Introduction

We are exploring applications of wireless sensor network technology to a range of medical applications, including pre-hospital and in-hospital emergency care, disaster response, and stroke patient rehabilitation.

Recent advances in embedded computing systems have led to the emergence of wireless sensor networks, consisting of small, battery-powered "motes" with limited computation and radio communication capabilities. Sensor networks permit data gathering and computation to be deeply embedded in the physical environment. This technology has the potential to impact the delivery and study of resuscitative care by allowing vital signs to be automatically collected and fully integrated into the patient care record and used for real-time triage, correlation with hospital records, and long-term observation.

This project is supported by grants from the National Science Foundation, National Institutes of Health, U.S. Army, as well as generous gifts from Sun Microsystems, Microsoft Corporation, Intel Corporation, and Siemens AG.

Wireless Vital Sign Sensors

We have developed a small, wearable wireless pulse oximeter and 2-lead EKG based on the Mica2, MicaZ, and Telos sensor node platforms. These devices collect heart rate (HR), oxygen saturation (SpO2), and EKG data and relay it over a short-range (100m) wireless network to any number of receiving devices, including PDAs, laptops, or ambulance-based terminals. The data can be displayed in real time and integrated into the developing pre-hospital patient care record. The sensor devices themselves can be programmed to process the vital sign data, for example, to raise an alert condition when vital signs fall outside of normal parameters. Any adverse change in patient status can then be signaled to a nearby EMT or paramedic.

Specifications: Our wireless vital sign sensors consist of a low-power microcontroller (Atmel Atmega128L or TI MSP430) and low-power digital spread-spectrum radio (Chipcon CC2420, compliant with IEEE 802.15.4, 2.4 GHz, approximate range 100 meters, data rate about 80 Kbps). The devices have a small amount of memory (4-10 KB) and can be programmed (using the TinyOS operating system) to sample, transmit, filter, or process vital sign data. These devices are powered by 2 AA batteries with a lifetime of up to several months if programmed appropriately. The basic hardware is based on the MicaZ and Telos sensor nodes, described above, and a custom sensor board integrating the pulse oximeter or EKG circuitry is attached to the mote devices.

The Pluto mote, designed here at Harvard, is a scaled-down version of the Telos designed to be small, lightweight, and wearable. The Pluto incorporates a tiny, rechargeable Li-ion battery, small USB connector, and 3-axis accelerometer. It will be used initially for monitoring physical activity and motor functions.

CodeBlue is also being used to by the AID-N project at Johns Hopkins Applied Physics Laboratory, which is investigating a range of technologies for disaster response. The AID-N wireless sensors (which run the CodeBlue software) include an electronic "triage tag" with pulse oximeter, LCD display, and LEDs indicating patient status; a packaged version of our two-led EKG mote, and a wireless blood pressure cuff.

In collaboration with the Motion Analysis Laboratory at the Spaulding Rehabilitation Hospital, we are developing a seperate sensor board for monitoring the limb movements and muscle activity of stroke patients during rehabilitation exercize. These boards, consisting of 3-axis accelerometer, gyroscope, and electromyogram (EMG) sensors, will permit researchers to capture a rich data set of motion data for studying the effect of various rehabilitation exercizes on this patient population.

Our sensor hardware designs are available under an "open source" license to research groups that are interested in experimenting with these devices. We are actively pursuing research collaborations with other medical groups, disaster response teams, and companies interested in this technology. Please contact us at the email address below for more information.

CodeBlue Software Platform

In addition to the hardware platform, we are developing a scalable software infrastructure for wireless medical devices, called CodeBlue. CodeBlue is designed to provide routing, naming, discovery, and security for wireless medical sensors, PDAs, PCs, and other devices that may be used to monitor and treat patients in a range of medical settings. CodeBlue is designed to scale across a wide range of network densities, ranging from sparse clinic and hospital deployments to very dense, ad hoc deployments at a mass casualty site. CodeBlue must also operate on a range of wireless devices, from resource-constrained motes to more powerful PDA and PC-class systems. For more information, please see the IEEE Pervasive Computing article about CodeBlue or this technical report with more details.

Part of the CodeBlue system includes MoteTrack, a system for tracking the location of individual patient devices indoors and outdoors, using radio signal information. In MoteTrack, a hospital, clinic, or other area is outfitted with a set of fixed radio beacon nodes that are used to calculate the 3D position of the wireless sensors, which may be attached to patients, carried by physicians or nurses, or attached as "location tags" to medical equipment. MoteTrack has been demonstrated in a building-wide deployment at Harvard and yields an 80th percentile error of about 2 meters, which is more than adequate for many location-tracking applications.

The CodeBlue system is currently under development and we anticipate a source code release soon. The MoteTrack system is currently available for download at the link above.

Our research focuses on the following areas:

• Integration of medical sensors with low-power wireless networks
• Wireless ad-hoc routing protocols for critical care; security, robustness, prioritization
• Hardware architectures for ultra-low-power sensing, computation, and communication
• Interoperation with hospital information systems; privacy and reliability issues
• 3D location tracking using radio signal information
• Adaptive resource management, congestion control, and bandwidth allocation in wireless networks

We are also investigating wide-area event delivery infrastructures for medical care, as part of the Harvard Hourglass project. Such a system will allow seamless access to patient care data by EMTs, emergency department personnel, and other physicians through a variety of interfaces, including handheld PDA and Web-based clients. In collaboration with 10Blade, we are integrating Vital Dust sensors into iRevive, a PDA-based patient care record database. The combined system will allow real-time vital sign capture and triage, automatically inserting time-stamped vital sign data in the patient care record (PCR) prepared by EMTs. This will lead to more accurate reporting and a significant reduction of paperwork for EMSs. Our PDA-based triage application displays vital signs for multiple patients and immediately alerts the EMT to a change in patient status.