What is the Carhart Notch in Pure Tone Audiometry?

Introductory
10 mins
Reading
01 May 2017

Description

The Carhart notch is a notch in a bone conduction audiogram of more than 2 kHz, and was first described by Raymond Carhart, Ph.D., in 1950.

 

Explanation

Stimulation of the ear via bone conducted vibrations is a well-established way to differentiate conductive from sensorineural hearing loss – but paradoxically, the accurate testing of bone conduction thresholds depends on normal middle ear function. Impairment of bone conducted vibrations, for example by stapes footplate fixation, results in raised thresholds by bone conduction. This effect arises across the frequency range and is related to the resonance properties of the ossicular chain. The result is a “notch” in the bone conduction audiogram which is more pronounced at 2 kHz as described by Carhart in 1950.

 

References

Carhart, R. (1950) Clinical application of bone conduction audiometry. Arch Otolaryngol 51, pages 798-808

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.

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