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

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http://instruct1.cit.cornell.edu/courses/ee476/FinalProjects/s2005/ww56_ws62/Final%20Project%20Web/

index.html