Stanford B型主动脉夹层撕破口局部计算流体力学研究

目的:探索Stanford B型主动脉夹层局部血流动力学改变对主动脉夹层发生、发展以及临床预后评估的作用,为临床治疗方案选择提供理论依据。方法:通过CT扫描获取临床常见典型形态的Stanford B型主动脉夹层断层序列,重建出三维主动脉夹层计算流体力学分析模型,对主动脉夹层真假腔内血液流场进行数值模拟计算。结果:血液流经Stanford B型主动脉夹层撕破口时会对血管局部壁面产生冲击,造成动脉管壁局部压强升高,此种"冲击效应"不但会出现在近端夹层撕破口附近管腔壁面,也会出现在中间段及远端夹层撕破口附近,当入口血流压强升高时,夹层撕破口附近局部壁面压强差值也会增加。在心动周期内,Stanford B型主动脉夹层壁面剪切应力异常升高区也主要集中在撕破口区附近的动脉壁面上。结论:对于Stanford B型主动脉夹层而言,撕破口的位置相对于撕破口直径而言似乎更有临床意义。对B型夹层患者采用降低血压治疗,可减低局部动脉管壁上的壁面压强差值,但无法消除此壁面压强差,即主动脉夹层管壁上的局部危险区始终存在。此现象揭示主动脉夹层中远端撕破口也可能是造成夹层局部危险因素的原因,采用手术治疗方法封闭撕破口,以消除局部壁面压强增高区,降低破裂风险,可能是更理想的治疗方法。     

Computational Fluid Dynamics Analysis of Upper Airway Changes after Protraction Headgear and Rapid Maxillary Expansion Treatment

Clinically, it is common for Class III patients with maxillary skeletal deficiency, which may result in a variety of adverse consequences. Protraction headgear and rapid maxillary expansion (PE) is an effective treatment, but its effect on upper airway hydrodynamics has not been reported. The main purpose of this study was to evaluate the changes of the flow in the upper airway after PE by computational fluid dynamics (CFD). The sample includes fifteen patients (6 males, 9 females, age 11.00 ± 1.00) and the paired T-test was used to analyze the differences between the measured data before and after treatment. The maximum flow velocity decreased from 8.42 ± 0.16 m/s to 6.98 ± 0.36 m/s (p < 0.05), and the maximum shear force decreased from 3.72 ± 1.48 Pa to 2.13 ± 0.18 Pa. The maximum negative pressure decreased from −101.78 ± 33.60 Pa to 58.15 ± 9.16 Pa, only the changes of velopharynx and glossopharynx were statistically significant; while the maximum resistance decreased from 140.88 ± 68.68 Pa/mL/s to 45.95 ± 22.96 Pa/mL/s. PE can effectively reduce the airflow resistance of the upper airway and the probability of airway collapse, thus improving the patient’s ventilation function.     

A Patient-Specific Computational Fluid Dynamic Model of Middle Cerebral Artery Aneurysm Before and One Year After Surgery

Computational fluid dynamics (CFD) has been widely used for studying intracranial aneurysm hemodynamics, while its use for guiding clinical strategy is still in development. In this study, CFD simulations helped informtreatment decision for a middle cerebral artery (MCA) aneurysm case was investigated. A patient with a 10.4 × 9.8 mm aneurysm attached with a small aneurysmat the edge of the trifurcation in the left MCA was included in this study. Forremoving the MCA aneurysm, two scenarios were considered: Plan-A involvedclipping the small aneurysm and Plan-B involved clipping the whole aneurysm.A suitable treatment plan was decided by comparing the clinical measurementsand CFD analysis between these two plans. One-year after the surgery, theCFD analysis was conducted again on the post-operative aneurysm model to verify the selected surgical plan in terms of morphometric and hemodynamic properties changes in the aneurysm. Based on the CFD simulation and clinicalexperience, surgical Plan-A was adopted. One-year after the surgery, both thehemodynamic and morphological properties improved in the post-operativeaneurysm model, indicating the recovery of the patient. The patient-specificaneurysm CFD analysis can help to determine a better surgical plan for patientswith special cerebral aneurysms. This study showed how CFD analysis can beused to aid clinical diagnosis and treatment.     

构建基于患者个体化的Stanford B型主动脉夹层计算流体力学数值模拟分析模型

目的:探索简便、高效、精确的构建基于真实人体解剖形态结构的Stanford B型主动脉夹层计算流体力学数值模拟分析模型的方法.方法:利用Siemens Sensation Cardiac 64层螺旋CT薄层扫描技术,基于1mm层厚获取6例Stanford B型主动脉夹层连续断层DICOM格式图像,导入Materialise MIMICS v12.11软件,界定目标区域后生成三维动脉模型,经网格优化处理去除低质量及相交面网格,保存结果输出,导入TGrid 5.0软件,对主动脉面网格模型进行几何修复,使面网格扭曲率<0.75,采用自由分网方式生成Stanford B型主动脉夹层计算流体力学分析体网格模型,并对所构建模型进行血流属性、流场边界等界定,初步验证模型的有效性.结果:通过初步计算求解,确定所构建的6例Stanford B型主动脉夹层计算流体力学分析模型分别包含1857030,1820501,1844181,1849651,1858246及1814914个四面体单元.结论:利用64层螺旋CT薄层扫描技术获取DICOM格式连续断层CT图像可快速、准确地构建Stanford B型主动脉夹层计算流体力学数值模拟分析模型,为进一步的计算流体力学分析奠定了良好的基础.     

Comparison of Aerodynamic Forces and Moments Calculated by Three-dimensional Unsteady Blade Element Theory and Computational Fluid Dynamics

In previous work,we modified blade element theory by implementing three-dimensional wing kinematics and modeled the unsteady aerodynamic effects by adding the added mass and rotational forces.This method is referred to as Unsteady Blade Element Theory (UBET).A comparison between UBET and Computational Fluid Dynamics (CFD) for flapping wings with high flapping frequencies (＞30 Hz) could not be found in literature survey.In this paper,UBET that considers the movement of pressure center in pitching-moment estimation was validated using the CFD method.We investigated three three-dimensional (3D) wing kinematics that produce negative,zero,and positive aerodynamic pitching moments.For all cases,the instantaneous aerodynamic forces and pitching moments estimated via UBET and CFD showed similar trends.The differences in average vertical forces and pitching moments about the center of gravity were about 10％ and 12％,respectively.Therefore,UBET is proven to reasonably estimate the aerodynamic forces and pitching moment for flight dynamic study of FW-MAV.However,the differences in average wing drags and pitching moments about the feather axis were more than 20％.Since study of aerodynamic power requires reasonable estimation of wing drag and pitching moment about the feather axis,UBET needs further improvement for higher accuracy.     

中性粒细胞计数、D-二聚体及Caprini血栓评分对脑血管狭窄介入术后下肢深静脉血栓形成的预测价值及模型构建

摘要 目的：探讨中性粒细胞计数、D-二聚体及Caprini血栓评分对脑血管狭窄介入术后下肢深静脉血栓形成（DVT）的关系及预测模型构建。方法：选择2021年2月至2022年2月于我院神经外科行血管内介入治疗的281例脑血管狭窄患者,术前检测外周血中性粒细胞计数、D-二聚体,并采用Caprini血栓评分评估患者DVT风险,并根据术后是否发生DVT将患者分为DVT组（31例）和无DVT组（250例）。收集临床资料,采用多因素Logistic回归分析影响脑血管狭窄介入术后DVT的危险因素,构建预测模型,Hosmer-Lemeshow检验预测模型拟合度,受试者工作特征（ROC）曲线分析预测模型对脑血管狭窄介入术后DVT的预测价值。结果：DVT组中性粒细胞计数、D-二聚体、Caprini血栓评分高危和极高危比例高于无DVT组（P＜0.05）。且中心静脉导管、卧床时间超过72 h、高中性粒细胞计数、高D-二聚体、Caprini血栓评分分级高危和极高危是脑血管狭窄介入术后DVT的危险因素（P＜0.05）。由上述指标构建的预测模型,其预测脑血管狭窄介入术后DVT的曲线下面积AUC（0.95CI）为0.871（0.779～0.938）,灵敏度为0.871（27/31）,特异度为0.832（208/250）。经Hosmer-Lemeshow检验模型拟合效果良好（P＞0.05）。结论：中心静脉导管、卧床时间超过72 h、高中性粒细胞计数、高D-二聚体、Caprini血栓评分分级高危和极高危是脑血管狭窄介入术后DVT的危险因素,根据回归分析构建预测模型对脑血管狭窄介入术后DVT的预测能效较好。     

Molecular Dynamics Simulations for 1:1 Solvent Primitive Model Electrolyte Solutions

Abstract

Molecular dynamics (MD) simulations at constant temperature have been carried out for systems of 1:1 solvent primitive model (SPM) electrolyte solutions. Equilibrium thermodynamics, mean cluster size, self-diffusion coefficients, and collision frequencies were computed to examine the electrostatic effects on the structural and dynamical properties. Coherent ionic cluster motion was deduced from a cluster analysis and from the dependence of the velocity and force autocorrelation functions (FACFs). The resulting MD data for the collision frequencies and self-diffusivities of both ions and hard-spheres were shown to be in good agreement with the theoretical predictions.     

A Structural Model for Apolipoprotein C-II Amyloid Fibrils: Experimental Characterization and Molecular Dynamics Simulations

The self-assembly of specific proteins to form insoluble amyloid fibrils is a characteristic feature of a number of age-related and debilitating diseases. Lipid-free human apolipoprotein C-II (apoC-II) forms characteristic amyloid fibrils and is one of several apolipoproteins that accumulate in amyloid deposits located within atherosclerotic plaques. X-ray diffraction analysis of aligned apoC-II fibrils indicated a simple cross-β-structure composed of two parallel β-sheets. Examination of apoC-II fibrils using transmission electron microscopy, scanning transmission electron microscopy, and atomic force microscopy indicated that the fibrils are flat ribbons composed of one apoC-II molecule per 4.7-Å rise of the cross-β-structure. Cross-linking results using single-cysteine substitution mutants are consistent with a parallel in-register structural model for apoC-II fibrils. Fluorescence resonance energy transfer analysis of apoC-II fibrils labeled with specific fluorophores provided distance constraints for selected donor-acceptor pairs located within the fibrils. These findings were used to develop a simple ‘letter-G-like’ β-strand-loop-β-strand model for apoC-II fibrils. Fully solvated all-atom molecular dynamics (MD) simulations showed that the model contained a stable cross-β-core with a flexible connecting loop devoid of persistent secondary structure. The time course of the MD simulations revealed that charge clusters in the fibril rearrange to minimize the effects of same-charge interactions inherent in parallel in-register models. Our structural model for apoC-II fibrils suggests that apoC-II monomers fold and self-assemble to form a stable cross-β-scaffold containing relatively unstructured connecting loops.     

Computational fluid dynamics modeling of mass transfer behavior in a bioreactor for hairy root culture. I. Model development and experimental validation

A two-dimensional axisymmetric computational fluid dynamics (CFD) model based on a porous media model and a discrete population balance model was established to investigate the hydrodynamics and mass transfer behavior in an airlift bioreactor for hairy root culture.During the hairy root culture of Echinacea purpurea, liquid and gas velocity, gas holdup, mass transfer rate, as well as oxygen concentration distribution in the airlift bioreactor were simulated by this CFD model. Simulative results indicated that liquid flow and turbulence played a dominant role in oxygen mass transfer in the growth domain of the hairy root culture. The dissolved oxygen concentration in the hairy root clump increased from the bottom to the top of the bioreactor cultured with the hairy roots, which was verified by the experimental detection of dissolved oxygen concentration in the hairy root clump. This methodology provided insight understanding on the complex system of hairy root culture and will help to eventually guide the bioreactor design and process intensification of large-scale hairy root culture.     

Consequences of Sequential Ca2+ Occupancy for the Structure and Dynamics of CalbindinD9K: Computational Simulations and Comparison to Experimental Determinations in Solution

Abstract

Molecular dynamics (MD) simulations of the structures of calbindin_D9K (CAB) with different occupancies of the two Ca²⁺ binding sites were carried out to gain insight into structural and energetic consequences of sequential Ca²⁺ binding. The aim of the study is to identify effects of Ca-binding site occupancy that relate to the properties and functions of Ca-binding proteins containing EF-hand motifs. Two different models of solvation were employed, one defined by a linear, distance dependent dielectric permittivity (ε = r) and inclusion only of the 36 crystallographically observed water molecules, and the other with the protein immersed in a 9Å shell of explicit waters and ε = 1. Experimental results from x-ray crystallography, and insights from NMR and from measurements of hydrogen exchange rates in these systems served as tests and guides for assessing the quality, validity and mechanistic interpretation of the results from the computational study. The results of the MD simulations agree very well with earlier experimental observations that the structure of calbindin_D9k is rather insensitive to removal of Ca²⁺, and indicate that this insensitivity is not dependent on the order in which the ions are removed. The calculated values of the electrostatic potentials at the Ca²⁺ binding sites are very similar, in agreement with the small differences in the measured microscopic binding constants. Details of the dynamic mechanisms of molecular flexibility revealed by the MD simulations are also in good agreement with experimental findings, including the local properties identified from comparisons of hydrogen exchange rates in various parts of the structures of sequentially occupied forms of CAB. Estimation of the changes in configurational entropy from the rms fluctuations in the structures of CAB at various levels of Ca²⁺ occupancy in the EF-hands, supports earlier suggestions relating the dynamic properties of the protein to the observed cooperativity in the binding of Ca²⁺. The computational approaches and the results of the MD simulations are evaluated in relation to the study of effects of Ca²⁺ occupancy in calmodulin and troponin C where ion binding determines function and is known to trigger significant changes in structural and dynamic properties.