Since the 1950s, a great deal of work has been carried out on pulse theory, pulse diagnosis methods, clinical diagnosis, and experimental research, and great progress has been made. The British Marey first designed a lever pulse sensor powered by a spring and recorded the pulse wave of the radial artery. In 1860, the lever and pressure drum type description pulse chart appeared for the first time. In 1890, the energy conversion method was used, and the lever type optical pulse descriptor appeared. In the 1950s, Chinese scholar Zhu Yan first introduced the lever pulse plethysmograph to the study of pulse diagnosis in traditional Chinese medicine. Since the 1970s, researchers have developed a wide variety of transducers to simulate pulse-cutting fingers of traditional Chinese medicine, collecting and recording pulse signals.
Typical pulse diagnosis instruments at home and abroad such as: BYS-14 pulse instrument produced by Beijing Medical Device General Factory and 28 pulse pulse instrument produced by Beijing Simaifu can detect and reproduce the pulse wave, and can identify common clinical Chinese medicine 37 Kind of pulse diagram. ZM-â…¢ Intelligent Pulse Apparatus is developed by Shanghai University of Traditional Chinese Medicine. It is a kind of advanced pulse apparatus currently in China. It can automatically collect pulse signal, and integrate the characteristics of the position, number, shape, potential and pulse diagram of TCM pulse. The parameters are automatically analyzed and processed. In order to achieve the purpose of layered pulse extraction, the CMB-3000 / 2000 radial artery pulse wave detector developed and produced by Colin Company of Japan uses the principle of tension method to carry out continuous blood pressure monitoring without damage.
This article mainly introduces the signal acquisition in different states of the pulse position at the three positions of the inch, close and ruler from the selection of the pulse sensor, the design of the signal conditioning circuit, the automatic control of the pulse pressure and the preliminary processing of the signal. , Which laid the foundation for further research on the objectification of pulse diagnosis.
1 Characteristics of pulse signal
The characteristics of the pulse signal are as follows:
(1) Weak signal under strong interference. Because the amplitude of the pulse signal is small, it is in the order of microvolts to millivolts. Therefore, it is very easy to introduce interference. These interferences include power frequency interference from 50 Hz, and artifact signals from body jitter and mental tension.
(2) Signals with low frequency but relatively concentrated energy. The pulse frequency of the human body is very low, about 0.5 to 4 Hz, and generally about 1 Hz. The pulse signal can be regarded as a quasi-DC signal or a low-frequency alternating signal. According to the pulse power spectrum energy analysis, most of the pulse energy of healthy people is distributed between 1 and 5 Hz, and the patient's pulse still has a considerable part of the energy distribution below 1 Hz and higher frequency bands (such as above 5 Hz or above 10 Hz).
(3) Complex and variable random signals. The pulse signal is different according to the physiology, pathology and psychology of the human body, and is affected by the environment, time and climate. It shows that the same person has different pulses at different times and places, and sometimes different diseases show the same Pulse.
2 Design requirements of the acquisition system
(1) Selection of sensors. Because different types of sensors have different principles, the original waveforms obtained are also different. In this system, the selected sensors are BP300T pressure sensor and PVDF piezoelectric film sensor.
(2) Design of hardware circuits such as isolation, amplification, filtering and shaping circuits.
Because the extracted signal is very weak and rich in changes, additional multiple filter circuits are required.
(3) Real-time acquisition system with STC89C52 as the core. The conditioned analog signal is converted to A / D, collected into the single-chip microcomputer, and immediately communicates with the host computer through the serial port to transmit the data.
(4) Automatic pressure control. Through the control of the air pump and the solenoid valve by the single chip microcomputer, the purpose of real-time control of the wristband pressure is achieved.
(5) Pulse waveform reproduction. Waveform reproduction of the collected data through the host computer software.
3 System design
The system takes the single chip microcomputer STC89C52 as the core, and the peripheral circuit is composed of sensors, signal conditioning circuits, and A / D converters. The block diagram of the system is shown in Figure 1.
The overall design of the hardware implementation of the system is shown in Figure 2.
Some functions of the system are as follows:
As the forefront of the measurement circuit, the piezoelectric sensor's role is to convert the dynamic information of the pulse into a voltage signal, which is convenient for collection.
The BP300T pressure sensor is used to monitor the pressure of the entire pressurization process, so that the pulse signal can be collected under different pulse pressures.
The pre-amplification and second-stage amplifier circuits amplify the weak pulse biological signal to meet the voltage conversion conditions.
The pulse wave signal of the band-pass filter circuit is weak, the frequency is low, and it is susceptible to external interference, so the filter must be used to remove the interference outside the signal band.
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