医学数字信号处理-心电图(详细).ppt

BIOMEDICAL DIGITAL SIGNAL PROCESSING 生物医学生物医学数字信号数字信号处理处理2009.03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BME在百年诺贝尔生理与医学奖中的份额 美国的保罗美国的保罗-劳特布尔和英国的彼得劳特布尔和英国的彼得-曼斯菲尔德共同获得了曼斯菲尔德共同获得了2003年诺年诺贝尔生理学或医学奖贝尔生理学或医学奖-核磁共振成像技术核磁共振成像技术-三维图象三维图象百年总计(1901-2000)91（届次）100%属于BME范畴1618%与BME密切相关1314%不采用BME方法、技术、设备与材料就不能完成的3943%与BME无关的2325%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 ProcessingISBN：7560925790页数：246Lecture 2ElectrocardiologyElectrocardiogramECG 第第2讲讲心电学心电学心脏机械收缩之前，先产生电激动，心房和心室的电激动心脏机械收缩之前，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。心脏每一心动周期所产生电活动变化曲线图形。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。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。三道心电图机 顺序记录导联心电图后重新排列在一幅纸上运动心电图记录系统 2.1Electrocardiologicbasis 2.1 心电学基础心电学基础2.1.1 three basic techniques 2.1.1 三种基本技术三种基本技术1.StandardclinicalECG（12leads）1.标准临床标准临床ECG（12导联导联）2.VCG(3orthogonalleads)3.MonitoringECG(1or2lead(s)2.向量心电图向量心电图 (三维正交导联三维正交导联)3.监护监护ECG(1或或2导联导联)2.1.2 Electrodes 2.1.2 电极电极Figure 2.3 A silver-silverchlorideECGelectrode.Manymodernelectrodeshave electrolyte layers thataremadeofafirmgelwhichhasadhesiveproperties.Thefirmgelminimizesthedisturbance of the chargedoublelayer.2.1.3 心电等效心电等效发生器发生器Figure2.4Boththeelectricalandmechanicalconditionsoftheheartareinvolvedindeterminingthecharacteristicsofthespreadofelectricalactivityoverthesurfaceoftheheart A model of this activity is called a cardiacequivalentgenerator2.1.3Thecardiacequivalentgenerator Figure2.5Einthovenequilateraltriangle.RAandLAaretherightandleftarmsandLListheleftleg.A current dipole is a currentsource and a current sinkseparatedbyadistance.Sincesuch a dipole has magnitudeand direction which changethroughoutaheartbeatasthecells in the heart depolarize,thisleadstothevectorrepresentation.电电流流偶偶极极子子是是相相隔隔一一段段距距离离的的电电流流源源和和穴穴(漏漏)。当当心心肌肌细细胞胞去去极极化化(读读注注：实实际际应应包包含含反反极极化化和和复复极极化化)时时，这这样样一一个个偶偶极极子子的的大大小小和和方方向向在在整整个个心心搏搏周周期期都都是是变变化化的的，这就导致了向量表示法。这就导致了向量表示法。P(t)=P(t)=PxPx(t)X(t)X 十十 PyPy(t)Y(t)Y 十十 PzPz(t)Z (2.1)(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.式式中中P(t)是是时时变变心心脏脏偶偶极极子子，Pi(t)为为该该矢矢量量的的正正交交分分量量，也也称称为为标标量量导导联联，X,Y,Z 是是X,Y,Z方方向向的的单单位位矢量。矢量。The forward solution providesthe potential at any arbitrarypointonthebodysurfaceforagivencardiacdipole.Expressedmathematically，对对于于给给定定的的心心电电偶偶极极子子，心心电电正正问问题题的的解解提提供供了了体体表表任任意意点点的的电电位位，数数学上表示为，学上表示为，v vn(t)=tnxPx(t)十十tnyPy(t)十十tnzPy(t)(2.2)Thisforwardso1utlonshowsthatthepotentialvn(t)(ie,theECS)atanypointnonthebodysurfaceisgivenbythelinearsumoftheproductsofasetoftransfercoefficientstn i uniquetothatpointandtheCorrespondingorthogonaldipolevectorcomponentsPi(t)TheECSsaretime-varyingasarethedipo1ecomponents,whilethetransfercoefficientsareonlydependentonthet h o r a c i c g e o m e t r y a n d inhomogeneitiesThusforasetofkbodysurfacepotentials(i.e.,1eads)，thereisasetofk equationsthatcanbeexpressedi n m a t r i x f o r m V=TP (2.3)WhereVisakxlvectorrepresentingthetime-varyingpotentials,T is a k x 3 matrix of transfer coefficients,Whicharefixedforagivenindividual,andPisthe3x1time-varyingheartvector心心电电信信号号与与偶偶极极子子分分量量一一样样是是时时变变的的，而而传传递递系系数数则则只只决决定定于于胸胸部部的的几几何何形形状状和和非非均均匀匀性性。因因此此，一一组组k体体表表电电位位(即即,导导联联)，就就有有k equations个个方方程程的的方方程程组组，并并可表示成矩阵形式。可表示成矩阵形式。Ofcourse,theheartvectorandtransfercoefficientsareunknownforagivenindividualHoweverifwehadawaytocomputethisheartvectorWecoulduseitintheso1utionoftheforwardproblemandobtaintheECSforanybodysurfacelocationTheapproachtosolvingthisproblemisbasedonaphysicalmodelofthehumantorsoThemodelprovidestransfercoefficientsthatrelatethepotentialsatmanybodysurfacepointstotheheartvector.Withthisinformation，wese1ectthreeECSleadsthatsummarizetheintrinsiccharacteristicsofthedesiredabnormalECStosimulateThenwesolvetheinverseproblemtofindt h e c a r d i a c d i p o l e v e c t o r.自然，对于任一个体心自然，对于任一个体心脏向量脏向量P和传递系数和传递系数T 是未知的。然而，若我是未知的。然而，若我们有计算心脏矢量的方们有计算心脏矢量的方法，就可用之解正问题法，就可用之解正问题并获得任意体表位置的并获得任意体表位置的ECS。解此类问题的方解此类问题的方法建立在人体胸廓物理法建立在人体胸廓物理模型的基础上。该模型模型的基础上。该模型提供了众多体表点的电提供了众多体表点的电位与心脏向量的关系的位与心脏向量的关系的传递系数。用该信息，传递系数。用该信息，则只选择三个则只选择三个ECS导联导联就能概括欲模拟的所希就能概括欲模拟的所希望的异常望的异常ECS的本质特的本质特征。然后，就解逆问题征。然后，就解逆问题以求出心脏偶极向量。以求出心脏偶极向量。Thus,forthreeheartvectorcomponent,therearethreelinearequationsoftheform因此，对于因此，对于三个心脏向量三个心脏向量的分量，有如下形式的三的分量，有如下形式的三个线性方程个线性方程Px(t)=bx1v1(t)+bx2v2(t)+bxkvk(t)(2.5)P=BV(24)WhereBisa3xkmatrixofleadcoefficientsthatisdirectlyderivedfrominvertingthetransfercoefficientsmatrixT.If we select k body surfaceECS leads v1(t),v2(t),，vk(t)for which the leadcoefficients，T(or B)，areknownfromthephysicalmodelofthehumantorso,wecansolvetheinverseproblemandcomputethetimevaryingheartvector,P,using Eq.(2.4).Once we have these dipolecomponents,wesolvetheforward problem using Eq.(2.3)tocomputetheECSforanypointonthebodysurface.如如果果选选择择了了K个个体体表表ECS导导 联联 v1(t),v2(t),vk(t)，且且由由人人体体胸胸廓廓的的物物理理模模型型得得知知了了导导联联系系数数T(或或B），则则就就可可由由(2.4)式式求求解解逆逆问问题题并并计计算算时时变变的的心心脏脏向向量量P。一一旦旦有有了了这这些些偶偶极极分分量量，则则就就可可用用方方程程(2.3)解解正正问问题题以以计计算算任任意意点点的的ECS.2.1.4 GenesisoftheECS2.1.4 心电的起源心电的起源TimevaryingmotionofthecardiacvectorproducesthebodysurfaceECSforoneheartbeatwithitscharacteristicPandTwavesandQRScomplex.心脏向量的时变运动心脏向量的时变运动产生体表心电，每搏产生体表心电，每搏都有其都有其特征性的特征性的P、T波和波和QRS复合波。复合波。Figure 2.7 Basic configuration for recording an electrocardiogram.Usingelectrodes attached to the body,the ECG is recorded with an instrumentationamplifier.(a)Transverse(top)viewofasliceofthebodyshowingtheheartandlungs.(b)FrontalviewshowingelectrodesconnectedinanapproximateleadIIconfiguration.Forthepointsintimethatthevectorpointstowardtheelectrodeconnectedtothepositiveterminaloftheamplifier,theoutputECSwillbepositive-goingIfitpointstothenegativeelectrode，theECSwillbenegative(Thefollowingstatementisbetterandmoredetailed.“Ifthevectorpointstotheelectrodeconnectedtothenegativeterminaloftheamplifier,theECSwillbenegative”)在心脏矢量指向的在心脏矢量指向的电极连到放大器正电极连到放大器正端的那些时间点，端的那些时间点，输出的输出的ECS为正的。为正的。若心电向量指向的若心电向量指向的电极连到放大器负电极连到放大器负端，则输出的端，则输出的ECS为负的。为负的。Figure2.8Electrocardiogram(ECG)foronenormalheartbeatshowingtypicalamplitudesandtimedurationfortheP,QRS,Twaves.Figure2.9Relationshipbetweenthespreadofcardiacelectricalactivationrepresentatvarioustimeinstantsbyasummingvector(intheupperframes)andthegenesisoft h e E C S (i n t h e l o w e r f r a m e s).InFigure2.9(a),theslowmovingdepolarizationoftheatriawhichbeginsatthesinoatrial(SA)nodeproducesthePwave.AsFigure2.9(b)shows,thesignalisdelayedintheatrioventricular(AV)noderesultinginanisoelectricregionafterthePwave,thenasthePurkinjesystemstartsdeliveringthestimulustotheventricularmuscle,theonsetoftheQwaveoccurs.InFigure2.9(c),rapiddepolarizationoftheventricularmuscleisdepictedasalarge,fast-movingvectorwhichbeginsproducingtheRwave.Figure2.9(d)illustratesthatthemaximalvectorrepresentsapointintimewhenmostofthecellsaredepolarized,givingrisetothepeakoftheRwave.InFigure2.9(e),thefinalphaseofventriculardepolarizationoccursastheexcitationspreadstowardthebaseoftheventricles(tothetopinthepicture)givingrisetotheSwave.InFigure2.9(a),theslowmovingdepolarizationoftheatriawhichbeginsatthesinoatrial(SA)nodeproducesthePwave.AsFigure2.9(b)shows,thesignalisdelayedintheatrioventri-cular(AV)noderesultinginanisoelectricregionafterthePwave,thenasthePurkinjesystemstartsdeliveringthestimulustotheventricularmuscle,theonsetoftheQwaveoccurs.InFigure2.9(c),rapiddepolarizationoftheventricularmuscleisdepictedasalarge,fast-movingvectorwhichbeginsproducingtheRwave.Figure2.9(d)illustratesthatthemaximalvectorrepresentsapointintimewhenmostofthecellsaredepolarized,givingrisetothepeakoftheRwave.InFigure2.9(e),thefinalphaseofventriculardepolarizationoccursastheexcitationspreadstowardthebaseoftheventricles(tothetopinthepicture)givingrisetotheSwave.图图2.9(a)中，始于窦房中，始于窦房结的、慢运动的心房结的、慢运动的心房去极化，产生去极化，产生P波。波。正如图正如图2.9(b)所示，所示，信号通过房室结时被信号通过房室结时被延迟，产生延迟，产生P波后的波后的等电区。然后，当等电区。然后，当Purkinje系统开始发系统开始发送刺激到心室肌时，送刺激到心室肌时，Q波开始发生波开始发生。在图。在图2.9(c)中，心室肌的快中，心室肌的快速去极化表现为大而速去极化表现为大而快速运动的矢量，开快速运动的矢量，开始产生始产生R波。图波。图2.9(d)说明，最大矢量代表说明，最大矢量代表了大多数细胞去极化了大多数细胞去极化的时间点，产生的时间点，产生R波波的峰。图的峰。图2.9(e)是激动是激动向心室的基底部向心室的基底部(向图向图的顶部的顶部)传播时的心室传播时的心室去极化的终末时相，去极化的终末时相，产生产生S波。波。2.1.5 Thestandardlimbleads 2.1.5 标准肢体导联标准肢体导联I+IIIII=0(2.6)Figure2.10LeadsI,IIandIIIarethepotentialsdifferencebetweenthelimbsasindicated.RAandLAaretherightandleftarmsandLListheleftleg.FromKirchhoffsvoltages law,the sumofthevoltagesarounda loop equals zero.Thus2.1.6 Theaugmentedlimbleads 2.1.6 加压肢体导联加压肢体导联 Figure2.11TheaugmentedlimbleadaVLismeasuredasshown.FromthebottomleftloopiR+iR-II=0 (2.8)oriR=II/2(2.9)FromthebottomrightloopiR+III+aVL=0(2.10)OraVL=iRIII(2.11)CombiningEqs.(2.9)and(2.11)givesaVL=II/2III=(II-2III)/2(2.12)Fromthetopcenterloop II=III+I(2.13)Substituting gives Substituting gives aVL=(IIII-2III)/2=(IIII)/2(2.14)2.2 ECSleadsystems 2.2 心电导联系统心电导联系统 心电学中有三种常用的基心电学中有三种常用的基本导联系统。最通用的是本导联系统。最通用的是12导联方法，该法定义导联方法，该法定义了了12种电位差的集合，种电位差的集合，构成标准临床构成标准临床ECG。第第二种导联系统规定了记录二种导联系统规定了记录VCG的电极位置。典型的电极位置。典型的监护系统只分析的监护系统只分析1或或2个导联。个导联。Therearethreebasicleadsystemsusedincardiology.Themostpopularisthe12-leadapproach,whichdefinesthesetof12potentialdifferencesthatmakeupthestandardclinicalECG.AsecondleadsystemdesignatesthelocationofelectrodesforrecordingVCG.Monitoringsystemstypicallyanalyzeoneortwoleads.2.2.1 12 leadECS 2.2.1 12 导联心电导联心电 Figure2.16 Standard12-leadclinicalelectrocardiogram.(a)LeadI.(b)LeadII.(c)LeadIII.Notetheamplifierpolarityforeachoftheselimbleads.(d)aVR.(e)VL.(f)aVF.Theseaug-mentedleadsrequireresistornetworkswhichaveragetwolimbpotentialswhilerecordingthethird.(g)ThesixVleadsarerecordedreferencedtoWilsonscentralterminalwhichistheaverageofallthreelimbpotentials.EachofthesixleadslabeledV1-V6arerecordedfromadifferentanatomicalsiteonthechest.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。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Figure2.17The12-leadECGofanormalpatient.Calibrationpulsesontheleftsidedesignate1mV.Therecordingspeedis25mm/s.EachminordivisionisImm,sothemajordivisionare5mm.ThusinleadI,theR-waveamplitudeisabout1.1mVandthetimebetweenbeatsisalmost1S(i.e.,heartrateisabout60bpm).ThenotesareID0042804,S=26,L=2,C=1,I,II,III,aVR,aVL,aVF,V1,V2,V3,V4,V5,V6,PatientNO:4307400respectively.2.2.2 VCS leadsystem2.2.2 向量心电导联系统向量心电导联系统Figure2.18TheelectrodeplacementfortheFrankvectorECSsystem.Figure2.19Theresistornetworkforcombiningbodysurfacepotentialstoproducethethreetime-varyingscalarleadsoftheFrankVCSleadsystem.Figure2.20Thevectorcardiogramofanormalmalepatient.Thethreetime-varyingscalarleadsforoneheartbeatareshownontheleftandarethex,yandzleadsfromtoptobottom.Inthetopcenteristhefrontalviewofthetipofthevectorasitmovesthroughoutonecomputedheartbeat.Inbottomcenterisatransverseviewofthevectorlooplookingdownfromabovethepatient.Onthefarrightisaleftsagittalviewlookingtowardtheleftsideofthepatient.2.2.3 MonitoringECS leadsystem2.2.3 监护心电导联系统监护心电导联系统Monitoringapplicationdonotusestandardelectrodepositionsbuttypicallyusetwoleads.Sincetheprincipalgoalofthesesystemsistoreliablyrecognizeeachheartbeatandperformrhythmanalysis,electrodesareplacedsothattheprimaryECShasalargeR-waveamplitude.Thisensuresahighsignal-to-noiseratioforbeatdetection.SinceLeadIIhasalargepeakamplitudeformanypatients,thisleadisfrequentlyrecommendedasthefirstchoiceofaprimaryleadbymanymanufacturers.Asecondaryleadwithdifferentelectrodeplacementsservesasabackupincasetheprimaryleaddevelopsproblemssuchaslossofelectrodecontact.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。2.3 ECScharacteristics2.3 心电信号特征心电信号特征Figure2.21 Bandwidthusedinelectrocardiography.Thestandardclinicalbandwidthforthe12-leadclinicalECGis0.005-250Hz.Monitoringsystemstypicallyuseabandwidthof0.5-50Hz.Cardiotachometersforheartratedeterminationofsubjectswithpredominantlynormalbeatsuseasimplebandpassfiltercenteredat17HzandwithaQ(Q-factor:qualityfactor)ofabout3or4.心电图机原理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。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。导联线导联线可记录的导联可记录的导联3芯线I or II or III5芯线aVR,aVL,aVF,V12芯线I,II,III,aVR,aVL,aVF,V1-V6谢谢！谢谢！