The Isolated Heart-Lung Preparation

41 Pages·1978·1.406 MB·English

by  P. H. Huisman, J. J. Schipperheyn (auth.)

The Isoated
Heart-Lung
Preparation
P. H. Huisman and J. J. Schipperheyn
with technical assistance of
H.M. Kleijn
K. Kroll
197.
I.4ARTNJSNLHOFFMEDICALOMSION
nEHAGUEIBOSTONIlOHDOH
Inthecourseofsomeexperimentsmadebymein
conjunctionwith Dr.W.T.Sedgwick,on blood pressurein
thecoronaryarteriesoftheheart,thefactwasimpressed
uponmethatthemammalianheartisnosuchfragileorgan
asoneisusuallyinclinedtoassume,butpossessesavery
considerablepowerofbearing manipulation.Ontheother
hand,Iknewofvariousunsuccessfulattemptstoisolatethe
mammalianheartandstudyitsphysiologyapartfromthe
influenceofextrinsicnervecentres,inamannermoreorless
lesssimilartothe methodssofrequentlyusedfor
physiological investigationsontheheartofacold-blooded
animal;themammalian heart,however,alwaysdiedbefore
anyobservationscould bemadeon it.Thinkingoverthe
apparentcontradiction,itoccurredtomethattheessential
differenceprobablylayinthecoronarycirculation;inthe
frog, asiswell known,therearenocoronaryarteriesor
veins,thethinauriclesandspongyventriclebeing nourished
bythebloodflowingthroughthecardiacchambers,butin
themammalthethick-walled hearthasaspecialcirculatory
systemofitsownandneedsasteadyflowthrough its
vessels,andcannotbenourished(asappearstohave
beenforgotten) bymerelykeeping upastreamthrough
auriclesandventricles.
H.NewellMartin june1881
from:Studiesfromthebiologicallaboratory
oftheJohnHopkinsUniversity.
MartinusNijhoff
P,O.B.566
TheHague.TheNetherlands
©1978PH.HuismanandJ.J.Schipperheyn
ISBN9024721075
Nopartofthisbookmaybereproducedinanyform,byprint,
photoprint,microfilmoranyothermeans,withoutwrittenpermission
fromthepublisher.
Thedevelopmentofan autoperfused canine
heart-lung preparation formed partof aresearch
projectofthe InteruniversityCardiologic Institute,
in which participatedthe Department ofCardiology
ofthe State UniversityofLeyden, the Netherlands.
The research was carried out inthe
LaboratoryofPhysiology, State Universityof
Leyden. Design and manufacturing of mostofthe
special equipment wasdone in the mechanical
workshop (Head: Mr. R.P. deGraan and electronics
departmentofthis laboratory(Head: Mr.C.G.Wou
ters).
Thepublicationofthisbookhasbeenmostgenerouslysupported
byAstraPharmaceuticaBV.,towhichtheauthorsaretrulygrateful.
CONTENTS
/'.1'1'.
1Introduction, history and contents 5
2Isolationprocedure 9
3 Perfusion box 14
4Cardiac metabolism. electrolyte shiftsand
acid-base problems 18
5Haemolysisand pulmonary edema 21
6Electricalmeasurements 25
7Haemodynamics 29
8Coronaryflow and oxygen consumption 36
LAYOUT OF PERFUSION BOX AND EQUIPMENT
(enclosure at the back ofthe book)
1INTRODUCTION
Needfor isolated heartpreparations
Thestudyofcardiacfunction inahearttotallyisolated
fromthebodyisrequiredwhen onetriestorelateproperties
ofisolatedcardiacmuscletoheartfunction intheintact
animal.Duetothefibrearrangementwithintheventricular
wall,thecomplexityofthespreadofexcitation,
thepresenceofvalvesandthedifferentproblemsrelatedto
relaxation andfillingoftheheartitisimpossibletoderive
relationsbetweenpressureandflowthroughoutthecardiac
cycledirectlyfrom lengthtension relationshipswhichare
obtainedfromstudiesontrabeculaorpapillarymuscles.
Anisolatedheartpreparationisindispensableforthestudy
ofdrugactionontheheart.Onlyfewdrugsactsolelyonthe
heart,moreoftenthevascularbed isinfluenced
simultaneouslyanddrugactioncannotbeascertaineddue
tothecomplexinteractionofheartandvascularsystem.
History
Theneedforstudieson isolatedheartshasalready
beenfUllyrecognizedaboutacenturyago.Twodifferent
techniquestoisolateheartshaveevolvedfromthatperiod
which arestillinusetoday,although inamodifiedversion.
In1881 NewellMartin12describedafunctionallyisolated
heart-lungpreparationinanopenchestdog,inwhich an
artificial haemodynamicresistorandareservoirareinserted
betweenaortaandcaval veins,whilethecirculationtothe
bodyisinterrupted.Loadedwithanartificial impedance
withasmallprimingvolume,theso-called Starling resistors,
theisolatedheart-lungpreparationofthedogservedto
5
studytheintrinsiccontractilepropertiesofthehearts,15,
cardiac metabolism14,regulation ofcoronaryflowlOandthe
effectsofvarious drugs.
IntheStarling resistorthebloodflowsthroughathin-walled
collapsibletube, which issurrounded byapressurized
cylinder.
Asecondapproachdatesfrom1895when
Langendorffdevelopedaperfusiontechniqueforthe
completelyisolatedrat'sheart9.Hedemonstratedthat
oxygencanbedissolvedinsufficientamountsinasaline
solutiontosupportaheart,which isperfused inthe
retrogradedirection.Clearlyitisofgreatadvantagetouse
simplesalinesolutionsasoxygenationofthesesolution
doesnotcreateaproblemandthereisnoneedtoinclude
lungsinthepreparation.
Bothtypesofisolatedheartpreparationshavetheir
weakpointsand manyinvestigatorshavetriedtoimprove
upontheoriginaldesign.First,letusconsiderimprovements
totheclassical Langendorffpreparation. Itrequiresahigh
coronaryflowtocompensateforthelowoxygencontentof
thesalinesolution. Ittendstodevelopedemawhich results
fromthelowviscosityoftheperfusionfluid anditobviously
doesnotperformanyexternalworkbecausetheleft
ventricleremainsemptythroughoutthecardiaccycle.
Mainlythroughthedevelopededemathemechanical
propertiesofthemusclechangecontinuouslyandeffective
experimentation islimited,dependingonthelimitationsof
thecriteriaforstability.Considerableimprovementis
obtainedbyadditionofwashed,usuallybovineerythrocytes
totheperfusionfluid. Coronarycirculationandcoronary
venous P02returntonormal andviscositycan be
increased,withouthamperingoxygen supply.Aperfusion
system, basedontheLan!=)endorfftechniqueand which
uses'reconstituted blood' (containing washederythrocytes
and bovineserumalbumine) allowsfornormalcoronary
flowregulationwithoutthegradualincreaseofcoronary
vascularresistancecaused byedemaformation3.Another
modificationwhich makestheLangendorffpreparation
much morepracticableistheaddition ofareservoir, filled
with perfusionfluidwhichhasaconstantpressureand
which isconnectedtoboththeleftatriumandtheaorta
throughasystemconsisting oftwoone-wayvalvesand an
artificialvascular impedance11.Theoutflowfromthe
coronarysystemthusiscollectedseparatelyand usually
notusedforrecirculation. Inthiswaytheleftventricleejects
and performsexternalworkwhilethefilling pressureand
theaortic pressurecan becontrolled separately.Asimilar
typeofpreparation hasbeendevelopedforcatheartsby
Elzinga5.
Asregardstheoriginal Starlingheart-lungpreparation,
6
ithasnotbeensubjectedtosomanymodificationsashas
theLangendorffdesign.Thisbookoffersadescriptionofa
modifiedStarling preparation,which originallywas
developedforthepurposeto studyelectricalactivationof
theventriclesandwaslateradaptedtostudyvalvular
function andmechanical behaviouroftheventricles.Those
studiesrequireisolationofratherlargeheartsofabout250
450gheartweight.pumpingagainstnormalpressureloads.
Forthosehearts(generallyfromdogsandcalves)the
modified Langendorfftechniqueisratherimpractical,
becauseitrequireslargequantitiesofperfusionfluid.
TheStarling preparation,however,offersdistinctadvantages
overthe modifiedLangendorfftechniqueinthistypeof
heart.Thelongperiodofstable mechanicalperformance
andahighsuccesrateduetothe simplicityofthemethod
areamongtheadvantages.An importantbenefitofthis
preparation isitsuse-ofwhole,practicallyundilutedfresh
blood with unchangedhaemodynamicproperties.Another
importantpointistheconservationofthedelicaterelation
shipbetween pulmonaryveins,leftatriumand leftventricle
which guaranteesanormalfilling patternfortheventricle.
Tocorrectfor itsweakpointstheoriginal Starling
preparation requires onlyafewminormodifications.
First,thepreparationshouldbetakencompletelyoutofthe
bodytoexcludeexternal influences,especiallyfromthose
ofneuronalcontrol. Secondlyaservocontrolledrollerpump
shouldreplacethereservoiratrightatrial levelfor practical
reasons, andalinearcapillaryresistorshould beused
insteadoftheStarling resistor soastoobtain morerealistic
pressureloadstotheleftventricle. Detaileddescriptionsof
modified Starling preparationsareremarkablyfewinthe
recentliterature17.
Contentsofthisbook
InthisbookadescriptionisgivenofaStarlingheart
lungpreparation,designedandslightlymodifiedwith
techniquesandequipmentavailablein1977,96yearsafter
theoriginaldescriptionbyNewellMartinand hisco-workers.
Thedescriptionis probablyofinterestnotonlyto
physiologistsandcardiologistsbutalsotopharmacologists
becauseofthepreparation'suniquefacilitiestostudydrug
action. Especiallytheactionofcatecholaminesand related
compoundsandofantiarrhythmicdrugsareeasilystudied
thisway.Thepreparationmayalsobeusedtosupport
other,even moredelicateorganslikebrainorliver.
Ourmodifiedheart-lungpreparationiscompletely
isolatedfromthebodyand issuspendedinalarge,perspex
box. Itisattachedwithitsaortatoacannulafromwhich it
hangsfreelyinahumid,warm atmosphere.Thepericardium
7
mayberemoved butnotnecessarilyso,ifrequiredtheheart
can besurrounded bywater.Anisolatedheartcanhavea
cardiacoutputofabout1.0l/min/100gagainstamean
aorticpressureof70mmHg,withoutcatecholaminedrive.
Astablemechanicalperformanceismaintainedduringa
periodofatleastfivehours.Toadaptthepreparationto
certainspecificstudiesmanymodificationsofthe
techniquearepossible.Arightheartbypassallowsfor
coronaryflowmeasurementsandcalculationofoxygen
consumption.Thisadaptationalsooffersthepossibilityfor
openingtherightventriclefor mappingofthespreadof
activationontheendocardium.Thepreparationcan be
alteredwith onlyminormodificationsintoaheartperfused
intheretrogradefashionforsimilarstudiesonthe
endocardialsurfaceoftheleftventricle. Baanandhis
co-workers! havedemonstratedthatthepreparationisan
excellentstarting pointforacompleteseparationofthe
coronaryfromthesystemiccirculation.Themaincoronary
arteriesaremoreeasilyaccessibleandcan becannulatedat
leisureandthusinamorereliablewaythanwithopened
thoraxonly.
8
fig.1
Viewintotheopenedthoraxcavitywhenthehearthasdeliveredall
availablebloodtothereservoir. Theazygosveinisligatedandcut
beforethecannulaisinserted.Thecaroticarteriesareclosedoff
afterthecannula'sstopcockisopened.Thecavalveinsareligated
anddividedlast,whenthebloodflowhasalmoststopped. Thestop
cockwillbeclosedbeforethepreparationistakenfromthethorax.
2THE ISOLATION PROCEDURE
Theheart-lungpreparationisusuallyobtainedfrom
largedogsofbetween20-30kgbodyweight.Calvescan
alsobeused.Therequiredanaesthesiaisachievedby
administrationofmethadonwithfirstadoseofdroperidol.
Theusualdoseis2mg/kgmethadoni.v.and1mg/kg
droperidolLv.
Theoreticallyanaesthesiawithvolatileagentsonlyshould
bepreferredbecausethesedrugswill induecourseoftime
disappearwhentheheartisisolatedandthelungsare
ventilated. Forpractical reasons, however,parenteraldrugs
9
arechosen.Thecardiaceffectsoftheemployedanaesthetic
2
drugsarewell documentedandareknowntobesmaIl ,4.
Afterinductionofanaesthesiatherequireddepthisusually
maintainedlongenoughtocompletetheisolationprocedure
withoutanadditionaldoseofanaesthetics.Theanimalis
intubatedandduringthoracotomyisartificiallyventilatedwitha
mixtureofairandoxygen.Acapnograph (Godart)
measuresend-expiratoryPC02levelsfromwhichaproper
level ofventilationisset.Amild metabolicacidosiswill bea
rathertypicalfinding in methadon anaesthesiaindogsand
inordertocompensateforthisanisotonicNaHC03-solution
isinfusedofwhich usually200-300ml isrequired.
Theexactquantityisdetermined bymeasuringthe
bicarbonateconcentration inthearterialblood.
Thoracotomyisperformed byamidlineincision
throughthe sternum.Theheartandthemajorbloodvessels
areexposed,thepericardium isusuallykeptintact.
Theazygosveinisligatedandcut between ligatures.
Boththecaval veins,thecarotidartieriesandthe
descending aortaaresubsequentlyligatedbutnotclosed
asyet. Heparinisgiven(200mg i.v.) and awidebore
cannula,innerdiameter10mm,isnextinsertedintothe
descending aorta.Thecarotidarteriesshould beclosed
aftercannulation(fig.1).Closingofthecarotidarteriesprior
tocannulationislikelytocausedamagetotheheart.The
aorticcannula,whichlaterintimeistobeusedtoconnectthe
preparationtotheperfusionsystem,willtemporarilybe
connectedtoaStarling resistor.Throughthisresistor the
heartcan pumparterial bloodintothereservoirofthe
perfusionsystem,whileaproperperfusion pressureforthe
coronaryarteriesis maintained.Theperfusion pressure
is usuallysetatabout 50mmHg.Thecavalveinsare
closedanddividedaftertheaorticflowhasstopped
completelyandtheheartisemptied byreleasingthe
pressurefromthe Starlingresistor.Theperfusionsystem
doesnotrequireaprimingvolume. Lungsarenextinflated
andthetracheaiscross-elampedandcut.Theaortic
cannulaisclosed withastopcockanddisconnectedfrom
theStarlingresistor.Atthatmomentashortperiodof
myocardial ischemiaisboundtooccur.Withinthisperiod
theheart-lungpreparationistakenfromthethoraxand
transferredtotheperfusionbox. Inthebox,thearterial
blood isalreadycirCUlatingand retrogradeperfusionofthe
coronaryarteries,oncetheheartisconnectedtothebox,
isstarted immediately.Perfusion pressureissetatabout
75mmHg bythepressureinsidetheStarlingresistor.
Ventilationofthelungsshould becontinuedwith.anair,
oxygen,carbondioxidemixture.Venousbloodreturningto
theemptythoraxcavityiscollected.Thisbloodcontains
verylittleoxygenand isseverelyacidotic.Asodium
10