A Bidomain Model Based BEM-FEM Coupling Formulation for Anisotropic Cardiac Tissue

A hybrid boundary element method (BEM)/finite element method (FEM) approach is proposed in order to properly consider the anisotropic properties of the cardiac muscle in the magneto- and electrocardiographic forward problem. Within the anisotropic myocardium a bidomain model based FEM formulation is applied. In the surrounding isotropic volume conductor the BEM is adopted. Coupling is enabled by requesting continuity of the electric potential and the normal of the current density across the boundary of the heart. Here, the BEM part is coupled as an equivalent finite element to the finite element stiffness matrix, thus preserving in part its sparse property. First, continuous convergence of the coupling scheme is shown for a spherical model comparing the computed results to an analytic reference solution. Then, the method is extended to the depolarization phase in a fibrous model of a dog ventricle. A precomputed activation sequence obtained using a fine mesh of the heart was downsampled and used to calculate body surface potentials and extracorporal magnetic fields considering the anisotropic bidomain conductivities. Results are compared to those obtained by neglecting in part or totally (oblique or uniform dipole layer model) anisotropic properties. The relatively large errors computed indicate that the cardiac muscle is one of the major torso inhomogeneities. © 2000 Biomedical Engineering Society. PAC00: 8719Nn, 8719Hh, 8719Ff, 8710+e, 8717Nn     

El modelo del Vórtex: una aproximación diferente a una vía aérea difícil

Airway management is an essential area in anaesthesia, and anaesthesiologists are considered the most expert professionals to manage airway tasks. However, complications related to inadequate airway management remain the most frequent cause of morbidity and mortality.Algorithmic strategy to solve difficulties fails, due to several factors related to its structure and clinical application.The Vortex Approach has emerged as a response to the limitations found in the algorithmic strategy of managing the difficult airway, by using a cognitive aid strategy to reduce cognitive load and fixation error. This new strategy may represent a solution to the elusive problem of the challenging airway and reduce the complications rate.     

应用血流向量成像技术观察心肌梗死患者左心室舒张期血流状态

目的应用血流向量成像技术(VFM)观察心肌梗死患者左心室舒张期血流状态的变化规律。方法选取36名健康志愿者(健康对照组)和39例左心室前壁心肌梗死患者(心肌梗死组)作为观察对象,获得其左心室血流向量成像图像,分析其舒张期不同时相涡流特征并比较两组的定量参数。结果健康对照组在等容舒张期未见明显涡流图像,舒张早期和晚期在二尖瓣前后叶下方可见2个较小且对称的涡流,舒张中期显示充盈左心室腔较大的整体涡流。心肌梗死组在舒张期各时相的涡流变化规律与健康对照组相似,但舒张早期、晚期的二尖瓣下涡流横径、纵径均大于健康对照组,差异有统计学意义[(33.42±6.77)mmvs(24.53±4.73)mm,(41.50±5.87)mmvs(25.55±4.72)mm,t=12.916、23.248,P均<0.05)];舒张早期、中期、晚期涡流横向距离和纵向距离均大于健康对照组,差异有统计学意义[(20.60±4.60)mmvs(13.23±4.25)mm,(28.65±3.75)mmvs(15.20±4.38)mm,(17.70±3.79)mmvs(12.59±4.20),(40.93±7.33)mmvs(26.13±4.83)mm,(51.69±11.41)mmvs(22.84±4.52)mm,(36.00±8.25)mmvs(21.50±3.59)mm,t=9.618、18.528、13.336、17.266、36.805、27.528,P均<0.05)]。心肌梗死组舒张期各时相涡强度均大于健康对照组,差异有统计学意义[(24.71±5.24)/svs(15.18±4.39)/s,(19.33±3.67)/svs(11.23±3.53)/s,(33.42±5.38)/svs(21.17±6.32)/s,t=8.542、10.358、9.751,P均<0.05)],而最大向量速度与健康对照组差异无统计学意义。结论 VFM可显示心肌梗死患者左心室舒张期血流状态的变化,并可对涡流的特点作定量分析。     

运用血流向量成像技术评价正常人左心室涡流状态

【摘要】目的应用超声血流向量成像（VFM）技术对正常人左心室（LV）心动周期各时相涡流变化进行初步分析,探讨左心室内涡流变化特征。方法50名健康志愿者采集连续4个心动周期的标准心尖三腔心切面彩色血流动态图像,应用VFM技术进行脱机分析,测量心动周期各时相左心室内漩涡的横向位置、纵向位置、横径、纵径、面积、漩涡最大流量、漩涡强度。结果①等容舒张早期：极少数人于二尖瓣前叶下方可见短暂的小漩涡,随即消失。②舒张早期（快速充盈期）：二尖瓣前后叶下方附近出现2个小漩涡,前叶下方漩涡出现率较高;舒张中期（缓慢充盈期）：左心室腔内可见一个大漩涡;舒张晚期（房缩期）：二尖瓣前叶下方可见一个漩涡,部分正常人后叶下方也可见一个很小漩涡。③等容收缩期：靠近二尖瓣前叶下方左心室流出道（LVOT）内可见一个小漩涡;射血早期：此漩涡位置更靠近二尖瓣前叶,漩涡纵径缩短,面积缩小,强度增大,随后漩涡逐渐减小至射血中期消失;射血晚期：部分正常人在左心室心尖可见一个短暂的小漩涡。④所有健康志愿者射血期主动脉瓣周可见漩涡。结论VFM技术可用于量化正常人左心室内涡流状态;VFM为研究涡流,评价心腔内血流结构提供了一种新的方法。     

血流向量成像定量评价急性心肌梗死患者等容收缩期左心室涡流

目的应用血流向量成像(VFM)技术分析急性心肌梗死(AMI)患者等容收缩期左心室内血液流场的特点。方法选择AMI患者25例和正常志愿者40名,采集两组心尖三腔心切面彩色血流动态图像,应用VFM分析软件测量等容收缩期左心室内涡流横径、纵径,涡流的横向、纵向相对位置及其最大向量速度、涡流强度等指标,比较上述两组各参数。结果与正常志愿者比较,AMI患者等容收缩期涡流纵径增大(P<0.05),横向位置更靠近后侧壁,最大向量速度、涡流强度均减低(P<0.05)。结论等容收缩期AMI患者左心室内涡流纵径、横向位置、最大向量速度、涡流强度与正常人相比存在差异,涡流形态、位置发生改变。VFM为评价心腔内血液流场特征提供了新的途径。     

A New Echocardiographic Method for Identifying Vortex Flow in the Left Ventricle: Numerical Validation

A new mathematical method for estimating velocity vectors from color Doppler datasets is proposed to image blood flow dynamics; this method has been called echodynamography or vector flow mapping (VFM). In this method, the concept of stream function is exploited to expand a 2-D distribution of radial velocities in polar coordinates, observed with color Doppler, to a 2-D distribution of velocity vectors. This study was designed to validate VFM using 3-D numerical flow models. Velocity fields were reconstructed from the virtual color Doppler datasets derived from the models. VFM captured the gross features of flow structures and produced comparable images of the distribution of vorticity, which correlated significantly with the original field (for velocity magnitudes, standard error of estimate = 0.003 to 0.007m/s; for vorticity, standard error of estimate = 0.35 to 2.01/s). VFM may be sensitive for depicting flow structures derived from color Doppler velocities with reasonable accuracy. (E-mail: t.uejima@nifty.ne.jp)     

基于PIV技术的人体上呼吸道流场测量实验装置的构建

目的针对人体上呼吸道气流运动形成涡结构、流动分流、二次流等特点,研制基于粒子图像测速（particle image velocimetry, PIV）技术的人体上呼吸道流场测量实验装置,为开展人体上呼吸道流场特性实验研究提供平台。方法 基于完整人体上呼吸道医学扫描图像制备透明的实物模型,通过选择合适的气路系统,结合二维PIV系统搭建整套实验装置,并利用该装置对人体上呼吸道流场速度进行初步实验,将实验结果和数值仿真结果进行对比。结果呼吸流量为30 L/min稳态呼吸模式下,实验装置测得的气流在口腔上部有涡结构的形成,口腔下部贴近舌苔上部及口腔中部的气流速度较高,其他部位气流速度较低,与数值仿真结果较为一致。结论 基于PIV技术的人体上呼吸道流场测量实验装置合理可行,运行可靠,可用于人体上呼吸道内气流组织形式和涡量分布等测量,并能够实现对数值仿真的验证。     

Management of difficult intravenous access: a qualitative review

BACKGROUND: A perennial challenge faced by clinicians and made even more relevant with the global obesity epidemic, difficult intravenous access(DIVA) adversely impacts patient outcomes by causing significant downstream delays with many aspects of diagnoses and therapy. As most published DIVA strategies are limited to various point-of-care ultrasound techniques while other “tricks-of-the-trade” and pearls for overcoming DIVA are mostly relegated to informal nonpublished material, this article se...     

不同部位心肌梗死对左心室收缩期涡流影响的初步研究

目的 应用血流向量图(vector flow map,VFM)技术对不同部位心肌梗死患者收缩期涡流特点进行连续动态观察,比较前壁和下后壁节段性运动异常对收缩期涡流的影响.方法 根据冠状动脉造影结果将冠心病心肌梗死患者分为单纯左前降支病变组(LAD组)和左旋支或(和)右冠病变组(LCX/RCA组).应用VFM技术观察两组收缩期心腔内血液流场特点,计算涡流持续时间等参数并与正常对照组相比较.结果 LAD组等容收缩期整体涡流同正常组无明显差异,射血早期涡流范围大,常在心尖部形成局部涡流;LCX/RCA组等容收缩期涡流范围较小,射血早期涡流较LAD组明显减小,较正常组增大,出现的部位多位于心腔中部.病例组涡流总持续时间和瓦解时间均较对照组延长,LAD组和LCX/RCA组比较差异无统计学意义;整体涡流持续时间三组间差异无统计学意义.结论 前壁心肌梗死对收缩期左室血液流场的影响较下后壁更明显,VFM技术可以用于显示并评价该变化.