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Copyright©IFACControlSystemsDesign,Bratislava,SlovakRepublic,2003IFAC~Publicationswww.elsevier.com/locate/ifacNONLINEARSYSTEMMODELSBASEDONINTERVALLINEARlZATION:AMEDICALAPPLICATIONJaroslavKultanAbstract:Thepaperdealswithanapplicationofmodelsbaseduponintervallinearizationinmodellinghumanorganismparameters,especiallyduringlong-termmedicaltreat-ments.Thegeneratedmodelenablestopredictpatient'sstateaswellastheimpactoftakentherapeuticsonit.Applicationofsuchmodelsbringsaboutimprovementofthetreatmentqualityandhelpsphysiciansinthedecisionmakingprocess.Copyright©2003IFACKeywords:identification.intervallinearization,parametersofhumanorganism,statepre-diction,nonlinearsystemsI. INTRODUCTIONInthemedicalpracticethereareoftenencountereddiseasesrequiringa long-termtreatmentwherebyitisalmostimpossibletocontinuouslymonitortheorganismparameters.Veryoften.physiciansareobligedtogorepeatedlythrougha hugeamountofdataacquiredfromtheblood,urineandotheranaly-ses,tobeabletotakedecisionsbaseduponthepa-tient'sstate.Thisprocesscanbesupportedbycreat-inga modelofpatient'sstate,basedonwhichitispossibletotakeacorrectdecision.Thereforewefocusedontheidentificationofhumanorganismparametersunderlong-termmedicaltreatments.Resultsofbloodtests,creationoftheirmodelanditsapplicationinthepatient'sstatepredictionhavefacilitatedthedecisionmakingaboutadditionalin-terventionsduringthetreatment.whichhelpedtoimprovethewholeprocess.Fortheidentificationandmodelgenerationwehaveusedtheintervallineariza-tionmethod.2.NONLINEARSYSTEMIDENTIFICATION2.1.Identificationusingtheintervallineari=ationmethodmanymodelsasincaseoflinearizationintheoperat-ingpoint,nortosearchintricatenonlinearfunctionswhichimplementationisoftenquestionable.Identificationofnonlineardynamicsystemsbytheintervallinearizationmethodhasbeeninventedin1986.Themethodhasbeenupdatedseveraltimesbyimprovingsomeoftheirpropertiesortheidentifica-tionprocessitself[2][3].Thepresentedmethodhasbeenappliednotonlyinnonlinearsystemmodellingbutalsoindesigningcontrollersfornonlinearsys-tems[4].Identificationofnonlineardynamicsystemsconsistsinsplittingthewholeworkingrangeoftheinputandoutputvariablesbythelimitsuk;andykj•respec-tively,intoseveralintervals(fromwherethenameofthemethod).Intersectoftheseintervalsdefinesthelinearizationinterval(Fig.I).Generatingasystemmodelusingthismethodre-quiresavailabilityofthemeasuredinputandoutputdata.Measurementsaretobecarriedoutduringthesystemoperationandorganizedina table.Next.thelimitsofindividualintervalsfortheinputandoutputvariablesaretobespecified.Intersectoftheseinter-valsdefinesthelinearizationsection.Foreverynonlinearsystemtherecanbeseveralsuchsectionsandtheidentificationyieldsmodelofeachlineariza-tionsectioninthefollowingform(I).I{I)1/+Iq'>{1-/7)+:tq'1/(1-(.J-d+1)7)o,"'I')..11f}.Jqkisvectorofmodelcoefficientsinthek-thlineari-zationsection.wherebynu- numberofsamplesoftheinputvariable(2)(3)(4)k=1.2....kknu+nyy(t)=z(t)qkwherez(t)=[I.y(t-I).....y(t-ny).u(t-d-I).....u(t-d-nu+I)]kkkqk=(qo·ql····qorconciselyTheintervallinearizationmethodisoneofrelativelynewmethodsfornonlinearsystemsmodelling.Basi-cally.itdifferentiatesfromotheridentificationandmodellingapproachesforsuchsystems.oneofwhichconsistsinsubstitutingtherealsystembya setofnonlinearfunctionsandrelationswhichdescribeprocessesinthesystem(thehumanorganismcanbeconsideredasa system);anotherpossibilityissubsti-tutionoftherealsystembya mathematicalmodelacquiredbyitslinearizationinachosenoperatingpoint,oritispossibletocreateabstractnonlinearmodels.Theintervallinearizationmethodoffersa substantiallydifferentapproach.generatinga linearmodelcreatednotonlyforoneoperatingpointbutfora wholeregioncalleda linearizationinterval[I].Sucha modelisabletoincludepropertiesofthegivensystem.wherebyitrequiresneithertocreateso495
ny-numberofsamplesoftheoutputvariablet -timewherer =1.2...n :ny+nu+I<nTheidentificationresultisthematrixQT -samplingtimed -inputvariableshiftk -indexofthelinearizationintervalAtotalnumbermoflinearizationintervalsfornu= 1andny=Iism =mu.myandfornu>1andny>1thenumberoflinearizationintervalsis givenbyqlqlql0Iml+,~rQkkkqqq0Inil+~\q"'q"'q"'0II1U+f~\'(9)kk=munu.myny(5)I-auxiliaryindexFormany systems.long-termoperationmeasure-mentsofu(t).y(t)proved.thatinpractice.thenum-bcroflinearizationintervalsdoesnotcomplywiththeirtheoreticalnumberandstronglydependsontheappropriatenessofchosenlimitsandthevolumeofmcasureddataa\ailable.Theprocedurefordeterminingtheindex"k"ofthelinearizationintervalisasfollows.Iftheoutput\'ari-abley(t-i).i=I.2nyisfromtheamplitudeband(yks.,.yk,>-s =1.2my.thenthisbandisdcnotedbyI,=s.Similarly.ifthevariableu(t-j-d+I).j=1.2...nuisfromtheband(ukr.,.uk),r =1.2.....mu.thecorre-spondingbandisdenotedI=r.ThesebandsnY"Jnotationsarecollectedinavector1=(11'12...Inu+ny).Thelinearizationintervalindexiscalculatedasfol-lows864inputu(t)2input/outputcharacteristics161412=-10>;:;8c.:;0642Fig.l.Input/outputcharacterisicsofthesystem3.IDENTIFICAnONOFBLOODSYSTEMPARAMETERS(6)(7)(8)1).8Itor1=1.2.....nuwherck81=ml-I)for1=1.2.....ny8-.n\"11-11It-ny-m)..muCalculationofthelinearmodel( 1)or(2)forthek-thlincarizationintenalconsistsindeterminingthe\'ectorofIinearizationcocrticients(4)frommeasuredsamplesy(t-i)andult-j-d+1)tori=1.....ny.j=l.....nu.\\ithinthek-thineari7.ationintcn·al.ThemodelitsclfisthenspecifiedfromtherelationA"q"=b", from\\hich\\eexpressthe\cctorofthemodelqkinthck-thlinearizationsectionusingtheleastsquaresalgorithm.Toappl)it.it isnecessaf)toksetupthematrixAfrommeasured\alucsy(t-i)andu(t-j-d+I)andthe\'cetorb"frommeasured\alues."y(t).Forthck-thnmoftht::matrixAholdsa\""O\= u(t-j-d+I)akl=I"au-l= y(t-i)fori=1.2nytorj=1.2nu(9)3.I.DatameaSllremel71Theconsideredmethod\\as\eriticdinmodellingleucocytesparametersforoneyear.Duringaone-yearchemothcrapeutictreatmentbloodsamples\\cretakensporadicallyandindividualparameters\\'eremeasured.Valuesofindi\idualparametersareorgan-izedinatablt::(Tab.1).Input\'ariablesarc\aluesofusedtherapeutics(V- vincristin.Cl'-C)splatinum).orofcertainsupportingpreparations(S).appliedincaseswhentheorganismparametersha\edecreasedconsiderabl).OutputparametersareHU.Ery.HKU.LE.TR.Medicineintakeis denotedby..1"inthedayofapplication.kTher-thentf)ofthen~ctorbsatisfiesb\=y(t-O)(10)496
CPI0.04vI0.3A.DTable2 summarizesvaluesofmeasured.andinterpo-lated(linearlyandquadratically)values.MeasuredvaluesofindividualvariablesareshowninFig.3.ComparisonoflinearlyandquadraticallyinterpolatedvaluesisdepictedinFig.4.Inmeasurementinstantsvaluesofindividualfunctionscoincide.LeucoeytesandinputvariablevaluesusedformodellingareshowninFig.5Thesimplestinterpolationmethodisthelinearinter-polation.Forvaluesinindividualdaysitsubstitutesthevaluesobtainedbya uniformdistributionofthestatesbetweentwomeasuredvalues.Thequadraticinterpolationmethodisa moreadvan-tageousone.usingaquadraticapproximationofvaluesbetweentwomeasurements.Thoughitisquitecomputationallydemandingitfollowsbettercon-tinuouschangesofindividualparameters.InputvariableshavebeensubstitutedbyexponentialsreachingtheirmaximumatapplicationtimeofbasictherapeuticswhentheirconcentrationInorganismdecreasessuccessively.Theexponentiallorgettingfactorchangeswitheachconsideredvariable.NTab.I.MeasuredvaluesofbloodparametersduringtheinitialperiodINPUTSOUTPUTSHKCyk\"CPSHG[I").GLETRDate14.07.99II1183.70.292.118620.07.99671244.40.371.622522.7.99291174.090.371.820529.7.99716933.260.37152143317.99218983.370381.21493.8.99321642.320.1I1105.8.99223822.860.371.2414325.8.99204321264130352922429998511133.70.371581846.9.99455953.090.381.041089.9.99358953410.271.314521.9.9912701093490381.3311727.9.99676104340.381.2123610999851133.740.361.0828113.10997921173760371.652432.11.995112963.180.380.741385.11.99311594330.270.81499.11.9941191013.350.361.1187AgraphofsomemonitoredquantitiesisinFig.2wherebytheleucocytes.whichcharacterizepatienrsimmunityarethemostinterestingparameter.5 -4.5days401183.70.292.1I193.730.292.083.520.74080%0801193.820.32.021193.730.292.0833054880.923101203.930.321.9312~4.010.311.892.540.40600.886901214.050.331.851254.~~0.331.74250.30120.852101224.170.341.771264370.351.641.560.22310.818701234.280.361.68In4.440.361580.57016530.7866D1244.40371.61264.460371.57080.12250.755801214.250.371.71244.40.371.61(])(])(])(])(])ClCl00000ClCl(])(])(])(])Cl000009109070.726101174090.3718I~O4.240.371.72.....<xioi(])(])ClCl00000~ ~NN~ ~NCl«)~0~~NNM'VNNN~~ ~~lCi100.8080697701143.97D371.761164.07D371.81coM0.....lCiNoiciNNNN"059860670301103.850.371.72109H40.371.85--Ery--LEI~044350.64401073.730.371.681033.650.37I8t>Fig.2Measuredvaluesofsomemonitored130.32850618801033.6~03716498.t>3.:'U.37I85quantities140.243405945o99.93.50371.695.~3.380.371.83.1.Processingolmeasl/reddata150.1803o571~0%.43.38lU71.569',3.30371.74.'-AstheinputdataweremeasuredInvarioustime161.13360.54880933.~t>D.37I 529~43.2t>0371.64intcl\als.theyneedtobepre-processedandappro-priatelyfor170.83980.5273o955' "037Ut>9553.330391.5adaptednextcomputations.Computed:J.:J_inll~l\alsbetweenindividualmeasurementsandmiss-180.62~10.50660983370.381.299.33430.41.33ing\alueshaveheeninterpolatedsoastoreflectinthebestwaythc\aluesexpectedinthe consideredtime.497
54.5respecttothepossibleapplicationofchemotherapeu-tics.Eventhestateofleucoc)tes(alongwithotherparameters.ofcourse)determineswhetheritispos-sibletogivethepatientthetherapeuticsornot.43.5I5 -3+---.----tt---~---;----__ft4.5Fig.3GraphicalrepresentationofthelinearapproximationofselectedorganismparametersEry--HKG--LE--400300200100O....:...-ll..L~.l1.....ll-...l....:...:>.L..lo.-'-'--.L.....l"----o-0.541.5--++-+--+-13.50.5322.5----ft---fl------tt---3002001000.5oo-0.5--v--cP22.51.55--v--CP--5--LE4.5Fig.5 Parametersoftheinputtherapeuticsandtheresponseoftheorganism- leucoc)tes3.3.Searcho/Iineari=ationintervalsAscriousdrawbackofthedescribedmethodisthesearchforlincarizationintervals.i.e.specificationoflimitstorindividualintervals.Inpracticcthisprob-lemisbcingsolvedinvariousways.Asmedicalprocessesarerclativelyslowa stepwisechangingthelimitsofdomainsandrangesofindi\'idual\uriableseansohethisproblem.Next.a modeliscalculatedforallobtainedintenals.anda simulationiscarriedoutwiththealreadya\ail-ablesamples.Individualmodelsarecomparedusingtheclassicalmethodofsummingsquareddiftcreneesbetwcenthemeasuredandthecalculated\·alues.Usinga graphicalrepresentationofindi\idualinput\'ariabksandmoditied\aluesofsquarederrorsumsf<lreachmodelwecanfindtheintenalswiththeleastdifferencebet\\eenthemodeloutputsandthereal\ alues.Table3shows\alucsofsomelimits(hrl.hr2.hr3.hr~andthc"sqc"-sumofsquarederrors).F300100200--v--CP-Ery--HKG--LE4~\'Y'3.53J2.5w21.50.5oo-0.5Fig.~.QuadraticapproximationofselectedparametersoftheorganismFormodellingbloodparamctersweha\cchosenoneofitsmostimportantrepresentatives.namelythenumbcrofleucoc)tesindicatingpatient'sstatcwith498
Tab.)Sumofs9uarederrors(Sge)asafunctionoflimits4.APPLICATIONOFGENERATEDMODELSForthenextanalysisa modelwiththelimits(hrI.hr2.hr3.hr4)= (0.3:0.3:0.7:0.5)hasbeenchosen.MathematicalmodelandsimulateddataareinFig.6.Fig.6SimulationofLEparameters--v--cp--8pchr110.120.130.140.150.160.370.180190.1100.1110.1130.1140.1150.1160.1170.1180.1190.1Basedontheanalysisofmeasureddataandsimula-tionofthepossiblepatient'sstate(Fig. 6)itispossi-blctoassumethatthepatient'sstatewillremainonalowlevelfixa long-timeandhecannotbegi\entherelevanttherapeuticsduetoit.Inastandardtreatmentthedoctortakesthebloodsamplesseveraltimesandafterhm'inggatheredlong-termresultshedecidestoskiponecycle.Someofthefollowingfactsunderliesucha decision:- oncheckingparametershesupposedthatthepa-tient'sstatewillimprove.howeverthisdidnothap-pen:- therewasa possibilityofhelpingbyothermeans.howe\errelati\elymuehtimehaspassedsincethenandtherdoresucha stimulationisalreadyinappro-priate.Ofcourse.therearea lotofotherfaetstobeconsid-eredina physician'sdecisionmaking.Simulationofpatient'sstatebeforestartinganewcuringcyclecouldbeonepossibletoolforhelpinghisdecisiontaking.Theobtainedmodelshowsthattheorganismparametersarcrelati\elylowandthepatientisnotabletocreatea sufficientamountofnecessarysu~-/.2.Simulationo/themedicaltreatment-/.1.Problems0/patient'streatment.Applicationofsometherapeuticsmaybringaboutaconsiderableworseningofsomehumanorganismparametersandthustheirintakeispossibleonlyundertheassumptionthatthepatienttoleratessuchatreatment.Oneofsuchproceduresistheapplicationofcytostaticsincuringoncogenousdiseases.Appli-cationoftherapeuticsispossibleonlyiftheleuco-cytesparametershavereachedsomespecifiedvalue(2000).Tofindoutthepatient'sactualstateitisnecessarytotakehisblood.evaluatetheparametersandtocontinuethetreatmentundertheassumptionthatthestateissufficientlygood.Iftherearelowleucocytes.thebloodtakinghastoberepeatedafter1-3days.Suchfrequentbloodtakingsdisturbthepatient.andmakehimsuffer.Takingintoaccounthisoverallstate.suchalargenumberofbloodwith-drawalscannotcontributetoanimprovedrecovery.Ontheotherhandfrequentbloodtakingsareimpor-tantbecauseitisnecessarytoapplythetherapeuticsinthespecifiedtime(necessitytokeepthecurativeprocedures)orwitha leastpossibledelay.Itusetohappenthatdespitenumeroustests.thepa-tient'sstatedoesnotimproveandinordertokeepcertaincurativeproceduresitisnecessarytoapplysupportingandstimulatingpharmaceuticals.Itisespeciallythedecisionmakingaboutwhethertomakethepatientsufferorstimulatetheorganismallthesame.whichcanbefacilitatedbytheproposedparametermodel.FromFig.6itisevidentthatinthelast250-300daysofcuring.theleucocytes(LE)numberdropsandatthetimeoftherapeuticsapplicationitevendoesnotreachthelowerlimit2.oLE--Lem0.410.610.831.121.47hr4sko2.40.392.40.581.40.710.41.080.81.380.22.442250.497.30.41241.22820.63400.63881.22.60.41.21.22hr2hr30.50.70.90.40.50.70.110.510.10.40.50.70.30.10.70.10.310.110.710.110.90.70.70.70.30.70.710.50.1JjVV~-.\[\l\l\1\\1\l\~\."-\.\1002003004-0.5o0.52.51.54.524353.5499
stances.Shouldthesefactsbeconfinnedbythere-sultsfromthefirstbloodtest.thephysiciancancon-siderapplicationofstimulatingtherapeutics.suppon-ingthisdecisionbya simulationonthemodels.Ina realsituationwehavefirstsimulatedtheimpactofthebloodtransfusiononotherparameters.Trans-fusionwascarriedoutalreadyatabouttheIOOthdayofthecuringprocedure.SimulationresultsunderstimulatorapplicationaredepictedinFig.7.Basedonobtainedresults(growthoftheLEvalueabove3)correctnessofsucha decisioncouldhavebeenan-ticipated.54.543.532.521.50.5o-0.5~.I-l--JVIII'"IVV~l\l\1\l\[\.....--l\\\.\.1002003004oCenainly.theintervallinearizationmethodisnottheonlysuitableonebuthopefullyitisnotthelastoneappliedinmedicine.anditsimplementationwillstimulateapplicationofothermethodsaswell.REFERENCESS.A.BilingsandW.S.F.Yoon:Piecell'iselinearnon-linearsystemidentification.InternationJournalofControl,1'01-16.,\'.1.1987HarsanyiL..KultanJ.:IdentifikiJcianelinearnychsys/(?mo\'metodouinten'alm'ejlineari=acie.JournalofElectricalEngineering.1-'01.-11...\'011,1990.str.825-836.HarsanyiL..KultanJ.:Alethod~fselectil'eforgellingfornonlinearsystemidentificationJournal({fElectricalEngineering.,/'01-13,,Vo7.207-210.Bratislava,1992Yesel~'Y..KultanJ.:Regulatorsynthesisfornonlin-earsystems.TechnicalreportEFSI"ST.De-partmentofAutomaticControlS)'stems.1992--v--cp--5LE--LemFig.7SimulationofLEparametersanerapplicationofa stimulatorThenthetransfusionwascompletedandthew'holecurati\ecyclewascompletedsuccessfully.Ofcourse.thee.'\perienceofphysiciansplayedanimponantroleinthewholetreatmentprocessas\\ell.andtheproposedmodelhassef\edonlyasonesupportingtoolforthedecision-making.CONCLlJSIOTheaimofthispaperwastopresenta practicalap-plicationofoneofthedynamicsystemsidentifica-tionmethodsinmedicine.Atthesametime\Iewantedtoemphasizethatimplementationofidentifi-cation.modelling.simulationandcontrolmethodsinthisfieldnotonlyimprmesthetreatmentprocessbutcanrem\welotofacheinthistreatmentas\Iell.andenablesamoree.'\actdecisionmaking.onene\'ensayingthepatient'slife.500