**OAEs and Meniere Disease**

Stavros Hatzopoulos, Andrea Ciorba, Virginia Corazzi and Piotr Henryk Skarzynski

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/66387

#### **Abstract**

Otoacoustic emissions (OAEs) are responses originating from the inner ear. Clinically they are evoked by different families of acoustic stimuli, such as transient acoustic clicks, tone pips, and pure tones. Upon stimulation, the acoustic energy is transformed in the middle ear at acoustic pressure acting upon the stapes footplate. The pressure wave inside the cochlea stimulates the OAE generators and a reverse acoustic energy (the OAE response) propagates from the inner ear, through the stapes and the middle ear structures, to the tympanic membrane. Considering that the acoustic energy has to cross the middle ear structures twice, the functional status of the middle ear can influence or attenuate considerably the OAE response. In this context, any vestibular alteration can influence the middle ear mechanics (mainly the middle ear impedance) and consequently the OAE response characteristics. The data in the literature indicate that OAEs are very sensitive to changes in the intracranial pressure. These pressure alterations during the Meniere's hydrops phase are expressed as changes in the intralabyrinthine pressure. Other studies have presented data supporting the assumption that OAEs can adequately monitor middle ear changes induced by the presentation of the glycerol test. The data in the literature suggest that OAEs can monitor the progress of Meniere's disease using reliable indices.

**Keywords:** Ménière, hearing threshold, glycerol test, vestibule, otoacoustic emissions, distortion product otoacoustic emissions, transient otoacoustic emissions, middle ear mechanics

#### **1. Introduction**

Otoacoustic emissions (OAEs) are responses originating from the inner ear and they were first described by David Kemp [1, 2]. They are evoked by different families of acoustic stimuli, such as transient acoustic clicks and chirps, tone pips, and pure tones. Upon stimulation, the

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acoustic energy is transformed by the middle ear in acoustic pressure applied to the stapes footplate. The pressure wave inside the cochlea stimulates the OAE generators and a reverse acoustic energy (the OAE response) propagates from the inner ear, through the stapes and the middle ear structures, to the tympanic membrane. There it can be recorded by a sensitive probe (microphone), inserted in the acoustic meatus.

The classical classification scheme categorizes OAEs according to their evoking stimulus [3]. In this context, the OAE responses can be elicited by transient clicks (TEOAEs), transient tone bursts (TBOAEs), or by pure tones (distortion product OAEs – DPOAEs). Responses evoked by random thermal noise in the cochlea are called Spontaneous OAEs (SOAEs), which have limited clinical applications. The newest and most accepted taxonomy classifies the responses according to their generation mechanisms [4]. According to Shera and Guinnan [4], the OAE responses are evoked by a linear reflection (of the travelling wave energy) on the basilar membrane, or by nonlinear processes "orchestrated" by nonlinear characteristics of the outer hair cells (OHCs) and the cochlear amplifier per se. The clinically used responses (TEOAEs or DPOAEs) are a mixture of these two mechanisms.

The OAE values, express a measure/metric of the cochlear amplifier functionality, which has found numerous applications in Audiology and Hearing Science. The most known application is in the area of hearing screening. TEOAEs can detect sensorineural deficits up to 35 dB HL; DPOAEs are more sensitive and can detect deficits up to 40 dB HL [3]. The great advantage of OAEs, in comparison to traditional audiometry tests, is that they can detect a deficit before it registers as a hearing deficit (i.e., it is in a subclinical phase) [3]. When an external or internal stressor causes severe mechanical alterations on the functionality of the OHCs, intrinsic and extrinsic apoptotic processes are initiated [5]. Within the next time-frames (days/months), the corresponding OAEs are severely altered and gradually, the OHC damage induces an intrinsic neural apoptosis and a subsequent hearing deficit.

Therefore, the OAE response characteristics are altered by inner ear disorders, such as Meniere's disease (MD), a condition in which the whole inner ear can be damaged, including all the structures of the cochlea (outer and inner hair cells) and the vestibular system.

This chapter is an excursus of the current scientific findings relating vestibular and middle ear alterations, as observed in various stages of the Ménière's disease, with measurements of otoacoustic emissions. The latter are considered the test of choice to identify preclinical effects on the human hearing threshold and alterations in the inner ear.
