Blood Flow Studies Research Articles

Numerical study of the non-Newtonian blood flow in a stenosed artery using two rheological models

The numerical simulation of blood flow in arteries using non-Newtonian viscosity model, presents two major difficulties; the first one is the choice of an appropriate constitutive equation, because no one model is universally accepted as a reflection of the true behavior of blood viscosity until now. Another difficulty lies in the numerical convergence of the complex scheme solving the highly non-linear set of equations governing the blood motion. In this paper, the pulsatile blood flow through an arterial stenosis has been numerically modeled to evaluate the flow characteristics and the wall shear stress under physiological conditions. The Navier-Stokes equations governing the fluid motion are solved using the finite element method in unsteady two-dimensional case. The behavior of blood is considered as the Generalized Power-law (Gpl) and Cross models, where the shear-thinning characteristics of the streaming blood are taken into account. Constants in the constitutive equations of previous models have been obtained by fitting experimental viscosity data. The numerical simulations are performed for a wide range of apparent shear rates (10 s-1-750 s-1) with good convergence of the iterative scheme. Results from the blood flow simulations indicate that non-Newtonian behavior has considerable effects on instantaneous flow patterns. However, it seems that the Gpl model will be slightly better for describing the non-Newtonian characteristics of blood than the Cross model.

Mathematical modelling of blood flow in vascular system of the brain with pathological changes

The paper presents numerical study of blood flow in vascular system without stenosis and with pathological changes. The Navier – Stokes system of equation is used for modeling of liquid flow in blood vessels. The numerical algorithm was based on projection method. At first stage, it is assumed that the transfer of the movement of amount occurred is due to convection and diffusion. The intermediate regions of velocity are determined by using the 5-step Runge – Kutta method algorithm. At second stage the intermediate velocity field is used to define the pressure field. The Poisson equation for pressure field is solved by Jacobi method. The numerical results are checked by comparing analytical solutions for the Poiseuille flow with numerical results. The influence of the blood velocity flow on behavior of the liquid in vascular system of brain was investigated. One of the characteristic features of blood flow in blood vessels affected by stenosis is an appearance of vortex currents, which manifests as a pathology, as opposite to normal blood circulation. The results of this work can be used in mathematical modeling investigations of blood circulation in brain and solving problems in practical medicine.

Blood Flow in Human Arterial System-A Review

The blood flow in human arterial system can be considered as a fluid dynamics problem. Simulation of blood flow in the arterial network system will provide a better understanding of the physiology of human body. Hence, hemodynamics play an important role in the development and progression of arterial stenosis, leading to the malfunctioning of cardiovascular system. Simulation studies of blood flow in the diseased condition can diagonise the health problem easily and also have many applications in the areas such as surgical planning and design of medical devices. This paper presents a review on the existing scenario of the simulation studies of blood flow, starting with a brief overview of the structure and function of arteries and veins followed by a discussion on pressure wave propagation, blood flow models and Fluid Structure Interaction in the arterial system.

Red blood cells radial dispersion in blood flowing through microchannels: The role of temperature

The behavior of suspensions of individual blood cells, such as red blood cells (RBCs), flowing through microvessels and microfluidic systems depend strongly on the hematocrit (Hct), microvessel topology and cell properties. Although it is well known that blood rheological properties are temperature dependent, to the best of our knowledge no work has studied the role of the temperature on the RBCs dispersion. A powerful way to investigate this latter effect is through a high-speed video microscopy system, which provides detailed flow measurements of each individual RBC. Hence, the effect of temperature on the RBCs dispersion flowing through a 100μm glass capillary was examined by means of a confocal micro-PTV system. Hundreds of labeled RBCs were tracked at moderate Hct (12%) and at four different temperatures, i.e., 25°C, 32°C, 37°C and 42°C. The results yielded an enhancement of the RBCs diffusion as the temperature increases. Hence, our findings show that RBCs radial dispersion is temperature dependent and as a result the temperature should not be ignored in future blood flow studies. We believe that this finding is important for a better understanding of blood mass transport mechanisms under both physiological and pathological conditions.

A longitudinal study of maternal endothelial function, inflammatory response and uterine artery blood flow during the second half of pregnancy

The objective of this study was to investigate serial changes in maternal endothelial function, inflammatory response and uterine artery blood flow in normal pregnancy, and to explore their inter-relation. In this prospective longitudinal observational study, 53 women with uncomplicated pregnancies were examined at 4-weekly intervals (248 observations) during 22-40 weeks of gestation. Uterine artery blood flow was measured using Doppler ultrasonography. Maternal endothelial function was assessed by flow-mediated vasodilatation (FMD) of the brachial artery. Circulating endothelial progenitor cells (EPC), defined as CD34(+) CD133(+) VEGFR2(+) cells, were quantified by flow cytometry. Biomarkers of inflammation, such as leptin and high sensitivity C-reactive protein (hsCRP), were measured in plasma samples. Multilevel modeling was used to investigate gestational-age-associated serial changes. The EPC increased from 6.5 to 12.3 per million mononuclear cells (p < 0.01) and FMD decreased from 16.3 to 13.4% (p = 0.20). Leptin increased from 18 to 22 ng/mL (p < 0.01), and hsCRP did not change significantly (p = 0.61). There was no significant association between FMD and EPC (p = 0.66). FMD was significantly associated with hsCRP (p = 0.002) and leptin (p = 0.003), but the EPC were not. Neither FMD nor EPC were significantly associated with uterine artery blood flow. Changes in FMD were significantly associated with inflammatory biomarkers, suggesting that the reduced nitric oxide-dependent vasodilatation in late gestation is related to maternal inflammatory response. As EPC and FMD did not correlate, mechanisms other than mobilization of EPC to repair endothelial damage must be responsible for the gestational-age-associated increase in EPC.

Нейропластичность эмбриональной ткани мозга крыс при нарушении гемодинамического обеспечения

The investigation was aimed to study of the local cerebral blood flow, partial pressure of oxygen&#x0D; (рО2) and the character of development of local vascular reactions at embryonic neurotransplant (ENT)&#x0D; through 4, 8 и 12 months after its transplantation into the barrel field of somatic recipient’s rat brain cortex.&#x0D; In experiments, a homotopical allotransplantation 17‐day embryonic nervous tissue was conducted in the&#x0D; Wistar rats. In microareas of embryonic neurotransplant there is an uneven distribution of local cerebral&#x0D; blood flow and decrease in intensity as compared with intact somatic cortex of control rats. A 4‐month period&#x0D; after transplantation in the embryonic neuro‐transplantation there is the desired level of hemodynamic&#x0D; and oxygen supply. Dilatatory ability of micro‐vessels increases in the exercise of regulatory adaptive responses&#x0D; aimed at regulating the blood flow in nerve tissue, as evidenced by the increasing amplitude of functional&#x0D; hyperemia and magnitude of the increase of partial oxygen tension. After 8 and 12 months after transplantation,&#x0D; perfusion intensity and efficiency of ENT micro‐vessels vasodilatation are decreased. The local&#x0D; functional hyperemia is reducing, the partial pressure of oxygen increases. 4 months after transplantation&#x0D; unique properties of immature tissue persist; ENT possesses protective properties and provides neuroplastic&#x0D; effect.

Abstract 18201: Effects of Epinephrine Administration on Cerebral Oxygenation During Cardiopulmonary Resuscitation

Introduction: Epinephrine has been presumed to improve cerebral oxygen delivery during CPR. Animal studies however have demonstrated that epinephrine-induced capillary vasoconstriction may actually decrease cerebral capillary blood flow and registry studies have suggested that adrenaline may actually worsen neurological outcome, The effects of epinephrine on cerebral oxygenation (rSO2) during CPR has not been documented in the clinical setting. Methods: Following ethics approval, rSO2 was measured continuously using cerebral oximetry in patients undergoing in-hospital cardiac arrest. During CPR, time event markers recorded the administration of 1mg epinephrine. rSO2% values were analysed for a 5 min window prior to and then 5 mins after the first epinephrine administration. Results: A total of 56 epinephrine doses were analyzed in 36 patients during CPR. Results are shown below. The average rSO2% in the 5 mins following epinephrine administration was 1.40% higher (95% CI=0.41-2.40%, P=0.0059) than in the 5 min period prior to epinephrine administration. After adjusting, for patients’ ROSC status, initial rhythm, hemoglobin and Charlson comorbidity index, this difference remained statistically significant (1.42% with 95% CI: 0.35-2.49%, P=0.009). There was no statistically significant difference in the gradient of rSO2% during the 5 min period immediately before (0.88) compared with immediately after (1.09) epinephrine administration. Conclusion: IV administration of 1mg epinephrine during CPR results in minimal changes to rSO2%. This is the first clinical data to demonstrate the effects of epinephrine on rSO2 and is consistent with animal studies. These results may go some way to explaining the limited effect of epinephrine on improving neurological recovery from cardiac arrest.

Voxel-wise meta-analyses of brain blood flow and local synchrony abnormalities in medication-free patients with major depressive disorder.

Published meta-analyses of resting-state regional cerebral blood flow (rCBF) studies of major depressive disorder (MDD) have included patients receiving antidepressants, which might affect brain activity and thus bias the results. To our knowledge, no meta-analysis has investigated regional homogeneity changes in medication-free patients with MDD. Moreover, an association between regional homogeneity and rCBF has been demonstrated in some brain regions in healthy controls. We sought to explore to what extent resting-state rCBF and regional homogeneity changes co-occur in the depressed brain without the potential confound of medication. Using the effect-size signed differential mapping method, we conducted 2 meta-analyses of rCBF and regional homogeneity studies of medication-free patients with MDD. Our systematic search identified 14 rCBF studies and 9 regional homogeneity studies. We identified conjoint decreases in resting-state rCBF and regional homogeneity in the insula and superior temporal gyrus in medication-free patients with MDD compared with controls. Other changes included altered resting-state rCBF in the precuneus and in the frontal-limbic-thalamic-striatal neural circuit as well as altered regional homogeneity in the uncus and parahippocampal gyrus. Meta-regression revealed that the percentage of female patients with MDD was negatively associated with resting-state rCBF in the right anterior cingulate cortex and that the age of patients with MDD was negatively associated with rCBF in the left insula and with regional homogeneity in the left uncus. The analysis techniques, patient characteristics and clinical variables of the included studies were heterogeneous. The conjoint alterations of rCBF and regional homogeneity in the insula and superior temporal gyrus may be core neuropathological changes in medication-free patients with MDD and serve as a specific region of interest for further studies on MDD.

Numerical study of unsteady blood flow through a vessel using Sisko model

A mathematical study for two-phase unsteady pulsatile flow of blood through a vessel in the presence of body acceleration is presented in this paper. The blood in the core region is modeled as a non-Newtonian fluid while in the peripheral region it is described as a Newtonian fluid. The effects of body acceleration are also taken into account in this study. The continuity and momentum equations are used to model the proposed problem in terms of a nonlinear partial differential equation. This equation along with initial and boundary conditions is made dimensionless and then solved numerically using finite difference method. The behavior of various flow quantitates is analyzed through a parametric study.

Influence of plaque stiffness on deformation and blood flow patterns in models of stenosis.

Blood flow in stenotic vessels strongly influences the progression of vascular diseases. Plaques in stenotic blood vessels vary in stiffness, which influences plaque behavior and deformation by pressure and flow. Concurrent changes in plaque geometry can, in turn, affect blood flow conditions. Thus, simultaneous studies of blood flow and plaque deformation are needed to fully understand these interactions. This study aims to identify the change of flow conditions attendant to plaque deformation in a model stenotic vessel. Three plaques of differing stiffness were constructed on a vessel wall using poly (vinyl alcohol) hydrogels (PVA-H) with defined stiffness to facilitate simultaneous observations of blood flow and plaque deformation. Flow patterns were observed using particle image velocimetry (PIV). Decreases in Reynolds number (Re) with increased plaque deformation suggest that velocity decrease is more critical to establishment of the flow pattern than expansion of the model lumen. Upon exiting the stenosis, the location of the flow reattachment point, shifted further downstream in all models as plaque stiffness decreased and depended on the increase in upstream pressure. These results suggest that in addition to luminal area, plaque stiffness should be considered as a measure of the severity of the pathology.

Dull Brains, Mountaineers, and Mosso: Hypoxic Words from on High.

Dull and hypoxic brains have been a frequent subject in the medical and mountaineering literature. Deterioration of cognitive and other neurological function occurs at high altitude, with or without high altitude cerebral edema. This historical essay explores a 2014 first-ever English translation of cerebral blood flow studies by nineteenth century physiologist Angelo Mosso. Some of the medical history and physiology of brain function is discussed, but much of the style focuses on quotations from the writings of mountaineers and mountaineering physicians to provide color commentary about dull brains at high altitude.

Radial Artery Grafts as Rescue Strategy for Patients with Moyamoya Disease for Whom Conventional Revascularization Failed

Failure of direct revascularization with superficial temporal artery (STA)-middle cerebral artery (MCA) bypass for Moyamoya disease (MMD) is comparatively rare. However, for those cases where a bypass fails to prevent further ischemic attacks, safe and efficient rescue strategies are needed. We present our experience with radial artery grafts for secondary revascularization of MMD. Between April 2007 and April 2014, we have performed STA-MCA bypass in 182 patients diagnosed with Moyamoya vasculopathy. Four patients with typical MMD who had an unsuccessful STA-MCA bypass required additional revascularization because they remained symptomatic. Digital subtraction angiography revealed delayed STA graft failure in these patients, who continued to have transient ischemic attacks after the initial surgery. Cerebral blood flow studies confirmed persistent impairment of cerebrovascular reserve capacity. As an escape strategy, we performed radial artery graft bypass surgery from the external carotid artery to the M2 or M3 portion of the MCA. The median duration between the 2 surgeries was 10 months. The mean follow-up period after rescue revascularization was 8.5 ± 3.3 months. Revascularization with the radial artery graft was successful in all cases without perioperative complications. Postoperatively, none of the patients experienced further cerebrovascular events. After 3 months, digital subtraction angiography revealed patent radial artery grafts and adequate revascularization in 3 patients; 1 patient presented with bypass graft failure but had developed transdural collateral vessels contributing to the filling of the cerebral vasculature. Rescue bypass with a radial artery graft provides a useful function. Although delayed graft failure may occur, this procedure is successful if the patients remain symptom free with the development of collateral flow.

Newtonian heating effect on unsteady hydromagnetic Casson fluid flow past a flat plate with heat and mass transfer

The influence of Newtonian heating on heat and mass transfer in unsteady hydromagnetic flow of a Casson fluid past a vertical plate in the presence of thermal radiation and chemical reaction is studied. The Casson fluid model is used to distinguish the non-Newtonian fluid behavior. The fluid flow is induced due to periodic oscillations of the plate along its length and a uniform transverse magnetic field is applied in a direction which is normal to the direction of fluid flow. The partial differential equations governing the flow, heat, and mass transfer are transformed to non-dimensional form using suitable non-dimensional variables which are then solved analytically by using Laplace transform technique. The numerical values of the fluid velocity, fluid temperature, and species concentration are depicted graphically whereas the values of skin-friction, Nusselt number, and Sherwood number are presented in tabular form. It is noticed that the fluid velocity and temperature decrease with increasing values of Casson parameter while concentration decreases with increasing values of chemical reaction parameter and Schmidt number. Such a fluid flow model has several industrial and medical applications such as in glass manufacturing, paper production, purification of crude oil and study of blood flow in the cardiovascular system.

Forearm vasodilator reactivity in healthy male carriers of the 3q22.3 rs9818870 polymorphism

BackgroundA genome wide association study has identified a robust risk locus for cardiovascular disease on 3q22.3. However, the mechanisms by which the [C]/[T] polymorphism rs9818870 increases cardiovascular risk are unknown. This forearm blood flow (FBF) study addressed the question if the genetic association with cardiovascular disease in patients is preceded by incipient vasodilator impairment in young, healthy carriers of this new risk locus on chromosome 3. Materials and methodsAfter a pre-screening of 74 subjects 17 male healthy volunteers homozygous/heterozygous for a single nucleotide polymorphism (SNP) risk allele on 3q22.3 and a control group of 17 healthy volunteers not carrying the allele were included into this case–control study. ResultsForearm vascular endothelium-dependent and -independent vasodilator responses were in the normal range in both groups, although endothelium-dependent FBF reactivity to acetylcholine was significantly higher in SNP carriers of the risk allele. ConclusionThe augmented endothelium-dependent vasodilation of the forearm resistance vasculature does not support the presence of endothelial dysfunction in young SNP carriers and indicates that other mechanisms are responsible for the strong association between coronary artery diseases and the rs9818870 polymorphism, located on 3q22.3.

The “medical” investigation of specific learning disorders

Specific learning disorders may well be due to loss of neurons in certain parts of the brain, or perhaps more frequently to interruption of circuits connecting one part of the brain with another; so-called non-connection and disconnection syndromes. This paper is concerned with the contribution that medical investigations can make to elucidating the localisation and causes of developmental disabilities of this type, especially of dyslexia and of disorders of language function. Brief descriptions are given of the various techniques that can be employed; and blood flow studies and functional magnetic resonance imaging can be particularly useful in this field. Studies on children with developmental dyslexia are among the most frequent that have been carried out, and some of these are reviewed to show the kind of information that can be acquired. Such tests can not only help in the localisation of function, but also in assessing the results of remedial teaching. Then the investigation of language function is discussed in the same way, and in showing evidence of cerebral plasticity, and in giving a prognosis after vascular lesions for example. Associated disabilities, such as the attention deficit hyperactivity disorder and autism, will obviously have a profound effect on learning, and can also be investigated with these methods. The advent of these techniques holds out great possibilities of increasing our knowledge of specific learning disabilities, and although many of the advances in this field will come from psychologists and teachers, there is no doubt that medicine can make a significant contribution. (J Pediatr Neurol 2004; 2(1): 3–8).

Cranial vault expansion with the split bone flap technique in shunt-related craniosynostosis

Shunt-related craniosynostosis causing craniocerebral disproportion represents a particular complication of the treatment of hydrocephalus. When the modification of the shunt opening pressure does not improve the symptomatology, surgery for correction of craniocerebral disproportion is indicated. We present the results and advantages of the split bi-frontal bone technique that is a modification of the previous used frontal bone advancement technique. We retrospectively reviewed 5 patients with iatrogenic craniosynostosis treated in our institution from 1995 to 2012. A splitting bi-frontal bone flap that is left floating posteriorly was performed to increase the cranial volume. All patients were cured. This technique increases the volume of the skull favoring the expansion of the brain and allows good cosmetical results. No perioperative complications were reported. The fact that the brain has a more appropriate volume allows the disappearance of the clinical symptomatology related to the split ventricle syndrome. The advantage is the respect of the fronto-orbital shape in children and adults with the same results of the classic frontal advancement in terms of volume expansion. The study of cerebral blood flow confirms the increase of the cerebral blood perfusion and the improvement of the regional cerebral blood flow in borderline regions. We preconize, for the treatment of slit ventricle syndrome, the bi-frontal split technique in children and adults for its efficacy, the low rate of complications and the respect of aesthetical constraints.

Computational study of blood flow in microchannels

Using the Theory of Interacting Continua (Mixture Theory), blood is modeled as a two-component mixture, namely, plasma and red blood cells (RBCs). The plasma is assumed to behave as a Newtonian fluid and the RBCs are modeled as a suspension of rigid spherical particles with a viscosity dependent on the shear-rate and the hematocrit. The drag and lift forces are implemented through RBC–plasma interaction forces. We solve the governing equations using the OpenFOAM, an open source CFD code for two phase flow simulations. The two-phase simulations predict RBC depletion in the corner of a sudden expansion channel. The RBC depletion length is found to increase with decreasing the flow rate and the hematocrit. There is a qualitatively good agreement between the simulation results and the experimental data.

Study of blood flow in several benchmark micro-channels using a two-fluid approach

It is known that in a vessel whose characteristic dimension (e.g., its diameter) is in the range of 20–500μm, blood behaves as a non-Newtonian fluid, exhibiting complex phenomena, such as shear-thinning, stress relaxation, and also multi-component behaviors, such as the Fahraeus effect, plasma-skimming, etc. For describing these non-Newtonian and multi-component characteristics of blood, using the framework of mixture theory, a two-fluid model is applied, where the plasma is treated as a Newtonian fluid and the red blood cells (RBCs) are treated as shear-thinning fluid. A computational fluid dynamic (CFD) simulation incorporating the constitutive model was implemented using OpenFOAM® in which benchmark problems including a sudden expansion and various driven slots and crevices were studied numerically. The numerical results exhibited good agreement with the experimental observations with respect to both the velocity field and the volume fraction distribution of RBCs.

Minimally Invasive Monitoring of Chronic Central Venous Catheter Patency in Mice Using Digital Subtraction Angiography (DSA).

BackgroundRepetitive administration of medication or contrast agents is frequently performed in mice. The introduction of vascular access mini-ports (VAMP) for mice allows long-term vascular catheterization, hereby eliminating the need for repeated vessel puncture. With catheter occlusion being the most commonly reported complication of chronic jugular vein catheterization, we tested whether digital subtraction angiography (DSA) can be utilized to evaluate VAMP patency in mice.MethodsTwenty-three mice underwent catheterization of the jugular vein and subcutaneous implantation of a VAMP. The VAMP was flushed every second day with 50 μL of heparinized saline solution (25 IU/ml). DSA was performed during injection of 100 μL of an iodine based contrast agent using an industrial X-ray inspection system intraoperatively, as well as 7±2 and 14±2 days post implantation.ResultsDSA allowed localization of catheter tip position, to rule out dislocation, kinking or occlusion of a microcatheter, and to evaluate parent vessel patency. In addition, we observed different ante- and retrograde collateral flow patterns in case of jugular vein occlusion. More exactly, 30% of animals showed parent vessel occlusion after 7±2 days in our setting. At this time point, nevertheless, all VAMPs verified intravascular contrast administration. After 14±2 days, intravascular contrast injection was verified in 70% of the implanted VAMPs, whereas at this point of time 5 animals had died or were sacrificed and in 2 mice parent vessel occlusion hampered intravascular contrast injection. Notably, no occlusion of the catheter itself was observed.ConclusionFrom our observations we conclude DSA to be a fast and valuable minimally invasive tool for investigation of catheter and parent vessel patency and for anatomical studies of collateral blood flow in animals as small as mice.

Pulsatile blood flow through stenosed artery with axial translation

The study of pulsatile blood flow through axisymmetric stenosed artery subject to an axial translation has been attempted with hematocrit concentration-dependent blood viscosity. The heart contraction and subsequent relaxation generate periodic pressure gradient in blood flow and translation in the artery can be represented by Fourier series. Numerical data required for computing Fourier harmonics for the pressure gradient and acceleration in the artery has been simulated from pressure waveform graph and biplanar angiogram. Velocity field has been obtained by solving governing equation using variational Ritz method. The hemodynamic indicators WSS, AWSS, OSI, RRT are derived and computed numerically. The effects of thickness of stenosis, and hematocrit concentration index on these indicators are computed and analyzed through graphs.