Non invasive

Fig. 1. : Photoplethysmography technique.
Non-invasive Blood Pressure Remote Monitoring
Instrument Based Microcontroller
Basem Abu Zneid1
, Mohammed Al-zidi1
, Tareq Al-kharazi1
1
Department of Biomedical Instrumentation And Signal Processing, Faculty of
Bioscience and Medical Engineering, Universiti Teknologi Malaysia, 81310 Skudai,
Malaysia.
Abstract— The paper presents design and development of a
Non-invasive wireless blood pressure data acquisition instrument
for remote monitoring based Micro-controller and Bluetooth
transmission kit. The real-time blood pressure biomedical signal
is measured using an optical measurement circuit based
Plethysmography technique (PPG) continuously for a long period
of time. The detected measured signal amplified using an
operational amplifier circuit and interfaced with the Micro-
controller. Blood pressure readings with help of developed
algorithm has been calculated and transmitted via Bluetooth kit
to the stationary computer. Numerical reading values of systolic
and diastolic blood pressure remotely recorded and displayed
with help of LCD as well stationary computer. Furthermore, the
obtained results were compared with existing devices data like a
Sphygmomanometer to verify the accuracy of the developed
Instrument.
Keywords- wireless; Noninvassive measurement; continuous
blood pressure; monitoring system; wireless
I. INTRODUCTION
Blood pressure (BP) is a measurement of the force applied
on the walls of artery vessels as heart pumps blood through the
body. Moreover, blood pressure measurement is known as one
of the vital signs and is widely used to monitor the
physiological condition of human beings along with other vital
signs such as heart rate, breathing rate, oxygen saturation and
temperature [1]. Blood pressure can be seen as two variation
systolic Blood pressures (SBP) and diastolic Blood pressure
(DBP), and systolic is the peak or the maximum pressure on
the walls of the arteries which happens when the ventricles of
the heart are contacting. While, diastolic is the minimal
pressure in the arteries, which happens near the end of the
cardiac cycle when the ventricles are filled with blood.
Typically, measured values for a healthy, resting adult are 115
millimeters of mercury (mmHg) (15 kilopascals [kPa]) systolic
and 75 mmHg (10 kPa) diastolic [2]. Systolic and diastolic
blood pressure measurements are not always static and Blood
pressure does tend to change during the day. They also change
in response to stress nutrition, drugs, and illness and exercise
[3].
The measurements of BP are of a great importance because
it is used for detection of hypertension (high blood pressure).
Hypertension is a continuous, consistent, and independent risk
factor for developing cardiovascular disease. Hypotension can
cause the blood supply to the brain, heart and other tissues to
be too low, and hypertension is strongly correlated with higher
risk for cerebral stroke and heart infarct [4]. Blood pressure
measurement is also important for particular disease patients,
such as hemodialysis patients. Hence, in the daily life, blood
pressure measurement and management is very useful for
handling health situation and plays a preventive function.
Most non-invasive blood pressure monitors are based on
either the auscultation or the oscillometric method [5].
Although both methods are generally accepted and widely used
but they severely restrain patients’ mobility, they require
uncomfortable cuffs; they are not suitable for home-care and
cannot be used for continuous long-term monitoring
applications. Continuous measurement of BP for homecare
requires an accurate and inexpensive method that is
independent from patient movement and does not require
continuous care by a practitioner. These requirements can be
found in this monitoring system which will be designed using
photoelectric plethysmography (PPG) technique.
PPG is a simple non-invasive method used to measure
relative changes in pulse blood volume in the tissues. It utilizes
the use of reflectance sensor that contains an infrared light
source. The light source illuminates a part of the tissue
(fingertip, toe, ear lope, etc.) and a photo-detector receives the
returning light. The waveform obtained from this technique
represents the blood volume pulse which can be used to
measure blood pressure. PPG concept is shown in fig. 1 where
an Infra-red (IR) sensor is used as the source and a
phototransistor is used as the detector. The sensor operates in
reflection (‘adjacent’) mode where the source and the detector
are place side by side.
More to the point, a developed technique based on a
noninvasive continuous blood pressure measurement using
2014 IEEE Region 10 Symposium
978-1-4799-2027-3/14/$31.00 ©2014 IEEE 248

Fig. 3. : Block diagram of our developed system
Fig. 2. Pictorial view of the developed system
volume oscillometric method and photoplethysmograph
technique has been investigated [6], and the study uses high
intensity LED and a LDR (Light Dependent Resistor) and
placed them at the edge of a finger. The concept is that the
resistance of the LDR changes according to the light intensity
received by the LDR. The change in resistance is proportional
to the change of blood volume and as well as blood pressure in
the finger. The result showed the systolic and diastolic blood
pressure on a mini LCD.
In addition, a non-invasive blood pressure monitor was
developed using photoplethysmograph method. Authors used
infrared transmitter and receiver to estimate blood pressure in
the fingertip. Authors were able to measure blood pressure and
concluded that the results are in agreement with the standard
blood pressure measurements [7].
On the other hand, a wireless digital measurement system
was implemented and developed. In approach, piezoresistive
transducer was used as the sensor and the device makes use of
a microcontroller and a Sallen-Key active. The system
transmits the collected data to a remote computer through a
wireless device [8].
Moreover, blood pressure measuring system at the wrist
based on the volume-compensation method has been developed
[9]. The authors used a method called volume-compensation in
which cuff pressure (Pc) is gradually increased, and then the
unloaded vascular volume (V0) is determined from the mean
level of the DC component of the photo plethysmography (PG)
signal (PGdc) at point of maximum amplitude of the pulsation
signal of PG (PGac) [9].
II. METHOD AND MATERIALS
The block diagram of the developed system is shown in
fig. 3. The system mainly consists of three stages: the sensing
measurement circuit, signal amplification circuit,
microcontroller and transmission unit.
A. Sensing stage
The detection of the blood pressure signal is based on using
optical measurement technique called photoelectric
plethysmography (PPG). This technique has the ability to
detect the volume of blood pressures in the arteries. The PPG
basic form utilizes two components: a light source to
illuminates a part of the tissue (e.g. fingertip) and a photo
detector to receive the light. Transparency of living tissue to
light makes it possible for some part of the light from the
source to pass through the tissue to the photo-detector.
However, some part of the light is absorbed by the blood, bone,
muscle and skin in the tissue. The volume of the blood in the
vessel varies while the volume of other part remains constant.
Therefore the light absorption is varied only by the change of
volume of blood (increases or decreases) and the returning light
to the photo-detector changes according to the change of blood
volume. The electrical resistivity of the photo-detector changes
depending on the amount of light falling on it. This change of
resistivity results is the change of electrical current flowing in
the detector which is converted into PPG signal.
In this system optical sensor is used where it consists of
infra-red emitting diode as the transmitter and a photodiode as
the receiver. The sensor operates in reflection (‘adjacent’)
mode where the source and the detector are placed side by side
as shown in fig. 5.
B. Signal conditioning stage
After the sensor detected the changes in the volume of
blood pressures, a low frequency and low magnitude bio-
potential signal is received by the photodiode. As the detected
PPG signal is so weak, it must undergo some signal
conditioning (e.g. amplifying and filtering) so that it can be
used for further processing. Since the output voltage of the
photo-detector has a large amount of dc component which
978-1-4799-2027-3/14/$31.00 ©2014 IEEE 249

Fig. 5. Multisim simulation of double stage
bandpassfilter.
Fig. 4. Fig. 5: The optical sensor [9]
requires a filter to suppress out the dc component. A good filter
choice will be the use of an active bandpass filter because its
first cut off frequency can be used to remove direct current
(DC) and its second cutoff frequency can be used to remove
unwanted high frequency components in the signal like power
line interference (50 Hz). In addition, the filter is also used with
a very high gain for amplifying the signal.Two stage bandpass
filter are used and each stage has different gain. The design of
is shown in fig. 6.
For first stage (from fig. 3.3), the gain is calculated using:
. = 122.95 (1)
Normally the frequency of An average person’s heart rate is
between 60 and 80 bpm (1Hz to 1.2Hz) [1], thus the bandwidth
of the filter will be set between 0.2 Hz to 2.5 Hz so that the
PPG signal frequency is saved and the noises are cancelled out.
The cut off frequencies are calculated using for low
frequency.
c= = = 0.2Hz (2)
For high frequency
c= = = 2.5Hz (3)
For second stage (from fig. 3.3), the gain is calculated
using:
= 661 (4)
The cut off frequencies are calculated using for low
frequency
c= = = 0.2Hz (5)
For high frequency
c= = = 2.8Hz (6)
The total gain of the system is calculated by multiplying the
gain of the first stage with the gain of second stage as
shown:
Total Gain is (A1*A2) = 68292
C. Microcontroller stage
The output of the signal conditioning stage is fed into a
microcontroller where it is processed (sampling and
quantizing). The Atmega32 microcontroller is used in this
system where it has a built-in ADC. The microcontroller
finds out the smallest (represents DP) and the largest
(represents SP) value form the output voltage using a
program written in ardunio software. The microcontroller
then displays the measured blood pressure information in
mini LCD and transmits them through a Bluetooth device
to any stationary enabled computer device.
The program flowchart is shown in fig. 7 where the
microcontroller is initialized and then set to read the analog
signal form pin A0. Timer interrupt 2 is used here so that
we can keep track if there are changes in the signal. The
microcontroller then finds the highest peak of the signal
and the lowest peak of the signal and then displays them as
systolic and diastolic readings respectively in the LCD and
Parallel serial terminal software via Bluetooth transmission
kit.
978-1-4799-2027-3/14/$31.00 ©2014 IEEE 250

Fig. 7. Flow chart for the developed system
Fig. 9. Microcontroller with l6x2 LCD.
(a). input signal (b) output signal
Fig. 6. Input and output waveform of amplifier in Multisim.
Fig. 8. Output of measurement circuit (left) and output of analog
signal (right).
Fig. 10. Result of the developed systm displayed on
LCD
The mini LCD display is interfaced with as shown in Fig. 8.
The Bluetooth technology used in this system is acquired
by using Bluetooth (SKKCA-21) Remote Control. SKKCA-21
module offers simple yet compact Bluetooth platform for
embedded applications. It has a surface mount layout which
makes the process of development and application easier.
The Bluetooth transmits the reading to the PC equipped
with Bluetooth. The display on computer is acquired using
special software called Parallax-Serial-Terminal. It is simple
terminal software which allows users to display results through
predefined serial ports.
In this project, the Bluetooth serial port is configured with
Parallax to display the results.
III. RESULT AND DISCUSSION
The input and output waveform of the amplifier circuit is
shown in Fig. 9:
After simulation, the analog circuit was tested in the lab
using oscilloscope. The oscillographic representation of the
blood pressure measurement circuit and the analog signal (
signal conditioning) are shown in Fig.10 ,which were
practically observed. The output of the measurement circuit
(on the left) was observed before amplifying. While, the output
of the signal conditioning or analog circuit (on the right) was
observed after using the two stage bandpass filter with
amplifier.
In Fig. 11, Systolic pressure (SP) and diastolic pressure
(DP) reading are shown on LCD.
The same results in fig. 11 are Then transmitted to the PC
via Bluetooth. The transmitted results are acquired by Parallax-
Serial-Terminal software and a snapshot of the result displayed
on the program is shown below in fig. 12.
978-1-4799-2027-3/14/$31.00 ©2014 IEEE 251

Fig. 11. Result of the developed systm displayed on LCD
Fig. 12. : comparison between proposed method reading and
standard reading
Fig. 13. : readings for one subject at different time
To verify our developed systems reliability we have
performed some test with 6 subjects using sphygmomanometer
at the right arm and compared it with our developed system
results. These readings are shown in Table 1.Where MAP is
Mean Arterial Pressure (mm Hg) which equals to (1/3 (Pulse
pressure) + Diastolic pressure,). And Pulse Pressure (mm Hg)
equals to Systolic Pressure minus Diastolic pressure.
According to American National Standard for electronics or
automated sphygmomanometers, the mean difference should
be ±5 mm Hg. So from the above table the difference in
PP of our system with sphygmomanometer is under standard
rule. Therefore, the proposed results are quite reliable and
according to international standards.
TABLE I. COMPARISON BETWEEN PROPOSED METHOD READING AND
STANDARD READING
To verify our developed systems accuracy we have also
performed some test with one subject using index finger with
our developed system and at the same time using
sphygmomanometer at the right arm. The test was performed
every ten minutes for six different time .These readings are
shown in Table 2.
The variation of SP and DP for index finger of proposed
system and standard or Sphygmomanometer of the same
person for six different times
TABLE II. READINGS FOR ONE SUBJECT AT DIFFERENT TIME
time index finger Sphygmomanometer
systolic diastolic MAP systolic diastolic
MAP
T1 122 75 90 119 77 91
T2 120 78 92 118 76 90
T3 125 84 97 127 86 99
T4 121 78 92 125 83 97
T5 124 83 96 129 85 99
T6 127 86 99 129 87 101
sub Sphygmomanometer
System
Proposed system readings
systolic diastolic
MAP
systolic diastolic
MAP
S1 117 72 87 122 75 90
S2 119 77 91 124 80 94
S3 122 79 93 126 82 96
S4 123 82 95 127 86 99
S5 123 83 96 125 84 97
S6 126 85 98 131 85 100
978-1-4799-2027-3/14/$31.00 ©2014 IEEE 252

IV. CONCLUSION
In this paper, we developed Noninvasive Wireless Remote
Monitoring Blood Pressure Measurement Instrument based
Microcontroller and using photoplethysmography technique.
The blood pressure was measured continuously for a long
period of time with help of developed algorithm the small
embedded system and displayed the systolic and diastolic
blood pressure on a mini LCD. The results were further
compared with existing devices data like
sphygmomanometer to verify the accuracy of the
developed system. Moreover, the developed system can
transmit the measured blood pressure values to any Bluetooth
enabled device though Bluetooth wireless technology. This
system provides users an easy-to-use interface and simple BP
management environment. The Bluetooth interface provides a
convenient and low-power consumption method for data
transmission.
REFERENCES
[1] Majid M. , Sreeraman R. , Miodrag B. and Voicu Z. . Blood Pressure
Estimation using Oscillometric Pulse Morphology . Ottawa, ON,
Canada. 33rd Annual International Conference of the IEEE. 2011.
[2] Inga Harris, blood pressure monitors , freescale , 2007.
[3] K. Bynum, "Experimental laboratory physiology BIOPAC Lab
exercise manual", lesson 16, lesson 17.
[4] Meir N. Automatic Noninvasive Measurement of Arterial Blood
Pressure. IEEE Instrumentation & Measurement Magazine. February
2011 .
[5] Seppo N., Mika S., Hannu S., Eija V. G., Risto M. , NON-INVASIVE
BLOOD PRESSURE MEASUREMENT BASED ON THE
ELECTRONIC PALPATION METHOD , University of Oulu,
Department of Electrical Engineering , 1998.
[6] Md. M., Fida H., Rafi, Abu F.,and M., A. Rashid, M. Fareq.
Development of a Noninvasive Continuous Blood Pressure
Measurement and Monitoring System. Department of Biomedical
Engineering Khulna University of Engineering & Technology. Khulna,
Bangladesh. 2012.
[7] M. Asif , Md Sabbir. blood pressure measurements using
PHOTOPLETHYSMOGRAPHY. University of Bangladesh .2011
[8] Shumei G. Yilin S. Shinobu T. and K.Yamakoshi . Development of
An Instantaneous Blood Pressure measuring System at the Wrist Based
on the Volume-
[9] JuneY. Kim. Design of InfraredSensor Based Measurement System
for Continuous Blood Pressure MonitoringDevice. University of
Minnesota.2011 J. Clerk Maxwell, A Treatise on Electricity and
Magnetism, 3rd ed., vol. 2. Oxford: Clarendon, 1892, pp.68–73.
978-1-4799-2027-3/14/$31.00 ©2014 IEEE 253

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