Forward and Reverse Middle Ear Transmission in Gerbil with a Normal or Spontaneously Healed Tympanic Membrane

Area of Science:

• Otoacoustic Emissions
• Auditory Physiology
• Biomedical Engineering

Background:

• Spontaneously healed tympanic membrane (TM) perforations exhibit structural changes, leading to conductive hearing loss (CHL).
• Understanding middle ear (ME) sound transmission alterations in pathological conditions is crucial for diagnosing hearing impairments.

Purpose of the Study:

• To investigate the functional consequences of healed TM perforations on ME sound transmission in a gerbil model.
• To analyze forward and reverse ME sound transmission asymmetries and their impact on hearing.

Main Methods:

• A gerbil model with a 50% pars tensa TM perforation was created and allowed to heal spontaneously for up to 4 weeks.
• ME sound transmission was measured in forward and reverse directions using two-tone stimulation at the TM, umbo, and scala vestibuli (SV).

Main Results:

• Forward ME pressure gain decreased in a frequency-dependent manner, with greater loss at high frequencies, primarily due to inefficient TM-umbo coupling.
• Reverse ME transmission variations were less pronounced compared to forward transmission.
• Altered ME transmission affected distortion product otoacoustic emissions (DPOAEs) by reducing stimulus levels and DP transfer efficiency.

Conclusions:

• Healed TM perforations significantly alter ME sound transmission, explaining high-frequency CHL in clinical cases.
• DPOAEs serve as a valuable tool for assessing both cochlear and middle ear health in the presence of TM abnormalities.