The Effect of Ossicular Chain Disorders on Sound Transmission and Tinnitus Perception using Electrical Model

Human middle ear ensures sound transfer due its ossicular chain, any disorder or abnormalities in this structure leads to a conductive hearing loss (CHL). Tinnitus is a health problem, associated with hearing loss, it remains a devastating symptom. In this work, we present an electrical model of the human middle ear including middle ear cavities (ZMEC), tympanic membrane with ossicular chain (ZTOC), and stapes complex with cochlea load (ZSC). This model is modified to represent more closely the related pathologies affecting the middle ear. We will focus our analysis on ossicular chain disorder by studying the effect of increasing ossicular chain (OC) stiffness and mass in both normal middle ear structures and disconnected stapes superstructure. The change in middle ear structures and impedance allows us to simulate ossicular chain disorder effects and analyze their impact on sound transmission. This analysis allowed us to know if this disorder can eventually cause tinnitus. The results showed that the effect of ossicular chain anomalies can be studied based on frequency response of middle ear transfer function by applying only the principle of mass and stiffness, and demonstrate compared to clinical results the efficiency and simplicity of using the electrical model.

THE EFFECT OF IMPLANTABLE TRANSDUCERS ON MIDDLE EAR TRANSFER FUNCTION — A COMPARATIVE NUMERICAL ANALYSIS

Several types of middle ear implants (MEIs) have been invented as an alternative to conventional hearing aids for the rehabilitation of sensorineural hearing loss. Temporal bone and clinical studies have shown that the implantation of MEIs’ transducers influences middle ear transfer function. But there is little comparative data available about these influences. We conducted comparative studies on the influences of three principal types of MEI transducers in respect to their attachment points on the ossicular chain. To aid the investigation, a human middle ear finite element model was constructed. The model was built based on a complete set of micro-computerized tomography section images of a human ear by reverse engineering technology. The validity of the developed model was verified by comparing the motions obtained by this model with published experimental measurements on human temporal bones. The results show that the eardrum driving transducer (EDT) and the floating mass transducer (FMT) decrease stapes displacement prominently at high frequencies. The greater these transducers’ mass, the smaller is the displacement of the stapes footplate. In contrast, the incus body driving transducer (IBDT) decreases stapes displacement severely at low frequencies, and its adverse effect on residual hearing increases with increasing stiffness of the IBDT’s driving rod.