3a-Wearable sensors for physiological signal measurement.pdf

Wearable sensors for physiological signal measurement

1. Wearable Technologies & IoT (CHI3005)
Module-3
Wearable Sensors For Physiological Signal
Measurement
Dr.Pratosh Kumar Pal
Assistant Professor, SCSE
VIT Bhopal University
Bhopal-Indore Highway, KothriKalan, Sehore, MP

2. ▪Itprovidesanoverviewofwearablesensorsforthemonitoringofphysical
andphysiologicalchangesindailylife.
▪Manytypesofbiosignalsneednotbemeasuredcontinuouslyfor24hours.
▪Thereasonsformonitoringarenotlimitedto“healthchecktofindanysigns
ofabnormality,”butvarywithapplication.
▪Partsofclinicalmonitoring:
▪checkingtheleveloffitness
▪acquiringchangesindiseaseconditionindailylife
▪asapartoftheclinicaldiagnosisand/ortreatment
▪Intheworkplace“monitoringofhealthconditiontopreventaccidentscanalso
beanimportantaspectofambulatorymonitoring.
Introduction
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3. Classification of Biological Signal Monitoring
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4. ▪Figureshowsthecurrentsituationofa
wearabledigitalbiologicalmonitoringdevice
anditsnearfuture.
▪Smartphonesarewidelyused,anditis
possibletotakeadvantageoftheircapabilities
formobilehealthmonitoringbyadding
biologicalsensors.
▪Here,thesensorisinterfacedtothe
smartphonethroughapopulardigitalinterface
suchasUSB.
▪Hence,digitizationofbiologicalsensordatais
important.
Mobile Digital BiosignalMonitor
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5. ▪Frequentlyusedbiosignalsensorsforhealthmonitoringindailylifeare:
1)ECGMonitoringbyNon-ContactElectrodes
2)BiosignalSensorsforCardiovascularSystemMonitoring
3)BiosignalSensorsforSleepMonitoring
4)WearableSensorsforPhysicalActivityMeasurement
Types of Frequently used Wearable Sensors For
Physiological Signal Measurement
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6. ▪Electrodesareessentialinthemeasurementof
bioelectricphenomena,suchasheartactivityand
muscleactivity.
▪Theskinelectrodecanberoughlycomparedtoa
resistorconnectingskinwiththesignalcable,
althoughtheactualcircuitismorecomplicated.
▪Foracapacitivelycoupledelectrode,acapacitoris
thecouplingcomponent.
▪Foradryelectrode,aparallelresistorandacapacitor
comprisethecouplingcircuit.
1)ECG Monitoring : Types of Electrodes
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7. ▪Needleelectrodes:Invasiveandimposesunnecessarypaintotheuser.
Types of Electrodes:
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8. ▪Theprincipleofthiselectrodeis
thatchargesaregeneratedonthe
metalsurfaceinresponsetothe
electricalfluctuationsoccurringat
adistance.
▪Inpractice,acapacitorcanbe
assumedbetweenmetalplates
andelectricalbodysignalsource
suchastheheart.
▪Ifinputresistanceofpreamplifieris
largeenough,andcapacitanceis
smallenough,i.e.,C
in<<C
E;C
G,
R
in>>1,then as
Measurement Principle of the Capacitively Coupled Electrode (1)
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9. ▪Inputimpedanceandcapacitanceoftheop-ampsusedforsuch
measurementsare10TΩand1pFmuchgreaterthanthatofacommonly
availableop-ampsuchasIC741(2MΩand1.4pF,respectively).
▪Limitation:
▪staticelectricitygeneratedbythefrictionbetweenclothesandelectrodesaccumulateon
thesurfaceoftheelectrode,andtheamplifier’soutputvoltageisoftensaturated.
▪thecapacitorformedbetweenskinandelectrodeshouldbeatleast30pFbasedonour
experiencesorthebiosignalwilldisappearintheenvironmentalnoise.
▪Toavoidamplifier’soutputvoltagesaturation,aresistorisinsertedbetween
theelectrodeandgroundtoreleasethisstaticcharge.
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Measurement Principle of the Capacitively Coupled Electrode (2)

10. ▪Figure(a)&(b)showthemeasurement
withbipolarleadsusingadifferential
amplifier,andallelectrodesarethe
capacitivelycoupledtype.
▪NogroundelectrodeusedinFigure(b).
▪Figure(c)showsthemeasurementwith
asingleelectrodeandasingle-ended
amplifier.
▪WhilethesignalinFigure(c)isnoisy,
thepeaksofR-wavearestilldetectable.
▪Heartactivitycanbeacquiredbyone
metalplatesetnearthehumanbody.
ECG Monitoring by Non-Contact Electrodes (1)
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11. ▪Anelectro-conductiveclothisplacedonthe
surfaceofthedriverseatasanindirect
electrode,i.e.,capacitivelycoupledelectrode
andametalbandisattachedaroundthe
steeringasagroundelectrode.
▪Theenvironmentinsidethecarisnoise-less
electricallyasinashieldedroom,anda
single-endedamplifiercanbeused.
▪Thetopplotistheplotwhenthecarwason
abumpyroad,andthebottomplotiswhen
thedriverturnedthesteeringwheel.
▪NoisecontaminatestheECGdatabecause
thegroundisunstable.
ECG Monitoring by Non-Contact
Electrodes : While driving
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12. ▪Sensorsformeasuringthechangeinphysiologicalconditionindailylifewill
bedescribedinthissection.
▪Awiderangeofbiosignalsshouldbemeasuredin“physiology,”butnotso
manykindsofbiosignalsarenecessarytobemonitoredindailylife.
▪Importantbiosignalstobemeasuredbysensorsare:
a)Measurementofbloodpressure
b)Pulsevolume
c)Bloodflow
d)SPO2(saturationofperipheraloxygen)
e)Respiration,and
f)Bodytemperature
2)BiosignalSensors for Cardiovascular System Monitoring
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13. ▪Bloodpressure,i.e.,thepressureintheartery,pulsatesperiodicallyin
responsetotheheartbeat.
▪Hypertensionisthecauseofcardiovasculardiseases,andisconsideredone
ofthethreemajorunderlyingcausesforstroke,togetherwithdiabetesand
hypercholesterolemia.
▪Therefore,theimportanceofmeasuringbloodpressurehasbeenrecognized
foralongtime,anditisconsideredoneofthefourclinicalvitalsigns.
▪Bloodpressuremeasurementisdividedintotwomethods:theindirect
methodtomeasurethebloodpressurewithoutinvadingthebodyandthe
directmethodtomeasurebyinsertingacatheterintoanartery.
▪Thedirectmethodisusuallynotsuitableforroutinebloodpressure
monitoring.
a)Measurement of Blood Pressure
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Various Indirect Blood Pressure
Measuring Methods

15. ▪Figureshowsthemeasurementprinciple
ofthe“volumecompensationmethod.”
▪Acuffisalsousedinthismethod,butthe
cuffpressuregeneratingcircuitanda
controlcircuitforpreciselycontrollingthe
cuffpressurearedifferentfromthewidely
usedauscultatorymethod.
a)Measurement of Blood Pressure (1)
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▪BloodvolumeinthefingerisdetectedbytheopticalsensorandLEDandthe
bloodvolumeiskeptconstantbyvaryingthecuffpressure,whichshouldmatch
thevariationofbloodpressure.

16. ▪Figure(a)and(b)introducesablood
pressuremeasurementmethodusinga
pulsewaveandECG.
▪Therelationshipbetweenflowrateandits
velocityisusedastheoperatingprinciple
ofthismethod,whichiswellknowninfluid
dynamics.
a)Measurement of Blood Pressure (2)
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▪Forexample,waterflowrateinawaterpipeisproportionaltowaterpressure.
Therefore,bloodpressurecanbeestimatedfromthevelocityofbloodflow.
▪ThebloodflowvelocitycanbeknownfromthepeaktimeoftheRwaveofECG
indicatingthetimingofbloodflowfromtheheartventricle,andthepeaktimeof
thepulsewavearrivaltimeofthebloodflowtotheperiphery.

17. ▪Figureshowstherelationshipbetweenthe
pulsewavepropagationvelocityand
systolicbloodpressure.
▪Asshowninthisfigure,thepropagation
velocityofthepulsewaveincreases
accordingtothebloodpressure.
a)Measurement of Blood Pressure (3)
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▪Limitation:Asarteryisactuallyanelasticbody,anditselasticmoduluschanges
continuouslywhichcansignificantlyaffectthebloodflowvelocity.
▪Thismethodisnotverypracticalfordailymonitoring,butitcanbeusedfor
chronicmonitoringwhenoneisonlyinterestedinthechangesinblood
pressureandnotitsactualvalue.

18. ▪Thepulsewaveiscomposedofapressurewave
generatedbythecontractionofheartventricleand
itsreflectionfromtheperiphery,whichisdifferent
fromthebloodflow.
▪Blood-flowvelocityintheaortaisabout1m/sec,
andthevelocityofthepulsewaveisabout10
m/sec,i.e.,10timesfasterthanbloodflowitself.
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▪Theactualpulsewaveismeasuredasthevolumechangeofbloodatthe
capillariesusingnear-infraredlight.
▪ItconsistsofLEDtransmitterandaphototransistoronoppositeside.
▪AshemoglobinintheRBCabsorbsinfraredlightwell,asignalsynchronized
withtheheartbeatcanbeobtainedasoutputofthephototransistor.
b)Plethysmogram

19. ▪Pulseoxymetrywasdevelopedusingextinction
coefficientphenomenonofdeoxyhemoglobinand
oxyhemoglobintomeasuretheoxygensaturationin
theblood.
▪Inthissystemtwosourcesoflightofdifferent
wavelengths,i.e.,infraredlightof910nmandred
lightof660nm,areused.
▪Theoxygensaturationinthebloodcanbeestimated
fromthedifferenceinabsorptionofthesetwo
wavelengths.
▪Theratiooftheamplitudesofpulsesatthesetwo
wavelengthsdeterminetherelativeoxygen
saturationofhemoglobinintheblood.
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c)Oximeter

20. ▪Respirationrateisclinicallyimportantasit
isalsooneofthefourvitalsigns.
▪Breathingmeasurementorrespirometryin
dailylifeisclassifiedbytwodifferent
categoriesofmeasurement.
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▪Oneisthemeasurementindailyactivitiessuchasduringworking,andthe
otheristhemeasurementofbreathingduringsleep.
▪Therespirationsensorisdifferentaccordingtothepurposeofthe
measurementandwhereitisbeingdone.
▪Respirationmeasurementbandiscomposedofanelastictubefilledwith
conductiveinkandastring,anditiswrappedaroundtheribcagetorecord
changesinthechestcircumferenceduetobreathing.
d)Respirometry

21. ▪Athermistorissetatthetipofthenasalrespiration
sensor.Thethermistorsensesthechangeinthe
temperatureduetoairintakeandexhalation.
▪Bothsensorsmeasuretheactualrespiration
waveformfromwhichtherespirationrateandapnea
canbedetermined.
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▪Therefore,thesesensorsarepopularindailymonitoring.
▪Abiometricsensorsheetwasdevelopedtomonitortherespirationduring
sleep.
▪Respirationmonitoringduringsleepshouldbeunrestrainedandunconscious
andthesensorshouldbesoft,flexible,andcanbeinstalledinapilloworunder
thesheets.
d)Respirometry: Thermistor sensors

22. ▪Temperatureisthethirdofthefour
vitalsignsinclinicalmedicine.
▪Temperaturesensorsareclassified
intocontacttype,e.g.,thermistor
andthermocouple,andnon-
contacttype,whichsenses
infraredlightemittedfromthebody
surfacebasedontheprincipleof
blackbodyradiation.
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▪Thethermistorutilizesthepropertythatresistanceofsemiconductorormetal
oxidechangeswithtemperature.
▪Anearphone-typeeardrumtemperaturemonitoringdeviceisnowavailable
commercially.
e)Measurement of Body Temperature

23. ▪Humanbeingsspendone-thirdofeachdaysleeping,andsleepisessentialfor
peopletomaintainhealthyphysicalfunctions.
▪Dailylong-termmonitoringofphysicalconditionduringsleepandsleepquality
isimportantforhealthmanagement.
▪Sleep-monitoringsystemshavebeendevelopedinrecentyearsthatare
usefulformanagingvitalphysiologicalsignals.
▪Thissectionintroducesfollowingsensors:
a)ballisticcardiogram
b)non-contactECG
c)sheettyperespiratoryandbodymotionsensors
d)videocameramonitoring
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3)BiosignalSensors for Sleep Monitoring

24. ▪Methodsdevelopedtodateinclude:
▪non-restrictivemeasurementofrespiratoryandheartratesfromtheinternalpressure
changesinanairmataffectedbybodymotionduetorespirationorheartactivity,and
▪non-restrictivemeasurementofrespiratoryandheartrateusingsheetsorpillowswitha
wire-shapedrespiratorypickupsensorattachedtoanairmat.
▪Thesemethodsareknownas“ballistocardiograph”.Itisamethodof
measuringdelicatebodymotionscausedbyheartactivityandbloodmovement
inbloodvessels.
▪Limitations:Itisinfluencedbybodyweightandmotion,movementoforgans
insidetheabdomen,andthedistortionoffatandmusculature.
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a)Ballistic Cardiogram

25. ▪Canfacilitatetheearlydiscoveryofavarietyof
illnessesandhealthconditionssuchas
▪Highbloodpressure,diabetesandobesityare
accompaniedbyadecreaseinheart-ratevariability,
▪psychologicalstress,lackofexerciseandother
factorsarealsoknowntoaffectheart-ratevariability.
▪Anon-restrictivemeasurementmethoduses
onlyanaccelerationsensorinstalledinmiddle
layerofadownquilt.Easilyusedathome.
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▪Thissystememploysapiezoelectricaccelerationsensorandwassetasits
sensitivityaxis(z-axis)orientedtotheEarth’sgravity.
▪Thesensitivitydependsmoreonthedistancefromthehearttothesensorthan
onthesubject’sposition.
b)Non-Restrictive Heart-Rate Measurement

26. ▪Principle:Basedonelectrostaticcapacitance.
▪Acapacitorisformedwithaconductingelectrodeonbothsidesofaninsulatingsheet.
▪Displacementoftheminutepressure,whicharisesfromahuman’sheartbeats,respiratory
movement,andbodymovement,ischangedintothecapacitancechangebetweenthe
electrodes.
▪Inordertodetectthecapacitancechangebytheminutedisplacementoriginatingfroma
heartbeatwithsufficientaccuracy,theLCoscillationtypedetectorcircuitisused.
▪Thiscircuitchangesminutevibrationsintothefrequencydomain.
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c)Sheet Type Respiratory and Body Motion Sensor

27. ▪Wearingsomesensors,evenadults
feelconstrainedandtied-up,andfor
childrenitisacauseofsignificant
stress.
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▪Unconsciousmonitoringofdailysleepusingvideocameraandimageanalysis.
▪Thismethodmonitorssleepstagewithonlybodymovementobtainedfromvideo
imagesrecorded.
▪Thebodymovementsduringsleepweredividedintothefollowingthreestatesby
Fukumotoetal.:twitchmovements(TMs),localizedmovements(LMs),andgross
movements(GMs).
▪GMsindicatethebodymovementsthatoccurforalongertimeperiod,suchas
turningoverinbed,whichusuallycontinuesforover2sec.
▪GMsaremostdirectlyrelatedtothesleep-wakecycle.
d)Video Camera Monitoring

28. ▪Physicalactivityindailylifeisthemostpreferablemonitoringaspectbecause
itisthenatureofhumanbeingstomove,andourdailyactivitiesareclosely
relatedtoourhealth.
▪Therearemanykindsofmotionsensorstomeasurephysicalactivities,sucha
accelerometers,gyrosensors,GPSsensors,etc.
▪Thissectionintroducesfollowingnewsensors:
a)FlexibleGoniometer
b)JointMotionMeasurementUsingTwoAccelerometersSetNearBothSidesoftheJoint
c)Flexibleforcesensorsduringwalking
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4)Wearable Sensors for Physical Activity Measurement

29. ▪Morimotodevelopedaflexiblegoniometerasanarticularmotionsensorthat
doesnotmakeuseofarotaryencodertomeasurehumanarticularmotion.
▪Thegoniometerhasastraingaugeattachedtobothsidesoftheflexibleplate
betweentheendblocks.
▪Itgeneratesavaluethatdependsontheangleθbetweenthetwoendblocks.
▪Itmeasuresthevalueofθbasedontheextensionandcontractionmovements.
▪Anaccuratemeasurementoftheanglescanbemadebysettingupabridge
circuitusingfourstraingauges.
▪Theuseoftheflexiblegoniometercanbeextendedtomeasurethebi-axial
rotationalanglesbyattachingstraingaugestothetopandbottomsides,as
wellastheleftandrightsidesoftheflexiblesquarerod.
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a)Flexible Goniometer for Articular Motion (1)

30. ▪(b)illustratesthe
configurationandthe
operatingprinciplesof
asingle-axisflexible
goniometer.
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a)Flexible Goniometer for Articular Motion (2)

31. ▪(a)istheschematicrepresentationoftheprincipleand
theequipmenttomeasuretheanglechangeofaone-
axisjoint,suchastheelbow.
▪Inthismethod,twoaccelerometersaresetonbothsides
ofthejointandascloseaspossible(“both-near-sides”)
toitsjointaxis.
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▪Nextmethodistomeasurethree-axisjointmotion,suchasa
shoulderjoints.
b)Joint Motion Measurement Using Two Accelerometers
Set Near Both Sides of the Joint

32. ▪Whilewalking,theexternalforceofthegroundactsonapersonthroughtheirfeet.This
forceiscalledthegroundreactionforce.
▪Thisgroundreactionforcemustbemeasuredforthepurposeofkinematicgaitanalysis.
▪Forthispurpose,afootsolepressuredistributionsensorisdeveloped.
▪Forthesesensors,theelectrodebandsareprintedonthetopandthebottomofaflexible
sheet,sothattheyintersectwitheachother.
▪Aconductiveinkisappliedonthesurfaceofalltheelectrodes.
▪Whenpressureisapplied,theinkiscompressedandtheresistancevalueforthe
conductiveinkinthatareadrops.
▪Thisismeasuredasthevariationinresistancebetweengridendsandcanbeobtainedfor
eachgridpointaspressurevalues.
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c)Force Monitoring During Walking