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Volume35，Number12，1990
摺Jlほ嬬1

鳶逐WearofHeartValveProsthesis

り∴・∵一

Shigehiro Hashimoto

ト−−∴Bioengineering，SchoolofMedicine，KitasatoUniversity（15−1，Kitasatol−｛home，Sagamihara−Shi，Kanagawa228）

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1．INTRODUCTION‥

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Avarietyofdurabili【ytestshavebeenconductedfortheheartvalveprosthesis【1−31．Several
researchers【1，4−111haverepor（edonitswear．Thewearof（heheartvalveprosthesisiswearthat
OCCurSWhileusingbloodasalubricant．Themechanicalcondi（ionofthefric（ionlngpartSOflheheartPrOSthesisvaryappreciablydependingonthevalveconstitution．Thepatternsoftheirmovementsare
rathercomplicated，Thus，theanalysisofthewearmechanismsofaheartvalveprosthesisisnota

Simpletask．

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一
2．STRUCTURES OFHUMANHEARTVALVES−十InthebloodcirculationloopofLhehumanbody，thereareseveralvalveswhosejobistoallow
Onlyonedirectionofbloodnow；lheyinhibitareversenow．Amongthevalvespossesslngthis
function，themostimportantarethoseintheheart，WhosemaJOrfunctionistocirculateblood
throughthebodybypumplng．WhentheheartvalvehlnCtionislos【，itmustbereplacedbyei（heratransplantorprosthesis．Therearefourvalvesinlhehumanhearl；1hetricuspidva］ve（entrytorightheartchamber），thepulmonaryvalve（exitofrightheartchamber），mitralvalve（entrytoler【heartChamber）andaorticvalve（exito‖eftheartchamber）．Eachvalveiscomposedof（WOtO（hreepiecesJ
Ofcusp．OneendorthecuspISattaChedtothewa1lofbJoodvessel．Thefreeendsofthesetofcuspsi．

Ithat create avalve that meets at the cen［er oflhebloodvesselto close thevessel．In thevalve

Openlngperiod，thefreeendsofthecuspsseparate．Thevesseldiame（erofthcvalvea）soexpands

toensureanerncientbloodLlow．ThenowresistanceatthevalveduringlheopenJngPeriodisvery
Small．Thefreeendsortheentryvalves（tricuspidandmitral）areattachedwithchordatendineaand

papiJlarymuscletotheinnerheartwallonlhedownstreamside．Thisinhibitstheundesiredbending
Ofthefreeendsofthecuspstowardtheup−Streamduringtheopeningperiod．（Fig．1）．

ReceivedMarch17，1989．

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1／Chorda（endinea
PapillaⅣmu5Ck
Btoodnowsrrom10ptObottom

Fig．1

Structureortricuspidvalveofhumanheart
3．MECHANICALENVTRONMENTSAROUNDlIUMANHEARTVALVES［12−14］

Theaveragemechanicalenvironmento＝hchcarlvalvcsillan adultwcighing60kgcanbe

describcdasfoIJows：thcvalvcinsidehasadialllCter＝2．5cmalcnlryand2．3clllalcxit，lhcb700d
now＝5．5／／minavcragcwilhacyclicfluctualionaroundO，8sduc10111ChcaTll・eat．TllCdivisions
ofthcO．8speriodorhcartmovcmclllare；40Omscnlryalld300mscxilrorlhcl−igll111Carlchaln
and460mscnlryand240mscxilforl】lC）ef111eartChambcr．TllCSeperiodsrcspeClivclycorrcsr，Ond

101hcopcnlngPCriodsforlhclricu5Pid，Pulmonary，milralandaorlicvalvcs．TllCreSIorlhchc

bcatperiodinvoIvcsthc101aJvalvcclosurc（conslant−VOlumcconlraclionandrclaxationpcriods）．The
aorticvalvchaslhcshorlcs10r）Cnlngperiodofa】Ilhchcarlvalvcs・Tl−Cn−aXimun−inslantancous
bloodJlowralecanrcachashighas30（／minlherc・WilhaO・8spcriodcyclicmVCmCnt7CaCllllCart
ValvcrcpcaLsasmanyas4×1080PCning／closingmolionsinlOycars・Wi11−1his・1nlind・iliscasy10

imaginchowhcavylhcJoadisforhumanhcartva）vcsduringa】irclimc．Tl−CpumPlngPrCSSurCIcvcIs

OfthchumanhcartarcasroIZows；3−7mmI7grorcnlryandlO−25mn汀Igforcxilinlhcrighthcartchan−bcr，and2〜10n−mIigrorcnlryand70−120mmHgrorexiliJllhc）crlhcarlchanlber．

Obvious】y，lhcpumplngprCSSurCisgrcaler forthc）cft hcartchambcr thanlhat rorlhcrightCl−aml）Cr．Thcrcforc，lhcrevcrsa】nowinhibilingfunclionisn−OrCCrilicalforvalvesintllCIcfLChanlberlhanrort）10SCil−1hcrigh〔chambcr．HcartvalvcproslhesiscascsdcalalmostexcIusivcly
Witl一】crlhcartchamt）CrS．Malf11nClionsorvalvcsinlhcrightIICarlchambcrcauscacerlaincxten10rt）1oodcnlryprcssurcriscl）uldono＝cadLodclrimcnl；l】bloodcirculalionproblcms．
4．PROPERTIES OFBLOOD

Bloodpasslnglhroughthehcarlvalvcshaver）fT＝7，40at37OcandconLainparliclessuchasrcdandwhitcl）】ood−CC））sandbloodr｝lcIc）cts，Organicsubs〔anccssuchasproIcins（nblinogcn，albumine，glol）u】inc），il−OrganicionsofNa＋，K＋，Ca＋＋，Mg＋＋，Cr，andHCO，−alldwaLcr．Al）Ou145％orlhct）1oodvolumciscomposcdofparlicIcswhoscn−aJOrCOmPOnCnLisrcdbloodqccllsorabicooncaavc
disk8Ilmdian−CLer．ProIcinn−01cculcspossessdiffcrcntshapes；70×5nn−C11ipsoidfornblinogcn

and20nl−1diamcIcrsphcrcforβ一1ipor）rOIcin［15】．Thcdcnsilyorthcbloodisl．06g／cm3andithas

aviscosilycocrncicntor6cP（avalucatshcarrategrcalcrthan50s￣1；nOteLhalbloodisanon−1368

ノ叩β〃g∫ピノ0〟川βJo／rrf占0わgγ

Newtoniannuid）．Takingintoaccountthebloodnowratesofthehumanheartsummarizedinthe

雲篭PreCedingchapter，theReym01dsnumberforbloodaroundthevalvesinthehumanheartcanbe
estimatedtoaverage400andhaveaninstantaneousmaximumof20CK）．Ar（erpasslngthroughthc
lung，thearteriall−1（10dnowstotheleftheartchamberandlhevenousblood，Whichreturnsar（CrCirculatingthroughthebody，nOWStOtherightheartchamber．Theoxygenpartialprcssureinthelert

芸くheartchamberis95mmHgandthatintherightchamberis4Ommlig．TheCO2parlialpressurein
theleftchamberis40mmHgandthatintherightchamberis45mmHg．
5．HTSTORTCALDEVELOPMENTOFmESANDMATERTALSOFHUMANHEARTVALVE

諜董嘗

PROSTHESIS【13］Surgicalhumanheartvalvereplacementswereinitiatedin1950s．Avarietyofvalvetypesandmaterialshavebecntried．SomeinvoIveaprostheticvalveuslngCuSpSPOSSeSSlngaSimi］argeometry
tothenaturalones，thetransplantofchemicallytreatedhumanaorticvalve，animal（coworpig）
heartvalves，thetransplantofartincialcuspsformedbyuslngabiormembrane，SuChasduramater

Or pericardialmembrane or polymeric materialwith sumcient deformability．Other types of
PrOStheticvalvessimulatethemechanicalpumplngfunctionofheart・Fig・2depictsthestructurcs
OfrepresentativetypesofmechanicalprostheticheartvalvesandtheirtypICdlfailures．Tat）1el
丘；．オーl一膚I

Summarizesthestructuralmaterialsusedforthesemechanicalprostheticvalves．Thenumberof
heartvalvereplacementoperationsinJapaninthepastfewycarsexceedsl∝旧peryear，WOrldwide
theyexceed200，000【1叶しDiskwear

Ballvalve

Disk valve

Tiltingdisksinglecusp

ⅠIingerailure

囁。。
lcuspTi】tingdiskdoublecusp TrjplecuspmadeoFbio−men−braneBloodrlowsfromlhetoptobouolll

Fig．2

Structuresorrepresentativemechanicalprostheticheart
Valvesandtheirtypicalfailures

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Table 1

Typicalmaterialsusedformechanicalprostheticheartvalves
Component

Malerials

Batt

Nylon，S‖ieon，hollowtitanium，PyrOIytic⊂arbon

Disk

Silicon，POIy4−nuOrOethyIeneぐrEFLON），POlyaeetalresin（DELRIN），graPhite，PyldytiecarboJl

Strut（Cage）andvalveseat

Po］y4−nuOrOelhy］ene，Co−CraT］oy，Co−Nialloy，Re−Moa】】oy，Slain】esssleet，Tial】oy，pymI叩iぐCarbonandthesematerialscoatedwithFK）1ypropyTene

Se雨ngnngtotheb】（Xカvesset Po】y4・nUOrOe仙ylene，F）lyeslerriber

6．WEARC＾SES REPORTEDFORPROSTHETICHEARTVALVES

TheparametervaIuessummarizedinTable2arecalcu）atedonthebasisofgeometricalfactors
giveninreports【1，4−107wherewearcasesofprosthclicheartvalvesweredescribedindclai
norma］loadonthefricLion］ngSurfaccwaseslimaledrromthepressuredifferencebetweenthe
Streamanddown−StreamSidcsorthevalve［17］orfromthemaximumloadonlhestrutof巧Shi］eyvalvc［18】measuredbyaninvilrosimu）atinglest．AspecincwearrangeoflOT14−10−15m2／Nissumcienttocausewearproblemsrorprostheticheartvalves．Table2citcsweartestresultsf
alumineceramicsuslng＋−ShapecrosslngrOtat；ngcylindcrarrangementinaglycerinesolutionasthe

refercncc［11］．Thosematerialswereusedindouble−CuSpValvemodels．Porousceramics（roughness＝70ILm）areexpectedtocxhibitacompatibilitywiLhbloodbutlhcwearperf

appearStObefarrromsatisfactory．Itmuslberememberedlhatlheslidingmolionortherrictionlng
Surfaceinprosthelicheartvalvecomponenlsisnot one−Waybut recIPrOCative．The fricli
distancevalucscitedinTable2refbr（OLhetotaldistanceofslidinginoppositedirec（ionsexceptforlheinvitrowearteslfortheceramicrods．Whenthewearvolumeexceededlmm3，thedesi
runctionorlhevalveappearedtobelos（．Noproblemscausedbywearpowderswererepor

Probablylhctotalvolumeorwcaristoosma］＝oyieldenoughpowdertocausclhisproblem．Othe

reportedcasesofprosthetichearLvalveprob］emsincludeclothwearduetorriclioningbelwecnthelitaniumballandva）veseatandthestrutcoatedwilhsyntheticribcr［2］，fai1ureorthewel

betweenthescatandstrutOftheva］ve［19】，andballvariance【4］andcracking【20】due（Othepenetrationorfattycomponenlsorbloodin10thesiliconba］1．According10thesurvcyrorthe
Shileyva］ve［19いhcrehavebeen9reporledproblcmsamong2102aorticvalvcs，10amomitralva）vcs，O among87tricuspjd valves and O among5pulmonaryvalves．Ar）parentIy
proslhelicvalvesinlherighLhcar（Chambcraretroub］e−rree．AsdescribedearlicrinChapter3，theextentorlhepressurenuctuationinlherightheartchamberisrarsma］］erthanLhatin

Chambcr．ThisiswhyLhcrelSPraClicallynowearlroublcforr）rOSlhclicrightchambcrvalvcs

hasbeennosignincantreductioninthemaleria）strenglhdue10lowoxygenpartialprcssureint
blood．

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7．CONCLUSIONNoneorlhecurrentlyavailab）eprostheticheartva】veshasasatisfactorydurability・Thebaseof

thisunforlunatesituationisduetothcinsur爪cientundcrstandingoffaLigueandwearmechanis

invivoandthcresultantfai】urctoestablishreliableinvitrosimulationtcststandards（currenltcst

StandardL3］strivestoprovcthedurabilityofthevalvefortheleastnumberofcyclescorrcspon

to5ycarsservicc）．Inthcactualserviceo［theprostheticheartvalve，prOblcmssuchasbloodclottin

anddestructionortheb］00dcellsoccltrductoclectricchargeconditionsatthcsurfaccofmaterials

andshearrateinbloodf］ow．Theseproblemsoccurpriortomcchanicalfai1urcoccurs【13，16
exanlPle，Cloltedbloodinhibilsthepenetrationofblood（consideredtobe alubricant）tofrictionlngPartOTthcprostheticvalveand，aSaCOnSequCnCe，thcwearo＝heprosthelicvalv
accelcrated．In past rcsearch efforts forprostheticheart valves，theprlmaryfocuswa

COmPalibiIitybetweenthcvalvemaleria】andb）00dinordertoavoidproblemswithclottlngan

dcstruction，Inthisrcspect，Tlr（一Slhcticcuspsmadeofhumanorallinla】Lissucsareprcrcrablc，durabilityofthistypeorcuspISPOOr．ThedurabiIityorcuspsmadcofdcformabIepolymcrisnotvcry

impressivecithcr．Coatingswithsilicon，POly4−f］uoroethy）cncandpo】y−PrOPylcnewercatollCinlroduccdforproslhetichcartvalvesbecauscorthcirra、▼Oral）1ccon−Palibilitywilhblood．Ⅰ†owcvcr，thcywcrcsoonabandoncdduetounsatisfactorydurabilily．Thcsolutiontolhisprob】emwasth

empIoyn−CntOraPyrO］yticcarbonwhoscspcci爪cwciglltiscomparab］ctotllatOfhumanbloo

Frcq11Cnlfailurcswhichoccurrcdatlhcwc］dedscclionbcIwccnLhcscatandslru10ftlleBj6rk

Shilcyvalvelcdtolhcdevclopmcn10favalvcwhosescatandstrutwcrcshapcdoutofaslnglcingot［18】・Itwasrealizedthatanundesiredthcrmaldcrormationoccurrcdtothcprosthcticvalvcduring
thcsterilizalionproccssinlhcau10C】avc．Thcrcwasalsoamccllanicaldeformalionwhichoccduringthe5urgicalimplantalionorthcprosthcticva7vc［9］．ThcscdcfornlationsgrcatlyconLributc
tothclossofvalvcdural）ilily，tllCrCforc，mOdiLIcalionsrorthestcrili7；llionproccduresandva
SCulngSurglCalopcrationcqulPmCntWeremadc．Proslhetichcartvalvcrcscarc］lisnowatthes
WhcrccffortscanfocusotlthcdurabiIityo［thesystcm．
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1372

J叩α〃e∫eJo〟r〃α／0／rr拍0わgγ【16】Y．Sakllrai：［nLroducLionLoProsLheLicOrgan∫，NipponKeizaiShimbunPub］・，Tokyo，1986・【17】K．OhtaeJd／．：F〟′−dd椚e′血／∫0／Pro∫J毎J′cOrgd〃∫d〃dr毎汗C／血血／」ク〆加Jわ′！∫，
Shu−jun−ShaPubl．，Tokyo，1980，P．37．

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【19］D．LindblomeL a／．：）．Thorac．Cardiovasc．Surg．，92，5（1986）894．

【20］R．C．BonnabeauJr．andC．W．Lillehei：）．Thorac．Cardiva∫C．Surgリ56，2（1968）258・【21］B．J．MessmereL a／．：Thorac．Cardiovasc．Surg．，65，3（1973）386．

つJ713