Computational fluid dynamics simulation to evaluate aortic coarctation gradient with contrast-enhanced CT

Coarctation of aorta (CoA) is a narrowing of the aorta leading to a pressure gradient (ΔP) across the coarctation, increased afterload and reduced peripheral perfusion pressures. Indication to invasive treatment is based on values of maximal (systolic) trans-coarctation ΔP. A computational fluid dynamic (CFD) approach is herein presented for the non-invasive haemodynamic assessment of ΔP across CoA. Patient-specific CFD simulations were created from contrast-enhanced computed tomography (CT) and appropriate flow boundary conditions. Computed ΔP was validated with invasive intravascular trans-CoA pressure measurements. Haemodynamic indices, including pressure loss coefficient (PLc), time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI), were also quantified. CFD-estimated ΔP values were comparable to the invasive ones. Moreover, the aorta proximal to CoA was exposed to altered TAWSS and OSI suggesting hypertension. PLc was found as a further geometric marker of CoA severity. Finally, CFD-estimated ΔP confirmed a significant reduction after percutaneous balloon dilatation and stenting of the CoA in one patient (e.g. from ΔP～52 mmHg to ΔP～3 mmHg). The validation of the ΔP computations with catheterisation measurements suggests that CFD simulation, based on CT-derived anatomical data, is a useful tool to readily quantify CoA severity.     

A geometry-based model for non-invasive estimation of pressure gradients over iliac artery stenoses

The aim of this study was to develop and verify a model that provides an accurate estimation of the trans-lesion hyperemic pressure gradient in iliac artery stenoses in seconds by only using patient-specific geometric properties obtained from 3-dimensional rotational angiography (3DRA).Twenty-one patients with symptomatic peripheral arterial disease (PAD), iliac artery stenoses and an ultrasound based peak systolic velocity ratio between 2.5 and 5.0 underwent 3DRA and intra-arterial pressure measurements under hyperemic conditions. For each lesion, geometric properties were extracted from the 3DRA images using quantitative vascular analysis software. Hyperemic blood flow was estimated based on stenosis geometry using an empirical relation. The geometrical properties and hyperemic flow were used to estimate the pressure gradient by means of the geometry-based model. The predicted pressure gradients were compared with in vivo measured intra-arterial pressure measurements performed under hyperemic conditions.The developed geometry-based model showed good agreement with the measured hyperemic pressure gradients resulting in a concordance correlation coefficient of 0.86. The mean bias ± 2SD between the geometry-based model and in vivo measurements was comparable to results found by evaluating the actual computational fluid dynamics model (−1.0 ± 14.7 mmHg vs −0.9 ± 12.7 mmHg).The developed model estimates the trans-lesional pressure gradient in seconds without the need for an additional computational fluid dynamics software package. The results justify further study to assess the potential use of a geometry-based model approach to estimate pressure gradient on non-invasive CTA or MRA, thereby reducing the need for diagnostic angiography in patients suffering from PAD.     

Patient-Specific Artery Shrinkage and 3D Zero-Stress State in Multi-Component 3D FSI Models for Carotid Atherosclerotic Plaques Based on <i>In Vivo</i> MRI Data

Image-based computational models for atherosclerotic plaques have been developed to perform mechanical analysis to quantify critical flow and stress/strain conditions related to plaque rupture which often leads directly to heart attack or stroke. An important modeling issue is how to determine zero stress state from in vivo plaque geometries. This paper presents a method to quantify human carotid artery axial and inner circumferential shrinkages by using patient-specific ex vivo and in vivo MRI images. A shrink-stretch process based on patient-specific in vivo plaque morphology and shrinkage data was introduced to shrink the in vivo geometry first to find the zero-stress state (opening angle was ignored to reduce the complexity), and then stretch and pressurize to recover the in vivo plaque geometry with computed initial stress, strain, flow pressure and velocity conditions. Effects of the shrink-stretch process on plaque stress/strain distributions were demonstrated based on patient-specific data using 3D models with fluid-structure interactions (FSI). The average artery axial and inner circumferential shrinkages were 25% and 7.9%, respectively, based on a data set obtained from 10 patients. Maximum values of maximum principal stress and strain increased 349.8% and 249% respectively with 33% axial stretch. Influence of inner circumferential shrinkage (7.9%) was not very noticeable under 33% axial stretch, but became more noticeable under smaller axial stretch. Our results indicated that accurate knowledge of artery shrinkages and the shrink-stretch process will considerably improve the accuracy of computational predictions made based on results from those in vivo MRI-based FSI models.     

Accuracy vs. computational time: translating aortic simulations to the clinic

State of the art simulations of aortic haemodynamics feature full fluid-structure interaction (FSI) and coupled 0D boundary conditions. Such analyses require not only significant computational resource but also weeks to months of run time, which compromises the effectiveness of their translation to a clinical workflow. This article employs three computational fluid methodologies, of varying levels of complexity with coupled 0D boundary conditions, to simulate the haemodynamics within a patient-specific aorta. The most comprehensive model is a full FSI simulation. The simplest is a rigid walled incompressible fluid simulation while an alternative middle-ground approach employs a compressible fluid, tuned to elicit a response analogous to the compliance of the aortic wall. The results demonstrate that, in the context of certain clinical questions, the simpler analysis methods may capture the important characteristics of the flow field.     

Estimation of valvular resistance of segmented aortic valves using computational fluid dynamics

Aortic valve stenosis is associated with an elevated left ventricular pressure and transaortic pressure drop. Clinicians routinely use Doppler ultrasound to quantify aortic valve stenosis severity by estimating this pressure drop from blood velocity. However, this method approximates the peak pressure drop, and is unable to quantify the partial pressure recovery distal to the valve. As pressure drops are flow dependent, it remains difficult to assess the true significance of a stenosis for low-flow low-gradient patients. Recent advances in segmentation techniques enable patient-specific Computational Fluid Dynamics (CFD) simulations of flow through the aortic valve. In this work a simulation framework is presented and used to analyze data of 18 patients. The ventricle and valve are reconstructed from 4D Computed Tomography imaging data. Ventricular motion is extracted from the medical images and used to model ventricular contraction and corresponding blood flow through the valve. Simplifications of the framework are assessed by introducing two simplified CFD models: a truncated time-dependent and a steady-state model. Model simplifications are justified for cases where the simulated pressure drop is above 10 mmHg. Furthermore, we propose a valve resistance index to quantify stenosis severity from simulation results. This index is compared to established metrics for clinical decision making, i.e. blood velocity and valve area. It is found that velocity measurements alone do not adequately reflect stenosis severity. This work demonstrates that combining 4D imaging data and CFD has the potential to provide a physiologically relevant diagnostic metric to quantify aortic valve stenosis severity.     

曲伏前列素滴眼液联合复方丹参片对老年青光眼患者房水屏障功能 及MMP2 水平的影响

目的:研究曲伏前列素滴眼液联合复方丹参片对老年青光眼患者房水屏障功能、MMP2及临床疗效的影响。方法:选择2012年5月-2015年10月期间在我院就诊的90例青光眼患者作为研究对象,随机分为实验组和对照组,实验组患者接受曲伏前列素滴眼液联合复方丹参片治疗,对照组患者接受曲伏前列素滴眼液治疗,比较两组患者治疗前后的平均眼压水平、房水屏障功能以及血清MMP2含量、MMP2/TIMP1比值。结果:治疗后1个月、2个月、3个月时,实验组患者的平均眼压水平(17.2±2.2 vs 19.7±3.1 mm Hg)、(17.0±2.8 vs 20.2±3.2 mm Hg)、(16.7±2.5 vs 18.2±3.5 mm Hg)均显著低于对照组(P0.05);治疗后3个月时,实验组患者的房水闪辉值(18.3±2.8 vs 33.1±5.6 pc/ms)、房水细胞数以及血清MMP2含量(2.77±0.46 vs 4.02±0.72μg/L)及MMP2/TIMP1比例(0.48±0.07 vs 0.76±0.09)均显著低于对照组(P0.05)。结论:曲伏前列素滴眼液联合复方丹参片治疗能够更为有效地降低眼压水平、改善房水屏障功能,可能与其降低MMP2含量有关。     

Effect of exercise on blood flow through the aortic valve: a combined clinical and numerical study

The aim of this study was to measure the cardiac output and stroke volume for a healthy subject by coupling an echocardiogram Doppler (echo-Doppler) method with a fluid–structure interaction (FSI) simulation at rest and during exercise. Blood flow through aortic valve was measured by Doppler flow echocardiography. Aortic valve geometry was calculated by echocardiographic imaging. An FSI simulation was performed, using an arbitrary Lagrangian–Eulerian mesh. Boundary conditions were defined by pressure loads on ventricular and aortic sides. Pressure loads applied brachial pressures with (stage 1) and without (stage 2) differences between brachial, central and left ventricular pressures. FSI results for cardiac output were 15.4% lower than Doppler results for stage 1 (r = 0.999). This difference increased to 22.3% for stage 2. FSI results for stroke volume were undervalued by 15.3% when compared to Doppler results at stage 1 and 26.2% at stage 2 (r = 0.94). The predicted mean backflow of blood was 4.6%. Our results show that numerical methods can be combined with clinical measurements to provide good estimates of patient-specific cardiac output and stroke volume at different heart rates.     

应用米索前列醇治疗妊高症产后出血的疗效观察

目的:探讨应用米索前列醇对妊高症产后出血的治疗效果。方法:选取我院诊治的200例妊高症产后出血孕妇,将患者分为观察组与对照组,每组100例患者,胎儿娩出后对照组肌注催产素,观察组直肠给予米索丽列醇,按摩子宫,比较治疗后两组患者的平均出血量以及血压状况。结果:治疗前对照组和观察组平均出血量分别为(623.2±45.8)m L、(630.0±46.3)m L(P1=0.176)。治疗后,两组平均出血量分别为(486.1±24.3)m L、(313.3±23.1)m L。与治疗前相比,治疗后两组产妇的出血量均有不同减少,观察组患者少于对照组患者(P2=0.026)。对照组中重度妊高症患者的收缩压及舒张压分别为(170.1±6.7)mm Hg、(113.2±2.1)mm Hg,中度(153.6±5.1)mm Hg、(104.5±5.3)mm Hg,轻度(138.9±4.2)mm Hg、(93.2±2.0)mm Hg。观察组重度妊高症患者中以上指标分别为(169.2±6.5)mm Hg、(114.4±2.5)mm Hg,中度患者(156.2±4.8)mm Hg、(105.9±4.9)mm Hg,轻度患者(140.2±4.4)mm Hg、(90.2±4.4)mm Hg,相应病情下两组患者血压方面均无统计学差异(P3=0.87,P4=0.88,P5=0.75,P6=0.83,P7=0.64,P8=0.92)。对照组和观察组患者中不良反应发生率分别为1.0%(1/100)、2.0%(2/100),差异无统计学意义(P0.05)。结论:米索前列醇直肠用药治疗妊高症产后出血,疗效显著、给药方便、安全性较高,值得进一步推广。     

The influence of inlet velocity profile on predicted flow in type B aortic dissection

In order for computational fluid dynamics to provide quantitative parameters to aid in the clinical assessment of type B aortic dissection, the results must accurately mimic the hemodynamic environment within the aorta. The choice of inlet velocity profile (IVP) therefore is crucial; however, idealised profiles are often adopted, and the effect of IVP on hemodynamics in a dissected aorta is unclear. This study examined two scenarios with respect to the influence of IVP—using (a) patient-specific data in the form of a three-directional (3D), through-plane (TP) or flat IVP; and (b) non-patient-specific flow waveform. The results obtained from nine simulations using patient-specific data showed that all forms of IVP were able to reproduce global flow patterns as observed with 4D flow magnetic resonance imaging. Differences in maximum velocity and time-averaged wall shear stress near the primary entry tear were up to 3% and 6%, respectively, while pressure differences across the true and false lumen differed by up to 6%. More notable variations were found in regions of low wall shear stress when the primary entry tear was close to the left subclavian artery. The results obtained with non-patient-specific waveforms were markedly different. Throughout the aorta, a 25% reduction in stroke volume resulted in up to 28% and 35% reduction in velocity and wall shear stress, respectively, while the shape of flow waveform had a profound influence on the predicted pressure. The results of this study suggest that 3D, TP and flat IVPs all yield reasonably similar velocity and time-averaged wall shear stress results, but TP IVPs should be used where possible for better prediction of pressure. In the absence of patient-specific velocity data, effort should be made to acquire patient’s stroke volume and adjust the applied IVP accordingly.

     

Computational assessment of model-based wave separation using a database of virtual subjects

The quantification of arterial wave reflection is an important area of interest in arterial pulse wave analysis. It can be achieved by wave separation analysis (WSA) if both the aortic pressure waveform and the aortic flow waveform are known. For better applicability, several mathematical models have been established to estimate aortic flow solely based on pressure waveforms. The aim of this study is to investigate and verify the model-based wave separation of the ARCSolver method on virtual pulse wave measurements.The study is based on an open access virtual database generated via simulations. Seven cardiac and arterial parameters were varied within physiological healthy ranges, leading to a total of 3325 virtual healthy subjects. For assessing the model-based ARCSolver method computationally, this method was used to perform WSA based on the aortic root pressure waveforms of the virtual patients. As a reference, the values of WSA using both the pressure and flow waveforms provided by the virtual database were taken.The investigated parameters showed a good overall agreement between the model-based method and the reference. Mean differences and standard deviations were −0.05 ± 0.02 AU for characteristic impedance, −3.93 ± 1.79 mmHg for forward pressure amplitude, 1.37 ± 1.56 mmHg for backward pressure amplitude and 12.42 ± 4.88% for reflection magnitude.The results indicate that the mathematical blood flow model of the ARCSolver method is a feasible surrogate for a measured flow waveform and provides a reasonable way to assess arterial wave reflection non-invasively in healthy subjects.     

Three-dimensional printer-generated patient-specific phantom for artificial in vivo dosimetry in radiotherapy quality assurance

Pretreatment intensity-modulated radiotherapy quality assurance is performed using simple rectangular or cylindrical phantoms; thus, the dosimetric errors caused by complex patient-specific anatomy are absent in the evaluation objects. In this study, we construct a system for generating patient-specific three-dimensional (3D)-printed phantoms for radiotherapy dosimetry. An anthropomorphic head phantom containing the bone and hollow of the paranasal sinus is scanned by computed tomography (CT). Based on surface rendering data, a patient-specific phantom is formed using a fused-deposition-modeling-based 3D printer, with a polylactic acid filament as the printing material. Radiophotoluminescence glass dosimeters can be inserted in the 3D-printed phantom. The phantom shape, CT value, and absorbed doses are compared between the actual and 3D-printed phantoms. The shape difference between the actual and printed phantoms is less than 1 mm except in the bottom surface region. The average CT value of the infill region in the 3D-printed phantom is −6 ± 18 Hounsfield units (HU) and that of the vertical shell region is 126 ± 18 HU. When the same plans were irradiated, the dose differences were generally less than 2%. These results demonstrate the feasibility of the 3D-printed phantom for artificial in vivo dosimetry in radiotherapy quality assurance.     

Computational simulations for aortic coarctation: representative results from a sampling of patients

Treatments for coarctation of the aorta (CoA) can alleviate blood pressure (BP) gradients (Δ), but long-term morbidity still exists that can be explained by altered indices of hemodynamics and biomechanics. We introduce a technique to increase our understanding of these indices for CoA under resting and nonresting conditions, quantify their contribution to morbidity, and evaluate treatment options. Patient-specific computational fluid dynamics (CFD) models were created from imaging and BP data for one normal and four CoA patients (moderate native CoA: Δ12 mmHg, severe native CoA: Δ25 mmHg and postoperative end-to-end and end-to-side patients: Δ0 mmHg). Simulations incorporated vessel deformation, downstream vascular resistance and compliance. Indices including cyclic strain, time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) were quantified. Simulations replicated resting BP and blood flow data. BP during simulated exercise for the normal patient matched reported values. Greatest exercise-induced increases in systolic BP and mean and peak ΔBP occurred for the moderate native CoA patient (SBP: 115 to 154 mmHg; mean and peak ΔBP: 31 and 73 mmHg). Cyclic strain was elevated proximal to the coarctation for native CoA patients, but reduced throughout the aorta after treatment. A greater percentage of vessels was exposed to subnormal TAWSS or elevated OSI for CoA patients. Local patterns of these indices reported to correlate with atherosclerosis in normal patients were accentuated by CoA. These results apply CFD to a range of CoA patients for the first time and provide the foundation for future progress in this area.     

重力对锥形血管中血流压力的影响——基于考虑体位改变的三维流固耦合数学模型

重力是体位改变过程中最基本的生物力学刺激因素．血流压力是表征心血管功能状态的一个基本指标．目前,体位改变影响心血管系统的确切内部机制尚不清楚．为此,采用在流体和固体方程中分别引入体力项的方法,建立一个基于血流动力学概念的三维流固耦合数学模型,用以研究体位改变,确切量化重力对血流压力的影响．通过数值计算,得到以下结果．水平卧位条件下：a．单一血管中血流压力由无重力影响的轴对称二维分布变为重力影响下的三维不对称分布;b．随着进出口压差由小变大,重力对压力分布和极值的影响由大变小,当压差值分别达到10 665.6 Pa(80 mmHg)和2 666.4 Pa(20 mmHg)时,重力的影响就不再随进出口压差增大而变化;对三维单一流体,重力影响的总体趋势类似．对正、倒直立位,压力均为二维轴对称分布,其重力影响强度约为水平卧位的2倍以上．结果表明：基于血流动力学概念,引入体力项,建立三维流固耦合模型为研究体位改变提供了一种新思路,重力对单一血管中血流压力分布和大小的影响因体位不同而不同,并与进出口压差密切相关,提示,若血管进出口压差较小,忽略重力影响,不考虑体位改变,以二维轴对称模型来研究血管中血流状态,须谨慎解释所得结果．     

Estimation of in vivo inter-vertebral loading during motion using fluoroscopic and magnetic resonance image informed finite element models

Finite element (FE) models driven by medical image data can be used to estimate subject-specific spinal biomechanics. This study aimed to combine magnetic resonance (MR) imaging and quantitative fluoroscopy (QF) in subject-specific FE models of upright standing, flexion and extension. Supine MR images of the lumbar spine were acquired from healthy participants using a 0.5 T MR scanner. Nine 3D quasi-static linear FE models of L3 to L5 were created with an elastic nucleus and orthotropic annulus. QF data was acquired from the same participants who performed trunk flexion to 60° and trunk extension to 20°. The displacements and rotations of the vertebrae were calculated and applied to the FE model. Stresses were averaged across the nucleus region and transformed to the disc co-ordinate system (S1 = mediolateral, S2 = anteroposterior, S3 = axial). In upright standing S3 was predicted to be −0.7 ± 0.6 MPa (L3L4) and −0.6 ± 0.5 MPa (L4L5). S3 increased to −2.0 ± 1.3 MPa (L3L4) and −1.2 ± 0.6 MPa (L4L5) in full flexion and to −1.1 ± 0.8 MPa (L3L4) and −0.7 ± 0.5 MPa (L4L5) in full extension. S1 and S2 followed similar patterns; shear was small apart from S23. Disc stresses correlated to disc orientation and wedging. The results demonstrate that MR and QF data can be combined in a participant-specific FE model to investigate spinal biomechanics in vivo and that predicted stresses are within ranges reported in the literature.     

Does clinical data quality affect fluid-structure interaction simulations of patient-specific stenotic aortic valve models?

Numerical models are increasingly used in the cardiovascular field to reproduce, study and improve devices and clinical treatments. The recent literature involves a number of patient-specific models replicating the transcatheter aortic valve implantation procedure, a minimally invasive treatment for high-risk patients with aortic diseases. The representation of the actual patient’s condition with truthful anatomy, materials and working conditions is the first step toward the simulation of the clinical procedure.The aim of this work is to quantify how the quality of routine clinical data, from which the patient-specific models are built, affects the outputs of the numerical models representing the pathological condition of stenotic aortic valve.Seven fluid–structure interaction (FSI) simulations were performed, completed with a sensitivity analysis on patient-specific reconstructed geometries and boundary conditions. The structural parts of the models consisted of the aortic root, native tri-leaflets valve and calcifications. Ventricular and aortic pressure curves were applied to the fluid domain.The differences between clinical data and numerical results for the aortic valve area were less than 2% but reached 12% when boundary conditions and geometries were changed. The difference in the aortic stenosis jet velocity between measured and simulated values was less than 11% reaching 27% when the geometry was changed. The CT slice thickness was found to be the most sensitive parameter on the presented FSI numerical model.In conclusion, the results showed that the segmentation and reconstruction phases need to be carefully performed to obtain a truthful patient-specific domain to be used in FSI analyses.     

Imidazoline receptors of the paraventricular nucleus on the pressor response induced by stimulation of the subfornical organ

In the present experiments we investigated a possible involvement of imidazoline receptors of the paraventricular nucleus (PVN) of the hypothalamus on the pressor effects of the angiotensin II (ANG II) injected into the subfornical organ (SFO), in male Holtzman rats (250–300 g) with a cannula implanted into the third ventricle (3rdV), PVN and SFO. At first we tested the participation of α₂ and imidazoline agonist and antagonist compounds on the pressor effect of ANG II injected into the 3rdV. Based on the results we may conclude that clonidine associated with rilmenidine was able to block the hypertensive response to ANG II. The ANG II (20 pmol) injected into SFO induced a robust increase in blood pressure (37 ± 2 mmHg). Isotonic saline (0.15 M) NaCl did not produce any change in blood pressure (5 ± 2 mmHg). The injection of rilmenidine (30 μg/kg/1 μL), an imidazoline agonist agent injected into PVN before ANG II injection into SFO, blocked the pressor effect of ANG II (5 ± 2 mmHg). Also, the injection of idazoxan (60 μg/kg/μL) before rilmenidine blocked the inhibitory effect of rilmenidine on blood pressure (39 ± 4 mmHg). The injection of clonidine (20 nmol/μL) prior to ANG II into the 3rdV produced a decreased in arterial blood pressure (37 ± 2 mmHg) to (15 ± 4 mmHg). The injection of yohimbine (80 nmol/μL) prior to clonidine blocked the effect of clonidine on the effect of ANG II (27 ± 2 mmHg). The injection of rilmenidine prior to ANG II also induced a decrease in arterial blood pressure (10 ± 3 mmHg). The injection of idazoxan prior to rilmenidine also blocked the inhibitory effect of rilmenidine (24 ± 3 mmHg). In summary, the present study demonstrated that rilmenidine decreases the hypertensive effect of ANG II, with more potency than clonidine, even when injected into 3rdV or PVN. This study established that the PVN interacts with SFO by imidazoline receptors in order to control the arterial blood pressure.     

Fluid-structure interaction modeling of aneurysmal arteries under steady-state and pulsatile blood flow: a stability analysis

Tortuous aneurysmal arteries are often associated with a higher risk of rupture but the mechanism remains unclear. The goal of this study was to analyze the buckling and post-buckling behaviors of aneurysmal arteries under pulsatile flow. To accomplish this goal, we analyzed the buckling behavior of model carotid and abdominal aorta with aneurysms by utilizing fluid-structure interaction (FSI) method with realistic waveforms boundary conditions. FSI simulations were done under steady-state and pulsatile flow for normal (1.5) and reduced (1.3) axial stretch ratios to investigate the influence of aneurysm, pulsatile lumen pressure and axial tension on stability. Our results indicated that aneurysmal artery buckled at the critical buckling pressure and its deflection nonlinearly increased with increasing lumen pressure. Buckling elevates the peak stress (up to 118%). The maximum aneurysm wall stress at pulsatile FSI flow was (29%) higher than under static pressure at the peak lumen pressure of 130 mmHg. Buckling results show an increase in lumen shear stress at the inner side of the maximum deflection. Vortex flow was dramatically enlarged with increasing lumen pressure and artery diameter. Aneurysmal arteries are more susceptible than normal arteries to mechanical instability which causes high stresses in the aneurysm wall that could lead to aneurysm rupture.     

Multi-patient study for coronary vulnerable plaque model comparisons: 2D/3D and fluid–structure interaction simulations

Several image-based computational models have been used to perform mechanical analysis for atherosclerotic plaque progression and vulnerability investigations. However, differences of computational predictions from those models have not been quantified at multi-patient level. In vivo intravascular ultrasound (IVUS) coronary plaque data were acquired from seven patients. Seven 2D/3D models with/without circumferential shrink, cyclic bending and fluid–structure interactions (FSI) were constructed for the seven patients to perform model comparisons and quantify impact of 2D simplification, circumferential shrink, FSI and cyclic bending plaque wall stress/strain (PWS/PWSn) and flow shear stress (FSS) calculations. PWS/PWSn and FSS averages from seven patients (388 slices for 2D and 3D thin-layer models) were used for comparison. Compared to 2D models with shrink process, 2D models without shrink process overestimated PWS by 17.26%. PWS change at location with greatest curvature change from 3D FSI models with/without cyclic bending varied from 15.07% to 49.52% for the seven patients (average = 30.13%). Mean Max-FSS, Min-FSS and Ave-FSS from the flow-only models under maximum pressure condition were 4.02%, 11.29% and 5.45% higher than those from full FSI models with cycle bending, respectively. Mean PWS and PWSn differences between FSI and structure-only models were only 4.38% and 1.78%. Model differences had noticeable patient variations. FSI and flow-only model differences were greater for minimum FSS predictions, notable since low FSS is known to be related to plaque progression. Structure-only models could provide PWS/PWSn calculations as good approximations to FSI models for simplicity and time savings in calculation.

     

Effects of wall distensibility in hemodynamic simulations of an arteriovenous fistula

Arteriovenous fistulae are created surgically to provide adequate access for dialysis patients suffering from end-stage renal disease. It has long been hypothesized that the rapid blood vessel remodeling occurring after fistula creation is in part a process to restore the mechanical stresses to some preferred level, i.e., mechanical homeostasis. The current study presents fluid–structure interaction (FSI) simulations of a patient-specific model of a mature arteriovenous fistula reconstructed from 3D ultrasound scans. The FSI results are compared with previously published data of the same model but with rigid walls. Ultrasound-derived wall motion measurements are also used to validate the FSI simulations of the wall motion. Very large time-averaged shear stresses, 10–15 Pa, are calculated at the fistula anastomosis in the FSI simulations, values which are much larger than what is typically thought to be the normal homeostatic shear stress in the peripheral vasculature. Although this result is systematically lower by as much as 50 % compared to the analogous rigid-walled simulations, the inclusion of distensible vessel walls in hemodynamic simulations does not reduce the high anastomotic shear stresses to “normal” values. Therefore, rigid-walled analyses may be acceptable for identifying high shear regions of arteriovenous fistulae.     

苯磺酸左旋氨氯地平在治疗老年轻中度高血压中的作用

目的:观察探讨苯磺酸左旋氨氯地平治疗老年轻中度高血压患者的临床疗效和安全性。方法:160例老年轻中度高血压患者随机分为研究组与对照组,研究组给予苯磺酸左旋氨氯地平;对照组给予苯磺酸氨氯地平,治疗过程中进行24h血压监测,总治疗8周为一疗程。结果:研究组4周末和8周末的总有效率分别为78.75%和96.25%,显著高于对照组的53.75%和86.25%,差异有统计学意义(P<0.05)。治疗前后两组的舒张压和收缩压均有明显降低,其中研究组收缩压平均下降(29.0±3.2)mmHg,舒张压平均下降(15.3±2.3)mmHg,对照组则分别下降(18.5±2.8)mmHg和(9.0±2.5)mmHg,差异具有统计学意义(P<0.05)。治疗8周末的24h、白昼和夜间的收缩压和舒张压均有明显降低,差异有统计学意义(P<0.05),但治疗组下降更明显,与对照组比较差异有统计学意义(P<0.05)。治疗后两组的脉压均有明显降低,差异具有统计学意义(P<0.05),但研究组下降更明显。结论:苯磺酸左旋氨氯地平治疗老年轻中度高血压临床疗效好,不良反应少,且对心脏具有保护功能。