低频超声场中微血管内微泡动力学仿真研究

在低频超声激励下,研究超声微泡的非线性声学响应,及其与周围生理环境之间的关系,对微泡定量成像、微血管早期病变检测及微泡靶向治疗等有重要的意义。基于集中参数模型,在COMSOL Multiphysics 4.4中构建激励超声、微泡与血管这三者间的耦合模型并进行仿真计算,结果表明:(1)激励超声声压增大时,微泡振动幅度增加、振动频率减小。(2)血管长度增长时,微泡振幅减小、振频增加;血管内径增大时,微泡振幅增加、振频减小。(3)微泡气体多方指数增加时,血管壁应力、血管形变程度及微泡最大振动速度减小、微泡振动频率增大。(4)血液动力粘度增加时,微泡振动幅度、振动频率、血管壁应力及微泡最大振动速度均减小。     

低载荷下耦合电刺激的骨重建数值模拟

目的 考虑电场影响的同时研究骨在低载荷刺激频率下的废用行为。方法 提出一个废用模型并通过参数激活频率来描述力学刺激与电刺激对骨重建过程的影响。通过建立股骨近端有限元模型,结合有限单元法,模拟低载荷刺激频率下耦合电刺激的骨重建过程,并分析骨密度的流失情况。结果 降低日载荷刺激频率会显著降低骨密度。电刺激可以在一定程度上抵抗由于低载荷刺激频率导致的密度流失,其主要影响区域分布在股骨头部与股骨颈部。电刺激持续时长会显著影响骨皮质与骨松质的密度流失情况。结论 模型可以模拟由于日载荷刺激频率降低导致的废用过程;同时,纳入了电场影响表现其抵抗密度流失的现象。     

椎体-椎间盘固液耦合的轴对称表达、建模与分析

目的研究集中载荷作用下椎体-椎间盘的固液耦合问题。方法将椎体-椎间盘视为多孔介质材料,包含固体骨架和隙间流体两相,采用Biot固液耦合方程描述两相影响过程。建立固相平衡方程与液相连续性方程的轴对称表达形式,应用加权残值法得到耦合方程轴对称表达的等效积分形式,离散后得到有限元格式,对时间的离散采用隐式向后差分法。应用有限元程序对椎体-椎间盘的轴对称模型进行数值分析。结果在集中力作用下,椎体-椎间盘孔隙压力随着时间的增大而减小,同时位移随着时间的增大而增大,逐渐两者趋于平衡;压力与位移在力作用点处最大,以此为中心向四周递减。结论载荷对孔压和位移有显著影响;计算结果与现有文献结果基本相符。     

基于三维有限元模型的人体全腰椎振动特性研究

振动暴露被认为是诱发腰椎退行性病变和下腰痛的重要原因,本研究旨在探寻振动载荷对腰椎生物力学的影响。基于人体腰椎L1节段至骨盆(L1-pelvis)的CT扫描数据,重构L1-Pelvis三维几何模型。对该几何模型进行网格划分和材料特性赋值,建立L1-Pelvis三维有限元模型,并利用可获得的实验数据对模型的有效性进行验证。基于该有限元模型,通过瞬时动态分析计算出腰椎各运动节段在幅值40 N,频率5 Hz轴向正弦振动载荷作用下的力学响应,并与-40 N和+40 N轴向静态载荷作用下的结果进行对比,响应参数包括椎体轴向位移、纤维环膨出变形和纤维环基质冯·米塞斯应力。研究结果表明,相比于静态载荷,振动载荷下腰椎各运动节段的椎体轴向位移、纤维环膨出变形、纤维环基质冯·米塞斯应力的幅值分别增加了0.550～1.020 mm、0.124～0.251 mm、0.043～0.099 MPa,最大增幅分别可达195.0%、175.7%、151.4%。从量化角度说明振动载荷下腰椎发生损伤的风险更高。     

基于可见光波段的L3光子晶体谐振腔集成微流槽折射率生物传感器

L3二维光子晶体谐振腔集成微流槽折射率生物传感器在氮化镓(GaN)衬底材料上制备而成,其表面集成微流槽用于盛装生物样本。谐振腔的共振峰的中心频率对微流槽内生物样本折射率的变化十分敏感。该文分别对微流槽内生物样本折射率是1.33,1.48,1.518的情况进行了理论仿真。结果表明,GaN衬底的L3二维光子晶体谐振腔共振峰的中心频率可以设计在650 nm附近,共振峰的半高宽度为9.8 nm,共振峰中心频率随折射率变化产生的频移(即灵敏度)是35 nm/RIU(Refractive Index Unit)。测量共振峰的频移可实现对生物样本折射率变化的检测。     

刚性微管内微泡动力学行为的有限元数值分析

本文建立了超声激励下微管内微泡的有限元数值分析方法。计算结果表明微管内微泡的振动受到一定程度的限制。微泡的有效半径膨胀率和振动频率随着微管半径的减小而减小。同时,微管内微泡的形变为非球形,且程度随着入射声压幅值的增大而变得明显。因此,微管内的微泡动力学行为不同于无限大液体中。     

纳米氢氧化钙根充糊剂溶血性及对根管微渗漏的影响

目的:观察纳米氢氧化钙根充糊剂的溶血性及对根管微渗漏的影响。方法:自制纳米氢氧化钙根充糊剂后进行红细胞溶血性和葡萄糖微渗漏检测试验。红细胞溶血性试验是将实验分为阴性对照组(Ⅰ组,0.9%生理盐水,n=3)、阳性对照组(Ⅱ组,蒸馏水,n=3)和纳米氢氧化钙根充糊剂组(Ⅲ组,新制备的纳米氢氧化钙根充根糊制剂成浸提液,n=3),观察各组红细胞溶血反应,确定纳米氢氧化钙根充糊剂的溶血率,初步评价其生物安全性。葡萄糖微渗漏检测试验是选取60颗单根直管前磨牙,经根管预备后随机分为A、B、C、D四组,每组各15颗牙齿。A组使用牙胶尖与Vitapex的复合根充糊剂;B组用牙胶尖充填,不使用根管封闭剂;C组为含主要成分氢氧化钙的Vitapex根充糊剂;D组为纳米氢氧化钙根充糊剂。各组牙齿置于微渗漏检测模型中,分别在第1、2、4、7、14、21、28天用葡萄糖氧化酶法检测从冠方向根方漏出的葡萄糖的量。结果:Ⅲ组的血红蛋白相对值明显低于Ⅱ组(0.05±0.02vs 0.70±0.08,P0.01),溶血率为4.41%,显著小于医用植入材料要求红细胞溶血率≤5%的允许范围。在相同时间段,D组较C组的葡萄糖微渗漏值显著减小(第28天为2.09±0.89mmol/L vs 5.04±0.98mmol/L,P0.01)。结论:本实验制备纳米氢氧化钙根充糊剂的溶血性及微渗漏均符合临床根管治疗要求。     

ZHD─1型微冲击振动仪诱发骨折端微动对骨折愈合的影响

兔实验性股骨干骨折髓针内固定，术后随机分成振动组、对照组，振动组用ＺＨＤ─１型微振仪（冲击力大小４３克，频率０．５Ｈｚ）诱发骨折段微动，对照组仅作对照，结果证明，振动组骨折愈合快，肢体血流量、骨痂光密度、骨折段的扭距优于对照组。     

视神经损伤后视神经及其内毛细血管的早期超微结构的变化

目的观察视神经损伤后视神经和神经内毛细血管的超微结构变化,探讨视神经损伤的机制。方法建立家兔视神经损伤的动物模型,利用透射电子显微镜观察视神经及神经内毛细血管超微结构的变化。结果视神经损伤0.5h后,轴突部分肿胀,髓鞘疏松,微管、微丝排列出现紊乱,线粒体肿胀,毛细血管内皮细胞中的吞饮小泡和微绒毛明显减少;损伤6h后,线粒体出现髓样变和空泡样变性,血管内皮细胞肿胀,管腔变窄;损伤12h后,轴突空泡样变性,髓鞘脱失,毛细血管周围间隙增宽;损伤48h后,轴质密度增加,部分髓鞘板层完全分离,微管、微丝及线粒体发生颗粒性溶解,内皮细胞中的线粒体出现广泛变性;损伤96h时,轴索崩解呈空泡状变性,髓鞘更广泛崩解,毛细血管扩张破裂,红细胞外溢。结论视神经损伤早期轴突肿胀、空泡样变性,线粒体水肿变性,微管、微丝数量减少;视神经内毛细血管扩张,通透性增加。     

囊式充液抗荷服过载响应特性仿真研究

目的高性能战机飞行时会产生很高的过载加速度,导致人体血液聚集在下肢和足部,不能回流到上肢和大脑,造成飞行员黑视、呼吸障碍以及丧失意识等。目前通常采用充气式抗荷服对抗过载造成的生理障碍,但使用充气式抗荷服操作复杂且反应延迟,会使飞行员产生疲劳。为解决充气抗荷服的这些问题,一种具有快速冲压效果的新型充液抗荷服已被提出。为研究充液抗荷服的过载响应特性,本文以囊式充液抗荷服为例,建立了人体下肢有限元模型,对不同充液水平、不同过载下的肌肉和服装进行了数值仿真研究。方法首先通过ABAQUS有限元软件进行建模,再将不同静水压模拟不同过载并通过改变充液管管腔厚度模拟不同充液水平,最后计算囊式充液抗荷服在不同过载、不同充液水平作用下的体表压力、肌肉变形等生理和物理参数变化情况。结果 (1)肌肉体表压力随过载增加而增大;(2)肌肉体表压力随充液量增加而减小;(3)服装最大应力和最大变形量随过载增加和充液水平增加而增大。结论应当寻找合适的充液水平,保证体表压力和服装应力在不同过载下均处于较合适的水平,从而保证囊式充液抗荷服的设计更为有效、安全。     

Nonlinear finite element analysis of the vibration characteristics of the maxillary central incisor related to periodontal attachment

The vibration characteristics of a maxillary central incisor were investigated by using the finite element method (FEM) according to nonlinear behavior of the human periodontal ligament (PDL). The effect of alveolar bone loss was also studied to obtain the relationship between the vibration property of the tooth in the periodontal system and the level of periodontal attachment for assessing the condition of periodontium. Three-dimensional (3D) finite element model of the tooth was constructed using CT image-reconstruction, and the elastic face foundation constraint was applied to the surface of the tooth root where the PDL was attached to. Modal analysis was performed by using FEM. The nonlinear behavior of the PDL was assigned and approached by the piecewise linearized method. The results indicated that the vibration of the maxillary central incisor in the periodontal system could be described by several modal frequencies and modes. The first four modes were dominant, which varied with the deformation of the PDL or the force applied on the tooth. The vibration frequency of the maxillary central incisor decreased with the losing of the alveolar bone, but the ratio of decrease had no significant correlation with the nonlinear behavior of the human PDL. The vibration frequency of the maxillary central incisor can be used to describe the loss of the alveolar bone and the level of periodontal attachment, under physiological short-term loading.     

The Effect of Physical Loading on Bone Broadband Ultrasound Attenuation

Objective: Physical loading changes bone microstructure and may influence quantitative ultrasound(QUS) parameters. This study aims at evaluating the effect of physical loading on bone QUS measurement. Methods: Ten fresh bovine bone specimens were studied, which were scanned by a micro-CT and the density and structure parameters were calculated. The QUS measurement was performed when specimens subjected to loading, which changed from 0 to 1,000 N with the step of 100 N. Statistical analysis was performed to evaluate the difference between n BUA measured with and without loading, and the relationship between n BUA and the parameters measured by micro-CT. Results: While the loading exerted on bone lugher than 200 N, the measured nBUA significantly higher than n BUA measured without loading. With the increasing of loading, which exerted on bone, the values of nBUA also increased. A new parameter, the slope of the linearity fitted curve of nBUA values measured under different loading conditions, was introduced to evaluate BMD. The correlation coefficient between the slope and BMD is-0.869(P=0.001). Conclusion: Physical loading substantially influences bone QUS measurement. QUS measurement performed under loading condition may be a new ultrasound method for osteoporosis diagnosis.     

猪胸主动脉血管各向异性力学性能的实验研究

目的 研究猪胸主动脉血管各向异性的力学特性。 方法 收集21条猪胸主动脉血管并分成3组。沿每条血管的轴向剖开并展成平面,以展开后血管的长方向（即血管轴向）0°为起始角,逆时针方向分别切取30°、 45°、 60°、90°、120°、 135°、 150°、180° 8个角度方向的样本。以1、5、10 mm/min的加载速率分别对3组样本进行单轴拉伸测试,以获得血管样本在8个不同方向及3种加载速率下的弹性模量和极限应力。 结果 不同角度样本的应力 应变曲线呈现出不同的黏弹性行为;随着样本角度的变化,从30°开始,弹性模量逐渐增大,到90°时弹性模量最大,然后逐渐减小,直到180°;极限应力与弹性模量的变化规律基本一致。不同加载速率对弹性模量和极限应力的结果具有明显的影响,但对血管的各向异性度影响较小。结论 猪主动脉血管呈现较强的各向异性,研究结果为有限元分析建模中材料属性的赋值提供参数参考,对理解血管生物力学特性具有重要的意义。     

Decrease in Fine T-cell Subset ratio MT2/MT1 During Steroid Reduction of Asthmatic Patients

Combining inhaled long-acting β-2 agonist (LABA) and inhaled corticosteroid (ICS) seems to offer asthma control at a lower dose of ICS than achieved by ICS alone. Fine mapping of T-cell surface markers by flow cytometry offers a detailed status of the individual's inflammatory response. The frequency of MT2 (CD4⁺CD45RA^–CD62L⁺CD11adim) and MT1 (CD4⁺CD45RA^–CD62L^–CD11abright) cells in peripheral blood, and their ratio, has been shown to differ predictably in atopics and patients with leprosy, where MT2 correlates with a Th2 phenotype and MT1 with a Th1 phenotype. Stable asthmatics, requiring fluticasone propionate (FP) 750–1000 µg daily or equivalent, were randomized to receive, double-blinded, either Seretide^®[salmeterol and fluticasone propionate (SFC, n  = 16)] 50 µg/500 µg bd or FP 500 µg bd ( n  = 17). If asthma was controlled based on lung function and symptoms at clinic visits every 6 weeks, ICS dose was tapered until asthma exacerbated or 0 µg was reached. The frequency and ratio of MT2 and MT1 T cells of the patients was monitored at 6 week intervals. As treatment tapered, the frequency of MT2 cells decreased ( P =  0038 from first to final visit), whereas that of MT1 cells increased. The ratio of MT2/MT1 decreased ( P =  0049 from first to final visit). In patients receiving LABA + ICS, the fall in MT2/MT1 ratio appeared to be more pronounced than in patients receiving ICS alone. Thus, the MT2 phenotype may be associated with stable asthma, whereas an imminent exacerbation may associate with an increase in the MT1 phenotype. LABA may allow for a greater effect of FP on the MT ratio.     

Lenke3型特发性侧凸脊柱的动态特性

目的 探讨Lenke3型脊柱侧凸有限元模型的动力学响应。方法 利用Lenke3型脊柱侧凸患者CT扫描图像建立有限元模型,对模型进行有效性验证。并对模型进行模态分析、谐响应分析和瞬态动力学分析。结果 本模型第1阶固有频率仅为1-2 Hz;在第1阶固有频率时,有限元模型的振幅最大。在同一共振频率时,胸弯曲椎体比腰弯曲椎体振幅大;从T6到L2椎体,各方向的振幅依次减弱。结论 人体脊柱畸形程度可能影响脊柱对振动的感知。脊柱畸形程度越高,对振动的敏感程度就越高。第1固有频率对Lenke3型脊柱侧凸患者危害最大;在循环载荷下,胸弯曲椎体比腰弯曲椎体更易产生较大变形;越靠近T1椎体,振动幅度就越大。     

振动对骨重建影响的三维有限元分析

目的观察不同振动频率刺激下股骨表观密度的变化情况,从而确定何种振动参数能对骨骼系统产生最有益影响。方法先获得兔股骨扫描图像,再利用UG软件对图像进行三维重建得到股骨的实体模型,最后导入ANSYS软件中,利用ANSYS软件布尔操作中的减操作,得到带有空腔的兔股骨生物力学模型。结果通过有限元仿真分析,发现添加振动激励后骨骼的应力分布和骨密度发生了变化,股骨部分部位骨密度增加。结论有限元分析不但为分析振动对骨重建的动物和人体实验打下基础,还为进一步深入了解骨骼结构与力学环境之间的关系、为进一步研究对抗航天失重引起的骨丢失和治疗骨质疏松症提供了帮助。     

基于超弹性模型的动脉血管数值计算

目的：实验研究表明。血管在周向与轴向两种单轴向拉伸作用下表现出不同的力学特性,本文通过对血管单轴拉伸的数值计算,给出分别适用于周向和轴向荷载的模拟方法。方法：基于超弹性本构模型对轴向和周向两种单轴拉伸作用下血管的应力一应变关系进行数值计算,并结合血管组织结构特点及模型适用范围对结果进行分析,同时通过数值计算对Holzapfel．Gasser-Ogden模型中的各向异性参数对结果的影响展开讨论。结果：计算结果显示单一使用各向同性超弹性应变势函数无法准确完整的模拟两种情况下的单轴拉伸实验,周向拉伸采用各向同性超弹性本构模型的数值结果较好的吻合实验,而轴向拉伸宜采用Holzapfel-Gasser-Ogden模型。Holzapfel。Gasser-Ogden模型中各向异性参数1描述血管中两组增强纤维主方向的分散程度,y值越大即纤维平均主方向与轴向加载方向夹角越小,在外荷载作用下越容易使得纤维旋转到荷载方向;参数K描述血管中每组增强纤维主方向上纤维的分散程度。K值越大,纤维在基体中分散越广泛,材料性子越接近纤维,宏观表现越硬。结论：本文基于超弹性本构模型对轴向和周向两种单轴拉伸作用下血管的应力应变关系进行数值计算,提出分别用多项式形式的各向同性超弹性本构模型数值计算周向荷载作用下应力应变关系、Holzapfel-Gasser-Ogden各向异性超弹性本构模型数值模拟轴向荷载下力学性质,数值结果与实验吻合较好,为心血管系统的数值模拟提供指导,对血管系统的力学机制和临床研究具有重要意义。     

Evaluation of specific pick-ups and preamplifiers for the recording of heart vibrations

Experiments have shown that pick-ups used for the recording of heart vibrations (apexcardiography, phonocardiography) can influence the vibrations of the soft tissue chest wall to which they are applied. This influence is most pronounced in the medium and high frequency range (10 . . . . . 1000 Hz). Owing to the mechanical loading effect of the pick-up on the chest wall, the vibrations are attenuated and distorted. This is also shown with respect to pure mass loading of the chest wall. The loading effect on the chest wall (coupling function) has been studied by us in the frequency-domain as well as in the time-domain on 6 normal subjects who were in the recumbent position. Typical parameters of the coupling function have been established in relation to mass loading. An empirical formula has been found for the degree of attenuation of the vibrations caused by the load. In order to perform these investigations, a special seismic pick-up FYSPac2 has been constructed which will load the tissue to a slight degree only. Its mass is 1 g and it has a flat frequency response up to 1 kHz and a high sensitivity (12 pC m-1s2). The problem of the vibration measurement on soft tissue is discussed here in its whole context: the loading effect of the pick-up, the sensitivity (and bandwidth) of the pick-up as well as the quality of the preamplifier as regards its transfer characteristics and its electronic noise level.(ABSTRACT TRUNCATED AT 250 WORDS)     

Frequency-dependent effects of muscle tendon vibration on corticospinal excitability: a TMS study

The aim of the present study was to investigate the effects of muscle tendon vibration at different frequencies on corticospinal excitability by means of transcranial magnetic stimulation (TMS). A second objective was to describe whether the observed modulations in motor evoked potentials (MEPs), as a function of vibration frequency, reflect the behavior of Ia afferents during and after vibration. In ten subjects, muscle tendon vibration (duration 30 s) was applied to the flexor carpi radialis (FCR) muscle at three different frequencies (20, 75 and 120 Hz). MEPs following single-pulse TMS were recorded from the targeted muscle during a previbration, vibration, and postvibration period. Muscle tendon vibration at 75 Hz increased the MEP amplitude significantly during vibration, whereas a smaller but still significant effect was observed during 120 Hz vibration. No significant MEP changes could be observed during 20 Hz vibration and during the postvibration period for each frequency. Our findings indicate that muscle tendon vibration exerts a frequency-dependent effect on corticospinal excitability. Furthermore, evidence is provided for the notion that the excitatory effect of muscle tendon vibration on the primary motor cortex is mediated by Ia afferent input.     

Stress distribution in implant-supported prostheses using different connection systems and cantilever lengths: digital photoelasticity

Photoelastic analysis was used to evaluate the biomechanical behaviour of implant-supported, double-screwed crowns with different connection systems and cantilever lengths. Three models were made in PL-2 photoelastic resin and divided into six groups, on the basis of the implant connection system (external hexagon [EH] or Morse taper [MT]), type of abutment (Mini Pilar [Neodent, Curitiba, Paraná, Brazil] or “UCLA”) and number of crowns in the cantilever (one or two). The implant-prosthesis unit was placed in a circular polariscope. Occlusal surfaces of the crowns were subjected to 100-N loads in the axial and oblique (45°) directions in a universal testing machine (EMIC). Generated stresses were recorded and analysed qualitatively in a graphics program (Adobe Photoshop). Under axial loading, all of the groups had similar numbers of fringes, which were increased when the crowns were subjected to oblique loading. The highest number of fringes was found during oblique loading in the EH?+?Mini Pilar group. In conclusion, although the type of implant connection system did not have a direct influence on the stress distribution for axial loading, the cantilever length did have a direct influence on stress distribution. Models with two crowns in the cantilever showed more stress, with a greater concentration of force on the cervical part of the implant.