Army researchers redefine altitude ascent guidance for high-altitude missions

By Ms. Mallory Roussel (USARIEM)October 23, 2017

Army researchers redefine return-to-duty standards for high-altitude missions
Two researchers from the U.S. Army Research Institute of Environmental Medicine, or USARIEM, Dr. Beth Beidleman, left, the principal investigator, and Bruce Cadarette, a research physiologist, monitor study volunteers' breathing, heart rates and phys... (Photo Credit: U.S. Army) VIEW ORIGINAL

NATICK, Mass. (Oct. 23, 2017) -- An Army-led altitude field study conducted last summer on the summit of Pikes Peak, Colorado Springs, Colorado, has redefined altitude ascent guidance for Soldiers who have to make multiple trips between sea level and high altitude.

"After returning to sea level, Soldiers can remain adapted or acclimatized to high altitude for two weeks without using altitude tents as a form of treatment," said Dr. Beth Beidleman, the principal investigator of the study from the U.S. Army Research Institute of Environmental Medicine, or USARIEM.

USARIEM published the study results in September in the Journal of Applied Physiology after conducting the field study and analyzing the data.

When Soldiers are deployed to mountainous ranges like Afghanistan, USARIEM's research has shown that giving Soldiers a few days to acclimatize to high altitude has always been the most effective way to help Soldiers combat altitude illness, officially known as Acute Mountain Sickness or AMS.

"If Soldiers are not acclimatized to high altitude, they could experience unpleasant symptoms of AMS," Beidleman said. "There is lower oxygen pressure at high altitude, which means that less oxygen is getting to critical organs, like the brain and working muscles. This could cause Soldiers to experience AMS symptoms, including headache, nausea, gastrointestinal distress, trouble sleeping, decrements in performance and general fatigue, especially during the first 48 hours after ascending. When Soldiers acclimatize, they perform much better."

Operational forces have long requested information from Drs. Stephen Muza and Beidleman, who both worked in USARIEM's Thermal and Mountain Medicine Division at the time of the study, to provide improved ascent guidance for Soldiers operating at high altitude. Without a way to sustain acclimatization, Soldiers could experience a reduction in performance and debilitating AMS symptoms all over again during later altitude missions.

The Army has used sealed normobaric altitude tents as a treatment method, which can create the hypoxic, or low-oxygen, environment that exists at high altitude to pre-acclimatize individuals prior to deployment. Until last year, there had been no research to back up how effective the treatment was in maintaining acclimatization after Soldiers return to sea level.

In the 1990s, Beidleman and her team conducted another altitude study, during which they found that Soldiers could maintain altitude acclimatization after spending one week at sea level. It was unknown whether acclimatization could be sustained for two weeks.

That was when Beidleman and a team of altitude researchers and technicians designed a study to take 18 volunteers 14,115 feet above sea level to the Pikes Peak summit in order to conduct a 12-day altitude acclimatization field study.

The researchers housed the study volunteers in the Maher Memorial Altitude Laboratory, a permanent lab owned by USARIEM that has stood for approximately 50 years as the "center of altitude research." The altitude lab, which contained a bathroom, kitchen and sleeping arrangements, allowed USARIEM researchers the unique advantage of being able to house and observe study volunteers for long periods of time to see how well they acclimatized to the altitude.

Beidleman explained that the goal of the study was to see how the volunteers acclimatized to altitude physically and cognitively over the 12 days. She also wanted to see if that acclimatization could be sustained after the volunteers returned to sea level, depending on whether or not they used normobaric altitude tents as treatment.

"We wanted to look at acclimatization over time to see how long it could last, and we also wanted to determine whether altitude tents could be used as a treatment method to sustain acclimatization to a greater degree," Beidleman said. "If the treatment worked, these altitude tents would be an economical and easily accessible system the Army could use in order to prevent Soldiers from experiencing debilitating physical and cognitive performance decrements, as well as AMS symptoms during altitude missions."

Dr. Mark Buller, a computational physiologist, and Beidleman used physiological status monitors to develop individualized models that could help predict which Soldiers are likely to get AMS and which Soldiers will remain symptom-free. When test volunteers stepped foot on Pikes Peak, they immediately donned chest harnesses that tracked minute-by-minute heart rates and arterial oxygen saturations for the first 24 hours of their exposure to 14,115 feet to help detect development of AMS during the altitude exposure.

Three times throughout the 12-day study, volunteers participated in time trials, where researchers assessed volunteers' physical performance. The volunteers ran on a treadmill for 3.1 miles at a 1-percent grade while researchers monitored their breathing, oxygen consumption and heart rates. The researchers collected blood samples and analyzed volunteers' breathing while at rest.

Volunteers also settled at computers to take daily cognitive tests, using the Automated Neuropsychological Assessment Metrics battery, a computer-based tool designed to detect reaction time, speed and accuracy of attention, short- and long-term memory and thinking abilities. They also took the Synthetic Work Program test, which evaluates multitasking ability.

On Day 13, the researchers and volunteers flew back to USARIEM at sea level for a 12-day treatment phase. The volunteers were split into two groups: One group spent three hours per day in a normobaric altitude tent that simulated an altitude environment by lowering the amount of oxygen but maintaining the same oxygen pressure at sea level. The other group received the same amount of treatment in a "sham altitude tent" that kept the same oxygen levels as sea level.

After completing 12 days of this treatment, the volunteers were re-exposed to 14,115 feet for 24 hours in USARIEM's hypobaric chamber. The sealed off hypobaric chamber, Beidleman explained, can simulate the conditions on Pikes Peak and altitudes as high as Mount Everest by, as Beidleman described it, "Acting like a big vacuum that sucks out air molecules to lower the barometric pressure." The researchers would learn if the treatment worked, depending on whether or not volunteers' AMS symptoms resurfaced in those 24 hours at high altitude.

When the researchers analyzed their data, they saw that the volunteers' acclimatization to high altitude was sustained--but not because of the altitude tent treatment.

"We found that those three-hour normobaric hypoxia treatments were not effective for sustaining high altitude acclimatization to a greater degree," Beidleman said. "The benefits of the normobaric hypoxia were not negative, but they were not positive either.

"What we did find was that the study volunteers were able to sustain acclimatization after spending 14 days at sea level without any form of treatment."

When the researchers investigated further, the volunteers' breathing and blood levels in the hypobaric chamber were the same as when they had acclimatized on Pikes Peak. Beidleman added that this study was the first to show that the improved cognitive performance attained during acclimatization was retained for two weeks after returning to sea level.

While the volunteers' aerobic endurance during the time trials improved the longer they stayed on Pikes Peak, it was the only factor that was not fully retained when they returned to high altitude. According to Beidleman, volunteers' aerobic endurance in the hypobaric chamber was the same as when they first suffered from AMS during the first 48 hours on Pikes Peak.

Researchers will be able to build on this study to see if acclimatization at a militarily relevant altitude could last even longer than two weeks. But for now, Beidleman said the results are advancing in the right direction.

"We found that allowing the study volunteers to acclimatize to high altitude for 12 days was enough treatment to sustain the effects of acclimatization for two weeks between missions," Beidleman said. "Soldiers do not have to use extraordinary or expensive treatment methods, such as altitude tents, to sustain acclimatization. The results published in this study will provide the military valuable guidance for navigating high altitudes while avoiding disastrous medical events during return trips."

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