This equipment allows the measurement of blood pressure and consists of a cuff, a compressor that allows pumping air to the cuff, a gauge that allows us to measure pressure entered at the cuff, a sensor system. The sphygmomanometer takes two systolic values, when the heart pumps blood and diastolic when the heart is at rest where the normal range is 120 - 80mmHg. For the systolic and diastolic value decision cuff should block the blood pass where you stop breathing until the 300mmHg, subsequently is desinsufla and at the moment that the pointer on the gauge starts scrolling the first time and this is the systolic and diastolic range when the last time.
The monitor works through the oscillometric method where it insufflates the cuff through the compressor until 400mmHg by opening the valve is desinsufla slowly taking first vibration which will be the systolic value where the gauge needle will continue to vibrating thus showing the heart rate and the diastolic value being the last vibration taken before opening the valve and that the cuff desinsufle completely.
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| http://www.tensoval.es/aparatos-de-medicion-oscilometrica.php |
The compressor is powered with 110v which is connected to the first relay and the valve connected to the second 12V relay these are set to send the arduino 5v, when you turn on the compressor and the valve had damage on the LCD for this was mounted on a stage of power control so the current when the engine does not cause damage to the circuit; designed with an optocoupler 4N26 in order to perform an optical coupling of power and isolation of land, a tip 122 and a 2N2222 transistor used to amplify the current sent by the arduino.The second stage of the mpx 5100 sensor
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| power control scheme |
MPX-5100 pressure sensor.
In this blood
pressure monitor was used a MPX5100 sensor. This sensor makes a comparison between
the bracelet and the atmospheric pressure, the pressure makes a voltage
difference when its increasing or decreasing, with a linear regression. When
the bracelet pressure is approximately 0 mmHg, the sensor has 0.18 volts and
when the pressure is 140mmHg the sensor´s voltages is 1v. With this information,
its possible predict the other pressure values along the functioning of the blood
pressure monitor with a linear regression. The first step is to know the slope´s
value with the following equation:
The first
point is P1(0.18,0) and the second point is P2(1,140), where the first value in
the point is the voltage (volts) and the second is the pressure(mmHg),
replacing in the equation, slope´s value is 170.73, indicating the change
between the voltage and the pressure. The following step is calculate the main regression
with the equation:
Y Is the
value to know and x is the sensor´s output voltage while y1 and x1 are the
points values, replacing:
we obtain
the finally result:
Programming code.
The blood
pressure monitor functioning is composed by three stage: the first stage is bracelet
insufflating, second bracelet desinsufflating and the third the information visualization.
b
To turn on
the air pump and the electrical valve must be opened, with a push button the Arduino’s
pin is in a high state and begins to insufflate the bracelet until the pressure
in the system is lower than 140mmHg, with the following code:
bracelet desinsufflating
when the pressure is 140mmHg, the air pump is
turned off, but the electrical valve continues turned on, throwing out the air
slowly. When the air is throwing out, the manometer begins to vibrate giving us
the systolic pressure value, to get this value in our system, when the
decreasing values are greater than the last value, we detect a manometer
vibration, the maximum value saved in an array, is the systolic pressure and
the minimum value in that array corresponds to the diastolic pressure. When the
two pressure values are taken, the electrical valve is turned off and the
bracelet comes back to 0mmHg. Each time that the manometer needle vibrates, we
detect the heart rate, with a counter during the bracelet desinsufflating. In the
next figure, is the code implemented:
Figure 1, Sistolic pressure
Figure 2, Diastolic pressure
Alarm
Generated a conditional if maximum value was greater than 125 or greater than 90 minimum patient had high blood pressure and if the maximum value was less 115 or minimum value was less than 75 presented hypotension as shown below, where it was shown on the LCD.
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| alarm |
