LabVIEW pulse signal detection and analysis system (1)

Application field: Automation measurement

Challenge: according to the human body impedance characteristics, through the pickup impedance measuring human pulse signal.

Use LabVIEW powerful digital signal processing feature to restore a pulse waveform, and feature extraction and storage of information. Collecting sufficient data, mainly using the language of mathematics library as well as the numerical analysis functionality for regression analysis, a mathematical model, revealing the pulse signal and cardiovascular diseases.

Scenario: using NI LabVIEW 8.5 as the company's software development platform, combined with its own design of pulse signal acquisition device, developed a signal analysis, processing, display and data features such as regression analysis of pulse signal measurement system.

Use of the products: LabVIEW8.5 Student Edition

Introduction

Worldwide, growing cardiovascular disease, has become the number one killer of human health.

United States Heart Association reported that each year approximately 240 million United States people died from cardiovascular disease, particularly in the proportion of patients with hypertension, is most common. The Ministry of health in China announced China has surpassed in patients with cardiovascular disease, cardiovascular disease 1.5 million is now the main cause of death among. Therefore prevent such diseases have become particularly important.

Human pulse system is an important part of the cardiovascular system, extracts from the pulse wave of human physiological and pathological information as a clinical diagnosis and treatment are based on the medical attention at home and abroad, pulse wave shape of the rendered out, strength, speed, rhythm, and other aspects of integrated information, to a large extent, reflect the human cardiovascular system in a number of physiological and pathological characteristics of blood flow.

Chinese medicine chooses the theory that the pulse wave propagation and cardiovascular system, blood, the blood vessel wall motion law are closely linked.

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Formation mechanism of pulse signal

Composition of the blood in cardiovascular circulation system in accordance with a direction of movement, known as the cycle of blood circulation, their power sources and cardiac, heart by doing an orderly contraction and relaxation activities, so that blood flow from the heart arteries, heart into each contraction, arterial pressure occurs once a cyclical fluctuations, this cyclical changes in arterial pressure fluctuations, called a pulse.

Pulse you can walk along arterial wall to peripheral vascular transmissions, this space propagation of the pulse wave fluctuation is called.

Impedance measurement principle

Bioelectrical impedance measurement, or the "impedance technology, is a biological tissues and organs of the electrical characteristics and its variation of extraction and human physiological and pathological conditions related to the detection of biomedical information technology.

It is usually placed on the body surface of the electrode allows systems to detect objects into a tiny AC measurements of current or voltage, testing the impedance and change, and then depending on the application of objective capture-related physiological and pathological information.

The client part (this is designed to arm) as in Figure 1 is equivalent to a cylindrical vessel with uniform conductor, located in its centre.

Figure 1 the human tissue and blood vessels in the simplified model

According to physics, conductor resistance R depending on the conductor's resistivity, length and size of the cross-sectional area.

R = ρL/S= ρL2 /V

In the formula, the resistivity ρ; S as conductor cross-sectional area; L-conductor length; v is the volume of the conductor.

Assuming that the length of the cylindrical conductor, export resistance change Δ Δ R changes with the volume V of the formula is:

ΔR = - ρL2ΔV/V2 = - RΔV/V

On-indicates that the volume of changes and changes of the closely related resistance, the negative sign indicates that the volume of increase will result in a reduction of the resistance, in other words sites of human subjects is equivalent to a cyclical change occurred on the resistance of the resistance, as long as the measured resistance changes waveform can be measured pulse signal.

Incentive to enter the human body, passes through the body impedance electric current is converted to a voltage signal, measuring the voltage signal to cyclical changes reflected impedance changes, eventually measured pulse signal.

Pulse signal acquisition design ideas

Pulse signals have the same with other bio-electrical signals, signal weak, less frequently and are highly susceptible to interference.

Assuming the human subjects of equivalent resistance to 1000 ohms, with the passing of pulse wave, impedance changes about 1 ohm, and this change of location, size and measurement of individual differences and electrode system conditions are more related to directly measure the signal has greater difficulty. On the human body, the resulting signal is not merely a pulse signal, also affected by the frequency and amplitude characteristics similar to those of other biological signal interference, meanwhile, comes from the outside-line interference, fluorescent interference on pulse signal extraction resulting in a high quality.

Application virtual instrumentation technology of bio-electrical signals, can effectively reduce the complexity of signal processing and difficulty, be a good solution to this problem, enable physiological signal processing analysis becomes more convenient and simple.

View LabVIEW for powerful digital signal processing and analysis functions, in order to save development time, improve development efficiency, the use of the software application written in LabVIEW, LabVIEW pulse signal detection and analysis system.

Pulse signal extraction based on the principle of modulation and demodulation, system diagram in Figure 2, the design of the measuring location for arm, through stimulating electrode (E1 to E4) to enter the human body, the carrier 0.6mA 100KHz, E1-E4 spacing set to 15cm, in this high-frequency signals excitation, the human equivalent impedance is approximately 200 ohms.

At this point human pulse signal is modulated in the excitation signal, the output signal is modulated wave, relative to the pulse signal, the signal of the letter for high-frequency oscillation frequencyNumber, the amplitude by measuring electrode (E2, E3) input to the pulse signal conditioning circuits, analog demodulation, filter out high frequency carrier, you can get the pulse wave. While conditioning circuit analog demodulation of sampling points for high-speed sampling, via serial communication with LabVIEW, leverage software on signal demodulation, and signal processing, extract, waveform display, regression analysis, and so on.

Figure 2 overall system block diagram