A New Pulse Pressure Simulator Designed Based on LabView

Abstract: A new pulse pressure simulator based on LabView is proposed, and its design concept, system hardware and software composition and application are introduced.

Hypertension is the most common cardiovascular disease in the world and one of the largest epidemics. This disease often causes complications in organs such as the heart, brain, and kidneys, seriously endangering human health. Therefore, regular blood pressure measurement is extremely important for early prevention and timely treatment. Electronic sphygmomanometers have the advantages of non-invasive detection, easy portability, digitization, rapid measurement, and accuracy, and have now entered thousands of households. The calibration of sphygmomanometers before they are put into use is very important. This paper proposes a new type of pulse pressure simulator, which generates a pulse pressure waveform (called dynamic pressure) by software, and superimposes it with the standard human diastolic and systolic pressures (these two are called static pressures) through hardware to output a normal human blood pressure waveform, thereby achieving the purpose of calibrating the sphygmomanometer.

The pulse pressure simulator is a simulation system and also a closed-loop control system, involving technologies such as A/D data acquisition, real-time display and processing of waveforms, and D/A analog output. The LabView virtual instrument technology of the American NI company just meets all the requirements of this system. LabView language is a very excellent graphical programming language. It can not only complete general mathematical operations, logical operations, and input and output functions, but also has library functions and development tools specifically for data acquisition and instrument control, especially its professional mathematical analysis package, which can meet complex engineering calculation and analysis requirements.

The use of virtual instrument technology to design test instruments has high development efficiency and strong maintainability. The test accuracy, stability and reliability can be fully guaranteed. It has a high cost-effectiveness, saves investment, and facilitates equipment updates, function conversion and expansion.

1 System Design Concept

The purpose of this system is to simulate a real blood pressure waveform. Blood pressure refers to the lateral pressure exerted on the blood vessel wall by blood flowing in the blood vessel. Blood pressure includes systolic pressure and diastolic pressure. Systolic pressure refers to the lateral pressure exerted on the blood vessel wall by blood when the heart contracts; diastolic pressure refers to the lateral pressure exerted on the blood vessel wall when the heart relaxes. The difference between systolic pressure and diastolic pressure is generally called pulse pressure, which only occurs when the heart is relaxed, and its frequency is the same as the heart rate. The blood pressure waveform can be artificially decomposed into static pressure waveform and dynamic waveform. The pressure waveform during the systolic and diastolic periods of the heart is basically a linear broken line, namely the static pressure waveform; each heartbeat produces a pulse pressure waveform, namely the dynamic pressure waveform. Figure 1 is a pressure waveform diagram.

Based on the characteristics of the cardiac pressure waveform, the simulation of the blood pressure waveform can be achieved through superposition. An air chamber is inflated to simulate the pressure curve of the cardiac contraction process, while a uniform deflation curve is used to simulate the pressure curve of the heart during relaxation. The inflation and deflation process proceeds at a uniform speed, which just meets the characteristics of the stable frequency of cardiac contraction and diastole. In this way, the static pressure waveform of the heart is realized, which is also the basic principle of sphygmomanometer measurement. During the uniform deflation process, at the arrival of each heartbeat, a pulse pressure waveform is generated by LabView software, and output to the air chamber that is always deflated and inflated through D/A; when the software generates it, its frequency is the same as the heart rate, which is just superimposed on the static pressure waveform to become a complete blood pressure waveform, thereby realizing the hardware superposition of the two waveforms. The superposition of Figure 2 and Figure 3 becomes the cardiac pressure waveform of Figure 1.

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2 System Hardware and Software Implementation

2.1 System Hardware Composition

The system hardware architecture includes an actuator, a pressure sensor, an A/D input, a computer, and a D/A output, as shown in Figure 4. The pressure signal output from the actuator's pressure sensor is amplified by a tuning circuit, sampled by an A/D, and processed and calculated by a computer to give a dynamic pressure signal. The dynamic pressure waveform signal is output by the D/A and amplified to drive the actuator to simulate human pulse pressure and blood pressure. At this time, the actuator generates a signal that is basically the same as the standard blood pressure of the human body.

2.2 System Software Implementation

This paper uses the NI6035E 16-bit data acquisition card produced by NI to collect data from the pressure sensor, and at the same time uses the powerful data acquisition and graphic display functions of NI's LabView development platform. The developed control software has well realized the software superposition of waveforms. Figure 5 is a functional module diagram of the pulse pressure simulator software. The digital signal of pressurization and decompression generated by the air chamber inflation and deflation read by the A/D is the static pressure waveform, which is displayed on the LabView graphic control. At the same time, according to the real-time collected static pressure waveform, the corresponding dynamic pressure waveform is selected for output as the final simulated pulse pressure waveform. It is output to the actuator through the D/A and superimposed on the static pressure waveform to form the required human blood pressure waveform.

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Establish a text resource file or database to store standard pulse pressure waveform data. The standard pulse pressure waveform data can be realized through the waveform editing submodule as needed, that is, by editing the standard human pulse pressure waveform corresponding to various static pressure ranges and storing it in the resource file. The waveform editing submodule is a separate program that can debug the pulse pressure library before running the pulse pressure simulation main program. Separating the main module and the submodule into two independent programs reduces the space occupied. Once the pulse pressure waveform library is edited, there is no need to call the waveform editing subprogram.

3 Experimental results and discussion

The pulse pressure simulator designed based on LabView software outputs a simulated blood pressure waveform after hardware superposition, as shown in Figure 6. From the simulated waveform results, it can be seen that except for the linear interpolation of the data making the waveform not smooth enough, it basically matches the real blood pressure waveform of the human body. This result illustrates the feasibility and accuracy of this system.

4 Application and Prospect

The pulse pressure simulator is based on LabVIEW virtual instrument simulation. The pulse pressure waveform is generated by software and simulated by hardware. The entire blood pressure waveform is simulated. The system has a clear principle, compact structure, and easy operation. It can be used to accurately calibrate the sphygmomanometer. On this basis, the author designed a blood pressure simulator (NIBPM) and has applied it to the research and development of sphygmomanometers and factory inspection of products, with good operation effect.

References

1 Guo Huijun, Zhao Xiangyang, Jia Huiqin. Virtual Instrument Design Based on LabVIEW. Beijing: Publishing House of Electronics Industry, 2003

2 Yang Leping, Li Haitao, Xiao Xiangsheng. LabVIEW Programming and Application. Beijing: Publishing House of Electronics Industry, 2001

3 Cai Jianxin, Zhang Weizhen. Biomedical Electronics. Beijing: Peking University Press, 1997

4 Chen Yanhang, Shen Liping. Biomedical Measurement. Beijing: People's Medical Publishing House, 1984