Andersons pediatric cardiology 596
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Equipment
Ergometers
Inmostpediatricexerciselaboratories,testingisprimarilydirectedtoward
measuringaerobiccapacity.Thereforeergometersshouldgenerateworkinthe
largemusclegroups.Thetwotypesofexercisetestingequipmentmost
commonlyusedarethemotorizedtreadmillandtheuprightcycleergometer.The
choiceofmodalitydependsonthetypeofinformationdesired,butthereareboth
advantagesanddisadvantagestoeachmodality(Tables23.1and23.2).35–37Itis
thereforebestthatalaboratorybeequippedtoperformtestingusingeithertype
ofmodality.
Table23.1
MatchingtheExerciseModalityWiththeIndication
ConditionorQuestion
Aorticstenosis/insufficiency
Repairedtranspositionofgreat
arteries
RepairedtetralogyofFallot
Coronaryarterialobstruction
(preorpostrepair)
Singleventricle/Fontan
Coarctationoftheaorta
Exercise-induced
asthma/bronchospasm/chest
pain
Maximalaerobicfitness
Arrhythmiaassessment/long
QT
Cycle
Treadmill Rationale
Ergometry
Preferred
ECGassessmentforischemiaandbloodpressure
monitoringeasierduetolessmotionartifact
Preferred
ECGassessmentforischemiaorarrhythmiaeasier
Preferred
Preferred
Either
Preferred
Arrhythmiaassessmentduringexerciseessential
Electrocardiographicassessmentforischemia
Either
Preferred
Preferred
Preferred
Dependentuponclinicalquestion
Bloodpressureassessmentmoreaccurate
Runningmorelikelythancyclingtoinducesymptoms
HigherVO2withtreadmillcomparedtocycle
LessmotionartifactonECG
Table23.2
RelativeStrengths:TreadmillVersusCycleErgometer
Features
Patientfamiliarity
Higherworkratesandoxygenconsumption
Greaterpediatricexperience
Treadmill
+
+
Cycle
+
Quantificationofworkperformed
LessECGandbloodpressureartifact
Safety
Expense
Noise
Compactness
+
+
+
+
+
+
Treadmill
Theadvantageofthetreadmillcomparedwiththecycleergometeristhe
familiaritythatmostchildrenhavewithwalkingorrunning.37Furthermore,
moremusclegroupsareusedwithtreadmilltesting,resultinginagreaterstress
onthecardiovascularsystemandhigherconsumptionofoxygen.Consumption
ofoxygenandtheoxygenpulseare,onaverage,higherby10%withtreadmill
testingcomparedwiththecycle.36Treadmilltestinghasbeenmuchmore
extensivelystudiedforischemiaevaluationthanhasbeencycletestingand,asa
result,ismuchmorecommonlyappliedtoadultsreferredforexercisetesting.
Thereisconflictingevidenceonwhethertreadmilltestingmaybemoresensitive
formyocardialischemiathancycleergometry.38,39
However,thetreadmillalsohasseveraldistinctdisadvantages.Itisnoisyand
mayfrightensmallchildren.Theincreasedmovementfromvigorousrunning
resultsinmuchgreaterdistortionofelectrocardiographicandbloodpressure
signalscomparedwiththecycle.Thetreadmillalsorequiresmorespaceandis
notportable,andthereisadangeroffallingoffthemovingplatform.Caremust
betakentoensurethatthepatientiscloselymonitoredanddoesnotattemptto
getoffthetreadmillabruptly.Anotherdisadvantageofthetreadmillisthe
inabilitytoaccuratelydeterminerateofwork(seeTable23.1).Althoughonecan
estimateworkrate,theamountofworkperformedatagivenstageofatreadmill
protocolcanvarywidelybasedonpatientweightandtechnique(e.g.,walking
vs.running;supportingweightwitharms).
TreadmillProtocols
TheBruceprotocolanditsmodificationsarethemostcommonlyusedtreadmill
protocolsinthepediatricexerciselaboratory.37Thisprotocolconsistsof3minutestages,withanincreaseinbothspeedandgradeofthetreadmillateach
stage.Despiteitspopularity,theincrementalincreasesinworkloadforthe
Bruceprotocolarelargeevenwhenmodifiedforchildren.Thisfrequentlymakes
theshiftinrateofworkbetweenstagesdifficultforyoungerchildren.The
relativelylongstagesalsomakeformoredifficultlyininterpretationof
metabolicdatafromanalysisofexpiredgases.Thegraphicdisplaysofvarious
metabolicmeasurements,suchasconsumptionofoxygenversustime,arenot
linearbutratherappearasaseriesofslopesfollowedbypartialplateaus.Such
nonlineargraphicdisplaysmakedeterminationofkeyparametersofexercise
performance,suchastheonsetoftheventilatoryanaerobicthreshold,more
challengingthaninprotocolswithacontinuousincreaseinworkload.
Inrecentyears,protocolswithshorterstages,usuallyof1or2minutes,and
smallerincrementalincreasesinratesofwork,havegainedpopularity.These
protocols,suchastheBalketreadmillprotocol,mayuseafixedspeed,with
increasesonlyingrade,ormayincreasebothspeedandgrade.Theseprotocols
canalsobemodifiedaccordingtotheage,size,andphysicalconditioninglevel
ofthechildbeingtested,therebyallowingthetotalexercisetimetoberelatively
constantforallsubjects.Sucharelativelyconstantdurationofexerciseis
importantbecausepreviousstudieshavedemonstratedthattotaltestingformore
thanapproximately12to15minutesisassociatedwithdecreasedaerobic
performance,duetobothshuntingofbloodtotheskinforthermoregulationand
poormotivationcausedbyboredom.Atargetedtotaltimeofmuchlessthan10
minutesmayresultinpooraerobicperformancebecausethepatientceases
exercisingduetoexcessivemusclefatiguecausedbythehigherratesofwork.36
TheBruceandBalkeprotocolsaresummarizedinFig.23.9.
