EXAMPLES OF THE USE OF WIRELESS TRANSMISSION SYSTEMS IN THE MONITORING OF PATIENTS DURING CARDIAC REHABILITATION AT HOME

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1 JOURNAL OF MEDICAL INFORMATICS & TECHNOLOGIES Vol. 17/2011, ISSN wirless transmition, monitoring system, Revitus, cardiac rehabilitation Zbigniew SZCZUREK 1, Adam GACEK 1, Jacek BRANDT 1, Adam CURYŁO 1, Paweł KOWALSKI 1, Katarzyna ŚWIDA 1, Marek GEODECKI 1, Andrzej MICHNIK 1 EXAMPLES OF THE USE OF WIRELESS TRANSMISSION SYSTEMS IN THE MONITORING OF PATIENTS DURING CARDIAC REHABILITATION AT HOME ITAM completed work on developing a prototype of the system designed to monitor and conduct cardiac rehabilitation at home. In the course of project execution, a number of devices have been made or adapted to work within the system. The primary problem to be solved was to develop a way of communication for these devices, which would allow the transmission of necessary data in a way that would be convenient for the patient and provide the staff supervising the patient with easy access to this data. Ensuring correct operation the system required a variety of cooperating transmission systems to be used. Communication within the apartment utilizes a wireless network based on a Bluetooth link. The parent node of this network is the Base Station, which is also an intermediary for communication between devices within the apartment and the Centre for Monitoring and Communications. The main module carried by the patient is the ECG module that, in addition to its measurement function, serves as a personal area network node based on elements of the ANT standard supporting the Messenger carried by the patient. This module is also tasked with supervising the patient outside the apartment, making communication with the Centre possible via a GSM/GPRS network. The Base Station exchanges information with the Monitoring and Communication Centre located on a server via the Internet. Access for the patient's doctor or support worker to the Monitoring Centre is possible from any computer with access to the Internet by logging onto the Centre's server. 1. PREFACE Chronic heart failure is one of the most common causes of illness and mortality. Cardiac rehabilitation through supervised exercise is beneficial for reducing symptoms and allowing return to normal life. Rehabilitation of this type conducted in an outpatient or hospital environment is expensive and its effects are short-term due to time constraints. Also, checkups on patients with chronic heart failure are carried out periodically after the hospital stay, which can often lead to significant deterioration in the patient's condition, including risk of death. Therefore a solution is to continue cardiac rehabilitation with adequate intensity at home and provide supervision of the key biological parameters throughout the treatment process. The increasing availability of different, often complementary means of communication, the relative decline in the cost of their purchase and operation have all made it possible to design a patient and support staff friendly system. It is based on the simultaneous use of different data transmission systems, which use the existing infrastructure of modern communication networks. 2. INTRODUCTION As a result of the performance of the research project, a prototype of a wireless system for monitoring and conducting cardiac rehabilitation at home has been designed and tested. The system allows the physician in charge of the patient to observe changes in the condition of the patient through remote access to biomedical data such as the ECG graph, trends in heart rate, respiratory rate, blood pressure, oxygen saturation, weight and degree of water accumulation in the chest. Observing changes in these parameters, especially during exercise, enables assessment of the patient's rehabilitation progress. In the event of changes in these parameters that require intervention, the system is to alert support staff and 1 Institute of Medical Technology and Equipment, Zabrze, Poland.

2 a doctor. The system is equipped with means for providing interactive communication between patient and physician with the possibility of remote control over the course of rehabilitation and treatment. The foreseen system configuration has been demonstrated in Figure 1 Three functional areas can be distinguished for the system. The first covers the apartment and the Patient in it. Since the Patient may also move outside the home, means for at least limited monitoring in this situation must be allowed. The second functional area of the system is the Monitoring and Communication Centre that communicates directly through the Internet with the first area. The Centre is a virtual space that uses dedicated or generally available servers that are running the system application. The third distinguished area of the system includes the system operator and the patient's doctor. Persons entitled to operate the system and use its resources will be able to log onto the application server running the system from any computer with Internet access. Depending on individual access rights, the access will be granted to information for a particular patient and given the possibility to influence the course of his rehabilitation and treatment, as well as make changes to the Revitus system configuration - adding new patients, expanding the functionality of the system. 160 Fig. 1. Configuring a wireless monitoring system. The completed project enables as little patient involvement in system operation as possible and maximum comfort during use of the system's components. Devices making up the system that cooperate with the patient are autonomous, they communicate with each other wirelessly and require minimal patient involvement in operation - it consists of periodic replacement of power sources in some of the modules. The transmission network organization ensures system openness, allowing equipment to be added or configuration to be changed. As Figure 1 shows, basic communication in the apartment is done via a Bluetooth [1,5] piconet. The "master" node of this network is the Base Station that consists of a "netbook" computer with an Internet connection. The Base Station communicates with the following modules: ECG module and respiration and accumulation of water module carried by the patient, the cycle ergometer designed to conduct the rehabilitation and a weighting scale located in the room. The ECG module communicates with other modules carried by the patient using a personal network based on Nordic's energy-saving components of the nrf24l01 [7] type and acts as their intermediary in communication with the Base Station. This network is responsible primarily for the exchange of information with the Messenger, the module used to notify Patients about system recommendations and allowing the Patient to alert the system. The ECG module is equipped with a module for connecting to a mobile communications network and transmitting data through GPRS [8]. This enables communication also with modules carried by the patient outside the apartment. Currently this type of communication is selected as supplementary, used to

3 provide only crucial information, and does not provide for full monitoring. This is due to limited bandwidth and transmission costs. The Base Station communicates with the Monitoring and Communication Centre via the Internet - transmitting collected data and receiving information for the patient and the system components in the apartment. The system operator or physician logs onto the MCC server using a personal computer and gains access to information about a given patient and can change the system configuration accordingly to access rights. 3. COMMUNICATION SYSTEM IN THE PATIENT'S HOME Wireless exchange of information between the Base Station and the system modules in the apartment is the key element for the proper functioning of the monitoring and rehabilitation system. Communication should take place autonomously, without patient involvement. The popular and inexpensive Bluetooth [1,5] communication standard was chosen for wireless data transmission between the Base Station and wireless modules in the patient's environment. The MBS (Mobile Base Station) software conducts periodic scans of the surrounding area in order to locate the Bluetooth modules registered as part of the diagnostic system. When an appropriate module is locates, the unit automatically connects to the module and commences patient monitoring, which is indicated on the MBS control panel. Bluetooth devices operate in small networks of up to eight nodes called piconets. One of the "master" nodes organizes data transfers across the whole micro network, while the other seven "slave" nodes exchange information only with the "master" node. In a basic monitoring and rehabilitation network, the Base Station is the "master" node and the four "slave" nodes are: the ECG module, breath and water accumulation module, cycle ergometer ERM-200 and the weighting scales. The Base Station software was developed in C++ for the "X-Windows" Linux [4] platform. Bluetooth device support used the extensive API (Application Programming Interface) from the BlueZ [2] organization that supports the Bluetooth standard at any logical (program) layer. Communication between the Base Station and the modules is done via a USB-Bluetooth adapter (built into the Base Station or external). Transmission between the Base Station and the ECG module and the Respiratory and water accumulation module is done through the RFCOMM layer, which emulates a virtual RS232 serial port. Transmission between the MSB and the ERM-200 cycle ergometer is done through the L2CAP logical layer. It is operated in a cyclical manner (with a 1-second interval) using a command-response pattern. Commands from the main controlling loop are buffered in a FIFO queue. No reply for 10 seconds from the cycle ergometer module means it has been disconnected. Each answer contains the acknowledgement of command execution and the current state of the cycle ergometer. There are many factors that may lead to interruption or temporary suspension of transmission within the Bluetooth piconet as per the Bluetooth standard. These include a weak radio signal level resulting from excessive distance between nodes (in Class I up to 100 m in open terrain) or radio signal propagation interference caused by objects or people located between a master-slave pair, as well as presence in the vicinity of other Bluetooth or Wi-Fi networks. It is easy to imagine that in synchronized or single thread communication, disturbances in communication between a single master-slave pair will cause temporary interruptions in communication with other network nodes. In order to eliminate this downtime, an asynchronous data exchange model between PC and devices was used. The model uses multithreading application mechanisms available in Linux. In the description of communication with the Base Station, the processing rules for the ECG signal in the ECG module have been shown. It was assumed that real-time monitoring will be conducted only during rehabilitation. In the remaining time, monitoring data is collected and sent periodically to the base station, ensuring energy savings. This also occurs when the patient goes beyond the range of the base station, for a walk outside the apartment for example. Data is then sent upon the patient's return within the base station's range. Equipping the ECG module with a GPRS connection is provided, so that, in emergency cases detected by the module, the Monitoring Centre and doctor will be notified of this fact, independently of communication with the base station. In addition to the notice of alarm, parameters for 161

4 MEDICAL MONITORING SYSTEMS AND REMOTE CONTROL signals which caused the alarm will be sent. The ECG module will also act as an intermediary station for other modules carried by the patient. The ECG module will exchange information with the Messenger module through an nrf24l01 (Nordic) transceiver. 4. PATIENT'S PERSONAL NETWORK The Messenger placed on the patient's wrist in the form of a module - watch, is one of the components of the patient's personal network. Its main task is to provide the patient with information from other system devices. The Messenger (Figure 2) will notify the patient of actions to be performed, for example to start training on the ergometer, weigh themselves, and take medicine. The screen displays symbols and messages from a list of messages or those sent from other modules. The patient is notified of new information by a signal from the vibrator. The screen is constantly turned off to save power and activated by the patient pressing a button. If there are no new tasks for the patient, pressing the button brings up the current time on the screen. The screen turns off automatically after a few seconds and the processor goes into a power-saving Sleep mode. Fig. 2. Messenger and block diagram of the functioning of the Messenger program. The button also plays the role of the patient's emergency button. If a patient presses the button for a long time, the alarm is activated, first on screen, and then the information is transmitted to the system. The Messenger exchanges information directly with the ECG Module via a link made using an energy-saving nrf24l01 [7] chip from Nordic. In the exchange of information with the ECG Module, the Messenger acts as the Master - it establishes communication by sending a packet and awaits in response an ACK with accompanying data package. The packet exchange session continues until the packet for an empty task arrives. The Messenger implements tasks received (if any). After the transmission session, if the tasks were performed and the screen and vibrator turned off, the CPU goes into Sleep mode. Subsequent transmissions are initiated by the Timer, which works in Sleep mode. The processor is also revived from its Sleep state at the press of a button. 5. THE COMMUNICATION SYSTEM BETWEEN THE BASE STATION AND THE MONITORING AND COMMUNICATIONS CENTRE AND PHYSICIAN OR OPERATOR ACCESS TO THE MCC The Revitus name has been selected for the system and communication software for the system. The software for the system consists of software modules running on computers in the Monitoring and Communication Centre, the Base Station and the ECG monitoring module. Communication between 162

5 modules carried by the patient and the ECG module is autonomous in relation to the system software. A block diagram of the functioning of the Revitus system software is shown in Figure 3. Fig. 3. Block diagram of the functioning of the Revitus program. The database and network software of the Monitoring and Communication Centre has been designed using PHP 5.x + MySQL 4.x. To assist in dynamic visualization of the course of the patient's examination in the Web application, the jquery library (trends of the biological parameters for HR, SpO2, organization of lists) and MS Silverlight 2.0 (Internet control for the ECG graph) have been used. Communication scripts of the network and database server in the MCC communicate with an independent TCP/IP Daemon with a fixed IP address, which organizes streaming communication between the Base Station in the patient's home and the Monitoring and Communication Centre (via TCP / IP), and the ECG Module and the MCC (TCP/IP and GPRS). Software for the Base Station has been designed on an OpenSUSE 11.1 [4, 6] system with GCC [3] + QT and the Bluez [2] library for communication using the Bluetooth interface with modules in the apartment (ECG monitoring module, cycle ergometer and weighting scales). The interface of the Base Station is an autonomous part of software for controlling modules and communicating with the patient by transmitting requests generated in the Monitoring and Communication Centre and receiving data sent by the modules. The TCP/IP daemon is an independent software module that uses network sockets to organize communication with modules used for measurement. It is located on the MCC server, where it works in the background by collecting information from the module operating in GPRS data transmission mode, or the Base Station over a broadband connection. Measurement data received is transferred via the HTTP protocol directly to the MCC base. Streaming data, such as the patient's ECG graph sent from the Mobile Base Station (MBS), are organized in the form of xml files, compressed using a zip archiver and placed in the MCC repository, after which the server receives information of a new incoming patient ECG, which allows recording of a new entry in the database indicating the new ECG file. The MBS communicates directly with the MCC server, via HTTP, and with the communication Daemon for transmission of ECG data. Scripts on the server, allow, by using parameter-based "GET" queries, MBS identification and a response in the form of MBS configuration. The MBS configuration contains basic configuration information and notices for the patient, which are then displayed on the MBS screen. Communication between the MBS and MCC is always initiated by the MBS by cyclical calls to parameter operated php scripts on the MCC. Training parameters and time of commencement of training on the cycle ergo meter are defined using MCC software. The MBS reads these parameters and at the appropriate moment commences the performance of the training, instructing the patient what actions should be performed at the given time. The MBS screen features two buttons - "Event" and "Alarm" - the pressing of which sends relevant information to the MCC. 163

6 The operator or the patient's doctor may connect to the system from any Internet-connected computer - the only requirement is that a web browser be installed with JavaScript support. Authentication has been implemented through the input of a LOGIN/PASSWORD pair and then by using the POST method for the form on the login page to perform verification with data in the MySQL database on the server side. The authentication process uses the encrypted HTTPS protocol. This prevents interception and modification of transmitted data. After successful login, information on the person using data gathered in the Centre is stored in the session and recorded on the server. Session mechanisms are handled through their built-in implementation in the PHP scripting language. Each users logging onto the system is assigned priorities - access levels, according to which they are given possibility of viewing and editing data. Two groups have been distinguished: administrators - with unlimited access to all data including the possibility of system configuration and doctors - with limited access allowing them to view data and configure diagnostic devices only for their patients. 164 Fig. 4. Example of data visualization using the jquery library. The jquery library was used to accelerate application performance, allow better user interaction and improve the visual side of the system (Figure 4). Thanks to AJAX mechanisms built into the library, a very effectively functioning system for data exchange together with its visualization has been obtained. The ECG graph presentation system was designed using Silverlight 2.0. The built-in control retrieves information from XML files and allows very efficient visualization of the ECE graph with settings for amplification and speed. For the presentation of the patient's biological parameters, a control was developed on the basis of the jquery library that allows dynamic generation of trends in HR, SpO2. Communication with the MySQL database, the scripts and controls, are performed using the SQL query language, allowing quick selection of relevant information. To compile tabular information on the course of the examination, lists of patients, examination lists, and a jquery plug-in called jquery.datatables was used, which solves the problems of visualization of lists with large amounts of data, and sorting lists by any column, thus simplifying the search process and recovery of needed information. The structure of the database is that of a set of relational data tables, linked together with identifiers, constituting at the same time the table's primary keys and key information fields optimized through indexing. 6. GSM/GPRS TRANSMISSION WITH THE ECG MODULE The GSM/GPRS module allows an alarm message or information on the biological parameters of the patient to be sent, regardless of the place where the patient is. The project uses a miniature module from SimCom, SIM900 [8], which is a quad-band GSM module (850/900/1800/1900MHz). The module chosen has built-in TCP and UDP protocol support. TCP was used in the project due to greater reliability of data transmission. The TCP protocol is based on a Client-Server architecture. In our case, the ECG

7 module is the client and the server is a computer at the Monitoring and Communications Centre. In the current project, two ways to send and receive messages are available. The primary channel for information exchange is packet transmission using the GPRS standard. In our project we are mainly interested in the situation where ECG module data is sent to an Internet connected computer, where the data transmission rate can reach up to 40kbps (for the configuration: multislot class 10, coding schema 4). This speed allows to send of slowly variable biological and environmental parameters, as well as sending a bandwidth limited single channel ECG signal. SMS messages constitute the second channel for information exchange, which can be used, for example, for daily reporting on the patient's biological parameters or signaling alarm conditions, such HR over a threshold, fall detected by the accelerometer, etc. The system also allows text messages to be sent to the display of the Messenger module on the patient's hand. A GPS [9] module works in conjunction with the GPRS module, which allows the location of the patient to be determined, which may be helpful in locating lost patients with Alzheimer's disease. The location procedure may function on the basis of two scenarios. In the first scenario, a lost patient sends an alarm using the button on the Messenger module, which sends his or her coordinates to the Monitoring Centre and/or an SMS message to the patient's doctor or caregiver. In the second scenario, a request for the patient's coordinates can be sent to the Monitoring Centre or by SMS from the patient's caregiver. 7. CONCLUSION 1. The development and testing of the system for patient monitoring and supervision of rehabilitation training at home has shown that systems can and should be built based on different wireless transmission network standards at the same time, which are capable of "ad hoc" configuration and are virtually maintenance free. 2. Methods of measuring physiological parameters currently used are still difficult to use for untrained patients and are the main drawback of domestic monitoring on a wider scale, in contrast to use of data transmission systems. 3. In future revisions of the system, use of voice calling capabilities ("loud speaker"), between a doctor or support staff and the patient via the ECG module could be a very valuable function of the device in the event of an emergency. 4. Progress in the development of mobile networks and a reduction in the system's running costs indicates that the system should be developed with greater use of such networks in mind, especially by adaptation to 3G and 4G (HSDPA and LTE) systems and the use of wireless Internet access through the local Wi-Fi network. 5. The use of a different network standard for the personal network should be considered, for example, based on Low Power Bluetooth ver. 4.0 [10], due to possibly greater resistance to interference. 8. ACKNOWLEDGMENT This work was financed by The National Centre for Research and Development resources in under Development Project No /2008. BIBLIOGRAPHY [1] Bluetooth Special Interest Group, Specification of the Bluetooth System, version 1.1, Vol. 1 and 2, February [2] (BLUEZ) Official Linux Protocol Stack, [3] GCC, the GNU Compiler Collection, [4] Linux - related documents, [5] MILLER B. A., BISDIKIAN C. Uwolnij się od kabli Bluetooth, Helion 2003, (in Polish). [6] The Linux Kernel Archives, 165

8 [7] nrf24l01+ Single Chip 2.4b GHz Transceiver Product Specification v1.0, [8] SIM900 Application Notes, [9] GPS module Gms-u1LP Application Notes, 3c7ee066e322e d&puid=3fff9662f76faafe1e5c3f81e571fa4d3c18ce86 [10] Specification of the Bluetooth system Core version 4.0, 166