Tensiometer

1. INTRODUCTION

In practice, a device was designed that allows the measurement of a patient’s blood pressure under normal conditions, with an error of less than 10%. For the design of the equipment with an MPX 5700 Dp pressure sensor, it was previously observed to know the corresponding voltage values ​​of each pressure, making use of a system consisting of a bracelet, a manometer and an insufflation pump.

The obtained reading of the system, the test for the Arduino board and by means of a programming code, the conversion required to perform the calculations corresponding to the systolic, diastolic and media evaluated was performed. An amplification of the voltage values ​​obtained from the pressure sensor for an adequate analog reading was taken into account. Subsequently, all data was displayed on the screen.

One of the first elements to measure blood pressure arose in 1816 after the invention of the stethoscope by the French physician Rene Laennec. In 1828 Jean Marie Poiseuille exhibited in his doctoral work, the first apparatus composed of mercury to measure blood pressure and Karl von Vierordt in 1854 designed the first device that allows to measure blood pressure in a non-invasive way.

In 1896, the Italian doctor Scipione Riva-Rocci created the cuff-mounted blood pressure cuff, based on research carried out in the 19th century. In 1905 Nikolai Korotkoff implemented the stethoscope on the brachial artery to perceive the most precise noises.
From 1950 the tensiometer has become an important device for medical diagnosis.

List of Equipment and Materials:
• Voltage source (Dual)
• Oscilloscope
• Connectors
• Multimeter
• BNC-Cayman
• Cayman-Cayman
• LCD (16×2)
• Arduino one
• Sensor MPX5700
• 1 Resistance 470 Ω
• 1 Resistance 470 KΩ
• 7 1 KΩ resistors
• 1 10 KΩ resistors
• 2 100 KΩ resistance
• 1 Resistance of 150 KΩ
• 1 tensiometer
• 1 compresor
• 1 Electrovalvule
• The Protoboard
• Protoboard cable

2. CONTEXT 

TENSIOMETER

It is a medical instrument used for the indirect measurement of blood pressure, which usually provides it in physical pressure units, usually in millimeters of mercury.
It consists of an inflatable cuff system, plus a manometer (pressure gauge) and a stethoscope to clearly hear the range of KorotKoff sounds (systolic and diastolic).

Blood pressure represents the pressure exerted by the blood against the wall of the arteries. It depends on the following factors:

1. Systolic debit (volume of ejection of the left ventricle)
2. Disability of the aorta and the great arteries.
3. Peripheral vascular resistance, especially at the arteriolar level, which is controlled by the autonomic nervous system.
4. Volemia (volume of blood within the arterial system)

Systolic pressure (using the auscultatory method)

The cuff is insufflated again, but this time the capsule of the stethoscope is placed in the fold of the forearm, over the place where the brachial pulse is palpated. The cuff is inflated to a little above the systolic pressure obtained by the palpation method and then slowly deflated. The pressure in which you start is to hear a noise related to the heart beats corresponds to the systolic pressure obtained by the auscultatory method.
Both the record obtained by the palpation method and the auscultatory should be similar. If this is not the case, the highest value is recorded as systolic pressure.

Diastolic pressure

 After identifying the auscultatory systolic pressure, the cuff continues to deflate until the noises disappear. This moment corresponds to the diastolic pressure. Sometimes, the noises are attenuated first and then disappear. In general, the diastolic pressure is considered as the moment in which the noises disappear. If it happens that the noises are attenuated, but never stop listening, even with the cuff deflated, the diastolic pressure corresponds to the moment when the noises were attenuated. Sometimes both moments are recorded: when the noises are attenuated and when they disappear.

Normal values ​​of blood pressure

Systolic pressure: between 100 and 140 mm Hg (ideally, it should have a systolic pressure that does not exceed 120 mm Hg, or, at most, 130 mm Hg). Diastolic pressure: between 60 and 90 mm Hg (ideally, you should have a diastolic pressure below 90 mm Hg).
A patient is considered to be starting to be hypertensive when his or her registration is equal to or greater than 140/90 mm Hg. Some people, especially young women, have pressures that are usually low (100/60 mm Hg or even less). In other situations, low blood pressure is a manifestation of shock or circulatory collapse, but in these cases, there are signs of poor tissue perfusion (compromise of conscience, cold extremities, poor diuresis).
When there is an accentuated arrhythmia, as in atrial fibrillation, the determination of blood pressure is a little more difficult. In these cases, it is advisable to deflate the cuff slowly and, if necessary, repeat the measurement to see how consistent the values ​​obtained are. In atrial fibrillation, automatic digital manometers can register erroneous values.

3. DEVELOPMENT

DIFFERENTIAL PRESSURE SENSOR MPX5700

Table 1. MPX5700 sensor technical specifications

CARACTERIZACIÓN

Table 2. Voltage values ​​obtained with the multimeter for the MPX 5700 Dp Sensor

Graph 1. Characterization of the MPX5700 sensor with multimeter

Using the multimeter, the characteristic voltage measurement of the MPX5700 sensor was made with respect to the pressure variation of the system as shown in table 2. For this purpose, a non-inverting gain amplifier 10 was designed to obtain more voltage values. elevated. The objective of the measurement was to obtain the equation of the line to be implemented in the programming code.

Table 3. Voltage values ​​obtained by the Arduino board for the MPX 5700 Dp Sensor

Table 3 shows the voltage values ​​obtained directly from the analog reading presented by the Arduino board, based on the pressure variation. This procedure was carried out in order to obtain a more precise equation of the line.

Table 4. Theoretical values ​​of systolic and diastolic pressure

DESIGN PRINCIPLES

Arduino Code

include

include

LiquidCrystal_I2C lcd(0x27,16,2); //
int a=0,b=0;
float sensor, sensora, sensorb,sensoru, sensorc[50], sensord[50], sumad, promediod, sumae, promedioe, sensore[50], presionpulso, p, pp, pm;

void setup()
{
lcd.init();
lcd.backlight();
Serial.begin(115200);

lcd.begin(16,2);
lcd.setCursor(0,0); //cursor en la posicion 1 0
lcd.print(«PRESION ARTERIAL; «); //imprime en la lcd lo que hay en la variable pulso

delay (2000);
lcd.clear();
lcd.print(«insufle… «); //imprime en la lcd lo que hay en la variable pulso

delay (9000);
sensor=analogRead(A0); //lee lo del sensor
sensora=(sensor*5)/1023; //convierte digital

}

void loop()
{

sensor=0;
sensord[50]=0;
sensore[50]=0;
sensorc[50]=0;
promediod=0;
promedioe=0;
lcd.clear();
delay(50);

for (int i=0; i<50; i++)
{
sensor=analogRead(A0); //lee lo del sensor
sensora=(sensor*5)/1023; //convierte digital
sensorb=(sensora/0.006);
sensoru=sensorb -0,2459; //pasa a unidades presion
sensorc[i]=sensoru;//guarda en el vector

}


for (int i=0; i<50; i++)
{    
   if (sensorc[i]>100 && sensorc[i]<160)
   {
   a++;
   sensord[i]=sensorc[i];
   sumad+=sensord[i];
   }
}
{
promediod=(sumad/a); 
lcd.clear();
lcd.setCursor(0,0);
lcd.print("PS:");
lcd.setCursor(3,0);
lcd.print(promediod);

delay(2000); 

}
for (int i=0; i<50; i++) { if (sensorc[i]>60 && sensorc[i]<100)
{
b++;
sensore[i]=sensorc[i];
sumae+=sensore[i];

delay (300);
}
}

promedioe=(sumae/b); 
{
lcd.setCursor(8,0);
lcd.print("PD:");
lcd.setCursor(11,0);
lcd.print(promedioe);
delay(2000); 

}

pp=promediod-promedioe;
p=(pp/3);
pm=(promedioe+p);

{
lcd.setCursor(2,1);
lcd.print(«PPM:»);
lcd.setCursor(8,1);
lcd.print(pm);
delay(2000);

lcd.clear();
Serial.println(sensora);  

  }

}

4. RESULTS 

link of video: https://youtu.be/9uluS68ePOk

5. GLOSARY
·arterial tension
·hypertension
·Transimpedance amplifiers
·Photodiodes
·Blood flow
·Beats per minute

6. ANALYSIS OF RESULTS

In the practice of tensiometer was made, making use of the differential pressure sensor MPX5700DP, to be able to check blood pressure in a patient under normal conditions. Initially the sensor was characterized, to know the voltage values ​​for each pressure generated from the tensiometer. These voltage values ​​were maintained in the order of the mv, for this reason a non-inverting gain amplifier 10 was implemented to be read by the arduino board. This characterization was carried out in two ways; the first was with the measurement of voltages by means of the multimeter and the second was done by measuring the values ​​directly from the arduino under an analogous reading.

Once the characterization of the sensor was obtained, we proceeded to plot the slope in Excel, to take the equation and use it in the programming code, to know the pressure values. The system had to record the systolic and diastolic pressures of the evaluated patient, by means of the voltage variation and by means of the theoretical equations, the pulse pressure and average could be calculated, but if the Bpm could be implemented, it can be evidenced in the video .

In the programming code, conditionals were used for each characteristic voltage range of each pressure, which were implemented in the theoretical formulas and later visualized on the screen. Finally, to verify the error percentage of the experimental values, a comparison was made with the (theoretical) values ​​obtained from the commercial tensiometer and a stethoscope, it was evidenced a very close approximation to the measurement made by the teacher who evaluated the procedure.

7. BIBLIOGRAPHY

• en: http://bioinstrumentacion.eia.edu.co.html
• IfentL. Amplificadores Operacionales [online].  2008. Disponibleen: http://www.ifent.org/temas/amplifica dores_operacionales.asp 
• Robert, L Boylestad and Louis Nashelsky, Electronica: Teoria de Circuitos y Dispositivos Electronicos, Desima ed., Castillo, Ed. Mexico: Pearson, 2009. 

• D. Schneider, “Ride by wire,” Proc. IEEEvol.pp. 22-23, May 2013.

• http://www.ifent.org/temas/amplificadores_operacionales.asp. 2015. Valencia, España. 

• Robert F. Coughlin. Amplificadores operacionales y circuitos integrados lineales.

• Malvino, Albert Paul (2007). Principios de Electrónica. McGraw-Hill. Págs. 964.

VERY THANKS for watched this blog.