Full Text Searchable PDF User Manual
B
LOOD
P
RESSURE
S
ENSOR
BT17
i
U
SER
’
S
G
UIDE
CENTRE FOR MICROCOMPUTER APPLICATIONS
http://www.cma-science.nl
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| BT17i
Blood Pressure Sensor User’s Guide
Short description
The Blood Pressure sensor BT17i allows measuring arterial blood pressure. The sensor
measures the pressure in the connected cuff caused by the interaction between the cuff
and the blood flow through the brachial artery. The systolic and diastolic blood pressure
can be calculated using the oscillometric method (non-invasive method).
The Blood Pressure sensor consists of:
•
a pressure sensor with measurement range between 0 .. 375 mmHg,
•
a standard adjustable blood pressure cuff (size: 24 cm to 35 cm),
•
a bulb pump with a control valve.
The blood pressure cuff consists of an inflatable bladder connected by one hose to a
hand pump bulb and by a second hose to the pressure sensor box. The user can set the
rate of cuff deflation manually with the control valve.
The sensor produces an output voltage, which varies linear with the measured pressure.
The special circuitry in the sensor minimizes errors due to temperature changes.
The Blood Pressure sensor can be directly connected to the analog BT inputs of the CMA
interfaces. The sensor cable BT - IEEE1394 needed to connect the sensor to an interface
is not supplied with the sensor and has to be purchased separately (CMA Article
BTsc_1).
Important:
The Blood Pressure sensor is not appropriate for medical applications. This sensor is to
be used only for educational purposes. Read this manual before you start measurements
with the sensor. Notice that over inflation of the cuff may cause pain and/or injury.
Sensor recognition
The Blood Pressure BT17i has a memory chip (EEPROM) with information about the
sensor: its name, measured quantity, unit and calibration. Through a simple protocol
this information is read by the CMA interfaces and the sensor is automatically
recognized when it is connected to these interfaces. If your Blood Pressure sensor is not
automatically detected by an interface, you have to manually set up your sensor by
selecting it from the Coach Sensor Library.
Calibration
The Blood Pressure sensor is supplied calibrated. The output of the Blood Pressure
sensor is linear with respect to pressure. The calibration function is:
p (mm Hg) = 83.34 * V
out
(V) – 16.67
The Coach software allows selecting the calibration supplied by the sensor memory
(EEPROM) or the calibration stored in the Coach Sensor Library. For better accuracy the
pre-defined calibration can be shifted.
BT17i
Blood Pressure User’s Guide
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3
How the Blood Pressure Sensor works
1. About blood pressure
During each heart beat the arterial blood
pressure varies between two utmost values:
the systolic and the diastolic pressure. The
peak pressure in the arteries is the systolic
pressure and the lowest pressure is the
diastolic pressure. In between these is the
Mean Arterial Pressure (MAP), which is
used to describe the average blood
pressure.
2. Oscillometric method
The blood pressure sensor allows determining blood pressure via the so-called
oscillometric method. With this non-invasive method, a cuff is placed around the arm
and inflated by means of a pump, after which the cuff deflates via a control valve. The
sensor measures the pressure of the air in the cuff.
With inflation of the cuff, the external pressure on the artery rises. At pressures
exceeding the systolic blood pressure, the artery will be occluded, no blood flow occurs
through the artery. When the cuff is slowly deflated, the cuff pressure, and hence the
external pressure on the artery will be lowered to that of the systolic blood pressure.
Now, the artery is no longer continuously occluded. At systolic blood pressure, small
amounts of blood flow through the compressed artery and cause changes in the artery
volume, conducted to the cuff. This leads to detectable pressure oscillations in the cuff.
These oscillations increase with lower cuff pressure values, as more blood passes
through the compressed artery. The maximum oscillation amplitude is reached around
the mean arterial blood pressure. Then, as the pressure decreases until the cuff
becomes fully deflated, the blood flow returns to normal and the oscillation amplitude
decreases and small pulses remain at a low level below diastolic pressure.
A similar method is used during the regular blood pressure measurement, a clinician,
using the stethoscope, listens at the brachial artery for characteristics sounds of the
pressure pulses (so-called Korotkoff sounds).
Measurements with the Blood Pressure sensor
Safety instructions
The cuff is put around the upper arm and produces pressure on the brachial artery. To
reduce the risk on injuries and pain it is important to read and follow the following
safety instructions:
•
Put on the cuff as described in the next section of the manual.
•
Do not inflate the cuff to a pressure above 180 mmHg.
Over inflation of the cuff
may cause pain and/or injury
.
•
Deflate the cuff immediately using the control valve when the pressure in the cuff
exceeds 200 mmHg.
•
Measurements with the cuff around the upper arm should
not take longer than 3
minutes
. In any case deflate the cuff immediately using the control valve when the
Figure 1
. Pressure course of the heart beat in
the brachial artery.
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| BT17i
Blood Pressure Sensor User’s Guide
cuff is inflated around the upper arm for more than 5 minutes.
•
There should be at least 10 minutes break between two measurements on the same
individual.
Placing the cuff around the upper arm
When performing blood pressure measurements, it is best to work with a partner.
1.
Connect the Blood Pressure sensor to
your interface.
2.
Attach the rubber hose from the cuff
to the connector on the sensor.
3.
Uncover the upper arm of the test
person and let the person sit with his
arm at chest height.
4.
Wrap the cuff firmly around the
upper arm, approximately 2-3 cm
above the elbow. The two rubber
hoses from the cuff should be
positioned over the bicep muscle
(brachial artery) and hanging down. The labels on the cuff indicate the correct
placement.
Adjusting the control valve
The release rate of the pressure in the cuff is adjusted with
the control valve. The valve is controlled by a simple finger
wheel, with an intuitive click feature. As the wheel is
rotated each click adjusts the deflation rate, and that rate
is maintained automatically by the inner mechanism of the
valve.
The actual blood pressure measurement should take
between 60 and 120 seconds, so the pressure valve should be set to an approximate
deflation rate between 2 and 3 mmHg/s. This slow rate of cuff deflation is necessary for
accurate measurement.
5.
Make a test measurement to adjust the control valve and find out the optimal
deflection rate.
•
Start your measurement.
•
Inflate the cuff up to a pressure between 150 mmHg and 170 mmHg by
squeezing the rubber air bulb several times.
•
During the deflation of the cuff adjust the deflection rate by turning the wheel.
Turn the wheel clockwise to let the cuff deflate more quickly and shorten the
measurement time. Turn the wheel counter clockwise to let the cuff deflate
slower and extend the measurement time.
•
When the pressure wheel is set you are ready to collect data.
Collecting data
After the cuff is placed correctly on the arm and the control release valve is adjusted
you can start your measurement.
Accuracy starts in the name
Page 9
ambi
dex
Innovative blood pressure cuffs
The cuff has a unique soft edge which replaces the weld found on other cuffs, allowing the
ambi
dex
cuff to be
applied to either the left or right arm with equal comfort for the patient.
The air inlet tube is positioned in the centre of the cuff face so that it is always out of the way of the
patient's arm, whether the left or right arm is chosen. This means that there are no tubes to interfere with the
stethoscope during manual measurement, and the tubes are tidy when a patient monitor is used.
Constructed in soft yet robust fabric, which has antimicrobial treatment, these one-piece cuffs come in a full range
of sizes which are based on the recommendations of the British Hypertension Society
(www.bhs.org)
Each cuff carries a RANGE marker and ARTERY position indicator, both printed so that they can be read when
using the cuff on either arm.
The Accoson
ambi
dex
bladderless blood pressure cuff can be used as a regular cuff, or for single patient
use, and carries a white panel on which a patient's name or the cuff location details can be recorded.
unique soft edge - tube exit on cuff face - latex-free - antimicrobial - easily cleaned - full range of sizes
The Accoson
ambi
dex
one-piece cuff has been developed to provide a blood pressure cuff which is easy to use,
clean, multi-purpose and cost-effective.
BT17i
Blood Pressure User’s Guide
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6.
Lay down the arm of the test person on the table with an open hand.
Important:
The test person must remain still during data collection—no movement of
the arm or hand during measurements.
7.
Start your measurement.
8.
Quickly and repeatedly squeeze the bulb to inflate the cuff on the test person’s arm.
Continue inflating the cuff to a pressure between 150 and 170 mm Hg. When this
pressure is reached, set the bulb pump down onto the table. The built-in pressure
release valve will slowly deflate the cuff.
9.
After the measurement is finished, release the remaining air in the cuff by turning
the valve. You should be able to hear air coming out of the cuff.
Extra tips
Blood pressure readings will differ from person to person and even between
measurements on the same individual. Do not expect to receive the same
measurements each trial since there are many factors that cause a person’s blood
pressure to increase or decrease. Use the following tips to take accurate measurements:
•
The test person’s arm and hand must remain still during measurements; hand open
– no fist!
•
The arm should be at heart level and is best supported.
•
Proper placement of the pressure cuff will increase the accuracy of your blood
pressure measurements.
•
Remove any clothing that may cover or constrict the portion of the arm being
measured.
•
The blood pressure increases with the age. The rule of thumb for the normal systolic
pressure is the formula 100 + age.
•
Blood pressure values are rounded to 5 mmHg.
Determining the heart rate
The heart rate (beats per minute) can be calculated using the following formula:
ℎ
𝑒𝑎𝑟𝑡
𝑟𝑎𝑡𝑒
=
𝑛𝑢𝑚𝑏𝑒𝑟
𝑜𝑓
𝑚𝑎𝑥𝑖𝑚𝑎
−
1
𝑡𝑖𝑚𝑒
𝑜𝑓
𝑡
ℎ
𝑒
𝑙𝑎𝑠𝑡
𝑚𝑎𝑥𝑖𝑚𝑢𝑚
−
[
𝑡𝑖𝑚𝑒
𝑜𝑓
𝑡
ℎ
𝑒
𝑙𝑎𝑠𝑡
𝑚𝑎𝑥𝑖𝑚𝑢𝑚
]
∗
60
•
Count the number of local maxima in the descending part of the graph.
•
In addition, use the scan option to read out the time of the first and the last maxima.
•
Calculate the heart rate.
Determining the blood pressure
The result of the measurement with the Blood Pressure sensor is a pressure versus time
graph, in which the pressure pulses of the blood are superposed on the decaying trend
pressure of the cuff.
1. Determining the blood pressure manually from the graph
The simple method of determining the blood pressure is manually, directly from the
pressure graph. The point at which the largest pressure pulses are occurring
corresponds to the Mean Arterial Pressure (MAP). The point above the mean pressure
at which the pressure difference grows rapidly correlates to the systolic pressure. The
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Blood Pressure Sensor User’s Guide
point below the mean pressure where the differences start to get small corresponds to
the diastolic pressure.
Figure 2
. A typical measurement with the Blood Pressure sensor.
1.
Identify the largest pressure “pulse”. This is an estimation of the MAP.
2.
Identify when the data begins forming rapid “pulses”. This is an estimation of the
systolic pressure.
3.
Identify when the data stops forming smaller “pulses”. This is an estimation of the
diastolic pressure.
2. Determining the blood pressure using oscillometric method
A more precise but laborious method to determine the blood pressure is the
oscillometric method. The pressure pulses, when extracted from the cuff pressure, form
an oscillating waveform. The peak-to-peak amplitudes of this waveform vs. pressure
create a bell shaped “envelope curve” (see figure 5). Within the envelope, the pressure
pulse amplitudes increase until maximum amplitude is reached (this point corresponds
to the MAP). After that the pulse amplitudes decrease further until hardly noticeable.
Generally, the systolic blood pressure is found by determining the point along this bell-
shaped envelope for pressure above MAP and for which the value of the pressure
amplitude is 50% of the maximum amplitude value. The diastolic blood pressure is
found using the same method for pressure below MAP and having an amplitude value
of 75% of the maximum amplitude value. These percentage values are obtained from
empirical research.
1
When this method is applied to the measured pressure graph, the bell shaped
“envelope curve” is extracted from the measurement graph as the difference graph of
the pulse pressure graph (the maximal values of the pressure pulses) and the cuff
deflection trend pressure graph. This procedure is described below in details for the
Coach program starting from version 7.3
2
, in 4 steps:
I.
Determining the cuff (trend) pressure
II.
Determining the pulse pressure
III.
Determining the envelope curve
IV.
Determining the blood pressure
1
Mehlsen J et al (1999). Vejledende retnigslinier for hjemmeblodtryksmåling. Ugesk Læ Klaringsrapport nr. 8, 1999.
2
If you use an older version of the Coach program consult the CMA Blood Pressure Sensor 0377i User’s Guide.
Systolic pressure around 115 mmHg
Diastolic pressure around 65 mmHg
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Blood Pressure User’s Guide
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I. Determining the cuff (trend) pressure
1.
From the data table determine the number of the measured points. In this
description we assume that the measured data are stored in Run 1.
2.
Right-click the graph and select
Analyze/Process > Select/Remove Data
.
3.
Select under Run the option
Run
1
and select under Selection
method
Point-by-point
.
4.
Mark the very first point, very last
point and points where the
pressure values are locally
minimal. These points indicate
the deflating pressure trend of
the cuff (i.e. without the pulses).
You may take every second
minimum.
Tip:
In Coach you can maximize
the Select/Remove Data dialog.
Find the point where the pressure value (displayed in the pressure coordinate field)
is locally minimal.
5.
Mark
Keep selected
and click
OK
. As the result you get Run 2 with only the selected
data points. These points determine the graph of the trend pressure.
6.
To extend the number of points in the graph you can smooth the graph.
•
Right-click the graph and select
Analyze/Process > Smooth
.
•
Select under Run the option
Run 2
(with the selected lower points).
•
Select the method
Spline
.
•
Click
Plot
to draw the smooth graph.
•
Click
OK
to accept
.
•
Type the number of points of the original pressure graph (determined in step 1)
in the
Number of Points
field and confirm.
•
As a result you get a new Run 3 with many more points. These are the trend
pressure data. You can rename this run into
p_trend
.
II. Determining the pulse pressure
7.
Repeat the steps 2 to 5. Mark the
very first point, very last point and
this time mark the maximal
pressure values, the tops of the
pulses. Take the upper points just
after the lower points, so you will
get exactly the same number of
selected data (see figure 3 and 4).
8.
As the result you get Run 4 with the
selected upper data points. These
are the pressure pulses.
9.
Repeat step 6 to smooth the data.
As the result you get Run 5 with
Figure 4
.
Select the points at which the pressure
value is maximal, just when pressure signal rises.
Figure 3
. Select the points at which the pressure value
is minimal, just before the pressure signal rises again.
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Blood Pressure Sensor User’s Guide
more points. These are the pulse pressure data, you can rename this run into
p_pulse
.
III. Determining the envelope curve
10.
To be able to calculate the pressure difference first copy the pressure data from Run
3
p_trend
into Run 5
p_pulse
.
•
Select a data series (at the right side of the table) or select a cell in a column of
the data series of Run 3.
•
When you start to drag a variable heading
p
the cursor changes into a graph icon.
Continue dragging until you place the cursor over run number 5, at the left side
of the table (to this run you are copying the data).
•
When the run number is selected (a blue frame appears) release the icon. A new
variable column with the heading
Copied of p(mmHg)
will be added to Run 5.
•
The data points from the column
p (mmHg)
of Run 3 are now copied into a new
column
Copy of p (mmHg)
of Run 5. You can see it by opening Run 5. You can
rename the variables to reflect the above:
p
to
p_pulse
and
Copy of p
into
p_trend
.
11.
Calculate a new variable
p_difference
.
•
Right-click the Data Table and select
Add a new variable > Into Data Series >
Formula
.
•
Give this variable the name
p_difference
and unit
mmHg
and enter the formula:
p_pulse – p_trend
. This calculates the pressure difference.
12.
Create a new graph
Envelope curve
, which displays
p-difference
against
p-trend
. The
resulting graph has a bell-shape form.
13.
Use the function fit option to approximate the graph with a function.
•
Right-click the
p-difference
vs.
p-trend
graph and select
Analyze/Process >
Function fit.
•
Select under Run the option
Run 5
(where the calculations were made).
•
Select the function
f(x)=a*exp(-(bx+c)
2
)+d
.
•
Press
Estimate
.
If necessary manually adjust the individual parameter values and
press
Refine
.
Press
OK
when you are satisfied with the result. The fit will be
added as a new variable
Fit of p_difference5
in the graph.
IV. Determining the blood pressure
The blood pressure values can be determined directly from the envelope curve or via its
derivative graph.
Method 1 - directly from the Envelope curve (see figure 5):
14.
Use the Scan option to read the highest point in the envelope curve. This point
corresponds to the Mean Arterial Pressure (MAP).
15.
Determine the systolic and diastolic pressures.
-
The systolic blood pressure is found as the pressure value at the point along this
bell-shaped envelope for pressure above MAP, for which the pressure difference
value is 50% of the pressure difference corresponding to MAP.
-
The diastolic blood pressure is found as the pressure value at the point along this
bell-shaped envelope for pressure below MAP, for which the pressure difference
value is 75% of the pressure difference corresponding to MAP.
BT17i
Blood Pressure User’s Guide
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9
Method 2 – via derivative graph
14.
Right-click the
p-difference
vs.
p-trend
graph and select
Analyze/Process > Derivative.
15.
Select under Run the option
Run 5
.
16.
Select under Variable the variable
Fit of p_difference5
17.
Select under Order
First derivative
and under Method
Differences
.
18.
Click
Plot
.
19.
Accept with OK.
20.
Click a pane to place the Derivative graph.
21.
Use the
Scan
function to read out the blood pressure values.
-
The pressure value of the intersection of the derivative with the horizontal axis
corresponds to the MAP value.
-
The pressure value of the minimum of the derivative graph corresponds to the
systolic pressure.
-
The pressure value of the maximum of the derivative graph corresponds to the
diastolic pressure.
Figure 5:
A bell shaped “envelope curve” vs. the trend pressure. As blood pressure values are
usually rounded to 5 mmHg we find a blood pressure of 120/80. A best-fit bell-shape envelope is
drawn in the graph to find the maximum (MAP).
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Blood Pressure Sensor User’s Guide
Reference values
The table below indicates normal heart frequency and blood pressure values for boys
and girls for ages between 10-19 years old.
Age
Heart frequency per
minute
Systolic pressure average ±
SD
Diastolic pressure average ±
SD
boys
girls
boys
girls
boys
girls
10 jr
132
129
108±12
109±13
67± 9
64±11
11 jr
160
131
109±11
110±12
65±11
66±10
12 jr
150
147
111±13
114±14
65±10
68±10
13 jr
144
141
116±14
116±14
66±11
68±10
14 jr
127
143
118±14
116±12
66±10
69± 8
15 jr
128
127
123±14
116±11
66±11
68±11
16 jr
106
135
125±14
118±12
68±11
69± 9
17 jr
107
115
126±13
121±13
70±11
70±10
18 jr
85
85
129±15
122±14
71± 9
71±11
19 jr
94
77
131±15
120±12
71±10
70±10
Table 1:
From: van den Brande, Heymans & Monnens,
Kindergeneeskunde
, Elsevier
Suggested experiments
The following experiments can be performed with the Blood Pressure sensor:
•
Using the oscillometric method to calculate blood pressure.
•
Measure blood pressure before and after exercise and while sitting or standing;
•
Compare blood pressure after voluntary isometric contractions (weight lifting) and a
rhythmic activity such as running or biking;
•
Study the effect of caffeine on blood pressure.
BT17i
Blood Pressure User’s Guide
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Technical Specifications
Sensor kind
Analog, generates an output voltage between 0 and 5 V
Measurement range
0 .. 375 mmHg
Resolution
0.1 mmHg
Calibration function
p (mm Hg) = 83.34 * V
out
(V) – 16.67
Max. pressure
1500 mm Hg
Temperature compensated
-0°C to 85°C
Response time
1 ms
Warming time
20 ms
Connection
IEEE1394 connector for BT-IEEE1394 sensor cable.
Sensor cable not delivered with the sensor.
Warranty:
The Blood Pressure sensor BT17i is warranted to be free from defects in materials and
workmanship for a period of 12 months from the date of purchase provided that it has
been used under normal laboratory conditions. This warranty does not apply if the
sensor has been damaged by accident or misuse.
Note:
This product is to be used for educational purposes only. It is not appropriate for
industrial, medical, research, or commercial applications.
Rev. 02
/11/2017