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Wearable Health Reports

The U.S. Army is testing medical sensors that can monitor everything from sleep patterns to whether a soldier is injured.

This May, the U.S. Army will conduct the first large-scale field test of a wearable health-status monitoring system for its soldiers. The technology, developed in a three-year, $9 million project that began in 2003, consists of sensors that collect data such as heart rate, and beam them to a processor worn on the body, which then analyzes the data and sends a simple health status rating to a medic’s PDA.

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Colonel Beau Freund, manager of the program, says the wearable sensors will “provide the medic with vital signs and location [of hurt soldiers] so he can decide who he goes to in what order.” But Freund emphasizes that “preventing injury is just as important.” For instance, the system monitors hydration and how much sleep a soldier has had. Measuring restfulness is “the first attempt to get at cognitive health – is the war-fighter capable of good decisions?” says Freund. A commander could then look at this information and send the freshest group of soldiers into combat.

A medic or commander can also view the information on a battlefield map that shows the location of each soldier and his or her health status: green (okay), yellow (look), red (look now), blue (unknown), or grey (absence of life signs for over five minutes). Or he could zero in on individual soldiers and get information about their vital signs, position, and how much they’ve slept or had to drink. Freund says that the system does not overwhelm medics with large amounts of data, yet gives them enough information to triage hurt soldiers. The system currently works with a Microsoft PDA designed for viewing medical records.

Freund and his team were faced with creating a light-weight monitoring system that would run without supplementary power for 72 hours, that could withstand submersion, and that soldiers could forget they had on or were carrying. Their solution was a series of sensors in a chest belt, watch, canteen, pill, and processing hub that together weigh about 720 grams (click on link above to see these items). Sensors in the chest belt, watch, canteen, and pill collect six categories of data: vital signs and body orientation, hydration, sleep status, body temperature, and whether the soldier has been shot. Mark Buller, a lead engineer on the project, estimates that if the system were manufactured in bulk, the price for a set of sensors and hub would run about $600.

The core of the sensing system is the chest belt, which reads pulse, respiration, skin temperature, body orientation, and ambulation (whether a soldier is still, in a vehicle, or walking). Buller says the belt contains three silver-loaded cloth electrodes that measure heart rate, and a temperature probe. Data from an accelerometer in the belt can be used to determine body position and whether a soldier is still or moving. The belt also senses the expansion of the chest to count breaths. An optional acoustic sensor is designed to pick up vibrations resulting from a ballistic wound, although this device has yet to be tested on the battlefield.

The sensors were built using existing technologies – it’s the algorithms in the hub that make the system unique, says Freund. For example, hydration is assessed by measuring how much water escapes from the bladder-style canteen. Based on an analysis of drinking patterns, the hub can tell the difference between a soldier’s sips and slow, steady water loss to a leak. The hub will send out a “grey” signal if there is no heart rate or respiration for five minutes, but it knows when this occurs because the soldier has taken off his sensors, and will send a “blue” signal instead, for “unknown.” Along with a health status report, the hub sends out a confidence rating – “You know when you don’t know,” as Freund puts it – so that medical resources won’t be misdirected.

Currently, the hub sends and receives information using radio frequencies, but this could change, since its architecture is open-ended. Using internal radios, it currently works at short range up to 100 meters; for long-range uses, it connects to commercial or field radios. Data from the system have also been sent through a cell-phone text-messaging system for long distances in real time.

Michael Cima, MIT professor of materials science and engineering who works on medical devices and is associated with MIT’s Institute for Soldier Nanotechnologies, is “very impressed” with the monitoring system. Because the system is modular, he says, it could easily be adapted for other uses in health care. Cima says he believes the Army research will lead to medical technologies for monitoring patients after they’ve left the hospital.

Actual deployment of the monitoring system will happen piecemeal. Buller says the sleep-monitoring watches are already being field-tested on pilots in Iraq. These devices use accelerometers to collect information about body movement – information that can be analyzed to determine whether the wearer is awake or asleep. Every branch of the armed services won’t want or need all the information the sensors are capable of generating. But the Army is collaborating with NASA, the Navy, and the Air Force, who are interested in using the system to create flight suits that respond to changes in G-force.

Home page image courtesy of the U.S. Army.

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