Effects of Tympanomeatal Blunting on Sound Transfer Function

Abstract

Objective. (1) To measure the peak-to-peak displacement of the round window membrane (RWM) prior to blunting procedure. (2) To evaluate the impact of blunting the anterior tympanomeatal angle (ATA) on middle ear sound transfer function.Study Design. Basic science study.Setting. Cadaveric temporal bone research laboratory.Subjects and Methods. Six fresh human temporal bones were prepared using a mastoidectomy and facial recess approach. Baseline RWM peak-to-peak displacements were obtained by single-point laser Doppler vibrometry (LDV) at 90-dB sound pressure level over a spectrum of 250 to 8000 Hz. Temporalis muscle was harvested and then fashioned into a graft for each temporal bone, mimicking ATA blunting. RWM displacement responses with the blunted ATA were measured using the LDV to judge the impact on middle ear transfer function.Results. For each of the 6 temporal bones, the average displacement decreased across all sound frequencies with the ATA blunting when compared with baseline (no blunting). Baseline velocity measurements for all sound signals averaged 4.5 × 10−3± 1.892 × 10−3(mean ± SEM) mm/s, while measurements averaged 2.2 ± 6.62 × 10−4mm/s with blunting of the ATA ( P < .001). This amounted to a 52% decrease in velocity of the RWM following blunting of the ATA.Conclusion. Blunting of the ATA decreases the sound transfer function of the tympanic membrane and middle ear. Prevention of blunting at the ATA during tympanoplasty should be emphasized.