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ENT
Middle Ear Mechanics in Otology
Built from Haynes-Glasscock-Shambaugh Surgery of the Ear, Seventh Edition
What’s inside
7 sections · 91 slides
Overview
- Scope of middle ear mechanics
- External ear canal contribution to sound pressure
Acoustics and vibration
- The decibel as a logarithmic ratio
- Non-linear behaviour of the decibel scale
- Clinical significance of small decibel changes
- Vibration in a mass-spring system
- Mass-spring vibration and its sine wave
- Amplitude, frequency and phase of a sinusoid
- Interference, vibration modes and rigid body motion
- Impedance: reactance and resistance
- Frequency dependence of mass and stiffness reactance
- Mass and stiffness reactance against frequency
- Resonance frequency
- Stiffness-dominated and mass-dominated systems
- Velocity-pressure phase as an index of dominance
- Limits of phase interpretation
- Force transmission through a compliance
- Clinical correlates of a compliant coupling
- Impedance dominance across the frequency range
The middle ear as a transformer
- From simple models to the real middle ear
- The middle ear transfer function
- Stapes velocity relative to ear canal pressure
- Surgical implication of low frequency stiffness control
- Multimodal vibration of flexible structures
- Vibration modes of a string and of the human eardrum
- Consequences of tympanic membrane break-up
- The impedance matching problem
- The impedance matching chain
- The area ratio lever
- Area ratio lever from eardrum to stapes footplate
- Ossicular and catenary levers
- Human area ratio and predicted pressure gain
- Frequency dependence of the effective lever ratio
- Middle ear pressure gain measured at the footplate
- Pressure gain measured in the vestibule
- Vestibular pressure gain relative to ear canal pressure
- The vibrating tympanic membrane as the engine of matching
Window pressure difference and pathology
- Oval and round window pressure difference
- Window pressures driving the basilar membrane
- Ossicular coupling and its dominance
- Hearing loss after total loss of the middle ear
- Acoustic coupling and round window shielding
- Requirements and limits of acoustic coupling
- Tympanic membrane perforation: area loss is not the mechanism
- The perforation as a pressure shunt
- Mechanism of hearing loss in tympanic membrane perforation
- Determinants of hearing loss in perforation
- Grafting: baffle effect and membrane loading
- Middle ear air volume and impedance
- Mechanisms of hearing loss from middle ear fluid
Ossicular reconstruction
- Problems with existing reconstruction terminology
- Basis of the reconstruction classification
- Two strategies for middle ear reconstruction
- Classification of middle ear hearing reconstruction techniques
- Classification of middle ear hearing reconstruction techniques
- Classification of middle ear hearing reconstruction techniques (continued)
- Classification of middle ear hearing reconstruction techniques (continued)
- Classification of middle ear hearing reconstruction techniques
- Vector of reconstruction: translation versus rotation
- Angulated versus in-line prosthesis on the stapes head
- Cosine rule and constraint of rocking
- Prosthesis rigidity
- Prosthesis mass
- Tension
- Prosthesis head size
- Prosthesis variables affecting hearing outcome
- Reconstruction to the stapes head versus the footplate
- Malleus reconstructions and angulation
- Reconstruction to the tympanic membrane versus the malleus
- Placement of the prosthesis on the footplate
Stapedotomy
- Mechanical starting point in stapedotomy
- Progression of conductive loss in otosclerosis
- Pressure gain versus volume velocity
- Piston diameter: model and temporal bone data
- Clinical evidence on piston diameter
Conclusions
- Non-linear interaction of multiple small losses
- Compromise between hearing efficacy and stability
- Planning for the eventual state of the middle ear
- References
- References (continued)
- References (continued)
- References (continued)
- References (continued)
- Haynes-Glasscock-Shambaugh Surgery of the Ear, Seventh Edition
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