血管内支架三角形截面结构流阻的数值模拟实验**

利用数值模拟方法分析新型的三角形截面支架的血液流阻，找出影响血流动力学的支架结构参数，为血管内支架结构设计和优化提供参考依据。通过SoildWorks软件构建了三角形截面裸支架在无限流场中的4种模型，借助ANSYS有限元软件分别对4种模型进行计算流体力学数值模拟，分析模型施加非定常流之后的流动情形、压力分布和流阻的变化情况。结果提示三角形截面形状的支架应用于动脉瘤可以使血流流入瘤腔的阻力大而流出瘤腔的阻力小，导致血液流出容易流入难，从而抑制瘤腔的血液灌注和流动，能够降低瘤腔内的压力，对于动脉瘤的治疗起到一定的效果，这为今后支架结构的设计提供了一些理论指导意义。     

血管内支架结构截面形状的生物力学实验

血管内支架置入体内后会影响血流动力学和血管壁剪切应力等生物力学耦合作用。分析支架杆件扩张受力弯曲的梯形截面比例系数,分别对二维支架梯形截面结构进行血管壁接触和血液流场流固耦合数值计算实验。结果显示,支架结构梯形截面比例系数为4时可减小支架对血管壁的接触应力,并改善支架表面的血流动力学状况。这可以避免支架置入后对血管壁形成的应力受损,显著减低支架表面血栓沉积的再狭窄率,对于血管内支架的设计具有重要的指导意义。     

采用动态推-拉技术增强动脉瘤分流器的导流作用：一项实验和模型研究

目的 神经血管分流器是治疗颅内动脉瘤的一种有弹性的、纵横交错的网状支架。本研究采用动态推-拉技术调节动脉瘤瘤口分流器的网格密度，以便最大化其导流作用。通过自主研发的高保真虚拟支架计算机模型技术联合计算机流体动力学，探讨动态推-拉技术对特定动脉瘤病人血流动力学的影响。方法采用动态推-拉技术和不同长度的传送导线，将两个Pipeline分流器放置到两个相同侧壁的大脑前动脉动脉瘤模型中。然后数字模拟操作过程，并验证模拟的网格几何结构。通过调节放置在侧壁动脉瘤和基底动脉主干梭形动脉瘤（前期已放置分流器）的分流器，采用计算机流体动力学分析，评估血流动力学的具体变化。同时评估来源于临床病例样本的分流器网格的影像。     

组织工程小血管支架移植于异种动物的实验

背景：脱细胞的异种小血管支架已被初步去除引起排斥反应的异种抗原。 目的：将脱细胞的Wistar大鼠尾动脉支架移植于日本大耳白兔耳血管间，长时间观察术后血流和管壁变化，探讨异种脱细胞小血管支架的实验移植应用。 设计、时间及地点：观察对比实验，于2003-03/2004-12在中国医科大学解剖学教研室完成。 材料：供体用Wistar大鼠15只，受体为日本大耳白兔15只。从15只Wistar大鼠每只取2条长2.50cm的尾动脉干共30条作为异种小血管，其中的15条作为供体尾动脉干（尾动脉移植组），另15条经1%Triton X-100脱细胞处理作供体组织工程小血管支架（小血管支架移植组）。受体为15只日本大耳白兔左右耳背面中央动脉。 方法：在外科显微镜下，用11-0线将实验兔中央动脉近侧断端套入供体血管近侧腔内，作全层套叠吻合；远侧断端按常规端端吻合。采用勒通试验法和常规血管管腔血液、管壁染色法连续观察血管内血流状况。 主要观察指标：血管吻合术后，外科显微镜下不同时间血流通畅和光镜、电镜下血管腔血液与管壁结构变化。 结果：血管移植术后的即刻通畅率达100%。 异种小血管支架移植术后最长通畅时间为46小时47分，而尾动脉干为14小时。两组远侧的端端吻合区首先出现血流不畅；套叠区小血管支架与中央动脉外膜间由蒂状结缔组织相连。第10天，小血管支架可见内膜纤维组织仍然呈梳头状整齐排列，未见细胞附着；在术后第100天，仍保留着血管支架的完整性。 结论：①异种小血管支架可以作为血管移植物吻合于异种动物宿主体内，到100天时仍保留着较完整结构。②异种小血管支架血液通畅最长时间为46小时47分，长于异种小血管移植。③异种小血管支架移植的套叠式吻合法优于经典的端端吻合法。     

血管内超弹性TiNi合金支架的有限元模型及流体动力学计算分析

利用有限元模型与计算流体动力学的方法，结合有限元软件COSMOS Works与计算流体动力学软件COSMOS FloWorks，分析了具有特殊形状记忆和超弹性功能的TiNi支架在置入过程中与斑块、血管的相互作用及其对血流情况的影响。计算结果表明，使用COSMOS可较为准确地模拟TiNi合金支架的超弹性；由于具有形状记忆特征，TiNi支架置入后对血管产生更好的顺应性，不易损伤血管壁；利用TiNi材料的超弹性，大变形时会产生更大的支撑力的优势，适当缩短支撑筋的长度来增加支架的支撑力；TiNi合金超弹性产生的柔顺性能让血液流动更畅通，降低血管的再狭窄率。     

家兔动脉瘤模型的刚性及弹性结构数值模拟的对比分析

目的 应用计算流体力学软件模拟家兔的动脉瘤模型,对比刚性及弹性两种结构模型的区别.方法 应用家兔建立侧方及顶端动脉瘤动物模型,测取所需参数.应用系列软件对动脉瘤模型分刚性及弹性结构进行数值模拟,并应用流体力学软件计算出两种模型结构的血流流速值,进行对比分析.结果 基于弹性及刚性结构的家兔动脉瘤的血液动力学参数明显不同,统计学结果显示在动脉瘤的流出道处的差异更加明显(P＜0.05).结论 动脉瘤的刚性及弹性结构的血液动力学参数存在明显差异,弹性结构更加科学合理.     

渐变网格球扩支架治疗兔囊状动脉瘤

目的评估单纯使用新型渐变网格球扩支架治疗动脉瘤的可行性。方法取新西兰大白兔12只,分为实验组（n=6）和对照组（n=6）。采用弹性酶诱导方法,在右侧颈总动脉起始部制作动脉瘤模型,实验组载瘤动脉内植入渐变网格球扩支架,对照组不植入支架。观察3个月,复查造影并行统计学分析,并处死动物行病理检查。对实验组支架植入前后造影结果进行分析．拟合动脉瘤内时间－密度曲线。结果实验组载瘤动脉内均成功植入渐变网格球扩支架,其中1个动脉瘤植入后即刻和3个月造影未见动脉瘤显影,其余5个动脉瘤显影较淡;3个月时,DSA显示支架位置均良好,载瘤动脉通畅,无支架内狭窄;支架植人后时间－密度曲线与术前相比,对流相降低而弥散相增加。对照组1只动物造影前死于麻醉意外,其余5只观察3个月,动脉瘤大小无明显变化。病理显示：实验组1只不显影的动脉瘤血管内膜已完全覆盖支架,而另5只未愈合的动脉瘤颈部支架仍然裸露：对照组动脉瘤体厚薄不均匀。弹力层均消失。结论单纯使用渐变网格球扩支架可促进兔囊状动脉瘤愈合,且对载瘤动脉无明显影响。     

基于生物力学性能的血管内支架弧梁单元结构优化设计

背景：在扩张置入体内支撑血管的过程中血管内支架的结构需具备多种生物力学性能，支架结构可以通过综合多目标优化达到其整体性能的最佳状况。 目的：鉴于国内外的血管内支架结构设计，提取支架结构特征参数，进行生物力学指标的综合多目标优序分析。 方法：基于金属覆盖率、扩张最大支架内应力、最大扩张支架半径、轴向回缩率、径向回缩率等5种生物力学性能的分析，使用ADINA有限元软件建立了81种不同周向单元数、梁宽和单元轴长的支架闭口、平行和开口弧梁单元结构，并使用无量纲化和多目标优序法分析支架性能。 结果与结论：结果显示，可设计以单元轴长较大的闭口和平行弧梁单元为主、具有较小的均匀弧梁宽度的闭口、平行和开口弧梁混合单元结构。实验结果对血管内支架的结构设计和力学性能评价体系具有重要的指导意义。     

足部有限元模型的构建与验证

背景：目前国内所建的足部模型大部分是采用自动划分网格的四面体有限元模型,虽然四面体网格自动剖分技术给三维实体的有限元网格自动剖分带来了极大的方便,但力学性能较差。 目的：基于CT图片构建六面体网格足部有限元模型。 方法：选取中国正常男性人体足部的CT数据,利用Mimics软件对足部几何模型进行重构,运用NURBS 曲面的节点插入算法,对足部几何模型进行了细化,构建了具有较高生物仿真度的人体足部有限元模型,利用Pam-crash软件对模型进行了碰撞仿真分析。 结果与结论：仿真结果与尸体实验结果基本一致,证明模型可信。实验基于CT图片构建的六面体网格足部有限元模型,添加了足底肌肉、肌腱、皮肤等结构,更真实的反映了足部解剖学结构特征,进而提高了有限元模型的质量,更能有效地研究足部损伤机制,从而为提高汽车安全性设计提供参考依据。     

颅内动脉瘤的三维数值模拟分析

目的应用计算流体力学软件结合有限元法对颅内动脉瘤进行三维数值模拟,分析动脉瘤的血液动力学特性。方法利用临床三维血管造影图像建立动脉瘤数值模型,用Matlab7.0软件及Ansys软件提取动脉瘤的立体轮廓并进行三维网格划分,然后应用Fluent6.02软件进行动脉瘤数值模拟及血流动力学分析。结果本例研究对象显示动脉瘤流入道的血流速度、动压及壁面切应力最高,流出道次之,顶部最低。结论①根据病人的解剖结构所构建的动脉瘤模型的三维数值模拟,把压力入口及脉搏波动应用其中,对血流动力学数据分析更先进、更接近临床实际。②动脉瘤顶部的血流流速、瘤内压力、壁面切应力均最低,这种特殊的结构导致了动脉瘤顶部可能成为动脉瘤破裂的部位。③动脉瘤三维数值模拟能够很好地反应动脉瘤的血液动力学特性,是一种极好的动脉瘤实验及临床研究方法。     

低孔率血流导向支架对兔腹主动脉分支动脉开口的影响

目的 评估低孔率血流导向支架对分支动脉开口的影响.方法 30只新西兰大白兔随机分入实验组(n=20)和对照组(n=10).低孔率血流导向支架植入实验组腹主动脉并覆盖分支开口,对照组动物只进行造影不植入支架.3个月后对所有动物再次造影并处死行病理学检查.结果 支架所覆盖的分支在造影随访中均无闭塞,分支开口处新生内膜增生程度和支架孔率呈负相关(r=-0.507,P=0.005),这些新生内膜主要由平滑肌细胞和胶原纤维组成.结论 造影显示低孔率血流导向支架所覆盖的分支开口在术后3个月无闭塞,但病理显示支架可引起分支开口处内膜增生.     

Understanding the effect of effective metal surface area of flow diverter stent’s on the patient-specific intracranial aneurysm numerical model using Lagrangian coherent structures

The effective metal surface area (EMSA) of flow diversions plays an essential role in the occlusion mechanism inside the aneurysm since the value of EMSA determines the amount of blood flow into the aneurysm sac. In the present study, three different models of a flow diverter stent, namely FRED 4017, FRED 4038, and FRED 4539, were virtually placed at the aneurysm neck of a 52-years-old female patient to identify the effect of EMSA on stagnation region formation inside the aneurysm sac. Lagrangian coherent structures (LCSs), hyperbolic time, and particle tracking analysis were employed to the velocity vectors obtained from computational fluid dynamics (CFD). It is noticed that use of FRED 4017 stent with 0.42 EMSA value caused nearly 40% of the weightless blood flow particles (more than FRED 4038 and FRED 4539) to stay inside the aneurysm while only 0.35% of the blood flow was remaining inside the aneurysm sac when no stent was placed into the aneurysm site. Furthermore, hyperbolic time computations illustrated the formation of stagnation fluid flow zones that can be associated with the residence time of the blood flow particles. Lastly, the results of hyperbolic time analysis are in good agreement with digital subtraction angiography (DSA) images taken in the clinic a few minutes after a FRED 4017 implantation.     

Evaluation of 99mTc-hexamethylpropyleneamine oxime cerebral blood flow mapping after acute focal ischemia in rats

Although the blood flow tracer hexamethylpropyleneamine oxime is now widely used for cerebral blood flow mapping using single-photon emission computed tomography, its uptake into acutely ischemic brain has not been well studied. We performed a double-label autoradiographic study in which 99mTc-hexamethylpropyleneamine oxime uptake was compared with [14C]iodoantipyrine-derived cerebral blood flow 0.5, 24, and 72 hours after middle cerebral artery occlusion in 11 rats. We noted excellent correspondence between iodoantipyrine and hexamethylpropyleneamine oxime autoradiograms at all times with both simultaneous tracer injection and 30-minute separation of tracer injections. When the ischemic and hyperemic areas were measured from the same brain section using the two different tracers, hexamethylpropyleneamine oxime underestimated the iodoantipyrine-derived areas by less than 1% (95% confidence interval -2.9% to 2.3%). The maximum discrepancy (-19%) was seen at high flows. When the two tracers were injected separately, the uptake of hexamethylpropyleneamine oxime was not linear compared with iodoantipyrine-derived cerebral blood flow, but the relation became linear after the Lassen correction factor was applied. Hexamethylpropyleneamine oxime uptake thus accurately represents cerebral blood flow 0.5-72 hours after acute cerebral ischemia.     

应用非参数逐步判别分析法建立颅内压半定量数学模型

目的 应用非参数逐步判别分析法（NSDA）建立颅内压（ICP）半定量数学模型,探讨其临床应用价值。方法对21例急性颅高压（ICH）病人采用硬膜外置探头监测ICP,同时连续20min采集大脑中动脉平均血流速度（VMCA）、平均动脉压（MAP）、呼气末二氧化碳分压（PmCO2）和心率（HR）。应用SAS软件,用这4个自变量建立3种ICP（正常至轻度升高、中度升高、重度升高）的NSDA半定量预测模型。结果模型对ICP正常至轻度升高、中度升高、重度升高阶段的错判率分别为5．20％、6．98％和10．17％,总体错判率为6．40％。结论NSDA模型对ICP的判定准确率较高,具有潜在临床应用前景。     

家兔不同程度颈动脉狭窄模型的建立及评价

目的 建立一种颈动脉狭窄模型,并对狭窄处的血液动力学进行分析。方法 用缝线将颈动脉与不同管径的塑料管结扎,形成不同程度颈动脉狭窄家兔模型,而后用数字减影血管造影（DSA）评价狭窄程度,用经颅多普勒（TCD）超声评价狭窄后血液动力学变化。结果 DSA检查狭窄率（CCA法）轻度为30%,中度为59%,重度为84%;TCD能清楚地检测到造模前后颈动脉血液动力学情况,造模后搏动指数(PI)和阻力指数（RI）均降低（除了重度狭窄的近端）;三种狭窄程度下均可见狭窄近端血流速度减低,PI和RI升高,狭窄处血流速度明显升高,RI和PI减低,狭窄远端血流速度、PI和RI均减低。结论 本实验建立的不同程度颈动脉狭窄模型,成模时间短,狭窄程度稳定,能够方便用于血管狭窄后的血液动力学分析,是一种较为理想的以分析血液动力学变化为目的的颈动脉狭窄模型。     

Evaluation of cross-circulation through circle of Willis using an ultrasonic Doppler technique. Part II. Comparison between blood flow velocity by ultrasonic Doppler flowmetry and cerebrovascular resistance

The correlation between the increase in velocity of blood flow in both the internal carotid and vertebral arteries during a carotid compression and the cerebrovascular resistance (CVR) was investigated in 11 patients with chronic ischemic cerebrovascular disease and 4 without organic brain lesions. The velocity of blood flow was measured by an ultrasonic Doppler flowmeter. CVR was calculated from cerebral blood flow and arterial blood pressure. There was no correlation between the increased velocity of blood flow in the internal carotid and vertebral arteries and CVR. The increased velocity of blood flow in patients with low CVR was, however, significantly higher than that of patients with high CVR. The investigation of cross-circulation by ultrasonic Doppler flowmetry is a useful non-invasive method for the detection of changes in cerebral vascular resistance.     

Hemodilution increases cerebral blood flow in acute ischemic stroke

We measured cerebral blood flow in 10 consecutive, but selected, patients with acute ischemic stroke (less than 48 hours after onset) before and after hemodilution. Cerebral blood flow was measured by xenon-133 inhalation and emission tomography, and only patients with focal hypoperfusion in clinically relevant areas were included. Hemodilution was done according to the hematocrit level: for a hematocrit greater than or equal to 42%, 500 ml whole blood was drawn and replaced by the same volume of dextran 40; for a hematocrit between 37% and 42%, only 250 ml whole blood was drawn and replaced by 500 cc of dextran 40. Mean hematocrit was reduced by 16%, from 46 +/- 5% (SD) to 39 +/- 5% (SD) (p less than 0.001). Cerebral blood flow increased in both hemispheres by an average of 20.9% (p less than 0.001). Regional cerebral blood flow increased in the ischemic areas in all cases, on an average of 21.4 +/- 12.0% (SD) (p less than 0.001). In three patients, a significant redistribution of flow in favor of the hypoperfused areas was observed, and in six patients, the fractional cerebral blood flow increase in the hypoperfused areas was of the same magnitude as in the remainder of the brain. In the last patient, cerebral blood flow increased relatively less in the ischemic areas. Our findings show that cerebral blood flow increases in the ischemic areas after hemodilution therapy in stroke patients. The marked regional cerebral blood flow increase seen in some patients could imply an improved oxygen delivery to the ischemic tissue.     

Effects of locus coeruleus stimulation on carotid vascular resistance in the cat

The locus coeruleus was stimulated in 62 cats in order to investigate the effect on cephalic blood flow and cephalic vascular resistance. Flow was measured by electromagnetic flow probes applied to the common carotid artery. Stimulation over a range of frequencies (0.2-200 s-1) produced a frequency-dependent fall in carotid vascular resistance, greater on the ipsilateral side. This response was not affected by either cervical sympathectomy or spinal cord section. The response was blocked by bilateral section of the facial nerve but was not abolished by classical cholinergic, histaminergic or adrenergic blocking agents. Stimulation of the locus coeruleus also resulted in a pressor response through spinal mechanisms in which coeruleo-hypothalamic projections were not involved. A post-stimulation constriction in the carotid vasculature followed the dilator response and was attributed to release of catecholamines from the adrenal medulla.     

单纯支架治疗梭形动脉瘤的计算机仿真及血流动力研究

目的血流导向是治疗颅内梭形或宽颈动脉瘤的重要概念。本研究拟通过计算机仿真技术,探讨单纯多支架治疗梭形动脉瘤的血流导向作用。方法选用病例特异性的椎动脉梭形动脉瘤CFD模型。使用快速虚拟支架植入法植入1～3枚Enterprise支架。使用ICEMCFD软件进行网格化处理,ANSYS软件进行血流动力学分析,比较不同数量支架植入后的各项血流动力学参数的变化。结果虚拟支架植入后支架位置良好、贴壁满意。虚拟植入1～3枚支架后,梭形动脉瘤壁的平均瘤壁面切应力（WSS）分别下降了10％、20．4％和28．3％;经过瘤体最大截面的血流量分别下降了9．6％、21％和32．6％;相对滞留时间延长至支架植入前的1．45倍、2．07倍和2．79倍;动脉瘤壁平均压力变化不大。结论单纯支架治疗颅内梭形动脉瘤具有血流导向作用,随着支架数量增加,上述作用明显增强。快速虚拟支架植入法仿真度高、操作时间短,是适用于临床的虚拟支架植入技术。‘