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suspectedofhaving,cardiacanomalies.However,abnormalitiesof
noncardiovascularoriginmayalsoplayaroleinlimitingexerciseperformance
eveninpatientswithsurgicallyrepairedcomplexcongenitalcardiacdefects.
Anymalfunctioningofthemuscles,bones,blood,ornervoussystemwillimpair
exerciseperformance.Thereforeamodernlaboratoryforexercisephysiology
mustbecapableofassessingallexercise-relatedsystems,includingthe
cardiovascular,pulmonary,neurologic,hematologic,andmusculoskeletal
systems.Furthermore,accurateinterpretationofexercisetestsrequiresthe
properequipmentandpersonnel.Thisisparticularlyimportantasthe
cardiologistsupervisingthelaboratoryfrequentlyevaluateschildrenwithrealor
suspectedexerciselimitations.Thesechildrenseldomhaveanycardiovascular
abnormalitiesbutmayhaveinvolvementofotherorgans,suchasdysfunctionof
thepulmonaryormusculoskeletalsystems.Properlyperformedexercisetesting
anditsinterpretationshouldalsobeabletoidentifyorexcludeabnormalitiesof
extracardiacorgansthatnormallycontributetoexerciseperformance.
Thischapterbrieflyreviewsbasicexercisephysiologyasitrelatesto
cardiopulmonaryexercisetesting.Discussedaretheequipmentrequiredfor
performinganexercisetestanditsapplicationsaswellasassessmentofthe
typesofdataobtainedfromexercisetestingandtheirusefulnessinthe
evaluationofthechildwithcardiovasculardisease.Alsoreviewedare
indicationsandcontraindicationsforexercisetestingincardiovasculardisease.


BasicExercisePhysiology
Assuringproperexerciseperformancerequirestheseamlessandcontinuous
meshingofmultiplesystemsoforgans.3,4TheclassicillustrationofWasserman
andcolleagues(Fig.23.1)depictstheinteractionofthekeysystemsthatcouple
internalcellularrespirationtoexternalpulmonaryrespirationduringexercise.It
showsthesystemsasaseriesofoverlappingcogs,allofwhichmustmesh
seamlesslytoallowexercisetooccur.Insuchfashion,mechanicalenergyis
producedfromchemicalenergyatthecellularlevel,withsubsequentdelivery

andremovalofsubstratesforenergyproductionandbyproductsofmuscle
metabolism.Allofthisisaccomplishedwhilemaintainingchemicalandthermal
homeostasiswithinnarrowranges.

FIG.23.1 Functionalinterdependenceofthemultipleorgansystems
duringexercise.Themeshinggearsrepresentthemusculoskeletalandthe
cardiopulmonarysystems,whichinteracttoensureadequatedeliveryof
oxygento,andremovalofbyproductsfrom,theexercisingmuscles.The
smoothcontinuousinteractionsofthesemultiplephysiologicsystemsare
essentialforproperfunctionofthemusclesduringexercise.(From
WassermanK,HansenJE,SueDY,etal.Exercisetestingand
interpretation:anoverview.In:PrinciplesofExerciseTestingand
Interpretation,vol1.2nded.Philadelphia:Lea&Febiger;1994:1–8.)


CellularMetabolism
Adenosinetriphosphateisthechiefsourceofchemicalenergyfortheexercising
muscle.Mechanicalenergyisproducedbytheprocessofexcitation-contraction
coupling,drivenbythebreakdownofadenosinetriphosphateandthereleaseof
inorganicphosphatesandadenosinenucleotides.Thestoresofadenosine
triphosphateandphosphocreatineinthemyocytesaresufficientonlyfor10to15
secondsofactivityandsomustcontinuouslybereplenished.Ascanbeseenin
Fig.23.2,adenosinetriphosphateisproducedinsmallamountsinthecytosolby
anaerobicmetabolism.Muchlargeramountsareproducedaerobicallyinthe
mitochondria.3,5