Andersons pediatric cardiology 1931
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cardiacoutputincreasewithzero-resistancecyclingandisunchangedwith
positiveinspiratorypressure.Withpositiveexpiratorypressure,strokevolume
fallstobaselinewhilecardiacoutputismaintainedbyincreasesinheartrate.
Thusitseemsthattheskeletalmuscleactivityactsasapump,augmenting
venousreturnandcardiacoutput,whereasnegativepressureassociatedwith
inspiratorychestwallmechanicsplaysaminorrole.
FIG.73.30 StrokevolumeaugmentationwithexerciseinFontanpatient.
Thelargestincreasefrombaseline(rest)inthestrokevolumeindex(yaxis)wasseenwithzero-resistancecycling(0W)(musclepump)condition.
Thestrokevolumeindexreturnedtonearbaselinevalueswiththe
expiratoryload(EL).IL,Inspiratoryload.*P=.05comparedwithbaseline
[rest]withingroups;†P=.05betweengroupswithincondition.(From
ShaferKM.,GarciaJA,BabbTG,etal.Theimportanceofthemuscleand
ventilatorybloodpumpsduringexerciseinpatientswithoutasubpulmonary
ventricle[Fontanoperation].JAmCollCardiol.2012;60:2115–2121.)
AlthoughchildrenwithaFontancirculationmayhavestrengthandbody
compositionsimilartocontrols,adultpatientswithaFontanhavereduced
skeletalmusclemassandimpairedaerobiccapacity(Figs.73.31and73.32).328
Encouraginginformationcomesfromseveralsmallstudiesinvolvingpatients
withaFontancirculation.Oneusedanintensivemuscleresistancetraining
program.Withtraining,therewasasignificantincreaseinleanbodymassandin
peakoxygenuptake(Fig.73.33).336Inaddition,restingcardiacoutputincreased.
IntheotherstudytherewassignificantincreaseinpeakVO2andexercise
durationfollowinga3-monthcontrolledrespiratorytrainingprogram.411
Interestinglytheimprovementinexercisecapacitywasgreaterthanthatseenin
short-termpulmonaryvasodilatortrials.Clearlymoreworkisrequiredinthis
area.
FIG.73.31 SkeletalmusclemassinFontansubjects.Atscorerepresents
thenumberofstandarddeviationsfromtheyoungnormalreferencemean.
Avaluelessthan−2.0representsmarkedmusclewasting,definedasin
thesarcopenicrange.(FromCordinaR,O'MeagherS,GouldH,etal.
Skeletalmuscleabnormalitiesandexercisecapacityinadultswitha
Fontancirculation.Heart.2013;1530–1534.)
FIG.73.32 Muscleaerobiccapacityasmeasuredbytherateconstant(k)
ofpostexercisephosphocreatineresynthesisduringcalfmuscle31P
magneticresonancespectroscopy.(FromCordinaR,O'MeagherS,Gould
H,etal.Skeletalmuscleabnormalitiesandexercisecapacityinadultswith
aFontancirculation.Heart.2013;99[20]:1530–1534.)
