My Biomedical Notebook_ Respiratory Physiology

10/28/2015 MyBiomedicalNotebook:RespiratoryPhysiology

http://tsbiomed.blogspot.in/2012/12/notesinrespiratoryphysiology.html 1/16

NotesinBiomedicalScience

MyBiomedicalNotebook

Friday,21December2012

RespiratoryPhysiology

GeneralFunctionsoftheRespiratorySystem:VentilationmovingairintoandoutofthelungsGaseousexchangereplacingO2andremovingCO2fromtheblood.RegulationofacidbasebalanceAirconditioningSpeech/smell(TemperatureandFluidBalance)

Thestructureoftherespiratorysystem:twolungs:coveredbyvisceralpleuralandconnecttotheinnerthoraxanddiaphragmbranchingnetworkofairwaysrespiratorymembranesupportingtissues''separated''into:conductingandrespiratoryexchangezones

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Conductingzone:tracheasegmentalbronchibronchiolesterminalbronchioles

Humidify,warmandfiltertheairtoPROTECT

Respiratoryexchangezone:respiratorybronchiolesalveolarductsalveoliCreatelargesurfaceareaandthinbarriertoAIDDIFFUSION

Knowthefunctionsofthelungsandrespiratorysystemandtheanatomicalandfunctionalzonesoftherespiratorysystem

NOW!LetstalkaboutthefollowingThethoraxandrespiratorymusclesMechanicsofbreathingPressurechangesinventilation

Zonesoftherespiratorysystem:



MechanicsofBreathingvideo

Whatcausesairtoflowinbulkintoandoutofthelungs?Expiration:DiaphragmmovesupInspiration:DiaphragmmovesdownAirPressureChangesDuringVentilationInspiration:P(atmosperic)>P(alveolar)=airmovesintothelungsExpiration:P(alveolar)>P(atmospheric)=airmovesoutofthelungs

FactorsaffectinglungmechanicsLungcompliancethedistensibilityoflungtissueLungElasticitytheabilitytostretchandreturntorestingstateSurfactantproducedbytypeIIalveolarcellsreducessurfacetensioninalveoli(causedbyH2O)increasestotallungcomplianceAirwayresistanceaircontactwithwallsofairwaysincludingnarrowingofairwaysduetodisease/infectionetclikeAsthmaetc,Thiscausesmoreenergytoberequiredtodeliversufficientair

Sotosummarizethemechanicsofbreathing:Inspiration:stimulustodiaphragm>diaphragmcontractsthoraxexpands>pressureinlungsdecreasesPatm>Palv>airflowsinbulkfromatmospheretoalveoli(fromhighpressuretolowpres.)Expiration:stimulustodiaphragmends>diaphragmrelaxesandthoraxmmovesinwards(passive)>pressureinlungsincreasesPalv>Patm>airflowsinbulkfromalveolitoatmosphere(fromhightolowpressure)

NOW!letstalkabout:LungvolumesandventilationratesNervouscontrolofventilationChemicalcontrolofventilationCarbondioxide(PCO2)HydrogenIons(H+)Oxygen(PO2)

Ventilationrates:AtrestPulmonaryventilationrate(minutevolume)=respiratoryrate(RR)xtidalvolume(Vt)=12Br/minx500ml=6000ml/minAlveolarventilationrate=(tidalvolumedeadspacevol.)xRR=(500150)x12=4200ml/min

RegulationofVentilation:NeuralgenerationofrhythmicventilationVentilationdependsonrhythmiconoffstimmulationofrespiratorymusclesvianervesautomaticstimuluscomesfromtherespiratorycontrolcentreinMedullaofthebrainstem.

attheendofexpiration=>restingmuscletoneneuronesrhythmically'fire'=>activeinspirationandthen'ceasefire'=>passiveexpiration

Theneuralpathwaysforventilation

WetSpirometry



DRGsendsanexcitatorystimulustothephrenicandintercostalnerveandthePons=>PhrenicandintercostalnerveconductthestimulustodiaphragmandintercostalmusclesActiveinspiration=>PneumotaxiccentreinPonssendsaninhibitorystimulusbacktotheDRGandinspirationstopsPassiveexpiration

ControlofventilationbyPCO2PCO2ofarterialbloodisthemaininputregulatingventilationundernormalconditionsIncreasedPCO2stimulatesventilationviacentralandperipheralchemoreceptors

CentralchemoreceptorsVentralsurfaceofMedullaissensitivetoCO2generated[H+]incerebrospinalfluid(CSF)surroundingmedulla.CO2+H2O>H2CO3>HCO3+H+pHofCSFismoresensitivethanbloodasitcontainsfewerproteinbuffersChangesinPCO2causeslarger[H+]inCSFcomparedtoblood.

Peripheralchemoreceptorscarotidandaortic'bodies'largebloodsupplybothrespondtoPCO2generated[H+]andbloodpHCarotidalsostimulatedbydecreasedPO2PO2onlydetectedwhenitfallsby~40%(hypoxia/attitude)

Othermodulatingfactorsincludeprotectivereflexesandhigherbraincentres



Summary:lungvolumesandventilationrate,neuralcontrolofbreathingandchemicalcontrolviacentralandperipheralchemoreceptors

Followingtopicsaboutrespiratoryphysiologytobediscussed:partialpressureofgasesO2andCO2transportinthebloodventilationandacidbasebalance

PartialPressureofgasesDalton'slaw:thetotalpressureofagasmixtureisequaltothesumofthepressuresthateachgaswouldexertindependentlywhenbarometricpressure(Pb)is760mmHgThecompositionofatmosphericairis:O220.93%0.2093CO200.03%0.0003N279.04%0.7904

Calculationofpartialpressures:thepartialpressureofanygascanbecalculatedbymultiplyingPbbythefractionofthegasExample:PO2=760x0.2093=...mmHgPN2=760x0.7904=...mmHg



...mlofO2iscarriedby100mlofblood.0.3ml(...%)isdissolvedinsolutioninplasmaandtherestiscombinedwithiron(Fe2+)onhaemunitsofhaemoglobin(Hb)moleculesinredbloodcells.FourO2moleculescombinewithHbformingoxyhaemoglobininareversiblereaction.........arterialbloodisfullysaturatedwithO2.

O2transportbytheblood



Oxyhaemoglobindissociationcurve:Thisrelatesthepercent%........ofHbtothePO2inblood.AhighPO2=loading(curve>right)whereasalowPO2=reducedaffinity=unloading(curve



FactorsaffectinglungmechanicsTransmuralpressuregradientCompliance,elastance,airwayresistance,ST

LungPressuresIntraalveolarpressure(IAP)=Pbatrest/+ve1mmHgmidwaythroughtidalbreathIntrapleuralpressure(IPP)4to8mHg



HelpskeepalveolipatentLosseswithage/disease

AlveolarsurfacetensionforcesAtairliquidinterfaceSurfacetension(ST)a.drawsliquidsclosertogetherb.resistsincreaseinsurfacearea

LawofLaplaceSTdirectsforce/pressuretocentreofbubbleConsequences:smallalveolimayhavegreaterP,maycreatepressuregradientsbetweenopposingalveolicausing'lunginstability'

SurfactantPhospholipidproducedbytypeIIcuboidalalveolarcellsMoreconcentratedinsmallestalveoliSighingreplenishlevelsPreventssmallalveoliemptyingintolargeronesPreventscollapseofalveoliKeepslungsdryish(osmotic>hydrostaticpressure)ReducessurfacetensionandincreasestotallungcomplianceIncreaseslung'stability'Reducesworkofbreathing

Surfactant:PathophysiologyAdequatelevels6weeksbeforebirthNRDSrequires+vepressurebreathingandsyntheticsurfactantLevelsreducedbyalveolardamageandincreasedmacrophageactivityEnergyisneededtoovercome'elasticresistance'oflungsandthorax.Posture:lying=decreaseincomplianceDisease:ifFRCisincreased,Clisincreasedandviceversa

Solungcomplianceisaffectedby?FibrosisdecreaseOedemadecreaseAgedecreaseAirwayblockagedecreaseEmphysemaincrease

AirwayResistanceGasflowproportionaltopressuregradientandinverselyproportionaltoresistancePoiseuillesLawResistanceproportionaltolength(L)andviscocity()andinverselyproportionaltoRadius(R)

RproportionaltoLx/r^4Ifradius=1:1/1^4=>R=1Ifradius=2:1/2^4=>R=Thereforedoubletheradious=1/16ththeresistanceandviceversaRadiusisprimarysourceTracheaandbronchi(rigidandsmallXSarea)=90%Bronchioles=10%(largeXSarea)Narrowingofsmallerairwaysproblemsdependsonnumberaffectedandcollapse

BrionchiolesReflexcontrolbyPSNSandhormonesLocalcontrolbyparacrines

LawofLaplace



Topicstobediscussednowingreaterdetail:Gaspressuresandgasexchange(recapabove)TypesofventilationVentilationandperfusionFactorsaffectinggasexchange

Remembercompositionofatmosphericair

O220.90%,0.2090(fraction),159mmHg(partialpressure)CO20.04%,0.0004,0.3mmHgN278.60%,0.7860,597mmHgH200.46%,0.0046,3.7mmHgtotal100%,1.0,760mmHginrealitytherearesomeothercomponentsintheairaswellbutinverylowconcentrationsthatwecanactuallyneglect

PartialPressure:thepartialpressureofanygascanbecalculatedbymultiplyingPbbythefractionofthegasExample:PO2=760x0.2090=159mmHgPN2=760x0.7860=597mmHg

(missing5thslideofpulm3BS2049module)

CompositionofalveolargasAffectedby:Ambientaircompositionandflow,gasexchange,mixingofgases,humidity

TypesventilationUpneaHyperneaHyperventilationHypoventilationTachypneaDyspneaApnea

10,12slidenotincludedputitin...

V/QmatchingLocalmechanismsadjustforpoorairflowand/orpoorbloodflowCapillariescollapsibleRegulationofarteriolesandbronchioles

Va/QaratioAlveolarbloodflowdecreasesfrombasetotheapexRatio=3.0inapexand0.5inbaseAverage=0.8(Va=5LQa=6L)Perfusion>Ventilationatrest



Abovewediscuss:partialpressures,effectsofbreathingpattern,definingtypesofventilation,effectsofhyper/hypoventilationonPAO2/PACO2,V:Qmatching,localcontrolofairandbloodflow

TopicsFick'slawofdiffusionOxygenationofbloodinpulmonarycapillariesGasexchange:problems

TypesofHypoxia:Hypoxic:lowarterialO2Anaemic:lowHbO2Ischemic:lowPO2deliveryHistotoxic:lowO2use

Fick'slawofdiffusion:Diffusionisproportionalto:partialpressuredifference(gradient)surfaceareaDiffusionisinverselyproportionalto:membranethicknessdiffusiondistance

Gasexchange:ProblemsCausehypoxiaandhypercapnia:Inadequate:O2inalveoliTransferofO2fromalveolitobloodTransport....Gasexchange:InadequateO2



abnormalairinadequatealveolarVe

Gasexchanges:inadequaciesintranferdecreaseinSAforexchangeincreaseinthicknessofmembraneincreaseindiffusiondistance

Someessayquestionthatareseeninexams:TheimpactofemphysemaonrespiratoryfunctionGasexchange:lossofalveolartissuedecreasedSAforgasexchange,lossoftraction>obstructionofairways,gastrapping>diffusiongradientaffectedLocalregulationofventilationandperfusion(V/Q)inthelungsMechanicsthatregulateventilationandperfusion(V/Q)inthelungFactorsthataffecttheefficiencyofgasexchangeinthelungsFactorsthataffectlungmechanicsandgasexchangeinhealthanddiseaseFactorsthataffecttheefficiencyofgasexchangebetweenthelungsandblood



nowwehavedonethisabovebutwewillextendabitfurtheronsomethingsparticularlyonexercise(justabit)Neuralandchemicalcontrolofventilationthemainareasofthebrainresponsiblefornormalcontrolofnormalventilationchemoreceptionandotherinfluencesresponsesduringexercise

Respiratorycontrolduringexercise:TheOxygenuptakeresponseVentilatorycontrol:mechanismsrelationshipswithenergydemand

Onthecurveontheleft,at50secthereisoxygendeficitat150secVO2atsteadystate

Respiratorycontrol

CONTROLCENTRES



AerobicmetabolismSupplies100%ofenergyrequirementstomatchlowtomoderatedemandsProcessesareratelimitedRelativelyslowtoadaptSupportedbyanaerobicprocessestomeetdemandatthestartSupportedbyanaerobicprocessestomeetdemandformoderatetoheavydemand.

VentribularcontrolduringexerciseAssociatedwithcombinationand/orsimultaneouseffectof:a.chemicalfactorsb.neurologicalfactors

Wecanseethreedifferentstatesatrightcurveforaconstantworkload

NonChemicalcontrolVerisesinstantlywhenexercisestartsfollowedbyashort(



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1comment:

ValentinaGavaChakr 21April2014at16:58

Congratulations for youblog! I'd like to know the sourceof figures (a,b,c,d,e) from "gasexchange".Thanks,ValentinaChakr,paediatricpulmonologistinBrazil.

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