What is the resonance frequency of a stiff tympanic (eardrum) membrane?

Resonance Frequency in Stiff Tympanic Membrane

The resonance frequency of a stiff tympanic membrane typically ranges from 226 Hz to 1,000 Hz, with 226 Hz being the standard frequency used for tympanometric assessment in adults and children over 6 months of age, while 1,000 Hz is more appropriate for infants under 6 months due to their naturally stiffer tympanic membranes. 1

Tympanic Membrane Mechanics and Resonance

• Tympanometry, which measures tympanic membrane mobility and middle ear function, typically uses a 226 Hz probe tone as the standard frequency for assessment in adults and children over 6 months of age 1
• For infants younger than 6 months, a higher frequency probe tone of 1,000 Hz is recommended as the 226 Hz tone is insensitive to middle ear effusion due to the naturally stiffer tympanic membrane characteristics in this age group 1
• The stiffness of the tympanic membrane directly affects its resonance properties and consequently the middle ear transfer function 2

Factors Affecting Tympanic Membrane Resonance

• The mechanical properties of the tympanic membrane, particularly its stiffness, significantly influence sound transmission and resonance frequency 3
• Storage modulus (stiffness component) of the tympanic membrane increases with frequency, ranging from approximately 15.1 MPa at 1 Hz to 27.6 MPa at 3800 Hz, indicating frequency-dependent properties 2
• Pathological stiffening of the tympanic membrane (as seen in conditions like tympanosclerosis or otitis media) can alter the normal resonance patterns and affect hearing 1

Clinical Assessment of Tympanic Membrane Stiffness

• Pneumatic otoscopy evaluates tympanic membrane mobility, with distinctly impaired mobility being highly predictive of middle ear effusion and increased stiffness 1
• Tympanometry provides objective measurement of tympanic membrane mobility by creating graphs showing how energy is reflected back while canal pressure varies from negative to positive 1
• Type A tympanograms (high-peaked) indicate normal tympanic membrane mobility, while Type B (flat) suggests increased stiffness due to middle ear effusion or perforation 1

Implications of Altered Resonance in Stiff Tympanic Membranes

• Increased stiffness of the tympanic membrane can lead to conductive hearing loss by impeding the transmission of sound energy to the middle ear ossicles 1
• The acoustic input impedance of the stapes and cochlea (ZSC) is affected by tympanic membrane stiffness, with stiffer membranes showing resistance-dominated behavior between 1-4 kHz 4
• In cases of tympanic membrane perforation, abnormal external ear resonance patterns emerge with 2-3 prominent peaks separated by valleys of reduced gain, and reduced responses in the lower frequency region (0.3-2 kHz) 5

Biomechanical Modeling Considerations

• Finite element models show that the dynamic behavior of the tympanic membrane is highly sensitive to Young's modulus, thickness, and the presence of prestrain 6
• Different combinations of elastic properties and prestrain can provide similar acoustic-mechanical responses, adding complexity to the determination of exact resonance frequency in stiff membranes 6
• The frequency-temperature superposition method has been used to study dynamic properties of human tympanic membrane, showing that both storage and loss moduli increase with frequency 2

Human tympanic membrane stiffness varies significantly between individuals, with inter-ear variations of up to a factor of 4 (12 dB), which may explain clinical variations in hearing performance with similar pathologies 4.