The invisible enemy of the Afghanistan mountains

Stephen R. Muza, Ph.D., of the U.S. Army Research Institute of Environmental Medicine's Thermal and Mountain Medicine Division, is studying the effects of altitude on Soldiers' mental performance and their susceptibility to Acute Mountain Sickness.

Photo Credit: David Kamm, NSRDEC Photographer

At heights exceeding 8,200 feet, they must worry about the effects of altitude on their mental performance and about their susceptibilities to Acute Mountain Sickness, or AMS. As acting chief of the Thermal and Mountain Medicine Division at the U.S. Army Research Institute of Environmental Medicine, Natick Soldier Systems Center, Stephen R. Muza, Ph.D., devotes a great deal of time to studying those problems.

"We need to know the actual, physiological basis for the development of these altitude illnesses," said Muza, "and specifically in this case, Acute Mountain Sickness, in order to target new pharmaceutical products."

Working toward that goal, Muza and his colleagues at USARIEM are collaborating with the Neural Systems Group, Massachusetts General Hospital, Harvard Medical School on "Neuroimaging of Acute Mountain Sickness," a research study sponsored by the Department of Defense Telemedicine and Advanced Technology Research Center. The study is using near-infrared neuroimaging, or NIN, to non-invasively measure changes in the brains of test subjects at sea level and 14,500 feet while doing cognitive tests and either light or heavy exercise.

Neuroscientist Gary Strangman, Ph.D., of MGH has been bringing his NIN equipment to Natick, where it is used on subjects in USARIEM's hypobaric chamber, which can simulate altitudes up to 30,000 feet. The NIN is a portable alternative to magnetic resonance imaging, or MRI.

"He can specifically look at what's going on in this brain tissue between the transmitter and the receiver," said Muza of Strangman. "We're not looking at the whole brain, but we're looking at the cortex, where most of the neurons are found. That's where really where all of the action is."

The collaborative study is focusing on 36 healthy civilian subjects from the Boston metro area, who have baseline measurements done at MGH and then spend two eight-hour sessions each in USARIEM's chamber. Light is beamed through their brain tissues and then analyzed for changes in blood volume, oxygenation, and fluid distribution.

"He was looking for an opportunity to use his equipment," said Muza of Strangman. "I was looking for an opportunity to use cutting-edge (equipment), basically what nobody else has in this world -- new portable imaging devices -- to study the changes in the brain at altitude in our hypobaric chamber, because you cannot bring an MRI (in there)."

As Muza pointed out, Soldiers' thought processes slow at altitude. So Strangman designed cognitive tests on a computer screen to measure subjects.

"We want to cause the brain to have to work, and to make the brain work, we do cognitive tasks," said Muza, "things that are very comparable to what a Soldier does."

Muza and Strangman also want to know what the brain is doing when a subject is experiencing headaches, lightheadedness, nausea and other symptoms associated with AMS.

"When you get above 14,000 feet, there's better than an 80 percent chance that you'll develop some degree of severity of Acute Mountain Sickness," Muza said. "We're interested in knowing what's going on in the brain in the hours that lead up to the development of Acute Mountain Sickness."

The study has been ongoing for a year and should be completed in May. The early data are encouraging.

"In the individuals reporting Acute Mountain Sickness versus those who do not report having symptoms of Acute Mountain Sickness, we see that there is a reduction in blood flow to the brain and, therefore, oxygen delivery to the brain in the individuals who are sick versus the individuals who are not sick at altitude," Muza said. "We do see, with 60 minutes of exercise, more Acute Mountain Sickness than we see with the 10 minutes of exercise. We expected that, and that's happening."

The only available pharmaceutical treatment, said Muza, improves breathing, not brain function. This study could help change that one day.

"Finding an alternative drug therapy is a long-term goal of our research program," said Muza, who added that the collaborative study has offered "the opportunity to bring what I think nobody else has in the world into our hypobaric chamber and use it to study these effects."

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