Intelligent System for Blood Pressure Monitoring

Transcription

1 Inelligen Sysem or Blood Pressure Monioring Aleksei Anisimov, Alyona Skorobogaova, Anasasiya Suyagina Sain-Peersburg Elecroechnical Universiy "LETI" Sain-Peersburg, Russia Absrac The srucure o he sysem or long-erm blood pressure monioring by pulse wave propagaion ime was presened. The algorihm or inelligen measuremen o uncioning parameers o he paien s cardiovascular sysem, providing decrease o an indirec arerial blood pressure esimaion errors and increase he reliabiliy o he predicion o hyperensive crisis, was developed. The aricle includes descripion o hardware par o he sysem or synchronous recording o ECG and pulse wave signals, wih using o he modern componens, such as analog ron ends or medical implemenaion and mulipurpose wireless communicaion. I. INTRODUCTION Arerial hyperension, being considered as a signiican risk acor or cerebrovascular disease, is one o he mos common cardiovascular diseases [1]. More han 40% o he world populaion has hyperension, his disease becomes younger, embracing more general populaion, especially in posindusrial counries []. The erm hyperension commonly reerred o elevaion o sysolic blood pressure (SBP), hen i becomes higher han 140 mmhg, or diasolic blood pressure (DBP) greaer han 90 mmhg. Essenial hyperension (also called primary hyperension) is he orm o hyperension ha by deiniion has no ideniiable cause, and i is he mos common ype o hyperension, aecing 95% o hyperensive paiens []. Essenial hyperension is a chronical disease in which high blood pressure is no associaed wih damage o any organs or sysems o he body, leading o he developmen o secondary orms o hyperension, and is caused by a number o inernal and exernal acors, which are usually very diicul o diagnose. Considering he signiican role o hyperension in he occurrence o dangerous cardiovascular diseases (hear aacks and srokes), urher developmen o ools or long-erm coninuous monioring o blood pressure, racking as lucuaions and orecasing hyperensive crisis becomes an imporan social problem. The only recognized by docor s mehod or deecing hyperension or a very long ime was BP measuremens held by rained specialis in a hospial (so called clinical BP measuremen). The measuremens were made wih he ausculaory mehod, invened in he early beginning o he 0- h cenury by Russian surgeon Nikolai Korokov. Nowadays docors sared (bu wih grea misrus o he accuracy o measuremens) o use auomaic devices or arerial blood pressure measuremens, mosly based on oscillomeric mehod, bu hey are allowed only in cases when heir accuracy is conirmed in clinical pracice during special sudies conduced in accordance wih inernaional clinical sandards. On he oher hand, according o he laes clinical guidelines or he reamen o hyperension, here is a growing prognosic value o home blood pressure monioring (HBPM) and is role in he diagnosis and reamen o hyperension [3], in addiion o he daily ambulaory blood pressure monioring (ABPM), held wih specialized medical equipmen. The choice o insrumens or HBPM is exremely limied and represened generally by he sandard cu blood pressure moniors, which are no suied or long-erm coninuous monioring, and provide only single discree measuremens. These devices (even suied or home use, hey are considered as medical equipmen) mus pass he iniial veriicaion according o sandard proocols, and heir accuracy should be periodically veriied (wih addiional calibraion i necessary) by echnical laboraory a leas once a year, which causes some diiculies in heir home use (people usually orge abou his procedure). Mos commercially available oscillomeric cu pressure moniors operae on he same principle: he measuremen occurs on he decompression phase, he upper cu pressure hreshold is seleced based on he maximum possible user SBP (and usually exceeds i wih mmhg), which may cause discomor and even pain in user s arm. The resuling vascular occlusion rom cu leads o endohelial-dependen lowmediaed vasodilaion o he brachial arery, and he blood circulaion in arm issues resores during 3-5 minues (depending on individual parameers). This does no allow perorming immediae repeaed measuremens, alhough he exising recommendaions assumed ha BP measuremen should be repeaed a leas 3 imes in a raw, wih urher averaging o resuls. Repeaed measuremens perormed exremely rare, which can lead o subsanial error in measuremen resuls. Devices ha measure blood pressure in he compression phase (wih lower limis o high cu pressure), presened only by a small number o manuacurers (or example, Omron Mi Elie) and usually included in he premium marke segmen wih much more expensive cos, which limis is urher spread. Ausculaion auomaic blood pressure moniors, based on he Koroko mehod, represened on he medical equipmen marke wih only ew models, among he mos popular we can call only wo - Tensoval Duo Conrol by Harmann and Nissei DS 700 by Nihon Seimisu Sokko. Wris oscillomeric blood pressure moniors, acquired large populariy in recen years due o is small size and ease o implemening, are no recommended or use in HBPM because o he low accuracy o measuremen resuls, especially or old people. ISSN

2 II. MATHEMATICAL MODEL The ask o consrucing a mahemaical model o hemodynamics, describing he uncioning o he enire cardiovascular sysem, remains unsolved. The main reason o his ac is conneced o he complexiy and nonlineariy o involved biological sysems and impac o a huge number o boh inernal and exernal acors on he process o is uncioning. Descripion o hese dependencies is a very diicul ask, even i we wan o ormalize hem on physiologically descripive level. An eecive way o solving his problem simulae he operaion o individual secions o he cardiovascular sysem, or example, a hear level, large vessels level, capillaries level, and so on. Theoreical and empirical models can describe hemodynamics o such small pieces accuraely enough. A. Arerial blood pressure regulaion sysem. The hear is no an engine coninuously pumps blood, bu runs in a discree manner, when he successive hearbeas lead o a series o varying RR-inervals and values o sysolic and diasolic arerial blood pressure [4]. Despie his, mos o he cardiovascular sysem models include a se o dierenial equaions relecing he relaionship beween coninuous signals such as he average blood pressure and hear rae (HR). To invesigae he long-erm records and slow changes in he values o blood pressure, his approach seems reasonable, bu isn suiable or sudying rapid changes over shor inervals o ime. Barorecepors, locaed in he blood vessels, coninuously monior changes in blood pressure, according o hem cenral nervous sysem conrols hear rae by aecing he vagus nerve and hrough he sympaheic nervous sysem, providing as changes o arerial pressure, which are he mos ineresing or us (humoral renin-angioensin-aldoserone and renal mechanisms o conrol are no covered here due o very complicaed diagnosic mehods). Barorelex also aecs he peripheral resisance, bu only hrough he aciviy o he sympaheic sysem. Hear rae (deermined by chronoropic eecs) and sroke volume (deermined mainly by myocardial conraciliy and exciabiliy and impulse conducion), aecs he value o he cardiac oupu, which, along wih peripheral resisance, deermines he curren value o arerial blood pressure, hus closing he enire regulaion sysem, and we ge he classical model o a sel-regulaing sysem wih negaive eedback (as shown in Fig.1).This is raher simpliied schemaic, relecing he impac o only hose parameers ha we can regiser wihou he use o expensive equipmen. Beao-bea changes in blood pressure and hear rae are mainly associaed wih he respiraory sysem (respiraory arrhyhmia) and Mayer slow waves (he mos signiican o which is he so-called 10-s rhyhm wih a 10 seconds period). From wrien above we can conclude ha pressure on he vessel wall a some poin o he circulaory sysem depends on a number o parameers and akes he orm o a complex nonlinear uncion [5]: (1) where - curren ime, L - disance rom he hear o he poin where we ake measuremens, - hear rae, causing pulse wave, V - pulse wave velociy, - viscosiy o blood, E - elasiciy o blood vessels, n - se o parameers, providing an indirec eec (emperaure, amospheric pressure, and many ohers). Formalizaion o his relaionship or culess blood pressure measuremen is an acual problem. Fig.1. Conrol circui o cardiovascular sysem Pulse wave velociy V (PWV) depends on he biomechanical properies (elasiciy) o vessels. For large vessels (aora and areries), PWV is described by Moens- Koreweg equaion [5]: () where E - modulus o elasiciy (Young's modulus) o vessel wall; h - wall hickness, d - inner diameer o vessel; blood densiy. This parameer ypically has a value o = 1,050-1,060 g/cm³. Individual value o blood densiy or each person can be considered as a consan. For blood vessels o elasic ype empirical relaion beween he modulus o elasiciy E and blood pressure P was developed [6-7]: (3) where E 0 and P 0 - iniial values o he Young's modulus and pressure, coeicien ha indicaes properies o he vascular wall (i has a value in he range o ~ 0.018). Wih regard o () and (3) we can calculae: (4) Assuming ha a he end par o arery wih lengh L PWV value is a consan, we deine V wih pulse wave propagaion ime (PWPT):. Then we can ransorm he equaion (4) ino he ollowing orm: (5) Finally, we can obain blood pressure dependence, geing

3 logarihm o he expression (5): (6) B. Disadvanages o he proposed model Equaion (6) shows ha i he vessel elasiciy remains consan, blood pressure changes are proporional o he changes o PWPT, which allows indirec measuremen o blood pressure by measuring pulse wave propagaion ime. Despie his, his relaionship beween PWPT and blood pressure is no so obvious. I is known rom pracical research ha age, gender, and a number o oher acors (like smoking, drinking alcohol, overweigh and many ohers) have a signiican impac on he vessels and PWPT, so his equaion can be used raher or regisraion o blood pressure dynamics and monioring as pressure changes during long periods, hen accurae measuremen o single arerial blood pressure values. 4) From he experimenal daa he raio o vessel wall hickness o diameer or each person varies insigniicanly, and i can be aken as a consan: h/d = 0.1; 5) Iniial value o he vessel walls elasic modulus E 0, which remains unknown, is calculaed using he equaion (6) a a known measured value o BP. The graphs in Fig. shows ha a a cerain value o blood pressure (P = 110 mm. Hg.) and ixed values o PWPT (rom 150 o 300 ms) modulus 0 can change heir values in a wide range. This explains he need or primary calibraion o culess blood pressure monior based on a preliminary assessmen o he values P, 0 and T. However, aer inding o individual depending o PWPT rom blood pressure or each paien, and aer appropriae calibraion wih a sandard oscillomeric pressure monior, we can measure he absolue blood pressure values wih suicien precision. We should noe ha he seleced model has a number o assumpions ha need urher adjusmen. Moens-Koreweg equaion was obained rom a simpliied mechanical model ha is insensiive o small changes in vessel diameer. This may cause an error while measuring arerial pressure o major areries, especially in healhy young paiens. Their areries have a high elasiciy, and passing pulse wave will cause increase o arery radius and decreasing o blood pressure. Because proposed equaion does no consider hese changes, we need o use correcion coeiciens. C. Experimens wih he model During pracical sudies [8], we analyzed he possibiliy o using he equaion (6) or monioring blood pressure. We ind ou ha in calculaing he values o blood pressure by equaion wo hings are crucial: he accuracy o calculaing PWPT values and seing iniial vascular elasiciy or a paricular subjec. Figure shows he dependence o calculaed pressure P rom vascular elasiciy modulus 0, obained rom he ormula (6) or various values o pulse wave propagaion ime T. The ollowing values o he basic parameers have been aken during calculaions: 1) Blood densiy has been acceped as a consan, because his parameer is changed slighly a healhy person: = 1,050-1,060 g/cm³; ) Dimensionless coeicien a, which indicaes he properies o he vascular wall, is lying in he range o ~ 0.018; 3) Disance L rom he hear o he poin o he signal regisraion is measured as he disance rom he subclavian riangle o he place o PWPT regisraion, in his sudy we used L = 75 cm as he average disance; Fig. Dependence o calculaed blood pressure P rom vascular elasiciy modulus 0 or dieren values o pulse wave propagaion ime T III. COMMON STRUCTURE OF INTELLIGENT MONITORING SYSTEM To monior he sae o human healh and o predic he disease exacerbaion he sysem is required o solve he complex o problems relaed o regisraion o signals, which characerise he aciviy o he body's sysems, processing and analysis o biomedical inormaion, assessmen o he curren sae o he human body, revealing o dynamic changes and predicion o acue condiions. I is obvious ha or he soluion o complex asks he sysem should have a mulilevel hierarchical srucure, each level o which should provide opimal soluions o speciic asks. A. The irs level o he hierarchical monioring sysem Wearable paien device provides he soluion or he ask o objecive and reliable regisraion o complex biomedical signals and indicaors o body sysems aciviies. Minimizaion o mehod errors o signals regisraion can be achieved by reducing he eec o regisraion devices on he uncioning o body sysems and on paien s lie aciviies. Sensors on he wearable paien device should have minimum size and weigh o provide non-invasive evaluaion o indicaors, be biologically compaible, no aec he spaial-emporal disribuion o he regisered biomedical signals. To ensure coninued reliable regisraion o biomedical signals a wearable device should have long baery lie (up o several

4 days). Tha means ha he wearable device is no advisable o use or signals pre-processing: complex handling o biomedical signals necessiaes using o high-perormance CPU, and as a resul, we have increased elecric curren consumpion and reduced o baery lie. Using inelligen algorihms or recording and ransmission o biomedical signals on he second level o he sysem he level o biomedical signals recep can signiicanly reduce curren consumpion and increase he auonomy o he device. Inellecualizaion is based on usage o a limied se o recorded biomedical signals o monior he saus o individual norms (e.g., ECG and respiraion). In case o deecion o uncional changes in he aciviy o body sysems, he wearable device can connec addiional regisraion channels o biomedical signals, change algorihms and regiser parameers o biomedical signals o improve accuracy and reliabiliy o he assessmen o he paien s healh condiion. The ransmission power o he signals by he radio channel rom he wearable device o he receiver should no exceed ens o mw. This conribues o addiional enhancemen o he work auonomy o he wearable device. The main uncion o he irs-level sysem can be ormulaed as ollows: accuracy and reliabiliy o regisraion and ransmission o signals in condiions o long auonomous work. B. The second level o he sysem The second level o he sysem is signals receiver. I provides preliminary processing o biomedical signals, esimaion o diagnosically imporan indicaors o paien healh, assessmen o he curren healh condiion, adminisraion o operaing mode and changes he seings o he wearable device recording channels. The analysis o indicaors o he body sysems uncioning, ormaion o he signals alers or he paien abou changes in his/her healh condiion and ransmission o biomedical inormaion by WLAN channel o he server o any medical insiuion, which perorms he monioring o he healh saus and prognosis o exacerbaion o chronic diseases, are also provided on his level. To solve all he asks speciied above he second level o he sysem mus have a high-perormance CPU. Taking ino consideraion he curren level o he compuer echnologies developmen i is implemened on a smarphone or a able compuer using a sand-alone or nework power source. C. The hird and ourh level o he sysem The hird level o he sysems is presened by cloud-based ools and echnologies o he medical insiuion server which perorms he monioring o he paien healh saus. I provides a deailed analysis o he dynamics o he uncional sae o body sysems, an inegral assessmen o healh saus, an adjusmen o indicaors o individual norms o he moniored paien and he crieria or diagnosics o diseases and predicion o heir exacerbaion, he ormaion o inormaional messages or a physician abou paien s healh hrea o uncional changes in body sysems. The objecive uncion o he sysem s hird level can be ormulaed as ollows: long-erm monioring o he paien healh saus and prognosis o he disease exacerbaion. The ourh level o he sysem is ormed by a microprocessor sysem o he aending (amily) physician and implemened on he porable (able) or deskop compuer. The docor receives deailed inormaion abou he paien s curren condiion, abou he dynamics o changes in healh saus during he long-erm monioring and abou he orecas o he paien s healh sae in he nex days. Typical soluions or using medical echnologies and medicines could be recommended or he docor o normalize he condiion o he paien in case o hreaening his lie and healh uncional disorders. Communicaion beween second, hird and ourh levels o he monioring sysem is implemened by using he WLAN communicaion channel. In accordance wih he above raionale, we propose he ollowing archiecure o he inelligen sysem o remoe monioring o paien healh condiion (Fig. 3). Fig.3. Inelligen sysem o remoe monioring o paien healh condiion D. Subsaniaion and developmen o he wearable paien device srucure The uncionaliy o he inelligen sysem or remoe monioring o he person s healh saus is largely deermined by he uncionaliy o wearable device measuring channels, since i provides recording o biomedical inormaion, which is used or evaluaion o he person s curren healh saus, monioring and predicion o disease exacerbaion. In order o provide improved echnical and merological characerisics o measuring channels, i s recommended o use highly inegraed Analog Fron End (AFE) modules or medical purposes, inended or regisraion o ECG, SO, pulse wave, respiraion rae and emperaure. Mos o he modern AFE modules have onboard various serial digial ineraces like UART and SPI, which allows us o oer he ollowing uniied srucure o he wearable device (Fig.4). Wearable paien device conains se o elecrodes and sensors or regisraion signal rom paien, N channel AFE modules, microconroller (MCU) or collecing digial daa rom he measuring channels and conrol heir operaion modes, radio channel (RFC) or ransmission/recepion o signals rom he second level sysem, and auonomous sandalone power supply source (APS). Sysem modules speciic ypes selecion is based on required daa ranser rae o recorded biomedical inormaion

5 3) During he period o ime = + we coninuously monior SBP and DBP by regisraion o PWPT (using phoomeric and ECG channels) and correcion o indirec esimaion resuls using he coeiciens A( ) and B( ). P SBP ( ) L )ln V( ) T( ) A( (10) Fig.4. Uniied srucure o he wearable device IV. BLOOD PRESSURE MONITORING ALGORITHM Finding ways o reduce he mehodological error o indirec measuremen o blood pressure wih regisraion o pulse wave propagaion ime, we came o soluion ha allowed implemening his mehod or coninuous monioring o blood pressure wih enough precision. The essence o he proposed soluion is o calculae SBP and DBP by PWPT and periodically adjusmen parameers o he ormula (6) wih resuls rom sandard blood pressure monior. In ac, in he proposed sysem o coninuous blood pressure monioring by PWPT, we add auomaic calibraion o he measuring channel or periodical indirec evaluaion o he characerisics o blood pressure wih ceriied device. Correcion algorihm o coninuous monioring is he resul o implemening he ollowing procedures: 1) Simulaneous evaluaion a a ixed ime via ceriied sphygmomanomeer sysolic P ) and diasolic P ) ( SBP ( DBP blood pressure, as well as measuremen o pulse wave velociy V( ) and pulse wave propagaion ime T( ). Resuls o evaluaion V( ) and T( ) are necessary or urher coninuous indirec measuremen o sysolic P SBP () and diasolic P DBP() pressures. I is clear ha or he momen o ime T( ) mus be perormed equaion: P ) = P ) ; P ) = P ) (7) ( SBP ( SBP ( DBP ( DBP ) Wih measured by using ceriied pressure monior parameers P ( SBP ), P ( ) DBP and he esimaion o L, V( ) and T( ) we calculae coeiciens A( ) and B( ), which will be valid or some ime c : L P SBP ( ) A( )ln (8) V( ) T( ) P( ) PSBP ( ) PDBP ( ) B( ) V ( ) (9) where 1 E A ( ) ; 0h V ( ) ; B( ) K. d P DBP ( ) PSBP ( ) B( ) V( ) (11) 4) In urher esimaion o arerial pressure we clariying parameers A() and B() a ime = + T U, and make correcion o SBP and DBP values, aking ino accoun changes in he blood vessel characerisics. The algorihm and he experimenal daa [8] indicae ha he use o ceriied blood pressure moniors or he periodic calculaion o he correcion acors can help successully solve he problem o he coninuous monioring o blood pressure over long periods wih he accuracy provided by he used onomeer. Because regisraion o pulse wave propagaion ime is he hear o he enire blood pressure monioring algorihm, is calculaion requires synchronous recording o pulse wave signal and elecrocardiogram (ECG) wih a leas one channel. Opion regisraion o wo pulse waves is no considered due o he echnical complexiy o implemening such sysem. The main problem wih his approach - mehod o mouning such device on he human body. Combine he wo channels in a single uni is exremely challenging, as he regisraion o he ECG signal requires removal o signals rom wo widely separaed poins. The only exising model o his device - a bracele WMe rom Rooi Labs Company allows he ECG recording, wih one measuring elecrode is buil ino he bracele; he second is locaed on is housing, which eliminaes he possibiliy o coninuous monioring. Such devices can regiser only ew ens o seconds, while he user keeps his inger on he second elecrode. Based on he above consideraions, a block diagram o he proposed coninuous blood pressure monioring sysem consiss o he ollowing main pars (Fig.5): breas locaed sensor, bracele on he wris and oscillomeric onomeer or correcion o blood pressure measuremen resuls. The signals rom all sensors and onomeer synchronized ogeher, hen daa ransmied wirelessly o he user's smarphone. Alhough he discrepancy o blood pressure beween he brachial arery and radial arery (here we regiser pulse wave) is around 10-0 mmhg, and he discrepancy o pulse wave velociy o he brachial and radial arery is large enough, we don consider i in our invesigaion. Since we are no alking abou he measuremen o blood pressure, bu raher monioring (changes o pressure is main ineres), he absolue values o blood pressure are no so imporan in his case, and reerence blood pressure onomeer is used only or providing some real level o paien s arerial blood pressure

6 Fig. 5. Block diagram o coninuous blood pressure monioring sysem Breas sensor is used or ECG signal recording (o selec reerence poins or calculaing PWPT, in his case R-wave) and a number o auxiliary parameers (emperaure, respiraory rae). The second par o he device - a bracele asened on he wris, wih a buil-in opical pulse wave sensor operaing in relecion. Bracele receives daa rom breas sensor or calculaing he curren PWPT values and ransmis he resuling daa o he user's smarphone over a wireless Blueooh-channel, which calculaes he curren blood pressure, using correcion acors obained rom oscillomeric onomeer. The algorihm o device includes he ollowing seps: 1) Deiniion o indicaors o individual paien norms on he basic parameers: hear rae, blood pressure magniude (high, low, wihin he normal range), he pulse wave propagaion ime. Device seing sage goes in a sae o res, he duraion o he background recording is approximaely 5-10 minues. Nex, based on he daa calculaed correcion coeiciens A( r ) and B( ) sysem calculae blood pressure. This phase also involves he paien's enry ino he smarphone basic anhropomeric parameers: heigh, weigh (or calculaion o body mass index). ) Monioring o paien s physical aciviy level wih he help o buil in bracele moion sensor and hear rae. A a low level o physical aciviy o paien all devices o he sysem running in he background (power-saving) mode and reduce he sampling rae o all signal channels. Only reerence ECG channel is powered or he evaluaion o hear rae variabiliy (HRV) and allocaion o R-waves, he pulse wave regisraion channel is swiched periodically wih a predeermined ime, addiional ECG, breah rae, and emperaure channels are swiched o. Program, insalled in he paien's smarphone, analyzes hear rae and PWPT. I some o values exceed he curren levels above he individual norms range, he sysem swiches o acive mode o operaion, make correcion o measured resuls by exernal oscillomeric onomeer. 3) Monioring o he paien's condiion in he acive mode. Sysem swiches signals recording o high sampling requency, connecs addiional channels or daa logging, recording signals coninuously on all channels. Processing and analysis soware provides coninuous daa analysis wih he deiniion o he naure o paien's condiion changes. 4) Monioring o he paien in emergency mode. This mode is se when he moniored parameers go beyond he level o individual norm, such as a as rising o blood pressure and he hrea o a hyperensive crisis. When his mode is se, device swiches o maximum sampling requency and issues a warning signal o he paien abou he need o ake emergency measures. For implemenaion o he mehod we mus simulaneously ake rom he paien's body wo signals: pulse wave and elecrocardiogram (ECG). As i s known, ECG signal is disribued hroughou he whole body wih excepionally lile or even no delay (as any oher elecrical signal), and pulse wave signal a each poin o he body has a ime delay relaive o sysole (aken as he reerence poin), so we can calculae he pulse wave velociy. As he irs reerence poin is aken R- wave rom ECG signal (momen o blood ejecion o he le venricle), as a second reerence poin - he irs maximum o pulse wave signal. Sandard lead (wo elecrodes which are placed on he arms or ches) is quie suiable or aking ECG signal. As he sysem should be mobile, wireless and as compac as i s possible, i was decided o use special inegraed circuis or achievemen o such challenge, manuacured by Texas Insrumens: ADS191 and AFE4400. ADS191 is a 16-bi Analog Fron-End or biopoenial measuremens, leas in he amily o Texas Insrumens AFE's (because his IC has only one channel or ECG recording, bu i s sill prey enough or our purposes). This chip implemens speciic uncions, designed or measuring o biological signals (such as ECG or elecroencephalography - EEG). This inegraed circui includes all necessary analog componens, such as insrumenal ampliier wih a programmable gain, se o analog ilers (including ilering o 50/60Hz noise) and embedded 16-bi sigma-dela ADC, which operaes a daa raes up o 8 ksps. This inegraion reduces o minimum he number o componens required or regisraion and preprocessing o he ECG signal. So, his IC makes possible he creaion o scalable medical insrumenaion sysems a signiicanly reduced size, power, and overall cos. Daa in digial orm can be ransmied over SPI inerace o microconroller uni. For debugging purposes has been designed evaluaion board, which schemaic is shown on Figure 1. AFE4490 IC represens a ully inegraed sysem on crysal, designed or aking pulseoximery signal (. This IC uses an opical sensor based on he use o he red and inrared LEDs in conjuncion wih a phoodiode or receiving he arerial pulse wave signal. This sysem allows deermining he level o blood oxygen sauraion and hear rae. AFE4490 combines a number o discree componens, required o perorm pulseoximery in he mos eecive way. Opimizaion o he sysem provides precise conrol over he characerisics o signals, minimizing power consumpion, as well as reducing cos and size o he whole device. The srucure o he chip includes a ransimpedance ampliier or convering he dierenial inpu curren rom he phoodiode ino a volage, buil-in analog circuiry or ilering consan componen o he signal, LED driver, which enables geing

7 supply curren up o 00 ma, which is essenial o obain a sable signal or designing o sensors ha don work on clearance (as sandard devices or aking signal rom ingerip or earlobe), bu on relecion. Buil-in sigma-dela ADC wih high resoluion ( bis) makes i possible o receive a good signal wihou addiional analog ilering. Combining o hese wo chips in one device allows us o creae a miniaure sysem or measuring pulse wave velociy. V. CONCLUSION Providing lower accuracy o wih compare o sandard oscillomeric arerial blood pressure moniors, indirec blood pressure measuremen sysem based on parameers o cenral hemodynamics (as pulse wave propagaion ime) is well suied or long-erm coninuous monioring o blood pressure and predicion o hyperension crisis. To improve he accuracy o blood pressure evaluaion in such sysems we need o apply a periodic auomaic correcion o coeiciens used or calculaion o blood pressure. To ensure a long baery lie and easy use, monioring sysem is necessary o use an inellecual operaion algorihm, which provide operaing modes and characerisics o measuring channels changes, depending on he physical aciviy o he moniored paien. The proposed srucure o he sysem or monioring blood pressure can only be realized wih he use o modern componens, such as Analog Fron Ends or medical implemenaion. REFERENCES [1] Lim SS, Vos T, Flaxman AD, Danaei G, e al, A comparaive risk assessmen o burden o disease and injury aribuable o 67 risk acors and risk acor clusers in 1 regions, : a sysemaic analysis or he Global Burden o Disease Sudy, Lance, vol. 380, No. 9859, Dec. 01, pp [] World Healh Organizaion oicial websie, A global brie on Hyperension,Web: hp:// ses /publicaions/global_brie_hyperension/en/ [3] G. Parai, G.S. Sergiou, R. Asmar, e al, European Sociey o Hyperension Pracice Guidelines or home blood pressure monioring, Journal o Human Hyperension, 010, pp [4] B. Bo Sramek, Sysemic Hemodynamics and Hemodynamic Managemen. InsanPublisher, 00. [5] Anisimov A.A., Yuldasev Z.M., Bibicheva Yu.G. Non-occlusion Monioring o Arerial Pressure Dynamics rom Pulsaion Wave Propagaion Time, Biomedical Engineering, vol. 48,., Jul. 014, pp [6] Jorge Proença, Jens Muehlse, Xavier Auber e al, Is Pulse Transi Time a good indicaor o Blood Pressure changes during shor physical exercise in a young populaion?, in Proc. IEEE Eng. Med. Biol. Soc., Argenina, Aug. Sep [7] Heiko Gesche, Dele Grosskurh, Ger Kuchler e al, Coninuous blood pressure measuremen by using he pulse ransi ime: comparison o a cu-based mehod, European Journal o Applied Physiology, vol. 11, Issue 1, Jan. 01. [8] A.A. Anisimov, T.V. Sergeev, The algorihm or arerial blood pressure esimaing by using he pulse ransi ime, Bioechnosphere, 4 (40), 015, pp