呼吸科呼吸系统课件

PartialPressureofIndividualGasesinaGasMixtureAbovetheabsolutetemperature,allmoleculesofallmatterarecontinuallyundergoingmotion.Pressureiscausedbymultipleimpactsofmovingmoleculesagainstasurfaceeitherinair,liquidorotherformsofmatter.Thepartialpressureisdirectlyproportionaltotheconcentrationofthegasmoleculeforair.第一页2023/10/161第二页，共28页。AppliedGasLawsQuestionAtthesealevel(barometricpressureis760mmHg),howmuchisthepartialpressureofoxygenifweknowairconsistsof21%oxygen?HintsDalton’slawstatesthatthetotalpressureexertedbyagaseousmixtureisequaltothesumofthepartialpressuresofeachgascomponentinthegasmixture.Inamixtureofgases,thepartialpressureofagivengasisdirectlyproportionaltothevolumethatgascontributestothetotalvolume.第二页2023/10/162第三页，共28页。AnswersPB=PN2+PO2+PHO2+PCO2(atthesealevel,PB=760mmHg).WherePB=barometricpressureatthesealevel.WherePN2isthepartialpressureofnitrogen.PO2

isthepartialpressureofoxygen(氧分压).PO2intheair=760mmHgX0.21=160mmHg.第三页2023/10/163第四页，共28页。第四页第五页，共28页。PartialPressuresofIndividualGasesattheSealLevel(PB=760mmHg)AmbientDryair(mmHg)MoistTrachealAir(mmHg)AlveolarAir(mmHg)SystemicArterialBlood(mmHg)MixedVenousBlood(mmHg)O21601501029540CO200404046WaterVapor047474747N2600563571571571Total760760760760704第五页2023/10/165第六页，共28页。WaterVapor(水蒸汽）LowersPO2onceAirIsBeingHumidified（湿化）Airisbeingwarmedandhumidifiedbeforereachingalveoli.WatervapordoesnotchangethepercentageofO2orN2butdoeslowthepartialpressureofO2orN2.Inhumidifiedair,PO2=(760–47)X0.21=150mmHgPN2=(760–47)X0.79=563mmHg第六页2023/10/166第七页，共28页。ThePartialPressureofOxygenintheAlveolarSpaceisdownto102mmHgTworeasonscausethis“down”TheexistenceofFRCresultsindilutionofairinthealveoli.Thecontinuousuptakeofoxygenbythebloodinpulmonarycapillaries.第七页2023/10/167第八页，共28页。TheDeterminantsofAlveolarPO2第八页2023/10/168第九页，共28页。FactorsthatDetermineAlveolarPCO2

第九页2023/10/169第十页，共28页。DiffusionofGasesthroughtheRespiratoryMembrane第十页2023/10/1610第十一页，共28页。2023/10/1611Alveolar-CapillaryMembrane

(RespiratoryMembrane)2023/10/1611SixlayersconstructabarrierAlveolarfluidlayerAlveolarepitheliumAlveolarbasementmembraneInterstitialmatrixCapillarybasementmembraneCapillaryendothelium第十一页2023/10/1611第十二页，共28页。GasesDiffuseaccordingtoTheirConcentrationGradientsBloodstaysinthepulmonarycapillariesfor0.75seconds.Ittakes0.25secforO2toreachtheequilibrium.PO2inthepulmonarycapillaries,pulmonaryvein,andsystemicarteriesshouldbecloseoridenticaltothatinalveolarspace.第十二页2023/10/1612第十三页，共28页。WhyisArterialPO2LowerthanThatofAlveolarAir?Twocontributors:ashuntandalowventilation/perfusionratio.Theconductingairwayshaveaseparatecirculation,calledbronchialcirculation.Abouthalfofvenousbloodfromthebronchialcirculationreturnstothepulmonaryveins,resultinginanadmixtureofunoxygenatedbloodandoxygenatedbloodandadropinarterialPO2.第十三页2023/10/1613第十四页，共28页。QuantitativeDescriptionofDiffusionFick’slaw:D=

P.T.A.S/d.(MW)1/2WhereD=diffusionrate

P=partialpressuregradient(drivingforce)T=temperatureA=membranesurfaceareaS=solubilityofgasinthebloodd=distanceofdiffusion(thethicknessofmembrane);MW=moleculeweightofthegas.S/(MW)1/2isalsodefinedasdiffusioncoefficient(扩散系数).第十四页2023/10/1614第十五页，共28页。BetweenOxygenandCarbonDioxide,WhichGasDiffusesFaster?

ConclusionsAtthesamepressuregradient,carbondioxidediffuses24.3timesfasterthanoxygen.Underphysiologicalpressuregradients,carbondioxidewilldiffuse2.35timesfasterthanoxygen.GasSolubilitycoefficientat37˚C(ml/dl/mmHg)Partialpressuregradient(mmHg)CO20.592X63.552O20.0244X621.5128CO2/O224.3X0.0972.35第十五页2023/10/1615第十六页，共28页。FactorsthatAffectGasDiffusionRateacrosstheRespiratoryMembrane

1.ThepartialpressuregradientbetweentwosidesofthemembraneDirectlyproportional2.Thediffusioncoefficientofthegas3.Thethicknessofrespiratorymembrane.4.Thesurfaceareaofrespiratorymembrane.Removeofthelung,emphysema第十六页2023/10/1616第十七页，共28页。FactorsThatAffectPartialPressureGradientAlveolarventilationLargeralveolarventilationhelpstoreducethebufferingpowerofFRC,enhancingPAO2andreducingPACO2.PulmonarybloodflowIncreasedpulmonarybloodflowrisesO2and

CO2partialpressuregradient.Thekineticsofhemoglobinbindingtooxygenandcarbondioxide.第十七页2023/10/1617第十八页，共28页。DiffusingCapacityoftheRespiratoryMembraneItisaparameterthatisusedformeasuretheabilityoftherespiratorymembranetoexchangeagasbetweenthealveoliandthepulmonaryblood.DefinitionThevolumeofagasthatwilldiffusethroughtherespiratorymembraneeachminuteforapartialpressuredifferenceof1mmHg.第十八页2023/10/1618第十九页，共28页。TheDiffusingCapacityoftheRespiratoryMembraneisnotFixedThediffusingcapacityforoxygeninyoung,healthymenis21ml/min/mmHg.Exerciseincreasesthediffusingcapacity.第十九页2023/10/1619第二十页，共28页。Ventilation/perfusionratioTheratioofalveolarminuteventilation(VA)tominutepulmonarybloodflow(Q)isventilation/perfusionratio.Itisusedtoindicatematchingofairflowandbloodflowforgasexchange.Theventilationisalveolarminutevolumewhereasminutepulmonarybloodflowequalsheartoutput.AsVAis4L/minandcardiacoutputis5L/mininnormaladults,VA/Qisapproximately0.8.第二十页2023/10/1620第二十一页，共28页。VA/QExplanationSignificanceHypoventilationand/orpulmonarybloodflowA-Vshunt(HypoxiawithorwithoutCO2accumulation)

Hyperventilationand/orpulmonarybloodflowIncreaseinalveolardeadspace(HypoxiawithorwithoutCO2accumulation)AbnormalVA/QRatiosAlterGasTensions第二十一页2023/10/1621第二十二页，共28页。GravityCausesUnevenPulmonaryBloodFlowintheUprightPerson第二十二页2023/10/1622第二十三页，共28页。GravityCausesaMismatchofRegionalVentilationandBloodFlowintheLungs第二十三页2023/10/1623第二十四页，共28页。Ventilation-PerfusionRatiosAffectCapillaryBloodGasTension第二十四页2023/10/1624第二十五页，共28页。VenousAdmixtureThemixingofunoxygenatedbloodwithoxygenatedbloodiscalledvenousadmixture.Venousadmixturehastworeason