Even astronauts are susceptible to "bends" - Decompression Sickness - medical research - Brief Article - Statistical Data Included

USA Today (Society for the Advancement of Education), Oct, 2002

From the depths of the ocean to deep space, the same type of medical treatment given to divers for the bends may prove useful to astronauts during the construction of the international space station, says Richard E. Moon, an anesthesiologist from Duke University Medical Center, Durham, N.C. The bends, also known as gas bubble disease or decompression sickness, occurs when divers, aviators, or astronauts move too quickly from higher to lower atmospheric pressures.

Working outside the international space station in spacesuits elevates astronauts' risk of decompression sickness, Moon indicates, since the transition from the stations to a space suit rapidly lowers the pressure to which the astronaut is exposed by two-thirds. Nitrogen exhaled under pressure dissolves in the body, but when pressure decreases too rapidly, nitrogen collects in tissues faster than the body can process it. The gas accumulates in joints and blood vessels, forming bubbles that impair oxygen flow to tissues. This causes severe pain, numbness, weakness, and, in some cases, paralysis.

"Although we know of no cases of decompression sickness in space, the number of extravehicular activities (EVAs), even with the Russian program, has been fairly small," Moon points out. "Cases of decompression sickness in space could occur as the number of EVAs soar into the hundreds during construction of the space station."

Severe cases of decompression sickness can be fatal, but the illness is usually highly treatable early on. Treatment primarily consists of having the patient breathe 100% oxygen at higher than normal atmospheric pressure inside an enclosed space called a hyperbaric oxygen chamber. The oxygen washes the nitrogen out of the body. There are two types of hyperbaric oxygen chambers: multiplace (holding more than one person) and monoplace (holding a single patient). The multiplace chamber is a large sphere or cylinder about 20 feet in diameter. A doctor or nurse accompanies the patient into the chamber, where the patient inhales oxygen through a head tent or a tightly fitting mask.

Treatment can consist of one to as many as 20 sessions, depending on the severity of the illness. Hyperbaric oxygen therapy also is used to treat patients with carbon monoxide poisoning, smoke inhalation, wounds in areas that have received radiation treatment or have impaired blood supply, and severe infections that destroy tissue.

"We could eliminate the risk of gas bubble disease by having the astronauts breathe pure oxygen for 24 hours, but they don't have the time," Moon explains. "Exercising while prebreathing offers a timesaving way to increase blood flow to the tissues and flush out nitrogen. We now know that the gas bubbles not only block the body's absorption of oxygen, but that they also damage the lining of the blood vessels." Damage to the endothelium--or blood vessels--then causes the white blood cells to stick to the linings, which, in turn, further reduces blood flow to the tissues for the next two to three hours. "We believe hyperbaric oxygen prevents white blood cells from sticking to the endothelium."