Objectives of middle-ear research

Ear, nose and throat cartoon

W. Robert J. Funnell
Dept. BioMedical Engineering, McGill University

1. Motivation

Hearing loss is the most common physical disability.
Diagnostic and corrective measures are often unsatisfactory.

2. Objectives

Plaster model of ear

Develop a quantitative understanding of the mechanics of the middle ear
Address clinical issues related to hearing loss

3. Diagnosis

Newborn

Noninvasive diagnosis, especially for screening of newborns

Hearing loss is the most frequent birth defect.
Hearing screening should be done within first month of life.
Diagnosis of type of loss should be done within first 3 months of life.

Current screening techniques:

OAE and ABR can detect hearing loss,
but they cannot distinguish between

conductive hearing loss (often transient) and
permanent sensorineural hearing loss.

Infant tympanograms

Tympanograms from 156-day-old infant for three frequencies. Right ear (top) was normal, left ear (bottom) had middle-ear effusions and failed hearing screening test.
Dark lines = susceptance, light lines = conductance.
Units for horizontal axes (static pressure) = daPa, vertical axes = mmho.

Possibility of differential diagnosis by

acoustical input admittance with static pressures (tympanometry)
wide-band reflectance

but ...

Newborn tympanogram is different from adult
Limited information in low-frequency measurements
Multi-frequency and wideband measurements are poorly understood

4. Treatment

4.1 Passive prostheses

Three types of prosthesis

Repair or replacement of the eardrum and ossicles is a frequent surgical procedure (thousands/year in Canada).
Many surgical options

Smith + Nephew prostheses

Smith + Nephew catalogue

Many different designs

Artificial stapes

Holger Wirtz, Fraunhofer Institute

Potential technology is increasingly sophisticated:
- new materials, e.g., nickel-titanium shape-memory alloys
- laser soldering & welding
- micro-scale solid lithography
- etc.

Knox G (2005): Nitinol shape-memory malleus-to-footplate prosthesis. 28th ARO Midwinter Mtg
Park MS & Min HK (2000): Laser soldering and welding for ossicular reconstruction: an in vitro test. Otolaryngol Head & Neck Surg 122(6): 803-807

but

Results are variable, with surprisingly good performance of some ears after surgery and surprisingly poor performance of others.
Closure of air-bone gap to within 20 dB in 70-80% of cases is considered to be good.

There has been little systematic analysis of mechanical performance.

E.g., Slater et al., 1997; Stupp et al., 1999

4.2 Passive external devices

Š2005-2009 Washington University School of Medicine, Bernard Becker Medical Library

4.3 Hearing aids and implants

Š2005-2009 Washington University School of Medicine, Bernard Becker Medical Library

Design and evaluation of active devices

5. Inner ear

5.1 Characterization of stimulus to inner ear

Diagram of ear

For interpretation of cochlear experiments.

Often, the input to the cochlea is characterized by measuring

sound pressure in front of the eardrum, or
the vibration amplitude of one point on the eardrum.

5.2 Otoacoustic emissions

Active nonlinear processes in the cochlea can generate detectable pressures in the external ear canal.

These pressure signals are useful diagnostically.

Diagnostic applications involve both forward and reverse transmission through the middle ear.

6. Teaching

Inner and middle ear

Davis3d project

Teaching of middle-ear anatomy and surgical techniques:

complex 3-D anatomy
delicate microscopic surgery

Can teach using

interactive 3-D models
surgical simulators

BMDE-501 Modelling middle-ear mechanics

Last modified: 2011-11-05 15:25:36