外文文献翻译压电传感器测定动脉脉搏波速度.docx
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外文文献翻译压电传感器测定动脉脉搏波速度.docx
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外文文献翻译压电传感器测定动脉脉搏波速度
Piezoelectricsensordeterminationofarterialpulsewavevelocity
Arterialpulsewavevelocity(APWV)isameasureoftheelasticity(orstiffness)ofperipheralarterialbloodvessels.ThepulsereferredtoherewillbethepressurepulseasopposedtotheflowpulsemeasuredbyultrasoundDoppler.
Thepressurepulsevelocityvariesovertherangefromabout12ms−1to
15ms−1instiffperipheralarteries,whereasinnormalarteriesithasavelocityintherangeof7to9ms−1。
Theaimofthisprojectwasthedevelopmentofafastandeasytousesystemforthedeterminationofperipheralarterialpulsewavevelocity。
TheprincipleofthePWVmeasurementisbasedonsimultaneousmeasurementoftwopulsewavesattwodifferentpositions,suchastheradialarteryatthewristandthebrachialarteryjustabovetheelbow.Bydeterminingthepulsetransittimebetweenthesepointsandthedistancemeasuredbetweenthetwolocations,pulsewavevelocitymaythenbecalculated。
Thepressurepulsedetectionisdonebyusingtwopiezoelectricsensorswhichgenerateameasurablevoltageattheoutputcontactsiftheyaremechanicallydeformed.Thedeformationproducedvoltageisfirstamplifiedandfilteredandthendigitalizedwithadataacquisitioncard.Theanalysisofthedataobtainedfromthesensorsincludesafilteringprocess,thecalculationofthePWVwiththreedifferentmethods—foot-to-foot,cross-correlationandpeak-to—peak-andthedeterminationofthearterialpulserate.
Extensivemeasurementswithhumantestsubjectswerecarriedouttooptimizethetechniquesofdataacquisitionandanalysis.Forexample,itwasfoundthatthebestprocedurewastoholdthesensorsinplaceusingelasticstrapsalone。
Thedataanalysiswasupgradedwithanadditionalsoftwaremodule,whichdeletes,ineffect,outridersorinvalidmeasurements.Withtheoptimizedsystem,aseriesinvolvingeighttestsubjectsranginginagefrom22to32yearswascompleted(allnormotensive).Thearterialpulsewavevelocitiesdeterminedcoveredarangefrom6ms−1to12ms−1,withanaveragestandarddeviationoflessthan2.5ms−1forindividualresults。
Theseareslightlyhigher,butclosetopublishedAPWVdata。
TheresultsshowedthatreproducibleresultscanbeobtainedwiththeexistingPWVacquirementandanalysissystem.
Themeasurementofarterialpulsewavevelocity(APWV)isoneofthemethodsusedtomeasurephysiologicalchangesinperipheralvasculardisease。
Othersincludepressurepulsecontour,arterialelasticity,pulsatileflow,complexvascularimpedanceandcardiacwork。
Therehavebeenmanyinvestigationsoverthepast30yearsorsotorelatechangesinageandprogressofarterialdisease,tovesselpathologyanddistensibilitybasedonthepropagationcharacteristicsofthearterialpulse(MalindzakandMeredith1970,McCormack1981,Perssonetal2001,Ramsey1995,Wilkinson1998).Theyhaveonlybeenpartiallysuccessfulfromaclinicalpointofview,mainlyduetothedifficultyincontrollingtheeffectsofpatientparameters(autonomicsystem,patientmovement,etc)。
Earlyon,themethodsofdeterminingAPWVinvolveddirectinvasivemeasurementofthepulsepressureattwopointsalonganarterialsegmentandmeasuringthetimetakenforthepulsetotravelthelengthofthesegment。
Suchinvestigationshadtobelimitedtoanimalsusuallydogs.
Thesensortechniqueusedinthisworkinvolvesthepiezoelectriceffectinpolyvinyllidenefluoride(PVDF),whichproducesanoutputvoltageinresponsetomechanicalpressureonthematerial。
ThreemethodsofAPWVdeterminationareused:
foot—to-footAPWV;peak-to—peakAPWVandcross—correlationAPWV。
TheFFAPWVandCCAPWVmethodsarelesssensitivetopressurewavereflectionsatbifurcations,etcinthearterialtree,thanthePPAPWVmethod.Meanvaluesandstandarddeviationswerecomputedforallthreemethodsandcompared.
‘Foot-to—foot’APWV(FFAPWV).Thisisbasedonthevelocityofthe‘foot',orleadingedge,ofthepressurepulsewave。
Thearrivaltimesofthefootofthepulsewaveattwopositionsalongthearteryarerecorded。
IfΔtisthedifferenceinarrivaltimesandΔsthedistancebetweenthetworecordingpositions(proximalanddistal),theFFAPWVissimply
FFAPWV=Δs/Δt.
‘Peak—to-peak’APWV(PPAPWV).ThisiscompletelyanalogoustotheFFAPWVexceptthatthepointsofobservationarethetwo(proximalanddistal)peaksofthepulsewaveand
PPAPWV=Δs/Δt。
Apparentpulsewavevelocity(AAPWV).Thepressurewavemayberepresentedasa
Fourierseries,
P(t)=P0+
Pnsin(nωt+θn)
WhereP0isthemeanfluidpressure,nistheharmonicnumber,Pnistheamplitudeofthenthharmonicandθnisthephaseangleofthenthharmonic。
Thespatialrateofchangeofthephaseforoneharmonicbasedontwosimultaneouspressuremeasurementsseparatedbyadistance_salonganartery,isrelatedtotheapparentarterialpulsewavevelocity(AAPWV)bythefollowingequation,
AAPWVn=(Δs)n(f)(360o)/(θx1−θx2)
WhereAAPWVnistheapparentpulsewavevelocityforthenthharmonic,fistheheartrate,θx1isthephaseanglefortheproximalharmonicnandθx2isthephaseangleforthedistalharmonicn.
Cross-correlationPWV.IfthearterialpulseattheproximalmeasurementpositionisrepresentedbythepressuretimeseriesP(x1,t)andthatatthedistalpositionbyP(x2,t)and
thecross—correlationcoefficientisΦx1,x2(τ),thenΦwillhaveamaximumvalueatsometimelag。
Thecorrelationfunctioncanbeexpressedas
Φx1,x2(τ)=(1/T)
P(x1,t)P(x2,t)dt.
Thevalueofτatwhichmaximumcorrelationoccursrepresentsthetransittime(_t)ofthepressurewavefrompositionx1topositionx2alongthearterialsegment。
Fromtheseparationdistanceandtransittimedatathecorrelationarterialpulsewavevelocityis
CCAPWV=(x2−x1)/Δt。
Inthisworknormal,youngtestsubjectswereused,andithastheprimaryobjectivesofoptimizingthemeasurementproceduresandestablishingthestatisticalspreadandmeanvaluesoftheobservedPWVsforaspecificperipheralarterialsegment。
Basedonthis,itisplannedtousethesysteminclinicaltrialsinvolvingpatientswithperipheralarterialdisease(duetodiabetes,hypertension,etc),pre-,duringandposttreatment(pharmaceuticalorsurgical).
Analogueanddigitalcircuitry
Analoguechargeamplifier.Piezoelectricmaterialsconvertmechanicalstressorstrainintoproportionateelectricalenergy,byproducingachargewhensubjectedtomechanicalstress.Thechargeisconvertedtoavoltagebyanoperationalamplifierconnectedasacurrentintegrator,calledachargeamplifier。
Thesignaloutputoftheamplifierisapproximately−30mV。
Itisaugmentedbysignalamplification.
Analoguesignalamplification.Thisisdonebyuseofaninvertingamplifier。
Becauseadcsignalappearsattheoutputofthechargeamplifier,dcoffsetremovalisessentialandisimplementedintheinvertingsumming
Thenextphaseoftheanaloguecircuitryisalowpassfiltertoremovethe50Hznoiseinterference。
Digitalcontrolleddataacquisitionandanalysis。
Adataacquisitionboard(DAQ)isrequiredwhenthetransducersignalsneedinterfacingwithaPC。
Theboardcontains12bitplussignandasuccessiveapproximationandself-calibratinganalogue-to—digital(ADC)converter。
TheADCincursasystematicerrorknownasthequantizationerror。
Itisduetolimitedresolutionandwiththeanalogueinputlimitsetat−5to+5V,thequantizationerroroftheA/Dconverterusedherewascalculatedtobe0.122mV。
ThedataacquisitionandanalysiswasdoneusingLabView—apowerfulinstrumentationandanalysisprogramminglanguageforPCs。
Digitaldataacquisitionprogram。
ThedataacquisitioncircuitperformsallthenecessaryoperationsforthedataacquisitionwithLabView.Thefunctionsofthecircuitinitializethedataacquisitionandreadthedatafromtheacquisitioncard.Thesedataarestoredforlateruseinthedataanalysispartoftheprogram。
LabViewprogramsarecalledvirtualinstruments(VIs)becauseoftheirappearanceandoperationsareanalogoustomeasuringinstruments.AVIthatiscalledwithinanotherVIiscalledasub-VIandisanalogoustoasubroutineintext—basedlanguages。
Thedataacquisition,analysisandpresentationarecomprisedofthreemainprocedures:
(1)DataacquisitioncardtointerfacethehardwaretothePC.
(2)Dataacquisitionprogramtoacquireandstoredatainaspreadsheetfile.
(3)Dataanalysistocarryoutdigitalsignalprocessing,calculatePWVandpresentresults。
PWVCalculation
1.PWVcalculationusingpeakdetection。
TocalculatePWVusingpeaks,thelocationofthepeaksmustfirstbedetermined,sothatthetransittimeofthewavebetweenthepeakscanbedetermined.Itwasfoundthatthebestmethodofpeakdetectionisthederivativeofthecurvemethod.Ifthefirstderivativeofacurveiszero,thenanextremevaluecanexist-either
apeakoraturningpoint。
Itisnecessarytotakethesecondderivativeatthispoint—ifthisisalsozero,thenanextremevalueexists.ThesecondVIusedtodeterminethePWVisPWVcalc,usingthetimeseparationbetweenthelocatedpeaks.
2.PWVwithpressurewavefootdetection.TheVInamedPWVFootdeterminestheleadingedge(foot)ofthepressurewaveattheupstreamanddownstreamlocations。
TheVInamedPWVcalcisagainusedtocomputethePWVfromthetimeseparationbetweenthetwoleadingedges(‘foot—to-foot'APWVorFFAPWV)。
3。
PWVwithcross—correlation.ThePWVdeterminationwithcross—correlationisdonewiththeVInamedCalcPWV。
TheVIisintwoparts:
apartfortheinitializationfunctionandapartforthecalculationoftheCCAPWV.
InallcasesPWVvaluesareassembledinanarrayandthemeanvalue,stan
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