View
219
Download
3
Category
Preview:
Citation preview
BME 273 – Spring 2011
Blood Pressure Monitor Re-calibration Final Report
Ross Hamilton
Lei Qu
Haniff Mohd Nor
David Lee
Advisor: Dr. Andre Churchwell
1
Abstract
Hypertension is one of the most common diseases in US. Approximately 32% of adults
are suffering from hypertension yet are non-institutionalized (Health, United States, 2009). In
order to fight this epidemic, close monitoring and regulation on the patients is strongly
suggested. Digital blood pressure monitor provides convenience for the patient to monitor their
blood pressure regularly; however, the variation between mercury sphygmomanometer and the
digital blood pressure monitor is commonly observed. These variations can be detrimental for
hypertension treatment (de Greeff, et al, 2008). These variations are also commonly observed in
many clinical settings for cardiologists across the nation, which is becoming a dangerous factor
in treating hypertension and regulating the blood pressure of hypertension patients (Mattu, et al,
2004, Belghazi, et al, 2007, and Chen, et al, 2008). In order to combat this issue, this project will
show that the variation between automatic blood pressure monitor and sphygmomanometer can
be verified under a clinically controlled experiment setting, which is aimed to verify the variation
that is commonly observed in clinical practice settings. In this project, the causes of variation
between automatic blood pressure monitor and sphygmomanometer is also investigated and a
recalibration circuit for the variation based upon the investigated causes is also proposed.
Introduction
Monitoring the blood pressure of a hypertension patient is one of the most effective ways
to treat hypertension. Digital blood pressure monitors are an invention which helps to aid the
monitoring of blood pressure for hypertension patients. However, after comparing the accuracy
of the measurements with the sphygmomanometer, the digital blood pressure monitor offers
convenience benefits but sacrifices the accuracy of the measurements (de Greeff, et al, 2008).
2
These variations were also observed in several literature reviews on clinical practice setting,
which is very detrimental for hypertension treatment processes (Mattu, et al, 2004, Belghazi, et
al, 2007, and Chen, et al, 2008). The traditional method to measure blood pressure is done using
a mercury sphygmomanometer. This device gives a very accurate reading of an individual’s
blood pressure but it requires training and certain skill set. It is also hard to determine the blood
pressure since it is done through listening. Thus it is not very convenient for the patient to do the
blood pressure checking alone. This device can also bring a “white coat” effect as most
cardiologists refer to, which is an effect that raises patient’s blood pressure because of seeing or
being in an environment where clinical equipment is used or white coat doctors are present (it
can be stressful). This effect can raise blood pressure for hypertension patient up to 15% to 30%
(Picker, et al, 1988). Thus, a user friendly device for the patient is necessary yet it has to have
the capability to obtain accurate blood pressure measurements. This is especially important in
present day because there are approximately 32% of 20+ yr old adults that are diagnosed with
hypertension yet are non-institutionalized (Health, United States, 2009). Currently, devices used
out in the field (and not in a medical office) are digital blood pressure monitors, such as Omron.
However, these digital monitors don’t have a method to re-calibrate the device resulting in it
being necessary to replace the devices pretty regularly in order to get an accurate reading of the
blood pressure for the hypertension patients. This is an obvious problem considering how it is
very inefficient and not very realistic for poorer countries who cannot afford this luxury. In this
project, we verified the common hypothesis that digital blood pressure monitor readings vary
significantly with the sphygmomanometer in a controlled clinical experiment setting. We also
investigated the causes of variation and proposed a possible circuit diagram that can solve this
impeding issue on our national healthcare.
3
Method
This project is aimed to verify the variation of blood pressure measurements between an
automatic blood pressure monitor and a sphygmomanometer as well as to investigate the causes
of these variations. The variations of blood pressure measurements are commonly observed
phenomena in clinical hypertension treatment across the nation (Mattu, et al, 2004, Belghazi, et
al, 2007, and Chen, et al, 2008). Since most of these variations were clinical experiences rather
than controlled studies under controlled clinical experimental settings, the blood pressure
measurements between a commonly used automatic blood pressure monitor and a clinical
commonly used sphygmomanometer had to be compared in a controlled experiment.
Experiment 1: The automatic blood pressure monitor that was used in this project is
Omron arm cuff blood pressure monitor, 5 series, model BP742. This blood monitor was chosen
for this project because the Omron brand is commonly used in hypertension treatment and blood
pressure monitor regulation processes in out-of-clinic settings base on Amazon.com (such as in
the field with Doctors Without Borders). The sphygmomanometer was used as the gold standard
because this is the method that is used by almost all of the clinics across the nation (Mattu, et al,
2004, Belghazi, et al, 2007, and Chen, et al, 2008). In order to test the variation that was
observed in most of the clinics (Mattu, et al, 2004, Belghazi, et al, 2007, and Chen, et al, 2008),
the following experiment was conducted on one of the team members for this project. Blood
pressure of the team member was taken three times a day throughout a five day period. The
blood pressure was measured first by Omron arm cuff blood pressure monitor, model BP742,
then the blood pressure was measured again immediately afterwards with the clinically viewed
gold standard, mercury sphygmomanometer. These data values were obtained and recorded for a
4
Figure 1: The CuffLink Non-invasive Blood Pressure
Stimulator used in this experiment.
five day period for this experiment. Next an equal variance, two tail t-test was used to analyze
these data which is shown in the result section of this report.
Experiment 2: To eliminate the
human error factor as much as possible, this
experiment was also conducted in the
following setup. The CuffLink Non-invasive
Blood Pressure Stimulator from the Clinical
Engineering Department from Vanderbilt
Medical Center was used to produce a
controlled blood pressure, which acts as an
artificial arm. Two blood pressure settings
were tested: normal blood pressure condition
and hypertension blood pressure condition.
The normal blood pressure condition was set
at 120/80 mmHg and the hypertension blood pressure condition was set at 150/100 mmHg. 20
measurements were taken for both conditions. Each condition was measured by both Omron arm
cuff blood pressure monitor and mercury sphygmomanometer, and an equal variance, two tailed
t test was performed in the end of this data collection. Figure 1 shows the CuffLink Non-
invasive Blood Pressure Stimulator that was used in this experiment.
Experiment 3: In order to investigate the causes of the blood pressure measurements
variation between the Omron blood pressure monitor and mercury sphygmomanometer, the
following experiment was conducted to verify the hypothesis that the air retained in the arm cuff
5
Figure 2: The experiment set up for experiment 3 for Omron measurements. The Omron
device used is model BP 742.
causes the variation.
The hypothesis was
formed for several
reasons. First, for the
mercury
sphygmomanometer,
the arm cuff releases
its entire arm cuff air
completely after each
usage due to the screw
of the air bulb for
pumping the air. However for the automatic blood pressure monitor that was studied in this
project (Omron, BP 742), only an air tube was put in place for this purpose. The whole air tube
was inside the device which is also embedded along with the pressure sensor and other important
electronic components. This could cause possible air pressure detection issues for the device,
since the device uses mostly pressure resistor sensor (US2007/00381278A1). Second, the
mercury sphygmomanometer was mostly used by trained nurses and physical assistance in a
clinical setting who has trained properly for the usage of this device. Thus, on a profession stand
point of view, they should aware the arm cuff deflation completion before each usage of the
device. The automatic blood pressure monitor was used mostly in the home setting for the
patient, thus there is a great increase of human error. Based on the reasons above, the hypothesis
that the arm cuff has not reached a complete deflation or that there is some air present in the
automatic blood pressure monitor could cause the variations that were observed in clinical
6
Figure 3: The experiment set up for experiment 3 for Mercury
Sphygmomanometer measurements.
practice and in this
project. The following
experiment was
conducted to test this
hypothesis. The
CuffLink Non-invasive
blood pressure analyzer
was used in this
experiment. The
pressure was set at
120/80 mmHg. 25 measurements were taken in this experiment for each device: Omron
automatic blood pressure monitor and mercury sphygmomanometer. A two-tailed, student t-test
for equal variance data was conducted at the end of the data collection to test the hypothesis.
Figure 2 shows the experiment setup for experiment 3 for the Omron automatic blood pressure
monitor. The CuffLink Non-invasive blood pressure analyzer was the device that Omron was
attached to in Figure 2. Figure 3 shows the experiment setup for the experiment 3 for the mercury
sphygmomanometer. The CuffLink Non-invasive blood pressure analyzer was the device used
and the pressure that was recorded in this experiment was the arm cuff pressure as shown in
Figure 3. In this experiment, right after each measurement that was taken by Omron, the arm cuff
is pressed to ensure there is no air left and ensures 100% deflation of the arm cuff before the next
measurements. This process was used as a step to eliminate the air retention in the blood pressure
monitor and to test the hypothesis that the variation is caused by the air retention in the arm cuff
or the device.
7
Figure 4: The schematic that Wattanapanitch and Suanmpun presented in their
studies.
Circuit Design: Base on the results from experiment 2 and 3, the hypothesis that pressure
resistor senses air at the zero voltage stage was used to build the proposed circuit diagram for
this project. The circuit diagram was also based on the schematic that was presented by students
from Cornell University
(Wattanapanitch and
Suampun).
Based on
Wattanapanitch and
Suampun’s studies, the
signal analysis for the
portable blood pressure
monitor was measured in
following fashion. The
pressure changes from the arm cuff will be sensed and transformed into electric signals by
pressure resistor. The pressure resistor will send these electric signals into an amplifier and band
pass filter. This data will then be analyzed by a microcontroller, which is programmed to analyze
the data and display the output as blood pressure based on the pressure-resistor to voltage
conversion. As shown in Figure 4, the cuff will send the pressure into the pressure sensor and the
pressure sensor will send the pressure changes into the amplifier and the band pass filter. The
microcontroller or the MCU will take both signals and take the measurements. The LCD will
display the measurements that were taken by the MCU and give a pressure read out.
8
Figure 5: The schematic for microcontroller programming
The MCU is a programmable circuit device. Base on the studies that were done by
Wattanapitch and
Suanmpun, the MCU
was programmed in the
fashion shown in the
Figure 5. The arm cuff
will be inflated with air
until there is no sense of
blood flow. Then the
MCU will slowly release
the air in the arm cuff. As
MCU releases the air in
the arm cuff, it starts to count the blood pulse. The first 4 blood pulses will be the blood flow that
starts initially. Since the arm cuff inflated until there is no blood flow, this starting of blood flow
will gives a systolic blood pressure. Thus the microcontroller takes the measurement and records
it. For diastolic pressure measurements, the MCU will continue releasing the air in the arm cuff
until it cannot sense any changes in the blood pressure. MCU will count for 2 seconds to check
the change of blood pressure, if none observed, and then the diastolic pressure will be recorded.
This similar schematic will be applied for the proposed circuit design in this project for the
programming of MCU.
9
Figure 6: The circuit diagram that was presented by Wattanapanitch and Suampun. The first op amp is the
amplifier; the second op amp is the band pass filter.
In order to amplify and filter out the right signals, Wattanapanitch and Suampun’s studies
presented a two part circuits. The pressure sensor signal is firstly sent to the amplifier, which will
amplify the signal. Then the signal is sent to a band pass filter which filters out the noises to
gather a readable signal for the MCU to calculate. As shown in Figure 6, the first op amp is the
amplifier; the second op amp is the band pass which will filter out the noises in the circuit
diagram. The proposed circuit diagram in this project was based on this schematic.
The schematic for the blood pressure monitor that was designed base on the hypothesis
that the pressure sensor still registers pressure when the device is just at zero. Therefore the
pressure is not at a truly zero pressure which causes the variation that was observed in this
project. Base on the studies done by Wattanapanitch and Suampun, the proposed schematic was
also two parts. One part is microcontrollers and the other part is the amplifier and filter stage for
the circuit diagram. For the circuit diagram part of the design, this project uses the cutoff
frequency of the high pass filter at 0.01Hz. This frequency was used because of the consultations
from PhD student, Jon Whitfield. This cutoff frequency should be able to get rid of most of the
10
Time Day Mercury Omron Mercury Omron
Systolic(mmHg) Diastolic(mmHg)
Morning
Monday
110 105 75 70
Lunch 119 115 85 75
Bedtime 110 115 72 80
Morning
Tuesday
110 112 70 75
Lunch 125 110 75 80
Bedtime 105 110 75 69
Morning
Wednesday
110 105 70 65
Lunch 123 115 80 75
Bedtime 107 105 72 65
Morning
Thursday
115 110 76 70
Lunch 120 115 83 80
Bedtime 115 110 76 72
Morning
Friday
115 119 78 73
Lunch 120 115 80 75
Bedtime 105 102 70 69
Average 113.93 110.87 75.80 72.87
P-value 0.15 0.11
Table 1: The data that was gathered during experiment 1, which shows that the measurements of
sphygmomanometer and Omron from the team member. The p value shows that there is no significant
difference between Omron and sphygmomanometer based on the team member’s measurement on
himself (p=0.15 for systolic and p=0.11 for diastolic.
noises and present the signal clearly to be calculate. Base on the circuit element that was used in
this project, the gain is governed by one resistor. The cut off frequency was calculated by the
formula:
Results
Experiment 1: The data analysis was done with a two-tailed, student t-test with equal
variance. The null hypothesis for this experiment was the blood pressure measurements for the
11
Measurement
Mercury
Sphygmomanometers
(mmHg)
Omron
(mmHg)
1 125/85 118/78
2 123/80 117/77
3 119/79 118/78
4 121/81 118/78
5 128/82 118/78
6 117/84 118/78
7 119/79 118/77
8 123/80 118/78
9 123/77 117/78
10 123/77 118/78
11 119/83 118/78
12 118/81 118/78
13 128/82 117/77
14 125/78 118/78
15 119/79 118/78
16 128/82 117/78
17 120/80 118/78
18 123/81 117/78
19 119/79 117/77
20 125/85 118/78
Table 2: The data that was collected with non-invasive
blood pressure analyzer with Omron and
sphygmomanometer, the pressure for blood pressure
analyzer was set at 120/80 mmHg
sphygmomanometer and Omron has no significant differences. Table 1 shows the blood pressure
measurements from Experiment 1, where the blood pressure measurements of a team member on
his own body were taken using the Omron BP742 and mercury sphygmomanometer for a period
of five days. As shown in Table 1, the p value is greater than 0.05, which shows that there is no
significant difference between Omron and
sphygmomanometer. This data is not very
conclusive for this study. The team
member has no special training on how to
use mercury sphygmomanometer, thus the
measurements from mercury
sphygmomanometer can be erroneous.
Also, the measurements were done by the
same person who was supposedly the
person who was to be tested on the two
devices, thus there will be a great amount
of human error in this study. Also, human
blood pressure changes every single second based on the conditions at the time; thus the readings
of the two blood pressures are not sufficient enough to draw a conclusion on whether these two
devices will give different results or not.
Experiment 2: This experiment was conducted with a non-invasive blood pressure
analyzer. As shown in Table 2, the Non-invasive blood pressure analyzer was set at 120/80 mmHg
for the normal condition measurements. 20 data points were taken for this condition. The Non-
12
Measurement
Mercury
Sphygmomanometers
(mmHg)
Omron
(mmHg)
1 153/103 151/96
2 149/99 151/96
3 151/101 150/96
4 150/100 151/95
5 149/102 150/96
6 150/100 151/97
7 150/100 151/96
8 150/100 151/97
9 148/100 151/97
10 150/98 150/96
11 152/98 151/96
12 150/100 150/96
13 152/103 151/97
14 151/97 151/96
15 149/99 151/96
16 151/101 151/97
17 149/100 150/96
18 148/100 151/96
19 150/98 152/96
20 150/100 150/96
Table 3: The hypertension condition that was
collected with non-invasive blood pressure
analyzer, the condition was set at 150/100 mmHg
Normal Blood Pressure
Device Systolic(mmHg) Diastolic(mmHg)
Sphygmomanometer 122.25 80.7
Omron 117.70 77.80
P-value 2.80E-34 6.08E-65
Hypertension Blood Pressure
Device Systolic(mmHg) Diastolic(mmHg)
Sphygmomanometer 150.10 99.95
Omron 150.75 96.20
P-value 0.05 2.43E-12
Table 4: t-test result for normal conditions and hypertension
comparing Omron and sphygmomanometer devices, p values for all
the conditions are below 0.05 thus these measurements are
significantly different.
invasive blood pressure analyzer applies 120/80 mmHg, and the arm cuff will sense the pressure
which in turn will then be displayed on the display of Omron or the sphygmomanometer.
As shown in Table 3, the hypertension
condition was also tested in this experiment. 20
data points were measured in each of the device
for this condition. The hypertension condition was
set at 150/100 mmHg with non-invasive blood
pressure analyzer.
A two tailed, equal variance t-test was
conducted to verify the difference between these
two measuring devices, Omron and mercury
sphygmomanometer. As shown in Table 4, the p
value for both conditions (normal and
hypertension conditions) is below 0.05. Base on
the null hypothesis of this study, which is that there is no significant difference between Omron
13
Measurement Omron Sphygmomanometer Omron Sphygmomanometer
Systolic (mmHg) Diastolic (mmHg)
1 117 118 79 78
2 117 115 79 75
3 117 117 78 77
4 119 116 78 76
5 119 120 78 77
6 118 117 79 76
7 117 117 79 77
8 118 116 79 77
9 117 119 79 76
10 117 120 79 78
11 119 117 79 76
12 118 116 79 77
13 118 116 79 77
14 119 118 78 76
15 118 118 79 77
16 119 118 77 75
17 118 118 78 77
18 118 117 79 76
19 118 119 79 77
20 118 118 79 75
21 118 117 79 78
22 118 120 78 75
23 118 117 78 76
24 118 116 79 75
25 118 117 79 77
Table 6: The data collected for experiment 3, which for Omron
measurements, each measurement applied with a flatten out the arm cuff
process.
Device Systolic (mmHg) Diastolic (mmHg)
Sphygmomanometer 117.48 76.44
Omron 117.96 78.64
P-Value 0.12 3.06E-11
Table 5: The t-test results for the experiment 3 data. The p value for
systolic pressure is at 0.12 and the p value for diastolic pressure is very
small. However, the diastolic pressure is only less than 2 mmHg greater
when Omron comparing with sphygmomanometer, thus can be ignored by
clinical practices.
device and sphygmomanometer device under normal and hypertension conditions, is rejected by
the t-test. The difference between the Omron and the sphygmomanometer is significant. As Table
4 shows, the sphygmomanometer and Omron has a measurement difference of 3 to 5 mmHg.
Experiment 3: This experiment was done with a completely deflated arm cuff (humanly
flattened out) and the Omron measurement, under only normal blood pressure condition (which
is set at 120/80 mmHg). As
shown in Table 5, the
measurements were all taken
under normal blood condition,
which was set at 120/80
mmHg. There were 25
measurements taken and they
were compared against each
other. The non-invasive blood
pressure analyzer will apply
the pressure set, which is at
120/80 mmHg to both devices
and both devices will try to
match the arm cuff pressure
with the pressure that was set
by non-invasive blood pressure
14
Figure 7: The proposed schematic design for the circuit that controls the
automatic blood pressure. Another MCU is added to check the pressure is at zero
when the voltage is at zero.
analyzer. Table 6 shows the two tailed, equal variance student t test results. As shown in the table,
the p value for systolic pressure is greater than 0.05. Therefore the null hypothesis that Omron
and the sphygmomanometer have no significant variation in their measurements stands.
However, for diastolic pressure, the p value is very small. But there are some human
reading errors during the operation process that can cause some variation. Also, the difference
between Omron and the sphygmomanometer is less than 2 mmHg, which is commonly ignored
in the clinical practice. Thus, as the data shows, by applying a flatten out process using the
completely deflated arm band, the variation between two devices for taking measurements,
Omron and sphygmomanometer, is significantly reduced, since both data shows no significant
difference among them. Thus, base on the data, the conclusion that the air resides in the
automatic blood pressure monitor device and/or the arm cuff is reached.
Circuit Design: Based upon the experiment results, the variation between the Omron
blood monitor and the sphygmomanometer seems to be less significant when the “flatten out”
process is applied.
From this observation,
the following circuit
design was proposed.
The following circuit
board is very similar to
the circuit schematic
that is proposed. The
15
Figure 8: The new circuit design. First part is an AD/Digital converter and second part is a
band pass filter. *Created with the help of Jon Whitfield.
schematic for the circuit design has an additional microcontroller added. As shown in Figure 7, the
MCU (microcontroller) at the bottom of the diagram will take measurements on the circuit at the
very beginning of the blood pressure measurement process. This MCU will detect any changes
on the voltage at the very beginning of the blood pressure measurement process. If there is a
voltage change or any voltage that is different than the initial voltage without any pressure that is
applied to the arm cuff, this MCU will send the signal to the LCD display that will inform the
user that there is possible air that is still being retained in the arm cuff of the device. Therefore
the user can flatten out the arm cuff to reduce the possible variation. The MCU at the top in Figure
7 will conduct the regular blood pressure measurements process. The programming of this MCU
will be similar to the schematic that is presented in Figure 5. The circuit design part in Figure 7 is a
design that is based upon the studies that done by Wattanapanitch and Suanpun. As shown in
Figure 8, the first
part is an
amplifier and
also acts as an
analog to digital
signal converter.
The gain of the
amplifier is
governed by Rg
in Figure 8. The
16
next op amp, which is divided into two parts to show the whole connection of the circuit
diagram, acts as a band pass filter, and the cut off frequency is governed by the equation:
.
Market analysis
The cost of the Omron BP742 monitor was $ 49.47 per unit (Amazon.com). The cost of
the manual inflate blood pressure kit (sphygmomanometer) was $ 18.64 per unit (Amazon.com).
Since there were two Omron devices needed for the purposes of the research, the budget cost
were $98.94. There were four sphygmomanometers that were needed for the experiments which
were cost $74.56. The CuffLink Non-invasive blood pressure analyzer that acts as an artificial
arm was obtained from Clinical Engineering Department of Vanderbilt Medical Center. So, there
was no cost for this unit. The combined costs were $173.50. The circuit components that were
needed to build for the blood pressure experimentation were approximately $420. This includes
the cost of the microcontroller (MCU), surplus amount of the op amps and instrumentation
amplifiers, and other miscellaneous features (e.g., buttons). The experimentation fee was used
solely for the purpose of constructing the first blood pressure monitor with a re-zeroing circuit
added unto the blood pressure monitor, which is still under development. Once the development
is finished, the conjectured cost of the recalibrating blood pressure monitor will have almost the
identical cost of the Omron blood pressure monitor. This is because the newly built circuitry will
not consist of just additional op amps and instrumentation amplifiers, which consume the largest
portion of the budget, but will be comprised of simple elements and a modified MCU that is
already inherent within Omron prototype blood pressure monitors. Thus, the estimated cost of
the finished product remains approximately $50.00 to $60.00, which includes the production cost
17
and the estimated profit for the developers. If the product is disseminated unto the market
effectively and the public responds with high demand, then the profit may be lowered by 3-4
dollars. The precise calculation of the final product depends on the effectiveness of the product
distribution and consumption. Dr. Churchwell generated and conceptualized the original
inspiration of the project, which was consequently pioneered by the BME 273 team. The team is
composed of members Lei Qu, Haniff Mohd Nor, Ross Hamilton, and David Lee. The
technological sketch (circuit diagrams and the MCU program) will be sold to the company that is
inclined to adopt and commercialize the product. Most likely, the innovations will be sold at the
estimations based on the economical analyses of the product feasibility within the 2011 to 2016
market space.
Cost Analysis
Expected Cost
Components Quantity
Unit Price
($)
Total
Price
Microcontroller 2 6.04 12.08
Power Supply 1 21.00 21
Pushbutton Switch (10 A) 3 3.09 9.27
Pushbutton Switch (1 A) 3 4.96 14.88
IC TVS Array 2-Line 1 1.17 1.17
Pressure Sensor (Max: 7.25
psi) 1 10.61 10.61
Amplifier 1 6.92 6.92
Op-amp 1 4.40 4.4
Linear Voltage Regulator 5 3.25 16.25
Voltage Regulator (5 V) 5 0.99 4.95
Resistors 9 Free 0
Capacitors 6 Free 0
Total Cost 101.53
*Actual expected cost of device without surplus supplies. See Appendix for other detailed
budget tables
18
Conclusions
Through the experiments from this project, the variation between automatic blood
pressure monitor and sphygmomanometer is confirmed. The variation between automatic blood
pressure monitor and sphygmomanometer is in the range of 3 to 5 mmHg when measured with
non-invasive blood pressure analyzer. After a “flatten out the arm cuff” process is applied, the
variation becomes insignificant with two tailed student t test under equal variance assumption.
Yet, the diastolic pressure is still significant, but there is human error to be considered in the
measuring process; also the variation is smaller than 2 mmHg which can be ignored by clinical
practices. A possible circuit design and circuit schematic are also both proposed in the end of this
project, which is aimed to solve the variation phenomenon that has been observed. The main
concept behind the proposed circuit diagram is using another MCU to regulate the change of
voltage at the beginning of the measurements. Base on the schematic that was presented by
Wanattapitch and Sumpun, the change of voltage implies the air is present in the pressure sensor.
Since “flatten out the arm cuff” process decreases the variation, the variation must be caused in
some degree by air that is retained in the pressure sensor.
Recommendations
Well first of all, it is necessary to test the re-calibration device over an extended period of time
(upwards of one year) to make sure that it will continually re-zero the blood pressure monitor. If
this is not the case, a re-design of the circuit is necessary because the main goal of this project
will not have been accomplished. During this period of time, an old blood pressure monitor
19
should be used in comparison to show exactly how much better this product is over the ones
which will de-calibrate after several uses. Once the device has been successfully tested, the
aesthetic and technical qualities will have to be adjusted to make it more compact and
desirable. Currently, the circuit that has been created is very bulky and large; however, once it
has been determined to be successful, it will be necessary to make it fit inside a volume that is
comparable to the current automatic blood pressure monitors out there. Also, a sleek design is
important for making this product have even more of an edge over the competitors. Next,
production costs need to be reduced by increasing the scale of production and by improving
efficiency of the circuit elements by using different and better starting materials. Finally, each
year the circuit diagram should be analyzed and optimized in order to continually test and
improve the ability of the device to re-zero the automatic blood pressure monitors so that this
product remains competitive with other manufacturers and remains as a high quality good for the
consumers (with their best interests and our profits in mind). It is crucial that the device is
continually improved because this product can control the fate of the patients due to its influence
on the physicians decision for diagnostic and therapeutic purposes.
20
References
Belghazi J, El Feghali RN, Moussalem T, Rejdych M, Asmar RG. Validation of Four Automatic Devices
for Self-Measurement of Blood Pressure According To the Internation Protocol of the European Society
of Hypertension. Vasc Health Risk Manag, 2007; 3(4): 389-400.
Chen HE, Cui Y, Sheng CS, Li LH, Li Y, Wang JG. Validation of the Health and Life HL868BA Blood
Monitor for Home Blood Pressure Monitoring According To the European Scoeity of Hypertension
Internation Protocol. Blood Press Monit, 2008 Oct; 13(5): 305-8.
de Greeff A, Shennan A. Blood pressure measuring devices: ubiquitous, essential but imprecise. Expert
Rev Med Devices. 2008 Sep;5(5):573-9. Review
Mattu GS, Heran BS, Wright JM. Overall Accurarcy of the Bp TRU- An Automated Electronic Blood
Pressure Device. Blood Press Monit 2004 Feb 9(1): 47-52.
Pickering T, James G, Boddie C, Harshfield G, Blank S, Laragh J (1988). "How common is white coat
hypertension?". JAMA 259 (2): 225–8. doi:10.1001/jama.259.2.225
Sawanoi et al. United States Patent Publication. US2007/0038128. Feb, 15, 2007.
http://www.highbloodpressureinfo.org/best-home-blood-pressure-monitor.html
http://instruct1.cit.cornell.edu/courses/ee476/FinalProjects/s2005/ww56_ws62/Final%20Project%20Web/
index.html
Recommended