1656 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 55, NO. 5, OCTOBER 2006Fig. 1. Functional block diagram of the WIHMD system. Fig. 3. Photograph of the developed WIHMD worn on the wrist. attached to the inner surfaces of the cuff, and a ﬁnger clip- type SpO2 sensor is connected to the main unit. Fig. 3 shows a picture of the developed system worn on the wrist. It alsoFig. 2. Schematic drawing of the prototype WIHMD. contains two printed circuit boards, which include analog and digital circuitry and other onboard sensors. The size of theeach component, analyzes the measured data, and then rapidly WIHMD is 60 × 50 × 20 mm, excepting the wrist cuff, andcommunicates with the patient’s caregivers, such as doctors the total system weighs 200 g, including two 1.5-V AAA-sizedor relatives, through a connected telecommunication device. batteries. The total power consumption is about 150 mA withThus, it is possible to get rapid and appropriate directions 3-V supply voltage in active mode, where all measuring mod-made to handle emergency situations and to enable the user or ules are in operation and about 5 mA in idle mode with only thecaregiver to detect and manage changes in the user’s health. fall detector in operation.The technical challenge in the development of such a device is The software of WIHMD was developed for operationalnot only to integrate several health monitoring devices into a simplicity and efﬁciency. Considering the fact that the possiblesmall wrist-wearable unit but also to make the system practical users are relatively old and inﬁrm, any complicated user inter-for healthcare service that is reliable under various operating face would be counterproductive in daily life or in emergencyconditions, easy to operate and manage, and affordable for situations. The WIHMD provides relatively large graphic iconsmost possible users. Ultimately, the WIHMD will enhance the on a 128 × 64 pixel graphic LCD and three input buttons as userquality of life for the elderly and patients in potential emergency interface and connects with public telecommunication devices,environments. like cellular phones, in a wireless manner. When it is ordered to do so, the microcontroller wakes up from a power-saving mode II. M ATERIALS AND M ETHODS and digitizes the analog output of each measurement module through its imbedded A/D converter with 10-bit resolution andA. System Description 100-Hz sampling rate. In emergency telemedicine mode, the The WIHMD consists of six vital biosignal measuring WIHMD starts to operate either if it automatically detects themodules, which include a fall detector, single-channel electro- emergency occurrence, mainly based on the fall detector output,cardiogram (ECG), noninvasive blood pressure (NIBP), pulse or if the wearer presses any button for longer than 5 s whenoximetry (SpO2 ), respiration rate, and body surface tempera- he/she feels something is wrong. In this mode, the WIHMDture (BST) measuring units. As shown in Fig. 1, the central performs all measurements and sends the measured data to pre-unit of a microcontroller (ATmega103L, Atmel, USA) with assigned caregivers as quickly as possible. The characteristics128 KB of in-system programmable ﬂash, 4 KB SRAM, of each measurement module and telecommunication deviceand programmable serial universal asynchronous receiver are given below.transmitter (UART) manages the operation of each measure-ment module and evaluates the patient state by collecting and B. Measurement Module and Telecommunicationanalyzing the measured data. As shown in Fig. 2, the hardware Device Descriptionof the actual device is made of a wrist cuff for the NIBPmeasurement and a main unit mounted on the cuff. Two textile 1) Fall Detector: Falls are one of the greatest obstacles toelectrodes for ECG and a semiconductor temperature sensor are independent living for frail and elderly people. People of all
KANG et al.: WIHMD WITH A TELE-REPORTING DEVICE FOR TELEMEDICINE AND TELECARE 1657ages fall, but these accidents rarely cause injury for the younger The NIBP module was constructed using a motor, pump,members of society; however, among the elderly population, solenoid valve, and wrist cuff from a commercialized productthey are often much more serious. Perhaps half of all falls in (SE-309, Sein Inc., Korea) and a small semiconductor pressureolder people result in minor soft-tissue damage, but 10%–15% sensor (MPXM2053, Motorola, USA). All electronic circuitrycause serious physical injury . So, early detection is an and the program for oscillometric pressure measurement wereimportant step in providing elderly people with the reassurance developed in this laboratory .and conﬁdence necessary to maintain an active lifestyle. 4) SpO2 : Pulse oximetry is a noninvasive method of moni- It is known that a combination of an accelerometer and toring the arterial oxygen saturation level based on Beer’s lawa gyroscope must be used to accurately detect the different for the absorption of light by hemoglobin and oxyhemoglobin.kinds of falls . We developed a simple fall detector using The pulse oximeter makes use of the pulsatile components ofa two-axis accelerometer (MMA3201, Motorola, USA) and a arterial blood’s absorbance values at two different wavelengths.in-house-made posture sensor that is basically composed of a We used red (660 nm) and infrared (940 nm) light emittingphoto-interrupter with a pendulum. As a result of a pendulum diode (LED) as the incident light source. The reﬂected light isswing, a photo-interrupter acts as an ON–OFF switch to indicate recorded by a photodetector, and variations in light intensitythe wearer’s wrist orientation with respect to gravity. The fall are caused by changes in ﬂow and pressure pulsations indetection scheme is as follows. First, the system is in idle mode blood. Then, the SpO2 value is calculated from the level ofto minimize power consumption. If peak acceleration exceeds variations in light intensity in each channel (Red, IR). For thisa predetermined threshold, the comparator output wakes up the system, a SpO2 module was developed using a commercialsystem into active mode. Then, after 1 s, the central processor ﬁnger clip sensor (8000H, NONIN, USA) connected to theunit turns on the posture sensor and reads its output for the main unit, which includes the required electronic circuitrynext 1 s. If the output of the posture sensor indicates that the and program.subject’s lower arm is laid on the ground, the central processor 5) Respiration Rate: In patients with chronic obstructiveunit determines an occurrence of fall; otherwise, it just returns pulmonary diseases and sleep apnea, it is important to evaluateto idle mode. Using this relatively simple operational scheme, the extent of obstruction of the respiratory system; regularwe achieved a remarkable reduction in the number of false testing is often useful in this regard . Long-term ambula-positive alarms caused by vehicle (elevator, car, etc.) riding or tory recording of respiration can provide more extensive andbrisk motions of arm and so on. speciﬁc information about the occurrence of abnormal patterns Since almost all emergency situations are accompanied by of breathing.a fall, the fall detector remains active all the time and is In this study, respiration rate was estimated from the R–Rcrucially used to detect emergency onset. When the WIHMD interval variation curve, which is the only possible way underdetects a fall event, it conﬁrms whether the wearer is con- the limitation that the measuring position is restricted to thescious or not by raising a sound alarm. Then, if there is no wrist. First, we calculate the R–R interval between each beatresponse from the wearer in a given time (10 s), the WIHMD from the ECG waveform using the QRS detection algorithm.starts the vital biosignal measurements and provides the emer- After rejecting false detection of the QRS peak using the meangency occurrence to preassigned caregivers with the appropriate time interval threshold, we acquire the R–R interval variationinformation. curve. Then, the respiration rate is calculated using the baseline 2) Single-Channel ECG: ECG is widely used as one of crossing algorithm .the most simple and effective methods of continuously mon- 6) BST: Central body temperature is one of the basic factorsitoring the heart for tele-healthcare and conventional med- that reﬂect homeostasis, and it can indirectly tell whether a pa-ical care. For ECG measurement on the wrist, we used only tient’s condition has worsened or whether the temperature of thetwo textile electrodes for a single channel (Lead I), which patient’s environment has changed. BST, as determined fromrecord the ECG between each arm. The textile electrodes are wrist skin, is quite different from the central body temperaturemade of a conductive sheet, which has a surface resistance of but can be used to detect changes in a patient’s environmental0.05–0.1 Ω/cm2 . One textile ECG electrode for the left arm or physiological state.is attached to the inner surface of the wrist cuff, and the right In the developed system, the BST module was fabricatedhand must touch the other electrode at the outer layer of the using an IC-type temperature sensor (TC1047, Microchips,cuff. The analog circuitry of the ECG module consists of an USA). It is small in size, low cost, consumes little power, andinstrumentation ampliﬁer, a notch ﬁlter, and a noninverting is highly accurate. The sensor is attached to the inner surface ofampliﬁer with a total gain and bandwidth of 80 dB and 40 Hz, the wrist cuff with its sensing surface contacting the skin.respectively. The ECG signal is converted into a digital signal 7) Tele-Reporting Device: The tele-reporting device is anwith sampling rate of 100 Hz for heart rate (HR) estimations. essential part of telemedicine or tele-healthcare systems like 3) NIBP: Abnormal blood pressure is the most powerful WIHMD. In the case of emergency telemedicine, it mustcardiovascular risk factor. Regular blood pressure monitoring at rapidly transfer the information acquired by the instrumenthome in free living conditions is helpful in the management of to caregivers. In home telecare for the elderly, such a rapidcardiovascular diseases . The accumulated NIBP data over transfer is not necessary, but transferring the measured data toan extended period can be used to evaluate a patient’s health a centralized server or doctor’s personal computer is still re-and indicate the time for medical treatment. In this study, a quired for later examination by healthcare services. Nowadays,conventional digital wrist sphygmomanometer was developed. many kinds of wireless communication devices are available,
1658 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 55, NO. 5, OCTOBER 2006 TABLE I SUMMARY OF PERFORMANCE EVALUATION RESULTSe.g., Bluetooth, wireless local area network (LAN), radio fre-quency (RF) transceiver, and a cellular phone. In our previous research, we compared the telecommuni-cation methods to be used with a chest strap type of patientmonitoring device for emergency telemedicine system (ETS). Based on the results of the previous study and consideringthe system complexity, power consumption, and reliability, wechose an RF transceiver and a cellular phone for short- andlong-range telecommunications, respectively. In the developedsystem, tele-reporting was accomplished in two separate ways.The ﬁrst involved an RF link between the WIHMD and a cellu-lar phone for short-range transmission. The second involved thetransmission of information to remote caregivers and/or a servercomputer through the commercial cellular phone network. Weused TXM-LC and RXM-LC (433 MHz, 10 mW, FM, LINXtech, USA) as RF transmission and reception modules, respec-tively; the latter is connected to a cellular phone (IM-3000, SKTeletech, Korea) via an RS-232 connection with 38400-Bd rate. Fig. 4. Screen display of the data acquisition program for the performance evaluation test. III. R ESULTSA. Performance Evaluation Prior to practical application, we evaluated the performanceof each measurement module using commercialized simulatorsand a test setup and by human trial as summarized in Table I.Except the human trial cases, the transducers or electrodes ofthe WIHMD were directly connected to the simulators or thetest setup. Fig. 4 shows a screen display of the data acquisitionprogram used for the performance evaluation test and systemdebugging. This program consists of one data block in whichthe measured parameters and patient information are shownand three waveform blocks for SpO2 , ECG, and oscillatory cuffpressure of NIBP measurement. Performance evaluation of the developed ECG module wasaccomplished using a commercial ECG simulator (Patient-Simulator 214B, DNI Nevada Inc., USA) . For varioussimulated ECG outputs with range of 40–240 bpm, the devel-oped ECG module produced HR outputs for normal waveformswithin a mean error of ±1%. The performance of the devel- Fig. 5. Respiration rate detection using R–R interval variability. (Above)oped NIBP module was veriﬁed using a commercial simulator Real respiration waveform using a spirometer. (Below) Extracted respiration(BPPump2M, BIO_TEK, USA) . For all simulator outputs waveform from R–R interval variability.
KANG et al.: WIHMD WITH A TELE-REPORTING DEVICE FOR TELEMEDICINE AND TELECARE 1659 TABLE II USER NEEDS ANALYSIS OF THE HEALTH MONITORING DEVICE FOR EMERGENCY TELEMEDICINE AT FOUR DIFFERENT SITUATIONSfor wrist measurement, the developed NIBP module provided activates the device by pressing the emergency button. Onceoutputs within an error range of ±5 mmHg. In the case of the an emergency has been detected, the main control unit sends anSpO2 module, we used a commercial SpO2 simulator (Oxitest emergency alarm and the patient’s health information throughplus7, DNI Nevada Inc., USA) for evaluation . Over various the connected cellular phone using the short messaging serviceranges of SpO2 levels, the output showed an accuracy within (SMS), which is basically a text transmission service providedan error range of ±2%. In a performance evaluation study, the by the cellular phone company. In this study, we transferredrespiration rate was simultaneously measured using a commer- six parameters, i.e., HR, respiration rate, blood pressure, SpO2 ,cial spirometer (WebDoc Spiro, Elbio Company, Korea) as a BST, and the location of the user as represented by the mobilereference. In Fig. 5, the upper plot shows the respiratory signal phone service base station ID. The advantages of the peer-of the spirometer, while the bottom plot shows the extracted to-peer SMS model are the rapid and safe transmission ofrespiratory signal as the R–R interval variability from the ECG. text messages without having to establish a centralized large-Extensive comparative tests showed that the respiratory signal scale service system. Furthermore, it is possible to assignby R–R interval variability was highly correlated with the real multiple receivers, including doctors or family members, sorespiration rate. However, the R–R interval variation is affected that interested parties may receive the message simultaneously.by many physiologic or emotional factors other than respira- In addition, recently, mobile phones are being equipped with ation. In addition, since the respiratory signal is sampled by each global positioning system (GPS), which can directly guide theheartbeat, the extracted respiratory signal showed a low corre- rescue team to the precise emergency location .lation with the actual over the range of 8–18 breaths/min . Due to the difﬁculty in applying the developed WIHMD to For the evaluation of the BST module, the developed module real emergency situations, we attempted to simulate emergencywas tested inside a heated chamber at temperatures that were situations and evaluated the performance of the system. Threeincremented over the range of 25 ◦ C to 40 ◦ C in 1 ◦ C steps. The volunteer subjects were asked to wear the WIHMD for 16 hresults showed good linearity and an accuracy within a mean a day during waking hours and were asked to make threeerror of ±1.5%. manual emergency alarms and three simulated falls per day. For the evaluation of the fall detector, a total of 150 simulated Fig. 6 shows the test result of the emergency telemedicinecases were tested. Five human subjects were asked to try three application. Fig. 6(a) shows typical accelerometer and posturedifferent types of movements, namely 1) fall while walking, sensor waveforms with parameters and events used in the fall2) fall while standing, and 3) sit from standing with ten times detection algorithm, while Fig. 6(b) shows a screen display ofrepetition of each. Our fall detection algorithm based on two- the emergency event-logging program during this testing. Thisstage checking of the posture after the falling acceleration program shows the logged emergency events with records of thesignals provided a good detection rate of over 90%. Table I patient information (ID, name, and age), the measured phys-summarizes the results of the performance evaluation. iological values, event type, and position/location ID. In real applications, a cellular phone was wirelessly connected to theB. Application to Emergency Telemedicine WIHMD and sent emergency messages and health information to other designated cellular phones shown on the right-hand The functional objective of the WIHMD with respect to side in Fig. 7. All subjects felt comfortable wearing the deviceemergency telemedicine is to provide patient health informa- for 16 h. All manually activated and simulated events weretion, such as vital biosignals and locational information, to the successfully detected, and the preassigned recipient cellularnearest emergency service center in a form that allows rapid phone received messages correctly.and appropriate expert response. We analyzed four possibleemergency scenarios in which the device would be useful; IV. C ONCLUSIONTable II summarizes the results. In the emergency telemedicine mode, the WIHMD starts We have developed a WIHMD for use in emergencyto operate as soon as it automatically detects an emergency telemedicine and home telecare for the elderly. The unit was de-occurrence using its built-in fall detector or when the user signed to provide tele-healthcare services for high-risk patients
1660 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 55, NO. 5, OCTOBER 2006Fig. 6. Test results for the emergency telemedicine application. (a) Typical waveforms of the accelerometer and the posture sensor for the simulated fall.(b) Screen display of the emergency event-logging program. rate, and 6) BST. The tele-reporting function of the WIHMD was realized by wireless connection to a cellular phone. All test results conﬁrm the applicability of the WIHMD to both emergency telemedicine and home telecare. A shortcoming of the WIHMD is the limited ﬁdelity of the measured biosignals due to the limited body contact with an area of the wrist. If we could measure biosignals at other sites, such as the chest, waist, and ankle, and connect such distributed measurement modules using a so-called personal area network (PAN), then more and higher ﬁdelity biosignals would be ac-Fig. 7. Photograph of the cellular phone connected to the developed WIHMD quired. Bluetooth will be a more promising and stable solutionand SMS display on the receiver’s cellular phone in the emergency telemedicine in this case because it has encryption, security, low powerapplication. consumption, ad hoc networking, and works at short range . Furthermore, a Bluetooth mobile phone is now available, whichand the solitary elderly at “any time/any place” in an uncon- will be a practical solution for the central unit of a PAN.strained fashion, in other words, ubiquitous healthcare services. In this preliminary study, we demonstrate that the developedThe transmitted vital information comprises six physiological WIHMD provides convenient and comfortable multiparameterparameters and variables, namely 1) fall detection, 2) single- health monitoring for a period of weeks or months or evenchannel ECG, 3) arterial blood pressure, 4) SpO2 , 5) respiration continuous monitoring in a very cost-effective manner with
KANG et al.: WIHMD WITH A TELE-REPORTING DEVICE FOR TELEMEDICINE AND TELECARE 1661acceptable ﬁdelity and reliability. With some modiﬁcation and Taiwoo Yoo received the M.D. and Ph.D. degreesa better ﬁtting for individual applications, the WIHMD will from Seoul National University, Seoul, Korea, in 1980 and 1989, respectively.ultimately enhance the quality of life for the elderly and those From 1980 to 1984, he completed family practicepatients at risk of requiring emergency treatment. residency and fellowship with the Department of Family Medicine, Seoul National University Hospi- tal. From 1984 to 1989, he again ﬁnished residency R EFERENCES and fellowship with the Department of Family Medi-  F. Castanie, C. Maihes, and M. Ferhaoui, “The U-R-Safe project: A cine, Case Western Reserve University, Cleveland, multidisciplinary approach for a fully ‘nomad’ care of patients,” in “IST OH, and Bowman Gray School of Medicine. Since Project Report,” IST-2001-33352, 2002. 1990, he has been a faculty member with the De-  K. Doughty, K. Cameron, and P. Garner, “Three generations of telecare partment of Family Medicine, Seoul National University Hospital, where he is of the elderly,” J. Telemed. Telecare, vol. 2, no. 2, pp. 71–80, Jun. 1996. currently a Professor and Chairman. His research interest is mobile telecare and  B. Meade, “Emergency care in a remote area using interactive video e-health. He has granted with major telemedicine projects from the government technology: A study in prehospital telemedicine,” J. Telemed. Telecare, several times. vol. 8, no. 2, pp. 115–117, Apr. 2002.  W. G. Scanlon, N. E. Evans, G. C. Crumley, and Z. M. McCreesh, “Low- power radio telemetry: The potential for remote patient monitoring,” Hee Chan Kim (M’95) received the Ph.D. degree in J. Telemed. Telecare, vol. 2, no. 4, pp. 185–191, Dec. 1996. control and instrumentation engineering (biomedical  K. Doughty, R. Lewis, and A. McIntosh, “The design of a practical and engineering major) from Seoul National University, reliable fall detector for community and institutional telecare,” J. Telemed. Seoul, Korea, in 1989. Telecare, vol. 6, suppl. 1, pp. 150–154, Feb. 2000. From 1982 to 1989, he was a Research Member  B. Najaﬁ and K. Aminian, “Measurement of stand-sit and sit-stand transi- with the Department of Biomedical Engineering, tions using a miniature gyroscope and its application in fall risk evaluation Seoul National University Hospital. From 1989 to in the elderly,” IEEE Trans. Biomed. Eng., vol. 49, no. 8, pp. 843–851, 1991, he was a Staff Engineer with the Artiﬁcial Aug. 2002. Heart Research Laboratory, University of Utah, Salt  I. B. Aris, A. A. E. Wagie, and N. B. Mariun, “An Internet-based blood Lake City, working on a National Institute of Health- pressure monitoring system for patients,” J. Telemed. Telecare, vol. 7, funded electrohydraulic total artiﬁcial heart project. no. 1, pp. 51–53, Feb. 2001. In 1991, he joined the faculty of the Department of Biomedical Engineering,  J. H. Park, J. M. Kang, and H. C. Kim, “Development of a digital College of Medicine, Seoul National University, where he is currently a wrist sphygmomanometer for emergency use,” in Proc. ICBME, 2002, Professor. From 1993 to 1994, he was a Visiting Professor with the Department pp. 181–183. of Pharmaceutics and the Artiﬁcial Heart Research Laboratory, University  C. Ruggiero, R. Sacile, and M. Giacomini, “Home telecare,” J. Telemed. of Utah. He is currently leading the Medical Electronics Laboratory, Seoul Telecare, vol. 5, no. 1, pp. 11–17, Mar. 1999. National University, where his major research activities are the development P. Z. Zhang, W. N. Tapp, S. S. Reisman, and B. H. Natelson, “Respiration of biomedical systems with special interests in electronic instrumentations, response curve analysis of heart rate variability,” IEEE Trans. Biomed. biosensors, and microsystems for the ubiquitous healthcare system. In these Eng., vol. 44, no. 4, pp. 321–325, Apr. 1997. areas, he has published over 73 peer-reviewed scientiﬁc papers in international D. G. Park and H. C. Kim, “Comparative study of telecommunication journals. methods for emergency telemedicine,” J. Telemed. Telecare, vol. 9, no. 5, Dr. Kim is a member of the Korea Society of Medical and Biological pp. 300–303, Sep. 2003. Engineering, IEEE/EMBS, and the American Society of Artiﬁcial Internal Speciﬁcation of PS214B. last checked 22 April 2006. [Online]. Avail- Organs. able: http://www.mtk-biomed.com/03_produkt/_PDF/englisch/214_e.pdf Speciﬁcation of BPPUMP2M. last checked 22 April 2006. [Online]. Available: http://us.ﬂuke.com/usen/products/speciﬁcations.htm?cs_id= 34927(FlukeProducts)&category=FB-SIMS(FlukeProducts) Speciﬁcation of Oxitest Plus7. last checked 22 April 2006. [Online]. Available: http://www.demaco-ben.nl/01c2c9944712bfa04/ spo2simulator/speciﬁcations/index.html Jae Min Kang (S’01) received the M.S. degree in biomedical engineering from Seoul National Univer- sity, Seoul, Korea, in 2000. He is currently working toward the Ph.D. degree at the Medical Electronics Laboratory (MELab), Seoul National University. Since 2001, he has been with the MELab, Seoul National University. He participated in various national fund projects including “Development of a Ubiquitous Biotelemetry System for Emergency Care,” “Development of a Intelligent Robot for Supporting the Human Life,” and “Development ofa Core Technology of Silver Medical Instrument for the Elderly.” His interestsinclude patient monitoring technology, emergency telemedicine, and the wire-less portable healthcare system. Mr. Kang is a Student Member of the Korea Society of Medical andBiological Engineering and IEEE/EMBS.