1、978142446497510$26.00?2010IEEE137620103rdInternationalConferenceonBiomedicalEngineeringInfmatics(BMEI2010)ADesignofNoninvasiveTesterofHumanArterialOxygenSaturationWangYongqing，ZhangZhipeng，WangHongrui，LiuXiulingSunRongxi

2、a(CollegeofElectronicnoninvasivetestingoxygensaturationcompoundsignalmovingaveragemethodI.INTRODUCTIONThearterialoxygensaturationisaimptantindexwhichestimateswhetherhumanbodycirculatysystemtherespiratysystemappearshicap[

3、1].Thebloodflowsthroughthelungsintheperiodicdiastolesystole.Acertainamountofreducedhemoglobininbloodiscombinedwithoxygeninthealveolusthusbecominghematoglobulin.Theoxygeniscarriedintocapillaryvesselthentheoxygenisreleased

4、fprovidingmetabolismofthecelltissuewithenergy.Atpresentthemeasurementmethodofarterialoxygensaturationisdividedintoinvasivemeasurenoninvasivemeasure.Becauseintheinvasivemeasurethetestingresultlackstimelinesscausingsufferi

5、ngtopatienteasilytheoperationmethodistoocomplicated.Sothenoninvasivemeasurewhichacterizedbycontinuityrealtimesafetygraduallyreplacestheinvasivemeasure.II.MeasuringPrincipleofArterialOxygenSaturationThenoninvasivetesterof

6、arterialoxygensaturationisdesignedaccdingtotheacteristicsthatthelightabsptionofarterialbloodvarieswithpulse.Becausethearterialpulseswaspresentperiodically.Thelightabsptionspectrumofarterialbloodisapulsatingchangewhichisc

7、alledpulsecomponent(namelyACsignal△I).Whenthesystoleispresentedthemostbloodvolumeispresentedtheminimummeasuringlightintensityisshown.Whenthediastoleispresentedtheminimumbloodvolumeispresentedthemostmeasuringlightintensit

8、yisshown.Butthelightabsptionintensityisregardedasaconstantcomponent(namelyDCsignalI)byotherhumantissuesuchasvenousbloodmusclecutis.Asshowninfigure1.Figure1.AbsptionCurveoftheRaybyHumanTissueThearterialoxygensaturationmea

9、nsthepercentofthecontentofthehematoglobulininthecontentofallincpableoxygenintheblood[2]namely:%10022=HbHbOHbOCCCS（1）WhenthelightofspecialwavelengthsirradiatesthetestingbodypartaccdingtotheLambertBeerlawthelightabsptionin

10、tensityismainlyrelatedtothecontentofhaemoglobinintheblood[3]theintensityofthetransmittedthemeasuringlightintensityIDCImaxIminIAC1378frequencyof200Hz(asshowninfigure4(b))drivesredLEDD1infraredLEDD2alternantirradiance.AtT1

11、Q1Q4isinconductingstatesotheredLEDD1isradiant.AtT3Q2Q3isinconductingstatesotheinfraredLEDD2isradiant.AtT2T4D1D2areallnotradiant.Itisrealizedthatthetestingsourcewksperiodicallyinthefollowingder:redlightextinctioninfraredl

12、ightextinction.(a)(b)Figure4(a).TheDrivingCircuitofTestingSourceFigure4(b).DSPSequenceControlSignalB.PhotoelectricIVConversionAmplifyingCircuitThetesterusesthesiliconphotocellasphotoelectricconversionelement.Thespectralr

13、esponserangeofthesiliconphotocellis400nm~1100nm[5]itspeakwavelengthisabout850nm.Sothesiliconphotocellsmatchethetwothelightsourceswiththepeakwavelengthat850nm940nm.ThesiliconphotocellIVconvertwhichoftheinputimpedanceisequ

14、ivalentto0isconnectedtokeepthesiliconphotocellinaquasishtcircuitstateasshowninfigure5.InderfthatthechangeislinearbetweentheshtcircuitcurrentilluminationintensitythetesteradoptsreversedinputtypeofIVconversioncircuittoconv

15、ertthecurrentsignalwhichhasbeenmeasuredbythephotocellintovoltagesignal.Itisknownthatthepulseoxygensaturationsignalisaantiphasesignalaccdingtofigure1.Theantiphaseamplifyingcircuitcanconverttheoxygensaturationsignalintoinp

16、hasesignal.Asshowninfigure5amongwhich71RiUBTO??=(7)Figure5.PhotoelectricIVConversionAmplifyingCircuitC.PrimarySecondderLowPassFilterVariouskindsofstraylightinterferencesignalisinterwovenwiththeredlightinfraredlightsignal

17、whichisreceivedbythephotocell.Themainfrequencyrangeofhumanpulsesignalis0.1Hz~10Hz[6].Sothepowerinterferenceotherhighfrequencyinterferencesignalwhichisabove50Hzisattenuatedfarthestbylowpassfilterwiththecutofffrequencyof20

18、Hztheoxygensaturationcompoundsignal(UDCUAC)isextracted.Becausetheactivefilterisacterizedbythosefollowingadvantagestheopenloopgainishighthefrequencyadjustmentrangeiswidethefrequencystabilityitsprecisioniswell.Consequently

19、thetesteradoptstheseconddervoltagecontrolledvoltagesourcelowpassfilterasshowninfigure6.Figure6.SecondderLowPassFilterAmongthemthecutofffrequencyHzRCfc2021==π(8)GetC1=C2=C=0.1μthenR10=R11=67.8K?.Becausetheamplitudefrequen

20、cyacteristicisthebestofallwhenQ≈0.707.SoAup=3－1Q≈1.586.because586.1189==RRAup(9)Accdingtotheprincipleofmaintainingabasicsymmetrybetweentheexternalconnectionresistanceofnoninvertinginputendthatofinvertedinputendinthesecon

21、dderhighpassfiltercircuititdeducesthat989810RRRRR=(10)Solvingthesimultaneousequationswhichiscomprisedoftheequation(9)(10)itgetsthatR8=5.7K?R9=3.3K?.D.AntiRossiCircuitofRedInfraredCompoundSignalTheoutputoxygensaturationsi