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Lost in space: Hearing can suffer on ISS

Who'd have thought that outer space was a noisy place? It is, at least in the International Space Station (ISS). Russian cosmonauts, who have spent the most time aboard the station so far, and a few other astronauts have suffered both temporary and permanent noise-induced hearing loss. And as space flights lengthen, hearing problems could get worse.

The space station is "not noisy at a level that you usually associate with hearing loss," says Dartmouth physician and former astronaut Jay Buckey, M.D. Buckey flew on the Space Shuttle Columbia in 1998 as part of the 16-day Neurolab STS-90 mission. Noise-induced hearing loss is typically caused by an exposure to sounds of 90 decibels or more. But the space station din is only about as loud as the inside of an airplane in flight—60 to 70 decibels.

"There are probably several factors at play," besides chronic exposure to the noise, Buckey explains. Genetic differences may play a role, with some people being more sensitive to noise than others. The slightly higher carbon dioxide levels in the ISS may also contribute. Even weightlessness, which causes a shifting of body fluids, including increased intracranial pressure, may be partly to blame.

Jay Buckey has designed a hearing test that can fit in a laptop computer, for use on space flights.

But before any of the reasons can be determined, there needs to be an
effective hearing test that can be administered in a noisy place like the space station. Buckey, with the help of an audiologist and an engineer and funding from NASA, has developed a system that he's sure will work. He teamed up with audiologist Frank Musiek, Ph.D.—a former DMS faculty member who's now director of audiology research at the University of Connecticut-Storrs—and engineer Robert Kline-Schoder,
Ph.D.—from Creare, Inc., a Hanover,

N.H.-based engineering and research development firm.

Probe: Musiek suggested a test that can automatically measure ear function, even in a noisy environment: an otoacoustic emissions test. The test, which is used on earth to screen newborns and some adults for hearing problems, is reliable, accurate, and objective. A small probe placed in the ear generates tones that travel to the inner ear and stimulate the hair cells in the cochlea; the hair cells send back signals that provide clues to how well the person's inner ear is working.

Buckey's team designed the test so it could be self-administered. And Kline- Schoder figured out a way to make the whole thing portable. He built miniaturized electronic components that fit into a laptop computer.

Astronauts will be tested preflight, regularly during a flight, on landing day, and several times postflight. A control group on Earth will take the same tests in a sound booth with real ISS noise (previously recorded in the space station itself) piped in. The only thing that can't be replicated is microgravity.

If all goes as planned, the testing system will fly on the ISS in 2007, says Buckey.

Laura Stephenson Carter

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