Air-bone gap in conductive hearing loss
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For a complete answer to this issue the reader is strongly urged to read Margolis et al. (2013) – citation below. The short answer is that there appears to be an average air-bone gap of around 10 dB in normally hearing people and around 14 dB in people with sensorineural hearing loss at 4 kHz. It seems intuitive that with no middle ear disorders this air bone gap should not be there. Traditionally it has been attributed to air conducted radiation propagating down the ear canal, and plugging the ear when measuring bone conduction thresholds has been quite commonplace, although often ineffective (Tate Maltby and Gaszczyk 2015) . The paper by Margolis et al suggests the real cause of the air bone gap is a dependence of bone conduction thresholds at 4 kHz on the extent of sensorineural loss (hence why the effect increases from around 10 dB to around 14 dB with hearing loss). The paper describes how the Reference Equivalent Threshold Force Level (RETFL) used in calibration of bone conduction instruments could be adjusted by the above figures to compensate. References and caveats Tate Malty, M.; Gaszxzyk, D. (2015) Is it necessary to occlude the ear in bone-conduction testing at 4 kHz, in order to prevent air-borne radiation affecting the results? International journal of audiology, 54(12), pp.918-23 Presenter Michael Maslin After working for several years as an audiologist in the UK, Michael completed his Ph.D. in 2010 at The University of Manchester. The topic was plasticity of the human binaural auditory system. He then completed a 3-year post-doctoral research program that built directly on the underpinning work carried out during his Ph.D. In 2015, Michael joined the Interacoustics Academy, offering training and education in audiological and vestibular diagnostics worldwide. Michael now works for the University of Canterbury in Christchurch, New Zealand, exploring his research interests which include electrophysiological measurement of the central auditory system, and the development of clinical protocols and clinical techniques applied in areas such as paediatric audiology and vestibular assessment and management. Popular Academy AdvancementsReturn to: General Clerkship ObjectivesSee also Cisplatin Ototoxicity Overview:Three major types of hearing loss:
Hearing Fork Tests:
Audiogram:
Conductive Hearing Loss:
Sensorineural Hearing Loss:
How much is the airThe air-bone gap (ABG) can be 0 dB, positive, or negative and is used to classify audiograms as conductive, sensorineural, or mixed hearing losses. In cases of normal hearing for pure tones and sensorineural hearing loss, the mean ABG is expected to be 0 dB.
What is an airThe difference between the results of air conduction and bone conduction tests is known as the air-bone gap. An air-bone gap may mean a problem in the outer or middle ear. If there is no gap between air and bone conduction this may indicate a problem in the inner ear (cochlea).
How much of an airDiagnosis is ordinarily made via observation of an "air-bone gap" on audiometry, meaning that hearing is superior when sound is transmitted in such a way that it bypasses the middle ear ossicular chain. The air-bone gap (ABG) should be at least 10 db.
What is the maximum airThe short answer is that there appears to be an average air-bone gap of around 10 dB in normally hearing people and around 14 dB in people with sensorineural hearing loss at 4 kHz.
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