Mixed signal microcontroller realizes application of electronic sphygmomanometer

With the development of society, economy and culture, people's diet, life, work habits have changed unhealthy, leading to cardiovascular disease becoming one of the main causes of death among the people. According to incomplete statistics, the number of deaths due to cardiovascular disease in China is increasing at a rate of 3% per year, and the number of children is increasing more severely. However, China’s prevention of cardiovascular diseases, especially hypertension, is extremely weak. Blood pressure and pulse are the most important health indicators.

If you can measure your blood pressure frequently, you will be able to get a good picture of your health. If you find problems early, you will get better results. In addition, the pulse information for diagnosing these diseases also contains many valuable physiological and pathological information, such as the size of vascular resistance; the volume of stroke volume; the extensibility of blood vessels; aortic stenosis and aortic valve atresia. The situation, etc. Pulse as a physiological reference information, it also plays an important role in blood pressure measurement and blood flow detection. The prevention and treatment of blood pressure and pulse for cardiovascular disease is a problem worthy of study and attention.

This paper is based on the high-precision ∑△ ADC of HYCONHY16F188 with LCD driver ICCY2613. The oscillometric method and arm measurement method are used to measure the blood pressure pulse. The test data shows that the electronic sphygmomanometer realized by this method has high measurement accuracy and resistance. Strong interference, easy to use, low cost, etc., suitable for mass production of health care instruments.

At present, the detection of blood pressure can be roughly divided into two categories: the Kopp's method (also called auscultation) and the oscillometric method (also called the shock method). Nowadays, most electronic sphygmomanometers basically use the oscillometric method to measure the blood pressure of the human body. The main reason is that the Kore's method has some inherent disadvantages: one is that it is difficult to determine the diastolic blood pressure; the other is that the method is based on human vision and hearing. Subjective factors, unless a professional doctor, it is difficult for the average person to measure blood pressure. In the 1970s, a variety of Korotkoff's electronic sphygmomanometers were introduced in an attempt to achieve automatic detection of blood pressure, but it was quickly discovered that such sphygmomanometers failed to overcome the inherent shortcomings of the Korotkoff method, with large errors and poor repeatability. At present, most foreign non-destructive automatic blood pressure automatic detection instruments use the oscillometric method.

The sphygmomanometer oscillometric method includes techniques for pressurization, constant velocity exhaust or inflation, and blood pressure measurement. The inflatable cuff is used to block the blood flow of the upper arm artery. Due to the hemodynamic effect of the heart beat, the pressure fluctuations that coincide with the heart beat will be overlapped on the cuff pressure, that is, the pulse wave. During the pressurization process, when the cuff pressure is less than the systolic pressure, the artery gradually bounces and the oscillation amplitude gradually increases; when the cuff pressure is equal to the average pulse pressure, the arterial wall is completely unloaded, and the amplitude reaches the maximum; the cuff When the pressure rises below the average pulse pressure, the arm band is gradually tightened and the amplitude is gradually reduced. The corresponding waveform is shown in the figure.

The criterion for determining the mean pulse pressure based on the statistical rule analysis method is that the corresponding minimum cuff pressure is the average arterial pressure when the oscillation signal reaches the maximum value in the cuff. When the pressure of the wristband is equal to the blood pressure, the blood begins to circulate and produces a so-called cuff sound. This is the systolic pressure. We must start recording from here until the last cuff sound is not present. This is the diastolic pressure. .

The sensor for human blood pressure signal is a special semiconductor material sensor US09111-006S, which is a resistive full-bridge pressure sensor with good linearity. The output voltage is proportional to the applied pressure. The wide operating temperature range is -40. °C—85°C. The HY16F188 internal LDO provides 2.4V at both ends of the pressure senor. It can directly convert the pressure of the arterial blood to the vessel wall into an electrical signal of 0-100mV, and the corresponding blood pressure value is 0-40KPa, which closely matches the design requirements of the sphygmomanometer. It is therefore particularly suitable for oscillometric pressure measurements.

The human blood pressure signal is converted into an electrical signal by the pressure sensing element, and this signal directly converts this signal into a digital quantity by using a maximum of 128 times amplification inside the HY16F188 and its high precision ADC and built-in LDO module to provide a reference voltage. Since the HY16F188 has the following characteristics, the measurement circuit of the blood pressure signal is very simple and the cost performance is very high.

External oscillating circuit input or internal high-precision RC oscillator, and there are 4 working clock switching options;

Built-in 4 kinds of signal input mode switching (forward input, S-short, S+ short, cross);

A data output rate of 10, 20, 40, 80, 160, 320, 640, 1280, 2560, 5120 or 10240 sps may be selected;

The main control part of the sphygmomanometer adopts 16F18832bit as the core of the single-chip microcomputer, and its built-in chargePump circuit used separately for the chip power supply; such power control can prevent the power supply when using the module due to the instantaneous high current when the DC motor is started. The moment is pulled low and the system is reset. And when starting the motor, the control of the 16F188 internal ChargePump only needs to switch the working power selection of the chip through software. Compared with other sphygmomanometer applications, the 16F188 power supply design is very simple. The power supply part is designed to be very compact. It does not require an external chargePump boost circuit, and it can be powered directly using two batteries.

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