Objectives of middle-ear research

© Joe Kohl

1. Motivation

• Hearing loss is common
• Hearing loss is serious
• Diagnosis is often late
• Therapy is often unsatisfactory

ENT = Ear, Nose & Throat = Oto(rhino)laryngology

2. Research objectives

• Develop a quantitative understanding of the mechanics of the ear
  • outer ear
  • middle ear
  • inner ear
  • auditory nerve
  • brain
• Address clinical issues related to hearing loss

3. Hearing loss

Hearing Health Foundation

3.1 Adults

• Hearing loss is most common physical disability
• Especially common in the elderly
• A lot is noise-induced; ‘temporary’ threshold shift
• ‘Hidden’ hearing loss
• If untreated
  • ↑ unemployment
  • ↑ social isolation
  • ↑ depression
  • ↑ dementia
• Need for screening

3.2 Newborns

 

• Hearing loss is one of the most frequent birth defects
  • A few per thousand
• If untreated
  • ↓ language development
  • ↓ psychosocial development
  • ↓ academic achievement

• Universal newborn hearing screening (UNHS)
  → Early hearing detection and intervention (EHDI)
  • Screening within first month (days) of life
  • Diagnosis within first 3 (or 2) months
  • Treatment within first 6 (or 3) months

Joint Committee on Infant Hearing. Year 2019 position statement: principles and guidelines for early hearing detection and intervention programs. J Early Hear Detect Interv. 2019;4(2):1-44. doi:10.15142/FPTK-B748

4. Screening and diagnostic techniques

4.1 Audiogram

• Pure-tone threshold
  • Intensity adjusted manually by audiologist
    or automatically (Békésy)
  • Behavioural
• Speech in noise
  • Behavioural
• Stapedius reflex
  • Physiological

Probst R, Grevers G & Iro H (2006) Basic otolaryngology: A step-by-step learning guide, Thieme, New York, NY

4.2 Auditory brainstem response

• Sources in cochlea, auditory nerve and brainstem
• Measured using surface electrodes
• Physiological

Threshold determination requires judgement about when waves disappear

• subjective
• can be automated for screening

Olubunmi V. Akinpelu, McGill University, 2013

Diagram of OAE measurement

4.3 Otoacoustic emissions

• David Kemp, 1978
• Due to non-linearities in cochlea, mainly in outer hair cells
• Spontaneous
• Evoked
  • transient-evoked (TEOAE’s)
  • distortion-product (DPOAE’s)
  • stimulus-frequency (SFOAE’s)
    • with & without a suppressor tone
• Physiological

Comparison of distortion-product amplitude to noise level

• subjective
• can be automated for screening

4.3.1 Limitations

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

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

Large numbers of false positives

Due to conditions in middle ear

4.4 Acoustical input admittance

Input admittance of electrical circuit = I/V

• Electrical, mechanical and acoustical equivalents

Diagram of admittance measurement

• Possible use for differential diagnosis
• Sound stimulus
  • single frequency (e.g., 226 Hz)
  • multiple frequencies (e.g., 226, 678, 1000 Hz)
  • wideband (e.g., chirp, up to 8 kHz)
• Ear canal + middle ear
• Reflectance
  • derived from admittance
  • reduce dependence on probe position?

After Cull (1989): The Sourcebook of medical illustration, Parthenon, Carnforth, xxiii+481 pp.

4.5 Tympanometry

Diagram of a tympanometer

Addition of static pressures

• correction for canal volume?
• additional information

but ...

After Cull (1989): The Sourcebook of medical illustration, Parthenon, Carnforth, xxiii+481 pp.

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

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

In this example

• right ear was normal
• left ear contained liquid

5. Treatment

5.1 Passive prostheses

Repair or replacement of the eardrum and ossicles

• A frequent surgical procedure (thousands/year in Canada)
• Many surgical options

After Cull (1989): The Sourcebook of medical illustration, Parthenon, Carnforth, xxiii+481 pp.

Smith + Nephew catalogue

Many different designs

• from a single manufacturer
• mostly named after surgeons

Nitinol prosthesis

www.kurzmed.com

Potential technology is increasingly sophisticated:

• new materials
  e.g., nickel-titanium: laser-induced heat-activated shape memory
• laser soldering & welding
  e.g., protein solder
• micro-scale solid lithography
  e.g., titanium prosthesis
• etc.

but

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

Little systematic analysis of mechanical performance

E.g.,
Slater PW, Rizer FM, Schuring AG & Lippy WH (1997): Practical use of total and partial ossicular replacement prostheses in ossiculoplasty. Laryngoscope 107: 1193-1198
Stupp CH, Dalchow C, Grun D, Stupp HF & Wustrow J (1999): Titan-Prothesen im Mittelohr. 3-Jahres-Erfahrungsbericht. Laryngo- Rhino- Otologie 78(6): 299-303

5.2 Passive external devices

F. C. Rein, ca. 1810

©2005-2009 Washington University School of Medicine, Bernard Becker Medical Library

• Pressure gain
• Directionality
• Bypassing middle ear

See also The History of Hearing Aids (IEEE, 2013)

5.3 Hearing aids and implants

1940’s ©2005-2009 Washington University School of Medicine, Bernard Becker Medical Library

Design and evaluation of active devices

• acoustical hearing aids
• bone-anchored hearing aids
• active middle-ear implants
  • floating-mass transducer (Symphonix ▶ MED-EL)
  • piezoelectric (Otologics)
  • piezoelectric (St-Croix ▶ Envoy)
  • ‘Earlens’
  • opto-electromagnetic

See also The History of Hearing Aids (IEEE, 2013)

6. Inner ear

Characterization of stimulus to inner 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

After Cull (1989): The Sourcebook of medical illustration, Parthenon, Carnforth, xxiii+481 pp.

7. Teaching

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
  • Visible Ear Simulator (Denmark) (video)

BMDE-501 Modelling middle-ear mechanics