NATICK, Mass. (Apr. 24, 2017) -- Temperatures are rising, and with warfighters operating in hot and humid conditions while wearing protective clothing or performing intense work, research to prevent heat illness from diminishing warfighter performance and posing significant health risks is on the rise, as well.

The military has long needed a non-invasive monitoring device that can track warfighters' physiological health during field operations and training. In this technological age when mission leaders and medics need to know the health status of their troops to make quick decisions, real-time guidance on heat illness prevention is more important than ever.

The Estimated Core Temperature, or ECTemp, algorithm, developed by Dr. Mark Buller at the U.S. Army Research Institute of Environmental Medicine, helps fulfill that need. The ECTemp algorithm provides accurate estimates of core body temperature simply by analyzing heart rate changes over time, allowing mission leaders to detect if a Soldier is at increased risk of heat illness.

The U.S. Army Medical Research and Materiel Command, or USAMRMC, non-exclusively licensed the ECTemp algorithm to Zephyr Technology a few years ago to use as one of the features of its Bioharness. The Bioharness system will be used to monitor team member health statuses to prevent and mitigate the risk of heat illness or injury.

According to a study the Air Force Research Laboratory, or AFRL, conducted, the algorithm has proven to be successful in real-world scenarios.

"Currently, the Airman Systems Directorate of AFRL and the 350th Training Squadron have been working together to utilize the Zephyr system, equipped with the ECTemp algorithm, to monitor trainees," said, Dr. Craig Murdock, one of the lead researchers from AFRL. "Using the ECTemp has helped them identify and mitigate over 30 cases of heat stress and prevented more serious heat stress casualty situations."

According to Buller, a research physiologist from USARIEM's Biophysics and Biomedical Modeling Division, the algorithm "uses mathematics from tracking problems to determine core temperature from heart rate observations, and it is based on years of physiological data from multiple studies.

"The algorithm assumes heart rate can be used as a 'noisy' observation of core body temperature. Physiologically, heart rate reflects both the blood flow to the muscles and the rate of blood flow to the skin, containing information about both heat production and heat loss from the body.

"The ECTemp algorithm provides a practical approach to monitoring warfighters' physiology in the least invasive way. You can get a very accurate assessment of core body temperature from a warfighter wearing a simple, chest-worn heart rate monitor."

Medical practitioners and researchers have used a variety of methods to record core body temperature, from oral, to rectal, to ear and more, all with varied results. USARIEM also uses swallowable thermometer pills in research studies to get an accurate reading of a warfighter's internal body temperature. Yet thermometer pills are also expensive, and they are best used as a research tool rather than as a monitoring device in training and battlefield scenarios.

In terms of accuracy, how does the ECTemp algorithm measure up?

"The ECTemp algorithm has now been tested on over 300 individual warfighters in the laboratory, during training and while deployed on missions," Buller said. "When you compare these ECTemp data to an ingestible thermometer pill, it performs as well as when you compare the thermometer pill to a rectal or esophageal probe."

Any healthy person's temperature can change slightly by a few degrees throughout the day, depending on different climates and circumstances. Body temperature declines during sleep, which reflects a normal circadian rhythm, or body clock, that determines when we need to be asleep or awake. USARIEM researchers have been able to detect even these slight temperature changes during overnight studies.

"In overnight studies in our metabolic chambers, our findings suggest the ECTemp algorithm can extract circadian rhythms from resting individuals," Buller said.

With proven accuracy in estimating warfighters' core body temperatures, the algorithm has opened the door to future monitoring apps and wearable technology for the military.

"By getting the basic science right, USARIEM provides the basis of the tools the AFRL and other individual units can use to meet their needs," Buller said.

Military leaders can use the algorithm to adjust missions in hot, humid and unpredictable environments, according to Buller. The ECTemp algorithm, by providing accurate core temperature information, can help leaders make timely, critical training and mission decisions.

"The technology, which USARIEM and the AFRL has provided and which the Battlefield Airman training utilizes, mitigates thermal injuries, keeping students in training rather than failing due to performance or being medically removed," said Lt. Col. Stephen Savell, 350th Training Squadron commander.

Echoing this viewpoint, Buller noted, "We want warfighters to work hard, but we also want them to complete their missions and training safely. The ECTemp algorithm provides objective information to military leaders and medics so they can make the best decisions for the mission."