Effects of Long Duration Space Flight on Low Frequency Hearing

Pure tone hearing threshold data has been collected on astronauts since the early days of spaceflight. Between 1981 and 2001 (STS-1 thru 108) it was found that of the 608 shuttle astronauts, 17% returned
home with a significant hearing threshold shift, and of that 6% had permanent changes in the high
frequencies. Believed to be due to prolonged noise exposure on the space crafts. (Hart, 2006)

As NASA aimed for longer duration missions the uncertainty about the effects of month-long noise
exposure needed to be addressed. To avoid constraining crewmembers to constant earplug usage, and
satisfying budget demands, a focused effort on overcoming the issues began.

Noise monitoring systems were introduced onto the International Space Station (ISS) and astronauts were
given education on the noise environment aboard the ISS, the hazards of noise induced hearing loss,
hearing conservation principles, and countermeasure strategies (earplugs, noise cancellation headsets).
As well as being trained on a new countermeasure effort that had been in trial testing on prior shuttle
missions (STS-6 thru 8), On-Orbit Hearing Assessment (OOHA). (Hart, 2006)

OOHA was implemented to routinely monitor the hearing thresholds of crewmembers who are on orbit
for longer than 30 days. Flight Surgeons on ground monitor these test for significant hearing changes while
aboard.

Between 2000 and 2021 the ISS OOHA system (EarQ) recorded changes in the low frequency hearing thresholds. Low frequency hearing changes are not typically caused by noise exposure, and it was initially believed that these changes were due to environmental noise interference. In 2021 an ISS software upgrade (KUDUwave) allowed for a more comprehensive hearing assessment. The new testing system allowed for additional tests that helped describe the type of hearing loss being experienced and determine the influence of ambient noise or other environmental factors.

OOHA Data indicates a low frequency hearing shift in 40% of all tests and 60% of all crewmembers.
Since 2021, OOHA results (using the KUDUwave) suggest that these shifts are sensorineural and are
not the result of ambient noise.

While hearing shifts are seen at both 250 and 500 Hz, metrics tracking these shifts have only used 500 Hz
data. The lack of 250 Hz has prevented accurate reporting of low frequency hearing shift recovery. The
aim of this study is to capture 250 Hz data and accurately present low frequency hearing loss recovery.