左心室局部心肌梗塞时的组分式模型及计算机仿真

为研究左心室局部心肌梗塞时心肌各部分的能量供需状况及心脏辅助装置对改善心肌能量供给的影响，我们建立了一个由左心室正常区域心肌和梗塞区域心肌两部分组成的组分式模型，我们的模型以Ｓｕｎａｇａｗａ的模型为基础，并在此基础上加以扩展，与Ｓｕｎａｇａｗａ的模型相比，我们的模型允许梗塞区域心肌的收缩性在一定范围内变化，从而可以模拟各种不同范围和不同程度的梗塞情况。用建立好的左心室组分式模型取代我们原有的狗的心     

虚拟咬合运动初步仿真模拟的研究与实现

我们试验了利用VR技术进行虚拟咬合仿真制作的全部过程。首先,采用光学三维测量仪对上下颌石膏模型进行数字化,通过预处理获取有效的三角网格曲面模型;其次,对咬合运动模型进行合理的简化,分解为一系列的平移运动和旋转运动;通过动态刷新完成开闭口运动、侧移运动的计算机运动仿真,可视化地观察咬合运动;然后利用模型碰撞检测算法动态地计算咬合接触位,并详细地分析了咬合接触时的咬合点位置分布和咬合剖切面上的咬合点接触关系;最后讨论了目前虚拟咬合仿真存在的问题和今后研究的方向。     

骨骼肌介电行为的理论模型仿真

在 10 0 Hz～ 10 0 MHz范围内 ,应用椭圆壳介电理论模型 ,经过模拟仿真蛙骨骼肌细胞的介电行为 ,确定了蛙骨骼肌细胞的椭圆壳模型各相参数。为将来对骨骼肌疲劳、肌营养不良和肌肉萎缩等病症的模型分析奠定理论基础。     

Stress analysis between implant prostheses with different moduli and surrounding bones北大核心

背景:应力遮挡效应会导致植入假体修复骨缺损手术失败,其主要原因是由于植入假体的弹性模量大于骨组织弹性模量。目的:分析植入假体弹性模量对应力分布的影响,寻求消除应力遮挡现象的方法。方法:通过CT扫描的方式获取实验犬与人体骨组织的模型,分别对其优化后进行梯度赋值,建立较为可靠的骨骼力学模型,并与植入假体组合后进行有限元仿真。首先,通过对比格犬骨骼模型和人体骨骼模型及其对应的植入假体进行有限元仿真,模拟了不同弹性模量对植入假体修复术后的应力和位移分布情况;其次,分析了较小弹性模量差仍会形成应力遮挡现象的原因,建立了骨骼模型及植入假体模型,确立了材料属性赋予方法;最后,验证了该模型及材料属性赋予方法的可行性,并通过随机选取受力点的方式,定量分析植入假体弹性模量与骨骼弹性模量之间的关系对应力遮挡形成的影响。结果与结论:通过梯度赋值法建立与骨骼力学性质更加接近的实验犬骨骼模型和人体骨骼模型,该方法重建的力学模型与真实骨骼的力学性质更为接近;通过有限元仿真力学测试证明,不同弹性模量植入假体对假体本身与周围骨骼间相对位移的影响较小;另外量化弹性模量对假体植入骨骼后对应力分布的影响,可为后续的相关研究提供帮助。     

A computer model for the study of breast cancer

A computer model was designed as a relational database to assess breast cancer screening in a cohort of women where the growth and development of breast cancer originates with the first malignant cell. The concepts of thresholds for growth, axillary spread, and distant sites are integrated. With tumor diagnosis, staging was performed that includes clinical and sub-clinical states. The model was parameterized to have staging characteristics similar to data published by the Surveillance, Epidemiology, and End-Results (SEER) Program. Validation was accomplished by comparing simulated staging results with non-SEER sources, and simulated survival with independent clinical survival data.     

Analysis of dynamic cerebral autoregulation using an ARX model based on arterial blood pressure and middle cerebral artery velocity simulation

The study aimed to model the cerebrovascular system, using a linear ARX model based on data simulated by a comprehensive physiological model, and to assess the range of applicability of linear parametric models. Arterial blood pressure (ABP) and middle cerebral arterial blood flow velocity (MCAV) were measured from 11 subjects non-invasively, following step changes in ABP, using the thigh cuff technique. By optimising parameters associated with autoregulation, using a non-linear optimisation technique, the physiological model showed a good performance (r=0.83±0.14) in fitting MCAV. An additional five sets of measured ABP of length 236±154 s were acquired from a subject at rest. These were normalised and rescaled to coefficients of variation (CV=SD/mean) of 2% and 10% for model comparisons. Randomly generated Gaussian noise with standard deviation (SD) from 1% to 5% was added to both ABP and physiologically simulated MCAV (SMCAV), with ‘normal’ and ‘impaired’ cerebral autoregulation, to simulate the real measurement conditions. ABP and SMCAV were fitted by ARX modelling, and cerebral autoregulation was quantified by a 5 s recovery percentage R5% of the step responses of the ARX models. The study suggests that cerebral autoregulation can be assessed by computing the R5% of the step response of an ARX model of appropriate order, even when measurement noise is considerable.     

IPFM，MIPFM模型产生的仿真心率变异性信号的周期图与AR谱分析研究

为了研究不同心电序列转换方式及不同谱估计方法对心率变异性（ＨＲＶ）信号谱分析结果的影响，本文对积分脉冲频率调制（ＩＰＦＭ）模型及修正积分脉冲频率调制（ＭＩＰＦＭ）模型在输入不同振幅与频率的正弦信号时所产生的随机点过程，用两种心电序列转换方法进行转换得到仿真ＨＲＶ信导；然后，采用周期图与自回归（ＡＲ）谱估计方法计算这种厉真ＨＲＶ信号的功率谱。研究结果表明：①对于ＭＩＰＦＭ模型产生的随机点过程，同一心电序列转换方法所得出的仿真ＨＲＶ信号的ＡＲ谱与周期图的谱峰功率估计基本一致；而对ＩＰＦＭ模型则不完全一致。②ＭＩＰＦＭ模型仿真实验表明，对实际ＨＲＶ信号谱分析，使用低，高频谱峰功率比（ＲＦ）作为反映心脏自主神经张力平衡的指标时，除心电序列传换及谱估计方法可能造成的误差外，当低频谱峰靠近极低频谱峰时，根据ＲＦ值解释生理实验结果会有校大误差。③座分析实际ＨＲＶ信号的工作中，不同心电序列转换方式产生的伪谐波对ＨＲＶ谱分析结果的影响不大。     

A method of analyzing of the “Dose-effect” dependence in multifactor medico-biological experiments

A conceptual-logical and mathematical approximation model has been created for the organism's response to external factors. The mathematical model of the “dose-effect” dependence for the combined effect of several factors is constructed using the basic equation of the Volterra mathematical theory of the struggle for existence. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 117, N ^o 3, pp. 328–331, March, 1994 Presented by L. A. Tiunov, Member of the Russian Academy of Medical Sciences     

Program for generation of three-dimensional finite element mesh from magnetic resonance imaging scans of human limbs

A PC-AT based program for conversion of magnetic resonance imaging (MRI) scans into coordinate input for finite element mesh generation is presented. The program is written in Borland C + +3.1 and is compatible with every general-use personal computer, permitting the use of MS-DOS 3.0 or higher with a Microsoft mouse. The program is menu driven and does not demand specialised knowledge from the user. The system and memory requirements are minimal -- 640 kB RAM -- and it runs as a stand-alone program. A second program allows the construction of a three-dimensional representation of the limb sub-structure and generation of the FE mesh from the converted cross-sectional scans. The capabilities of the program are demonstrated using cross-sectional scans of the upper arm; the fat, muscle and bone contours were obtained to a very high level of precision (0.4 mm).     

Localisation of myocardial ischaemia from the magnetocardiogram using current density reconstruction method: computer simulation study

A computer simulation study is performed to investigate the method of current density reconstruction to localise myocardial ischaemia. A computer model of the entire human heart is used to simulate the excitation and repolarisation process in eight topographically different cases of myocardial ischaemia. The associated magnetocardiogram is calculated at 37 positions of the KRENIKON^* biomagnetic measurement equipment. The method of current density reconstruction is applied at the S-point (the last discemible deviation from the ST-segment at the end of the QRS-complex) of the MCG to find characteristics of the myocardial ischaemia simulated by the model. The results show that it is possible to determine the location of the ischaemia. The current density distribution may be interpreted physiologically in terms of the so-called ‘injury current’. This indicates that magnetocardiography might be a suitable method for noninvasive ischaemia diagnosis, and further investigations of the current density reconstruction method for the injury current should be performed on patients with ischaemic heart disease.