NATICK, Mass. (Dec. 21, 2018) -- Scientists from the U.S. Army Research Institute of Environmental Medicine, or USARIEM, are developing a new device, called the Personal Heating Dexterity Device, or PhD2, for warming the hands and fingers in cold weather without the help of gloves.
Anyone who has spent time in freezing temperatures knows that picking the right winter gloves has always been a trade-off. You can have either warm hands or dexterous fingers, but having both has been nearly impossible. For most civilians, this means they might have a tougher time texting their friends or adjusting their snow boots. For Soldiers, the loss of hand function in the cold can have a negative impact on performance, survivability and lethality, according to Dr. John Castellani, the principal investigator.
"One of the biggest issues for Soldiers operating in a cold environment is the loss of hand function and dexterity," Castellani said. "Thick gloves can reduce Soldiers' touch sensation and can decrease fine-motor dexterity by 50 to 75 percent. As a result, Soldiers tend to remove their gloves when they need to use their fingers. Unfortunately, this causes blood flow to decrease in the hands, also impairing movement.
"This is a primary concern because hand function and dexterity are important for many tasks, such as loading ammunition, handling equipment and technology and treating injured Soldiers."
Castellani, a research physiologist who specializes in cold weather, explained that this decrease in blood flow is the body's natural reaction to the cold. The body sends more blood to protect and warm its core, where all of the major organs are located. This means there is less blood flow to the hands and feet, causing temperatures in the skin, muscles and other tissues to drop.
He added that researchers have spent the past 80 years developing technology for different parts of the body, in an effort to increase blood flow in the hands without obstructing hand movement. Researchers have successfully developed warming devices for the torso, but the technology has not been practical for operations. Such a device would have required a lot of power to function. Each Soldier would have had to carry a heavy power source along with the rest of their load.
USARIEM researchers set out to create something small and unobtrusive for a Soldier on the move.
"We want to see if there is a way to improve hand dexterity in a cold environment that does not involve covering the hands and fingers," Castellani said. "In our study, we focused on warming the forearms and face."
Castellani's team reasoned that by increasing blood flow just above the hand, some of that warmth would travel to the fingers. The team also focused on warming the face because previous research had suggested there were nerves in the cheeks and forehead that, when they got cold, caused blood flow to decrease in the hands.
USARIEM researchers developed prototypes of forearm and facial warming devices, which resembled heating pads, to test on eight research volunteers. Volunteers wore the prototypes while sitting for two hours in USARIEM's environmental chamber, a room where researchers can adjust the temperature, humidity and wind speed. Volunteers wore cold-weather Army ensembles but kept their hands uncovered during testing at 32�F.
The researchers wanted to test if hand dexterity and finger strength improved when warming the forearms and face individually and together. They also wanted to see if there were differences in hand dexterity when volunteers kept the device powered for the entire two hours, versus if they turned on the device after skin temperatures had already dropped.
They measured volunteers' hand dexterity and finger strength before, during and after the cold exposure by having volunteers load ammunition into an M16 cartridge and take the Purdue Pegboard Test, which involved picking up and moving small pegs into sockets.
"We found that just heating the forearms worked," Castellani said. "Heating the face by itself was not effective, and heating the face and forearms together was not a significant improvement. We also found that turning on the device after the fingers had cooled significantly was just as effective as keeping it on the entire time."
The research team is now working with the Medical Support Systems and Evacuation Project Management Office in the U.S. Army Medical Materiel Development Agency, or USAMMDA, to advance the prototype of the patent-pending PhD2, making the device more portable and user-friendly for the uniforms of the future.
"Maintaining dexterity is so important for many occupations, including Soldiers, electrical lineman and others who work outdoors," Castellani said. "When people think of cold weather, they usually concentrate on the worst-case scenarios, like hypothermia, which is life-threatening, and frostbite, which is debilitating and can cause life-long issues. But in order to have lethal Soldiers who can complete their missions, they have to be able to use their hands."
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author(s) and are not to be construed as official or as reflecting the views of the Army or the Department of Defense.