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Development of a Noninvasive Continuous BloodPressure Measurement and Monitoring System

Md. Manirul Islam, Fida Hasan Md. Raf, Abu

Farzan Mtl and Mohiddn Ahmad,2

1Department of Electrical and Electronic Engineering2

Department of Biomedical EngineeringKhulna University of Engineering Technology

Khulna, Bangladesh

Email: moniryahoo@gmailcom.ahmad@eeeketacbd

Abstract- Non invasive continuous blood pressure measurement

system is more useful than conventional blood pressure

measurement systems. The arterial system is extraordinarily wellregulated blood delivery network in human body. It responds

very quickly according to the body movements like altered body

position, or in sudden excitation. So now a day's continuousblood pressure monitoring devices are becoming more essential.

Many types of blood pressure measurement devices are available.Those devices allow only few blood pressure readings in every 0minutes. In contrast to them, we develop a very low cost

noninvasive continuous blood pressure measurement and

monitoring system. It measures blood pressure using volumeoscillometric method and photoplethysmography technique

during a long time period continuously. The rate of change of

blood volume in an organ such as nger has a linear relationshipwith blood pressure. This rate of change of blood volume innger is measured by an optical sensor network which estimatesblood pressure. It displays the numerical value of systolic and

diastolic blood pressure in a mini LC Our developed system is

reliable, accurate and less expensive.

KwodNoninvive ; c ; ; cc mehod;

I. NTRODUCTION

Arterial blood pressre is te force exered by te blood onthe wall of a blood vessel as the heart pumps (conacts) andrelaxes. Blood pressre is coprised of two ners: Systolicpressure (the force of blood in areries as the heart conactsand pses it ot) and diastolic pressre (te force of blood inarteries as the heart relaxes) Understanding circulation wilelp aot nderstanding and accatey easreent of blood

pressure. Circulating blood provides transportation andconication syste between te bo's cells and serves tomaintain a relatively stable ineal environment for optimumcear activit. Blood crcates ecase te eart pps itthrough a closed circuit of blood vessels Blood ow throughte eat and te blood vessel is nidirectiona, owing to tehear om the pulmonar and systemic veins, and out of the

ear into ponar and systeic arteries.

Blood transports O2 and nuients to tissues, and carriesetabolic waste ay o te cells. Te ansporation ismade possible by a pressurized vessel" system, the arteries,

978-1-4673-1154-01/$31.00 01 IEEE

M. A. Rashd3 oh aq b b ak Scool of Electrical Systes Engineering

University Malaysia Peris (UNiMAP)

Peris, Malaysia

E-mail: abdurrashid@unimapedumy

veins, arterioles, vacuoles and capillaries and o of the heartinto ponar and systeic arterial. Te standard arerialbloodpressure cuve

is shown in Fig 1.

Blood pressre easreent syste can be classied into

two categories: (i) Invasive (direct) (ii) Noninvasive (indirect)

Figure 1. Standard terial blood pressure curve [10]

Invasive techniqes of BP easreent involve insertg acatheter into the vascular system which brings high risks ofebolis, tia, ear attack and a cerain percent ofmortalit This method is not convenient for everdayapplication. It will only be sed wen asotey necessar.The non invasive devices are safer, easier to use and can betiized in ost sitations Varios nonvasive etods areavailable like Eleconic Palpation method, Volume

Oscilloetric (VO) etod, Voe Copensation (VC)etod, Arerial Tonoetr etod etc. Aong toseascultator methods, Oscilometric methods are continuous

For conventional cff-spygoanoeter syste teblood pressure readings are not continuous Moreover it useste invasive prciple for blood presse easreentwic isbothersome for patients So we have designed a continuousnoninvasive blood pressre easreent and onitoringsystem The overal cost for this system is also being lowertan present devices.

t is oublesome to monitor a patient's blood pressurecontinosy ding sgeries or in critical sitations singconventional mechanical blood pressure measurement devicesde to ter invasive etod and several flt readings

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ode digital devices. But once our syste is calibrated for apatient it will continuously sow BP readings using noninvasive easureent techniue. Te syste is developed byconsidering volue oscilloetric etod.

Volue-Oscilloetric (VO) etod is based on tevascular unloading principle and te caracteristics of tepressure volue relationsip in te arter. [t eployspotoelecic pletysograpy 1] to detect te volue ofblood canges in te arer. Te VO etod is siilar to teoscilloetric etod except tat it is based on aterial bloodvolue oscillations instead of cuff pressure oscillations. [t caneasure Systolic Presse, Diastolic pressure, Mean ArterialPressure and can be used for long ter abulator onitoring.Te concept for tis volue oscilloetric etod ebeddedsyste is sown in Fig. .

Cover

Figure 2. Photoplethysmography technique in nger.

A ig intensit LED and a LR (Ligt DependentResistor) is placed at te edge of a nger as sown in Fig. .Te resistance of te LR canges according to te ligtintensit received by te LDR. Te cange in resistance isproporional to te cange of blood volue and as well asblood pressure in te nger. Tis teciue is used ere.

Te ain conibution in our work is te use of visible ligtinstead of ina red (IR), ulasonic sound or electroagnetic

wave (EMW). Tese oter sources ave soe adverse effect onuan body if tose are focused continuously on uan bodyfor a long period of tie. Also ligt sources (LED) and sensors(LDR) are ceaper tan previously entioned sources.Moreover we ave ipleented te aplier circuit wit OpAp 741 for ig gain aplication and ATMEGA 8icroconoller for copiling te blood pressure witpreloaded progra. Te icro conoller as a built-in ADC.Terefore no need for extra AD converter and tis results lowcost copact BP easureent syste. Our syste kit can beused in clinics, ospitals and personal usages. [t is ver elplin situations like sger were continuous and accate BP

onitoring is needed.

Autor in , 5] designed a wearable blood pressure sensortat suits into te existing MEMSWEAR platfo. Te bloodpressure easureent was sei continuous and usingpotopletysograpy techniue. Autor used a otor wit asall sensor in te design to easure blood pressure.

Autors in 3] developed a lly autoated non-consciousonitoring syste for oe ealt care. [n te paper, autorsdescribed te structural detail of a newly developed toilet-seatinstalled blood presse easureent syste and soe resultswere obtained by te syste. Autors also described teoutline of a newly designed syste for easuring ydrostatic

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pressure difference between te eart and te easuring site,i.e., tig, during blood pressure easureent.

Autors in 4] offered a novel alteative or copanion toexisting oscilloetric BP easureents tat uses natural a

otions to provide BP easureents. Teir paper presented anew principle for noninvasive blood pressure easureentsthroug a odied volue-oscilloetric techniue ] tateliinates an inatable pressure cuff, and instead takesadvantage of natal ydrostatic pressure canges caused by

raising and lowering te subjects ar. Tis etodologyprovided te advantage of using an absolute gauge pressereference for easureents, and does not necessarily reuireadditional actuation. Autors in 6] estiated te bloodpressure estiation etod was based on a presuption tattere was a singular relationsip between te pulse wavepropagation tie in arterial syste and blood pressure. Teparaeter used in tis study is pulse wave transit tie. [n 7],autors deonstrated a new etod for continuous real-tieeasureent of blood pressure during daily activities. Tisetod was based on blood presse estiation o pulsewave velocity calculation.

Autors in 8] developed a syste using Korean traditionaledicine, te degree of te pulse dept to diagnosis analysiswit pulse wave. Using clinical data Autors selected AP(applied pressure wic as a axiu value of pulse wave),elasticit of wrist tissue, dept of blood vessel, cadiac ouutand as paraeters to estiate blood pressure. Tey alsosowed te differences in spygoanoeter data and teirsystes data for SP, DP, MAP and PP, according to AericanStandard.

Autors in 9] developed a new techniue for deteiningservo reference value (Vo) for te volue-copensationetod. In teir etod, te period of tie for Vodeteination was signicantly reduced copared wit te

volue-oscilloetric etod. Tis result also indicatesavailabilit of tis etod for swi resetting of Vo during noninvasive beat-by-beat BP easureent. Copaed to tisetod, we also get swi response of noninvasiveeaseent due to use of potopletysograpy techniueBP using volue oscilloetric etod.

Te perforance of o developed syste is bettercopared to te perfoance of previous works. Ourexperients result sows less ean difference (MD) adstandard deviation (S).

Tis paper is organized as follows: Section II describes tedeveloped noninvasive blood presse easureent syste.

Section III explains te siulation results as well as calculationof real results. Finally, section IV concludes te entire paper.

II. ROPOSED EVELOPED YSTEM

Fig. 3 sows te block diagra of our developed syste.Fig. 4 illustrates te pictorial view of te developed syste.Te detailed electronic circuit of te aplier circuit witautoatic reference selector is sown in Fig. 5. Te workingprinciple of te developed syste for different blocks isdiscussed below.

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[n our designed syste, a ig intensit LE is placed atone side of a ger and a LDR (Ligt Dependent Resistor) isplaced at anoter side. Te ligt is absorbed by te blood,ussels, skin and bones of te ger. Wit te cange of bloodpressure te volue of blood vessels are varied. Te volue ofoter pats of te nger reains constant. So te ligtabsorption is varied only by te cange of volue of blood.We know te resistance of te LDR is ig in dark and

becoes low wen ligt falls on it. Its resistance is inverselyproporional wit ligt intensit.

Ampli 1Automatic

reference

P

l

DCselector

Mini

LCD Microcontroller

Calibrationcontrol

Figure 3. Block diagram of our developed system.

Figure 4. Pictorial view of our developed system.

[n our designed syste, a ig intensit LE is placed atone side of a ger and a LDR (Ligt Dependent Resistor) isplaced at anoter side. Te ligt is absorbed by te blood,ussels, skin and bones of te ger. Wit te cange of bloodpressure te volue of blood vessels are varied. Te volue ofoter pats of te nger reains constant. So te ligtabsorption is varied only by te cange of volue of blood.

We know te resistance of te LDR is ig in dark andbecoes low wen ligt falls on it. Its resistance is inverselyproporional wit ligt intensit.

Wen systolic blood presse occued in te uan body,te blood volue in te nger becoes axiu and ligtabsorption is also axiu. Terefore ligt falls on te LDRis iniu and its resistance is axiu. uring systolicpressure resistance of LDR is ig (axiu). Siilarlyduring diastolic presse resistance of LR is low (iniu).So, it can be concluded tat blood pressure is directlyproporional to te resistance of LR. A low agnitude and

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low euency signal is received by te LR. Te cange inresistance of LDR is ver low even in illioh range.

Terefore, te output voltage o te LR as a largeaount of dc coponent wit a sall aount of accoponent. For exaple if te pulse rate is 75 BPM tenfreuency of ac signal is 75/60=.5Hz. Te eleconiceuivalent circuit of weak bio-signal is sown in Fig. 6.

Rl

C

D -

2" sg

Vol

I

O F ;' . /

k

oV

, _ _

. - -t '

'

I \ ' I

r

LI

2u5

'V : : " 4

: : Ll .I Da w V Y ' \ ,,

VI

a

,. -

Figure 5. PSpice simulation of double stage amplier.

T. - - _ LO\ up g n I

EEFigure 6. Electronic equivalent of Weak bio signa\.

Tis weak bio signal is ten aplied by a double stagever ig gain aplier using Op Ap as sown in Fig. 5. Butte ouut voltage of te LR as a large aount of dccoponent as entioned earlier and apliing te signaldirectly results in saturation of te aplied signal. So to avoid

tis penoenon, a subtractor circuit is used wic canautoatically null te dc coponent. But lter cant be used

ere as euency of ac signal is 0.8 Hz to 1.4 Hz. Tereforete subactor circuit is ade by an Op-ap wic acts asautoatic reference selector to suppress te dc coponent.

For rst stage (Fro Fig. 5),

VOl = - RI(Vi -Vref = Al (Vi - Vref

.

Wen R= and F1=R3.

Here, F= 80K and R\=\ K So A\=8

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For nd stage (Fro Fig. 5),

V02 - (VOl ) A2(Vol )

9()

Were F =80 K and R9=K.So te gain A=80

Finally,

FlxF2V V -Vrf , V - Vrflx982x82

V - Vrf 6724V - Vrf1xl

(3)

Were AI is te total gain of te aplier and AI= 6740. Avariable resistor ay be used instead of F and te total gainof te aplier can be varied o 8 to 6740. So we caneasily analyze te low aplitude (ay be in icro volt range)bio-signal o te LDR using tis aplier circuit.

Te apliers ouut is ten fed to a icrocontrollerwere it is sapled and uantized. To nd out te largest

(represents SP) and te sallest (represents DP) value for teouut sapled and uantized voltage a progra is writtenusing BASCOM-AVR soware into te icro controller. Teicroconoller displays SP, DP and Pulse rate in ini LCDusing te following algorith of Fig. 7.

Moreover te ow cart of te developed syste is sownin Fig. 8. In Fig. 8 x, x, x3 are continuous sapled data. Assystolic pressure is te largest value aong te sapled datafor a paticula period, so x ust greater tan x and x3. Fordiastolic pressure tis condition is vice versa. More

easureents can be loaded to te icro conoller using tesefoulas.

ain

{

}

start:

get_adc_input;

store_input;

ceck_systolicressure;

ceck_diastolicressure;

ceckulseJate;

if (systolic){ display_systolic _pressure;}

if (diastolic){ displadiastolic ressure;}

if (pulseJate){ displayulse_rate;}

goto star;

Figure 7. Algorithm for systolic and diastolic pressure and pulse ratemeasurement in the microcontroller.

Pulse Presse ( Hg) = Systolic Pressure - Diastolicpressure.

Mean Arerial Pressure (MP) ( Hg)pressure) + Diastolic presse.

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1/3 (Pulse

Pulse Rate (BPM) = 60 Pulse to Pulse Interval (seconds).

Te ini LCD display is interfaced wit icrocontroller assown in Fig.9.

(x x x)

Figure 8. Flow chart for the developed system.

For continuous onitoring of blood presse o developedsyste is to be calibrated wit a standard syste beforeeasureent. Te accuracy of tis syste depends ainly ontis calibration. Aer standard calibration for a subject teicro conoller takes data and display result continuously.

Figure 9. Microcontroller interfaced with l62 LCD.

III. ALCULATIONS D SULTS

At rst, te calibration for ADC is perfored. We use 10bit ADC. So its output varies o 0 to 103. Huan systolicblood pressure varies o 30 Hg to 50 Hg anddiastolic blood presse varies o 140 Hg to 35 mHg.ADC is calibrated o 0 to 300 Hg.

M 1' 3

utlpymg lactor-=3.41"3.50

3 = 0 +35 Hg

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Were, Pi is instantaneous pressure at any instant and iste ouut 10 bit data of ADC. Te input and output wavefoof te aplier circuit is sown in Fig. 10.

(0 Schematidt

(a) Input

(c) 2nd stage output (d) Input &outputsFigure 10. : Input and output waveform of amplier in PSpice.

According to aplier gain E. (1), E. () and E. (3) wecan see te ig gain caracteristics of weak bio signal oFig. 10. Te oscillograpic representation of te aplierinput-ouut is sown in Fig. 11 wic is practically observed.Siulated gain and observed gain of te aplier ave a sligtdifference.

Figure 11. Amplier input & output in oscilloscope.

We perfor te blood pressure easureent wit 3subjects using spygoanoeter and our developed systeand te results are sown in Table I.

TLE . SYOLIC PEUE SP, DIAOLIC PEUE DP ANPULE PU PP AING.ub phygmmanmeter rpsed ystem

readings readingsSP DP PP SP DP PP

S 120 70 50 123 73 50S2 126 90 36 126 86 40S3 130 90 40 127 89 38

According to Aerican National Standard for electronics orautoated spygoanoeters, te ean difference souldbe 5 Hg or less wit a standard deviation (SD) of 8

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Hg or less. So fro te above table te difference in PP andMAP of our syste wit spygoanoeter is under standardrule. Terefore, te proposed results are uite reliable andaccording to inteational standards.

To veri our developed systes accuracy we ave alsoperfored soe test wit 6 subjects using ring ger, iddlenger, Tub wit our developed syste and at te sae tieusing spygoanoeter at te rigt . Tese readings aresown in Table II and Table III.

TLE II. SYOLIC PU SP, DIAOLIC PU DP ANMEAN ERIAL PU M REAING.

Ring fnger iddle fnger

b SP DP MAP SP DP MAP 126 78 94 128 77 94B 121 80 93.7 120 79 92.7

C 130 91 104 131 90 103.7

128 86 100 127 86 99.7E 115 75 88.3 116 74 88

F 121 78 92. 3 120 77 91.3

We ave recorded several data aer calibrating ourdeveloped syste for continuous onitoring of te proposedsyste in noral condition and excited condition. And wefound tat o proposed syste displays rapid responseaccording of SP and P according to different conditions and

we can get uite a vaiation between two different conditionsfor sae subject. Terefore we can say te developed systeworks approxiately accate bot in noninvasive andcontinuous ode.

TLE III.

b

B

CEF

SYOLIC PU SP, DIAOLIC PU DP ANMEAN ERIAL PU AING.

Thumb rm pressure byphygmmanmeter

SP DP MAP SP DP MAP

128 77 94 125 79 94.3120 79 92. 7 122 81 94. 7

131 90 103.7 131 90 103.7127 86 99.7 129 87 101

116 74 88 116 75 88.7120 77 91.3 120 78 92

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30

20Eg 0QL: 00

QL 90" 80

70

l-

Time (sec)

Figure 12. Systolic and Diastolic pressure in normal condition.

Te variation of SP and DP for noral and excitedcondition for a subject is sown in Fig. 1 and Fig. 13respectively.

I

5Eg

QL: 5QL

" 5

o

5

F

5 5

ime (sec)Figure 13. Systolic and Diastolic pressure in excited condition.

Te aplier calibration using spygoanoeter fordifferent patients is te liitation for o developed syste.We ave to calibrate te aplier ever tie for differentsubjects. Tis is because our developed syste works involue oscilloetric etod and different patients avedifferent blood volue in teir ngers. So ever tie propercalibration is reuired before recording accate readings ofdifferent patients. But once te calibration is done for a subject,it can continuously display SP, DP of te subject witout anyfault results. Te proble can be solved by easuring te

volue of blood in te ger. Te calibration is done byvarying a variable resistor Te calibration proble can besolved by easuring te rate of cange of blood volue in adenite organ o optical sensor network signal. Tis signal

as a linear relationsip wit blood pressure as discussedabove.

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IV. ONCLUSION

In tis paper, we developed a low cost device fornoninvasive continuous easureent of blood pressure usingpotopletysograpy techniue. Te blood pressure waseasured using volue oscilloetric etod continuously fora long period of tie wit te sall ebedded syste anddisplayed te systolic and diastolic blood pressure on a iniLCD. Te results were rter copared wit existing devices

data like spygoanoeter to veri te accuracy of tedeveloped syste. Te developed syste sows less eor inBP readings copare to conventional devices. Moreover it asno side effect on uan body wile running in continuousode. So te developed syste is uite reliable and preferablefor continuous BP easureent. In near ture we will connectte syste wit coputer ad local area network (LAN).Terefore rter data analysis and reote onitoring will be

possible.

EFERENCES

[1] C. K. Wei, "Photoplethysmography blood pressure measurement, M.Sc. Engg. Thesis, Department of Mechanical Engineering, National

University of Singapore,2009.[2] H. Shimazu, H. Ito, H. Kobayashi, "Idea to measure diastolic arterial

pressure by volume oscillometric method in human ngers,"department of physiology, Kyorin University school of medicine,

Mediccal & Biological Engineering & Computation, vol. 24, no 5, pp.549-554, 1986.

[3] S. Tana, M. Nogawa, and K. Yakoshi, "Fully Automatic Systemfor Monitoring Blood Pressure om a Toilet-Seat Using the VolumeOscillometric Method, Proceedings of the Annual Conference onEngineering in Medicine and Biolo, pp. 3939-3941, Shanghai, China,September 1-4,2005.

[4] P A Shaltis A T Reisner and H H Asada "Cuess Blood PressureMonitoring Using Hydrostatic Pressure Changes, IEEE TransactionsOn Biomedical Engineering,vol. 55,no. 6,pp. 1775-1777,June 2008.

[5] X. F. Teng and Y. T. Zhg, "Continuous d Noninvasive Estimation

of rterial Blood pressure using a photoplethysmographic Approach,Proceedings of the 25th Annual International Conference of the IEEEEMBS, vol. 4,pp. 3153-3156, Ccun Mexico, September,2003.

[6] J. Lass, I. C. Meigas and D. Karai, R. Kattai, J. Kaik, M Rossmann,"Continuous blood pressure monitoring during exercise using pulse

wave transit time measurement, Proceedings of the 26th AnnualInteational Conference of the IEEE EMBS San Francisco, pp. 2239-2242,CA,USA, September 2004

[7] G Lopez, H. Ushida, K. Hidaka, M. shuzo, I. Yamada, "ContinuousBlood pressure measurement in daily activities, The Universi ofToko. IEEE SENSOR 2009 conference

[8] M. Park, H. 1 Kang, Y. Huh, K. C. Kim, "Cuess and NoninvasiveMeasurement of systolic blood pressure, diastolic blood pressure, meanarterial pressure and pulse pressure using Radial rtery Tonometrypressure sensor with concept of Korean Traditional medicine,Proceedings of the 29th Annual International Conference of the IEEE

EMBS, pp.3597-3600,2007.[9] S. Tanaka, M. Nogawa, Y. Sawanoi, T. Yamakoshi and K. Yamakoshi,

"A New Method r Determining the Sero Reference Value (Vo) of theVolume-Compensation Method, Proceedings of the 29th AnnualInteational Conference of the IEEE EMBS, pp. 2354-2356, Lyon,France, August 23-26,2007.

[10] K. Bynum, "Experimental laboratory physiology BIOPAC Lab exercisemanual, lesson16,lesson 17.

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