基于生物阻抗谱的人体细胞内外液容量计算方法研究

生物电阻抗测量技术是一种无创的提取人体生理及病理信息的检测技术,其中对生物阻抗与人体生理参数之间关系的分析方法是该项技术环节中很重要的一部分。为了更加精准地计算人体细胞内外液容量,在计算人体细胞内外液容量的莫斯尔(Moissl)方程的基础上,本文提出了一种分段式人体生物阻抗谱测量模型及改进的细胞内外液容量计算方法,设计了人体摄入水分前后的细胞内外液容量的测量与计算实验,并与Moissl方程进行比较。结果表明,本文提出的改进计算方法能够更有效地计算细胞内外液容量,相对误差在5%以内,今后或可为人体成分的分析及疾病的诊断治疗提供新的思路或更为准确的方法。     

基于EIT不同面积银导电布电极的试验研究

目的研究不同面积的电极对电阻抗成像的影响,选择一种最适合电阻抗成像的电极。方法使用不同面积的电极对人体进行电阻抗成像测量,通过对测得数据进行统计分析,来选择最适合人体电阻抗成像的电极。结果使用1.5cm×5cm的电极所测得的信号强于其他面积的电极,并且信号的标准差比其他电极小。结论通过试验,初步确定了基于EIT电极的最优面积,为整个EIT电极系统的研究做了必要的前提准备。     

人体通信中发送端接触阻抗的实验研究

本研究着眼于电流耦合型人体通信方式,抽象并简化人体前臂的发送端等效电路模型。通过施加交变方波电流激励,测量使用不同尺寸电极时的模型参数,并比较不同频率下接收端的信号衰减率。结果表明人体前臂的信号衰减率随接触阻抗的增大而增大。在小腿处的测量也得到类似的结果。所以,在人体通信过程中应尽可能减小发送端“电极一皮肤”的接触阻抗,可提高通信质量。     

生物组织穿刺电极的设计及其结构对电阻抗测量的影响

设计用于生物组织穿刺过程中进行实时电阻抗测量的电极,并研究其对电阻抗测量结果的影响.设计一种同心圆状排列的双电极结构,分别改变正、负极面积和两极间距离3个参数进行生物电阻抗测量.结果显示:正极面积和两极间距离与测量结果呈线性变化,负极面积与测量结果呈非线性变化.在人体组织进行穿刺的过程中,建立的同心圆状排列的双电极结构能较为精确地测量即时生物电阻抗值,负极面积的微小变化将对阻抗测量结果产生较大的影响.     

生物阻抗测量技术及其临床应用研究进展

生物阻抗技术是利用细胞外液和细胞内液的电学性质测量人体成分及器官变化的一种较新的医学诊断技术。因其具有无创、安全、有效及功能信息丰富等优点,广泛应用于疾病的动态检测。本文阐述了在临床中生物阻抗的测量方法、电极大小形状及贴放位置等的技术研究,并总结了生物阻抗在人体成分分析、心脑血管系统疾病的动态监测、消化系统疾病和肺部疾病的监测,以及乳腺癌检测中的应用。     

密闭流动池脉冲流动液流速的电阻抗参数表征方法研究

目的:利用流过输血输液装置密闭流动池的脉冲流动液的电阻抗参数表征流动液的流速。方法:应用精密阻抗分析仪测量该装置5个档位输液速率下的密闭流动池脉冲流动液的电阻抗模值的波形;对获得的电阻抗波形进行频谱分析,计算出各个电阻抗波形频谱主频,统计分析各个流速对应主频的差异;通过相关性分析和曲线估计确定脉冲流动液流速和其电阻抗波形频谱主频之间的回归关系。结果:直观测量和统计分析均表明脉冲流动液的电阻抗波形的变化频率随其流速的增加而升高（P<0.05）;脉冲流动液流速与其电阻抗波形频谱主频具有相关性（r=0.99, P<0.05）,两者符合二项式关系y=-0.001 2x2+0.176 9x-0.134,R2=0.999 8。结论:可以用密闭流动池脉冲流动液的电阻抗参数表征其流速。     

生理盐水对细胞射频介电响应的影响

生理盐水的介电响应对细胞悬液的介电测量具有重要意义,我们在1～500MHz频率范围内对之进行了测量;结果表明,生理盐水的介电响应对电极有选择性,低频区电极效应明显;16℃、25℃和36℃下的测量结果指出,介电响应有强烈的温度依赖性。采用铂电极对红细胞悬液进行的介电测量时,有必要取压积大于40％,以保证有小的电极效应,使测量结果能反映出红细胞的本征特性。     

动物组织复电阻抗谱随离体时间的变化

建立基于四电极法的测量系统，测量了犬和兔部分离体组织的复阻抗谱，观察了部分动物组织复电阻抗谱随离体时间而发生的变化，结果发现，随着动物组织离体时婚的延长，其复阻抗谱发生显著变化：1、低频段电阻显著增加；2、复阻抗谱的虚部增加(容性成份增加)；3、特征频率降低。结合动物组织离体后发生的组织、细胞水平的变化，我们认为：动物组织复电阻抗谱随离体时间的变化应该与组织细胞内液、细胞外液的离子成份变化相关，同时应该与细胞膜活性相关。     

3D-EIT系统电极优化设计

探究三维电阻抗成像系统电极结构对数据测量及图像重建的影响。考虑到电极形状和电极在边界上的分布状态对成像效果的影响,在构建的3D电阻抗系统模型及层间准对角激励相邻（QBD）测量工作模式下,对方形电极（I型）、圆形电极（II型）、同心圆复合电极（III型）和方圆复合电极（IV型）4种 形状电极,就0.2到0.7之间8种不同电极占空比(DR)情况进行对比研究。采用重建图像的相关度R,敏感场的灵敏度均匀性P,测量电压动态范围D进行评价。对比结果表明,在DR为0.4～0.5之间,4种电极结构下的图像相关度R均优于其他DR情况,而且IV型电极的R和P指标略优于I ～ III型,但复合型电极（III和IV型）在DR为0.3和035时边界测量电压动态范围D偏大,稳定性差。对三维场域中5个高度不等（7.5～30 cm之间）、电导率相同的物体,采用共轭梯度算法进行图像重建。数据经归一化处理,截取2个电极层、1个电极间层及2个电极外层共5个等间隔的不同断层图像进行对比,4种电极模型下的成像结果均与真实分布相吻合,IV型电极所成图像伪影略小,效果较好,与指标评价结果一致。本研究为QBD模式的三维电阻抗成像系统确定了电极形状及电极分布,为进一步研究三维空间的电阻抗分布奠定基础。     

人体水分测量技术综述

目的：通过对三种人体水分测量技术进行阐述,对于不同的个体或情形下,使用不同的人体水分测量技术提供参考和依据。方法：对三种人体水分测量技术,包括同位素稀释法、中子活化分析法和生物电阻抗分析法的原理、方法和应用分别进行阐述。比较三种测量技术之间的优点和缺点,探寻它们可应用的领域和范围。结果：中子活化分析法被认为是所有元素检测的参考标准,测量精确率最高,但是,测量技术十分复杂,分析成本昂贵,几乎不能用于普通人群体内水分的测量：同位素稀释法的测试精确率较高,测试技术较复杂,测试成本较昂贵,对受试者有一定的危害,一般用于实验室内的测试。生物电阻抗法的测量精确率尚可,测试技术简单,成本低廉,可用于普通人群的测试。结论：三种人体水分测量技术都能够测量出人体内的总体液、细胞外液和细胞内液。但是这三种人体水分测量技术还有其劣势,有待人们进行发展和探索。其中,生物电阻抗分析法是一种成本低廉、安全、无创,能快速而准确地测量出人体水分的技术,测试对象易接受,有较大的应用前景。     

Measuring lower leg swelling: Optimum frequency for impedance method

The optimum measuring frequency of the impedance plethysmograph is determined for the estimation of leg volume increase caused by a sitting work load. Ten subjects sit for 1 h without leg movement. Right calf impedance is measured by the four-electrode method. The detecting electrodes are fixed on the calf with an inter-electrode distance of 15 cm. The measuring frequencies are 5, 10, 50 and 100 kHz. As the indices of leg swelling, three values are calculated: percentage change in impedance, volume change and percentage change in volume. The mean, standard deviation and coefficient of variation (CV) are calculated from the mean values of indices for each subject and frequency. The CV of all three indices increases when measurements are taken at higher frequencies. Among the three indices across all measuring frequencies, the volume change shows the highest CV (0.42 at 5 kHz, 0.82 at 100 kHz), and the percentage change in impedance shows the lowest CV (0.32 at 5 kHz, 0.72 at 100 kHz). It is concluded that the measuring frequency of 5 to 10 kHz is the best to obtain accurate data for the evaluation of lower leg swelling.     

模拟失重对大鼠血液电阻率频谱特性的影响

目的利用电阻抗法观察模拟失重大鼠血液电阻率变化并探讨其机制。方法实验动物分为正常对照组和模拟失重组,模拟失重采用大鼠尾部悬吊法。血液阻抗谱测量采用Agilent4294A阻抗分析仪完成。在0．01～100MHz频率范围选取80个频率点,设定每个频率点自动循环扫描测量3次取均值,交流激励信号源电压0．5V。通过Bode图、Nyquist图和Nichols图的数据分析,观察模拟失重对大鼠血液电阻率频谱特性的影响。结果血液电阻率降低：模拟失重组的低频复电阻率幅值｜ρ^＊｜0、高频复电阻率幅值｜ρ^＊｜m、复电阻率幅值增量（△｜ρ^＊｜=｜P’｜0-｜ρ^＊｜m）、相位角峰值θp幅度、低频复电阻率实部值ρ^＊0、复电阻率虚部峰值P^Hp幅度、低频复电阻率幅值对数lg｜ρ^＊｜0较对照组均降低。血液特征频率：第一特征频率fc1,和第二特征频率fc2较对照组均增加。结论模拟失重引起大鼠血浆、红细胞膜和血红蛋白的电阻率降低,导电性能增加。     

Skin impedance measurements using simple and compound electrodes

We have studied the effect of the electrode configuration on the measurement of body impedance and found that the electrode configuration greatly affects the impedance measurement using the four-electrode method. We studied the characteristics of the compound electrode and found that the compound electrode provides the four-electrode method in a compact form. A new method of measuring the skin impedance using simple electrodes at low frequencies was developed. At high frequencies where the effect of internal tissue impedance is not negligible, we used the compensation method using compound electrodes, because they measure the voltage right under the skin. At 50 kHz, we measured the real part of the skin impedance of less than 80 Ω on the thorax. We propose a simple instrument which can measure accurate skin impedance at various frequencies.     

Characteristics of skin admittance for dry electrodes and the measurement of skin moisturisation

The properties of skin adminttance were investigated with the intention of applying them to skin moisturisation measurement. Skin admittance is determined by measuring relative permittivity and the resistivity of the stratum corneum, and by contact ratio between dry electrode and stratum corneum. It was found, however, that the contact ratio is the predominant factor producing the change of skin admittance induced by changes in the water content of skin. To measure skin admittance, the following conditions were found to be approriate: (a) frequency of about 100 kHz; (b) concentric electrodes, the diameter of the measuring (inner) electrode being about 5 mm, and (c) an electrode pressure of about 100 g cm⁻². Based on these optimal conditions, a system for measuring skin admittance was constructed. All measuring procedures were automated. Experimental observations made with this system have indicated its usefulness for the measurement of skin moisturisation.     

Best Electrode Locations for a Small Bipolar ECG Device: Signal Strength Analysis of Clinical Data

New miniaturized portable electrocardiogram (ECG) measuring devices may require small interelectrode distance. However, finding a suitable location for a tiny measurement device may prove tedious, as reducing interelectrode distance reduces signal strength. The objective of the study was to define the optimal location for a very closely located (5 cm) bipolar electrode pair. A total of 120 bipolar leads were analyzed from a body surface potential map (BSPM) data with 236 subjects with a normal ECG. The average and standard deviation (SD) of the QRS-complex and the P-wave amplitudes in each electrode location and for each subject were determined. The results showed that deviation in signal amplitude between different subjects is significant. However, judging from average values, the best orientation for a closely located bipolar electrode pair is diagonally on the chest. The best locations for QRS-complex and P-wave detection are around the chest electrodes of the standard precordial leads V2, V3, and V4, and above the chest electrodes of leads V1 and V2, respectively.     

Extra-and intracellular volume monitoring by impedance during haemodialysis using Cole-Cole extrapolation

A method is presented for monitoring the relative variation of extracellular and intracellular fluid volumes using a multifrequency impedancemeter and the Cole-Cole extrapolation technique. It is found that this extrapolation is necessary to obtain reliable data for the resistance of the intracellular fluid. The extracellular and intracellular resistances can be approached using frequencies of, respectively, 5 kHz and 1000 kHz, but the use of 100 kHz leads to unacceptable errors. In the conventional treatment the overall relative variation of intracellular resistance is found to be relatively small.     

The impedance of a spherical monopolar electrode

The impedance of a monopolar electrode immersed in an environmental volume conductor consists of two parts; the impedance of the active electrode-electrolyte interface, and the resistance of the environmental conductor. Two studies were carried out to quantitate these components. First, impedance-frequency data were collected for five spherical stainless-steel electrodes (ranging from 0.473 to 1.11 cm in diameter) immersed in 0.9% saline (ρ=70 Ω-cm). Impedance measurements were made from 100 Hz to 100 kHz and two sets of data were obtained; one before and one after each electrode was polished with fine emery paper. At low frequency, the measured impedances were high and varied with electrode surface preparation. However, above a transition frequency, the impedances were resistive, independent of the electrode surface preparation, and equal to ρ/2πd as predicted from the theory. This study indicates that the low frequency impedance of a monopolar electrode is dominated by the impedance of the electrode-electrolyte interface. Above a transition frequency, the resistance of the environmental conductor dominates, the value of this resistance depending on the electrode geometry and the resistivity (ρ) of the environmental conductor. A second study was conducted, to examine the effect of the distance to the indifferent electrode. A frequency (100 kHz) above the transition frequency was used and impedance data were collected for various distances between the monopolar and indifferent electrodes. The measured resistance increased asymptotically as the distance between the electrodes was increased. When the indifferent electrode diameter was at least 10 times the diameter of the spherical monopolar electrode, the measured resistance was within 5% of the value predicted for an indifferent electrode at infinity.     

Optimisation of transcutaneous cardiac pacing by three-dimensional finite element modelling of the human thorax

The goal of the study is to determine by finite element analysis (FE) the optimal electrode placement, size and electrolyte resistivity that minimise the pain experienced by patients during successful transcutaneous cardiac pacing (TCP). The three-dimensional FE model generated for this purpose has 55 388 nodes, 50 913 hexahedral elements and simulated 16 different organs and tissues, as well as the properties of the electrolyte. The model uses a non-uniform mesh with an average spatial resolution of 0.8 cm in all three dimensions. To validate this model, the voltage across 3 cm² Ag−AgCl electrodes is measured when currents of 5 mA at 50 kHz are injected into a subject's thorax through the same electrodes. For the same electrode placements and sizes and the same injected current, the FE analysis produced results in good agreement with the experimental data. The optimisation analysis tested seven different electrode placements, five different electrode sizes and six different electrolyte resistivities. The analysis indicates that the anteriorposterior electrode placement, electrode sizes of about 90 cm² and electrolytes with resistivity of about 800 ω·cm yield the most uniform current distribution through the skin, thus having the best chances to minimise the pain delivered to the patient during successful TCP. The anterior-anterior electrode placement is the second most efficient.     

A new approach for detection of leg movement using segmental electrical impedance changes

The purpose of this paper is to provide a new approach for detection using bio-impedance. This impedance is measured by the four-electrode method. As the impedance changes resulting from ankle, knee, and hip movements depend on electrode placement, we determined the optimal electrode configurations for these movements by searching for high correlation coefficients, large impedance changes, and minimum interference in ten subjects (age: 20?±?4). Our optimal electrode configurations showed very strong relationships between the ankle joint angle and ankle impedance (γ?=???0.913?±?0.03), between the knee joint angle and knee impedance (γ?=?0.944?±?0.02), and between the hip joint angle and hip impedance (γ?=?0.823?±?0.08). This study showed that lower leg movement could be easily measured by the impedance measurement system with two pairs of skin electrodes.     

A new approach for detection of leg movement using segmental electrical impedance changes

The purpose of this paper is to provide a new approach for detection using bio-impedance. This impedance is measured by the four-electrode method. As the impedance changes resulting from ankle, knee, and hip movements depend on electrode placement, we determined the optimal electrode configurations for these movements by searching for high correlation coefficients, large impedance changes, and minimum interference in ten subjects (age: 20 +/- 4). Our optimal electrode configurations showed very strong relationships between the ankle joint angle and ankle impedance (gamma = - 0.913 +/- 0.03), between the knee joint angle and knee impedance (gamma = 0.944 +/- 0.02), and between the hip joint angle and hip impedance (gamma = 0.823 +/- 0.08). This study showed that lower leg movement could be easily measured by the impedance measurement system with two pairs of skin electrodes.