Nonacid GERD.docx
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Nonacid GERD.docx
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NonacidGERD
TransAmClinClimatolAssoc.2005;116:
321–334.
Non-acidGastroesophagealReflux:
DocumentingitsRelationshiptoSymptomsUsingMultichannelIntraluminalImpedance(MII)
DonaldOCastell,InderMainie,andRaduTutuian
FromtheDivisionofGastroenterology—Hepatology,MedicalUniversityofSouthCarolina,Charleston,SC
Correspondingauthor:
DonaldO.Castell,MD,DivisionofGastroenterology/Hepatology,MedicalUniversityofSouthCarolina,96JonathanLucasStreet,210CSB,Charleston,SC29425,Phone:
(843)792-7522,Fax:
(843)792-8593,Email:
Castell@musc.edu
Abstract
Multichannelintraluminalimpedance(MII)isanewtechniqueforevaluatingesophagealfunctionandgastroesophagealreflux.Thistechniquedependsonchangesinresistancetoalternatingcurrentbetweentwometalelectrodesproducedbythepresenceofliquidorgasbolusinsidetheesophageallumen.Combinedmultichannelintraluminalimpedanceandmanometry(MII-EM)providessimultaneousinformationonintraluminalpressurechangesandbolusmovementwhereascombinedmultichannelintraluminalimpedanceandpH(MII-pH)allowsdetectionofgastroesophagealreflux(GER)episodesirrespectiveoftheirpHvalues(i.e.acidandnon-acidreflux).
CombinedMII-pHtestingpresentsanewparadigmforrefluxtesting.InMII-pHstudiesrefluxeventsarenolongerprimarilydetectedbypH.Refluxatepresence,distributionandclearingisprimarilydetectedbyMIIandsimplycharacterizedasacidornon-acidbasedonpHchangeandasliquid,gasormixedbasedonMII.MIIdeterminesrefluxateclearancetimewhilepHmeasuresacidclearancetime.MII-pHshowspromisetobecomeanimportantclinicaltool,particularlytoassessGERinthepostprandialperiodandinpatientswithpersistentsymptomsonacidsuppressiontherapy.
KeyWords:
multichannelintraluminalimpedance(MII),acidandnon-acidgastroesophagealreflux,gastroesophagealrefluxtesting
Introduction
Multichannelintraluminalimpedanceisanewtechniqueforevaluatingesophagealfunctionandgastroesophagealreflux.Esophagealfunctiontestingisanimportantstepinevaluatingpatientswithpossibleesophagealsymptoms.Thisiscurrentlyperformedusingacombinationofesophagealmanometryandbariumorradioisotopeesophagram.Thecurrent“goldstandard”forgastroesophagealreflux(GER)testingisambulatorypH-metry,amethodbasedondetectionofchangesinacidcontentintheesophageallumen.EventhoughthepathophysiologicroleofacidinproducingGERlesionshasbeenwellestablishedbyanumberofstudiesinbothanimalsandhumans
(1),GER-typesymptomsoftenpersistdespitetreatmentwithmedicationsthatdecreasegastricacidsecretion.IthasbeensuggestedthatthesesymptomsmaybeduetorefluxhavingpH≥4.0(i.e.non-acidreflux)
(2),atypeofrefluxthatisdifficulttoidentifywithconventionalpH-metry.
ThisreviewwilldiscussprinciplesofimpedancetestingandtheuseofcombinedmultichannelintraluminalimpedanceandpH(MII-pH)tomonitorgastroesophagealreflux.
BasicPrinciplesofImpedanceTesting
Theprinciplesofthistechniquewerefirstdescribed1990bySilnyetal.(3)anddependonchangesinresistancetoalternatingcurrent(i.e.impedance)betweentwometalelectrodes(i.e.impedancemeasuringsegment)producedbythepresenceofbolusinsidetheesophageallumen.Electricconductivity(theoppositeofresistanceorimpedance)isdirectlyrelatedtotheionicconcentrationoftheintraluminalcontent.Intraluminalcontentwithhighionicconcentrations(i.e.refluxate,food)havearelativelowresistance(highconductivity)comparedtotheesophagealliningorair.Simultaneousvideo-fluoroscopicandimpedancemeasurementsofesophagealfunctionduringswallowinghavevalidatedtypicalchangesobservedwithbolusentry,presenceandclearingintheimpedance-measuringsegment(Figure1
)(3,4).Intheabsenceofbolus,impedanceisdeterminedbytheelectricconductivityoftheesophageallining.Uponarrivalofbolusbetweentheelectrodesimpedancewilloftenriseabruptlyduetothepresenceofairinfrontoftheheadofthebolus.Intraluminalimpedancethenrapidlydecreasesashighioniccontentofthebolusprovidesgoodelectricconductivity.Whilethebolusispresentintheimpedancemeasuringsegmentintraluminalimpedanceremainslow.Esophagealcontractionsclearingtheintraluminalcontentincreasetheimpedancewithaslight“overshoot”duetoadecreaseinesophagealcross-sectionduringcontractionbeforereturningtobaseline.
Fig.1
Impedancechangesobservedduringbolustransitoverasinglepairofmeasurementringsseparatedby2cm.Arapidraiseinresistanceisnotedwhenairtravelinginfrontofthebolusheadreachestheimpedancemeasuringsegmentfollowedbyadropin(more...)
Multipleimpedancemeasuringsegmentswithintheesophagusallowdeterminationofdirectionofbolusmovementwithintheesophagus;i.e.multichannelintraluminalimpedanceorMII(Figure2
).Antegradebolusmovement(i.e.swallows)isdetectedbyimpedancechangesduetobolusprogressingproximaltodistal(Figure3
).Retrogradebolusmovement(i.e.reflux)isdetectedbychangesinimpedanceprogressingdistaltoproximalfollowedbyproximaltodistalclearanceofbolusbyeitheraprimaryorsecondarycontractionwave(Figure4
).
Fig.2
Multipleimpedancemeasuringsegmentswithintheesophagusallowdeterminationofdirectionofbolusmovementwithintheesophagus;i.e.multichannelintraluminalimpedanceorMII.
Fig.3
Antegrade(i.e.swallows)bolusmovementdetectedbyimpedancechangesofboluspresenceprogressingproximaltodistal.
Fig.4
CombinedMII-EMtracinginwhichretrogradebolusmovementisdetectedbychangesinimpedance(MII)progressingdistaltoproximalfollowedbyproximaltodistalclearanceofbolusacontractionwave.
TheabilityofmultichannelintraluminalimpedancetodetectintraesophagealbolusmovementbychangesinelectricresistanceaswellasmountingoftheimpedancemeasuringsegmentsonstandardmanometryorpHcathetersallowsMIItocomplementtraditionalmanometryorpHtesting.Combinedmultichannelintraluminalimpedanceandmanometry(MII-EM)willnotbediscussedinthismanuscript.Rather,wewillreviewtheconceptofcombinedmultichannelintraluminalimpedanceandpH(MII-pH)todetectGERepisodesofbothacidandnon-acidrefluxtypeandwilldiscusstheevolvinginformationontheadvancesindiagnosisofpotentialGERsymptomsthatthistechnologybringsintotheclinicalarena.
GastroesophagealRefluxMonitoringUsingCombinedMultichannelIntraluminalImpedanceandpH(MII-pH)
ThecurrentlyacceptedgoldstandardfortheassessmentofgastroesophagealrefluxisdistalesophagealpHrecording(5),whichbasesdetectionofrefluxofacidicmaterialintotheesophagusonchangesinhydrogenionconcentration.ConventionalpHrecordinghasdifficultiesdetectingnon-acidrefluxalthoughsomeauthorshaveproposedthatrefluxcanbedetectedbypHmetryevenwhenintraesophagealpHremainsabove4.0butshowadefinitefallgreaterthatonepHunit(6).Currentlyavailabletechniquesforthestudyofnonacidoralkalinerefluxhaveseverallimitations:
aspirationtechniques(7)allowforonlyshortanalysisperiodsandtheaccuracyofenzymaticdeterminationofthecontentsoftheaspirateshasbeenquestioned(8),scintigraphicmethods(9,10)areexpensive,involveradiationexposureandarelimitedtoshortmonitoringperiods,ambulatorycombinedpHmonitoringandbilirubinmonitoring(Bilitec®)(11)requiresthepresenceofbilirubinandisthereforeincapableofmeasuringbile-freenonacidrefluxwhichaccountsfor≥90%ofnon-acidreflux(12).FurthermoretheBilitecdevicerequiresspecialliquiddietsduringthemonitoringperiodtoavoidfalsepositivereadings(13).
MultichannelintraluminalimpedanceusedincombinationwithpHmetry(MII-pH)hasbeenshowntoallowaccuraterecordingofgastroesophagealrefluxatallpHlevelsandisemergingasausefultooltostudybothacidandnonacidreflux(14,15).Thetechniquehasbeenvalidatedfluoroscopicallyandmanometricallytodetectbolusmovementintheesophagusbothintheoralandaboraldirection(16),andthusenablesmeasurementofanddistinctionbetweenswallowsandreflux.BecauseMIIrecordsretrogradeflowofgastriccontentsintotheesophagusinapH-independentfashion,combiningthetechniquewithpHmetryenablesdetectionofnonacidaswellasacidreflux.Additionally,MII-pHprovidesdetailedcharacterizationoftherefluxepisode,includingdeterminationofthecomposition(gas,liquidormixed)andtheheightreachedbytherefluxate(17–19).
CombinedMII-pHequipment
ThecombinedMII-pHcatheterissimilartoastandard2-mmflexiblepH-catheter.The“classic”6MII-1pHassembly(Figure5
)hasfourimpedancemeasuringsites(Z1–Z4)inthedistalesophagusandtwoimpedancemeasuringsitesintheproximalesophagus(Z5–Z6).ThepHsensoronthisassemblyisatthesamelevelasthecenterofthesecondimpedance-measuringsegment.ThecatheterisplacedtransnasallyintotheesophagusandpositionedsothatthepHsensorislocated5cmabovetheproximalborderoftheloweresophagealsphincter(LES).ManystudiesnowincorporateasecondpHsensorlocated15cmmoredistalonthecathetertorecordpHinthegastricfundus.Theimpedancemeasuringsegmentswillbelocatedat3cm,5cm,7cmand9cmabovetheLESinthedistalesophagusandat15cmand17cmabovetheLESintheproximalesophagus.InitialstudiesusingMII-pHweredonewithstationaryset-upsandoverrelativelyshortperiodsoftime(2to3hourrecordingsessions).Morerecently,equipmenttoperformambulatoryMII-pHstudi
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