呼吸科呼吸系统课件.ppt
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呼吸科呼吸系统课件.ppt
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5.2.5.2.GasExchangeGasExchange2024/2/71lDefinitionlDiffusionofoxygenandcarbondioxidebetweenthealveoliandthebloodinsidethepulmonarycapillaries.lWhatwehavetoknow?
lBasicprinciplesofgasdiffusionlFactorsthatdeterminetherateofgasdiffusionPartialPressureofIndividualGasesinaGasPartialPressureofIndividualGasesinaGasMixtureMixtureAbovetheabsolutetemperature,allmoleculesofallmatterarecontinuallyundergoingmotion.Pressureiscausedbymultipleimpactsofmovingmoleculesagainstasurfaceeitherinair,liquidorotherformsofmatter.Thepartialpressureisdirectlyproportionaltotheconcentrationofthegasmoleculeforair.2024/2/72AppliedGasLawsAppliedGasLawsQuestionnAtthesealevel(barometricpressureis760mmHg),howmuchisthepartialpressureofoxygenifweknowairconsistsof21%oxygen?
HintsnDaltonslawstatesthatthetotalpressureexertedbyagaseousmixtureisequaltothesumofthepartialpressuresofeachgascomponentinthegasmixture.nInamixtureofgases,thepartialpressureofagivengasisdirectlyproportionaltothevolumethatgascontributestothetotalvolume.2024/2/73AnswersAnswersPB=PN2+PO2+PHO2+PCO2(atthesealevel,PB=760mmHg).WherePB=barometricpressureatthesealevel.WherePN2isthepartialpressureofnitrogen.PO2isthepartialpressureofoxygen(氧分压).PO2intheair=760mmHgX0.21=160mmHg.2024/2/74PartialPressuresofIndividualGasesatthePartialPressuresofIndividualGasesattheSealLevel(PSealLevel(PBB=760mmHg)=760mmHg)2024/2/76AmbientDryair(mmHg)MoistTrachealAir(mmHg)AlveolarAir(mmHg)SystemicArterialBlood(mmHg)MixedVenousBlood(mmHg)O21601501029540CO200404046WaterVapor047474747N2600563571571571Total760760760760704WaterVapor(WaterVapor(水蒸汽)水蒸汽)LowersPOLowersPO22onceAironceAirIsBeingHumidifiedIsBeingHumidified(湿化)(湿化)Airisbeingwarmedandhumidifiedbeforereachingalveoli.WatervapordoesnotchangethepercentageofO2orN2butdoeslowthepartialpressureofO2orN2.Inhumidifiedair,nPO2=(76047)X0.21=150mmHgnPN2=(76047)X0.79=563mmHg2024/2/77ThePartialPressureofOxygenintheThePartialPressureofOxygenintheAlveolarSpaceisdownto102mmHgAlveolarSpaceisdownto102mmHgTworeasonscausethis“down”TheexistenceofFRCresultsindilutionofairinthealveoli.Thecontinuousuptakeofoxygenbythebloodinpulmonarycapillaries.2024/2/78TheDeterminantsofAlveolarPTheDeterminantsofAlveolarPOO222024/2/79FactorsthatDetermineAlveolarPCOFactorsthatDetermineAlveolarPCO222024/2/7102024/2/711DiffusionofGasesthroughtheDiffusionofGasesthroughtheRespiratoryMembraneRespiratoryMembrane2024/2/7122024/2/712Alveolar-CapillaryMembrane(RespiratoryMembrane)2024/2/712Sixlayersconstructabarrier1.Alveolarfluidlayer2.Alveolarepithelium3.Alveolarbasementmembrane4.Interstitialmatrix5.Capillarybasementmembrane6.CapillaryendotheliumGasesDiffuseaccordingtoTheirGasesDiffuseaccordingtoTheirConcentrationGradientsConcentrationGradients2024/2/7131.Bloodstaysinthepulmonarycapillariesfor0.75seconds.2.Ittakes0.25secforO2toreachtheequilibrium.3.PO2inthepulmonarycapillaries,pulmonaryvein,andsystemicarteriesshouldbecloseoridenticaltothatinalveolarspace.WhyisArterialPOWhyisArterialPO22LowerthanThatofLowerthanThatofAlveolarAir?
AlveolarAir?
2024/2/714nTwocontributors:
ashuntandalowventilation/perfusionratio.nTheconductingairwayshaveaseparatecirculation,calledbronchialcirculation.nAbouthalfofvenousbloodfromthebronchialcirculationreturnstothepulmonaryveins,resultinginanadmixtureofunoxygenatedbloodandoxygenatedbloodandadropinarterialPO2.QuantitativeDescriptionofDiffusionQuantitativeDescriptionofDiffusionFickslaw:
D=P.T.A.S/d.(MW)1/2WhereD=diffusionrateP=partialpressuregradient(drivingforce)T=temperatureA=membranesurfaceareaS=solubilityofgasinthebloodd=distanceofdiffusion(thethicknessofmembrane);MW=moleculeweightofthegas.S/(MW)1/2isalsodefinedasdiffusioncoefficient(扩散系数).2024/2/715BetweenOxygenandCarbonDioxide,BetweenOxygenandCarbonDioxide,WhichGasDiffusesFaster?
WhichGasDiffusesFaster?
ConclusionslAtthesamepressuregradient,carbondioxidediffuses24.3timesfasterthanoxygen.lUnderphysiologicalpressuregradients,carbondioxidewilldiffuse2.35timesfasterthanoxygen.2024/2/716GasSolubilitycoefficientat37C(ml/dl/mmHg)Partialpressuregradient(mmHg)CO20.592X63.552O20.0244X621.5128CO2/O224.3X0.0972.35FactorsthatAffectGasDiffusionRateacrosstheFactorsthatAffectGasDiffusionRateacrosstheRespiratoryMembraneRespiratoryMembrane1.ThepartialpressuregradientbetweentwosidesofthemembraneDirectlyproportional2.Thediffusioncoefficientofthegas3.Thethicknessofrespiratorymembrane.4.Thesurfaceareaofrespiratorymembrane.Removeofthelung,emphysema2024/2/717FactorsThatAffectPartialPressureGradientFactorsThatAffectPartialPressureGradientAlveolarventilationnLargeralveolarventilationhelpstoreducethebufferingpowerofFRC,enhancingPAO2andreducingPACO2.PulmonarybloodflownIncreasedpulmonarybloodflowrisesO2andCO2partialpressuregradient.Thekineticsofhemoglobinbindingtooxygenandcarbondioxide.2024/2/718DiffusingCapacityoftheRespiratoryDiffusingCapacityoftheRespiratoryMembraneMembraneItisaparameterthatisusedformeasuretheabilityoftherespiratorymembranetoexchangeagasbetweenthealveoliandthepulmonaryblood.DefinitionThevolumeofagasthatwilldiffusethroughtherespiratorymembraneeachminuteforapartialpressuredifferenceof1mmHg.2024/2/719TheDiffusingCapacityoftheRespiratoryTheDiffusingCapacityoftheRespiratoryMembraneisnotFixedMembraneisnotFixedThediffusingcapacityforoxygeninyoung,healthymenis21ml/min/mmHg.Exerciseincreasesthediffusingcapacity.2024/2/720Ventilation/perfusionratioVentilation/perfusionratioTheratioofalveolarminuteventilation(VA)tominutepulmonarybloodflow(Q)isventilation/perfusionratio.Itisusedtoindicatematchingofairflowandbloodflowforgasexchange.Theventilationisalveolarminutevolumewhereasminutepulmonarybloodflowequalsheartoutput.AsVAis4L/minandcardiacoutputis5L/mininnormaladults,VA/Qisapproximately0.8.2024/2/7212024/2/722VA/QExplanationSignificanceHypoventilationand/orpulmonarybloodflowA-Vshunt(HypoxiawithorwithoutCO2accumulation)Hyperventilationand/orpulmonarybloodflowIncreaseinalveolardeadspace(HypoxiawithorwithoutCO2accumulation)AbnormalVA/QRatiosAlterGasTensionsGravityCausesUnevenPulmonaryBloodGravityCausesUnevenPulmonaryBloodFlowintheUprightPersonFlowintheUprightPerson2024/2/723GravityCausesaMismatchofRegionalGravityCausesaMismatchofRegionalVentilationandBloodFlowintheLungsVentilationandBloodFlowintheLungs2024/2/724Ventilation-PerfusionRatiosAffectCapillaryVentilation-PerfusionRatiosAffectCapillaryBloodGasTensionBloodGasTension2024/2/725VenousAdmixtureVenousAdmixtureThemixingofunoxygenatedbloodwithoxygenatedbloodiscalledvenousadmixture.Venousadmixturehastworeasons:
AshuntandalowVA/Q.Ashunthasaanatomicstructurethatallowsbloodtobypassalveolithroughachannel,suchasfromtherighttotheleftheartthroughanatrialorventricularseptaldefect.Ananatomicshuntisoftencalledaright-leftshunt.2024/2/726SummarySummaryTheuptakeofoxygenisdeterminedbydiffusionpropertiesofthealveolar-capillarymembrane,theO2partialpressuregradient,andpulmonarybloodflow.Thetransferofoxygeninthelungislimitedprimarilybybloodflow.Diffusioncapacityofthelung(DL)isdefinedasthevolumeofgivengasdiffusedacrosstherespiratorymembraneperminuteunderapartialpressuregradientof1mmHg.2024/2/727Summary-ContinuedSummary-ContinuedTheratioofalveolarminuteventilation(VA)tominutepulmonarybloodflow(Q)isventilation/perfusionratio.Itisusedtoindicatematchingofairflowandbloodflowforgasexchange.Gravitycausesamismatchofregionalventilationandbloodflowinthelungs.2024/2/728
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