Middle ear pathology call affect the ear-canal sound pressure generated byaudiologic earphones

Objective: To determine how the ear-canal sound pressures generated by earp hones differ between normal and pathologic middle ears. Design: Measurements of ear-canal sound pressures generated by the Etymtic Research ER-3A insert earphone in normal ears (N = 12) were compared with t he pressures generated in abnormal ears with mastoidectomy bowls (N = 15), tympanostomy tubes (N = 5), and tympanic-membrane perforations (N = 5), Sim ilar measurements were made with the Telephonics TDH-49 supra-aural earphon e in normal ears (N = 10) and abnormal ears with mastoidectomy bowls (N = 1 0), tympanostomy tubes (N = 4), and tympanic-membrane perforations (N = 5), Results: With the insert earphone, the sound pressures generated in the mas toid-bowl ears were all smaller than the pressures generated in normal ears ; from 250 to 1000 Hz the difference in pressure level was nearly frequency independent and ranged from -3 to -15 dB; from 1000 to 4000 Hz the reducti on in level increased with frequency and ranged from -5 dB to -35 dB, In th e ears with tympanostomy tubes and perforations the sound pressures were al ways smaller than in normal ears at frequencies below 1000 Hz; the largest differences occurred below 500 Hz and ranged from -5 to -25 dB, With the supra-aural earphone, the sound pressures in ears with the three p athologic conditions were more variable than those with the insert earphone . Generally, sound pressures in the ears with mastoid bowls were lower than those in normal ears for frequencies below about 500 Hz; above about 500 H z the pressures showed sharp minima and maxima that were not seen in the no rmal ears. The ears with tympanostomy tubes and tympanic-membrane perforati ons also showed reduced ear-canal pressures at the lower frequencies, but a t higher frequencies these ear-canal pressures were generally similar to th e pressures measured in the normal ears. Conclusions: When the middle ear is not normal, ear-canal sound pressures c an differ by up to 35 dB from the normal-ear value. Because the pressure le vel generally is decreased in the pathologic conditions that were studied, the measured hearing loss would exaggerate substantially the actual loss in ear sensitivity. The variations depend on the earphone, the middle ear pat hology, and frequency. Uncontrolled variations in ear-canal pressure, wheth er caused by a poor earphone-to-ear connection or by abnormal middle ear im pedance, could be corrected with audiometers that measure sound pressures d uring hearing tests.