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,

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

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 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.

2.2.1 Direct (Invasive) Technique

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).

Figure 2.6 explain that when the artery is fully closed or when the cuff is

inflated to maximum by squeezing the bulb, no sounds is heard, in while the air in

cuff is released gradually by opening the bulb valve artery is opened slowly and

sounds heard. Then there is no sound is heard means artery is fully opened when the

cuff is fully deflated. The mercury manometer or aneroid gauge can be used to

indicate the measurement of systolic and diastolic pressure.

Sphygmomanometer

bbef cuft

tery - ."d"m d

Uo sounds (artery is closed)

Sounds heard (artery is opening and closing)

N

ai. .,.., L squeezabh

inflates cul e bulb Y with air

'40 sounds :artery is open)

ounds are he rith stethosco

Figure 2.6: Illustration of the auscultatory measurement technique

2.2.2.2 Oscillatory Technique

Most automatic devices and semi-automatic devices base 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 of detecting the Korotkoff sounds, a

pressure transducer is used to record the cuff pressure oscillation while the cuff is

being slowly deflated. Therefore in the oscillometric technique, high environmental

noise levels such as those found in a busy clinical or emergency room do not disturb

the measurement. However any movement or vibration during the measurement will

cause inaccurate readings (R.S. Kahndpur, 2005; Isik 2006).

The oscillometric technique operates on the principle that as an 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 deflates and blood flow

returns to normal.

The cuff pressure at the point of maximum oscillations usually corresponds to

the mean arterial pressure. Figure 2.7 shows the point above the mean pressure at

which the oscillations begin to rapidly increase in amplitude correlates with the

diastolic pressure.

Figure 2.7: Oscillations in cuff pressure (R.S. Kahndpur, 2005)

These correlations have been derived and proven empirically but are not yet

well explained by any physiologic 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.

Figure 2.8: A typical organization of algorithms components of oscillatory blood

pressure measurement (Isik C., 2006).

Blood Pressure Estimation/

Display

Most 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

4

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 (PWV), the pulse transit time (PTT), the velocity pulse, the

arterial diameter and the reflection coefficient. Thus, BP can be calculated by

continuously and simultaneously determining the R wave of electrocardiogram (ECG)

and the pulse oximeter waveform utilizing the pulse oximeter of

PhotoPlethysmoGrarnrn .

Works by J. Y. Lee et al., (2005) then has shown that low accuracy and

incompatibility of using oscillometric. Then by utilizing a blood pressure

measurement in finger artery the authors come out with new measurement algorithm

Pulse Profile/ Feature

Extraction 4

Cuff Pressure Measurement

for systolic and diastolic blood pressure measurement utilize PhotoPlethymoGramm

which is measured in finger branch and tip for calibration.

K. P. Sanghvi and Peter Steer (1998) from their experiment for two month at

Neonatal Intensive Care Unit, Brisbane confirmed that non-invasive measurement of

systolic blood pressure with sphygmomanometer and pulse oximeter is accurate and

reliable.

Khalili GT et al. (2002) later then make a comparison 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 pressure.

Foo et al. (2005) in his experiment found that the PTT measured from finger

PhotoPlethysmoGramm (PPG) will increase when the position of tested arm was

vertically changed.

C. C. Y. Poon and Y. T. Zhang (2005) successfully developed cuff-less blood

pressure measurement technique based on Moens-Korteweg's formula as describe by

N. Lutter et al, (2002). In the modeling, by substituting Young's modulus, change in

arteries dimensions, and neglected some changes in undesired factor, into Moens-

Korteweg'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 et al (2005) then has been working on the development of BP

sensors based on PhotoPlethysmoGram (PPG) which is a non-invasive circulatory

signal related to the pulsatile volume of blood in tissue, displayed by most pulse

oximeter along with the computed arterial oxygen saturation. PPG is a desirable

sensor modality for wearable health monitoring, since it is miniaturizable and

consume low power. Figure 2.9 illustrate the layout design of devices have the

potential for long-term, continuous monitoring of pulse, oxygen saturation, and pulse

rate variability and proposed by Hany Asada research team.

- con- Po1,luer con-,e Polymer Actuator is ylchorrd Xctu3tw to the control unit at

these points Control

/ unit

Photo

LED Amy 7-- ----' I Conducting. Polymer Actuator is anchored

to the sensor unit at this point

Figure 2.9: Illustration of the conducting polymer actuated wearable blood pressure

sensor

Yinbo Liu and Y.T Zhang (2006) then studies the phenomenon describe Foo

et al. (2005) to hrther the potential used of the Pulse Transit Time based approach to

monitor peripheral blood pressure non-invasively while allowing the limb

maintaining at different positions from heart level.

Carmen C. Y et al. (2006) then developed novel technologies that enable the

wearable devices and body sensor network for telemedicine and M-health for non-

invasive monitoring especially for blood pressure by cuff-less pulse transit time

technique. Even though the PTT based technique have to comply with Advancement

of Medical Instrument (AMMI) a standard which is required 5*8mmHg difference

between the estimated and reference diastolic blood pressure (DBP).

Y. T Zhang et al. (2006) and Iris R.F Yan et al. (2007) then evaluate the

prototype of wearable medical devices using wireless heart rate finger ring sensor

and watch utilize personal digital assistant PDA for wireless and cuff-less blood

pressure meters to introduce long-term monitoring of heath condition utilize body

sensor networks (BSN). The designed uses electrodes and infrared sensor to estimate

blood pressure based on pulse transit time (PTT). Result from their experiment,

shows the PTT based technique almost achieved a B grade in British Hypertension

Society (BHS) protocol.

Sujay Deb et al. (2007) conduct an experiment to estimate systolic blood

pressure using Pulse Arrival Time (PAT) using linear regression model and then

compare with estimation of systolic blood pressure using Pulse Transit Time using

regression model. Determine the PAT and PTT from ECG and PPG waveform taken

from brachial and finger using algorithms developed in MATLAB by offline process.

The research teams then conclude that SBP variation is more closely related with

PAT variation which is summation of PTT and pre-ejection period (PEP) compare to

variation due to PTT.

In experiment conducted by Klein J. D et al. (2008), they measured the PTT

at different position on body which is right finger, left finger and left ear and then

applied linear fitting to measured systolic arterial pressure. Via National DAQ Card

the data is collected by National Labview software and by performing offline

algorithm to select the R wave of ECG to search the valid PPG signal give

conclusion that is possible to estimate systolic arterial pressure.

Stefan Hay et al. (2009) in his studies for psycho-physiological stress

monitoring measured the pulse transit time fiom ECG and finger probe PPG

conclude that a disadvantage of this method is a sudden movement of hand will

cause a big signal distortion.

Based on previous work of the researchers, then it is decided to estimate the

BP using the pulse transit time method. This PTT will utilize pulse oximeter and

ECG as describe by Stefan Hay et al. (2009) and the estimation will base on equation

(2.1) and equation (2.2) modeling by C. C. Y. Poon and Y. T. Zhang (2005). The

different is the ways of using sensor circuit configuration to construct the PPG

waveform utilize the finger probe oximeter to detect the light in appearance of finger

in between the light source and the photo detector sensor.

CHAPTER 3

METHODOLOGY

3.1 Project Approach

In order to design this blood pressure measurement system, a stage by stage

problems needs to be go throughout in this research.

At the beginning, initial studies of blood pressure concept in-term of

measurement, techniques and related research is done and then a measurement

method based on Pulse Transit Time (PTT) is proposed for this project.

Based on the chosen method, the PhotoPlethymoGramm (PPG) circuit is

designed to acquire PPG waveform. Here the concept on how it works for the finger

probe sensor, amplifier circuit, filtering circuit is studies. Then it is decide to use

ECG generator to acquire ECG waveform.

Both data from PPG and ECG then is used for offline measurement to ensure

the algorithm to measured PTT from ECG and PPG is corrected before online

measurement is made.

Then the software is developed for PTT measurement algorithm and a

graphical user interface (GUI) to display the estimated systolic blood pressure and

diastolic blood pressure measurement is designed. This software is designed to be

able to perform offline and online estimation. For the online estimation, the

integration of software and hardware is connected via Bluetooth interface to describe

the m-health system. The ideas on how to do this research is describe in Figure 3.1

where the offline measurement is initially done before the online measurement is

tested.

The experiment procedure is described in section 3.4 of this chapter.

hod ction

uit Desi~

Genera Data Acc

Software Development Debugging

C n

C n

stimatio

stimatio

Result 6 Figure 3.1 : Flowchart of Research Methodology

3.2 Chosen Method

Blood Pressure measurement based on Pulse Transit Time (PTT) approach is

chosen for this project. As being describe in chapter 2, PTT is a delay time measured

from R wave of electrocardiogram (ECG) to base point of PhotoPlethysmoGramm

(PPG). Since PPG can be acquired from finger, ear, brachial or toes, in this project

the PPG is taken fiom finger utilize the finger probe of pulse oximetri. Figure 3.2

describe the PTT which is measured from time of peak of ECG (R) to the foot point

of PPG corresponding to the R wave before it rises.

-+ Pulse transit time (PlT) I I I I

\ ,/ .u

Figure 3.2: Measurement of pulse transit time from ECG and PPG (Stefan Hay, 2009)

Then based on estimation equation of diastolic blood pressure (equation 2.1)

and systolic blood pressure (equation 2.2) provide by C. C. Y. Poon and Y. T. Zhang

(2005), the blood pressure is being estimate using PTT measured from R wave of

generated ECG waveform and PPG measured from finger using Nellcor Pulse

Oximetri Sensor.

3.3 Apparatus

A block diagram of the equipment used is shown in Figure 3.3. Sensor for

this project is Nellcor Finger Pulse Oximeter Sensor while the ECG data is generated

by software.

Figure 3.3: Basic block diagram of measurement system

ECG Generator

1

3.3.1 PPG Circuit Design

Sensor

To acquire the PPG waveform, the circuit is constructed from a sensor unit

designed by Nellcor consists of Red LED, Infra Red LED and Photodiode Detector is

used which is special designed to be pulsed so that the peak power can be increased

without increasing the average power and this is possible to detect light transmitted

through the finger with a solid-state photodiode. Through several op-amps, the signal

from photodiode is amplified and filtered before it being converted to digital format

through microprocessor. Through digital oscilloscope the signal is verify and the data

is log for offline analysis.

Detail construction of the PPG circuit and acquisition system is reported in

Chapter 4 of this thesis.

b

1 1

Signal Conditioning & Amplifier Unit

Offline Measurement

Online Measurement

b Data Acquisition - To PC through

Bluetooth Interface

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 ECG Generator

In this research a Java ECG Generator Version 1.0 as shown in figure 3.5 is

used to provide ECG waveform. This software is available online provided by

Patrick E. McSharry and Gari D. Clifford, Biomedical Engineering MIT. Java ECG

Generator and all its components are free software under GNU General Public

License as published by the Free Software Foundation.

The parameter for Generated ECG is set based on standard ECG devices with

sampling frequency 256 Hz (0.004s) and based on Heart Rate Mean taken from

automatic blood pressure monitor (Model: UA-774, A&D Medical, Japan).

Wahoo ECG kbb

'7 mvllns muww 7 h u n w n . h W V

w.n,*mwhn~ Jsoo

?~OZm.m_o.om~.L~

Figure 3.5: Java ECG Generator 1 .O (MIT, 2003)

3.4 Software

Visual Basic 6 (VB6) was selected to develop the algorithm and graphical

user interface (GUI) for the blood pressure reader system. This programming

language Visual Basic is chosen because it takes a different approach to

programming for GUI system where it provides interface builder and there is no

longer 'program' but rather draw the interface. Later on, the code is simply attached

to the interface and the software is ready to execute (Vincent Himpe, 2002).

In addition, a few applications such as Excel, Word and Access all include a

subset of Visual Basic programming language which enable programmer to used it

function to manipulated the data such as data plotting (chart) in Excel application and

data selection using Access function. Moreover, it also includes a programming

philosophy called Object Oriented Programming (OOP). Figure 3.6 illustrate the

GUI in object classes that was designed for this project.