外文文献翻译压电传感器测定动脉脉搏波速度电子教案.docx

外文文献翻译压电传感器测定动脉脉搏波速度电子教案.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电子教案

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,