table of Contents:
1. Prerequisite P. 2
2. Principles and symptoms of blood pressure P.4
ï¼ What is blood pressure? P.4
ï¼ Symptoms of hypertension P.4
3. Compare the measurement methods of traditional sphygmomanometer and electronic sphygmomanometer P.4
ï¼ Traditional sphygmomanometer measurement method P.4
ï¼ Measurement method of electronic sphygmomanometer P.5
Fourth, the introduction of finished products P.6
ï¼ System Functions and Features P.6
ï¼ Circuit related knowledge and principle P.6
ï¼ System Block Diagram P.8
@System block diagram action description P.9
ï¼ Circuit Diagram P.11
ï¼ Program flow chart P.12
V. Production process and experience P.26
6. Reference Materials P.27
1. Prerequisites
In early 2000, the Executive Yuan formulated an important regulation, that is, “Medical records belong to patients, not hospitals.†This new regulation allows personal medical records to be quickly transferred between hospitals, eliminating many referrals And the inconvenience caused by the clinic.
After the promulgation of this decree, the previously written medical records will be changed into digital electronic media for storage,
Including various dynamic or static physiological signal data, which also makes the acquisition of digital data a problem.
In order to obtain digital data, some hospitals will hire special personnel to carry out the conversion work, making everyone doubt whether the electronic medical record system can bring real convenience. Therefore, in the medical information research room, we borrowed this PIC Cup The single-chip competition, as well as the expertise in the hospital database, tried to develop this new set of products.
With this system, the precise blood pressure waveforms of the testers can be easily input into the back-end Sever for storage, and the direct acquisition of these blood pressure waveforms and data can be easily operated by the doctor without the need for others Help, even, we developed this wireless transmission sphygmomanometer, which can be measured within a certain range, just press a key, the electronic medical record can be easily stored in the database, convenience is not to mention .
According to the survey, the most common measurement in hospitals is blood pressure measurement, and the most inaccurate is blood pressure measurement. This is why we started with blood pressure measurement, hoping to overcome various difficulties and make a MiCcroChip
16F877 is the core wireless transmission sphygmomanometer.
Impact of blood pressure on people
In the long-term course, excessively high blood pressure mechanically damages the intima of arterial blood vessels, permeability increases, and blood cholesterol deposits on the walls of blood vessels, causing atherosclerosis in the heart, brain, and renal arteries. Eventually, coronary heart disease, cerebral arteriosclerosis, stroke, and renal systolic failure will form. Some scholars have pointed out that 45.4% of hypertensive patients die of cardiovascular disease, and stroke is eight times higher than normal.
The importance of blood pressure
The Buck Aging Research Center in Novato, California, USA recently published a 28-year data collection of large-scale research results of 6,500 people. They claimed that the four most important indicators of health and longevity are:
(1) Not overweight
(2) No smoking
(3) Normal blood pressure
(4) Normal blood sugar
Due to the affluence of material life, the chance of modern people suffering from civilized diseases has greatly increased. When adults over the age of 40, their prevalence of hypertension has reached one-fifth.
Compared with the traditional measurement of blood pressure, not only is it inconvenient to carry the instrument but also requires special technology when measuring, so we thought of using digital electronics to allow the subject to easily carry and operate the blood pressure value. The biggest difference with the commercially available sphygmomanometer is that in addition to the electronic sphygmomanometer designed by us, it can also be displayed on the LCD, and can also transmit data through the RS232 interface via wireless real-time transmission, and change the blood pressure on the personal computer And display the data on the display of the monitor for long-term monitoring and physiological analysis.
In the following description, we will make an in-depth introduction based on the principles and symptoms of blood pressure, the comparison of traditional and electronic blood pressure monitors, the functions and features of finished products, hardware circuits and principles, and software flow control.
Second, blood pressure principles and symptoms
ï¼ What is blood pressure?
Blood pressure is the pressure when blood flows through the walls of blood vessels. The blood coming out of the heart needs to be pushed to go around the body for a week,
The heart is pushing blood forward by constantly contracting and relaxing.
There are two ways to express blood pressure (1) systolic blood pressure: systolic blood pressure is also called cardiac systolic blood pressure, which is the blood pressure measured when the heart contracts and hits blood to the blood vessels.
(2) Diastolic blood pressure: Diastolic blood pressure, also known as cardiac diastolic blood pressure, is the pressure that the heart does not contract.
According to the World Health Organization definition:
(1) The systolic blood pressure exceeds 140 mm Hg
(2) Diastolic pressure exceeds 90 mm Hg
Meeting these two conditions is called hypertension.
ï¼ Symptoms of hypertension
Most patients with high blood pressure do not necessarily have any special symptoms, so regular blood pressure check is very important.
3. Compare the measurement methods of traditional sphygmomanometer and electronic sphygmomanometer
ï¼ Traditional sphygmomanometer measurement method
1. Bring your own sphygmomanometer and stethoscope.
2. In a lying or sitting position, place your arms in a supported position to expose your upper arms.
3. The zero point of the sphygmomanometer is on the same level as the heart, and the cuff is wrapped around the upper arm 1 inch (about 2.5 cm) from the elbow joint.
4. Use the index finger and middle finger to palpate the pulsation of the brachial artery (inside the inner surface of the elbow joint).
5. Place the membrane surface of the stethoscope on the brachial artery, close the inflatable sac of the sphygmomanometer, and squeeze it to drive the air into the balloon. At this time, the mercury column of the sphygmomanometer will slowly rise to about 180mmHg.
6. Then deflate slowly (at a rate of about 2mmHg per second), listening to the sound while looking at the reading on the sphygmomanometer, the first popping sound is systolic pressure, and the last disappearing sound is diastolic pressure.
7. After the measurement, record the date, time and blood pressure value. If in doubt, re-test again to confirm that it is correct.
Source: Blood Pressure Measurement of Taipei Rongmin General Hospital (http: //)
ï¼ Measurement method of electronic sphygmomanometer
1. Bring your own electronic blood pressure monitor.
2. In a lying or sitting position, place the arm in a supported position (this will be more accurate), no need to roll sleeves
child.
3. The zero point of the sphygmomanometer is on the same level as the heart (this way it will be more accurate).
4. After pressing the key, wait for the LCD display.
From the above comparison, we can know the convenience of the electronic sphygmomanometer. It only needs one instrument, unlike traditional sphygmomanometers that require other relatively heavy and bulky equipment.
In addition, when people measure blood pressure, they hope that the simpler the measurement operation, the better, it is better to overcome the technical problems, and the electronic sphygmomanometer does it, it only needs a button action to measure blood pressure. It is different from traditional blood pressure complicated and requires technical action, so it has a higher applicability to the public.
Finally, let's look at the measurement time. The measurement time of the electronic sphygmomanometer we made only takes about 30 seconds (measurement under normal circumstances), so it also meets the time-saving needs in the measurement time. People who are busy recording life are also very suitable.
4. Product introduction
ï¼ System functions and features
The characteristics of the digital electronic sphygmomanometer we made are as follows:
1. Accurate blood pressure waveform data is sent to the PC database, giving doctors more accurate consultation data.
2. Personalized blood pressure data is digitized to facilitate the future development of electronic medical records.
3. Wireless operation enhances convenience.
4. Special anti-shock program design to avoid artificial or natural external forces and increase accuracy.
5. In case of special error measurement (Ex: sphygmomanometer is not tied up), the possible causes of the error will be displayed on the LCD and PC for reference by the user and the physician.
6. Wrist type sphygmomanometer is more convenient and faster than arm type sphygmomanometer.
7. Can be carried around, suitable for office or traffic.
8. The measurement time is short, about 30 seconds under normal circumstances.
9. Due to the embedded A / D converter and USART transmission mechanism of 16f877, there is no need to add other peripherals, which saves more power and is more efficient.
ï¼ Circuit related knowledge and principle
What is blood pressure?
We can know that if a river was originally unblocked, but if it is forcibly blocked, when the pressure is too great,
The force of the water pressure will be enough to break through these resistances to maintain the flow. The concept of blood pressure is the pressure when blood flows through the walls of blood vessels.
The blood coming out of the heart needs to be pushed to circumvent the body for a week. The heart pushes the blood forward by continuously contracting and relaxing.
How to convert blood pressure to voltage?
After knowing the principle of the sphygmomanometer, we choose the pressure sensor. The main purpose is to convert the physical quantity of blood pressure into a voltage signal. Its working principle is to adjust the pressure of the gas through the inflation and leakage of the pump. Because the pressure deforms the material inside the pressure sensor, the relative voltage difference is reflected after passing the Wyeth bridge. In turn, we can also know the pressure at that time from the change in its voltage.
What is the signal we want?
When the pressure on our wristband is equal to the blood pressure, blood begins to circulate and a so-called cuff sound is produced. This is the systolic pressure. We must start to record from here until the last time when the cuff sound is no longer available. Pressure.
How to get the signals of systolic and diastolic blood pressure?
When the pressure sensor is controlled by our linear inflation and deflation, there will be a DC voltage change. If we amplify the signal from the pressure sensor by a certain proportion, we can find that the pressure is between the systolic and diastolic pressure. At that time, we can see on the oscilloscope that there will be another communication signal. At this time, we divide the signal into two places. Once the high-pass filter occurs, when the systolic and diastolic pressures occur, the relative AC signal also occurs, then the signal corresponding to another low-pass filter (that is, the pressure at that time) ), So you can know the systolic and diastolic blood pressure of this person.
How to express the signal?
We will convert the obtained blood pressure signal by A / D Converter, and then display the converted data on LCD and
on the monitor.
ï¼ System block diagram
human body
Signal source
pump
pressure
Sensor
LCD
Output
System chip
PIC 16F877
Instrumentation amplifier
High-pass filter (0.8 Hz)
Non-inverting amplifier (150 ~ 200 times)
Low pass filter (38Hz)
Schmitt trigger
RS-232 interface
Wireless transmitter
RS232 interface 1
VB
application
clinical
database
monitor
Wireless receiver
AD0
AD1
CCP1
TX
START
â—Ž System block diagram action description:
1. The human blood pressure signal is amplified by the pressure sensor and instrument and enters the system. The resulting waveform is shown below.
2. After this signal undergoes 0.8Hz second-order high-pass filtering, the DC level value is removed to prevent the amplifier from entering the saturation region when the vascular pulsation signal is amplified. The resulting waveform is shown below.
3. The signal undergoes 150 ~ 200 times non-inverse amplification to become a blood pressure pulsation waveform. After 38Hz second-order low-pass filtering, the high-frequency noise of the power supply and skin and armband friction is removed, and the signal is maintained at 0 ~ 5Volt Between, for
PIC16F877 capture, the resulting waveform is shown below.
4. Combine the obtained blood pressure pulse waveform with LM311 pulse shaping circuit input CCP1 of pic16f877 RB2 for A / D
Trigger work
5. The signal enters PIC16F877 via A / D (VCC / 2 is used as the DC level value; the blood pressure waveform uses A / D two
channel for additional data conversion)
6. The signal is processed in the PIC16F877, and it is automatically controlled (to control the action of the pump switch and the air valve).
7. The oscillating blood pressure generated by the amplifier is as shown in the figure below. First find the maximum amplitude value Amax. Find the value of 0.5Amax in advance to be the systolic pressure, and then find the value of 0.8Amax to be the diastolic pressure. For comparison, the volts corresponding to the DC voltage value are converted to the values ​​of systolic and diastolic blood pressure, as shown in the figure below.
8. The calculated data is first sent to the PC via the asynchronous USART and wireless transmission mechanism.
9. Real-time unidirectional reception is performed on the PC side, and the waveform graph is shown on the VB. This data is stored in the virtual hospital database.
10. After all signals are acquired and calculated, the systolic and diastolic blood pressures are displayed on the LCD monitor.
ï¼ Circuit diagram
ï¼ Program flow chart
NO
YES
START
1. Initialization of PIC16F877 registers, interrupts, variables, peripherals, and I / O ports
2. Initialization of LCD
Did you press the RB0 key?
NO
Inflate the small pump, turn off the air stop valve, and detect whether the blood pressure DC value is greater than 4 volts?
Is it greater than 4 volts?
NO
YES
Detect whether the AC value of blood pressure is between 1.57 volts and 4.9 volts. Exceeding 4.9 volts may be caused by vibration, and less than
1.57 volts means that the pressurization is insufficient and needs to be repressurized
Between 1.57 and 4.9 volts?
Pressurize or ignore this value
YES
Use the trigger of CCP1 to capture the blood pressure communication signal of A / D Channel1 and store it in the temporary memory
The blood pressure value is displayed on the LCD (approximately 1 to 2 times per second) and on the monitor (approximately 30 points per second, and stored in the hard disk.
Start deflation and record the relevant data. After the deflation is complete, calculate the systolic and diastolic pressure
Display the subject's systolic blood pressure, diastolic blood pressure and pulse rate on the LCD and monitor
END
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