Effect of loading of the central part of the tympanic membrane on pure tone audiometry

Abstract

This study was conducted to determine the effects of loading of the central part of the tympanic membrane by different weights on pure tone audiometry of healthy ears. Sixty patients with normal otoscopic view, normal pure tone audiometry and wide external auditory canal to allow direct and endoscopic visualization of TM, but without any history of ear surgeries, were selected and divided equally and randomly into two groups. Loading of the central part of the TM was carried out using weights ranging from [(1 λ) 13.6 mg] to [(40 λ) 544 mg]; (λ) is a symbol for the weight of 1 microliter of mercury. The study was carried out in two steps assisted by direct oto-endoscopy, and pure tone audiometry was used to measure the effects of loading on both air and bone conduction hearing. Air conduction hearing thresholds increased in a statistically significant pattern at low frequencies, 500 Hz, 1000 Hz and 2000 Hz, when the TM was loaded by 340 mg (25 λ). The maximal effect was recorded at 544 mg (40 λ), which affected air conduction hearing at all tested frequencies (500 Hz, 1000 Hz, 2000 Hz and 4000 Hz). However, no statistically significant effect was detected on bone conduction hearing thresholds throughout the study. In conclusion, loading of the tympanic membrane by different masses affects the air conduction hearing threshold by only 340 mg (25 λ), which is very large in comparison to the mass of ossicles, without any significant effects on bone conduction hearing.