医学数字信号处理心电图ppt课件

BIOMEDICAL DIGITAL SIGNAL PROCESSING,生物医学数字信号处理,1,霍金教授的办公室（剑桥大学）,“我的书每增加一个公式，读者就减少一半” 霍金教授,2,BME在百年诺贝尔 生理与医学奖中的份额,美国的保罗-劳特布尔和英国的彼得-曼斯菲尔德共同获得了2003年诺贝尔生理学或医学奖-核磁共振成像技术-三维图象,3,教材,作者：美国威斯康辛大学电气与计算机工程系教授 前IEEE生物医学工程学会主席 Willis J.Tompkins 书名：Biomedical Digital Signal Processing ISBN：7560925790 页数：246,4,Lecture 2 Electrocardiology Electrocardiogram ECG,第2讲 心电学,5,心脏机械收缩之前，先产生电激动，心房和心室的电激动可经人体组织传到体表。心电图是利用心电图机从体表记录心脏每一心动周期所产生电活动变化曲线图形。,6,心脏的特殊传导系统由窦房结、结间束（分为前、中、后结间束）、房间束（起自结间束，称Bachmann束）、房间交界区（房室结、希氏束）、束支（分为左、右束支，左束支又分为前分支和后分支）以及普肯耶纤维（Pukinje fiber）构成。心脏传导系统与每一心动周期顺序出现的心电变化密切相关。正常心电活动始于窦房结，兴奋心房的同时经结间束传导至房室结（激动传，然后循希氏束-左、右束支-普肯耶纤维顺序传导，最后兴奋心室。这种先后有序的电激动的传播，引起一系列电位改变，形成了心电图上相应的波段。,7,心电图机是记录心电图的专用仪器，有单道心电图机和多道心电图机，多道心电图机可以同时记录多导联的心电，最多有同时记录12导联的，而单道心电图机只能顺序记录12个导联，有手控的心电图机，也有程控的、微电脑控制或数字式的心电图机，在很多其它仪器中也常有心电记录电路模块。,8,2.1Electrocardiologicbasis,2.1 心电学基础,2.1.1 three basic techniques,2.1.1 三种基本技术,1. Standard clinical ECG（12 leads）,1. 标准临床 ECG （12 导联）,2. VCG (3 orthogonal leads),3. Monitoring ECG (1 or 2 lead(s) ),2. 向量心电图 (三维正交导联),3. 监护 ECG (1或2 导联),9,2.1.2 Electrodes,2.1.2 电极,Figure 2.3 A silver-silver chloride ECG electrode. Many modern electrodes have electrolyte layers that are made of a firm gel which has adhesive properties. The firm gel minimizes the disturbance of the charge double layer.,10,2.1.3 心电等效发生器,Figure 2.4 Both the electrical and mechanical conditions of the heart are involved in determining the characteristics of the spread of electrical activity over the surface of the heartA model of this activity is called a cardiac equivalent generator,2.1.3 The cardiac equivalent generator,11,Figure 2.5 Einthoven equilateral triangle. RA and LA are the right and left arms and LL is the left leg.,12,A current dipole is a current source and a current sink separated by a distance. Since such a dipole has magnitude and direction which change throughout a heartbeat as the cells in the heart depolarize, this leads to the vector representation.,电流偶极子是相隔一段距离的电流源和穴(漏)。当心肌细胞去极化 (读注：实际应包含反极化和复极化)时，这样一个偶极子的大小和方向在整个心搏周期都是变化的，这就导致了向量表示法。,P(t) = Px(t)X 十 Py(t)Y 十 Pz(t)Z (2.1),Where P(t) is the time-varying cardiac vector, Pi(t) are the orthogonal components of the vector also called scalar leads, and X,Y,Z are unit vectors in the x, y, z directions.,式中P(t) 是时变心脏偶极子，Pi(t) 为该矢量的正交分量，也称为标量导联， X,Y,Z 是X,Y,Z方向的单位矢量。,13,The forward solution provides the potential at any arbitrary point on the body surface for a given cardiac dipole. Expressed mathematically，,对于给定的心电偶极子，心电正问题的解提供了体表任意点的电位，数学上表示为，,vn(t) = tnxPx(t)十tnyPy(t)十tnzPy(t) (2.2),This forward so1utlon shows that the potential vn(t) ( ie,the ECS) at any point n on the body surface is given by the linear sum of the products of a set of transfer coefficients tn i unique to that point and the Corresponding orthogonal dipole vector components Pi(t),14,The ECSs are time-varying as are the dipo1e components, while the transfer coefficients are only dependent on the thoracic geometry and inhomogeneitiesThus for a set of k body surface potentials (i. e., 1eads)， there is a set of k equations that can be expressed in matrix form,V = TP (2.3),Where V is a k x l vector representing the time-varying potentials, T is a k x 3 matrix of transfer coefficients, Which are fixed for a given individual, and P is the 3 x 1 time-varying heart vector,心电信号与偶极子分量一样是时变的，而传递系数则只决定于胸部的几何形状和非均匀性。因此，一组 k 体表电位(即, 导联)， 就有 k equations个方程的方程组，并可表示成矩阵形式。,15,Of course, the heart vector and transfer coefficients are unknown for a given individualHowever if we had a way to compute this heart vectorWe could use it in the so1ution of the forward problem and obtain the ECS for any body surface locationThe approach to solving this problem is based on a physical model of the human torsoThe model provides transfer coefficients that relate the potentials at many body surface points to the heart vector. With this information，we se1ect three ECS leads that summarize the intrinsic characteristics of the desired abnormal ECS to simulateThen we solve the inverse problem to find the cardiac dipole vector.,自然，对于任一个体心脏向量P和传递系数T 是未知的。然而，若我们有计算心脏矢量的方法，就可用之解正问题并获得任意体表位置的ECS。解此类问题的方法建立在人体胸廓物理模型的基础上。该模型提供了众多体表点的电位与心脏向量的关系的传递系数。用该信息，则只选择三个ECS导联就能概括欲模拟的所希望的异常ECS的本质特征。然后，就解逆问题以求出心脏偶极向量。,16,Thus, for three heart vector component, there are three linear equations of the form,因此，对于 三个心脏向量的分量，有如下形式的三个线性方程,Px(t) = bx1v1(t) + b x2 v2(t) + + bxk vk(t) (2.5),P = BV (24),Where B is a 3 x k matrix of lead coefficients that is directly derived from inverting the transfer coefficients matrix T.,17,If we select k body surface ECS leads v1(t), v2(t), ， vk(t) for which the lead coefficients，T (or B)，are known from the physical model of the human torso, we can solve the inverse problem and compute the timevarying heart vector, P, using Eq. (2.4). Once we have these dipole components, we solve the forward problem using Eq. (2.3) to compute the ECS for any point on the body surface.,如果选择了K个体表ECS导联v1(t), v2(t), vk(t) ，且由人体胸廓的物理模型得知了导联系数T (或B） ，则就可由(2.4)式求解逆问题并计算时变的心脏向量P 。一旦有了这些偶极分量，则就可用方程(2.3)解正问题以计算任意点的ECS.,18,2.1.4 Genesis of the ECS,2.1.4 心电的起源,Time varying motion of the cardiac vector produces the body surface ECS for one heartbeat with its characteristic P and T waves and QRS complex.,心脏向量的时变运动产生体表心电，每搏都有其 特征性的P、T 波和QRS复合波。,Figure 2.7 Basic configuration for recording an electrocardiogram. Using electrodes attached to the body, the ECG is recorded with an instrumentation amplifier. (a) Transverse (top) view of a slice of the body showing the heart and lungs. (b) Frontal view showing electrodes connected in an approximate lead II configuration.,19,For the points in time that the vector points toward the electrode connected to the positive terminal of the amplifier, the output ECS will be positive-goingIf it points to the negative electrode，the ECS will be negative(The following statement is better and more detailed. “If the vector points to the electrode connected to the negative terminal of the amplifier, the ECS will be negative”),在心脏矢量指向的电极连到放大器正端的那些时间点，输出的ECS为正的。若心电向量指向的电极连到放大器负端，则输出的ECS为负的。,20,Figure 2.8 Electrocardiogram (ECG) for one normal heartbeat showing typical amplitudes and time duration for the P, QRS, T waves.,21,Figure 2.9 Relationship between the spread of cardiac electrical activation represent at various time instants by a summing vector (in the upper frames) and the genesis of the ECS (in the lower frames).,22,In Figure 2.9(a), the slow moving depolarization of the atria which begins at the sinoatrial(SA) node produces the P wave. As Figure 2.9(b) shows, the signal is delayed in the atrioventricular (AV) node resulting in an isoelectric region after the P wave, then as the Purkinje system starts delivering the stimulus to the ventricular muscle, the onset of the Q wave occurs. In Figure 2.9(c), rapid depolarization of the ventricular muscle is depicted as a large, fast-moving vector which begins producing the R wave. Figure 2.9(d) illustrates that the maximal vector represents a point in time when most of the cells are depolarized, giving rise to the peak of the R wave. In Figure 2.9(e), the final phase of ventricular depolarization occurs as the excitation spreads toward the base of the ventricles (to the top in the picture) giving rise to the S wave.,23,In Figure 2.9(a), the slow moving depolarization of the atria which begins at the sinoatrial(SA) node produces the P wave. As Figure 2.9(b) shows, the signal is delayed in the atrioventri-cular (AV) node resulting in an isoelectric region after the P wave, then as the Purkinje system starts delivering the stimulus to the ventricular muscle, the onset of the Q wave occurs. In Figure 2.9(c),rapid depolarization of the ventricular muscle is depicted as a large, fast-moving vector which begins producing the R wave. Figure 2.9(d) illustrates that the maximal vector represents a point in time when most of the cells are depolarized, giving rise to the peak of the R wave. In Figure 2.9(e), the final phase of ventricular depolarization occurs as the excitation spreads toward the base of the ventricles (to the top in the picture) giving rise to the S wave.,图2.9(a)中，始于窦房结的、慢运动的心房去极化，产生P波。正如图2.9(b)所示，信号通过房室结时被延迟，产生P波后的等电区。然后，当Purkinje系统开始发送刺激到心室肌时，Q波开始发生。在图2.9(c)中，心室肌的快速去极化表现为大而快速运动的矢量，开始产生R波。图2.9(d)说明，最大矢量代表了大多数细胞去极化的时间点，产生R波的峰。图2.9(e)是激动向心室的基底部(向图的顶部)传播时的心室去极化的终末时相，产生S波。,24,2.1.5 The standard limb leads,2.1.5 标准肢体导联,I + III II = 0 (2.6),Figure 2.10 Leads I, II and III are the potentials difference between the limbs as indicated. RA and LA are the right and left arms and LL is the left leg.,From Kirchhoffs voltages law, the sum of the voltages around a loop equals zero. Thus,25,2.1.6 The augmented limb leads,2.1.6 加压肢体导联,Figure 2.11 The augmented limb lead aVL is measured as shown.,From the bottom left loop,iR+iR-II=0 (2.8) or iR=II/2 (2.9),From the bottom right loop,iR+III+aVL=0 (2.10) Or aVL=iRIII (2.11),Combining Eqs. (2.9) and (2.11) gives,aVL=II/2III=(II-2III)/2 (2.12),From the top center loop,II = III + I (2.13),Substituting gives,aVL=(IIII-2III)/2=(IIII)/2 (2.14),26,2.2 ECS lead systems,2.2 心电导联系统,心电学中有三种常用的基本导联系统。最通用的是12导联方法，该法定义了12种电位差的集合，构成标准临床ECG。第二种导联系统规定了记录VCG的电极位置。典型的监护系统只分析1或2个导联。,There are three basic lead systems used in cardiology. The most popular is the 12-lead approach, which defines the set of 12 potential differences that make up the standard clinical ECG. A second lead system designates the location of electrodes for recording VCG. Monitoring systems typically analyze one or two leads.,27,2.2.1 12 lead ECS,2.2.1 12 导联心电,28,Figure 2.16 Standard 12-lead clinical electrocardiogram. (a) Lead I. (b) Lead II. (c) Lead III. Note the amplifier polarity for each of these limb leads. (d) aVR. (e) VL.(f) aVF. These aug-mented leads require resistor networks which average two limb potentials while recording the third. (g) The six V leads are recorded referenced to Wilsons central terminal which is the average of all three limb potentials. Each of the six leads labeled V1-V6 are recorded from a different anatomical site on the chest.,29,30,中心电端C相连。所有单极导联皆参考此点电压。所有输入端皆采 用高输入阻抗电路。,31,12个标准心电图导联,双极肢体导联：I、II、III 单极加压肢体导联：aVL、aVR、aVF 胸导联：V1、V2、V3、V4、V5、V6 电极安放的位置： 肢体导联 监护导联,32,Figure 2.17 The 12-lead ECG of a normal patient. Calibration pulses on the left side designate 1 mV. The recording speed is 25 mm/s. Each minor division is I mm, so the major division are 5 mm. Thus in lead I, the R-wave amplitude is about 1.1 mV and the time between beats is almost 1 S (i. e., heart rate is about 60 bpm). The notes are ID 0042804, S=26, L=2, C=1, I, II, III, aVR, aVL, aVF, V1, V2, V3, V4, V5, V6, Patient NO: 4307400 respectively.,33,2.2.2 VCS lead system,2.2.2 向量心电导联系统,Figure 2.18 The electrode placement for the Frank vector ECS system.,Figure 2.19 The resistor network for combining body surface potentials to produce the three time-varying scalar leads of the Frank VCS lead system.,34,Figure 2.20 The vectorcardiogram of a normal male patient. The three time-varying scalar leads for one heartbeat are shown on the left and are the x, y and z leads from top to bottom. In the top center is the frontal view of the tip of the vector as it moves throughout one computed heartbeat. In bottom center is a transverse view of the vector loop looking down from above the patient. On the far right is a left sagittal view looking toward the left side of the patient.,35,2.2.3 Monitoring ECS lead system,2.2.3 监护心电导联系统,Monitoring application do not use standard electrode positions but typically use two leads. Since the principal goal of these systems is to reliably recognize each heartbeat and perform rhythm analysis, electrodes are placed so that the primary ECS has a large R-wave amplitude. This ensures a high signal-to-noise ratio for beat detection. Since Lead II has a large peak amplitude for many patients, this lead is frequently recommended as the first choice of a primary lead by many manufacturers. A secondary lead with different electrode placements serves as a backup in case the primary lead develops problems such as loss of electrode contact.,监护应用不采用标准电极位置，典型使用两个导联。因该系统的主要目标是可靠识别每一心搏，完成节律分析，所以电极的放置以能获得最大R波幅度为准，这样就能保证检测心搏时有高的信噪比。因II导联对很多病人都有大的峰值，故该导联常被很多厂家推荐为首选导联。第二种导联有各种电极方法，作为主要导联发生问题(如电极接触不良)时的备用导联。,36,2.3 ECS characteristics,2.3 心电信号特征,Figure 2.21 Bandwidth used in electrocardiography. The standard clinical bandwidth for the 12-lead clinical ECG is 0.005-250Hz. Monitoring systems typically use a bandwidth of 0.5-50Hz. Cardiotachometers for heart rate determination of subjects with predominantly normal beats use a simple bandpass filter centered at 17Hz and with a Q(Q-factor: quality factor) of about 3 or 4.,37,心电图机原理,体表心电经电极、导联线送至心电图机，心电图机主体从原理上可分为输入回路、导联选择、放大电路、描笔驱动和走纸部分，现代心电图机通常还有程控部分。,38,39,40,导联线,导联线是连接电极和心电图机的多股电缆线，各股电缆线应绞合在一起以减小磁场干扰，并屏蔽以减少电场干扰。,41,谢谢！,42,