Army Lab Tests Effects of Altitude Change on Soldiers

By Ian Graham
Special to American Forces Press Service

July 13, 2009 - Army researchers are simulating environmental extremes, such as the summit of Mount Kilimanjaro or the high desert of Afghanistan, to better understand and protect troops from the challenges of operating in such conditions. A scientist at the U.S. Army Research Institute of Environmental Medicine described the research during a July 8 webcast of "Armed with Science: Research and Applications for the Modern Military" on Pentagon Web radio.

"We conduct research into environmental medicine and occupational work, or physiology and nutrition research, all of this specifically to identify problems that the warfighter would encounter in the environmental extremes of heat, cold and high altitude, and across a wide spectrum of military tasks," said Dr. Stephen Muza, Mountain Medicine Team leader in the institute's Thermal and Mountain Medicine Division.

The institute, based in Natick, Mass., is a part of the U.S. Army Medical Research Materiel Command. The institute explores environmental factors -- from extreme temperature to altitude -- that can hamper military operations. Research facilities can reproduce everything from arctic cold to tropical heat by controlling temperature and humidity levels. The institute's 370-square-foot hypobaric chamber can simulate altitudes from sea level to about 30,000 feet above sea level.

High altitudes are any location 1,200 meters above sea level, or about 3,900 feet, Muza explained. That's the lowest altitude at which studies have shown altitude-related problems.

"By the time you have ascended to this altitude, there are very measurable decrements in ... what we call our VO2 max, or maximum aerobic performance," he said. "And as you proceed higher, straight up above 7,000 feet or 2,400 meters, you actually start to encounter the possibility of developing altitude illness; and of course the higher you go, the bigger the impact on your work performance and the greater likelihood of developing altitude ailments."

Strength and the ability to perform short, intense activities aren't especially affected by altitude, Muza said. But even a "modest" increase in altitude can significantly hamper long-term aerobic work.

"If you have to maintain a prolonged work such as an approach march or patrol, particularly with a heavy workload..., that's going to have a significant negative impact," he said.
Muza said the noticeable effect of high altitude and decreased aerobic performance is the need to slow down or take more rest breaks to complete the same job.

"Usually what happens is you have to slow down," he said. "As you go higher, your ability to perform maximal work decreases."

In higher altitudes, a soldier may become nauseated, dizzy or light-headed in what is known as acute mountain sickness. At the highest altitudes, more than 12,000 feet above sea level, one begins to lose mental capacity.

"Above 10,000 to 12,000 feet, we really start to see cognitive performance deficits," Muza said. "Your ability to make a decision is impaired. In particular, it takes longer to arrive at the decision, especially when you're trying to assemble new information."

In addition to testing the general biochemical and physiological aspects of high-altitude operations, Muza said his lab often creates military-specific tests for human research volunteers, a majority of which are military personnel, such as decision-based marksmanship in which the soldier has to distinguish friend and foe.

"We can stress these individuals out by sleep deprivation or ... maybe depriving them of food or rations like may be common in a military situation, and then look at ways to intervene to improve their performance," Muza said.

Acclimatization is the best way to adapt to high altitude, he said. People who rapidly ascend -- particularly above 6,000 feet -- are more likely to suffer problems, especially acute mountain sickness.

Muza said he recently tested subjects from the Boston area by flying them to the Air Force Academy in Colorado Springs, Colo., about a 7,000-foot altitude increase, then a week later driving them to the summit of Pike's Peak, Colo., another 7,000-foot climb. His research team discovered that troops with as little as six days to acclimate were highly successful at adjusting to the altitude difference and completing their physical activities with minimal altitude illness.

Medications have not been effective enough to be ground-breaking, Muza noted. The Army has stockpiled the Food and Drug Administration-approved drug, Diamox, but the drug has unusual side effects that "although [they are] relatively mild, they can be a little disturbing," he said.

"There is some emerging data that suggests a class of new drugs, which have yet to be tested in humans under the conditions of altitude exposure, may in fact induce acclimatization so that when you arrive at altitude you're in much better shape to conduct your duties," he said.

Maintaining a diet heavy in carbohydrates has proven to be a successful helper in performing high-altitude tasks, Muza said. A high-altitude soldier's diet should be at least 60 percent carbohydrates.

Consuming carbohydrates in a beverage about every 10 to 15 minutes has shown significant results in improving work ability after extreme altitude change, he explained.

"An individual who rapidly ascends to 14,000 feet and then has to perform prolonged physical work on the order of 90 minutes to two hours ... performs that work 25 to 30 percent better than an individual taking placebo," Muza said. This finding has led to the development of a new high carbohydrate ration that is currently being tested.

(Ian Graham works for the Defense Media Activity emerging media directorate.)