Beating the Heat

New sensors that gather data on a soldier's physiological state may help prevent heat-related injuries.

by Dorothy Ryan | Communications and Community Outreach Office

In warm climates, heat strain diminishes the effectiveness of first responders and warfighters and can pose significant health risks. Fatigue, cognitive impairment, nausea, vomiting, and heat stroke are the most common heat-related problems. The U.S. Army Public Health Center reports that more than 1200 active Army personnel were victims of heat-induced ailments in 2014 and that on average 2 to 3 fatalities caused by heat strain have occurred among Army personnel each year in the last decade.

To help prevent heat-related injuries, a team from MIT Lincoln Laboratory, the U.S. Army Research Institute of Environmental Medicine (USARIEM), and the U.S. Marine Corps (USMC) Expeditionary Rifle Squad (MERS) have worked together to prototype and test a real-time physiological status monitor (PSM) that can indicate when an individual is at risk for heat strain.

During the first field test of the Laboratory's Open Body Area Network physiological status monitor (OBAN PSM), the squad leader reads the smartphone display to check the status of the U.S. Army Reservists on the 5 km road march. All four test subjects' readings are in the green (safe range); if the OBAN PSM system were to detect signs that a squad member were at risk for heat strain, that soldier's horizontal bar would change to a color that indicated the level of strain.During the first field test of the Laboratory's Open Body Area Network physiological status monitor (OBAN PSM), the squad leader reads the smartphone display to check the status of the U.S. Army Reservists on the 5 km road march. All four test subjects' readings are in the green (safe range); if the OBAN PSM system were to detect signs that a squad member were at risk for heat strain, that soldier's horizontal bar would change to a color that indicated the level of strain.

Lincoln Laboratory and USARIEM tested commercial PSMs in 2012 and 2013 with the Army's 22nd Chemical Battalion (Aberdeen Proving Ground, Maryland) and with the National Guard's 1st and 95th Civil Support Teams (Hanscom Air Force Base, Massachusetts, and Heyward, California, respectively). Although these and earlier USARIEM and USMC tests demonstrated the value of PSMs, commercial PSMs lack sufficient battery life and the tactically acceptable wireless communication that are needed for operational use in military environments. Moreover, commercial PSMs typically have proprietary architectures that complicate integration of new sensors and algorithms or access to raw data to improve system performance.

In 2013, USARIEM tasked Lincoln Laboratory with prototyping a PSM that would address these shortcomings. The underlying government-owned open architecture and tactically acceptable wireless technology are referred to collectively as the Open Body Area Network (OBAN), and the overall system is referred to as the OBAN PSM. This wearable component consists of a small electronics unit, or "hub," that mounts on a commercial heart-rate strap. In addition to measuring heart rate, the hub measures skin temperature and accelerometry, employs USARIEM algorithms to estimate body core temperature and a physiological strain index, and communicates wirelessly with a smartphone carried by a team leader. The smartphone integrates with a dongle (small plug-in device) developed by the Laboratory to support the tactically acceptable communication.

A soldier wears the commercial off-the-shelf (COTS) strap equipped with the Lincoln Laboratory–developed sensor hub, which communicates via a custom tactical wireless link with the squad leader or medic who is monitoring the squad members' physiological strain index on a COTS smartphone modified with a Lincoln Laboratory–designed radio software component (dongle).

The physiological strain index incorporates both thermal- and work-strain estimates computed from the body's core temperature and heart rate, which one might picture as analogous to a vehicle's engine temperature gauge and tachometer. A smartphone app displays the 0–10 score from the physiological strain index in an easily understood color-coded format. A value of 9 or 10 indicates that thermal and work strain are high and that a heat injury may occur if an individual does not take steps to cool off.

A series of field tests were conducted in 2015 to progressively prove out OBAN PSM capability. Initial engineering tests with the Army Reserve's 743rd Transportation Company were facilitated by Richard Gervin, a Lincoln Laboratory employee who was also a sergeant in the unit. The first test was conducted at Hanscom Air Force Base with SGT Gervin leading four volunteers on a ruck march as part of their training. Following that testing, nine volunteers from the unit wore the system continuously for 24 hours during exercises at the Camp Ethan Allen Training Site in Jericho, Vermont. Gervin was enthusiastic: "As a squad leader, I think this system will be a great tool to gauge the effectiveness of my team." The company's commander, First Lieutenant Ronald Veleztoala, was very supportive and said that "testing the system was a way for my unit to help the Army move its technology forward."

To try out the system in a hot climate, the Lincoln Laboratory/MERS/USARIEM team took the system to the Marines' School of Infantry–East at Camp Geiger in North Carolina. Marines tested nine OBAN PSM hubs for 42 consecutive hours, followed by an additional 19 hours of testing after a brief data download. The volunteers wore the systems through varying weather conditions—sunny, rainy, and a sunny-cloudy mix. "We measured heart rates, core temperatures, and the soldiers' rate of acceleration, asking ourselves if the incoming data made sense," said Delsey Sherrill of the Laboratory’s Bioengineering Systems and Technologies Group. "The answer was 'yes.'"

During the field testing in North Carolina, the physiological strain index (PSI) for seven Marines was tracked, as shown by the differently colored plots in the left-hand chart. The chart shows a 200-minute span during a 15 km march. The green range shows a safe level in PSI index (0 to 6); the yellow range indicates some heat effects, and the red range indicates a potentially unsafe level of heat strain. Most of the seven Marines were in the safe range during the time period shown. The system correctly identified the one Marine (black line) who was at risk for heat-related injuries. This Marine's bar on the smartphone readout turned red when the PSI hit the 9–10 range, warning the squad leader that the Marine needed attention. 

During the field testing in North Carolina, the physiological strain index (PSI) for seven Marines was tracked, as shown by the differently colored plots in the left-hand chart. The chart shows a 200-minute span during a 15 km march. The green range shows a safe level in PSI index (0 to 6); the yellow range indicates some heat effects, and the red range indicates a potentially unsafe level of heat strain. Most of the seven Marines were in the safe range during the time period shown. The system correctly identified the one Marine (black line) who was at risk for heat-related injuries. This Marine's bar on the smartphone readout turned red when the PSI hit the 9–10 range, warning the squad leader that the Marine needed attention.

Other members of the test team provided valuable perspectives. Paula Collins, assistant leader of the Bioengineering Systems and Technologies Group, observed, "Soldiers are often in very good physical condition and used to pushing themselves physically, so they can be unaware that they are being badly affected by the heat." Thus, the system can help a team leader identify potential heat sufferers before they are seriously affected.

Bill Tharion, USARIEM, described the value of the testing: "We're dependent on real warfighters doing real military tasks and making sure that our equipment will meet their needs. What we're trying to do is put this system through its paces using real and valid military training." Commander James Balcius, MERS, agreed that "OBAN PSM demonstrated the potential benefits of physiological data to small-unit leadership in a training environment."

Following the successful 2015 field tests, OBAN PSM continues to be matured and advanced. Lincoln Laboratory is transitioning OBAN PSM technology to a small company to develop into a product. The Open Body Area Network wireless has additionally been transitioned to the Army's Program Executive Office Soldier, responsible for acquisition of soldier equipment, and the Laboratory is integrating OBAN with the Army's Nett Warrior End User Device, an Android phone used by squad leaders for situational awareness.

A next generation of technology is being developed to significantly reduce the system's size, weight, and power usage (SWaP). In particular, an ultralow SWaP system-on-chip being developed under a contract with PsiKick will allow the next phase of OBAN PSM to operate for more than a month of continuous use while powered by a coin cell battery. This work is progressing toward a vision of a suite of body-worn sensors—for example, load-sensing devices, hydration monitors, or speech analyzers—that will integrate with the OBAN to provide data that will enable soldiers and first responders to maximize their physiological and cognitive performance.

Posted January 2017

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