Download Blood Pressure Measurement

CHAPTER 6
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GSM BASED NIBP MEASUREMENT SYSTEM
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6.1 Introduction
Blood pressure measurement is one of the basic clinical examinations. The
origin of blood pressure is the pumping action of the heart and its value depends on
the relationship between cardiac output and peripheral resistance. Therefore, blood
pressure is considered as one of the most important physiological variables with
which to assess cardiovascular hemo-dynamics.
Blood pressure (BP) is the pressure exerted by circulating blood upon the
walls of blood vessels and is one of the principal vital signs.
Blood pressure is also defined, as it is the force created by the heart as it
pushes blood into the arteries through the circulatory system. Each time the heart
contracts or “beats” the blood is pumped out and creates a surge of pressure in the
arteries. Blood pressure is the force exerted by circulating blood on the walls of blood
vessels. The pressure of the circulating blood decreases as blood moves through
arteries, arterioles, capillaries, and veins; the term blood pressure generally refers to
arterial pressure [1], i.e., the pressure in the larger arteries, arteries being the blood
vessels which take blood away from the heart. Fig 6.1 shows the force applied to
artery walls for measureement of Blood Pressure. Blood pressure usually refers to
the arterial pressure of the systemic circulation, usually measured at a person's upper
arm.
Fig 6.1: Blood pressure is the measurement
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A person’s blood pressure is usually expressed in terms of the systolic
pressure over diastolic pressure and is measured in millimeters of mercury. The
systolic arterial pressure is defined as the peak pressure in the arteries, which occurs
near the beginning of the cardiac cycle. The diastolic arterial pressure is the lowest
pressure (at the resting phase of the cardiac cycle). The average pressure throughout
the cardiac cycle is reported as mean arterial pressure. The pulse pressure reflects the
difference between the maximum and minimum pressures measured. The blood
pressure values are reported in millimeters of mercury (mmHg).
Systolic Pressure (SP)
The maximum pressure reached during peak ventricular ejection. Systolic
pressure [2] is the pressure generated when the heart contracts.
Diastolic Pressure (DP)
The minimum pressure just before beginning of ventricular ejection. Diastolic
pressure is the blood pressure when the heart is relaxed.
Table 1: Classification of blood pressure for adults
Category
Systolic (mmHg)
Diastolic (mmHg)
Hypotension
< 90
or < 60
Normal
90 – 119
and 60 – 79
Prehypertension
120 – 139
or 80 – 89
Stage 1 Hypertension
140 – 159
or 90 – 99
Stage 2 Hypertension
≥ 160
or ≥ 100
Typical values for a resting healthy adult human are approximately
120 mmHg (16 kPa) systolic and 80 mmHg (11 kPa) diastolic written as 120/80 mmHg.
These measures of arterial pressure are not static, but undergo natural variations from
one heartbeat to another and throughout the day, they also change in response to
stress, nutritional factors, drugs, or disease. Hypertension refers to arterial pressure
being abnormally high, as opposed to hypotension, when it is abnormally low along
with body temperature. The table 1 shows the classification of blood pressure for
adults aged 18 and older.
Pulse pressure (PP) is the difference between SP and DP, i.e., PP = SP - DP.
The period from the end of one heart contraction to the end of the next is called the
cardiac cycle. Mean pressure (MP) is the average pressure during a cardiac cycle.
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Mathematically, MP can be decided by integrating the blood pressure over time.
When only SP and DP are available, MP is often estimated by an empirical formula:
MP = DP + (PP/ 3) ----------------------------------- (1)
The values of blood pressure vary significantly during the course of 24 h according
to an individual’s activity [3]. Basically, three factors, namely, the diameter of the
arteries, the cardiac output, and the state or quantity of blood, are mainly responsible
for the blood pressure level. When the tone increases in the muscular arterial walls so
that they narrow or become less compliant, the pressure becomes higher than normal.
Unfortunately, increased blood pressure does not ensure proper tissue perfusion and in
some instances, such as certain types of shock, blood pressure may seem appropriate
when peripheral tissue perfusion has all but stopped. The observation of blood
pressures affords dynamic tracking of pathology and physiology affecting the
cardiovascular system. This system in turn has pro- found effects on the other organs
of the body. The measurement of blood pressure requires the anatomy and physiology
of heart.
6.2 Anatomy & Physiology of the Heart
The human heart is located under the ribcage in the center of the chest
between the right and left lung. It’s shaped like an upside-down pear. Its muscular
walls beat, or contract, pumping blood continuously to all parts of the body. The
size of the heart can vary depending on the age, size, or the condition of the heart. A
normal, healthy, adult heart most often is the size of an average clenched adult fist.
Some diseases of the heart can cause it to become larger. The exterior human heart
of a normal and healthy person is as shown in fig 6.2. The heart has four chambers.
The right and left atria (AY-tree-uh) are shown in purple. The right and left
ventricles (VEN-trih-kuls) are shown in red. Connected to the heart are some of the
main blood vessels—arteries and veins—that make up the blood circulatory system.
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Fig 6.2: External Heart Anatomy
The ventricle on the right side of the heart pumps blood from the heart to the
lungs. When a person breathes air in, oxygen passes from the lungs through blood
vessels where it’s added to the blood. Carbon dioxide, a waste product is passed from
the blood through blood vessels to the lungs and is removed from the body when the
person breathes air out.
The atrium on the left side of the heart receives oxygen-rich blood from the
lungs. The pumping action of the left ventricle sends this oxygen-rich blood through
the aorta (a main artery) to the rest of the body.
6.3. Blood Pressure Measurement Principle & Techniques
BP measurement is a physiological variable, which indicates the status of
cardiovascular system. Determination of only its maximum and minimum levels
during each cardiac cycle, supplemented by information about other physiological
parameters is an invaluable diagnostic and to assess the vascular condition and certain
aspects of cardiac performance.
In the heart, blood is pumped by the left heart into the aorta, which supplies it
to arterial circuit, due to load resistance of arterioles and precapillaries. It loses most
of its pressure and returns to heart at low pressure via highly distensible veins. Right
heart pumps it to the pulmonary circuit. This operates at lower pressure.
Blood
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pressure measurements are made with reference to atmospheric pressure, which saves
persons. If BP is high, i.,e hypertension [4], it gives warning to provide treatment.
Arterial pressure is most commonly measured via a sphygmomanometer [5]
which uses the height of a column of mercury to reflect the circulating pressure. The
blood pressure is measured by means of indirect method using sphygmomanometer
(i.e. sphygmo means pulse). This method is easy to use and can be automated. It can
measure systolic and diastolic arterial pressure readings. Modern vascular pressure
devices no longer use mercury, vascular pressure values are reported in millimeters of
mercury (mmHg).
The basis of any physiological measurement is the biological signal, which is
first sensed and transduced or converted from one form of energy to another. The
signal is then Conditioned, Processed and Amplified. Subsequently, it is displayed
and recorded. Blood pressure sensors often detect mechanical signals, such as blood
pressure waves, to convert them into electric signals for further processing or
transmission. They work on a variety of principles, for example, resistance,
inductance, and capacitance. For accurate and reliable measurements a sensor should
have good sensitivity, linearity and stability [6]. In general the Blood Pressure
measurement techniques are made using two types. They are
 Direct Blood Pressure Measurement
 In- Direct Blood Pressure Measurement
6.3.1. Direct Blood Pressure Measurement
Direct measurement is also called Invasive measurement because bodily entry
is made. Arterial blood pressure (BP) is most accurately measured invasively through
an arterial line. For direct arterial blood pressure measurement an artery is cannulated
or catheter. The equipment and procedure require proper setup, calibration, operation,
and maintenance [7]. Such a system yields blood pressures dependent upon the
location of the catheter tip in the vascular system. The cannula must be connected to a
sterile, fluid-filled system, which is connected to an electronic pressure transducer.
The advantage of this system is that pressure is constantly monitored beat-by-beat and
a waveform (a graph of pressure against time) can be displayed. When massive blood
loss is anticipated, powerful cardiovascular medications are suddenly administered or
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a patient is induced to general anesthesia, continuous monitoring of blood pressures
becomes vital. This is usually done by an anesthesiologist or surgeon in a hospital.
Most commonly used sites to make continuous observations are the brachial
and radial arteries. The femoral or other sites may be used as points of entry to sample
pressures at different locations inside the arterial tree or even the left ventricle of the
heart. Entry through the venous side of the circulation allows checks of pressures in
the central veins close to the heart, the right atrium, the right ventricle and the
pulmonary artery. A catheter with a balloon tip carried by blood flow into smaller
branches of the pulmonary artery can occlude flow in the artery from the right
ventricle so that the tip of the catheter reads the pressure of the left atrium, just
downstream. These procedures are very complex and there is always concern of risk
of hazard as opposed to benefit [8].
Invasive access to a systemic artery involves considerable handling of a patient.
The longer a catheter stays in a vessel, the more likely an associated thrombus will
form [9]. In the newborn, when the arterial catheter is inserted through an umbilical
artery, there is a particular hazard of infection and thrombosis, since thrombosis from
the catheter tip in the aorta can occlude the arterial supply to vital abdominal organs.
Some of the recognized contraindications and complications include poor collateral
flow, severe hemorrhage diathesis, occlusive arterial disease, arterial spasm, and
hematoma formation [10].
Direct blood pressure measurement is generally accepted as the gold standard of
arterial pressure recording and also confers the benefit of continuous access to the
artery for monitoring gas tension and blood sampling for biochemical tests. It also has
the advantage of assessing cyclic variations and beat-to-beat changes of pressure
continuously and permits assessment of short-term variations [11], [12].
Disadvantages with invasive blood pressure measurement
The cannulation for invasive vascular pressure monitoring is infrequently
associated with complications such as thrombosis, infection, and bleeding. Patients
with invasive arterial monitoring require very close supervision, as there is a danger
of severe bleeding if the line becomes disconnected. It is generally reserved for
patients where rapid variations in arterial pressure are anticipated.
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6.3.2 Indirect Blood Pressure Measurement
Indirect measurement is often called Non-Invasive measurement because the
body is not entered in the process. The upper arm, containing the brachial artery, is
the most common site for indirect measurement because of its closeness to the heart
and convenience of measurement, although many other sites may have been used,
such as forearm or radial artery, finger, etc. Distal sites such as the wrist, although
convenient to use, may give much higher systolic pressure than brachial or central
sites as a result of the phenomena of impedance mismatch and reflective waves [13].
An occlusive cuff is normally placed over the upper arm and is inflated to a pressure
greater than the systolic blood pressure. The cuff is then gradually deflated, while a
detector system simultaneously employed determines the point at which the blood
flow is restored to the limb. The detector system does not need to be a sophisticated
electronic device. It may be as simple as manual palpation of the radial pulse. The
most commonly used indirect methods are Auscultation and Oscillometry each is
described below.
6.3.2.1. Auscultator Method
The Auscultator method most commonly employs a mercury column, an
occlusive cuff and a stethoscope [14]. The stethoscope is placed over the blood vessel
for auscultation of the Korotkoff sounds, which defines both SP and DP. First raised
cuff pressure until it stopped blood circulation on the distal side of the hand, indicated
by palpating the radial artery. During the following slow pressure drop, audible
sounds could be heard through the stethoscope, which was placed on the skin beyond
the sleeve. These sounds were affected by the blood wave in the artery under the cuff
and were audible at 10-12 mmHg, slightly before the pulse could be palpated on the
radial artery [15]. At this point, cuff pressure is taken to indicate maximum blood
pressure, while minimum blood pressure is achieved when the murmur sounds
disappear. The appearance and disappearance of sound can be used to determine
systolic and diastolic blood pressure, respectively.
The Korotkoff sounds are mainly generated by the pulse wave propagating
through the brachial artery [16]. The Korotkoff sounds consist of five distinct phases.
The onset of Phase I Korotkoff sounds (first appearance of clear, repetitive, tapping
sounds) signifies SP and the onset of Phase V Korotkoff sounds (sounds disappear
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completely) often defines DP [17]. Fig 6.3 shows the summary of the five Korotkoff
sounds a patient. The pressure is then reduced slowly (about 2−3 mmHg a second)
and 4 (or 5) different ‘phases’ of Korotkoff sounds are by the clinician over sequential
pressure ranges:
i.
Initial "tapping" sounds.
ii.
The tapping sounds increases in intensity are less precise in time.
iii.
The loudest phase, more akin to a thump than a tap.
iv.
A much more muffled sound.
v.
Silence − no Korotkoff sounds
Fig 6.3: A summary of the five Korotkoff sounds for a healthy human
Observers may differ greatly in their interpretation of the Korotkoff sounds.
Simple mechanical error can occur in the form of air leaks or obstruction in the cuff,
coupling tube or Bourdon gage. Mercury can leak from a column gage system. In
spite of the errors inherent in such simple systems, more mechanically complex
systems have come into use. The impetus for the development of more elaborate
detectors has come from the advantage of reproducibility from observer to observer
and the convenience of automated operation. Examples of this improved
instrumentation include sensors using plethysmo-graphic principles, pulse-wave
velocity sensors and audible as well as ultrasonic microphones [18].
The readings by auscultation do not always correspond to those of intra-arterial
pressure. The differences are more pronounced in certain special occasions such as
obesity, pregnancy, arteriosclerosis, shock, etc. Experience with the auscultation
method has also shown that determination of DP is often more difficult and less
reliable than SP. However, the situation is different for the oscillometric method
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where oscillations caused by the pressure pulse amplitude are interpreted for SP and
DP according to empirical rules [19].
Measurements based on the auscultator method are difficult to automate,
because the frequency spectrum of the different phases of Korotkoff sounds is closely
related to blood pressure. When a patient’s blood pressure is high, also the recorded
frequency spectrum is higher than normal and decreases as a function of blood
pressure. With hypotensive patients and infants, on the other hand, the highest
spectrum components can be as low as 8 Hz (Whitcher et al. 1966 and 1967), which is
below the human hearing bandwidth. Normotensive subjects, in turn, require a
bandwidth of 20 Hz to 300 Hz for a sufficient reproduction of Korotkoff sounds
(Geddes 1991), although most of the energy of the signal spectrum is below 100 Hz.
Fig 6.4: Indirect blood pressure measurements: Oscillometric & Auscultator
measurement.
6.3.2.2. Oscillometric Method
In recent years, electronic pressure and pulse monitors based on oscillometry
have become popular for their simplicity of use and reliability. The principle of blood
pressure measurement using the oscillometric technique is dependent on the
transmission of intra-arterial pulsation to the occluding cuff surrounding the limb. An
approach using this technique could start with a cuff placed around the upper arm and
rapidly inflated to about 30 mmHg above the systolic blood pressure, occluding blood
flow in the brachial artery. The pressure in the cuff is measured by a sensor. The
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pressure is then gradually decreased, often in steps, such as 5 to 8 mmHg. The
oscillometric signal is detected and processed at each step of pressure. The cuff
pressure can also be deflated linearly in a similar fashion as the conventional
auscultator method.
Fig 6.4 illustrates the principle of oscillometric measurement along with
auscultator measurement. Arterial pressure oscillations are superimposed on the cuff
pressure when the blood vessel is no longer fully occluded. Separation of the
superimposed oscillations from the cuff pressure is accomplished by filters that
extract the corresponding signals. Signal sampling is carried out at a rate determined
by the pulse or heart rate. The oscillation amplitudes are most often used with an
empirical algorithm to estimate SP and DP. Unlike the Korotkoff sounds, the pressure
oscillations are detectable throughout the whole measurement, even at cuff pressures
higher than SP or lower than DP. Since many oscillometric devices use empirically
fixed algorithms, variance of measurement can be large across a wide range of blood
pressures [20].
MP is determined by the lowest cuff pressure of maximum
oscillations [21] and has been strongly supported by many clinical validations [22],
[23].
6.4. Review of Earlier literature of Blood pressure measurement
The ancient Greek physician Galen first proposed the existence of blood in the
human body. Building on ideas conceived by Hippocrates, the body was comprised
of three systems. The brain and nerves were responsible for sensation and thought.
The blood and arteries filled the body with life-giving energy. He also believed that
the liver and veins provided the body with nourishment and growth.
The first recorded instance of the measurement of blood pressure was in 1733
by the Reverend Stephen Hales [24]. A British veterinarian, Hales spent many years
recording the blood pressures of animals. In 1847 human blood pressure was
recorded. The method used Carl Ludwig's kymograph with catheters inserted
directly into the artery.
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Etienne Jules Mary, a French physician/cinematographer, developed this idea
further in 1860. His sphygmograph could accurately measure the pulse rate, but was
very unreliable in determining the blood pressure. Yet this design was the first that
could be used clinically was a small degree of success.
Fig 6.5: sphygmomanometer
In 1881, Samuel Siegfried Karl Ritter von Basch invented the
sphygmomanometer shown in fig 6.5, consisted of a water-filled bag connected to a
manometer. The manometer was used to determine the pressure required to obliterate
the arterial pulse. Direct measurement of blood pressure by catheterisation confirmed
that von Basch's design would allow a non-invasive method to measure blood
pressure. Feeling for the pulse on the skin above the artery, was used to determine
when the arterial pulse disappeared.
Scipione Riva-Rocci developed the mercury sphygmomanometer in 1896.
This design was the prototype of the modern mercury sphygmomanometer. An
inflatable cuff was placed over the upper arm to constrict the brachial artery. This cuff
was connected to a glass manometer filled with mercury to measure the pressure
exerted onto the arm. Riva-Rocci's sphygmomanometer was spotted by the American
neurosurgeon Harvey Cushing while he was travelling through Italy. Seeing the
potential benefit he returned to the US with the design in 1901. After the design was
modified for more clinical use, the sphygmomanometer became commonplace.
Cushing and George Crile were major advocates of the benefits.
Nikolai Korotkoff was the first to observe the sounds made by the
constriction of the artery in 1905. Korotkoff found that there were characteristic
sounds at certain points in the inflation and deflation of the cuff. These Korotkoff
sounds [25] were caused by the abnormal passage of blood through the artery,
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corresponding to the systolic and diastolic blood pressures. A crucial difference in
Korotkoff's technique was the use of a stethoscope to listen for the sounds of blood
flowing through the artery. This auscultatory method proved to be more reliable than
the previous palpitation techniques and thus became the standard practice.
Modern
developments
have
led
to
more
accurate
auscultatory
sphygmomanometers, and newer oscilliometric models. These sphygmomanometers
measure the pressure imparted onto the cuff by the turbulent blood squirting through
the constricted artery over a range of cuff pressures. This data is used to estimate the
systolic and diastolic blood pressures.
Most noninvasive blood pressure monitors are based either on the auscultation
(AUS) [26] or the oscillometric (OSC) method [27]. The former relies on detecting
so-called Korotkoff sounds (automated recording or manual auscultation with a
stethoscope) using decreasing cuff pressure and is mainly used in the clinical
environment.
The electronic palpation (EP) method was firstly introduced in 1998 by
Nissila, Sorvoja and Vieri-Gashi. It uses a standard occlusion cuff around the upper
arm and a wristwatch type of multi-element pressure transducer array to sense
pulsations in the radial artery. Measurements can be made both during increasing and
decreasing cuff pressure, also referred to as inflating and deflating pressure mode in
this presentation. In these measurements, diastolic blood pressure was defined as the
point where the pulse amplitude of the blood pressure signal starts to decrease, while
systolic blood pressure was defined as the last pulse detected. Diastolic blood pressure
can be defined using two fitted lines that cross at the diastolic pressure.
6.5. Hardware Development
In general Blood pressure is typically measured using a sphygmomanometer
and stethoscope of oscillometric methods by Doctors, which are analog devices.
A similar method is used in the present study to measure blood pressure [28],
which is called the oscillometric method [29]. There is an electronic pressure sensor
connected to the cuff instead of a sphygmomanometer. The cuff is inflated to a
pressure high enough to stop circulation to the wrist and then slowly decreased. At
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systolic pressure, oscillations will begin in the pressure sensor output. Continuing to
decrease the pressure, the diastolic pressure is read when the oscillation stops.
Automated electronic devices have been developed to take blood pressure
readings at the press of a button can reduce error and require no training and stores the
data with real time for further processing and analysis of BP. In the present work we
design the BP meter using Raspberry Pi and Pressure Sensor.
6.6 Hardware
The present design is a non-invasive Blood Pressure meter. The
implementation of Blood Pressure meter device is by cascading several stages as
shown in fig 6.6 which depicts the system block diagram and fig 6.7 describes the
circuit diagram of GSM based Blood pressure measurement system. The device
hardware consists of different units and explanation for each unit is given
individually. They are
Block diagram
Fig 6.6: Block diagram of the GSM based Blood Pressure System
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Circuit diagram
Fig 6.7: circuit diagram of Blood Pressure Measurement system
1. Sensor unit with Cuff
2. Signal conditioning unit
a.
Filter
b. Analog to Digital converter PCF8591
3. Central processing unit ARM11J6JZF
4. Motor control unit
5. Graphical LCD Display.
6. Universal Serial Bus
7. GSM-SIM500
6.6.1. Sensor Unit with Cuff
In this unit the pressure sensor senses the signals from the patient and transmits
the signals to next stage of signal condition unit. The pressure transducer used is a
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piezoresistive pressure sensor, which generates a changing output voltage proportional
to the applied pressure, with a measurement range from 0 to 50 kPa (0–7.3 PSI) with
high accuracy. This sensor has temperature compensation and offset calibration. It is a
monolithic silicon pressure sensor in which the “strain gauge”, the diaphragm and the
resistive network are integral parts of the same chip. Applying pressure to the
diaphragm results in a resistance change in the “strain gauge”, which in turn causes a
change in the output voltage in direct proportion to the applied pressure [30]. The
diagram of fully integrated pressure sensor MPXV5050GP of pressure sensor is
shown in fig 6.8. The output of the pressure sensor connecting with amplifier LM224,
ADC is shown in fig 6.9 and fig 6.10 respectively.
.
Fig 6.8:
The Schematic Diagram of Fully Integrated Pressure
Sensor
The MPXV5050GP is piezoresistive transducer is a state-of-the art monolithic
silicon pressure sensor designed in present applications, which particularly employing
a micro controller with A/D inputs. This is a single element transducer combines
advanced micro machining techniques, thin-film metallization and bipolar processing
to provide an accurate, high level analog output signal that is proportional to the
applied pressure.
Specification of the CUFF SIZE AND PLACEMENT
Both the length and width of an occluding cuff are important for accurate and
reliable measurement of blood pressure by indirect methods. A too-short or toonarrow cuff results in false high blood pressure readings. Several studies have shown
that a cuff of inappropriate size in relation to the patient's arm circumference can
cause considerable error in blood pressure measurement [31]. The cuff should also fit
around the arm firmly and comfortably. Some manufacturers have designed cuffs with
a fastener spaced so that a cuff of appropriate width only fits an arm of appropriate
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diameter. With this design, the Cuff will not stay on the arm during inflation unless it
fits accordingly.
According to American Heart Association (AHA) [32] recommendations the
width of the cuff should be 40% of the mid circumference of the limb and the length
should be twice the recommended width.
The proper cuff and bladder size used in the assessment of blood pressure is
important for accurate measurement. We sought to determine the most commonly
used cuff size [33] needed for accurate blood pressure measurement for patients. The
cuff size chosen for measure of blood pressure with a mercury sphygmomanometer
was determined based on the following cuff size parameters:<9.5 inches (Child's
cuff); 9.5-12inches (Regular adult cuff); 13-16.5 inches (Large adult cuff); >16.5
inches(Thigh cuff)
Based on mean arm circumferences, the most frequently used cuff size
required for accurate blood pressure measurement in this hypertensive, overweight
population is the large adult cuff. Recommended cuff sizes are listed in Table 2.
Table :2 Recommended Cuff Sizes for Accurate Measurement of Blood Pressure
PATIENT
RECOMMENDED CUFF SIZE
Adults (by arm circumference)
22 to 26 cm
12 × 22 cm (small adult)
27 to 34 cm
16 × 30 cm (adult)
35 to 44 cm
16 × 36 cm (large adult)
45 to 52 cm
16 × 42 cm (adult thigh)
Children (by age)*
Newborns and premature infants
4 × 8 cm
Infants
6 × 12 cm
Older children
9 × 18 cm
*—A standard adult cuff, large adult cuff, and thigh cuff should be available for use
in measuring a child’s leg blood pressure and for children with larger arms
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6.6.2
Signal conditioning unit
Any Instrumentation measurement systems consist of various units staring from
sensors to data representation units. Among that signal conditioning is a vital process.
This system consists of Amplifiers, Filters, ADC etc. the Bio-Medical instrumentation
consists of signal conditioning and processing for very low frequencies. During study
of these signals, noise interference is a major problem and complex.
The signals from pressure sensors are processed by using RASPBERRY Pi
ARM11J6JZF micro controller. The processing unit consists of Amplifier with
LM224, ADC and a comparator circuit for processing the signals from the sensor.
The signal-conditioning unit consists of the following parts explained below.
6.6.2.1. Filter
The amplifier receives the signal obtained from the previous stage and it is used to
provide high gain, in order to adapt the signal to the later stage (A/D converter) to full
scale. It also includes a zero adjustment. The signal is handled as a D.C. signal [34]. In
the present design we are using LM224 used as an amplifier for amplifying the
pressure sensor signal and the output of the amplifier is given to the Analog to Digital
converter. The LM224 is a Single Supply, low–cost, quad operational amplifiers with
true differential inputs. They have several distinct advantages over standard
operational amplifier types in single supply applications. The quad amplifier can
operate at supply voltages as low as 3.0 V or as high as 32 V. A simple interface
diagram of LM224 is as shown in fig6.9.
150k
3.3V
5v
11
R23
1M
Vo
0.33uf
4
Input from BP
sensor
1
+
3
LM224
-
2
C27
R22
1k
C28
33uf
Fig 6.9: Lm224 signal amplifier
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The LM224 is made using four internally compensated, two–stage operational
amplifiers. The first stage of each consists of differential input transistors with input
buffer transistors and the differential to single ended converter. The first stage
performs not only the first stage gain function but also performs the level shifting and
transconductance reduction functions. By reducing the transconductance, a smaller
compensation capacitor (only 5.0 pF) can be employed. The Tranconductance
reduction is accomplished by splitting the collectors of transistors.
Another feature of this input stage is that the input common mode range can
include the negative supply or ground, in single supply operation, without saturating
either the input devices or the differential to single–ended converter. The second stage
consists of a standard current source load amplifier stage. The pressure sensor unit
interface with operational amplifier LM224 is as show in fig 6.10. The output of the
opamp is applied to the analog to digital converter for further processing.
ADC1
ADC2
3.3V
C24
3.3V
U8
33.3.V_PRESS
U7
2
Vout
N/C8
R7
N/C5
N/C7
GND
N/C1
N/C6
2
R10
8
3
OUT4
R8
6
4
R9
5
6
C22
7
R11
14
OUT1
IN1-
IN4-
IN1+
7
3
5
1
Vs
MPXV5050GP
1
4
IN4+
LM224
VCC
GND
IN2+
IN2-
IN3+
IN3-
OUT2
C20
OUT3
13
12
11
10
9
8
C19
C23
Fig 6.10: operational amplifier interfacing circuit
The pressure sensor is connected directly to the cuff, which is inflated or
deflated via a motor and valve. The output of the pressure sensor is split into two
signals. The PCF8591 is a single-chip analog to digital converter with four analog
inputs and a serial I2C-bus interface. Both signals are input to the serial PCF8591
ADC. The first signal is input directly into the microcontroller without any
amplification because the MPX5050GP pressure sensor outputs between .2V and
4.7V, which is acceptable for the micro controller’s through ADC. This signal
contains both the cuff pressure signal and the oscillation signal. The second signal is
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input through a two-pole high-pass filter to block the cuff pressure signal and amplify
the oscillation signal. It is assumed that the oscillation signal is around 1Hz
(corresponding to 60 heartbeats per minute) and the cuff pressure signal is less than.
04Hz. These frequencies are important when designing the high-pass filter.
6.6.2.2. Analog to Digital Converter PCF8591
The PCF8591 [35] is a single-chip with four analog inputs, one analog output
and a serial I2C-bus interface. Three address pins A0, A1 and A2 are used for
programming the hardware address, allowing the use of up to eight devices connected
to the I2C-bus without additional hardware. Address, control and data to and from the
device are transferred serially via the two-line bidirectional I2C-bus. The functions of
the device include analog input multiplexing, on-chip track and hold function, 8-bit
analog-to-digital conversion and an 8-bit digital-to-analog conversion. The functional
block diagram of analog to digital converter is as shown in figure 6.11.
Figure 6.11. : Block diagram of ADC PCF8591
The A/D converter uses the successive approximation conversion technique.
The on-chip D/A converter and a high-gain comparator are used temporarily during
an A/D conversion cycle. The I2C-bus is for bidirectional, two-line communication
between different ICs or modules. The two lines are a Serial Data line (SDA) and a
Serial Clock line (SCL). Both lines must be connected to a positive supply via a pullup resistor. An I2C-bus is activated by sending a address to the PCF8591 device. The
address consists of address pins A0, A1 and A2. The address is always sent as the first
byte after the start condition in the I2C-bus protocol. The last bit of the address byte is
the read/write-bit which sets the direction of the data transfer. A/D conversion cycle
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is started after sending read mode address to a PCF8591 device. The A/D conversion
cycle is triggered at the trailing edge of the acknowledge clock pulse. Once a
conversion cycle is triggered, an input voltage sample of the selected channel is stored
on the chip and is converted to the corresponding 8-bit binary code. The conversion
result is stored in the ADC data register and awaits transmission. The first byte
transmitted in a read cycle contains the conversion result code of the previous read
cycle.
An on-chip oscillator generates the clock signal required for the A/D
conversion cycle.
The sensor used can measure up to 377 mmHg; the gain of the amplifier was
adjusted so that 1 mmHg coincides with each one of the possible values of the
converter. The value obtained from A/D converter in binary code is applied to the
micro controller.
6.6.3. Central Processing Unit ARM11J6JZF
The signals from analog digital converter are processed by using
RASPBERRY Pi ARM11J6JZF micro controller. ARM stands for Advanced RISC
Machine. The ARM11 is based on the ARMv6 instruction set architecture. The block
diagram of the internal architecture of the micro controller ARM11J6JZF is shown in
fig 6.12. The Raspberry Pi uses the Broadcom BCM2835 system on a chip (SoC). The
Raspberry Pi model B has 512MB of primary memory (RAM). Clock speed is
700MHz. The Broadcom BCM2835 is the specific implementation of an ARM11
processor. The CPU core is the ARM11J6JZF-S which is a member of the ARM11
family (ARMv6 architecture with floating point). The GPU is a Videocore IV GPU.
This is mainly consists of the following units embedded inside the chip
the important features of the ARM11J6JZF-S core is of the following

Eight stage pipeline

Internal coprocessors CP14 and CP15

Three instructions sets

32-bit ARM instruction set (ARM state)

16-bit Thumb instruction set (Thumb state)

8-bit Java bytecodes (Jazelle state)

Data path consist of three pipelines:

ALU, Shift, Sat pipeline (Sat implements saturation logic)
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
MAC pipeline (MAC executes multiply and multiply-accumulate operations)

Load or store pipeline
The ARM Memory Management Unit (MMU) translates virtual addresses to
physical addresses using page information. The MMU supports four page sizes: 4KB
small pages, 64KB large pages, 1MB sections and 16MB super sections. Address
mapping is performed using two levels of translation look aside buffers: the Main
TLB and two micro TLBs. The Main TLB backs separate micro TLBs for each of the
instruction and data caches. Address translation is first attempted in a MicroTLB. If
the address cannot be translated in the MicroTLB, then the Main TLB is tried. If the
address cannot be translated through the Main TLB, then hardware page walking is
invoked. The functional block diagram of the ARM11J6JZf is as shown in fig 6.12.
Figure 6.12: Blocks Diagram of the ARM11J6JZF
The circuit diagram of interfacing motor, filter, memory...Etc to a micro
controller is as shown in fig 6.8. In the present design ARM11J6JZF is the central
processing unit do the total processing. The micro controller is connected to all
external devices like motor’s , filter, amplifier, ADC, USB, Graphical LCD. Every
external device has their own input/ output lines. The motors, sensor output are
connected to the GPIO pins of the micro controller. LCD communicates serially with
the micro controller. 5 lines are used to interface with the micro controller. Universal
Serial Bus uses Differential lines to communicate between micro controller and
RASPBERRY Pi.
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6.6.4. Motor control unit
The motor control design is very crucial in this design, where we needed to on
and off the motor at a correct time using micro controller ARM11J6JZF. The motor
unit work with a Complementary power Darlington transistor MJD122T4, it is
integrated anti parallel Collector-emitter diode and it is a form of complementary
NPN - PNP pair. In this design MJD122T4 used as a switch to control a motor.
The system first turns on the motor and pump the air in to wrist cuff to
maximum range. This can be determined by the pressure sensor, and the motor is
turned off at some point. Once the cuff is inflated, the motor is stopped and the
pressure is slowly decreased by switching on the motor 2 to open the valve.. At this
time, the micro controller processes the oscillation signal and records the pressure
from the cuff pressure signal. The cuff is inflated and deflated using motors. The
motor control unit with micro controller is as shown in fig 6.13.
Fig 6.13: Interfacing of Motor Control unit With Micro controller
6.6.5. GRAPHICAL LCD DISPLAY (TOUCH SCREEN - AT070TN92
The output of the device is sent to a liquid crystal display to display the data of
systolic and diastolic blood pressure. In present design we are using GRAPHICAL
LCD DISPLAY TOUCH SCREEN - AT070TN92 [36]. The pin description and the
specification of AT070TN92 are as shown in table 2 and 3. The Graphical LCD
interfacing circuit is as shown in fig 6.17.
AT070TN92 is 800x480 dots 7" color TFT LCD module display with OTA7001A
controller, optional 5 points capacitive multi-touch panel with connector and 4-wire
resistive touch panel screen with connector. A thin-film-transistor liquid-crystal
259
display (TFT LCD) is a variant of a liquid-crystal display (LCD) that uses thin-film
transistor (TFT) technology to improve image qualities such as addressability and
contrast. A TFT LCD is an active-matrix LCD, in contrast to passive-matrix LCDs or
simple, direct-driven LCDs with a few segments. It has superior display quality, super
wide view angle and easily controlled by MCU ARM. It can be used in any embedded
systems, car, mp4, gps, industrial device, security and hand-held equipment which
require display in high quality and colorful image. It supports RGB interface. FPC
with zif connector is easily to assemble or remove. The detailed explanation for the
touch screen given in the earlier chapters. The photograph of Graphical LCD display
is as shown ing fig 6.17.
Figure 6.17: AT070TN92 - 7" color TFT LCD display with OTA7001A
6.6.6. Universal Serial Bus- USB
The LDO Regulator generates the 3.3V reference voltage for driving the USB
transceiver cell output buffers. The main function of this block is to power the USB
Transceiver and the Reset Generator Cells rather than to power external logic. The
USB Transceiver Cell provides the USB 1.1 / USB 2.0 full-speed physical interface to
the USB cable. The output drivers provide 3.3V level slew rate control signaling,
whilst a differential receiver and two single ended receivers provide USB data in,
SEO and USB reset condition detection. The USB DPLL cell locks on to the
incoming NRZI USB data and provides separate recovered clock and data signals to
the SIE block. The Serial Interface Engine (SIE) block performs the Parallel to Serial
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and Serial to Parallel conversion of the USB data. In accordance to the USB 2.0
specification, it performs bit stuffing / un-stuffing and CRC5 / CRC16 generation /
checking on the USB data stream. The USB Protocol Engine manages the data stream
from the device USB control endpoint. It handles the low level USB protocol requests
generated by the USB host controller and the commands for controlling the functional
parameters of the UART. Data from the USB data out endpoint is stored in the FIFO
TX buffer and removed from the buffer to the UART transmit register under control
of the UART FIFO controller. Data from the UART receive register is stored in the
FIFO RX buffer prior to being removed by the SIE on a USB request for data from
the device data in endpoint. The UART FIFO controller handles the transfer of data
between the FIFO RX and TX buffers and the UART transmit and receive registers.
Together with the UART FIFO Controller the UART Controller handles the
transfer of data between the FIFO RX and FIFO TX buffers and the UART transmit
and receive registers. It performs a synchronous 7 / 8 bit Parallel to Serial and Serial
to Parallel conversion of the data on the RS232 (RS422 and RS485) interface. Control
signals supported by UART mode include RTS, CTS, DSR, DTR, DCD and RI. The
UART Controller also provides a transmitter enable control signal pin option
(TXDEN) to assist with interfacing to RS485 transceivers. RTS / CTS, DSR / DTR
and X-On / X-Off handshaking options are also supported. Handshaking, where
required, is handled in hardware to ensure fast response times. The UART also
supports the RS232 BREAK setting and detection conditions. A new feature,
programmable in the internal EEPROM allows the UART signals to each are
individually inverted. Another new EEPROM programmable feature allows high
signal drive strength to be enabled on the UART interface and CBUS pins.
6.6.7. GSM MODEM - SIM500
The Global System [37] for Mobile communications (GSM: originally from
Groupe Spécial Mobile) is the most popular standard for mobile phones in the world.
A GSM modem is a specialized type of modem which accepts a SIM card, and
operates over a subscription to a mobile operator, just like a mobile phone. From the
mobile operator perspective, a GSM modem looks just like a mobile phone. A GSM
modem can be a dedicated modem device with a serial, USB or Bluetooth connection,
or it may be a mobile phone that provides GSM modem capabilities. The term GSM
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modem is used as a generic term to refer to any modem that supports one or more of
the protocols in the GSM evolutionary family, including the 2.5G technologies GPRS
and EDGE, as well as the 3G technologies WCDMA, UMTS, HSDPA and HSUPA.
GSM module is the kernel part to realize wireless data transmission. Wireless
communication module SIM500 based on standard of GSM produced by SIMCOM
company is used in the developed application. SIM500 module consists of main
frame, antenna, serial communication line, power line. It provides services of wireless
modem, wireless fax, short message and speech communication. The short message
service is suitable to apply in the situation of frequent transmittance of small data
flow.
SIM500 is a Tri-band GSM/GPRS engine that works on frequencies EGSM
900 MHz, DCS 1800 MHz and PCS1900 MHz. With a tiny configuration of 40mm x
33mm x 2.85 mm, SIM500 can fit almost all the space requirement in your
application, such as Smart phone, PDA phone and other mobile device. The physical
interface to the mobile application is made through a 60 pins board-to-board
connector, which provides all hardware interfaces between the module and customers’
boards except the RF antenna interface. The keypad and SPI LCD interface will give
you the flexibility to develop customized applications. Two serial ports can help you
easily develop your applications. Two audio channels include two microphones inputs
and two speaker outputs. This can be easily configured by AT command. SIM500
provide RF antenna interface with two alternatives: antenna connector and antenna
pad. The antenna connector is MURATA MM9329-2700. And customer’s antenna
can be soldered to the antenna pad. The circuit of SIM500 is shown in Figure 6.18.
262
Figure 6.18 SIM500 Circuit
The SIM500 is designed with power saving technique, the current
consumption to as low as 2.5mA in SLEEP mode. The SIM500 is integrated with the
TCP/IP protocol, Extended TCP/IP AT commands are developed for customers to use
the TCP/IP protocol easily, which is very useful for those data transfer applications.
The leading features of SIM 300 make it ideal for virtually unlimited applications,
handheld devices and much more. It is compatible with AT cellular command
interface.
The features of SIM500 are

Tri-Band GSM/GPRS 900/1800/1900 MHZ

Complaint to GSM phase 2/2+

Dimensions: 40mm x 33mm x 2.85mm

Weight : 8g

Control via AT commands

SIM application tool kit

Supply voltage range 3.4 …. 4.5v

Low power consumption
All hardware interfaces except RF interface that connects SIM500 to the
customers’ cellular application platform is through a 60-pin 0.5mm pitch board-toboard connector. Sub-interfaces included in this board-to-board connector are Dua,l
serial interface ,Two analog audio interfaces, SIM interface
SIM500 provides two unbalanced asynchronous serial ports. The GSM
module [38] is designed as a DCE (Data Communication Equipment), following the
traditional DCE-DTE (Data Terminal Equipment) connection, the module and the
client (DTE) are connected through the following signal as shown in figure 6.19. Auto
bauding supports baud rate from 1200 bps to 115200bps.
Serial port 1
Port/TXD @ Client sends data to the RXD signal line of module
Port/RXD @ Client receives data from the TXD signal line of module
Serial port 2
Port/TXD @ Client sends data to the DGBRXD signal line of module
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Port/RXD @ Client receives data from the DGBTXD signal line of module
Figure 6.19 : Interface of serial ports
The TXD, RXD, DBG_TXD, DBG_RXD, GND must be connected to the IO
connector when user need to upgrade software and debug software, the TXD, RXD
should be used for software upgrade and the DBG_TXD, DBG_RXD for software
debug. The PWRKEY pin is recommended to connect to the IO connector. The user
also can add a switch between the PWRKEY and the GND. The PWRKEY should be
connected to the GND when SIM500 is upgrading software.
The SIM interface supports the functionality of the GSM Phase 1 specification
and also supports the functionality of the new GSM Phase 2+ specification for FAST
64 kbps SIM. Both 1.8V and 3.0V SIM Cards are supported. The SIM interface is
powered from an internal regulator in the module having nominal voltage 2.8V. All
pins reset as outputs driving low.
The Figure 6.20 is the reference circuit about SIM interface. The 22Ω resistors
showed in the figure should be added in series on the IO line between the module and
the SIM card for matching the impedance. The pull up resistor (about 10KΩ) must be
added on the SIM_I/O line. The SIM_PRESENCE pin is used for detecting the SIM
card removal. We can use the AT command “AT+CSDT” to set the SIMCARD
configure. We can select the 8 pins SIM card.
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Figure 6.20：SIM interface reference circuit with 8 pins SIM card
The GSM 07.05 AT commands are for performing SMS and CBS related operations.
The Overview of AT Commands According to GSM07 [39] is listed in Table 3.
Table: 3 . Overview of AT Commands According to GSM07
6.6.8. Power supply
In present design the BP meter operates on 3.3V, 5V and 12V power supply
where, the motor control unit and Display uses 12V. RS-232 uses 5V power supply
and the remaining parts of the design used 3.3 V. The circuit diagram of the power
supply is given below. All these voltages are derived from 9v Battery package. 5V
,12v and 3.3 V are as shown in fig 6.21, 6.22, 6.23 respectively.
7805
5v
Vin
3
Vout
2
1
Gnd
9v
C26
10uf
C18
10uf
C27
47uf
Fig 6.21: 5 v Power supply circuit
D3
MBR120LSFT1
9v
LM2621MM
L1
7
VDD
R6
510 ohms
6
EN
FREQ
C14
68uf
200k
R3
C15
0.1uf
3
PGND
5
1
FB
2
ENABLE
+12v
BOOT
SGND
C10
22uf
SW
4
8
6.o uH
R4
150k
R5
18k
C13
33pf
Fig 6.22: 12-v Power supply circuit
265
Fig 6.23: 3.3-v Power supply circuit
6.7 Software development of Blood pressure meter
The software part in the present design is used to determine the blood pressure
values. The micro controller program controls the external devices and measures the
input signals from the patient and displays the output.
6.7.1. Algorithm
1. Initialize central processing unit
2. Initialize Ports, LCD, Operational Amplifiers
3. Initialize LCD, memory
4. Initialize ADC sampling rate using timer
5. Enable interrupts
6. Start the motor
7. Read the signals from the sensor and transmit signals to the amplifier
8. Convert analog signal to digital signal using inbuilt ADC
9.Calculate systolic and diastolic pressure
10. Display the signals on GLCD
11. Store systolic and Diastolic pressure values in memory
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6.7.2. Flowchart
Main
Start
Initialization
Initialize memory &
GLCD
Start measurement
of Blood Pressure
Inflating Cuff
Memory
Motor
Memory ( )
Motor ( )
Set ADC sampling
rate with Timer
Write/ read data in
memory
Control motor
speeds
Release Air
Read input signal & Calculate
systolic and diastolic pressure
Display Blood pressure
Return
Return
GLCD
Set_LCD ( )
Store BP values in
Memory
Display BP values, and
transmit to personal computer
End
Set common and
segment lines
Return
Figure 6.24 : Flowchart of GSM BP Measurement System
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In present study the c language used for the development of Blood pressure meter.
The ‘C’ programming language is growing in importance and has become the standard
high-level language for real-time embedded applications. The PC is the standard
computing device for the ‘C’ compiler. [40]. To development of C programs for an
ARM11J6JZF executing on a PC is embedded linux and its GUI design developed is QT.
This largely due to the inherent language flexibility, the extent of support and its potential
for portability across a wide range of hardware [37]. The developed software program for
the BP meter is given in Annexure I.
6.7.3. EMBEDDED LINUX - QT Programming
In the present work the software development for the development of Blood
pressure meter was developed using the software of embedded linux and its GUI design
developed is QT. Linux itself is a kernel, but ‘Linux’ in day to day terms rarely means so.
Embedded Linux generally refers to a complete Linux distribution targeted at embedded
devices. There is no Linux kernel specifically targeted at embedded devices, the same
Linux kernel source code can be built for a wide range of devices, workstations,
embedded systems, and desktops though it allows the configuration of a variety of
optional features in the kernel itself. In the embedded development context, there can be
an embedded Linux system which uses the Linux kernel and other software or an
embedded Linux distribution which is a pre-packaged set of applications meant for
embedded systems and is accompanied by development tools to build the system.
The Qt framework first became publicly available in May 1995. It was initially
developed by Harvard Nord (Troll tech's CEO) and Eirik Chambe-Eng (Trolltech's Chief
Troll). Qt has long been available to non-C++ programmers through the availability of
unofficial language bindings, in particular Py.Qt for Python programmers. In 2007, the
Qyoto unofficial bindings were released for C# programmers.
In 2007, Troll tech
launched Qt Jambi, an officially supported Java version of the Qt API. Since Troll tech's
birth, Qt's popularity has grown unabated and continues to grow to this day. This success
is a reflection both of the quality of Qt and of how enjoyable it is to use. In the past
decade, Qt has gone from being a product used by a select few "inthe know" to one that is
268
used daily by thousands of customers and tens of thousands of open source developers all
around the World.
The signals and slots mechanism is fundamental to Qt programming. It enables
the application programmer to bind objects together without the objects knowing
anything about each other. We have already connected some signals and slots together,
declared our own signals and slots, implemented our own slots, and emitted our own
signals. Let's take a moment to look at the mechanism more closely.
Slots are almost identical to ordinary C++ member functions. They can be virtual;
they can be overloaded; they can be public, protected, or private; they can be directly
invoked like any other C++ member functions; and their parameters can be of any types.
The difference is that a slot can also be connected to a signal, in which case it is
automatically called each time the signal is emitted.
Qt provides a complete set of built-in widgets and common dialogs that cater to
most situations. we present screenshots of almost all of them. A few specialized widgets
are deferred. Main window widgets such as Q MenuBar, Q ToolBar and Q StatusBar and
layout-related widgets such asQ Splitter and Q ScrollArea. In thescreenshots shown in
figure, all the widgets are shown using the Plastique style.
A widget is a user interface component such as a button or a scroll-bar are
Reusable,Well defined interface ,Uses C++ inheritance, All widgets derive from a
common base, Widgets may contain other widgets, Custom widgets can be created from
existing widgets or they can be created from scratch
QT DESIGNER
 Written using Qt so it is available on all platforms where Qt is available
 Used to speed design of Qt applications
 Supports all Qt widgets and can be used to incorporate custom widgets
FEATURES
 Fully object-oriented
 Consistent interfaces
269
 Rich set of widgets (controls)
– Have native look and feel
– Drag and drop
Customizable appearance
Fig 6.25 : QT designer
 Utility classes
 OpenGL support
 Network support
 Database support
 Plugin support
 Unicode/Internationalization support
 GUI builder
Based on the above advantages, we used the Qt software for the present work.
The algorithm and flow chart of the touch screen based electronic voting machine as
shown below.
After creation of project and the program, we executed the program. Then
executed program is downloaded in to the micro controller. The download program is
executed in micro controller with external hardware interface then we can get the results.
If we get wrong results then modify the program and do the same process as above till to
270
get the correct results. Software program for Blood pressure measurement is present in
Annexure –I
6.8. Operation of Blood Pressure Measurement system
The circuit diagram of interfacing motor, filter, memory..Etc to a micro
controller is as shown in fig 6.9. The micro controller must first turn on the motor
and pump the air into arm cuff to approximately 160mmHg. Then the pressure sensor
can determine the pressure, and the motor is turned off at this point. A threshold level
must be set in the software to differentiate between true pulses in the pressure and
premature pulses. This is set to 1.75V. Once the cuff is inflated to 160mmHg, the
motor is stopped and the pressure is slowly decreased. At this time, the micro
controller Raspberry Pi processes the oscillation signal and records the systolic
pressure taken from the cuff pressure signal when the oscillation signal first exceeds
the threshold voltage. Further decreasing the pressure, the last pulse above the
threshold before there are no more pulses for 450ms is considered the diastolic
pressure. This requires the use of memory and processing previous measurements.
Once the systolic and diastolic pressures are determined, the cuff is fully deflated. The
pressure signals are measured by using analog to digital converter and display the
results in the Graphical LCD display. The measured values are stored in the memory
and transmit to the RASPBERRY Pi for further analysis to download the
measurement on to Neonatal monitoring system.
6.9. Calibration and Analysis
Instrumentation system employed for the measurement of physicochemical or
biological parameters needs systematic calibration. The calibration is utmost
important for the measuring instruments. The calibration process involves study of
influence of various kinds of parameters on the final measurement systems. Especially
in bio-medical instrumentation it is very important, because most of the instruments
may be used as life saving instruments. Malfunctioning and bad calibration of the
system leads to wrong diagnosis leading to catastrophic results. Hence the calibration
regarding to life saving instruments need vast studies and precautions. The present
271
work on blood pressure meter is based on noninvasive instrumentation principle. The
measurement of systolic and diastolic pressure is obtained by oscillometric method.
The blood pressure measurement by noninvasive methods encounters problems from
cuff leakage, movement of measurement, cuff size etc. hence the calibration processor
is more complex involving number of volunteers for the measurements of blood
pressure. As large number of data being collected before arriving conclusion on the
response of blood pressure measurement. The steps for the measurement of the
system are as follows in the following photos. The neonatal monitoring system for
NIBP is as shown in potograph1.
Photograph 1: Neonatal Monitoring system for NIBP
When we start the monitoring, the main window of the GSM based Neonatal
Intensive Care Monitoring system consists of the following menu for selection. The
main window is as shown in photographs. They are
1. Temperature
2. Phototherapy
3. Pulse oxygen(SPO2) and pulse rate
4. NIBP
5. Total system and
6. Exit
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Photograph 2: Main Window of Neonatal Monitoring system for NIBP
When NIBP button touched on the main window display screen , the Blood
pressure measurement of neonates process will start and display the window related to
the BP parameter . The GSM based blood pressure measurement system photograph
is as shown in photograph 3 with the values of systolic, Diastolic in mm/Hg and pulse
rate in number of beats per minute of the heart. The close button will close the process
of BP measurement.
Photograph 3: NIBP measurement window
273
The NIBP measurement window shows the current record of the neonate stored
in the memory of the Sony SD memory card. The record consists of the systolic,
Diastolic and pulse rate of the patient as a real time measurement with date and time
for further analysis. The measurement records are shown in photograph 4.
Photograph 4: NIBP measurement records window
The measurements for different Neonates are with accuracy by +1%.
The
measurements are carried out with the present designed instrument and with standard
blood pressure meter of OMRON make.
The measurements were carried out on the system is good agreement with
values measured with standard meter. The empirical calibration process, the
measurements exhibited slight deviation, but all these measurements are within the
tolerance range. The response time of the instrument was also equal with standard
meter. As the system is compact it can be used at ambulance services also. The
measured values are present in table 4.
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Table 4: Measurement of BP values
Actual Blood Pressure with
OMRON pressure
Present designed
S. No
Sphygmomanometer mmHg
meter (mmHg)
Blood pressure meter mmHg)
1
137/92
136/91
137/92
2
147/95
148/96
146/95
3
136/89
134/88
136/89
4
126/83
127/83
126/82
5
122/81
121/80
122/81
6.10 Results & discussion
The main aim and objective of this work is to develop a GSM based Neonatal
Intensive Care Monitoring system with Temperature, Phototherapy, Blood Pressure
and Pulse Oximetry measurement. Hence an attempt has been made by the author to
develop a Blood Pressure meter using the advanced micro controller ARM11J6JZF.
The instrument is a handheld, rugged, low cost, wearable device and also it is cost
effective compared to other meters operated with minimum power consumption by
the device.
275