Hearing loss induced by viscous fluids in the middle ear

Area of Science:

• Otolaryngology
• Auditory Physiology
• Biomedical Engineering

Background:

• Otitis media with effusion (OME) is a common condition causing conductive hearing loss.
• The physical properties of middle ear effusions, such as viscosity, are hypothesized to influence hearing impairment.

Purpose of the Study:

• To investigate the relationship between the viscosity of middle ear effusions and the degree of conductive hearing loss.
• To determine if effusion viscosity affects middle ear mechanics.

Main Methods:

• Dextran solutions of low (7.5 cP) and high (2.2 P) viscosity were instilled into the middle ear of guinea pigs.
• An open bulla preparation was used for direct instillation.
• Cochlear microphonic potentials were measured to assess conductive hearing loss.

Main Results:

• Both low and high viscosity dextran solutions induced comparable conductive hearing loss.
• The hearing loss was frequency-dependent, with greater loss at lower frequencies (30 dB at 500 Hz) and minimal loss at higher frequencies (near zero at 4000 Hz).

Conclusions:

• The viscosity of a middle ear effusion does not significantly alter the degree of conductive hearing loss.
• Conductive hearing loss in otitis media with effusion is primarily determined by the effect of the effusion on middle ear compliance, not its viscosity.