IMTC 2005 – Instrumentation and Measurement Technology Conference Ottawa, Canada 17-19 May 2005

Design and Implementation of an Embedded Remote ECG Measurement System Ying-Wen Bai, Chien-Yung Cheng, Chou-Lin Lu and Yung-Song Huang Department of Electronic Engineering, Fu Jen Catholic University Taipei, Taiwan, 242, R.O.C. Email: [email protected]

Abstract – Since an embedded circuit board is lower in cost, smaller in size, and lower in power consumption than a PC. In this paper, we use an integrated embedded circuit board instead of using a PC and interface circuit board with our system, which can provide the ECG measurement of a patient who is outside of a hospital. The collected medical information through computer networks will be stored in the medical information databases for accessing by the medical doctors, nurse, and other related health professionals. Our design integrates several modules such as, an embedded circuit board, a database, a Web server, wireless or Internet transmission, and remote user devices. Overall, our system can transmit the heart beat-rate, body temperature and electrocardiogram to the medical information database from a remote site. Keywords: Medical Measurement System, ECG, Embedded Circuit Board, Web Server.

I. INTRODUCTION Traditionally, the medical measurement system can be expensive and a medical measurement system can be difficult to access for a needed patient. Moreover such a system is neither compatible with the PC and communication standards nor is it easily upgraded. In addition, a special patient may need a medical measurement system to monitor one’s body condition even if that individual is located in the hospital. Based on these requirements and available technology, our design provides a convenient operational procedure utilizing an embedded circuit board and Web server to provide a remote electrocardiograph measurement. Typically, an electrocardiogram is generated by a nerve impulse stimulus to a heart, whereby the current is diffused around the surface of the body surface. The tiny current at the body surface will build on the tiny voltage drop, which is a couple of µV to mV with an impulse variation. This very small amplitude of electrocardiograph, needs to be amplified a couple of thousand times for recording and displaying. Simultaneously, the amplified signal is then inputted into an analog to digital conversion and through the digital interface inputted into an embedded circuit board. The embedded circuit board uses client-server network programming to transmitting this digital medical signal to the remote database by wireless or wire networks. Based on the current software and hardware technology, our design provides a convenient operational procedure to conduct a remote electrocardiograph measurement from outside of a hospital. All of the basic modules can be easily

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designed and implemented and they can be compatible with the currently used systems. In 2003, people used a GSM module to transmit this digital medical data [1], but the Internet transmission has proved faster than a GSM module. In our design, we used an embedded circuit board network module to transmitting this digital medical data. Moreover, due to the improvement of the current software and hardware technology of both computer systems and networks, a remote medical system needs to be redesigned by using more modern technologies, such as: a Web server, the Internet and wireless networks and an embedded circuit board. Hence, Our design includes several modules: an interface circuit board, an embedded circuit board, the software on the embedded circuit board for wireless or Internet transmission, and the software for the remote medical servers. As the embedded circuit board software is a module design using an ANSI C, therefore it is compatible with most current computer devices. Finally, our explanation emphasizes the design of an embedded circuit board and the remote server software module of an embedded remote electrocardiogram measurement system. The rest of this paper is organized as follows. In Section 2, a brief overview of a remote medical measurement system is provided. In Section 3, the hardware modules are discussed. In Section 4, the software modules are designed. In Section 5, the implementation and specification of the design are provided. In the last Section, the conclusion is drawn. II. A BRIEF OVERVIEW OF A REMOTE MEDICAL MEASUREMENT SYSTEM An electrocardiogram is generated by a nerve impulse stimulus to a heart, whereby the current is diffused around the surface of the body surface. The current at the body surface will build on the voltage drop, which is a couple of µV to mV with an impulse variation [2-3]. This very small amplitude of impulse needs to be amplified to enable the recording and displaying. Usually, the electrocardiograph needs a couple of thousand times of amplification. The function blocks of the interface circuits of a remote electrocardiogram system are used to amplify the tiny ECG signal with noise reduction. In our design, the interface circuit is used to pick up the electrocardiograph and amplify this signal by using noise suppression and electricity isolation. The amplified ECG signal is then inputted into an analog to digital converter and through the digital interface inputted into an embedded circuit

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rewritten to tighten up and slim down the code base. Overall, the uClinux kernel used in an embedded system is much smaller than the original Linux 2.0 kernel used in an PC, while at the same time retaining the main advantages of the Linux operating system: stability, excellent network capability, and file system support [7-8]. LAN Ethernet Networks Interface Circuit Board Electrocardiogram Heart Beat-rate Body Temperature

‧ ‧ ‧

Analog To Digital V in

B1

Ethernet Port

GND V ref

Hub

Power connector

GPIO

board. The embedded circuit board uses a LCD to display the signal in the board at the client site and uses client-server network programming to transmit this digital medical signal to a remote medical Web server by use of wireless or wire networks. Eventually, the electrocardiograph can be seen at the remote site by Web browsers from different users such as medical doctors and nurses. Section 3 shows the hardware block diagram and the function of the embedded remote electrocardiogram system. The detail of the hardware and software design will be seen at references [2]. Usually, the Web applications can be designed and implemented by Microsoft Active Service Page and the clients can use the HTTP protocol to access the medical information from the medical Web server, which can be updated by a way of the real time. Fig. 1 shows the system architecture of the remote medical information system. There are a few common types of medical information such as, the heart beat-rate, body temperature, and electrocardiogram can be picked up by using the measurement circuit boards and the necessary transmission facility such as a hub, an Ethernet and the Internet. This medical information can be transmitted into the Web server and can be accessed by means of a client’s PC Web browser [4-6].

B8 Sign

ARM CPU

Embedded Circuit

Board

Fig. 2. The medical measurement interface and embedded circuit boards

A. Interface Circuit Board LAN

Hub

Ethernet Networks Signal Sensor

Hospital Measurement Circuit Board

Electrocardiogram Heart Beat-rate Body Temperature

‧ ‧ ‧

AD Converter

Embedded Circuit Board

Interface Circuit Board

Fig. 3. The function of the interface circuit board

Wireless LAN Interface Home PC

‧‧‧ PDA

Doctors &Nurses

Fig. 1. System architecture of the embedded remote medical information system

III.

Filter

(Transducer)

Medical Information Server

Measurement Circuit Board

‧ ‧ ‧

Amplifier

Internet

HARDWARE MODULES

Fig. 2 shows the hardware design of the medical measurement interface circuit board and the embedded board used to transmit this digital medical signal to a medical web server by networks [5]. The medical signals of patients are transmitted in digital form to a medical information server through an embedded circuit board and Internet. The embedded circuit board comes equipped with a full Internet interface and its operating system (OS), which is a derivative of the Linux 2.0 kernel intended for microcontrollers without Memory Management Units (MMUs). However with this kernel multitasking can be hard to execute. The uClinux OS has a full TCP/IP stack which is Internet-ready, as well as support for numerous other networking protocols. Some user applications that run on top of uClinux, however, will not require any multitasking. In addition, in our design, most of the binaries and source code for the kernel have been

The operation procedure shown in Fig. 3 can be explained as follows: 1. In Fig. 3, the ECG sensor is used as the input stage, which requires very high impedance that is often attained by using a CMOS input circuit in order to both match the impedance of the ECG signal source and to pick up a larger amplitude of the ECG signal. 2. Due to the difficulty of the reduction of the noise in the very small amplitude of an electrocardiogram signal, we need to use a differential amplifier to suppress the common-mode noise. In addition to preventing any electrical shock to the tested body, we use an isolated amplifier that can not only amplify the ECG signal but also provide DC power supply isolation by means of a magnetic coupling mechanism. To amplify the electrocardiogram signal further, we use a main amplifier. However, because the DC offset voltage could saturate the amplifier, we must adjust the DC offset voltage of the amplifiers very carefully. 3. Because the medical signal can induce the noise nearby the location of the ECG, we need to use a 60 Hz band rejection to suppress this noise and a low pass filter to reduce the high frequency noise. In addition, to minimize the error of any component, we shall use an adjustable component in order to locate the best band rejection frequency. Usually, the

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bandwidth of the medical signal is low frequency; we, therefore, use a high-order low pass filter to suppress the high frequency band. 4. The sampling rate of the analog to digital conversion will decide the resolution of the medical signal. The embedded circuit board is used to control the analog to digital converter, to receive the data of conversion, and to send out the digital data to the embedded circuit board. B. Embedded Circuit Board Our embedded circuit board is equipped with the embedded platform provided in a fully-fledged Linux development environment by leveraging the generous, free, and open-sources in Linux world, in which we can focus on our applications without bothering with low-level implementation details [12]. The embedded circuit board is built around a cost effective high performance ARM series microprocessor unit that provides complete interface architectures of software and hardware at a very low cost. A number of versatile applications on Linux can be applied to this platform such as, FTP server, Web server, database, IP forward, network applications, controls and communication functions which are all easily implemented on this board. With appropriate expansion interfaces, this platform can be readily connected to an LCD module for further embedded product development. Finally, this embedded circuit board can transmit the digital medical signal to a remote medical Web server by TCP/IP packet [9-10].

Physical signal 1

Vin

Physical signal 3

Vin

Physical signal 4

Vin

DB CS RD ADC WR INTR DB CS RD ADC WR INTR

Interface Circuit Board

XDATA16~ XDATA23 XDATA24~ XDATA31 nECS1 nOE nWBE0

P0

(1) Load OS (2) Start the Web Server Conversion

(03) Conversion or sending

(4) ADC Conversion

GPIO

(5) Conversion Finish ？

ARM7 I/O Embedded Circuit Board

Yes

Fig. 3. The interface circuit board and embedded circuit board IO Port connection.

IV.

Start

bank 1

DB CS RD ADC WR INTR

Physical signal 2

XDATA0~ XDATA7 XDATA8~ XDATA15

Fig. 4 shows the software flowchart of our embedded circuit board for the remote medical measurement system. We use the ANSI C of our embedded platform development environment to design the control program. This embedded platform programming provides us with a very easy way of writing the control program. The major functions of this program are to collect the ECG digital data into the remote medical server from the embedded circuit board through the Internet. In addition, our software modules can also store the digital ECG signal data and display the ECG on the LCD display of the embedded circuit board, and transmit information to the remote medical server through either the Internet or wireless networks. During the transmission, the embedded circuit board can select the server IP address to locate the server computer. The basic operational steps of Fig. 4 may be briefly described as follows: (1) Load Operation System and reset the system; (2) Start the Boa web server; (3) Analog to Digital Conversion; (4) If Converted, finish; (5) Store the digital data to buffer; (6) If Continue, convert; (7) If Data buffer full; (8) Send the digital data from the socket to Internet; (9) Send finish and wait.

External I/O

DB CS RD ADC WR INTR

Vin

A. Programming of the Embedded Circuit Board

Yes (6) Store Data to Buffer (7) Continue？

SOFTWARE MODULES

This embedded circuit board provides uClinux development environment, which is a generous, free, and open source. Our software modules are separated into embedded circuit board programming and remote medical server programming.

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Sending

(8) Data Buffer Full ? No

No

Yes (9) Send the Digital Data from the Socket to Internet (10) Send Finish ？

No

Yes

No End

Fig. 4. The software flowchart on the embedded circuit board for the ECG data collecting and sending.

The Software Flowchart of Embedded Circuit Board for the Remote Medical Measurement System (Fig .4) (1) (2) (3) (4) (5) (6) (7) (8) (9)

Load Operation System and reset the system. Start the Boa web server. Analog to Digital Conversion. If Converted, finish. Store the digital data to buffer. If Continue, convert. If Data buffer full. Send the digital data from the socket to Internet. Send finish and wait.

B. Boa Web server and CGI We use the Web server to remotely execute the CGI program to control the embedded circuit board. Three very important servers for an embedded system under uLinux are httpd, thttpd and Boa [13]. Such a server is based on the HTTP protocol (hypertext transfer protocol) and allows access via Web browser. By using such a browser, an on-line maintenance or a remote configuration for an embedded system can be implemented. A graphical user interface (GUI) is often implemented with the help of a Web-server. We propose an implementation of a remote Web server control by active Web page. The Web server runs in the background and waits for connect attempts by clients. In our design, the Boa Web server is a single-tasking HTTP server, which is unlike a traditional Web server. It does not fork for each incoming connection, nor does it fork many copies of itself to handle multiple connections, because the uClinux is a derivative of Linux 2.0 kernel intended for microcontrollers without Memory Management Units (MMUs). This OS internally multiplexes all of the ongoing HTTP connections, and forks only for CGI programs, which must be separate processes. In the pursuit of speed and simplicity, some aspects of Boa are different from the popular Web servers. In no particular order, the remote host environment variable is not set for CGI programs. This is easily worked around because the IP address is provided in the remote address variable, so the CGI program actually gets the host by address return or else a variant can be used. There are no server sides included in this Web server. The Boa Web server isn’t like the traditional Web servers, which are too slow to parse. Hence, the Boa Web server can be a much more efficient alternative. C. Programming of the Remote Medical Information Server We use the software components of a C++ software development environment to design the Graphical User Interface (GUI) in the medical server for the embedded remote ECG measurement system. This design provides us with a very easy method of learning the execution results. When a remote user opens the TCP/IP port and enables this

medical server, then the embedded circuit board will try to connect to the medical server and transmit the digital medical data to the remote database by the Internet. The major function of the embedded circuit board is to collect the medical measurement signal into the remote medical information server and then our software can store the received signal in the medical database that can be displayed in the server through accessing either the Internet or wireless networks. Fig. 5 shows the software flowchart of a remote medical information server. First, the system creates a new form, resets the system, opens the TCP/IP port and selects the user numbers. If the system receives the medical information data, then it will store the data in the database and display the data waveform in the monitor. SATRT

(1) Create Form and Reset (2) Open TCP/IP Port (3)Select User Number

No No

(4)IF TCP/IP Port Get Data ? Yes

Yes

(7)Close TCP/IP Port ? (6)Display Medical Information

(5) Store Data To Databsae

Fig. 5. The software flowchart of remote medical information server

The Software Flowchart of the Remote Medical Information Server (Fig .5) (1) Create a new form and reset the system. (2) Open the TCP/IP Port. (3) Select User Number. (4) Yes or no receive the medical information data. (5) Storage data in the database. (6) Display the medical information data. (7) Yes or no close the TCP/IP Port V. EXPERIMENTAL RESULTS Fig. 6 and 7 show the measurement interface circuit board and the embedded platform of our embedded remote ECG measurement system. In this design, we use some low-cost ICs to fulfil the basic functions of the electrocardiogram measurement system. The embedded circuit board controls the analog to digital converter, and receives the converted digital data, and sends out the digital data to the memory of

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the embedded circuit board. In the measurement interface circuit board, the high-order low pass filter suppresses the high frequency noise.

Body Temperature Circuit ECG Circuit

Analog to Digital Converter

dB by an optimum adjustment, the bandwidth of ECG signal 1~200Hz, and the power dissipation less than 500mW. In addition, due to the bandwidth limitation of the ECG signal, with a transmission rate of 144kbps through a wireless network, we have demonstrated the real time transmission of the remote ECG signal through either a wireless or a wire Internet.

Heart Beat-Rate Circuit

Fig. 6. The interface circuit board of the embedded remote medical measurement system. Fig. 8. The GUI interface of the client PCs by accessing the remote medical server system

Body Temperature

Table I. The specification of our ECG measurement interface circuit board

ECG Waveform Etherne t

Embedded Circuit Board

Name

Conditions

ECG System

Units

RIN

Input Resistance

~

1012

Ω

ROUT

Output Resistance

~

75

Ω

VOUT

Output Voltage

RL≅10KΩ

±12

V

AV

Amplification Gain

Max.

4×103

Common-mode- Optimum CMRR rejection-ratio Adjustment

Fig. 7. The embedded circuit board of the embedded remote medical measurement system.

The users or patients can see the ECG waveform both from the LCD display of the embedded circuit board at the client site and from the GUI interface of the client PCs by accessing the remote medical server system as shown in Fig. 8. Fig. 8 shows the GUI picture of the embedded remote ECG measurement system, which provides the basic functions of the medical records such as, the ECG signal viewing selection, body temperature and the heart beat-rate statistics. By using the Internet or wireless to browse the medical Web page the doctor can read the patient the medical information on the Web page from the Web server. Table 1 shows the specification of our ECG measurement interface circuit board. We set the input resistance at more than 50M , the CMRR (common-mode-rejection-ratio) 90

Ω

Symbol

V

V

90

dB

BW

ECG Signal Bandwidth

~

0∼200

HZ

PD

Total Power Consumption

~

≤500

mW

VI.

CONCLUSIONS

The special patients may need a medical measurement system to monitor one’s body condition even if that individual is not in a hospital. This paper proposes a design and implementation of an embedded remote ECG measurement system. In the measurement interface circuits of embedded remote ECG measurement system, we use some low-cost ICs to fulfill the basic functions of the interface hardware. The measurement interface circuits pick up a very weak ECG signal and provide amplification, isolation and noise suppression. Our design also provides a fine-tuning

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mechanism, which has a minimum error rate. In addition, the embedded circuit board provides the ECG buffering, displaying and network transmitting, which are supported by the fully-fledged Linux development environment. The embedded circuit board is lower in cost, smaller in size, and lower in power consumption than a PC. The embedded circuit board controls the analog to digital converter and through the expansion interface inputs the digital data. We transmit this digital medical signal to a remote medical web server by TCP/IP packet. In addition, our software interface provides a friendly operation, Internet network transmission modules, and a LCD displaying module at the client site for the remote embedded ECG measurement.

[12] Embedded Linux/Microcontroller Project, http://www.uclinux.org/ [13] The Boa Web server homepage, http://www.boa.org/

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Al-Ali, A.R.; Al-Rousan, M.; Al-Shaikh, M. “Embedded system-based mobile patient monitoring device”, 2003. Proceedings. 16th IEEE Symposium Computer-Based Medical Systems, 26-27 June 2003, pp. 355-360. [2] Ying-Wen Bai, Chien-Yung Cheng, Cheng-Kai Lu, Chuang-Hsiang Huang, Yuh-Ting Chen and Ya-Nan Lin, “Adjustable 60Hz Noise Reduction and ECG Signal Amplification of a Remote Electrocardiogram System,” Proceedings of the 20th IEEE Instrumentation and Measurement Technology Conference, pp.197-202. [3] Pavlopoulos, S.; Tagaris, T.; Berler, A.; Koutsouris, D. “Design and development of a Web-based hospital information system”, Engineering in Medicine and Biology Society, 1998. Proceedings of the 20th Annual International Conference of the IEEE, Volume: 3, 29 Oct.-1 Nov. 1998, pp. 1188 -1191. [4] Belardinelii, A.; Palagi, G.; Bedini, R.; Ripoli, A.; Macellari, V.; Franchi, D.; “Advanced technology for personal biomedical signal logging and monitoring”, 1998. Proceedings of the 20th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Vol. 3, Nov. 1998, pp. 1295-1298. [5] Barro, S.; Presedo, J.; Castro, D.; Fernandez-Delgado, M.; Fraga, S.; Lama, M.; Vila, J.; “Intelligent telemonitoring of critical-care patients”, IEEE Engineering in Medicine and Biology Magazine, Vol. 18 Issue: 4, July-Aug. 1999, pp. 80-88. [6] Ratib, O.; Dahlbom, M.; Zucek, J.M.; Kong, K.; McCoy, M.; Valentino, D.J.; “Web-based video for real-time monitoring of radiological procedures”, IEEE Transactions on Information Technology in Biomedicine, Vol. 4 Issue: 2, June 2000, pp.108-115. [7] Kyung-Hwan Ahn; Sung-Kwang Kim; Kwan-Pyo Hong; Ki-Jun Han; “Design and implementation of browser/server environment-based hospital information search system (BS-HISS)”, TENCON 99. Proceedings of the IEEE Region 10 Conference, Volume: 2, 15-17 Sept. 1999, pp: 1569 -1572. [8] Ma Zhongming; Ng Nai Fatt; “Medical signal transmission and analysis based on the Internet”, 4th International IEEE EMBS Special Topic Conference on Information Technology Applications in Biomedicine, 24-26 April 2003, pp. 74-77. [9] Kollmann, A.; Kastner, P.; Schreier, G.; Rotman, B.; Lercher, P.; Scherr, D.; Klein, W.; “Web-based telemedical system for collaborative pacemaker follow-up”, Information Technology Applications in Biomedicine, 2003. 4th International IEEE EMBS Special Topic Conference on, 24-26 April 2003, pp.314-317. [10] Gouaux, F.; Simon-Chautemps, L.; Adami, S.; Arzi, M.; Assanelli, D.; Fayn, J.; Forlini, M.C.; Malossi, C.; Martinez, A.; Placide, J.; Ziliani, G.L.; Rubel, P.;” Smart devices for the early detection and interpretation of cardiological syndromes”, Information Technology Applications in Biomedicine, 2003. 4th International IEEE EMBS Special Topic Conference on, 24-26 April 2003, pp. 291-294. [11] Embedded Linux Platform on ARM of the product development platforms, http://www.ancher.com.tw/7525b.html

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