Rifle impulse noise affects middle-ear compliance in soldiers wearing protective earplugs

Area of Science:

• Audiology
• Occupational Health
• Otoacoustic Emissions

Background:

• The middle ear's function is crucial for hearing.
• Intense noise exposure, such as from firearms, is a known risk for hearing damage.
• Previous assumptions suggested small-caliber firearms might not significantly affect the middle ear.

Purpose of the Study:

• To investigate the effects of intense impulse noise from small-caliber firearms on human middle-ear function.
• To evaluate changes in middle-ear impedance, acoustic reflex, and otoacoustic emissions following firearm noise exposure.

Main Methods:

• A cross-over design study involving 59 soldiers.
• Measurement of middle-ear impedance, acoustic reflex, distortion product otoacoustic emissions (DPOAEs), and transient evoked otoacoustic emissions (TEOAEs).
• Measurements were taken before and after training involving firearm noise exposure (LAeq8h ≈ 106 dB SPL).

Main Results:

• Significant increases in tympano-ossicular chain compliance and gradient were observed post-exposure.
• Acoustic reflex reactivity showed no significant change.
• DPOAEs and TEOAEs decreased slightly, particularly at 2 kHz, with asymmetry favoring the left ear.

Conclusions:

• Small-caliber firearm noise exposure, even with earplugs, alters middle-ear function.
• These alterations may contribute to the initial stages of auditory fatigue, potentially leading to tinnitus.
• The findings challenge previous assumptions about the safety of such noise exposures for the middle ear.