Airman Bill Kennedy marshals a U.S. Air Force C-17 at Dover Air Force Base, Del., April 26, 2015. (U.S. Air Force photo/Airman 1st Class William Johnson)

Over the last 15 years, the United States has flown its wounded troops out of combat zones to hospitals around the globe. The logic: get those hurt in places where medical supplies are limited to places where they are not. The fastest way to do this? By air.

Yet according to a new, first-of-its-kind study conducted by the University of Maryland School of Medicine, rapid air evacuation has the potential to cause more damage to those patients suffering from an extremely prevalent battlefield affliction–traumatic brain injury.

More than 330,000 U.S. service members have suffered from traumatic brain injuries, one of the leading causes of death and disability for those returning from Iraq and Afghanistan, according to the study that was published Monday in The Journal of Neurotrama.

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The study, funded by a $2.5 million U.S. Air Force grant, was helmed by Alan Faden, a professor of anesthesiology at the University of Maryland School of Medicine.

The study used rats that had been given traumatic brain injures and then subsequently placed them in chambers that would simulate air pressure in a military transport aircraft, such as a C17. A pressurized cabin in a military transport aircraft at cruising altitude roughly equates to being in the open air 9,000 feet above sea level, according to Faden, while a civilian airliner feels like being around 6,000 feet.

“What we found is that they were materially worse at the end,” Faden said. “They were worse in behavioral terms, and when we actually looked at the brains they lost cells in the critical hippocampal regions, the place where one makes memories.”

The tests also found that the inflammation of the brain that typically occurs after a head injury was “substantially enhanced” after the rats were subjected to the pressure changes.

Faden used what’s known as the “fluid percussion model” to create the head injuries in the rats. According to Faden, the model is common for examining the effects of head injuries on rodents and the potential ramifications for humans. While some scientific tests on rodents do not carry over to humans, they have been mostly accurate when it comes to examining certain effects of head injured, Faden added.

Typically after a battlefield injury, U.S. troops have been stabilized at a field hospital in either Iraq or Afghanistan before being flown to Landstuhl, Germany. From there they usually receive additional treatment before being sent back to the United States.

In follow on-tests, Faden put the injured rats in two pressurized sessions separated by two days, simulating what a service member might go through if they were say, flying from Afghanistan to Germany and then Germany to the United States. Faden found that repeated exposures to pressurized cabins with a mild injury compounded the effects to mimic a larger head injury.

The study also looked at the results of air transport in the days following an injury. According to Faden, there was added inflammation to the brain after transport seven days post-injury.

In the majority of the tests, the rats were given oxygen to ensure the oxygen levels in their blood were normal, while in some tests—to mimic real world medical treatment– the rats were given 100 percent supplemental oxygen to simulate the treatment often prescribed to patients in transport.

“What we showed is that if you give 100 percent supplemental oxygen in this condition of air evacuation pressure, it was worse than just giving enough oxygen to normalize the oxygen tension,” Faden said.

To Faden, the study highlights the need to weigh the benefits of rapid air evacuation versus keeping patients stabilized closer to the battlefield prior to airlifting them home.

“The major point of this is to rethink this issue,” Faden said, adding that he hopes in the future the Air Force will look at ways to better pressurize their aircraft or find other methods to lessen the effects of pressurization.