~PORTABLE, REAL-TIME, 12-LEAD ECG MONITORING SYSTEM

PLEASE SCROLL DOWN FOR ARTICLEThis article was downloaded by: [Zhejiang University]On: 24 April 2011Access details: Access Details: [subscription number 932491367]Publisher Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UKInstrumentation Science & Technology Publication details, including instructions for authors and subscription information:/smpp/title~content=t713597258PORTABLE, REAL-TIME, 12-LEAD ECG MONITORING SYSTEM Yi-Li Tseng a ; Yo-Zong Shi a ; Fu-Shan Jaw aa Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, Republic of China Online publication date: 04 September 2010To cite this Article Tseng, Yi-Li , Shi, Yo-Zong and Jaw, Fu-Shan(2010) 'PORTABLE, REAL-TIME, 12-LEAD ECG MONITORING SYSTEM', Instrumentation Science & Technology, 38: 4, 305 — 312To link to this Article: DOI: 10.1080/10739149.2010.508331URL: /10.1080/10739149.2010.508331Full terms and conditions of use: /terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. 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The publisher shall not be liable for any loss,actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.PORTABLE,REAL-TIME,12-LEAD ECG MONITORING SYSTEM Yi-Li Tseng,Yo-Zong Shi,and Fu-Shan JawInstitute of Biomedical Engineering,National Taiwan University,Taipei,Taiwan,Republic of China&This article introduces a wireless 12-lead electrocardiogram (ECG)recording system to monitor high-risk cardiovascular diseases.The design overcomes the limitation of wireless transmission by analog multiplexing.The proposed technique provides three leads of ECG at a time and requires less than 15sec to display the total 12leads ECG signals on a remote computer.This increases the chances to discover certain acute symptoms earlier.In addition,the synchronous display of three-lead ECG allows the clinician to survey the ECG from the same plane of the heart.The system is designed with low power consumption and is capable of long-term monitoring.Keywords ECG,electrocardiogram,12-lead,multiplexing,real-time,wireless INTRODUCTION The development of wireless monitoring systems [1–4]used for home healthcare has gained more interest both in research and marketing.The aim of such systems is to increase the rate of early detection and to monitor the high-risk group of patients who suffer from cardiac infarction.[5,6]To comfort the patients,the technique of wireless transmission had been used to transmit the physiological signals.[7,8]However,limitations regardingtransmission rate,power consumption,and transmitting distance greatly reduce the facility of these monitoring systems.The disadvantage of fewer channels of information being transmitted at a time potentially postpones detection of sudden symptoms.Although the transmission rate may be able to be increased,increasing data transfer speeds and the transmitting distance is a trade-off.[9]These issues sometimes make the system totally unsuitable to diagnose diseases.As a result,it is our goal to implement aAddress correspondence to Fu-Shan Jaw,Institute of Biomedical Engineering,National Taiwan University,No.1,Sec.4,Roosevelt Road,Taipei,10617Taiwan,Republic of China.E-mail:jaw@.tw;f95548014@.tw Instrumentation Science and Technology ,38:305–312,2010Copyright #Taylor &Francis Group,LLCISSN:1073-9149print/1525-6030onlineDOI:10.1080/10739149.2010.508331D o w n l o a d e d B y : [Z h e j i a n g U n i v e r s i t y ] A t : 01:53 24 A p r i l 2011feasible monitoring system that is suitable for wireless transmission and can provide the essential information of high risk diseases.Many treatments in cardiac diseases are highly time-dependent,espe-cially those for acute coronary syndromes.[10]To rapidly diagnose and cate-gorize acute coronary syndromes,a 12-lead electrocardiogram (ECG)is essential in a hospital emergency system and for a remote home healthcare service.A 12-lead ECG system helps diagnose early symptoms,such as ST elevation in acute myocardial infarction (AMI).Other cardiac diseases,ischemia or fibrillation for instance,would also be verified by a 12-lead ECG system.However,due to the limitations of transmission rate under low power consideration,it is difficult for biotelemetry monitoring systems today to synchronously measure and display the 12-lead ECG.Most systems provide only a single-lead ECG,[2,3,11]and some of them use time division to measure 12-lead ECG,but only with one lead ECG dis-played at a time.[1]Sudden cardiac death occurs in less than 3minutes for some sudden symptoms,such as ventricular fibrillation (VF)or ventricular tachycardia (VT).Taking a few minutes to finish the 12-lead ECG recording or display delays the time for patients to get medical treatment.The aim of this study is to overcome the limitations of wireless com-munication when continuously monitoring the 12-lead ECG.Some proto-cols of wireless transmission were ascertained to afford a sufficient data transfer rate,but the transmission distance was sacrificed.[9]This limited the activity of the patients.In addition,a high-power protocol is considered inadequate,even if the data transfer rate performs well.In this article,a smart technique of multiplexing was utilized in implementing a 12-lead ECG into an acceptable protocol.The trade-off between bandwidth and transmission distance of wireless transmission was optimized by the pro-posed method.By our system,three-lead ECG was able to be measured sim-ultaneously,and the leads of the frontal plane (I,II,and III in one group while aVL,aVR,and aVF in the other)or the horizontal plane (V1$V3and V4$V6)were displayed at a time.The system was,therefore,familiar and easier for clinicians to examine the leads from the same plane.Further-more,our design made the best use of applicable wireless bandwidth,and scaled down the complete hardware with ultra-micro-power components as well.The time in which the 12-lead ECG finished recording was also shor-tened,in comparison with the previous systems that measured ECG one lead at a time.MATERIALS AND METHODSTo meet the requirement of portable applications,the power consump-tion and size of the device should be minimized.Therefore,the protocol306Y.-L.Tseng et al.D o w n l o a d e d B y : [Z h e j i a n g U n i v e r s i t y ] A t : 01:53 24 A p r i l 2011used in our wireless system has the characteristic of low-power con-sumption.The Zigbee protocol features high reliability (AES encoder techniques),low cost (low complicity),and most important,an extremely low power consumption (1mW).[9]As a result,Zigbee was chosen as the transmission platform,instead of other comparatively high-power proto-cols,such as Bluetooth.Additionally,to acquire non-aliasing and high resolution signals,the characteristics of ECG must be considered.The spectrum of ECG covers from 0.01to 150Hz,[12]and this should be the transmission bandwidth for each lead.In the case of a 10-bit resolution with a sampling rate of 600Hz,the total required bandwidth of the 12-lead ECG is 72kbps.Though this bandwidth is within the range of Zigbee (250kbps),the trade-off between distance and bandwidth of transmission will limit the distance up to 15miles only.Therefore,the technique of multiplexing was utilized in the design.By using the multiplexing technique,not only can the limitation of bandwidth be overcome,but the size also can be dramatically scaled down.Although a 12Â1design records 12-lead ECG signal at a time with optimal speed,the size and power consumption would be relatively larger.Systems with 6Â2design (two groups with six leads in each)provided six vertical or six horizontal leads at a time,which is helpful for clinicians to diagnose,but the size still cannot be effectively scaled down.Consequently,a 3Â4system is a better choice,as it is compatible with present ECG monitors in hospitals and is,at the same time,scaled down both in size and in power consumption.As illustrated in Figure 1,the 12-lead ECG recording system could be partitioned into a control unit,Zigbee device,and three 3Â4multiplexing modules.Each of the modules was separated into three parts:channel-selecting circuit,preamplifier,and filter sections.In the channel-selecting circuit,a multiplexer (CD4052)was used to switch analog inputs digitally by the control unit.In each state,three leads of ECG signals were trans-ferred at a time,so the required bandwidth was decreased.An instru-mentation amplifier (IA)was employed as a preamplifier to reduce the interference.The third part was the filter and gain stage,which consisted of three operational amplifiers (OP),OP296,offering a suitable bandwidth and gain for the ECG signals.In the control unit,a microcontroller,PIC18F4620,was programmed to switch between four states and manage the Zigbee Device.Figure 2shows a flowchart of the firmware design.The program always checks the time flag while the A =D converter processes the analog signal continuously.After a suitable duration,the time flag was pulled up to 1,and the controller then switched to the next state.Because the characteristics of the multiplexer were crucial to the Portable,Real-Time,12-Lead ECG Monitoring System 307D o w n l o a d e d B y : [Z h e j i a n g U n i v e r s i t y ] A t : 01:53 24 A p r i l 2011overall performance of the system,the requirements of the multiplexer included low on-state resistance,low off-state current leakage,and low settling time to accommodate the capability of fast-switching and smooth propagation.In addition to its transmission specifications,it was neces-sary to keep the quiescent power dissipation as low as possible because of the application of the portable device.Thus,the multiplexer,CD4052,which fulfills all of these requirements above,was used to implement this section.The detail circuitry of each module is shown in Figure 3.The preampli-fier and filter components were implemented by the low power IA (AD627)[13]and the general-purpose OP (OP296).AD627offered excel-lent specifications —high CMRR (83dB),a wide range of power supply (þ2.2V to Æ18V),and low noise while operating at a maximum of 85m A.The characteristics of micropower make it ideal for battery-powered medical applications and just suitable for the implementation of our portable device.The gain of AD627was set with an external resistor and programmed at65.An automatic DC suppression was also designed with a negative-feedback loop formed by an integrator.The low power OP,OP296,was used to implement the functions of amplification and filtration with a fix gain of 6.1and the second-order Butterworth low-pass filter (0.01–150Hz).Because the pass-band of the Butterworth filter is flat,it was utilized for the ECG signal applications.In the Zigbee device,UZ2400FIGURE 1Differential four-channel multiplexer with control unit.308Y.-L.Tseng et al.D o w n l o a d e d B y : [Z h e j i a n g U n i v e r s i t y ] A t : 01:53 24 A p r i l 2011(UBEC,Inc.)was used as the RF circuit.The A =D converter in the microcontroller transformed the measured signals into digital signals.Then the processed signals were transferred to the Zigbee Stack,which would manage the wireless transmission.Finally,the 12-lead ECG could be displayed on the monitor,and then analyzed by the physician at thereceiver.FIGURE 2Firmwareflowchart.FIGURE 3Circuit diagram of the signal-conditioning unit.Portable,Real-Time,12-Lead ECG Monitoring System 309D o w n l o a d e d B y : [Z h e j i a n g U n i v e r s i t y ] A t : 01:53 24 A p r i l 2011RESULTS The frequency response of the circuit is plotted in Figure 4.The cutoff frequency of the preamplifier was 5kHz.As shown in Figure 4,the actual passband of the Butterworth filter was 0.9–160Hz,and the overall gain of the system is380.FIGURE 4Bandwidth of thecircuit.FIGURE 5Recording trials of 12-lead ECG.310Y.-L.Tseng et al.D o w n l o a d e d B y : [Z h e j i a n g U n i v e r s i t y ] A t : 01:53 24 A p r i l 2011The recording trials are illustrated in Figure 5.The ECG signals were sensed by electrodes formed by a disposable Ag-AgCl pester attached by an adapter to our circuit.The subject we chose was a normal young adult,24years old.DISCUSSIONMulti-lead ECG was developed in the last decade.Most previous studies have focused on more precise diagnosis of acute coronary syndromes.Holter recording system techniques were already established,but they restricted the number of leads and limited the information they could offer.[14]Several articles support the sensitivity for detection of ischemia using 12-lead monitoring over three leads.[15]The three-lead Holter recording system still exists to obtain information of total of twelve leads using software.However,the transformation delay raises the difficulty of real-time transmission,so the expansion of hardware is needed for real-time purposes.The technique of wireless transmission was included in the real-time recording of multi-lead ECG recently,while most of these sys-tems provided only one-lead ECG at a time.[2,3,11]The proposed system provides separate detailed messages about the horizontal and frontal plane at a time by means of multiplexing technique.This technique completes the full recording of 12-lead ECG within 15sec and improves the prob-ability of discovering some sudden symptoms in early stages.Additionally,the power consumption of the overall system is designed to be extremely low,so it could keep working for over 72h on three 1.5-V batteries.In addition to hardware design,it also provides the flexibility for analytical programs to be added as required.Consequently,the whole design should be useful for the purpose of long-term ECG monitoring.ACKNOWLEDGMENTSThis work was supported by grant 97-2221-E-002-004-MY3from the National Science 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