外文文献翻译压电传感器测定动脉脉搏波速度.docx

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