NONINVASIVE.docx
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NONINVASIVE.docx
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NONINVASIVE
NON-INVASIVEMONITORINGOFREFLEXIVESWALLOWING
HelenFIRMIN1,SheenaREILLY2,AdrianFOURCIN
1UCLandCamdenandIslingtonHealthAuthority
2InstituteofChildHealth
Abstract
Twostandardtechniquesareusedfortheclinicalexaminationofabnormalswallowing:
Videofluoroscopywhichdependsonirradiation,andCervicalAuscultation,whichmakesuseofastethoscope.Bothofthesetechniqueshaveimportantdisadvantages.Thefirstdoesnotlenditselftoroutineuseandthesecondprovidesnoreliablequantitativeinformation.TheaimofthisworkwastoinvestigatetheutilityofsomeofthemethodsusedinSpeechandHearingSciences.Thesemethodsdonotuseradiationandhavethepotentialtogivemoreaccuratetiminginformationthancanbederivedfromauditory/acousticmonitoring.Pilotdatawereobtainedfromthesimultaneoususeoffoursensors:
anear-plugmicrophoneofthetypeusedsuccessfullyforthedetectionofotoacousticemissions;astandardminiatureelectretmicrophoneordinarilyusedforspeechrecording;aminiatureaccelerometerofthetypesometimesusedformonitoringnasality;andastandardelectrolaryngograph.Swallowmeasurementsweremadewithtwentynormaladultsubjects.Themosteffectivesinglesignalwasthatprovidedbytheuseofstandardelectrolaryngographhardwareandsoftware.Asmallbutsignificantincreaseinreliabilitycamefromthecombinedappraisaloftwosignals,fromthelaryngographandanaccelerometer.
1.Background
Itmayseemalittleoddthatworkinthefieldsofspeech,hearingandlanguageshouldimpingeon,andstandtobenefitfrom,aknowledgeofthephysiologicalprocessesbasictodeglutition.Theintricatelycoordinatedmechanismsofvoiceproductionare,however,linkedtothoseofswallowingandthereisapotentiallyusefuloverlapofexperimentalapproaches,equipment,andunderstanding.
1.1Characteristicsofanormalswallow
Theactofswallowingisordinarilydescribedasconsistingoffourstages(egLogemann,1983):
oralinitial
oralfinal
pharyngeal
oesophageal
Thefirsttwoofthesestagesareunderconsciouscontrol.Thesecondtwostagesarenormallyautonomicandoccuraspartsofacompleteperistalticgestureinwhichfoodanddrinkare,asitwere,sweptfrompharynxtostomach.Althoughthepharyngealandoesophagealstageshaveherebeengivenspecialexperimentalattention,thefollowingbriefoverviewofallfourstagesisintendedtoplacetheminthecontextofthecompleteprocess(figuresbasedonLogemann,1983).
2.Phasesofaswallow
2.1Oralinitialphase
Figure1
Duringtheoralinitialphaseofswallowing,tonguemovementsdifferbetweensubjects;theoralenclosureis,however,relativelyconsistentlydefined.Typicallyalabialsealpreventstheescapeofliquidfromthefrontofthemouth.Escapeofliquidintothepharynxispreventedbyarearoralcavityenclosureproducedbythepositioningofthevelumagainstthebackoftheelevatedtongue.
2.2Oralfinalstage
Figure2
Theoralfinalstageoccurswhenthetongueismovedsoastosqueezethebolusorliquidvolumeagainstthehardpalatesothatitispropelledpasttheanteriorfaucalarches.Itisatthisstagethattheautomaticreflexivegestureofswallowingistriggered.Normallythisgivesrisetothecoordinatedperistalticreflexsequencedescribedbelowwithreferencetofigures3and4.
2.3Pharyngealstage
Figure3
Thetriggeringoftheperistalticreflexisthebeginningofthepharyngealstageofswallowing.Thisstagehasfourmainphases:
∙materialispreventedfromenteringthenasalcavitybytheelevationandretractionofthevelumsoastoclosethevelopharyngealport
∙thebolusistransferredfromthelevelofthefaucalarchesthroughthepharynxtothecricopharyngealsphincteratthetopoftheoesophagus
∙materialispreventedfromenteringthetrachealairwaybytheelevationofthelarynxandtheclosureofthethreesphinctersassociatedwith:
thearyepiglotticfolds;theventricularfolds;andthevocalfolds.
∙thebolusmaterialisfinallypassedintotheoesophagusbytherelaxationofthesphincteratthecricopharyngealjuncture.
2.4Finalstage
Figure4
Inthefinalstageoftheswallow,thebolusistransferredinacontinuationoftheperistalticgesturefromthecricopharyngealtothegastro-pharyngealjunctureattheentrancetothestomach.
2.5Aspectsofabnormalswallowing
Disordersofswallowingmaymanifestthemselvesinavarietyofways.Duringtheneonatalperiod,persistentlypoorfeeding,characterisedbyweaksucking,andcoughingandchoking,leadingtoprolongedfeedingtimes,aretypicalsigns.Theremaybeassociatedrespiratorydifficultyandevenapnoea.Alternatively,difficultiesmayemergewhenweaningisattemptedwiththeintroductionofspoonedsolids.Swallowingdysfunctioninchildhoodmayalsopresentmoreunusuallyasanisolatedweaknessintheabsenceofothersignsandpresentsinadultsasapartofotherneurologicaldisorders.
Theclinicalsequelaeofswallowingdysfunctionmayincluderepeated"penetration",whenfoodgetsbetweenthevocalfolds,and"aspiration",whenfoodisinhaledintothetrachealairway.Poororalintakeleadstomalnutritionandconsequentfailuretothrive-adverselyaffectingthechild'sgrowthanddevelopment.Theresultsofabnormalswallowingcanalsoleadtorecurrentchestinfectionsandthedevelopmentofchroniclungdisease.
Clinically,itisessentialthatswallowingbemonitoredinindividualsinordertoensurethatsafefeedingprotocolscanbeestablished.Anumberofapproacheshavebeendevelopedtoassessswallowing.
3.Methodsofmonitoring
3.1Establishedapproaches
Allmethodsdependonatleastaninitialassessmentwhichinvolvestakinganappropriatehistorytogetherwithmakingaclinicalexamination.Thisapproachhasmanyadvantagesbutitisnotquantifiable,maynotdefinetheprecisenatureofthetroubleandmaynotdetectsilentaspiration-whentheclientinhalesfoodintothelungsbutdoesnotcoughorshowdiscomfort.Complementarymethodshavebeenintroducedtoreducethesedisadvantages.Thethreemostfrequentlyusedmethodsarelistedbelowinorderofrelativeimportance.
3.1.1Videofluoroscopy
Thismethodmakesitfeasibletoexamineboththestructureandfunctionoftheorgansinvolved(Ekberg,1992).Dysphagiacanbeidentifiedandsilentaspirationdetected.Recordingscanbemadeandusedforreferenceand,ifrequired,measurement.Itssuccessdepends,however,ontheswallowingofacontrolledquantityofradio-opaquematerial,whichmaybeunpleasant,andexposuretoradiation,whichmustbebrief.Themethodcannotbeusedfrequently.Itmayberatherdauntinginapplicationforthechild,anditisnotabasisforinteractivetherapy.
3.1.2Endoscopy
FibrescopicEndoscopicExaminationofSwallowing(FEES:
Langmore,Schatz,&Olsen,1988)makesuseessentiallyofanasopharyngolaryngoscope-aflexibleendoscopeofthetypeusedinthevoiceclinic.Althoughitisaninvasiveprocedureitismoreacceptableforsomeadultpatientsandavoidsthegaggingassociatedwithrigidoralendoscopy.Italsocanbeusedforbiofeedbackbutitisinessenceacumbersometechniqueandnotadaptedforreadyusewithchildren.
3.1.3Electromyography
EMG(Cooper&Perlman,1996)recordingsarealsousedandtheyconfertheadvantagesofprecisioninidentificationandaccuracyoftemporalmeasurement.Thismethodis,however,dependenttoalargeextentonsignalsderivedfromelectrodesinsertedsubcutaneously.WhilstEMGisavaluableresearchtoolitisnotwellsuitedtoroutineclinicalinvestigation.
3.1.4CervicalAuscultationCA
Thismethodinvolvestheplacementofasensor(originallyastethoscopewasused)ontheneckofthesubjectandeitherlisteningand/orrecordingtheacousticsignalswhichareproducedfromamicrophoneasby-productsoftheswallowingprocesses.Thesesignalsaretypicallyvisuallypresentedandexaminedaswaveformsorspectrograms.ThefirstworkusingthesesignalsledtothedescriptionbyBosmaandhiscolleaguesofthenormalswallowasbeingassociatedwithtwodiscreteandperceptuallydistinctsounds-the"InitialDiscreteSound"(IDS)andthe"FinalDiscreteSound"(FDS)(Bosma1992;Heinzetal1994).Manyotherinvestigatorshaveexploredtheuseofthisapproachfortheexaminationofdysphagia.Avarietyofsensorshavebeenemployedinattemptstodefineanoptimalconfigurationbutthebestchoiceofsensor,orofsensorcombination,isstillnotclear.
3.2Othersensors
TheessentialadvantageoftheCAmethodisthatitprovidesusefulinformationinarapidandsimplenon-invasivefashion.Itsessentialdisadvantageisthattheauditory/acousticinformationthatitprovidesisnotreadilylinkedtoparticularphysiologicalsourcesandisoftennotveryclearphysically.Dataaregeneratednotasadirectresultoftheprocessesofswallowingbutratherasanadventitioussideproduct.Itistheintrinsicandrelativemovementsoftheorgansassociatedwithdeglutitionthatareimportantintheunderstandingofnormalityandthedetectionofpathology.FollowingBosma'sinitiallead,auditoryCAhas,nevertheless,madeasubstantialcontributiontotheclinicaldetectionandmanagementofswallowingproblemsandthishasledtotheinvestigationofthepossibleuseofothersensorsinplaceofthemicrophone.
3.2.1EarProbe
Thissensorhasbeenshowntorespondtothe"intrinsicsoundsofswallowing".Anadvantageoftheearprobeisitssiteofplacement.Whilstscarsandskinchangespost-radiationcanmakeneckmountingofasensordifficult(poormountingcanleadtoextraneousnoiseinthesignal)nosuchdifficultiesareen
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