Cuff less blood pressure meter system

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;

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

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

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)

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)

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

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,

invention of nanotechnology promises a better innovation in medical instrumentation which optimistically sustains human healthiness

PleMry Mood pressure gauge

r=l

Figure 2.2: Mercury and aneroid blood pressure gauges

Figure 2.3: Digital blood pressure meter

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 probes or transducers inserted directly into blood stream But the additional information is obtained at the cost of increased disturbance to the patient and complexity of the equipment

Meanwhile, the indirect methods or non-invasive techniques consist of simple equipment and cause very little discomfort to subject but intermittent and less informative (Walter W et al, 1976; R.S Kahndpur, 2005) However, the accuracy gap between the invasive and the non-invasive methods, and has been narrowing with the increasing computational power available in portable units, which can process signal algorithms in speed of nanosecond (Isik C., 2006)

Section 2.2.1 and 2.2.2 draw some further differences between the direct and the indirect techniques

The operation of direct measurement uses a pressure transducer that is coupled to the vascular system through catheter that is inserted to blood vessel The measurement is done to a very high level of accuracy and repeatability and is continuous, resulting in a graph of pressure against time Therefore the direct technique is used when it is necessary to accurately monitor patients' vital signs during critical care (R.S Kahndpur, 2005)

Figure 2.4 shows 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, 2005)

2.2.2 Indirect (Non-invasive) Techniques

The conventional technique of making an indirect measurement of blood pressure is by the used of a cuff over the limb containing the artery This technique was introduced by Riva-Rocci for the determination of systolic and diastolic pressures (Jeremy B., 1977) The majority of blood pressure measurements do not require continuous monitoring or extreme accuracy Therefore non-invasive techniques are used in most cases, maximizing patient comfort and safety

Currently available devices for non-invasive measurement are manual devices that use auscultatory techniques, semiautomatic devices which use oscillatory techniques and automatic devices whereas most of these devices use oscillatory techniques (Isik C., 2006)

2.2.2.1 Auscultatory Technique

Auscultatory techniques use a stethoscope over Riva-Rocci cuff to observe the sounds made by constriction of the artery which is introduced by a Russian surgeon, Nikolai Korotkoff in 1905 (Jeremy B., 1977) Korotkoff found that there were characteristic sounds at certain points in the inflation and deflation of the cuff These 'Korotkoff sounds' were caused by the passage of blood through the artery, corresponding to the systolic and diastolic blood pressures A crucial difference in Korotkoffs technique was the use 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 Kahndpur, 2005; Isik 2006)

Figure 2.5: Principal of blood pressure measurement based on Korotkoff sounds (R.S Kahndpur, 2005)