呼吸科呼吸系统课件.ppt

呼吸科呼吸系统课件.ppt

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5.2.5.2.GasExchangeGasExchange2022/11/51lDefinitionlDiffusionofoxygenandcarbondioxidebetweenthealveoliandthebloodinsidethepulmonarycapillaries.lWhatwehavetoknow?

lBasicprinciplesofgasdiffusionlFactorsthatdeterminetherateofgasdiffusionPartialPressureofIndividualGasesinaGasPartialPressureofIndividualGasesinaGasMixtureMixtureAbovetheabsolutetemperature,allmoleculesofallmatterarecontinuallyundergoingmotion.Pressureiscausedbymultipleimpactsofmovingmoleculesagainstasurfaceeitherinair,liquidorotherformsofmatter.Thepartialpressureisdirectlyproportionaltotheconcentrationofthegasmoleculeforair.2022/11/52AppliedGasLawsAppliedGasLawsQuestionnAtthesealevel（barometricpressureis760mmHg）,howmuchisthepartialpressureofoxygenifweknowairconsistsof21%oxygen?

HintsnDaltonslawstatesthatthetotalpressureexertedbyagaseousmixtureisequaltothesumofthepartialpressuresofeachgascomponentinthegasmixture.nInamixtureofgases,thepartialpressureofagivengasisdirectlyproportionaltothevolumethatgascontributestothetotalvolume.2022/11/53AnswersAnswersPB=PN2+PO2+PHO2+PCO2（atthesealevel,PB=760mmHg）.WherePB=barometricpressureatthesealevel.WherePN2isthepartialpressureofnitrogen.PO2isthepartialpressureofoxygen（氧分压）.PO2intheair=760mmHgX0.21=160mmHg.2022/11/54PartialPressuresofIndividualGasesatthePartialPressuresofIndividualGasesattheSealLevel（PSealLevel（PBB=760mmHg）=760mmHg）2022/11/56AmbientDryair（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=563mmHg2022/11/57ThePartialPressureofOxygenintheThePartialPressureofOxygenintheAlveolarSpaceisdownto102mmHgAlveolarSpaceisdownto102mmHgTworeasonscausethis“down”TheexistenceofFRCresultsindilutionofairinthealveoli.Thecontinuousuptakeofoxygenbythebloodinpulmonarycapillaries.2022/11/58TheDeterminantsofAlveolarPTheDeterminantsofAlveolarPOO222022/11/59FactorsthatDetermineAlveolarPCOFactorsthatDetermineAlveolarPCO222022/11/5102022/11/511DiffusionofGasesthroughtheDiffusionofGasesthroughtheRespiratoryMembraneRespiratoryMembrane2022/11/5122022/11/512Alveolar-CapillaryMembrane（RespiratoryMembrane）2022/11/512Sixlayersconstructabarrier1.Alveolarfluidlayer2.Alveolarepithelium3.Alveolarbasementmembrane4.Interstitialmatrix5.Capillarybasementmembrane6.CapillaryendotheliumGasesDiffuseaccordingtoTheirGasesDiffuseaccordingtoTheirConcentrationGradientsConcentrationGradients2022/11/5131.Bloodstaysinthepulmonarycapillariesfor0.75seconds.2.Ittakes0.25secforO2toreachtheequilibrium.3.PO2inthepulmonarycapillaries,pulmonaryvein,andsystemicarteriesshouldbecloseoridenticaltothatinalveolarspace.WhyisArterialPOWhyisArterialPO22LowerthanThatofLowerthanThatofAlveolarAir?

AlveolarAir?

2022/11/514nTwocontributors:

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）.2022/11/515BetweenOxygenandCarbonDioxide,BetweenOxygenandCarbonDioxide,WhichGasDiffusesFaster?

WhichGasDiffusesFaster?

ConclusionslAtthesamepressuregradient,carbondioxidediffuses24.3timesfasterthanoxygen.lUnderphysiologicalpressuregradients,carbondioxidewilldiffuse2.35timesfasterthanoxygen.2022/11/516GasSolubilitycoefficientat37C（ml/dl/mmHg）Partialpressuregradient（mmHg）CO20.592X63.552O20.0244X621.5128CO2/O224.3X0.0972.35FactorsthatAffectGasDiffusionRateacrosstheFactorsthatAffectGasDiffusionRateacrosstheRespiratoryMembraneRespiratoryMembrane1.ThepartialpressuregradientbetweentwosidesofthemembraneDirectlyproportional2.Thediffusioncoefficientofthegas3.Thethicknessofrespiratorymembrane.4.Thesurfaceareaofrespiratorymembrane.Removeofthelung,e