES (60%), in the CD39-deficient mice ( P =0.003 and P =0.015, respectively, n=7-11). CD39-haploinsufficient mice had 1.8-fold greater enhanced platelet reactivity in response to ADP compared to controls ( P =0.03, n=3-8). Macrophages from CD39-deficient mice had significantly higher lipoprotein uptake in vitro . Correspondingly, CD39 overexpression in RAW cells inhibited scavenger receptor expression and lipoprotein uptake. Altered fluid mechanics contribute to atherosclerosis, with non-laminar shear stress enhancing regional plaque formation as seen in arterial bifurcations. We examined coronal sections of aortas from apoE −/− mice and observed that CD39 is poorly expressed in the endothelium in regions of turbulent blood flow, where plaque develops, supporting our hypothesis that endothelial CD39 can be induced by fluid phase shear forces. HUVEC treated with physiologic laminar shear stress (LS) (15 dynes/cm 2 ) had a 5.9-fold increase in CD39 protein ( P =0.004, N=3-7) and a concordant increase in nucleotidase activity ( P =0.03 N=3) compared to static controls (SS). We identified Krüppel like factor 2 (KLF2) as an upstream candidate for transcriptional regulation of CD39 induction by fluid shear forces. Silencing KLF2 in vitro led to a 55% decrease in CD39 mRNA induction with LS vs SS controls ( P =0.002, N=3-4). Chromatin immunoprecipitation revealed that KLF2 binds to the CD39 ( P =0.01, N=3) and this binding was further enhanced under laminar shear stress ( P =0.0007, N=3). These data show that CD39, an anti-thrombotic, anti-inflammatory enzyme is a critical regulator of atherosclerosis by modulating platelet, macrophage and endothelial function and mechanistically identify KLF2 as a direct, upstream regulator of CD39 expression.

An In Vitro Evaluation of the Impact of Eccentric Deployment on Transcatheter Aortic Valve Hemodynamics

Patients with aortic stenosis present with calcium deposits on the native aortic valve, which can result in non-concentric expansion of Transcatheter Aortic Valve Replacement (TAVR) stents. The objective of this study is to evaluate whether eccentric deployment of TAVRs lead to turbulent blood flow and blood cell damage. Particle Image Velocimetry was used to quantitatively characterize fluid velocity fields, shear stress and turbulent kinetic energy downstream of TAVRs deployed in circular and eccentric orifices representative of deployed TAVRs in vivo. Effective orifice area (EOA) and mean transvalvular pressure gradient (TVG) values did not differ substantially in circular and eccentric deployed valves, with only a minor decrease in EOA observed in the eccentric valve (2.0cm(2) for circular, 1.9cm(2) for eccentric). Eccentric deployed TAVR lead to asymmetric systolic jet formation, with increased shear stresses (circular=97N/m(2) vs. eccentric=119N/m(2)) and regions of turbulence intensity (circular=180N/m(2) vs. eccentric=230N/m(2)) downstream that was not present in the circular deployed TAVR. The results of this study indicate that eccentric deployment of TAVRs can lead to altered flow characteristics and may potentially increase the hemolytic potential of the valve, which were not captured through hemodynamic evaluation alone.

PP-217 Hypertrophic Cardiomyopaty with Mid-Ventricular Obstruction: One Obstruction, Three Dictinct Jet in One Chamber

A 65-year-old male admitted to outpatient clinic with shortness of breath. He had no known cardiac disease. The electrocardiography showed left ventricular (LV) hypertrophy and strain pattern(A).Echocardiography demonstrated concentric hypertrophy of LV with an apical aneurysm and mid-ventricular obstruction(MVO).ColorDoppler displayed a turbulence of blood flow at midventricular(MV) level and pulsed wave Doppler mapping ofLV demonstrated systolic intra-ventricular gradient at MV.Continuouswave Doppler envelope consisted of3distinct high velocity jet peaks(B).There was nomitral regurgitation flow detected with colorM-mode(C).Myocardial perfusion imaging revealed focal reversible ischemia at LV apex.Obstructive coronary artery disease wasexcluded by coronary angiography as a cause of ischemia and apical aneurysm formation.However, ventriculography displayed typical hourglass appearance ofLVcavity with a delayed apical emptying(D).Also cardiac magnetic resonance imaging(MRI) showed late gadolinium enhancement of the scarred rim of the aneurysm(E).Toprotect the patient from sudden death because of arrhythmic events we implanted implantable cardiac device.

4D UTE flow: A phase-contrast MRI technique for assessment and visualization of stenotic flows

Inaccuracy of conventional four-dimensional (4D) flow MR imaging in the presence of random unsteady and turbulent blood flow distal to a narrowing has been an important challenge. Previous investigations have revealed that shorter echo times (TE) decrease the errors, leading to more accurate flow assessments. In this study, as part of a 4D flow acquisition, an Ultra-Short TE (UTE) method was adopted. UTE works based on a center-out radial k-space trajectory that inherently has a short TE. By employing free induction decay sampling starting from read-out gradient ramp-up, and by combining the refocusing lobe of the slice select gradient with the bipolar flow encoding gradient, TEs of ≈1 msec may be achieved. Both steady and pulsatile flow regimes, and in each case a range of Reynolds numbers, were studied in an in-vitro model. Flow assessment at low and medium flow rates demonstrated a good agreement between 4D UTE and conventional 4D flow techniques. However, 4D UTE flow significantly outperformed conventional 4D flow, at high flow rates for both steady and pulsatile flow regimes. Feasibility of the method in one patient with Aortic Stenosis was also demonstrated. For both steady and pulsatile high flow rates, the measured flow distal to the stenotic narrowing using conventional 4D flow revealed more than 20% error compared to the ground-truth flow. This error was reduced to less than 5% using the 4D UTE flow technique.