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

By Randy Dotinga HealthDay Reporter

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.

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