With the aging of the population, family medical care has an increasingly widespread market. As an important physiological parameter reflecting the cardiovascular system and heart state, blood pressure has become an important part of family medical monitoring. Although the traditional mercury sphygmomanometer is considered to be the gold standard for measuring blood pressure, the electronic sphygmomanometer has received extensive attention because its measurement needs to be trained and inconvenient to carry.
The measurement methods of the electronic sphygmomanometer include: oscillometric method, constant volume method, Korotkoff method, double cuff method, ultrasonic method, tension method, pulse wave velocity method, multi-parameter regression method, etc. [1]. Among all methods, the oscillometric method is the first choice for blood pressure meter manufacturers because of its mature theory and easy implementation.
The method of measuring blood pressure based on the oscillometric principle can be divided into two categories: one is called the waveform feature method, and the blood pressure is discriminated by analyzing the waveform characteristics of the pulse wave envelope; one is called the amplitude coefficient method, and the pulse wave is analyzed by analyzing the pulse wave. The proportional relationship between the amplitudes is used to discriminate blood pressure. Since the waveform features are difficult to identify [2], the second method is easier to implement than the first method.
To date, oscillometric blood pressure meters have undergone three generations of technological innovation. In the first generation, the air pump quickly pressurized the cuff to a certain pressure value, deflated through the air core at a speed of 3~5mmHg/s, and measured the blood pressure during the deflation; the second generation, compared with the first generation, According to the blood pressure of the testee, the air core is changed to an electronic fixed speed exhaust valve, and the deflation speed is more accurate. In the third generation, the air pump is pressurized at a constant speed, and the blood pressure is measured during the pressurization process. The first two generations of technology are called the lower gas method, and the third generation is called the upper gas method. The mainstream domestic practice is to adopt the first generation technology. The disadvantage is that the gas core is not uniformly vented, which affects the accuracy of the measurement results. The mainstream international practice based on Japan is to adopt the third generation technology, which has the advantages of short measurement time and wrist feeling. Comfort, the disadvantage is that there is motor interference and cuff expansion interference during measurement, which requires high filtering algorithm [3].
Based on the calculation and measurement accuracy, the system uses the amplitude coefficient method and the upper gas measurement technology. Because pulse waves are generated during blood pressure measurement, heart rate is an important measurement parameter of the system in addition to systolic and diastolic blood pressure.
1. The principle of measuring blood pressure on the air
As mentioned earlier, the upper air pressure measurement is a blood pressure measurement during the process of pressurizing the cuff by the motor. In this process, the corresponding cuff pressure is collected by the sensor, and the cuff pressure is considered to be a mixed signal of blood pressure and pulse wave. The mixed signal is filtered by the bandpass to obtain the pulse wave. Since the amplitude of the pulse wave is much smaller than the amplitude of the blood pressure, the mixed signal can be estimated as the blood pressure signal, and the characteristic point corresponding to the blood pressure signal is obtained by using the proportional relationship of the amplitude of the pulse wave. Systolic and diastolic blood pressure. A detailed description is shown in Fig. 1. In the figure, the horizontal axis represents time, the unit is s, and the vertical axis represents cuff pressure, and the unit is mmHg. Since the pulse wave is difficult to filter due to the small cuff pressure, the pressurization process can be divided into two stages. In the first stage (0~t1 period in the figure), the motor is controlled to quickly pressurize the cuff to about 40 mmHg, and the pressing speed is generally 10 mmHg/s, and the cuff pressure indicated by the OA line in the figure is obtained. In the second stage, the motor is controlled to slowly pressurize the cuff, and the pressurizing speed is generally 2~3 mmHg/s, and the cuff pressure indicated by the AB curve segment in the figure is obtained. And through the filtering to get the corresponding pulse wave, that is, the blue wave curve in the figure. The cuff corresponding to the maximum value Am of the pulse wave peak is referred to as the average pressure pm. On the left side of the maximum value of the pulse wave peak, the cuff pressure pd corresponding to the pulse wave whose peak amplitude is Ad=Am*kd (kd is the diastolic pressure characteristic coefficient) is recorded as diastolic pressure. On the right side of the maximum value of the pulse wave peak, the cuff pressure ps corresponding to the pulse wave whose peak amplitude is As=Am*ks (ks is the diastolic pressure characteristic coefficient) is referred to as systolic pressure. The heart rate is defined as the number of pulse waves obtained per minute, the number of pulse waves obtained at this stage, and the required time, and the heart rate is calculated. In the third stage, after systolic blood pressure, diastolic blood pressure, and heart rate are calculated, rapid deflation is performed [4].
Figure 1 Schematic diagram of upper blood pressure measurement
It should be emphasized here that the second stage can be deflated by the third stage as long as it is pressurized to the systolic pressure of the individual to be tested. The lower blood pressure is generally added to 160mmHg or more, which is much higher than the normal systolic blood pressure range. Therefore, compared with the lower blood pressure measurement, the time required for the upper gas measurement method is shortened, and the comfort of the test subject is enhanced.
2. Hardware and software overall design
2.1 hardware overall design
The overall hardware design is shown in Figure 2. Due to the rich on-chip and peripheral resources of the single-chip ATmega128, the system is connected to the air pump, air valve, cuff and pressure sensor to realize the cuff pressure collection. The measurement algorithm is implemented by the single chip microcomputer, and the display device and the button are connected to the single chip to increase the human-computer interaction function, and the serial port is connected to realize communication with the PC.
Figure 2 overall block diagram of sphygmomanometer hardware
Dried White Flower Shiitake Mushroom
Organic Dried Shiitake Mushrooms,Using Dried Shiitake Mushrooms,Dried Shiitake Mushrooms Bulk,Whole Foods Dried Shiitake Mushrooms
SHANDONG JOIN & SHARE AGRICULTURAL DEVELOPMENT CO., LTD , https://www.joinsharemushroom.com