The influence of tympanic membrane defects on the transfer function of the middle ear

Introduction:

Injury or inflammation of the middle ear often results in persistent tympanic membrane defects. If there is a discrepancy between defect size and hearing loss, a different pathology might be present. In this study we evaluated the effects of tympanic membrane defect size and localization on the middle ear sound transmission properties.

Methods:

The middle ear transfer functions of tympanic membrane defects with a diameter of 1 mm and upwards were evaluated on six non-fixated human petrous models. Likewise, the defect localization was evaluated. The sound-induced velocity of the stapes footplate was measured using single point laser-vibrometry and the stimulus intensity recorded, which allowed for the calculation of the transfer function.

Results:

The middle ear transfer function showed frequency and defect size dependent losses at all defect localizations. Starting at low frequencies, the reduction expanded with increased perforation size to higher frequencies. With total tympanic membrane defect, a relative decrease in transfer function of up to 30 dB can be observed. In direct comparison, posterior defects affect the transmission properties to a greater extent.

Conclusions:

The size and localization of tympanic membrane defects determine the middle ear transfer function. This helps to distinguish isolated tympanic defects from other pathologies in clinical practice.

Publication History

Publication Date:
23 April 2019 (online)