Development of Cost Effective ECG Data Acquisition ... - IEEE Xplore

2014 IEEE 10th International Colloquium on Signal Processing & its Applications (CSPA2014), 7 - 9 Mac. 2014, Kuala Lumpur, Malaysia

Development of Cost Effective ECG Data Acquisition System for Clinical Applications using LabVIEW M Murugappan1 Reena Thirumani1 Mohd Iqbal Omar1 Subbulakshmi Murugappan2 1

School of Mechatronic Engineering 2Institute of Engineering Mathematics Universiti Malaysia Perlis (UniMAP) Campus Ulu Pauh, Arau, Perlis, Malaysia [email protected]

before processing the ECG signal to derive any give useful information about the cardiac abnormalities.

Abstract— The main objective of this work is to develop a portable and cost effective data acquisition (DAQ) system for clinical applications. This DAQ consists of several modules such as power supply, analog to digital converter (ADC), amplifiers, isolators, filters and interfacing circuits. The complete data acquisition circuit has been developed using This system mainly aims to collect the ECG signals of frequency between 0.05 Hz and 113 Hz with a gain of 3113. This frequency information from the ECG signal is highly useful clinical applications such as SCA prediction, cardiovascular disease (CVD) detection, etc. ECG signals will be collected from the subjects using 3 leads system and given to DAQ for recording the ECG signal. The acquired signal through this DAQ will then be transferred to the Notebook through NI6008 data acquisition card. This DAQ interface is used to convert the input analog signal to digital signal output and to save the ECG data in the notebook using Labview software. This acquired signal from Labview software is used for further clinical investigation. We also developed a Graphical User Interface (GUI) in LabVIEW software to continuously monitor the ECG signal traces and to record the ECG data with higher precision. The morphology of the acquired ECG signal in the system is highly precise and useful for clinical diagnosis. Furthermore, this proposed system is used for developing sudden cardiac arrest (SCA) prediction in our university. Index Terms—ECG, Data Instruments (NI), LabVIEW.

acquisition

system,

Fig 1: The elements of ECG complex

Zeli Gao et.al, developed an 2 lead ECG device with lead I configuration, Right Leg Driven circuit and used total gain of 1000. The active filter is used to obtain ECG signal with a frequency range of 0.05 Hz to 150 Hz and used NI USB 6008 DAQ card to integrate with LabVIEW [3]. In [4], the researchers have developed a lead II ECG data acquisition device with a cut off frequency of low pass and notch filter with a value of 150 Hz and 60 Hz, respectively. They used ADuC831 DAQ system to be integrated to JFreeChart for ECG data acquisition [4]. Steve et.al used lead II configuration with a gain of 987 [5]. These researchers acquired ECG signal with a frequency range of 0.1-50Hz and implemented inverting amplifier before hardware integration to myDAQ to be read by LabVIEW software [5]. Based on the literature, this present work consists of several stages such as, pre-amplification, isolation, filtering and second stage of amplification to acquire the ECG signals using three ECG leads [6-7]. In general, multi-stage amplifiers are required to amplify the ECG signals with a larger gain. Meanwhile, the amplifiers should have a high common-mode rejection ratio (CMRR) to amplify the ECG signal. This amplified usually amplify the most useful information of heart activities along with inherent noises developed in a system during data acquisition. These noises are filtered using both high and low pass filters to extract the ECG signal between 0.05 Hz and 113 Hz. This filtered signal is digitized by using NI USB 6008 card and to be read and interpreted using Labview software. LABVIEW is a software application from

National

I. INTRODUCTION Electrocardiogram (ECG) signals plays a vital role in clinical diagnosis especially for diagnosing heart related diseases and disorders such as, cardiovascular disease (CVD), pulmonary disease, sudden cardiac arrest (SCA), etc [1]. ECG signal is generated by a nerve impulse stimulus to a heart. The current is diffused around the surface of the body and build on the voltage drop, which is a normally 0.0001 to 0.003volt and the signals are within the frequency range of 0.05 to 100 Hz [1] [2]. ECG signals are usually recorded at the surface of the body and processed to give important information about the electrical activity of heart. A typical ECG tracing of a normal heartbeat consists of a P wave, a QRS complex and a T wave (Figure 1). Usually, the signal which is acquired from the human body is of very low potential and difficult to analyze the signal variance. Hence, necessary amplification is required

978-1-4799-3091-3/14/$31.00 ©2014 IEEE

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The INA118 is chosen because it is a general purpose chip with low power instrumentation amplifier which offers excellent accuracy. The three lead ECG electrodes are placed on the human body surface based on Einthoven triangle. The electrode at RA (right arm) is connected to the negative input of INA118 and electrode at LA (left arm) is connected to a positive input of INA118. The third electrode is placed on the subject right leg (RL) and considered as common ground. The gain of INA118 is controlled by resistor value (RG) by and it does not depend on the existing impedances at pin 1 and pin 8. The resistor value of 4.7kΩ is used as RG to get gain of 11.64 on this work (Equation 1). The output of preamplifier (INA118) is given to a Isolation amplifier for electrical safety purpose. This isolation amplifier provides electrical isolation between the input and output signal. In this work, ISO124 amplifier is chosen as isolation amplifier. The output of isolation amplifier is given to bandpass filter (a combination of high and low pass filter) with a cut off frequency of 0.05 Hz – 113 Hz. Thus, active 2nd order Sallen Key highpass and lowpass filter were built by using LF353P JFET dual operational amplifier. By using R1 and R2 as 300kΩ and C1 and C2 as 10µF, the highpass filter can provide cutoff frequency of 0.05Hz (fc1). Similarly, the resistor R4 and R3 of value 1kΩ and 2kΩ and C as 1µF used to pass the low frequency information of ECG signal at a cut off frequency of 113 Hz (fc2). The last stage of this ECG device circuit is 2nd stage amplification. At this stage, the AD620 is used because it has high common mode rejection ratio, low noise, low input bias current, low power and high input impedance which well suited for medical application. The gain at this stage can be calculated by using the Equation 2. The gain resistor used to obtain gain of 66.87 is 750Ω.

National Instruments that is specially designed for easy and powerful data recording, visualization and analysis. It can display the ECG signal that has been amplified and filtered the unwanted noises and also calculate the heart rate for detection of abnormalities after interface with DAQ system. The organization of this paper is given as follows: Section II describes the data acquisition system design procedure including amplifiers design, filters design and NI USB 6008 interface. Section III describes the interfacing of hardware circuit with LabVIEW software. Section IV presents the experimental results; and finally, conclusions are provided in Section V. II. DATA ACQUISITION SYSTEM DESIGN The block diagram of the proposed data acquisition system is given in Figure 2.

Gain = 1 +

49 . 4 k Ω RG

(2)

Thus, the total magnification that used in this ECG circuit design is: G=11.64 x 2 x 2 x 66.87= 3113.47 Fig 2: Block diagram of basic data acquisition system design

In the ECG data acquisition circuit, some of IC’s require ±12V (preamplifier, filter) and other component requires ±15V (isolation amplifier) (Figure 4). Hence, we have developed a dual power supply output for this circuit. Two different power supplies has been developed using LM series IC’s. LM7812 and LM7912 are used for obtaining ±12V and LM7815 and LM7915are used for getting ±15V. Different voltage values can be obtained from the transformer by rectification circuits as shown below. A transformer of 230/15 V step down transformer with 1A current is used to transferring the AC electrical power from the input power supply.

ECG signals used to record the electrical activity of heart and it potential varies from 1mV to 3mV. Hence, a minimum gain of 1000 is required to derive an ECG signal for further processing. The hardware design of the ECG acquisition system is divided into few stages such as amplification, filtering and isolation. In this work, two Direct Current (DC) power supplies such as ±12 V and ± 15 V are used to electrifying the hardware circuit. The 1st stage of this ECG hardware is pre-amplification using instrumentation amplifier; INA118 is used as preamplifier for this work. The gain of this amplifier is set to 11.64.

Gain

=1+

50 k Ω RG

(1)

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Fig 3: Block diagram of basic data acquisition system design

Fig 4: Schematic diagram of Power Supply Unit (PSU)

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The complete schematic diagram of power supply circuit (Figure 6) and ECG data acquisition circuit (Figure 5) has been designed using Multisim software and tested in breadboard circuit. After the testing, the complete circuits has been made using Printed Circuit Board (PCB). This fabrication of circuits in PCB enables the circuit to be stable and reduces the noise interferences.

GUI was designed using LabVIEW2012 to create an interaction among the user and the ECG device. The special features that designed using GUI are as listed below: • Able to acquire the signal from the ECG device. • Display of continuous time ECG signal traces • Able to filter the signal acquired through different types of filter. • Stores the ECG data in .xls format in computer. The ECG output from the circuit will be the input data of DAQ Assistant in the LabVIEW where the data can be stored or display in a graph. The ECG signal will be multiplied with desired gain and band stop filter used to remove frequency in between 50Hz to 60Hz [8]. The bandpass filter also used to ensure the signal in the range of 0.05-113Hz. The complete hardware system has been shown in Figure 7.

Fig 5: Complete power supply circuit fabrication on PCB

Fig 6: Complete ECG data acquisition circuit fabrication on PCB

Fig 7: Complete ECG data acquisition system using proposed design

This complete circuit has been connected the notebook/personal computer (PC) through NI-USB-6008. This DAQ is usually low cost multifunctional data acquisition card. This card has a 12 bit Analog to Digital Converter (ADC) at a sampling frequency of 10 KHz. This device has 8 analog input and 2 analog outputs. It is compatible with LabVIEW and the basic data acquisition functionality is provided in NI USB6008 for various applications. In this work, this DAQ card is used to acquire the real time signal from the ECG circuit, digitalize the analog signal and save the data in the chosen file format in PC.

IV. DISCUSSION This work aims to design a low cost ECG data acquisition circuit and to integrate with LabVIEW software for recording the ECG data. Initially, the output of dual power supply circuit has been measured and reported in Table I. TABLE I. OUTPUT OF DUAL POWER SUPPLY UNIT

Expected Voltage (V) +12 -12 +15 -15

III. INTERFACING OF HARDWARE WITH LABVIEW In this work, LabVIEW software is used to acquire the ECG signal samples from NI6008 data acquisition card to save the data and to display ECG signal traces [6] [10]. LabVIEW software used to provide the users for a graphical programming environment used to develop sophisticated measurement, test and control system using intuitive graphical icons and wires. The graphical user interface (GUI) allows the interface between human and computer. In this project, the

Measured voltage (V) +11.86 -11.77 +14.88 -14.82

The hardware of power supply unit does not produce the exact voltage which is expected from the circuit. Because, this power supply circuit had internal resistance in the voltage regulator and noises from the circuit affects the output. The power supply should be stable or else any disturbance from the environment might directly affect the circuit and cause instability. So, the power supply circuit was keep inside a

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black box as chassis to reduce the effect of external interferences to the power supply circuit and also reduce the electromagnetic interferences produced by this circuit to the ECG data acquisition circuit. However, the two capacitors (C8 and C9) of 200µF is used to stabilize the output and to reduces the ripple effect.

by different researchers. However, complete circuit design with LabVIEW software interface were not reported in many of the research works. In addition, this proposed DAQ has been followed the universal electrical testing procedure for human safety and has electrical isolation circuit to prevent the patients from any electrical feedback of circuit components. This proposed DAQ is compared with the different products listed in [12] and proves that, the proposed system is highly effective in terms of its performance and cost compared to other existing systems.

Fig 8: Output of ECG preamplifier

After giving the power supply to the ECG data acquisition circuit, the ECG simulator is used to generate the ECG signals at peak amplitude of 1 mV of 1000 Hz sampling frequency. The expected output of the preamplifier is 11.64 mV since the gain of the INA118 preamplifier is set for 11.64 gain value. But, the circuit gives the maximum of 37.68 mV from the preamplifier. This is because of the occurrence of high frequency noises in the ECG signal at which the amplitude of the noise is higher than the amplitude of the ECG signal. Hence, the effects of noises are reduced by passing this preamplified output to the bandpass filter with a cut off frequency of 0.05 Hz to 113 Hz. This filtered signal is further given to second stage amplifier for amplifying the ECG signal. From the calculation, the gain calculated at this second stage of amplification was 66.87, because the RG set up to 750Ω. Hence, the total gain at this stage is 3.113. Thus, the expected result when the amplitude set on the ECG simulator which is 1.0 mV multiplied with the voltage peak to peak is 3.113mV. On practical, the voltage peak to peak was measured is 2.699V which the value is slightly less than the theoretical part. This difference is mainly due to the tolerance of resistor values and some effect of resistances in amplifiers or other components. The NI USB 6008 card can be easily for signal in this frequency without any distortion. Figure 9 shows the output ECG waveform which is acquired by the data acquisition circuit. This analog ECG signal is converted into digital data and stored inside the PC. For this purpose, we have designed a Graphical User Interface (GUI) in LabVIEW software to display the ECG traces and to record the ECG data over continuous recording. Figure 10 shows the GUI layout of ECG data acquisition using LabVIEW. The signal which is acquired using this proposed DAQ is highly useful to extract the ECG signal morphology without any noise contaminations. There are several DAQ are existing in the literature and developed

Fig 9: Output of ECG wave in LabVIEW software

Fig 10: GUI design of ECG acquisition using LabVIEW software

V. CONCLUSION This work aims to design and develop a portable, cost effective and clinically feasible ECG data acquisition system using LabVIEW software. The ECG signal has been generated using ECG Simulator and acquired using 3 lead ECG data acquisition circuit. The generated signal is preamplified using INA118 instrumentation amplifier and filtered at a cut of frequency of 0.05 Hz – 113 Hz. Because, ECG signal does not

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have any useful information beyond 100 Hz. This filtered signal is further amplified using AD620. This amplified input is passed to the PC through NI6008 data acquisition card. This DAQ card is used to convert the analog ECG signals into digital ECG signals at a resolution of 12 bits. Furthermore, the GUI developed on this work is more interactive and user friendly tool to easily collect the ECG data from the simulator. The proposed hardware circuit is simple and effective to suppress the noises developed during the data acquisition. This system has an ability to record the ECG signal for continuous monitoring and stored the ECG data in .xls format in contrast with other existing systems [9-11]

[11] P Bhardwaj, R R Choudhary, R Dayama, Web based Design for Collection and Filtering of ECG Signal, International Journal of Computer Applications, Vol 33, No 8, pp, 1-3, 2011. [12] D Bansal, M Khan and A K Salhan, A Computer based wireless system for online acquisition, monitoring and digital processing of ECG waveforms, Computers in Biology and Medicine, Vol 39, pp, 361-367, 2009.

ACKNOWLEDGMENT This work is financially supported by University Malaysia Perils (UniMAP) Staff Grant from Institute of Engineering Mathematics and Ministry of Science and Technology (MOSTI), Malaysia. Grant No: 9005-00053. REFERENCES [1] M.K Islam, A.N.M.M Haque, G. Tangim, T. Ahammad, and M. R. H. Khondokar, Study and Analysis of ECG Signal Using MATLAB & LABVIEW as Effective Tools, International Journal of Computer and Electrical Engineering, Vol.4, No.3, pp. 404-408, 2012.. [1] T Wang, H P Shen, C H Lin, and Y L Ou, Detection and prediction of Sudden Cardiac Death (SCD) for Personal Healthcare, Proceedings of the 29th Annual International Conference of the IEEE EMBS, pp. 2575-2578, 2007 [2] J. Clerk Maxwell, A Treatise on Electricity and Magnetism, 3rd ed., vol. 2. Oxford: Clarendon, 1892, pp.68–73. [3] Z Gao, J Wu, J Zhou, W Jiang, et.al, Design of ECG Signal Acquisition and Processing System, International Conference on Biomedical Engineering and Biotechnology, pp 762-764, 2012. [4] P O. Bobbie, C Z Arif, H Chaudhari, and S Pujari, Electrocardiogram (EKG) Data Acquisition and Wireless transmission, Proceedings of WSEAS International Conference on System Engineering, pp, 1-7, 2004. [5] S Warren, Lesson learned from The Application of Virtual Instruments and Portable Hardware to Electrode Based Biomedical Laboratory Exercise, American Society for Engineering Education, 2012. [6] I. S. Jacobs and C. P. Bean, “Fine particles, thin films and exchange anisotropy,” in Magnetism, vol. III, G. T. Rado and H. Suhl, Eds. New York: Academic, 1963, pp. 271–350. [7] J Malmivuo, R. Plonsey, Bioelectromagnetism - Principles and Applications of Bioelectric and Biomagnetic Fields, Oxford University Press, New York, 1995. [8] J.J Carr, J.M Brown, Introduction to Biomedical Equipment Technology, 3rd Edition, Prentice Hall, Upper Saddle River, New Jersey, 1998. [9] T.Bragge, M.P Tarvainen, P.O Ranta-aho, P.A Karjalainen, High-Resolution QRS Fiducial Point Corrections in Sparsely Sampled ECG Recordings, Journal of Physiological Measurement, Vol 26. Issue 5, pp. 743-751, 2005. [10] AK Bhoi, S Srivastava, P Basnett, A Bajpai, An ECG Biotelemetry system with NI ELVIS-II DAQ, International Journal of Advanced Electrical and Electronics Engineering, (IJAEEE), Vol 2, Issue 1, pp 103-108, 2013.

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