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Review
USGastroenterologyReview2005-April2005
Published:
October2008
downloadarticle
Technology&Services
areportby
RaduTutuian,MDandDonaldOCastell,MD
FellowinGastroenterology,andProfessorofMedicine,DivisionofGastroenterology,Hepatology,Medical
UniversityofSouthCarolina
Esophagealfunctiontestingandmonitoringare
importantclinicaltestsinpatientspresentingwith
esophagealsymptoms.Manycliniciansandinvestigators
consideresophagealmanometrythegoldstandardto
evaluatethemotorfunctionoftheesophagus,and
esophagealpHmonitoringthegoldstandardto
diagnosegastroesophagealreflux.Asthesetechniques
offeronlyindirectinformationaboutintraesophageal
bolusmovementandpresence,videofluoroscopicor
radioisotopicimaginghavebeenusedtoevaluatebolus
transit.Multichannelintraluminalimpedance(MII)isa
relativelynewtechniquefirstdevelopedalittleovera
decadeagoattheHelmholzInstituteinAachen,
Germany.1Thisnewtechnologyofferstheopportunity
toevaluatebolusmovementintheesophaguswithout
theuseofradiationand,combinedwithmanometryor
pH,expandstheinformationcollectedbythese
modalities.2
PrinciplesofMultichannelIntraluminal
Impedance
Impedanceisameasurementoftheoppositionto
electriccurrentflowinanalternatingcurrentcircuit.
Placedinsideaholloworgan(i.e.theesophagus)
impedanceisinverselyrelatedtotheconductivityof
thewallandcontentoftheesophagus.Thebasic
componentofthistechnologyistheimpedancecircuit.
Twometal(steel)ringsseparatedbyanisolator(i.e.the
bodyofthecatheter)areconnectedtoanalternating
current(AC)generator.Inorderforthecircuittobe
closed,electricchargesbetweenthetwometalrings
havetotravelintheareasurroundingtheisolator.When
surroundedbyairthereisalmostnocurrentflow
betweenthetworingsandthereforetheimpedance
measuredbetweentheelectrodesisveryhigh.When
placedwithintheesophagus,currentflowbetweenthe
twometalringsisenabledbytheelectriccharges
withintheesophagealmucosa.Anyothermaterial
presentwithintheesophaguswillproduce
characteristicchangesdueto:
ýtheelectricconductivity(directlyrelatedwithionic
concentration);and
ýthecross-section(i.e.thelowerthecross-sectionthe
highertheimpedance).
Theelectricalimpedance,beingtheoppositeof
conductivity,decreasesfromair,tomucosallining,to
saliva/swallowedmaterialtorefluxedgastriccontents
(lowestimpedance).
Thepresenceofaliquidbolusbetweenthetwo
impedanceringsisidentifiedbyfollowingchanges:
ýadropinimpedancewhenthecurrentflowis
enhancedbythebolus;followedby
ýariseinimpedanceasthebolusisclearedfromthis
segmentbyaperistalticwave;
ýanýovershootýinimpedancecorrespondingto
decreasedluminalcross-sectionduringmuscle
contraction;and
ýreturntobaseline(seeFigure1a).
Thepresenceofairbetweenthetwoimpedancerings
isidentifiedbyarapidriseinimpedance(typically
above5,000Ohm)witharapidreturntobaseline(see
Figure1b).Thepresenceofmixed(gasýliquidor
liquidýgas)bolusesischaracterizedbyacombinationof
bothliquidandairchanges(seeFigure1c).
Currentconventionsconsiderthebolusentrypoint
atthe50%dropfrombaselinetonadirandbolusexit
attherecoveryofimpedancetothis50%value.
StudiesusingcombinedMIIandfluoroscopyhave
validatedtheseimpedanceparameters.Simrenetal.3
reportedoncombinedMII-videofluroscopystudies
andfoundagoodcorrelationbetweenimpedance
andvideofluoroscopyofdeterminingbolushead
(r2=0.89)andbolustail(r2=0.79)transittimes.In
anotherstudy,Inmanetal.4reportedverygood
correlation(97%)betweenimpedanceand
fluoroscopytoidentifyswallowswithcompleteand
incompletebolustransit.
Theuseofserialimpedancemeasuringsitesona
singlecatheter(i.e.multichannelintraluminal
impedance;MII)allowsdeterminingnotonlybolus
presenceatvariouslevelsintheesophagus,butthe
directionofbolusmovementintheesophagus.
Progressionofimpedancechangesfromproximalto
distalindicateanantegradebolusmovementas
observedduringswallowing(seeFigure2a)while
ClinicalApplicationofImpedance-ManometryforMotilityTestingand
Impedance-pHforRefluxMonitoring
BUSINESSBRIEFING:
USGASTROENTEROLOGYREVIEW2005
1
progressionofimpedancechangesfromdistalto
proximalindicatearetrogradebolusmovementas
observedinreflux(seeFigure2b).Inordertodetect
thesechanges,MIIsystemssampleimpedancedataat
highfrequencies(50ý1,000Hz).Evaluatingvarious
samplingrates,Bredenoordetal5reportedthatsample
ratesaslowas8Hzaresufficienttoidentifybolus
transitduringswallowingbutsamplingratesofatleast
50Hzarerequiredforanaccuratedetectionof
refluxepisodes.
Combinedwithmanometry(MII-EM)impedance
offerstheopportunitytoevaluatepressurechangesand
bolustransitduringthesameswallowherebyproviding
informationonthefunctionalityofesophageal
peristalsis.CombinedwithpH(MII-pH)impedance
offerstheopportunitytodetectalltypesofreflux
episodes,independentofthepHoftherefluxate.
CombinedMultichannelIntraluminal
ImpedanceandManometry
Impedancemeasuringcapabilitiescanbeaddedtoboth
water-perfusedandsolid-statemanometrysystems.The
designofcurrentlyavailablecathetersallowscollecting
impedanceandpressuredataatthesamelevelsinthe
esophagus.The9-channelcombinedMII-EMcatheter
(seeFigure3)providesinformationonpressureand
boluspresenceatfive,10,15,and20cmabovethelower
esophagealsphincter(LES)andtheLESresidual
pressureduringswallowing.CombinedMII-EMtesting
isperformedinaverysimilarwaytoconventional
manometry.Aftersuccessfulesophagealintubationand
positioningofthecatheterusingstationpull-through
technique,subjectsaregiven10liquidand10viscous
singleswallowsin20ý30secondsintervals.
NormalvaluesforcombinedMII-EMtestinghave
beenestablishedinamulticenterstudyincluding43
normalvolunteers.6Normalvaluesforboluspresence
andtransitintheesophagusweredefinedbasedonthe
5thý95thpercentilevaluesrecordedinthesehealthy
volunteers.Inaddition,thisstudyfoundthatmorethan
90%ofnormalhealthyvolunteersclearmorethan80%
ofindividualliquidswallowsandmorethan70%of
individualviscousswallows.
Theadditionalinformationobtainedfromthe
impedancedatahasbeendescribedinastudyin350
patientswithvariousmanometricfindings.7Whileall
patientswithachalasiaandsclerodermawerefoundto
haveabnormalbolustransit,themajority(>95%)of
patientswithnormalesophagealmanometry,
nutcrackeresophagus,andisolatedLESabnormalities
(i.e.poorlyrelaxingLES,hypertensiveLES,and
hypotensiveLES)wasfoundtohavenormalbolus
transit.Approximately50%ofpatientswith
manometricfeaturesofineffectiveesophagealmotility
(IEM)ordistalesophagealspasm(DES)werefoundto
havenormalbolustransitforliquid(seeFigure4).
EvaluatingpatientswithIEMinmoredetail,itwasfound
thatthereisnoperfect(i.e.highlysensitiveandhighly
specific)manometriccut-offthatwouldpredict
completebolustransit,andthecurrentmanometric
criteriafordiagnosingIEM(i.e.30%ormore
manometricineffectiveswallows)istoosensitiveand
lacksthespecificityofidentifyingpatientswithabnormal
bolustransit.Thestudyalsofoundthatapproximately
one-thirdofpatientswithIEMhadnormalbolustransit
forliquidandviscous,approximatelyone-thirdhad
abnormalbolustransitforeitherliquidorviscous,and
theremainingthirdofIEMpatientshadabnormalbolus
transitforbothliquidandviscous.8Basedonthese
findings,agradingscaleofesophagealfunctiondefectin
patientswithIEMhasbeenproposed:
2
BUSINESSBRIEFING:
USGASTROENTEROLOGYREVIEW2005
Technology&Services
512
3309
Figure1:
ImpedanceChangesProducedbyLiquid
(a),Gas(b),orMixed(c)Boluses
400
7592
297
6710
(a)
(b)
(c)
6897
1222
597
8582559
4953955
3546986
5077
2619
362
4694
739
181
2712835
3884332
2852420
4183
2318
186
Figure2:
Usingmultipleimpedancemeasuring
sitesMIIcandetectdirectionofbolusmovement
(a)(b)
Progressionofimpedancechangesfromproximaltodistal(a)areindicativeof
antegradebolusmovementasobservedduringswallowingwhileprogressionof
impedancechangesfromdistaltoproximal(b)areindicativeforretrogradebolus
movementasobservedinreflux.
1.Milddefectforpatientswithnormalbolustransitfor
bothliquidandviscous.
2.Moderatedefectforpatientswithabnormalbolus
transitforeitherliquidorviscous.
3.Severedefectforpatientswithabnormalbolus
transitforliquidandviscous.
Asimilardetailedanalysiswasperformedforpatients
withmanometricDES.9Inthisgroupofpatients,itwas
foundthattheonsetofcontractioninthedistal
esophagusandthecontractionamplitudeinthedistal
esophagusinfluencebolustransit.Incontrasttothe
resultsinpatientswithIEMitwasfoundthat
approximately50%ofDESpatientshavenormalbolus
transitforbothliquidandviscous,approximately25%
havenormalbolustransitforliquidorviscousandthe
remaining25%haveabnormalbolustransitforboth
liquidandviscous.
Outcomestudiesarewarrantedtoevaluateifgradingof
esophagealfunctiondefectinpatientswithmanometric
IEMandDEShasthepotentialofidentifyingpatients
atriskfordevelopingpost-operativedysphagia(i.e.
thosewithsever
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