Wu and Young (2009) reported their longitudinal study of cochlear and saccule function. They recruited 20 male police officers as subjects in 1997. All subjects were right-handed. The mean age upon entry into the study was 31 years (range 23 to 37 years). All subjects reportedly wore earplugs and earmuffs during their monthly target shooting. A noise dosimeter located under the hearing protection and capable of integrating impulse noise recorded the weapons fire as between 74 to 107 dBA.

Twelve subjects were available 10 years later for audiometric and vestibular evoked myogenic response (VEWP) testing.

In 2007, audiometry was evaluated using controls who were not exposed to weapons fire to exclude aging effects. Results revealed the subjects thresholds at 4000 (28 dBHL) and 6000 Hz (33 dBHL) on the left ears (only) showed significant differences from the controls (14 dBHL and 17 dBHL, respectively). There were no other significant differences in the left or right ears between subjects and controls.

VEMP test data was not recorded upon entry to the study in 1997. However, abnormal VEMP responses were noted in nine subjects in 2007. VEMPs were absent in seven subjects, and delayed in two subjects. One hundred percent of the controls demonstrated normal VEMPS.

The authors note the TULLIO phenomenon (vertigo or imbalance after exposure to intense noise) arises from vestibular activation secondary to acoustic stimulation. They note the abnormal VEMP responses noted above may have been related to saccular damage secondary to gunshot/noise exposure and they note the combined earplugs and earmuffs may not be sufficient to protect the saccule from long term noise exposure.

Source:http://www.audiology.org