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 RivaRocci, 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).
To display the estimated value of systolic blood pressure and
diastolic blood pressure using graphic user interface.
1.4
Research Scope
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 1881 till today.
Figure 2.1 : Von Basch's sphygmomanometer invented about 1881
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
r=l
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 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
Uo sounds
(artery is closed)
Sounds heard
(artery is opening
and closing)
'40 sounds
:artery is open)
ounds are he
rith stethosco
Nbbefcuft
tery
-
.,..,
ai.."d"m
d
L squeezabhe bulb
inflates culY with air
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.
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).
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
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
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 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 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
Actuator is ylchorrd
to the control unit at
con-,e
Polymer
Xctu3tw
these points
Control
/ unit
Photo
I
----'
LED Amy 7--
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 noninvasive 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~
Data Acc
Genera
Software Development
C
stimation
C
stimation
6
Result
Figure 3.1 : Flowchart of Research Methodology
Debugging
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.
ECG Generator
1
Sensor
b
Signal
Conditioning &
Amplifier Unit
b Data Acquisition
-
To PC through
Bluetooth
Interface
1
Offline
Measurement
1
Online
Measurement
Figure 3.3: Basic block diagram of measurement system
3.3.1 PPG Circuit Design
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.
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
mvllns
'
7
7
muww
hunwn.hWV
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.