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Washington University Researchers Seek to Bring Mobility to ICU Patients

The group is testing a wireless sensor mesh network to track the vital signs of at-risk patients at Barnes-Jewish Hospital, allowing them to move around without being tethered to bulky medical monitoring devices.
By Claire Swedberg
Aug 12, 2011At Barnes-Jewish Hospital, located in St. Louis, Mo., researchers are testing a ZigBee-based RFID sensor system that tracks patients' vital signs. The solution provides hospital employees with data regarding the vital signs of patients moving about the facility, using a sensor attached to the finger, and a transmitter worn around the neck.

The system is the result of years of research and collaboration between computer scientists at Washington University in St. Louis, the hospital's IT department, and medical doctors, according to Chenyang Lu, a computer science professor and the project's leader. Lu partnered with physician Tom Bailey to develop a distributed sensor network that would enable hospital staff members to monitor the vital signs of patients who are not in the intensive care unit (ICU), but who require medical attention, including the regular tracking of their vital signs. The solution, the prototype of which is currently being tested, includes sensors known as pulse oximeters that measure a patient's heart rate and blood oxygenation level. The sensors are wired to what researchers call a telemetry pouch—a microcomputer and an RFID tag that transmits data to relay devices plugged into wall power outlets. Those devices form a ZigBee-based mesh network, transmitting information to each other, and ultimately to a gateway consisting of a laptop cabled to the hospital's back-end system, where the software—created by Washington University researchers—resides.

Chenyang Lu demonstrates a finger sensor attached to a ZigBee-based transceiver.
The system's goal is to provide hospitals with real-time data about patients' health, in what could be called a virtual ICU, allowing patients to move around the hospital while still being monitored. ICU patients are typically confined to their beds, with sensor data managed via wired connections, while the nursing staff closely attends to the patients 24 hours a day. Some are well enough to leave the ICU and begin moving about, but still need to be monitored closely in the event that their condition degenerates, thereby necessitating a return to the ICU. It is this population that researchers are targeting with the wireless technology. The nurses in these "step-down" ICU departments (for those who require monitoring but are well enough to leave the intensive-care area) are often overloaded with tasks, and thus can not monitor patients' vital signs as frequently as an automated system could.

The wireless system has been through two phases of testing. Initially, from 2009 to 2010, the research team tested the hardware at one step-down cardiac-care unit at Barnes-Jewish Hospital. The goal was to determine whether patients' vital signs were being measured by the sensor nodes, as well as whether that data was being transmitted as programmed to the relays, and then forwarded to a gateway and the back-end system.

The sensors measure vital signs at preprogrammed rates—for example, every five minutes—and that information is received by the telemetry pouch, which contains a microprocessor, a Texas Instruments (Chipcon) CC2420 ZigBee-compliant transceiver chip and antenna, and a 9-volt battery. The pouch transmits a unique ID number (linked to the particular patient wearing the device) that is sent with the vital-sign data via 2.4 GHz transmissions. All hardware was built by researchers using off-the-shelf components.

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