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.

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.

The Effect of Hematocrit on the Clearance of Small Molecules during Hemodialysis

1983 ◽  
Vol 6 (3) ◽  
pp. 127-130 ◽  
Author(s):  
C. Woffindin ◽  
N.A. Hoenich ◽  
D.N.S. Kerr
Keyword(s):  
Blood Flow ◽  
Regression Analysis ◽  
Small Molecules ◽  
Flat Plate ◽  
Flow Rate ◽  
Distribution Curve ◽  
Blood Flow Rate ◽  
Hollow Fibre ◽  
Urea Clearance ◽  
Flow Rates

Data collected during the evaluation of a series of hemodialysers were analysed to see the effect of hematocrit on the clearance of urea and creatinine. All evaluations were performed on patients with a range of hematocrits with a mean close to 20%. The urea clearance of those in the upper half of the distribution curve (mean hematocrit 29.4%) was not significantly different from that of patients in the lower half of the distribution curve (mean hematocrit 16.9%) whether the clearance was studied at high or low blood flow rates and with hollow fibre or flat plate disposable hemodialysers. Likewise, there was no correlation between hematocrit and urea clearance by regression analysis. In contrast, the clearance of creatinine was affected by hematocrit being greater at lower hematocrit values. This difference was independent of blood flow rate and dialyser type and was confirmed by regression analysis.

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.

scholarly journals In vivo / in vitro Correlation of Pharmacokinetics of Gentamicin, Vancomycin, Teicoplanin and Doripenem in a Bovine Blood Hemodialysis Model

2021 ◽  
Vol 12 ◽  
Author(s):  
M G Vossen ◽  
S Pferschy ◽  
C Milacek ◽  
M Haidinger ◽  
Mario Karolyi ◽  
...  
Keyword(s):  
Blood Flow ◽  
Renal Replacement Therapy ◽  
Protein Binding ◽  
Replacement Therapy ◽  
Flow Rate ◽  
Blood Flow Rate ◽  
Bovine Blood ◽  
Flow Rates ◽  
Dialysate Flow Rate

Background: Elimination of a drug during renal replacement therapy is not only dependent on flow rates, molecular size and protein binding, but is often influenced by difficult to predict drug membrane interactions. In vitro models allow for extensive profiling of drug clearance using a wide array of hemofilters and flow rates. We present a bovine blood based in vitro pharmacokinetic model for intermittent renal replacement therapy.Methods: Four different drugs were analyzed: gentamicin, doripenem, vancomicin and teicoplanin. The investigated drug was added to a bovine blood reservoir connected to a hemodialysis circuit. In total seven hemofilter models were analyzed using commonly employed flow rates. Pre-filter, post-filter and dialysate samples were drawn, plasmaseparated and analyzed using turbidimetric assays or HPLC. Protein binding of doripenem and vancomycin was measured in bovine plasma and compared to previously published values for human plasma.Results: Clearance values were heavily impacted by choice of membrane material and surface as well as by dialysis parameters such as blood flow rate. Gentamicin clearance ranged from a minimum of 90.12 ml/min in a Baxter CAHP-170 diacetate hemofilter up to a maximum of 187.90 ml/min in a Fresenius medical company Fx80 polysulfone model (blood flow rate 400 ml/min, dialysate flow rate 800 ml/min). Clearance of Gentamicin vs Vancomicin over the F80s hemofilter model using the same flow rates was 137.62 mL vs 103.25 ml/min. Doripenem clearance with the Fx80 was 141.25 ml/min.Conclusion: Clearance values corresponded very well to previously published data from clinical pharmacokinetic trials. In conjunction with in silico pharmacometric models. This model will allow precise dosing recommendations without the need of large scale clinical trials.

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.

scholarly journals Blood flow rate and wall shear stress in seven major cephalic arteries of humans

2019 ◽  
Vol 236 (3) ◽  
pp. 522-530
Author(s):  
Roger S. Seymour ◽  
Qiaohui Hu ◽  
Edward P. Snelling
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Rate ◽  
Blood Flow Rate ◽  
Wall Shear

High Blood flow Rates with Adjustment of Needle Diameter do not Increase Hemolysis during Hemodialysis Treatment

2007 ◽  
Vol 8 (4) ◽  
pp. 252-257 ◽  
Author(s):  
F. Techert ◽  
S. Techert ◽  
L. Woo ◽  
W. Beck ◽  
H. Lebsanft ◽  
...  
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Venous Pressure ◽  
Blood Flow Rate ◽  
Needle Size ◽  
Flow Rates ◽  
Blood Damage ◽  
Before And After ◽  
Needle Diameter ◽  
Hb Concentration

Background Higher blood flow in dialysis therapy is often avoided due to concerns about shear-induced blood damage despite the lack of reliable data. Objective This study investigated the influence of higher blood flow rates on plasma free hemoglobin (Hb) concentration after hemodialysis (HD) treatment. Methods Thirty-two chronic HD patients were treated once with a blood flow rate of 250 mL/min using a 17G needle, and once with a blood flow rate of 500 mL/min using a 14G needle. Arterial and venous pressure and blood pressure (BP) were recorded before and after treatment. Blood samples were taken before and after treatment for analysis of plasma free Hb, pH, HCO3, base excess, hematocrit value, urea, sodium, potassium and calcium. Results HD treatment at blood flow rates of 500 mL/min did not increase plasma free Hb compared to treatments at blood flow rates of 250 mL/min. Frequency of intradialytic BP drops was not different either. By adaptation of the needle size, negative arterial pressure could be kept at a similar level. Urea reduction rates were significantly higher during treatments with higher blood flow rates. Conclusion Higher blood flow rates can be applied without an increased hemolysis risk provided that needle sizes are adapted accordingly.

Effect of blood flow rate and blood flow history on newborn pulmonary microcirculation

1991 ◽  
Vol 261 (2) ◽  
pp. H271-H279 ◽  
Author(s):  
C. D. Fike ◽  
M. R. Kaplowitz
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Left Atrial ◽  
Total Pressure ◽  
Pulmonary Blood Flow ◽  
Blood Flow Rate ◽  
Atrial Pressure ◽  
Left Atrial Pressure ◽  
Flow Rates ◽  
Pulmonary Arterial

The purpose of this study was to determine whether increased pulmonary blood flow and/or the history of pulmonary blood flow alters microvascular pressures in lungs of newborns. Using the direct micropuncture technique, we measured pressures in 20- to 60-microns-diameter arterioles and venules in isolated lungs of newborn rabbits at consecutive blood flow rates of 50 (baseline), 100, and/or 200 ml.min-1.kg-1. Then in some lungs we returned blood flow rate to baseline and repeated microvascular pressure measurements. We kept left atrial pressure the same at all blood flow rates. When blood flow rate increased and left atrial pressure was maintained constant, pulmonary arterial, 20- to 60-microns-diameter arteriolar, and 20- to 60-microns-diameter venular pressures increased such that the percentage of total pressure drop that occurred across veins increased. When we returned blood flow to baseline, venular pressure returned to baseline, but arteriolar and pulmonary arterial pressures returned to values less than baseline so that the percentage of the total pressure drop that occurred across microvessels decreased. Thus both blood flow rate and blood flow history are important determinants of the longitudinal distribution of pulmonary vascular pressures across newborn lungs. These findings also suggest that in newborn lungs venules greater than 60 microns diameter are poorly distensible such that higher blood flow rates result in increased microvascular pressures. Hence, under conditions of increased pulmonary blood flow, such as occurs with left to right shunts, the tendency for edema formation will increase in newborn lungs even if left atrial pressure does not increase.

On the Use of In Vivo Measured Flow Rates as Boundary Conditions for Image-Based Hemodynamic Models of the Human Aorta

2011 ◽  
Author(s):  
Diego Gallo ◽  
Gianluca De Santis ◽  
Federica Negri ◽  
Daniele Tresoldi ◽  
Giovanna Rizzo ◽  
...  
Keyword(s):  
Blood Flow ◽  
Boundary Conditions ◽  
Rigid Wall ◽  
Patient Specific ◽  
Human Aorta ◽  
Computational Domain ◽  
Healthy Human ◽  
Flow Rates ◽  
Measured Flow

It has been demonstrated that computational fluid dynamics (CFD) have the potential to enhance the comprehension of the role played by hemodynamic factors involved in atherosclerosis. Recently, phase-contrast magnetic resonance imaging (PC-MRI) has emerged as an effective tool for providing accurate vascular geometries for CFD simulations and quantitative data on blood flow rates, which can be used to specify realistic boundary conditions (BCs). However, the application of acquired flow waveforms at boundaries is not straightforward, mainly (i) due to possible occurrences of phase shifts and attenuations of outflow with respect to inflow rate and (ii) due to the instantaneous mass conservation constraint, which is required in hemodynamic simulations with rigid wall models, but is not guaranteed in in vivo measurements. As an alternative, new boundary conditions schemes have been developed in an effort to consider the interaction between the computational domain and the upstream/downstream vasculature by coupling through-scale hemodynamic models [1]. However, the identification of the parameters of these simplified vascular models on a subject-specific base involves both pressure and flow rates measurements [2]. In this context, it is clear that the direct application of individual PC-MRI measured flow rates waveforms as BCs in patient-specific simulations should be preferred [3]. In order to overcome the limitations mentioned above, measured flow rates should be combined with stress-free conditions or fixed mass flow ratio (derived from the same set of PC-MRI data) between inlet and multiple outlet sections. However, prescribing different BCs at boundaries can affect the solutions of the equations governing blood flow [1]. For this reason, different strategies in combining outlet BCs could lead to different simulated hemodynamics. This work analyzes the influence of different possible strategies of applying PC-MRI measured flow rates on an image-based hemodynamic model of a healthy human aortic arch with supra-aortic vessels. A total of six flow simulations was carried out applying six different schemes for treating BCs at outlets. Three common wall shear stress (WSS)-based indicators of abnormal flow were considered and the sensitivity of these indicators to the outlet treatment strategy was evaluated.

Preglomerular resistance and glomerular perfusion in the rat and dog

1976 ◽  
Vol 231 (3) ◽  
pp. 961-966 ◽  
Author(s):  
WR Chenitz ◽  
BA Nevins ◽  
NK Hollenberg
Keyword(s):  
Blood Flow ◽  
Cardiac Output ◽  
Flow Rate ◽  
Blood Flow Rate ◽  
Radioactive Microspheres ◽  
Flow Rates ◽  
Afferent Arterioles ◽  
The Difference ◽  
Inner Cortex ◽  
Fractional Distribution

Glomerular blood flow in the rat, measured with radioactive microspheres, averaged 233 +/- 59 nl/min per glomerulus, significantly less than the glomerular flow rate in the dog (568 +/- 115; P less than 0.005). The difference in glomerular blood flow rate could not be attributed to differences in mean or cortical flow rates, the fraction of acrdiac output received, cardiac output normalized to body weight, or the fractional distribution of blood flow or glomeruli from outer to inner cortex in the two species. The size of microspheres reaching the glomerulus, however, was significantly larger in the dog than in the rat (P less than 0.0005) suggesting that afferent arterioles were larger in the dog than rat. The difference in afferent resistance calculated from the size of microspheres delivered to the glomeruli was larger than the difference in glomerular blood flow. With a similar arterial pressure, a lower afferent resistance suggests a higher glomerular capillary pressure in the dog, consistent with a number of suggestions that filtration equilibrium is less likely in this species.

Sign in / Sign up

Export Citation Format

Share Document