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Middle ear mechanics in normal, diseased and reconstructed ears

Published online by Cambridge University Press:  29 June 2007

Saumil N. Merchant*
Affiliation:
Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. Eaton-Peabody Laboratory of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts, USA. Speech and Hearing Sciences Program, Harvard-MIT Division of Health Sciences and Technology, Boston, Massachusetts, USA.
Michael E. Ravicz
Affiliation:
Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. Eaton-Peabody Laboratory of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
Susan E. Voss
Affiliation:
Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. Eaton-Peabody Laboratory of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. Speech and Hearing Sciences Program, Harvard-MIT Division of Health Sciences and Technology, Boston, Massachusetts, USA.
William T. Peake
Affiliation:
Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. Eaton-Peabody Laboratory of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. Speech and Hearing Sciences Program, Harvard-MIT Division of Health Sciences and Technology, Boston, Massachusetts, USA. Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
John J. Rosowski
Affiliation:
Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. Eaton-Peabody Laboratory of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA. Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts, USA. Speech and Hearing Sciences Program, Harvard-MIT Division of Health Sciences and Technology, Boston, Massachusetts, USA. Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
*
Address for correspondence: Saumil N. Merchant, M.D., Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114, USA. Fax: (617) 573-3914

Abstract

A review of the structure-function relationships in normal, diseased and reconstructed middle ears is presented. Variables used to describe the system are sound pressure, volume velocity and acoustic impedance. We discuss the following

(1) Sound can be transmitted from the ear canal to the cochlea via two mechanisms: the tympanoossicular system (ossicular coupling) and direct acoustic stimulation of the oval and round windows (acoustic coupling). In the normal ear, middle-ear pressure gain, which is the result of ossicular coupling, is frequency-dependent and smaller than generally believed. Acoustic coupling is negligibly small in normal ears, but can play a significant role in some diseased and reconstructed ears.

(2) The severity of conductive hearing loss due to middle-ear disease or after tympanoplasty surgery can be predicted by the degree to which ossicular coupling, acoustic coupling, and stapes-cochlear input impedance are compromised. Such analyses are used to explain the air-bone gaps associated with lesions such as ossicular interruption, ossicular fixation and tympanic membrane perforation.

(3) With type IV and V tympanoplasty, hearing is determined solely by acoustic coupling. A quantitative analysis of structure-function relationships can both explain the wide range of observed postoperative hearing results and suggest surgical guidelines in order to optimize the post-operative results.

(4) In tympanoplasty types I, II and III, the hearing result depends on the efficacy of the reconstructed tympanic membrane, the efficacy of the reconstructed ossicular chain and adequacy of middle-ear aeration. Currently, our knowledge of the mechanics of these three factors is incomplete. The mechanics of mastoidectomy and stapedectomy are also discussed.

Type
Toynbee Memorial Lecture 1997
Copyright
Copyright © JLO (1984) Limited 1998

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Footnotes

Presented at the Royal Society of Medicine, London, November 7, 1997.

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