| Abstract: | The resonance qualities of the external auditory canal can increase the sound pressure level (SPL) at the tympanic membrane by as much as 20 dB between 2 and 4 kHz. Surgery on the canal, particularly in the form of a modified radical mastoidectomy, might be expected to affect this with resultant implications for speech discrimination. The creation of a modified radical mastoidectomy in 6 temporal bones altered the SPL at the tympanic membrane by +10 dB at 2 kHz, +14 dB at 2.5 kHz, -2 dB at 3 kHz, -12 dB at 3.5 kHz, -20 dB at 4 kHz, -16 dB at 5 kHz and -8 dB at 6 kHz. When this transfer function was applied to 2 subjects, speech discrimination in noise was reduced by 6%. Whether this is of any magnitude compared with the effect of the disease requires prospective studies in individuals undergoing a modified radical mastoidectomy. |
