最新Chapter10 Gears 机械零件设计英文PPT全套教案ppt课件.ppt 83页

进入夏天，少不了一个热字当头，电扇空调陆续登场，每逢此时，总会想起那一把蒲扇。蒲扇，是记忆中的农村，夏季经常用的一件物品。　　记忆中的故乡，每逢进入夏天，集市上最常见的便是蒲扇、凉席，不论男女老少，个个手持一把，忽闪忽闪个不停，嘴里叨叨着“怎么这么热”，于是三五成群，聚在大树下，或站着，或随即坐在石头上，手持那把扇子，边唠嗑边乘凉。孩子们却在周围跑跑跳跳，热得满头大汗，不时听到“强子，别跑了，快来我给你扇扇”。孩子们才不听这一套，跑个没完，直到累气喘吁吁，这才一跑一踮地围过了，这时母亲总是，好似生气的样子，边扇边训，“你看热的，跑什么？”此时这把蒲扇，是那么凉快，那么的温馨幸福，有母亲的味道！　　蒲扇是中国传统工艺品，在我国已有三千年多年的历史。取材于棕榈树，制作简单，方便携带，且蒲扇的表面光滑，因而，古人常会在上面作画。古有棕扇、葵扇、蒲扇、蕉扇诸名，实即今日的蒲扇，江浙称之为芭蕉扇。六七十年代，人们最常用的就是这种，似圆非圆，轻巧又便宜的蒲扇。　　蒲扇流传至今，我的记忆中，它跨越了半个世纪，也走过了我们的半个人生的轨迹，携带着特有的念想，一年年，一天天，流向长长的时间隧道，袅Chapter10Gears机械零件设计英文PPT全套教案 10.1TypesofGearsSelectionofthetypeofgearingdependsuponmanyfactors:geometricarrangement,reductionratio,power,speedsofrotation,efficiency,noise-levellimitations,andcost.Threeshaftingarrangementsforthetransmissionofpowerormotionfromonerotatingshafttoanother:(1)applicationsinwhichtheshaftaxesareparallel,(2)applicationsinwhichshaftaxesintersect,(3)applicationsinwhichshaftaxesareneitherparallelnodotheyintersect. SometypesofGearsinApplicationclassifiedaccordingtothemutualpositionofshaftsStraight-toothspurgearsimposeonlyradialloadsonsupportingbearings.Theirtoothprofilesareordinarilyinvoluteinshapeandsmallvariationsincenterdistancearethereforeusuallywelltolerated.Althoughspurgearscanbeusedatspeedsashighasothertypesofgears,theyareusuallylimitedtopitch-linevelocitiesaround20m/stoavoidhigh-frequencyvibrationandunacceptablenoiselevels. Asforaccuracyofgears,theelementsofgearwheelsandhousingshouldbemanufacturedwithsufficientaccuracyinordertoensurenormaloperationofgearset.Thedegreeofaccuracyisspecifieddependingonthekindofserviceofthegearandthedemandsithastomeet.Bythehousingdesignitgivestheopenorclosedtypegearset:intheclosed-typegearsthelubricantisfedcontinuously,whileintheopentype----periodically.Geartypesclassifiedbyotherfeatures Thestandardsprovidefortwelvedegreesofaccuracy:from1to12,1beingthehighest.Indesigningtoothedgearsthedegreeofaccuracymustbecorrectlyselected.Thedegreesofaccuracies6to9arethosemostcommonlyused.Higheraccuracyincuttingtheteethconsiderablyreducesnoise.Therefore,thewheelsofimportantgearstransmittingmuchpowerathighperipheralvelocitieshavehelicalofherringboneteethofhigheraccuracy. 10.2PotentialFailureModesGearsmaybevulnerabletofailurebyanyofseveralpotentialfailuremodes:breaking-off(fracture),pitting,surfaceabrasionandseizure.Teethusuallyfailduetoconsiderableinadequaciesindesign,inaccuratecalculationordeviationsfromthenormalservice.TheAmericanGearManufacturersAssociation(AGMA)categorizedthevariouskindsofobservedgearfailuresandestablishedastandardizednomenclaturetodescribethem. Figure10.2illustrates,qualitatively,theoperatingregionsinwhicheachofthemorelikelyfailuremodesmaybeexpectedtooccur. Teethmainlybreakoffduetofatigue.Eachtimethetoothengagesandtakesavaryingloadalternatingbendingstressesaredevelopedattheroot.Acrackisthereforeliabletodevelopintheareaofmaximumstressconcentrationatadefiniteloadrate.Ifthecontactismadeeachtimeononesideofthetooth,thecrackusuallyoccursinthetensionzone.Theresistanceofatoothtobendingcanbeimprovedbyincreasingthebeamstrengthofthededendumportionanddecreasingstressconcentrationattheroot.Thiscanbeachievedbyincreasingtheradiusoffillet(forinstance,bymeansofpositivecorrection),improvingthegearrigidity,theaccuracyofmachiningandthemechanicalpropertiesofthewheelmaterial.1)BendingFatigueandFracture Teethmainlybreakoffduetofatigue.Eachtimethetoothengagesandtakesavaryingloadalternatingbendingstressesaredevelopedattheroot.Acrackisthereforeliabletodevelopintheareaofmaximumstressconcentrationatadefiniteloadrate.Ifthecontactismadeeachtimeononesideofthetooth,thecrackusuallyoccursinthetensionzone.Theresistanceofatoothtobendingcanbeimprovedbyincreasingthebeamstrengthofthededendumportionanddecreasingstressconcentrationattheroot.Thiscanbeachievedbyincreasingtheradiusoffillet(forinstance,bymeansofpositivecorrection),improvingthegearrigidity,theaccuracyofmachiningandthemechanicalpropertiesofthewheelmaterial.1)BendingFatigueandFracture Pittingofthetoothsurfacesisthemostfrequentfailureofwheelsinclosed-typecopiouslylubricatedtoothedgears.Itusuallyoccursinthededendumportionnearthelineofaction.Pittingmayberestrictedorprogressive.Theformerfaultariseswithinasmallportionofthewheelwidthduetotemporaryoverloadingofthisportion.Progressivepittingmeansthattheprocessofpitformationspreadsovertheentirewidthofthetoothedwheelsundersufficientlyhighstress.Thegreatertheoilviscositythegreateristhesurfaceendurancelimitoftheteeth.Viscousoileffectivelydampsdynamicloadsontheteethandthusincreasestheservicelifeoftoothedwheels.2)ContactFatigueandPitting Theharderandsmoothertheworkingsurfacesoftheteethare,thegreatertheloadtheycantakewithoutsufferingfrompitting.Sotheresistanceofthetoothsurfacestopittingcanbeimprovedbyincreasingtheirstrength,surfacefinishandemployingcorrectlubricants.Inopen-typegearswherethereislittleornooil,pittingisanextremelyrarephenomenonsincetheinitialcracksdevelopedinsurfacelayerareusuallywornoffbeforetheprogressivepittingsetsin. UndertheactionofexcessiveloadsthesurfaceofsteelteethatHB<350maysufferplasticdeformations,whileatHB>350thesurfacesofcast-ironteethmaybesubjectedtobrittlefailure.Becauseoftherelativemotionbetweenthemeshedsurfaces,adhesiveorabrasivewearmayoccur.Thewearofteethdistortsitsinvoluteprofile,increasesdynamicloadandweakensthededendumportion,aphenomenonleadingtoincreasedstressesattheroot.Toothwearcanbesloweddownbyreducingunitslidingandcompressivestresses,increasingthewearresistanceofthetoothsurfacesandusingcorrectlubricants.3)Otherfailures Seizureariseswhenoilfilmiscrushedunderhighpressuredevelopedinthecontactzone,thesurfacesoftheteethmeshsotightlytogetherthattheadhesivewearbehaviormaydegeneratetogalling.Inlow-speedgearsseizureiseliminatedbytheuseofextremelyviscouslubricantsandinhigh-speedgearsbyanti-scuffinglubricants.Itisdeducedfromabovethatclosed-typegearsshouldbesodesignedastoprecludeallthefaultsmentionedabovewhileopen-typegeardesignsshouldbefreefromthefailureofbreaking-off,wearandplasticdeformationsoftheteeth. 10.3GearMaterialsandHeatTreatmentRequirements:possibletocutandfinishtheteethwiththerequiredaccuracyandtoensuresufficientbeamstrengthundertheactionofvaryingandimpactload,adequatestrengthofthetoothsurfacesandhighresistancetoabrasion.Steelandcastironcanbeusedtoproducewheelsofanyproportions.Thesematerialsareeasilycast,especiallycastiron,whilesteelhasagoodforgeability.Steelisusuallyusedinanormalizedortemperedstate,butagreatvarietyofsteelandthepossibilityofobtainingvariouspropertiesbymeansofheattreatmentallowofthemostfavorablecombinationofrequiredproperties. Themechanicalpropertiesofcarbonsteel(steel35,40,45,50and51)obtainedafterheattreatmentdependonthecross-sectionsizeofthewheel.Themechanicalpropertiesarerarelyaffectedbythewheelsizeforalloysteels.Ofallalloysteels,40Crand40CrNiarepreferedforgears.Finishcuttingofsuchgearsisdoneafterfinalheattreatment;thesurfaceshardnessofthewheelisthereforeHB<350.Inordertoincreasetheload-carryingcapacityandreducetheoveralldimensionsofthegears,gearswithsurfacehardnessaboveHB350areoftenused,achievingbythroughorsurfacehardening,casehardening,cyanidingandnitriding.Through-hardenablealloy:45or40Cr;Carburizingsteel:20Cr,20CrMnTi.Thenitridingalloys:35CrAlAor38CrMoAlA.Steelsandheattreatmentforgears Byathroughhardeningforcarbonandalloysteel:Rc=50-65.Forimportantgears:steel40Cr,40CrNiand40CrNiMoAThemaximumcorehardnessforcarbonsteelshouldneverexceedRc=45,andforalloynickelandmolybdenumsteel—Rc=50,sinceotherwiseimpactstrengthdropssharply.Thedisadvantagesofthroughhardening:warpingandareductioninthetoughnessofthetoothcorewhichreducestoothresistancetobendingunderimpactload.Surfacehardeningforlargegears:thesurfacehardnessobtainedamountstoRc=51-57Casehardeninggivessurfacehardnessoftheteethwhileretainingpropercoretoughness.Steelsandheattreatmentforgears Alloychromiumsteel,15Crand20Cr,ensuresbetterqualityofthegears,reducedwarpingandgreatercorestrength.Whenoverloadsorimpactloadsareanticipatedandwhentheimpactresilienceandplasticpropertiesofthecoreareofspecialimportance,12CrNi3,15CrV,15CrMrTiandotheralloysteelscanbeused.Forgearswithinternaltoothing,38CrMoAlAisoftenemployedfornitriding.Gearswithnitridedteethareemployedforsteadyloadsunderwell-lubricatedconditiontoprecludeorreduceabrasivewear.Largegearsarecastfromcarbonsteelscontaining0.35-0.55%ofcarbon.GearsofcastironHT300,HT400andHT350areoftenemployedtocarrysmallloadinlow-speedopen-type.Sometimestoothedwheelsaremadeformfabriclaminatedandveneerlaminatedphenolicplastics,artificialleatherandfibre.Othermaterialsforgears 10.4SpurGears;ForceAnalysisForceanalysisofspurgears:thedrivingtorqueT1,PeripheralforceRadialforceThenormalforce: Thisnormalforceactsinthecontactplanenormaltothetoothsurfaces(frictionisneglectedbecauseitonlyslightlyaffectstheseforces).Theperipheralforceactsinanoppositedirectiontotheperipheralvelocityonthedrivingwheelandcoincideswithitonthedrivenwheel.Theradialforceisdirectedfromthepointofcontacttowardsthecenterofthewheelwithexternalteethandawayfromthecenterofthewheelwithinternalteeth.Forcedirectionanalysis 10.5SpurGears;StressAnalysisandDesignInprinciple,gear-toothdesignprocedureisnodifferentfromthedesignprocedureforanyothermachineelement;loadingseverityparameters(e.g.,stresses)arecalculatedandcomparedwithcriticalcapacities(e.g.,strengthscorrespondingtogoverningfailuremodes),adjustingmaterialsandgeometryuntilanappropriatesafetyfactororreliabilitylevelisachieved.Inpractice,theresultsobtainedbyapplyingfundamentalprinciplesaretypicallyrefinedbyusingaseriesofexperience-basedmodifyingfactorstoaccountforthevariabilitiesofmanufacturing,operationaldynamics,strength,environmental,andmountingandassembly. 1)CalculationofTeethforSurfaceStrength(1)ThedesignloadUsedforfurthercalculationforthestrengths.Thedesignloadistheloadaccountingforabovevariabilities,bymultiplyingnominalloadcarriedbyagearwithload-influencingcoefficient=KFn TheapplicationfactorKA,asshowninTable10.1,isusedtoaccountforshockorimpactloadingcharacteristicsoftheprimemoverandthedrivenmachine.ThedynamicfactorKVisusedtoestimatetheeffectofdynamicloadingwhenadetaileddynamicsystemanalysisisnotavailable.Themountingfactorisusedtoaccountfornonuniformloaddistributionacrossthetoothfaceduetomanufacturingvariabilities,bearingclearances,andsupportdeflections.Loadinfluencingfactors ThedynamicfactorThedynamicfactorisrelatedtogearingaccuracyandpitchlinevelocity ThemountingfactorThemountingfactordependsonsurfacehardnessandmountingarrangement Whencurvedsurfaces,suchasmeshinggearteeth,arepressedtogether,thetriaxialstressdistributionsatandbelowthesurfacesofthecontactingbodiesmaybedescribedbytheirpertinentHertzcontactstressequations.Hertzfirstdevelopedthecontactstressequationsforparallelcylindersincontact.(2)HertzContactstresses SimulationofcontactbetweengearteethSincecontactinggearteethemulatecylindersincontact,theHertzcylindricalcontactstressequationcanbeappliedtotheteethofmatinggearsbyreplacingtheparameterswithgearterminology.Pittingusuallybeginsintheareaofthelineofaction(pitchcircle).Forthematingmomentinthepitchpoint: Infacthestrengthofthetoothworkingsurfacesdependsnotonlyonthereducedradiusofcurvatureandthemodulusofelasticityofthematerial,butalsoonthequalityofthetoothsurface,onheattreatment,lubrication,etc.Owingtothesimplicityofthisrelation,Hertzcontactequationisstillusedindesigninggears,whilethedifferencebetweenthetheoreticalpresumptionsandtheactualconditionsofloadonthetoothsurfacesiscompensatedforbyusingallowablecompressivestressesfoundexperimentally.ForthiscasethemaximumnormalHertzstresscomponentalongthecenterlinebyusinggeartoothterminologytoaccountforsurfacefatiguewear.Thebasicsurface-pitting-resistanceassessmentismadebycomparingthesurfacefatiguecontactstresswiththeallowablesurfacefatiguestrength.Considerationsonsurfacestrengthdesign (3)Designforsurfacestrengththefactorofoverlap-ratiothereduction-ratio Checkinganddesigncalculationforsurfacestrengthofgears ChoiceofgearwidthratioshouldneverexceedthevaluesgiveninTable10.3.Indesigncalculations,thevaluesgenerallyvarieswithinawiderange:0.1-1.2,andisspecifiedonthebasisofthefollowingconsiderations.Forclosed-typemedium-speedgearsofmediumpoweristakenintherangeof0.4-0.6.Inopen-typegearswheretheaccuracyofassemblyandrigidityofthebearingsisnothigh,≤0.3.Thegreaterthetransittedpower,themorerigidthereductiongearhousingandthemoreaccuratelythegearisdesigned,thelargerthevalueshouldbe.Thepinionwidthissometimesincreasedby5-10mm.Ifthepinionismadefromplasticsitswidthshouldbelessthanthewidthofthewheel. (4)AdmissiblesurfacecontactstressesPublisheddataforsurfacefatiguestrengthareobtainedfromexperimentsongearsandareallindexedtoareliabilityof99percentforalifeofcyclesofone-wayloading.Fordesignlivesotherthancycles,orreliabilityrequirementsotherthan99percent,thestrengthmaybemodified.Thentheadmissiblesurfacecontactstressis Underconstantload,thenumberofloadcyclesNis:Here,nisthegearrevolutionsperminute;istheworkinghoursintheentireservicelife.ZNcanbealsoreadfromFigure10.9.canbeobtainedfromTable10.4.andmaredependentupongearmaterialanditsheattreatment; Lewisexpressionfornominalbendingstressatthetensile-siderootfillet(criticalpointa)duetotransmittedforceis:2)CalculationofTeethforBendingStrengthAgeartoothidealizedasacantileverbeamsubjectedtoanendloadisthetoothformfactor.Note:withagivenformofthetoothSFandhFareproportionaltothemodule,YFdoesnotdependonthemagnitudeofthemodule. ThevaluesofthetoothformfactorcanbefoundgraphicallyintheFig.ThetoothoutlinechangesdependingonitsnumberZandthecorrectionfactorxConsideringtheload-influencingcoefficientK,stressmodifyingfactor,andthefactorofoverlappingeffect,,wecanget DesignformulaThecalculationsforstrengthcheckingThefactorofoverlappingeffectThestressmodifyingfactor ,theallowablebendingstressattheroot,canbecalculatedbyThemagnitudeofallowablebendingstressdependsonthematerialanditsheattreatment,thenatureofloadcarriedbythetooth(ononeoronbothsides),andserviceofthegear.ThebendingendurancelimitcanbefoundfromtheFig.10.8.ThevaluesofthelifeadjustmentfactorandsafetyfactorforbendingstrengthcanbefoundfromabovefigureandTable10.4,respectively.Lifeadjustmentfactor Boththebendingstressintheteethofthepinionandthestressinitsmeshinggearshouldbecheckedby:Whiledesigningby(10-15),themaximumvalueofshouldbeused:Afterobtainingthecomputedmodulebyaboveformula,weshouldapproximateittotheneareststandardvalue. TheresolutionofFnrequirescomponentsFtandFr,andanaxialthrustcomponentFaasshowninFigure10.16.10.6DesigningofHelicalGearsForceanalysisofrighthanddrivenhelicalgear1)Loadanalysisforhelicalgears Similartospurgears,Ftisdirectlyrelatedtopowertransmissionandtorquedeveloped,andradialcomponentFrisa(useless)separatingforcebetweenthedrivingpinionanddrivengear.Thedirectionoftheaxialforcedependsonthedirectionofrotationandtheinclinationoftheteeth.Fig.10.16c)showstheforceswithteethinclinedtotherightonadrivingwheelrotatinganticlockwise.TheaxialforceFa,generatedbytheinclinedhelicalteeth,dictatesthatthesupportbearingsmusthavetheabilitytoresistnotonlytheforcecomponentsFtandFrinthetransverseplane,butalsotheaxialthrustcomponentFa. Thedesignloadforhelicalgearsis:Considering2)Calculationofteethforsurfacestrengththecheckingcalculationsforhelicalgearscanbewrittenas:Forthedesigncalculation: Thehelixanglecoefficientfortoothbending,canbefoundinFig.10.17.Theequivalentnumberofteeth,Zv=,,isusedtofindand3)Calculationofteethforbeamstrength 10.7SummaryofGearDesign1)SuggesteddesignprocedureBasedonfunctionalspecificationsandcontemplatedsystemconfiguration,generateafirstconceptualsketchofthegeartrain,includingrequiredreductionratio,proposednumberofteethforeachgear,gearshaftcenterlinesandbearinglocations,andanyothergeometricalconstraints.Identifypotentialfailuremodes,andselecttentativegearmaterials.Selecttentativemanufacturingandfinishingmethodsappropriatetotheapplication.Tentativelyselectatoothsystem,then,usingspecifiedpowerandspeedrequirements,performacompleteforceanalysistodeterminetorques,speeds,andtransmittedloadsateachmeshinthegeartrain. Calculateatentativediametralpitch(ormodule),basedoncalculationsforsurfaceendurance(orbendingcalculations),whichindicatesthatthereisabalancebetweenfailurebytoothbendingfatigueandsurfacefatiguedurability.Calculatethecenterlinedistance.Foreachgear,calculateorestimatetheothergeometricaldimensionsaswellasthepitchlinevelocities.Ifnecessary,repeatthedesignprocess.Thedesignprocedureforhelicalgearsfollowsthesamepatternasforspurgearsexceptforthecomplicationsintroducedbytheinclinedteeth. Usually,fortheclosed-typegearset,whenthesurfacehardnessisHB<350,thepitchdiameterofthepinionandthecenterdistancearefoundfromthecalculationsofthesurfaceenduranceoftheteeth.Thenthecheckingcalculationofbendingisusedtoseeifthebendingstrengthissecured.WhenthehardnessoftheworkingsurfacesisHB≥350,designcalculationofisusedtofindthemodule,thenotherproportions,finallythesurfaceenduranceischecked.Sincewehavenotestablishedareliablemethodforcalculatinggearwearyet,theoveralldimensionsofanopen-typegeararefoundfromthecalculationsoftheteethforbeamstrengthbuttheweakeningofteethduetoareductioninthicknessbypossibleweariscompensatedforbyacertainincreaseinthemodule.Designprinciplesforgears 2)SomeconsiderationinthedesignofgearsInclosed-typegearsthenumberofteethshouldbeaslargeaspossible(withthesamediameterofthegearsfoundfromthestrengthdesignoftheteethsurfaces).Whentheteethareveryhard(HB>350)andthediametersofthegearsfoundfromcalculationsforsurfaceenduranceoftheteetharesmall,theirnumbermayhavetobedecreasedtoincreasetheirmoduleandtherebyensuretherequiredbeamstrength.Itwaspointedoutthattheuseofangularcorrectionimprovesthesurfacestrengthofteeth.Correctioncanalsoinfluencethebendingstrengthofteeth.Apositiveshiftofthetoolincreasestooththicknessattherootandimprovesthebeamstrengthofthetooth. 1)SuggesteddesignprocedureIfthediameterofthepiniondedendumcircleislargeenoughforthepiniontobesecureddirectlytotheshaftbyanymethod,thepinionismadeseparateformtheshaft(Fig.a).Ifthediameterofthepiniondedendumcirclediffersbutlittlefromtheshaftdiameterthepinionismadeintegralwiththeshaft(Fig.b).10.8StructuralDesignofPinionsandGears Gearsofdiameterlessthan500mmaremadefromopen-dieorclosed-dieforgings(dependingonthescaleofproduction).Forgedwheelsaremadesolidorcoredwithroundholes.Foramoreconvenientclampingorhandling,ortoreduceweight,holesaredrilled.Castwheelswithcrossedspokesareusedwhenda≤1,000mm;Whenda>1,000mm,castwithI-shapedspokes.Whenproducedinlimitedquantitiesandalsotoreduceweightweldingisemployed.. Forlightloads,lowspeeds,lowpowertransmission,andintermittentoperation,unenclosedsetsmaybelubricatedbyusinganoilcan,dripoiler,orperiodicallybrushedgrease.Whengearsoperateinanenclosedhousing,oracase,splashlubricationiswidelyusedforgearingsubjectedtomoderateloads,speeds,andtransmittedpowerlevels.Inthiscase,oneofthegearsinapairdipsintoanoilsupplysumpatthebottomofthegearcaseandcarriestheoiltothemesh.10.9LubricationofGears Forhighspeedsandhigh-capacitygearingsystems,positiveoilcirculationsystemsareoftenrequired,usingaseparatepumptodrawoilfromthesumpanddeliveritatacontrolledratetothemeshingteeth.Thelubricantisselecteddependingonperipheralvelocityandunitload.Table10.5givestherecommendedvaluesofarbitraryviscosityofoilinEngler’sdegrees,thevaluesofoilviscosityat100℃beinggiveninbrackets.Thegradeofoilischosenaccordingtotheviscosityrequired.Themainlossesareduetoslidingfriction,whichdependsonthesurfacefinishoftheteeth,thepropertiesandamountofthelubricant,thevelocityofgearsandthetransmittedload. TheendofChapter10 急性肺栓塞的诊治进展2009 ESC急性肺栓塞诊治指南2008中国急性肺血栓栓塞症诊断治疗专家共识2009 基本概念易患因素诊断策略溶栓指征如何抗凝抗凝疗程腔静脉滤器植入指征 基本概念肺栓塞(pulmonaryembolism，PE)是内源性或外源性栓子阻塞肺动脉引起肺循环障碍的临床和病理生理综合征，包括肺血栓栓塞症、脂肪栓塞综合征、羊水栓塞、空气栓塞、肿瘤栓塞等。肺血栓栓塞症(pulmonarythromboembolism，PTE)是指来自静脉系统或右心的血栓阻塞肺动脉或其分支所致疾病，以肺循环和呼吸功能障碍为主要临床表现和病理生理特征，占肺栓塞的绝大多数，是最常见的肺栓塞类型，通常所称的PE即指PTE。肺梗死(pulmonaryinfarction，PI)定义为肺栓塞后，如果其支配区域的肺组织因血流受阻或中断而发生坏死。 基本概念大块肺栓塞(massivepulmonaryembolism)是指肺栓塞2个肺叶或以上，或小于2个肺叶伴血压下降(体循环收缩压＜90mmHg，或下降超过40mmHg/5分钟)。次大块肺栓塞(submassivepulmonaryembolism)是指肺栓塞导致右室功能减退。 基本概念深静脉血栓形成(deepvenousthrombosis，DVT)是引起PTE的主要血栓来源，DVT多发于下肢或者骨盆深静脉，脱落后随血流循环进入肺动脉及其分支，PTE常为DVT的合并症。静脉血栓栓塞症(venousthromboembolism，VTE)由于PTE与DVT在发病机制上存在相互关联，是同一种疾病病程中两个不同阶段的不同临床表现，因此统称为VTE。 静脉血栓栓塞易患因素易患因素患者相关环境相关强易患因素（OR＞10）骨折（髋部或腿）髋或膝关节置换普外科大手术大创伤脊髓损伤弱易患因素（OR＜2）卧床＞3天久坐不动（如长途车或空中旅行）年龄增长腹腔镜手术（如胆囊切除术）肥胖怀孕/产前静脉曲张易患因素患者相关环境相关中等易患因素（OR2－9）膝关节镜手术中心静脉置管化疗慢性心衰或呼衰激素替代治疗恶性肿瘤口服避孕药治疗中风发作怀孕/产后既往下肢静脉血栓血栓形成倾向 诊断流程临床诊断评价评分表>4分为高度可疑，≤4分为低度可疑分值DVT症状或体征3PE较其它诊断可能性大3心率>100次/分1.54周内制动或接受外科手术1.5既往有DVT或PE病史1.5咯血16月内接受抗肿瘤治疗或肿瘤转移1 诊断流程疑诊肺栓塞病史、体格检查、血气分析、胸片、心电图临床判断评价≤4分临床判断评价＞4分D-Dimer高CT肺动脉造影正常排除肺栓塞阳性诊断肺栓塞正常排除肺栓塞 急性肺栓塞治疗 2000年ESC急性肺栓塞临床分型大面积肺栓塞（massivePTE)：临床上以休克和低血压为主要表现，即体循环动脉收缩压<90mmHg或较基础值下降幅度>40mmHg,持续15分钟以上。须除外新发生的心律失常，低血容量或感染中毒症所致血压下降。非大面积肺栓塞（non-massivePTE)：不符合以上大面积肺栓塞标准的肺栓塞。次大面积肺栓塞（submassivePTE)：非大面积肺栓塞患者伴有右心室运动功能减弱或出现右心功能不全的表现。 2008年新版指南取消临床分型，代之以危险分层。原因：急性肺栓塞严重程度与肺动脉内血栓的形态、分布和血栓量的多少不呈平行关系。急性肺栓塞的严重程度与急性肺栓塞早期（住院或发病后30天）死亡危险程度密切相关。 急性肺栓塞危险分层的主要指标危险分层指标临床表现休克低血压(收缩压<90mmHg，或血压下降超过40mmHg持续15min)右室功能不全征象超声心动图提示右室扩张、压力超负荷CT提示右室扩张右心导管检查提示右室压力过高脑钠肽(BNP)或N末端脑钠肽前体(NT-proBNP)升高心肌损伤标志TnI或TnT阳性 a:当出现低血压后休克时就不需要评估右心功能和心肌损伤情况。肺栓塞死亡危险休克或低血压右室功能不全心肌损伤推荐治疗高危(>15%)＋aa溶栓或肺动脉血栓摘除术－＋＋中危(3%~15%)－＋－住院治疗－－＋低危(<1%)－－－早期出院或门诊治疗急性肺栓塞危险分层 基于危险度分层制定急性肺栓塞治疗策略急性肺栓塞危险度分层临床评价肺栓塞范围肌钙蛋白、脑钠肽、N末端脑钠肽前体右室功能低危高危抗凝治疗溶栓或肺动脉血栓摘除术＋抗凝治疗 2008年溶栓建议心源性休克及/或持续低血压的高危肺栓塞患者，如无绝对禁忌证，溶栓治疗是一线治疗。高危患者存在溶栓禁忌时可采用导管碎栓或外科取栓。导管内溶栓与外周静脉溶栓效果相同。对非高危(中危、低危）患者不推荐常规溶栓治疗。对于一些中危患者全面权衡出血获益风险后可给予溶栓治疗。低危患者不推荐溶栓治疗。 溶栓治疗时间窗溶栓时间窗通常在急性肺栓塞发病或复发后2周以内，症状出现48小时内溶栓获益最大，溶栓治疗开始越早，疗效越好。 溶栓药物及溶栓方案尿激酶：4400IU/Kg静脉负荷量10min，继以4400IU/Kg/h维持12-24小时快速给药：300万IU（2万IU/kg）静点2hrt-PA：50－100mg静点2小时或0.6mg/Kg静点15分钟（最大剂量50mg）尽管尿激酶和rt-PA两种溶栓药物12小时疗效相当，但rt-PA能够更快发挥作用，降低早期死亡率，减少血栓在肺动脉内停留时间而造成的肺动脉内皮损伤，以及减少血栓附着在静脉瓣上的时间，从理论上讲可以降低远期慢性血栓栓塞性肺高压及下肢深静脉瓣功能不全后遗症的发生危险，因此推荐首选rt-PA方案。 急性肺栓塞溶栓治疗禁忌证绝对禁忌证任何时间出血性或不明原因的脑卒中6个月内缺血性脑卒中中枢神经系统损伤或肿瘤3周内大创伤、外科手术、头部损伤近一月内胃肠道出血已知的活动性出血相对禁忌证6个月内短暂性脑缺血发作口服抗凝药妊娠或分娩1周内不能压迫的血管穿刺创伤性心肺复苏难治性高血压(收缩压>180mmHg)晚期肝病感染性心内膜炎活动性消化性溃疡 抗凝治疗急性肺栓塞初始抗凝治疗的目的是减少死亡及再发栓塞事件。急性肺栓塞患者长期抗凝治疗的目的是预防致死性及非致死性静脉血栓栓塞事件。 抗凝治疗怀疑急性肺栓塞的患者等待进一步确诊过程中即应开始抗凝治疗。高危患者溶栓后序贯抗凝治疗。中、低危患者抗凝治疗是基本的治疗措施。常用的抗凝药物非口服抗凝药：普通肝素、低分子量肝素、磺达肝素（Arixtra）口服抗凝药：华法林、利伐沙班（拜瑞妥）。阿司匹林和波立维不推荐应用于治疗静脉血栓。 抗凝治疗普通肝素应用指征血流动力学不稳定的高危肺栓塞患者（因为目前一些比较普通肝素和低分子量肝素的抗凝效果和安全性的临床试验中并不包括这些高危患者）。肾功能不全患者（因普通肝素经网状内皮系统清除，不经肾脏代谢）。高出血风险患者（因普通肝素抗凝作用可迅速被中和）。对其他急性肺栓塞患者，低分子量肝素可替代普通肝素。磺达肝癸钠与低分子量肝素具有同样的抗凝效果,且无需监测。 抗凝治疗常用的普通肝素给药方法是静脉滴注，首剂负荷量为80U/kg（一般2000－5000U)，继之700～1000U/h或18U/kg/h维持。用普通肝素治疗需要监测激活的部分凝血活酶时间（APTT）,APTT至少要大于对照值的1.5倍（通常是1.5倍～2.0倍）。使用低分子肝素一般情况下无需监测。但对肾功能不全的患者需谨慎使用低分子量肝素，并应根据抗Ⅹa因子活性来调整剂量，当抗Ⅹa因子活性在0.6~1.0IU/ml范围内推荐皮下注射每日2次，当抗Ⅹa因子活性在1.0~2.0IU/ml范围内推荐皮下注射每日1次。 根据体重调整普通肝素用量的“Raschke”方案APTT肝素剂量的调节秒控制倍数首剂负荷量80IU/kg,随后18IU/(kg.h)维持<35<1.280IU/kg静脉推入,然后增加4IU/(kg.h)36451.21.540IU/kg静脉推入,然后增加2IU/(kg.h)46701.52.3维持原剂量71902.33.0将维持量减少2IU/(kg.h)>90>3.0停药1h,随后减量3IU/(kg.h)继续给药 低分子量肝素和磺达肝癸钠给药方案药物剂量间隔时间Enoxaparin1.0mg/kg每12h一次（克赛）or1.5mg/kg每天一次Tinzaparin175U/kg每天一次（亭扎肝素）Fondaparinux5mg(体重50kg)每天一次（磺达肝素）7.5mg(体重50–100kg)10mg(体重100kg) 抗凝治疗肝素需与华法林重叠使用，直到INR达标（2.0－3.0）2天后再停用肝素。最常用口服药物为华法林，对于年轻患者或者既往健康的院外患者而言，起始剂量通常为10mg；而对于老年及住院患者，起始剂量通常为5mg，（国人：起始剂量为2.5～3.0mg/d）以后根据国际标准化比值（INR）调整剂量,长期服用者INR宜维持在2.0～3.0之间。 抗凝治疗时程急性肺栓塞的抗凝时间长短应个体化，一般至少需要3个月。如果急性肺栓塞（0.5％－5％患者）发展成慢性血栓栓塞性肺动脉高压者应长期抗凝治疗。如果急性肺栓塞治疗成功，症状基本消失，无右心压力负荷，影像学检查肺栓塞基本消失者应根据血栓形成的诱发因素类型决定抗凝时程。 抗凝治疗时程由暂时或可逆性诱发因素（服用雌激素、临时制动、创伤和手术）导致的肺栓塞患者推荐抗凝时程为3个月。对于无明显诱发因素的首次肺栓塞患者（特发性静脉血栓）建议抗凝至少6个月，对于再次发生的无诱发因素的肺栓塞患者建议长期抗凝。对于静脉血栓栓塞危险因素长期存在的患者应长期抗凝治疗，如癌症患者、抗心脂抗体综合征、易栓症等。 下腔静脉滤器植入适应证肺栓塞合并抗凝治疗禁忌或抗凝治疗出现并发症者充分抗凝治疗后肺栓塞复发者高危患者的预防：①广泛、进行性静脉血栓形成；②行导管介入治疗或肺动脉血栓剥脱术者；③严重肺动脉高压或肺心病者。因滤器只能预防肺栓塞复发，并不能治疗DVT，因此安装滤器后如无抗凝禁忌仍需抗凝，防止进一步血栓形成。