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Middle-ear function with tympanic-membrane perforations. I. Measurements and mechanisms
S E Voss1, J J Rosowski, S N Merchant
1Picker Engineering Program, Smith College, Northampton, Massachusetts 01063, USA. svoss@email.smith.edu
The Journal of the Acoustical Society of America
|September 27, 2001
Summary
Sound transmission through ears with tympanic membrane (TM) perforations causes frequency-dependent hearing loss, primarily due to reduced pressure differences across the TM. Larger perforations lead to greater low-frequency sound transmission loss.
Area of Science:
- Otoacoustic emissions
- Bioacoustics
- Medical engineering
Background:
- Sound transmission through the middle ear with tympanic membrane (TM) perforations is not fully understood.
- Understanding these mechanisms is crucial for diagnosing hearing loss accurately.
Purpose of the Study:
- To quantitatively describe sound transmission through human cadaver ears with experimentally induced TM perforations.
- To identify the primary mechanisms responsible for sound transmission loss in the presence of TM perforations.
Main Methods:
- Measurements of stapes velocity, middle-ear cavity sound pressure, and acoustic impedance at the TM.
- Acoustic stimulation was applied to the TM in human cadaver ears with perforations ranging from 0.5 to 5.0 mm.
Main Results:
- TM perforations cause frequency-dependent sound transmission losses, most significant at low frequencies and increasing with perforation size.
- Reduced pressure difference across the TM is the dominant cause of hearing loss, contributing more than changes in TM-to-ossicular coupling.
- Middle-ear input impedance with perforations increasingly resembles middle-ear cavity impedance as perforation size increases.
Conclusions:
- The effects of TM perforations on sound transmission can be modeled by considering the air-volume flow path from the ear canal to the middle-ear cavity.
- Quantitative data on perforation-induced losses can aid clinicians in differentiating hearing loss caused solely by perforations from other underlying pathologies.