Cuff less blood pressure meter system

CUFF-LESS BLOOD PRESSURE METER SYSTEM AMINURRASHID BIN NOORDIN A project report submitted in partial fulfilment of the requirements for the award of the degree of Master of Engineering (Electrical - Mechatronics and Automatic Control) Faculty of Electrical Engineering Universiti Teknologi Malaysia MAY 2009 ABSTRACT Most of blood pressure (BP) measuring devices nowadays rely on a common concept of inflatable cuff to the arm which applied auscultotary or oscillometry principle. By having a cuff, the efficiency of the device will be reduced in terms power consumption, restriction of frequency and also ease of use. Therefore this project is aimed at designing a noninvasive cuff-less blood pressure estimation system based on pulse transit time (PTT) technique. Based on previous work of others, the photo-plethysmographic (PPG) circuit is designed to be interface to personal computer utilize PIC 16B77A as data acquisition system and Bluetooth as communication interface. The algorithm to measure PTT from R of generated electrocardiogram (ECG) to base point of PPG waveform was developed using Visual Basic 6 (VB6) which this programming also used to develop the graphical user interfaces (GUI) to display the estimated SBP and DBP by offline and online process. The results have shown that the PTT measurement between ECG and PPG of pulse oximeter have a great potential for blood pressure estimation. ABSTRAK Di masa ini, kebanyakan alat pengukuran tekanan darah bergantung kepada konsep yang sama iaitu pengembangan kuf di lengan yang mengunakan prinsip osilometrik atau prinsip auskultatori. Penggunann kuf ini menyebabkan kecekapan alat pengukuran akan berkurang dari segi pengunaan tenaga, keselesaaan dan kekerapan pengunaannya. Oleh itu, projek ini bertujuan untuk merekabentuk sistem anggaran tekanan darah secara tidak langung tanpa kuf berdasarkan prisip masa alihan nadi. Berdasarkan kajian yang telah dilaksanakan oleh penyelidik lain, litar foto-pletismografi direka untuk dihubungkan kepada komputer peribadi menggunakan mikropengawal PIC 16F877A sebagai sistem pemerolehan data dan Bluetooth sebagai antara muka komunikasi. Algoritma untuk menentukan masa alihan nadi dari nilai R elektrokardiogram terjana hingga ke dasar titik gelombang foto-pletismografi dibina menggunakan perisian pengaturcaraan Visual Basic 6 di mana perisian ini juga digunakan untuk mereka antara muka grafik pengguna (GUI) untuk memaparkan angaaran tekanan darah sistolik dan tekanan darah distolik. Keputusan menunjukan bahawa pengukuran masa alihan nadi di antara elektrokardiogram dan oksimeter nadi mempunyai potensi yang baik untuk anggaran tekanan darah. CHAPTER 1 INTRODUCTION 1.1 Project Background Blood pressure is the most often measured and the most intensively studied parameter in medical and physiological practice. The blood pressure signal is important to determine the functional integrity of the cardiovascular system. Supplemented by information about other physiological parameters, the blood pressure is an invaluable diagnostic aid to access the vascular condition of certain illnesses (R.S. Kahndpur, 2005; Isik C., 2006). Blood Pressure measurement techniques are basically put into two classes: direct and indirect. The direct method measurement is used when the very high level of accuracy, dynamic response and continuous monitoring is required. In invasive or direct measurement, the operation uses a pressure transducer that is coupled to the vascular system through catheter that is inserted to blood vessel (Walter W et al, 1976; Isik C., 2006). In early eighteenth century, the first blood pressure measurement is attributed to Reverend Stephen Hales, who has conducted an experiment by connected water-filled glass tubes in the animals' arteries and correlated their blood pressure to the height of the column of fluid in the tube (Jeremy B., 1977). The classical method of an indirect measurement of blood pressure is by using a cuff over arm containing the artery. The indirect techniques are non-invasive, with improved patient comfort and safety, but at the expense of accuracy (Shantanu Sur and S. K. Ghatak, 2005; Isik C., 2006). This technique was introduced by Riva- Rocci, an Italian Physician during 1896 for determining of systolic and diastolic pressures using the devices that are ease of application, rapidity in action, precision, and harmlessness to patient (Jeremy B., 1977; Gareth B. et al., 2001). In early 1970, Penaz J. introduce a continuous blood pressure recording system using a pneumatic-driven finger cuff and then in 1980, Yamakashi, K et a1 extended the ideas and develop a continuous blood pressure recording system using water-driven cuff (Tatsuo T. et. al., 1997). At present, since technology grow, the development of wearable cuff-less blood pressure measurement device using new techniques, such as Pulse Wave Velocity (PWV), Pulse Transit Time (PTT) and PhotoPlethymoGramm (PPG) amplitude approach becomes interest among biomedical engineering researchers. Assist by nano-technology semiconductor, the bio-instrument can be designed smaller and light to carry around by users thus, their heath conditions can be monitored during daily activities. 1.2 Problem Statement In modem world, demands to improve living styles causes most people not to really concerned about their healthiness (NHLBI, 2008), however since the awareness of high blood pressure is the biggest known cause of disability and premature death through stroke, heart attack and heart disease, medical doctor recommended a regular self monitoring of blood pressure to make sure of the necessary to control blood pressure and prevent it from taking the shape of either hypertension or hypotension (Martin Bald and Peter F. Hoyer, 2001; George Stergiou, 2004). R. S. H. Istepanian et al., (2004) mention that the evolution of e-health systems from desktop platform to wireless mobile shows the disadvantages of conventional blood pressure meter that limited their application in home monitoring. These conventional blood pressure meters can be consider as bulky and the capability to use these instrument several times for daily monitoring is inconvenience. Indeed, the invention of wireless technology in medical system and different approach to measure blood pressure is the basic motivation of the present work. Herein, this research is done to estimate blood pressure, using cuff-less method base on pulse transit time. In addition, a graphic user interface is designed to display the measurement of systolic and diastolic blood pressure via computer platform wirelessly to describe wireless mobile healthcare as future trend. 1.3 Research Objective This research is intended to estimate blood pressure different fiom conventional oscillation technique. Therefore, the objectives of this research are: To design a non-invasive cuff-less blood pressure meter based on pulse transit time (PTT). 1.4 Research Scope To display the estimated value of systolic blood pressure and diastolic blood pressure using graphic user interface. In order to archive the objectives, this project research is done guided by the following scope: Designing an electronic circuit which consists of sensor, amplifier circuit and a band-pass filter to obtain the PhotoPlethymoGramm (PPG) waveform. Calculating the Pulse Transit Time from generated ECG waveform and PPG waveform and then estimate the diastolic blood pressure and systolic blood pressure base on equation describe by C.C.Y Poon and Y.T. Zhang (2005). Designing of micro-controller circuit to perform an analog to digital converter and to transmit the signal to computer via Bluetooth module interface. Designing software to perform an algorithm to measure the Pulse Transit Time and then a graphic user interface to display the estimated systolic blood pressure and diastolic blood pressure base on equation describe by C.C.Y Poon and Y.T. Zhang (2005). 1.5 Thesis Outline This thesis consists of five chapters. Each chapter elaborates different stage development of this project until to conclusion. The first chapter of this thesis presents the background of the project, problem statements, objectives, scopes and project methodology. The second chapter of the thesis is the literature review to explain the overview blood pressure in terms of unit, classification, measurement technique, and further explore the current research on pulse transit time technique. The third chapter of the thesis describes the methodology used to ensure the smooth running of this project which is done step by step. The forth chapter of the thesis present the electronics design of the PPG circuits which includes the designs of current-to-voltage, band-pass filter that consists of high pass filter and low pass filter, amplifier circuit. Also include in this chapter is the graphic user interface design and algorithm to measure the Pulse Transit Time. The fifth chapter shows the result acquired fiom the experiment while developing the circuit and result obtain from the offline and online estimation of the system. The last chapter of the thesis briefly explains the conclusion and recommendation for future works of the project CHAPTER 2 LITERATURE REVIEW 2.1 A Blood Pressure Measurement Overview Blood pressure is the measurement of the force applied to the blood vessels during blood circulating which is decrease as it moves away from the from the heart through arteries and capillaries, and toward the heart through veins which is represent one of the principal vital signs often measured and the most intensively studied parameter in medical and physiological practice (R.S. Kahndpur, 2005; Wikipedia, 2009; BHS, 2009). For each heartbeat, blood pressure measurement varies between systolic and diastolic pressures. The highest pressure occurs when blood is travels through the arterial circulation by the contraction of the heart which known as the 'systolic' blood pressure (SBP), while 'diastolic' blood pressure (DBP) measurement is taken during the heart relaxes between beats when the pressure in the arterial circulation falls to its lowest level (Hellen, 2001). When the measurements are written down, both are written one above or before the other with the systolic being the first number, example 120180mmHg. Table 2.1 shows the standard categories of blood pressure related to measurement of systolic blood pressure and diastolic blood pressure for any adults which in the Stage 1 for high blood pressure is discovered from a systolic pressure measurement at more than 140 mmHg and/or from a diastolic pressure measurement if more 90 mmHg (S. Colak and C. Isik, 2003). 7 Table 2.1 : Classification of blood pressure for adults (C. Isik, 2006) Blood pressure is most commonly measured via a sphygmomanometer which consists of a combination of cuff, inflating bulb with a release valve and a manometer. A manometer is a device which historically used the height of a column of mercury to reflect the circulating pressure. Sphygmomanometer has been the "gold standard" in noninvasive measurement for over 100 years (C.C.Y. Poon and Y.T. Zhang, 2005). Figure 2.1, 2.2 and 2.3 illustrate the apparatus used to measure blood pressure invention on 188 1 till today. Figure 2.1 : Von Basch's sphygmomanometer invented about 188 1 Today blood pressure values are still reported in millimeters of mercury (mmHg), though electronic devices which eliminate the used of mercury. In future, [...]... between blood pressure measurement using pulse oximeter method and conventional technique to determine that blood pressure reading based on pulse oximeter is in best agreement with value obtained by conventional method during slow inflation and deflation of cuff As a result, blood pressure reading during inflation of the cuff gives the best correlation between systolic blood pressure and pulse oximeter blood. .. PleMry Mood pressure gauge Figure 2.2: Mercury and aneroid blood pressure gauges Figure 2.3: Digital blood pressure meter 2.2 Blood Pressure Measurement Techniques Blood pressure measurement techniques are generally put into two basic methods; namely direct and indirect Direct techniques or invasive techniques provide continuous and much reliable information about the absolute vascular pressure from... a typical setup of a fluid-filled system for measuring blood pressure which consist of catheter that is inserted to blood vessel, pressure transducer and pressure monitor for continuous monitoring blood pressure for patient in intensive care unit The invasive techniques will not be further discussed in this research Figure 2.4: Typical setup of a pressure measuring system by direct method (R.S Kahndpur,... their blood pressure estimations on variations in the pressure of the occluding cuff, as the cuff is inflated and deflated Similar to the auscultatory technique, oscillometric also applies an inflated cuff to the arm or wrist These variations are due to combination of two effects that are the controlled inflation or deflation of the cuff and the effects of arterial pressure changes under the cuff Instead... occluding cuff deflates from a level above the systolic pressure, the artery walls begin to vibrate or oscillate as the blood flows turbulently through the partially occluded artery and these vibrations will be sensed by the transducer system that monitoring cuff pressure As the pressure in the cuff further decrease, the oscillations increase to maximum amplitude and then decrease until the cuff is fhlly... available product is automatic type where instead of manually inflated the cuff, the automatic devices taking cuff- pressure measurements while releasing the cuff pressure in a controlled way 2.2.2.3 Pulse Transit Time Technique Studies by N Lutter et al (2002) express that the blood pressure slightly depends on blood density, blood viscosity and damping, but essentially relies on the pulse wave velocity... of a stethoscope to listen for the sounds of blood flowing through the artery during inflation and deflation of the cuff Figure 2.5 below shows the appearance of the first Korotkoff sound is the systolic pressure value and the diastolic pressure value is fixed by the last Korotkoff sound is heard When the cuff pressure is above the systolic pressure, blood pressure cannot flow and no sound is heard (R.S... Detail construction of the PPG circuit and acquisition system is reported in Chapter 4 of this thesis 3.3.2 Digital Blood Pressure Monitor For calibrating and comparison the blood pressure was measured by Automatic Digital Blood Pressure Monitor model UA-774, A&D Medical, Japan . ! f :' DIA I - - * \ I -** Ad PUL Figure 3.4: Automatic Blood Pressure Monitor (Model: UA-774, A&D Medical, Japan) 3.3.3... theory The actual determination of blood pressure by an oscillometric device is performed by a proprietary algorithm developed by the manufacturer of the device as shown in Figure 2.8 Blood Pressure Estimation/ Display 4 Pulse Profile/ Feature Extraction Cuff Pressure Measurement 4 Figure 2.8: A typical organization of algorithms components of oscillatory blood pressure measurement (Isik C., 2006)... arteries dimensions, and neglected some changes in undesired factor, into MoensKorteweg's formula, the systolic blood pressure and diastolic blood pressure then can be estimated from the equations as below which conclude that the difference in systolic blood pressure and diastolic blood pressure is inversely proportional to the square of pulse transit time (PTT) SBP = DBP + (SBP, - DBP, Harry Asada . PleMry Mood pressure gauge r=l Figure 2.2: Mercury and aneroid blood pressure gauges Figure 2.3: Digital blood pressure meter 2.2 Blood Pressure Measurement Techniques Blood pressure. of blood pressure related to measurement of systolic blood pressure and diastolic blood pressure for any adults which in the Stage 1 for high blood pressure is discovered from a systolic pressure. non-invasive cuff- less blood pressure meter based on pulse transit time (PTT). 1.4 Research Scope To display the estimated value of systolic blood pressure and diastolic blood pressure using