Brain Lesions More Common in High-Altitude Pilots, Study Finds

Results could also apply to deep-sea divers, mountain climbers

MONDAY, Aug. 19 (HealthDay News) — Pilots of U.S. Air Force U-2 reconnaissance planes may be at risk of developing brain lesions, a new study suggests.

America’s involvement in two wars has increased the workload of U.S. airmen, and cases of decompression sickness — a potential hazard of high-altitude flying — have tripled over the past two decades, the researchers say. But this study suggests that U-2 pilots in general are more vulnerable to bruises in the brain, a sign that decompression damages the brain even in the absence of illness.

The findings, published in the Aug. 20 issue of the journal Neurology, indicate that decompression sends tiny bubbles known as emboli into the brain where they don’t necessarily make people ill but may still cause harm, said study lead author Dr. Stephen McGuire, a neurologist with the U.S. Air Force School of Aerospace Medicine in San Antonio, Texas.

“If the bruise is not too severe, the brain recovers,” he said. However, “we don’t really know what the long-term implications are.”

Decompression sickness, also known as “the bends,” occurs when pressure around a person suddenly dips. High-altitude pilots, miners, mountain climbers and scuba divers can be affected.

Dr. Adam Bender, a diver and attending neurologist at Lenox Hill Hospital in New York City, described what happens with decompression sickness this way: “Tiny bubbles of nitrogen gas form in the blood and coalesce in the blood vessels of the joints. Bubbles can also coalesce in the blood vessels of the skin, causing itching and skin rash. Most dangerously, the blood vessels of the brain and spinal cord can be involved, causing multiple small strokes,” he explained.

“The blood actually ‘boils’ at these very low atmospheric pressures,” Bender said. “The effect is similar to the bubbles seen when you quickly open a bottle of soda or champagne. The decrease in pressure in the bottle causes the release of carbon dioxide gas, previously dissolved under pressure in the liquid, to come out in the form of small bubbles.”

Bender said the resulting lesions can be harmful. “They can accumulate and result in symptoms varying from mild (slowed thought process) to severe (speech difficulty, confusion and unresponsiveness),” he said.

Commercial airline pilots and passengers fly in pressurized airplanes and shouldn’t be concerned. U-2 pilots, however, fly at very high altitudes — often above 18,000 feet — with limited cabin pressurization.

The number of decompression sickness incidents per U-2 flight has grown threefold over the last 20 years, although they’re still rare at well under 1 percent, McGuire said. The rise in cases could be attributed to increased flight demands related to the wars in Iraq and Afghanistan, he said.

In the new study, researchers examined brain scans of 102 male and female U-2 pilots and 91 people of similar age, health and education level.

The U-2 pilots had 295 percent more lesions than the non-pilots and almost 400 percent more brain lesions by volume. The findings suggest that decompression sickness is caused by “micro-emboli” instead of large air bubbles, McGuire said. And these tiny bubbles often seem to enter the brain without causing symptoms, he added.

What do the study findings mean for pilots, divers and others? “If you have someone being exposed to altitude, even on oxygen (to prevent decompression sickness), you have to be concerned about potential brain injury,” McGuire said. It’s possible, but unproven, that the bruises contribute to senility, he suggested.

Bender said possible prevention strategies include oxygen treatment, fewer flights and less exposure to extreme altitude. Another idea is to make U-2 planes that don’t expose pilots to extreme pressure.

“Although such planes are not yet being produced,” Bender said, “research is currently underway to design U-2 planes with these specifications.”

More information

For more about decompression sickness, see the Undersea and Hyperbaric Medical Society.