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

Abstract

Objective: We tested middle-ear functioning in humans following intense exposure to noise. Noise generated by small caliber firearms was thought to have no effect on the middle-ear. Design: A cross-over design. We measured middle-ear impedance, acoustic reflex, distortion product otoacoustic emissions (DPOAEs), and transient evoked otoacoustic emissions (TEOAEs) before and after practice rounds performed twice per day. Study sample: Fifty-nine soldiers equipped with earplugs undergoing regular training for a special mission. The mean noise exposure (LAeq8h) was estimated to be 106 ±1 dB SPL. Results: Impedancemetry revealed a significant increase in the compliance and gradient of the tympano-ossicular chain after impulse noise exposure in the right and left ears. Acoustic reflex reactivity did not show a significant change. DPOAEs and TEOAEs were slightly decreased at 2 kHz, and showed a marked asymmetry in disfavor of the left ear. In soldiers with initial high reactivity of acoustic reflex, increased compliance was associated with a significant decrease in left TEOAEs at 1.5 and 2 kHz.Conclusion: Our results suggest that the use of small-caliber firearms, even while wearing earplugs, affects middle-ear function and may play a role in the early stage of auditory fatigue encompassing tinnitus.

Key Words:

• Noise
• tympanometry
• middle-ear
• otoacoustic emissions
• firearms
• medical audiology

Acknowledgements

We thank the soldiers of the ‘16ème BC’ in Bitche (68) in France, and the medical center staff for their cooperation. This study was partially financially supported by a grant from Délégation Général de l’Armement-DGA (11 CA 801 or PDH-1-SMO-3-0802).

Declaration of interest: The authors report no conflicts of interest.