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).     

人体膝关节平地行走时的动力学模拟

基于美国BRG公司的运动及动力学仿真分析软件LifeMOD,建立包括股骨、胫骨、腓骨、4条主要韧带及肌肉在内的较完整的膝关节动力学模型,并用该模型模拟了人体下肢在平地行走时膝关节的动力学行为以及前交叉韧带缺损对膝关节接触力大小的影响。通过动力学分析,得到人体在平地行走时,胫股关节之间最大的接触力值为2645N,最大韧带张力为590N,发生在内侧副韧带上;当胫股关节之间的滑动受到限制时,最大的韧带张力发生在前交叉韧带上,为560N,研究结果与文献较接近。通过动力学模拟,可以得出结论：胫股关节之间的滑动对韧带张力有较大影响;前交叉韧带缺损使得胫股关节之间的接触力变小。     

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.     

数值模拟鼻甲的切除对鼻腔内气体流场的影响

量化研究鼻腔结构的变化对鼻腔内气体流场分布的影响.通过CT图像对鼻腔结构进行三维重建并用有限元方法对气体流场进行数值分析.对重建的鼻腔模型的一侧,分别去掉部分中鼻甲和部分下鼻甲并用有限元方法再次进行数值分析,将得到的结果与原始模型进行比较.观察气体流场分布的变化,在两侧鼻腔的流量分布均有变化,在去掉部分鼻甲的一侧流场和气压的分布也有所改变.通过数值模拟,我们量化的显示了鼻腔结构的变化对鼻腔内气体流场分布的影响.     

不同运动强度对骨质疏松影响的数值模拟

探讨数值模拟不同运动强度对因废用引起的骨质疏松的影响。依据骨的功能适应性和力学调控系统理论,遵循骨重建的生理过程,建立了一个带有时间历程的描述松质骨骨质疏松过程的计算模型,用C语言编制程序。得到了不同运动负荷对因废用引起的骨质疏松(孔隙率)的影响曲线。结果表明:较大的运动强度可以减缓因废用引起的骨质疏松。这对于运动防治骨质疏松有一定的参考价值。     

人行走时骨盆上下运动参数的模型分析

为了研究正常人行走过程中骨盆在垂直方向的运动特征,提出了一种以测量数据为基础建立骨盆运动参数数学模型的新思想。介绍了基于跑步机的骨盆运动轨迹测量系统,并对30名健康男性青年进行了获取骨盆运动参数的实验研究。实验结果得到了不同受试者分别以不同速度行走时的骨盆在垂直方向的多组运动轨迹,以及运动幅值、周期、初始相位等与行走速度和受试者身高的关系曲线。通过对曲线拟合,建立了各参数及骨盆运动轨迹的数学模型。通过对该模型进一步完善,可使其对康复评定、类人机器人等领域具有一定的应用价值。     

Simulation of cardiovascular physiology: the diastolic function(s) of the heart

The cardiovascular system was simulated by using an equivalent electronic circuit. Four sets of simulations were performed. The basic variables investigated were cardiac output and stroke volume. They were studied as functions (i) of right ventricular capacitance and negative intrathoracic pressure; (ii) of left ventricular relaxation and of heart rate; and (iii) of left ventricle failure. It seems that a satisfactory simulation of systolic and diastolic functions of the heart is possible. Presented simulations improve our understanding of the role of the capacitance of both ventricles and of the diastolic relaxation in cardiovascular physiology.