scholarly journals Patient-specific computational haemodynamics associated with surgical creation of an arteriovenous fistula

2021 ◽  
Author(s):  
George Hyde-Linaker ◽  
Pauline Hall Barrientos ◽  
Sokratis Stoumpos ◽  
Asimina Kazakidi
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Disease Patient ◽  
Blood Flow Rate ◽  
Fold Increase ◽  
Transitional Flow ◽  
Patient Specific ◽  
Venous Anastomosis ◽  
End Stage

Abstract Despite arteriovenous fistulae (AVF) being the preferred vascular access for haemodialysis, high primary failure rates (30-70%) and low one-year patency rates (40-70%) hamper their use. The haemodynamics within the vessels of the fistula change significantly following surgical creation of the anastomosis and can be a surrogate of AVF success or failure. Computational fluid dynamics (CFD) can crucially predict AVF outcomes through robust analysis of a fistula’s haemodynamic patterns, which is impractical in-vivo. We present a proof-of-concept CFD framework for characterising the AVF blood flow prior and following surgical creation of a successful left radiocephalic AVF in a 20-year-old end-stage kidney disease patient. The reconstructed vasculature was generated utilising multiple contrast-enhanced magnetic resonance imaging (MRI) datasets. Large eddy simulations were conducted for establishing the extent of arterial and venous remodelling. Following anastomosis creation, a significant 2-3-fold increase in blood flow rate was induced downstream of the left subclavian artery. This was validated through comparison with post-AVF patient-specific phase-contrast data. The increased flow rate yielded an increase in time-averaged wall shear stress (TAWSS), a key marker of adaptive vascular remodelling. We have demonstrated TAWSS and oscillatory shear distributions of the transitional-flow in the venous anastomosis are predictive of AVF remodelling.

Anoxia and adenosine induce increased cerebral blood flow rate in crucian carp

1994 ◽  
Vol 267 (2) ◽  
pp. R590-R595 ◽  
Author(s):  
G. E. Nilsson ◽  
P. Hylland ◽  
C. O. Lofman
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Crucian Carp ◽  
Blood Flow Rate ◽  
Fold Increase ◽  
Liver Glycogen ◽  
Glycolytic Flux ◽  
Brain Blood Flow ◽  
Atp Production ◽  
The Brain

The crucian carp (Carassius carassius) has the rare ability to survive prolonged anoxia, indicating an extraordinary capacity for glycolytic ATP production, especially in a highly energy-consuming organ like the brain. For the brain to be able to increase its glycolytic flux during anoxia and profit from the large liver glycogen store, an increased glucose delivery from the blood would be expected. Nevertheless, the effect of anoxia on brain blood flow in crucian carp has never been studied previously. We have used epireflection microscopy to directly observe and measure blood flow rate on the brain surface (optic lobes) during normoxia and anoxia in crucian carp. We have also examined the possibility that adenosine participates in the regulation of brain blood flow rate in crucian carp. The results showed a 2.16-fold increase in brain blood flow rate during anoxia. A similar increase was seen after topical application of adenosine during normoxia, while adenosine was without effect during anoxia. Moreover, superfusing the brain with the adenosine receptor blocker aminophylline inhibited the effect of anoxia on brain blood flow rate, clearly suggesting a mediatory role of adenosine in the anoxia-induced increase in brain blood flow rate.

Is the Maturation of Arteriovenous Fistulas a Mechanical or Biological Problem?

2016 ◽  
Author(s):  
Daniel Jodko ◽  
Damian Obidowski ◽  
Piotr Reorowicz ◽  
Krzysztof Jozwik
Keyword(s):  
High Pressure ◽  
Blood Flow ◽  
Shear Stress ◽  
Flow Rate ◽  
Blood Flow Rate ◽  
Average Diameter ◽  
Patient Specific ◽  
Maturation Process ◽  
Arteriovenous Fistulas ◽  
Biological Problem

During the maturation the high pressure blood from the artery inflows directly to the vein, extends its diameter, and finally the blood flow rate in the vein is even 500-times greater than normal one. The changes of the wall shear stress (WSS) in the vein are thought to play a key role in the remodelling of its wall. However, this process is still not well understood. The aim of this paper is to show an innovative approach for modelling of the vein deformation during the maturation process of a-v fistulas. Dilation of the vein was modelled as two-step complex biomechanical process. The obtained results concerning final diameter of the vein are compared with average diameter obtained for large group of patients. Moreover, this study shows the changes in the flow rate and the WSS that occur after maturation in the patient-specific fistula.

scholarly journals Integrating Patient-Specific Electrocardiogram Signals and Image-Based Computational Fluid Dynamics Method to Analyze Coronary Blood Flow in Patients during Cardiac Arrhythmias

2019 ◽  
Vol 40 (2) ◽  
pp. 264-272
Author(s):  
Szu-Hsien Chou ◽  
Kuan-Yu Lin ◽  
Zhen-Ye Chen ◽  
Chun-Jung Juan ◽  
Chien-Yi Ho ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Blood Flow ◽  
Coronary Artery ◽  
Cardiac Arrhythmia ◽  
Coronary Arteries ◽  
Flow Rate ◽  
Blood Flow Rate ◽  
Patient Specific ◽  
Ecg Signals

Abstract Purpose The aim of this study was to use the computational fluid dynamics (CFD) method, patient-specific electrocardiogram (ECG) signals, and computed tomography three-dimensional image reconstruction technique to investigate the blood flow in coronary arteries during cardiac arrhythmia. Methods Two patients with premature ventricular contraction-type cardiac arrhythmia and one with atrial fibrillation-type cardiac arrhythmia were investigated. The inlet velocity of the coronary artery in simulation was applied with the measured velocity profile of the left ventricular outflow tract (LVOT) from the Doppler echocardiography. The measured patient central aortic blood pressure waveform was employed for the coronary artery outlet in simulation. The no-slip boundary condition was applied to the arterial wall. Results For the patient with irregular cardiac rhythms (Case I), the coronary blood flow rate under the shortened and lengthened cardiac rhythms were 0.66 and 0.96 mL/s, respectively. In Case II, the maximum velocity at the LVOT under a normal heartbeat was found to be 101 cm/s, whereas the average value was 73 cm/s. In Case III, the patient was also diagnosed with a congenital stenosis problem at the myocardial bridge (MCB) at the LAD. The measured blood flow rate at the MCB of the LAD for the three heartbeats in Case III was found to be 0.68, 1.08, and 1.14 mL/s. Conclusion The integration of patient-specific ECG signals and image-based CFD methods can clearly analyze hemodynamic information for patients during cardiac arrhythmia. The cardiac arrhythmia can reduce the blood flow in the coronary arteries.

Perceived vessel lumen and cell-blood velocity ratio: impact on in vivo blood flow rate determination

1992 ◽  
Vol 262 (4) ◽  
pp. H1156-H1163 ◽  
Author(s):  
G. R. Cokelet ◽  
I. H. Sarelius
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Average Velocity ◽  
Velocity Ratio ◽  
Blood Flow Rate ◽  
Mass Conservation ◽  
Red Cell ◽  
Vessel Lumen ◽  
Image Width

Microscopic images of blood flow through individual capillary segments and divergent capillary bifurcations in cremaster muscle of golden hamster were videotaped, and the data from the videotapes (projected vessel image width and individual red cell velocities) were used in two ways to evaluate blood flow rate. The first method assumes 1) that the vessel lumen is circular with a diameter equal to the projected image width and 2) that the blood average velocity is proportional to the average red cell velocity. The second method makes neither of these assumptions but relies only on the principle of mass conservation. It is demonstrated that the two assumptions of the first method can lead to significant errors in hemodynamic relationships deduced from in vivo data. Although the second method cannot independently give absolute values of average velocity at one vessel location, it can give absolute values of the ratio of blood flow rates through two (or more) vascular lumina.

Blood flow rate and cellular influx of glucose and arginine in mouse liver in vivo

1980 ◽  
Vol 238 (4) ◽  
pp. H553-H560
Author(s):  
E. M. Cornford ◽  
L. D. Braun ◽  
W. M. Pardridge ◽  
W. H. Oldendorf
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Mouse Liver ◽  
Blood Flow Rate

Sensitivity of patient-specific numerical simulation of cerebal aneurysm hemodynamics to inflow boundary conditions

2007 ◽  
Vol 106 (6) ◽  
pp. 1051-1060 ◽  
Author(s):  
Prem Venugopal ◽  
Daniel Valentino ◽  
Holger Schmitt ◽  
J. Pablo Villablanca ◽  
Fernando Viñuela ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Boundary Conditions ◽  
Numerical Simulations ◽  
Flow Rate ◽  
Artery Aneurysm ◽  
Blood Flow Rate ◽  
Patient Specific ◽  
Stress Distributions ◽  
Flow Rates

Object Due to the difficulty of obtaining patient-specific velocity measurements during imaging, many assumptions have to be made while imposing inflow boundary conditions in numerical simulations conducted using patient-specific, imaging-based cerebral aneurysm models. These assumptions can introduce errors, resulting in lack of agreement between the computed flow fields and the true blood flow in the patient. The purpose of this study is to evaluate the effect of the assumptions made while imposing inflow boundary conditions on aneurysmal hemodynamics. Methods A patient-based anterior communicating artery aneurysm model was selected for this study. The effects of various inflow parameters on numerical simulations conducted using this model were then investigated by varying these parameters over ranges reported in the literature. Specifically, we investigated the effects of heart and blood flow rates as well as the distribution of flow rates in the A1 segments of the anterior cerebral artery. The simulations revealed that the shear stress distributions on the aneurysm surface were largely unaffected by changes in heart rate except at locations where the shear stress magnitudes were small. On the other hand, the shear stress distributions were found to be sensitive to the ratio of the flow rates in the feeding arteries as well as to variations in the blood flow rate. Conclusions Measurement of the blood flow rate as well as the distribution of the flow rates in the patient's feeding arteries may be needed for numerical simulations to accurately reproduce the intraaneurysmal hemodynamics in a specific aneurysm in the clinical setting.

scholarly journals Time Course of Anoxia-Induced Increase in Cerebral Blood Flow Rate in Turtles: Evidence for a Role of Adenosine

1994 ◽  
Vol 14 (5) ◽  
pp. 877-881 ◽  
Author(s):  
Patrick Hylland ◽  
Göran E. Nilsson ◽  
Peter L. Lutz
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Flow Rate ◽  
Time Course ◽  
Blood Flow Rate ◽  
Fold Increase ◽  
Systemic Blood Pressure ◽  
The Brain ◽  
Survival Mechanisms

The exceptional ability of the turtle brain to survive prolonged anoxia makes it a unique model for studying anoxic survival mechanisms. We have used epiillumination microscopy to record blood flow rate in venules on the cortical surface of turtles ( Trachemys scripta). During anoxia, blood flow rate increased 1.7 times after 45–75 min, whereupon it fell back, reaching preanoxic values after 115 min of anoxia. Topical super-fusion with adenosine (50 μ M) during normoxia caused a 3.8-fold increase in flow rate. Superfusing the brain with the adenosine receptor blocker aminophylline (250 μ M) totally inhibited the effects of both adenosine and anoxia, while aminophylline had no effect on normoxic flow rate. None of the treatments affected systemic blood pressure. These results indicate an initial adenosine-mediated increase in cerebral blood flow rate during anoxia, probably representing an emergency response before deep metabolic depression sets in.

scholarly journals Fossil skulls reveal that blood flow rate to the brain increased faster than brain volume during human evolution

2016 ◽  
Vol 3 (8) ◽  
pp. 160305 ◽  
Author(s):  
Roger S. Seymour ◽  
Vanya Bosiocic ◽  
Edward P. Snelling
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Metabolic Rate ◽  
Flow Rate ◽  
Brain Volume ◽  
Brain Size ◽  
Blood Flow Rate ◽  
Fold Increase ◽  
Cerebral Tissue ◽  
Cerebral Metabolic Rate

The evolution of human cognition has been inferred from anthropological discoveries and estimates of brain size from fossil skulls. A more direct measure of cognition would be cerebral metabolic rate, which is proportional to cerebral blood flow rate (perfusion). The hominin cerebrum is supplied almost exclusively by the internal carotid arteries. The sizes of the foramina that transmitted these vessels in life can be measured in hominin fossil skulls and used to calculate cerebral perfusion rate. Perfusion in 11 species of hominin ancestors, from Australopithecus to archaic Homo sapiens , increases disproportionately when scaled against brain volume (the allometric exponent is 1.41). The high exponent indicates an increase in the metabolic intensity of cerebral tissue in later Homo species, rather than remaining constant (1.0) as expected by a linear increase in neuron number, or decreasing according to Kleiber's Law (0.75). During 3 Myr of hominin evolution, cerebral tissue perfusion increased 1.7-fold, which, when multiplied by a 3.5-fold increase in brain size, indicates a 6.0-fold increase in total cerebral blood flow rate. This is probably associated with increased interneuron connectivity, synaptic activity and cognitive function, which all ultimately depend on cerebral metabolic rate.

scholarly journals Computational Fluid Dynamics-Based Estimation of Blood Flow Rate in Doppler Analysis: In Vivo Validation by Means of Phase Contrast Magnetic Resonance Imaging

2009 ◽  
Author(s):  
Raffaele Ponzini ◽  
Christian Vergara ◽  
Giovanna Rizzo ◽  
Alessandro Veneziani ◽  
Alberto Redaelli ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Blood Flow ◽  
Flow Rate ◽  
Ad Hoc ◽  
A Priori ◽  
Maximum Velocity ◽  
Blood Flow Rate ◽  
In Vivo Validation

In this work we carry out an in vivo validation of a method for estimating blood flow rate from the peak velocity, as it is usually done in single-wire Doppler catheter measurements. This method, originally proposed in [1] stems from the application of numerical analysis of the blood flow with Computational Fluid Dynamics (CFD) techniques. It proposes a new formula linking the maximum velocity and the flow rate, which, however, has the same practical cost of classical approaches based on a priori assumptions on the velocity profile. After the first clinical observations indicating the improved accuracy in flow rate estimates introduced by the new method discussed in [2, 3], in this paper we present an ad hoc in vivo validation, as firstly suggested in [4], still confirming the reliability of the new approach.

scholarly journals Modeling autoregulation in three-dimensional simulations of retinal hemodynamics

2016 ◽  
Vol 1 (1) ◽  
pp. 88-115
Author(s):  
Matteo Aletti ◽  
Jean-Frédéric Gerbeau ◽  
Damiano Lombardi
Keyword(s):  
Experimental Data ◽  
Blood Flow ◽  
Flow Rate ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Blood Flow Rate ◽  
Patient Specific ◽  
Initial Attempt ◽  
Structural Part ◽  
3D Network

Purpose: Autoregulation is a mechanism necessary to maintain an approximately constant blood flow rate in the microcirculation when acute changes in systemic pressure occur. Failure of autoregulation in the retina has been associated with various diseases, including glaucoma. In this work, we propose an initial attempt to model autoregulation in a 3D network of retinal arteries.Methods: The blood flow is modeled with the time-dependent Stokes equations. The arterial wall model includes the endothelium and the smooth muscle fibers. Various simplifying assumptions lead to a fluid-structure model where the structural part appears as a boundary condition for the fluid. The numerical simulations are performed on a patient-specific network of 25 segments of retinal arteries located in the inferior temporal quadrant.Results: The simulations performed on the patient-specific artertial network have provided velocities which are in good agreement with published experimental data. In addition, the model allowed to reproduce flow rate-pressure curves which are comparable with experimental data or results obtained with 0D models. In particular, a characteristic plateau of the flow rate has been found for pressures ranging from 40 to 60 mmHg.Conclusion: This work proposes the first 3D simulation of blood flow in a real network of retinal arteries and it also incorporates an autoregulation mechanism. This can be viewed as a first step towards a more complete 3D model of the hemodynamic of the eye.

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