Round Window Occlusion Affects Bone Conduction in Cadaver Heads

Mechanical Energy Dissipation Through the Ossicular Chain and Inner Ear Using Laser Doppler Vibrometer Measurement of Round Window Velocity

HYPOTHESIS

Round window velocity measurements should correlate closely with vibration measurements taken at proximal points along an intact chain over a set frequency range. These round window vibration measurements should be similar to the vibration measurements taken of the ossicles if mechanical energy is conserved through the vestibular organ.

BACKGROUND

To date there has not been a study which compares vibratory velocity measurements through an intact ossicular chain to the level of the round window. This study attempted to quantify the degree of mechanical energy transmission and suspected dissipation through the ossicular chain and vestibular organ through incus, stapes, and round window velocity measurements in response to sound stimulus.

METHODS

Five thawed human temporal bones with intact ossicular chain and tympanic membrane underwent complete mastoidectomy and a facial recess approach. A laser Doppler vibrometer (LDV) was mounted on the operating microscope to measure vibration of incus, stapes, and round window in response to a sound stimulus within the external auditory canal. Sound stimulus frequencies ranged from 0.5 to 4 kHz at 90 dB SPL.

RESULTS

Vibration velocity was measured across the frequency range for each incus, stapes, and round window. Vibration velocity curves obtained over the frequency range were similar for each of the bones with a notable resonant frequency around 2 kHz. The incus and stapes curve amplitudes were nearly identical with similar maximum velocity and frequency at which this maximal velocity was noted. Round window vibration velocity demonstrated a unique peak velocity. Transfer function measurements of the stapes and round window demonstrated markedly similar curves. The variation in velocity between temporal bones in response to the standardized stimulus was more dramatic in the round window measurements when compared with the incus and stapes.

CONCLUSIONS

This study supports the concept that round window transfer function is equivalent to stapes footplate transfer function when subjected to the same acoustic stimuli. This study also demonstrates that the round window is a much more difficult target to measure when using LDV technology and improvements in experimental design are required to better understand round window physiology in relation to transfer of acoustic vibratory stimulus transferred throughout the middle ear. A complete and thorough understanding of the biophysical properties of the middle and inner ear are critical for optimal ossiculoplasty outcomes and the development of future ossicular prosthetics.

Effect of Oval Window Blockage on Bone Conduction in Cadaver Heads

OBJECTIVE

This study aimed to explore the feasibility of medical adhesive in the molding of oval window (OW) blockage in cadaver heads and to study the effect on bone conduction (BC).

METHODS

Four cadaver heads were selected to establish OW blockage model. The daub type of medical adhesive was used to immobilize OW. The vibration properties of the round window membrane (VRWM) in response to the acoustic stimulation, and the vibration properties of the round window membrane and cochlear promontory (VCP) in response to the BC transducer B-71 stimulation were assessed by laser Doppler vibrometer in both pre-OW blockage and post-OW blockage.

RESULTS

After blocking the oval window, the mean values of the sound-induced velocities amplitude responses of the round window membrane by air conduction were decreased significantly beyond 30 dB in all measured frequencies (p < 0.05). The round window membrane relative velocity (VRWM/VCP) shows a decrease of about 1 dB at 1 and 3 kHz frequencies and a slight increase of around 0.5 dB from 4 to 8 kHz frequencies in post-OW blockage. However, it should also be noted that the VRWM/VCP is a significant decrease of 1.2 dB at 3 kHz in post-OW blockage compared with pre-OW blockage (p < 0.05).

CONCLUSION

Medical adhesive was available for the immobilization of oval window. In cadaver heads, the effect of OW blockage on the BC was the notching at 3 kHz.

Bone conduction hearing in the blockage of oval and/or round windows in cats

BACKGROUND

Simple or non-syndromic types of oval window (OW) or round window (RW) atresia are relatively rare in clinical. Few studies have assessed bone conduction (BC) hearing in OW or RW atresia patients, with some reporting that BC hearing lies within the normal range, whereas others observing impaired BC hearing.

AIMS/OBJECTIVES

This study explored the effect of blocking the OW and RW during BC in cat models.

MATERIAL AND METHODS

Twenty-four cats were randomly divided into three immobilization groups (OW blockage, RW blockage, and OW + RW blockage) and control group. Each immobilization group also had the initial control state before blockage. Medical adhesive and ear mould glue were used to immobilise the stapes footplate and RW, respectively. Comparisons were made of the auditory brainstem response (ABR) thresholds before and after immobilization for the three immobilization groups during three different stimuli [air conduction (AC) click, BC click, and BC pure tones].

RESULTS

The AC click thresholds increased after immobilisation in three experimental groups compared to the control group (p < .05). The AC click thresholds increased compared to their initial control state after all three immobilization groups (p < .05). With an increase in frequency from 2 to 8 kHz, there was a general decrease in the difference between pre- and post-immobilization BC hearing thresholds in all three immobilization groups. The BC click threshold and BC tone thresholds at 2-4 kHz in both OW blockage and OW + RW blockage groups exceeded those in RW blockage group (p < .05).

CONCLUSIONS AND SIGNIFICANCE

The use of medical adhesive and ear mould glue for the blockages of OW and RW, respectively in cats was feasible. The effect of blocking the OW and RW in BC hearing was larger at low frequencies than high frequencies between 2 and 8 kHz. OW blockage had a greater effect than RW blockage on BC hearing at 2-4 kHz range.