Kathleen Yaremchuk, MD
Elizabeth Huang, MD
Henry Ford Health System
Incidence of Otologic Trauma Following Air Bag Deployment
It has been estimated that there have been 2.1 million airbag deployments in the past ten years in the United States. Early research on noise from airbag deployments in animals and humans dismissed the possibility of hearing damage to humans. The only study of noise from airbag deployments on volunteers was performed by Nixon thirty years ago at Wright Patterson Air Force Base. Only one case of permanent hearing loss occurred and was attributed to the individual's employment around loud noise and not because of exposure to the airbag deployment.
Up until 1998, there were several isolated case reports of hearing loss secondary to airbag deployments. Because of concern that the incidence was greater than previously recognized the American Academy of Otolaryngology/Head and Neck Surgery requested that, its members send case reports and documentation of patients that presented with otologic complaints secondary to airbag deployments. Since that request was made, 70 cases of hearing loss, tinnitus, aural fullness, and vertigo were submitted.
Since the case reports were submitted by multiple physicians not all contain pertinent demographic data such as the sex, age, whether they were the driver or passenger, or the number of airbags deployed. Hearing tests, before and after the airbag deployments were available on some patients but not all. Some patients had post motor vehicle accident hearing tests.
Of the 70 patients with otologic symptoms, 61 had post airbag deployment audiograms. Of these, 50 showed hearing loss in one or more frequencies in the ear with otologic complaints.
Noise associated with airbag deployment varies with the type of airbag. Deployment of a driver side only airbag will generate mean peak sound pressure level (SPL) of approximately 160 dB, a passenger side only airbag will generate mean peak SPL of 168 dB and dual airbags create a mean peak SPL of 170 dB. Side airbags available as optional equipment in some vehicles generate a mean peak SPL of 178 dB. The SPL generated by a motor vehicle accident is 140 dB. The pain threshold from noise is about 140 dB. It was previously reported that a single exposure to an SPL of 140 dB in a cordless telephone was responsible for permanent severe hearing loss in several individuals.
There is an opportunity to document hearing in individuals that are seen after motor vehicle accidents and determine the extent airbag deployments are responsible for hearing loss.
All patients involved in a motor vehicle accident will undergo standard evaluation by the Department of Emergency Medicine. In addition, all patients will be asked questions directed specifically towards acoustic trauma (hearing loss, tinnitus, and vertigo) and prior otologic history. Questionnaires will be supplied for this purpose and are attached for review. Specific questions regarding driving conditions and vehicle specifications are included. All patients who are able to cooperate with the interview will have an audiogram (air and bone conduction thresholds and speech discrimination) and otoacoustic emissions performed within 72 hours of presenting to the emergency room to determine if a temporary threshold shift has occurred. Patients with demonstrated hearing loss will have a repeat audiogram at six weeks to determine if a permanent hearing loss has occurred. Patients involved in accidents were airbags were not deployed will serve as control subjects.
One hundred patients will ultimately be enrolled in each group. The initial study will have forty patients in the study group and forty in the control group. Submission of a proposal with preliminary data to obtain further funding from the SAE Cooperative Research Program so as to achieve a sample size of 200 patients that will give a 95% confidence interval around the hearing loss rate of .00-0.04 if the rate of hearing loss in the population is 1%. The Emergency Rooms at several Henry Ford Health System Hospitals will be involved in the studies to identify eligible patients.
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