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.