呼吸科呼吸系统4-课件.ppt

5.4 Control of Respiration l Breathingisacriticalrobusthomeostaticprocessthatensuresadequatelevelsofoxygeninbloodandprovidesameanstoremovecarbondioxidefromthebody2023/5/26 1Basic Requirements for Respiratory Regulation2023/5/262l Itmustbeautomaticl MaintenanceofCO2andO2levelsshouldnotdependonlevelsofconsciousnessoralertnessl Itmustbeadaptabletotheneedsoftheorganisml TheremustbemechanismstocompensateforchangesinoxygenuptakeorCO2production.l Itmustbesubjecttovoluntarycontroll TheremustbemechanismstovoluntarilyoverridetherespiratorycontrolmechanismsatleastforbriefperiodsoftimeRespiratory Centers and the Basic Respiratory Centerl Respiratory centerl Brainregionsorthespinalcordthatinvolveinthegenerationofrhythmicrespiratorypatternandtheregulationofrespiratorymovement;theyarelocatedinthespinalcord,brainstem,cortex,thalamusetc.l Basic respiratory centerl Brainpartsthatareresponsibleforgenerationofbasicrespirationpatternsl ItislocatedinthebrainstemThe Experiment Done by Lumsden in the CatConclusionsUpper pons-pneumotaxic center;lower pons-apneustic center(not accepted);Spinal cord-Basic respiratory center;spinal cord:Cut at Breathing pattern(vagus nerve intact)Breathing pattern(vagus nerve cut off)Midbr ainandtheponsNear l ynormal Deepandslo wMidpons Near l ynormal Apneusticbr eathingP onsandmedullaIrr egular Che yne-St ok esbr eathingMedullaandthespinalcor dNobr eathing Nobr eathingIs the Pre-Btzinger Complex Essential for the Generation of Basic Respiratory Pattern?Modified from Brain 2011:134;2435Medullaoblongata=延髓Pons=脑桥Lateralreticularnucleus(LRN)=外侧网状核XII=面神经Obex=栓、门MSA=multiplesystematrophySCA3=spinocerebellarataxiatype3Multiple Systems Atrophy vs.Spinocerebellar Ataxia 3 Patientswithmultiplesystemsatrophypresentwithcentralrespiratorydeficitsbutwithoutswallowingproblems Pre-BtzingerComplexneuronsarereducedwhereasambigualmotoneuronsarepreserved.Patientswithspinocerebellarataxia3hasnocentralrespiratorydeficitsbutwithdysphagia,Pre-BtzingerComplexneuronsarepreserved,whereasambigualmotoneuronsarediminished.Neural Mechanisms underlying the Generation of Rhythmic RespirationTwoHypothesesOscillatorytheoryorthepacemakerhypothesis(起步细胞学说)Networktheory(神经网络学说)Neurons in pre-Btzinger can Burst spontaneously RegularfiringinducedbycurrentinjectioninahippocampalgranulecellSpontaneousburstingInaratpre-BtzingerneuronNeurons in pre-Btzinger can Burst spontaneously RegularfiringinducedbycurrentinjectioninahippocampalgranulecellSpontaneousburstingInaratpre-BtzingerneuronlVoluntary control of respiration is needed in suckling,swallowing,sniffing,chewing,coughing,vomiting and vocalization.lVoluntary control over pulmonary ventilation originates in the motor cortex of cerebral frontal lobe.lThe impulses are transmitted down the corticospinal tracts to the respiratory neurons in the spinal cord,bypassing the brainstem respiratory centers.Voluntary Control of Breathing Respiratory Activity is Sensitive to Oxygen,Carbon Dioxide,and Hydrogen Ions in the Blood l Theoverallgoalofrespirationistomaintainproperconcentrationsofoxygen,carbondioxide,andhydrogenionsinthetissues.l Respiratoryactivityishighlysensitivetochangesineachofthese.l Excesscarbondioxideorexcesshydrogenionsinthebloodmainlyactonthecentralchemoreceptorsystemwhereashypoxiaactsentirelyontheperipheralchemoreceptorsystem.PeripheralChemosensoryReceptorSystem2023/5/2616Afferent PathwaysCarotid bodies Carotid sinus nerve glosopharyngial(IX CN)medulla near nucleus tractus solitarius(NTS)Aortic bodies Join the vagus(X CN)medulla near nucleus tractus solitarius(NTS)Functions of Peripheral Chemoreceptorsl SensePO2,PCO2andH+inthearterialbloodl PrimarilysensitivetoarterialPO2hyperventilationl Intheabsenceofperipheralchemoreceptors,hypoxiaresultsinCNSneuronaldepressionanddepressedventilationl PaCO2andincreasedH+concentrationstimulatethesereceptorstoalesserextentbutmakethemmoreresponsivetohypoxemiaCentralChemoreceptorSystemLocation:Ventral lateral surface of the medullaStimuli:Increased H+or high CO2 in CSF or extracellular space2023/5/26 20Arterial PCO2 is the most Important Factor in Regulation of Respiration The arterial CO2 is held within 2-3 mmHg.The arterial CO2 is the most important factor in controlling respiration in physiological conditions.With increased arterial PCO2,both the rate and the depth of respiration increase.Peripheral chemoreceptor denervation studies showed 20-30%of the response from carotid bodies(rapid);the remaining 80%from central chemoreceptors(slow).Mechanisms Underlying Hyperventilation following PaCO2 IncreaseDirect stimulationlStimulation of peripheral chemoreceptprslStimulation of central chemoreceptorsIndirect stimulation CO2 Arterial H+Peripheral chemoreceptorsTheEffectsofHydrogenIonsonRespirationl AnincreaseinH+concentrationinarterialblood,CSForthelocaltissueofbrainstemstimulatesrespiration.l IncreasedH+stimulatesbothperipheralandcentralchemoreceptorswithstimulationoftheperipheralchemoreceptorplayingthemainrole.l AsH+cannotpassthroughthebrain-bloodbarrier,increasedH+inarterialbloodstimulatescentralchemoreceptorsthroughCO2.l Atbothperipheralandcentralchemoreceptors,H+mediatesincreasedrespirationbyCO2accumulation.l CentralchemoreceptorsaremoresensitivetoH+thanperipheralchemoreceptors.2023/5/2624HowDoesIncreasedArterialH+ActontheCentralChemoreceptorsSignificancesofHydrogenIonsonRespirationl Coordinatesmetabolicneedsandrespiration.l MaintainspHhomeostasis.2023/5/2626CentralAlveolarHypoventilation(OndinesCurse)l Centralalveolarhypoventilationisararediseaseinindividualswhoarebornwithoutventilatorychemosensitivityl Breathingadequatewhenawake,butnotwhenasleeporduringsleepingl NoresponsetohypercapniaandhypoxiaEXERCISE AND VENTILATION Acute Respiratory Response to Graded Dynamic Exercise Exercise IntensityVentilation(L/min)V/Q PAO2(mm Hg)PaO2(mm Hg)PaCO2(mm Hg)Arterial pHRest 5 1 103 100 40 7.40Walking 20 2 103 100 40 7.40Jogging 45 3 106 100 36 7.40Running 75 4 110 100 25 7.32ConclusionHyperventilationduringexerciseisprimarilycausedbymechanismsbeyondchemicalchangesinthebloodThecortexsendssignalstothebasicrespiratorycenter?Isthereinteractionbetweenthecardiovascularandbasicrespiratorycenters?MECHANICALREFLEXESSeveralmechanicalreflexesthatarisefromthechestwallandlungsaffectventilationandventilatorypatterns.Receptors Are Localized in Lung Tissue and Airwaysl Pulmonaryreceptorscanbedividedinto3groups:pulmonarystretch,irritantandJreceptors.l Afferentfibersofallthreetypesliepredominantlyinthevagalnerves.Pulmonary Stretch Receptorsl Thestretchreceptorsaresensoryterminalsofmyelinatedafferentfibersthatliewithinthesmoothmusclelayerofconductingairways.l Thestretchreceptorssensechangesinlungvolume.l Thestretchreceptorsmediatelunginflationrefelx(Hering-Breuerreflex).Lung Stretch Reflexesl Pulmonaryinflationreflex(Hering-Breuerinspiratory-inhibitoryreflex)l Inflationoflungsorstretchofairwaysswitchesfrominspirationtoexpiration.Asaresult,inspirationisshortenedwithincreasedbreathingrate.l Pulmonarydeflationreflex:Deflationoflungspromotesinspirationiscalledpulmonarydeflationreflex.l Botharemediatedbythevagalfibers;cuttingofvagalnerveeitherunilaterallyorbilaterallycoulddeepenandprolonginspiration.More about the Hering-Breuer Inspiratory-Inhibitory Reflexl TheHering-Breuerinspiratory-inhibitoryreflex(pulmonaryinflationreflex)isstimulatedbyincreasesinlungvolume.l Thisstretchreflexismediatedbyvagalfibers;itsreceptorsarelocatedinairwaysmoothmuscles.l Thisreflexresultsinthecessationofinspirationbystimulatingtheoff-switchneuronsinthemedulla.l ItisinactiveduringquietbreathinganditplaysaroleonlyinventilatorycontrolinadultswhenVTisgreatthan1L.l Itmaybemoreimportantinnewborns.Irritant Receptorsl Theirritantreceptorsaresensoryterminalsofmyelinatedafferentfibersthatarefoundinthelargerconductingairways.l Theyarerapidadaptingreceptors.l Theyareinvolvedincoughing,gasping,andprolongedinspirationtime.J Receptorsl ThesereceptorsarecalledjuxtapulmonarycapillaryreceptorsorJreceptors.l TheyareC-fiberendings.