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Airbags may be embedded in the steering wheel, as well as be deployed on the side. This adds to the potential of ear injuries from airbag deployment.
There is a significant incidence of vertigo and hearing disturbance after airbag deployment (Yaremchuck and Dobie RA. 2000). The injuries appear to be due to a combination of loud noise, and occasional "explosive" forces to the ear drum. This mechanism of injury might also be a cause of a perilymph fistula. As airbag deployment usually occurs in auto accidents, there is also sometimes the possibility of malingering in these cases.
One would expect that persons with the enlarged vestibular aqueduct syndrome would be more liable to develop hearing loss after airbag deployment.
Cunningham et al (1999) presented a single case of an individual whose middle ear was shattered by an airbag deployment. Ossicles (inner ear bones) were displaced into the inner ear resulting in total deafness and facial paralysis. In this case, the patient's head was turned to the right (so the air bag struck the left ear). In a larger study, having the ear turned towards the airbag was correlated with hearing loss, aural fullness and TM perforation. (McFeely et al. , 1999)
Loud noise is a well known source of hearing loss and/or tinnitus or hyperacusis.
Huelke and Moore (1999) reported that permanent hearing deficit occurs in about 1.7% of persons with airbag deployment. There are also reports of tinnitus after airbag deployment. The hearing loss, often accompanied by tinnitus, occurs immediately (Buckley, et al. 1999). There is also a temporary threshold shift -- in other words, hearing should improve rather than worsen over time.
Regarding the loud noise, according to Saunders et al, the loudness may exceed 170 dB SPL. In their 6 patients with airbag related hearing loss, high frequency patterns were the most common. Oddly, although the SPL of the sound decreases in larger cars, models suggest that there is more danger to persons when the cabin of the vehicle is open, such as when the window is open. Having a crash with the windows closed, is evidently safer for hearing than with the windows open.
Price and others have worked on developing a model of noise trauma for the military. In their 1999 paper, they documented that sounds as loud as airbag deployment can injure hearing in cats (1999).
Occasional cases have been reported in which a PLF was repaired after airbag deployment. This injury pattern seems reasonable.
According to Saunders et al, the low frequency carrier wave during airbag deployment causes maximum displacement of the stapes and annular ligament. This mechanism might cause tearing of the annular ligament, and stapes hypermobility. Stapes hypermobility may lead to sound induced vertigo as well as hyperacusis.
Hearing loss can be simulated, but fortunately there are many excellent methods of detecting discrepancies of this nature. Tinnitus is more difficult to confirm, as it generally intrinsically subjective, but generally the methodology has to do with correlating objective and subjective measures of inner ear function.
The diagnosis is suggested by immediate onset of hearing symptoms after airbag deployment, and lack of preexisting symptoms. We recommend:
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