Ebook System Architecture Of A Wireless Body Area Sensor Network For Ubiquitous Health Monitoring
Recent technological advances in wireless networking, microelectronics integration and miniaturization, sensors, and the Internet allow us to fundamentally modernize and change the way health care services are deployed and delivered. Focus on prevention and early detection of disease or optimal maintenance of chronic conditions promise to augment existing health care systems that are mostly structured and optimized for reacting to crisis and managing illness rather than wellness.
The anticipated change and emerging new services are well timed to help cope with the imminent crisis in the health care systems caused by current economic, social, and demographic trends. The overall health care expenditures in the United States reached $1.8 trillion in 2004, though almost 45 million Americans do not have health insurance. On the other hand, many companies have already been plagued by high rising costs of healthcare liabilities. With current trends in healthcare costs, it is projected that the total health care expenditures will reach almost 20% of the Gross Domestic Product (GDP) in less then 10 years from now, threatening the wellbeing of the entire economy. The demographic trends are indicating two significant phenomena: an aging population due to increased life expectancy and Baby Boomers demographic peak. Life expectancy has significantly increased from 49 years in 1901 to 77.6 years in 2003. According to the U.S. Bureau of the Census, the number of elderly over age 65 is expected to double from 35 million to nearly 70 million by 2025 when the youngest Baby Boomers retire. This trend is global, so the worldwide population over age 65 is expected to more than double from 357 million in 1990 to 761 million in 2025. These statistics underscore the need for more scalable and more affordable health care solutions.
Wearable systems for continuous health monitoring are a key technology in helping the transition to more proactive and affordable health care. They allow an individual to closely monitor changes in her or his vital signs and provide feedback to help maintain an optimal health status. If integrated into a telemedical system, these systems can even alert medical personnel when life threatening changes occur. In addition, the wearable systems can be used for health monitoring of patients in ambulatory settings. For example, they can be used as a part of a diagnostic procedure, optimal maintenance of a chronic condition, a supervised recovery from an acute event or surgical procedure, to monitor adherence to treatment guidelines (e.g., regular cardiovascular exercise), or to monitor effects of drug therapy.
During the last few years there has been a significant increase in the number and variety of wearable health monitoring devices, ranging from simple pulse monitors, activity monitors, and portable Holter monitors, to sophisticated and expensive implantable sensors. However, wider acceptance of the existing systems is still limited by the following important restrictions. Traditionally, personal medical monitoring systems, such as Holter monitors, have been used only to collect data. Data processing and analysis are performed offline, making such devices impractical for continual monitoring and early detection of medical disorders. Systems with multiple sensors for physical rehabilitation often feature unwieldy wires between the sensors and the monitoring system. These wires may limit the patient's activity and level of comfort and thus negatively influence the measured results. In addition, individual sensors often operate as stand-alone systems and usually do not offer flexibility and integration with third-party devices. Finally, the existing systems are rarely made affordable.
One of the most promising approaches in building wearable health monitoring systems utilizes emerging wireless body area networks (WBANs). A WBAN consists of multiple sensor nodes, each capable of sampling, processing, and communicating one or more vital signs (heart rate, blood pressure, oxygen saturation, activity) or environmental parameters (location, temperature, humidity, light). Typically, these sensors are placed strategically on the human body as tiny patches or hidden in users’ clothes allowing ubiquitous health monitoring in their native environment for extended periods of time.
A number of recent research efforts focus on wearable systems for health monitoring. Researchers at the MIT Media Lab have developed MIThril, a wearable computing platform compatible with both custom and off the shelf sensors. The MIThril includes ECG, skin temperature, and galvanic skin response (GSR) sensors. In addition, they demonstrated step and gait analysis using 3 axis accelerometers, rate gyros, and pressure sensors. MIThril is being used to research human behaviour recognition and to create context aware computing interfaces. CodeBlue, a Harvard University research project, is also focused on developing wireless sensor networks for medical applications. They have developed wireless pulse oximeter sensors, wireless ECG sensors, and triaxial accelerometer motion sensors. Using these sensors, they have demonstrated the formation of adhoc networks. The sensors, when outfitted on patients in hospitals or disaster environments, use the adhoc networks to transmit vital signs to healthcare givers, facilitating automatic vital sign collection and real time triage.
In this paper we describe a general WBAN architecture and how it can be integrated into a broader telemedical system. To explore feasibility of the proposed system and address open issues we have designed a prototype WBAN that consists of a personal server, implemented on a personal digital assistant (PDA) or personal computer (PC), and physiological sensors, implemented using off the shelf sensor platforms and custom built sensor boards. The WBAN includes several motion sensors that monitor the user’s overall activity and an ECG sensor for monitoring heart activity. We describe the hardware and software organization of the WBAN prototype.
The rest of the paper is organized as follows. Section 2 outlines the general WBAN architecture, defines the role of each component, and describes its integration into a broader telemedical system. Section 3 presents a case study, walking through a typical system deployment and its use. Section 4 describes the hardware architecture. Section 5 details the software architecture of the personal server and sensor nodes, and introduces energy efficient WBAN communication protocol. Section 6 concludes the paper and discusses possible future research directions.
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