Fausti Sa

A Prospective Study of High-Frequency Auditory Function in Patients Receiving Oral Neomycin

Orally administered, neomycin is reported to cause ototoxicity rarely. Most reports on hearing loss due to oral neomycin have been case studies. One prospective study of a pediatric sample demonstrated a significant loss of hearing in the frequency range of 2 to 8 kHz in 9 of 17 children. To our knowledge there are no published prospective studies on this type with adult samples and therefore little is known of the true incidence or nature of ototoxicity from oral neomycin. This prospective study presents the results of long-term use of oral neomycin in 30 adult subjects. Hearing sensitivity was serially monitored in the frequency range 250-20,000 Hz. Two of the 30 subjects subsequently revealed ototoxicity. Thus the results of this investigation suggest that clinical use of oral neomycin implies relatively little risk of ototoxicity.

Effects of steady-state noise upon human hearing sensitivity from 8000 to 20 000 Hz

Young adults with steady-state noise exposure histories were evaluated with a high frequency (8--20 kHz) test system. High frequency hearing threshold shifts were most prominent from 12-20 kHz and were often highly individual-specific. Good standard range (.25-8 kHz) sensitivity does not assure good hearing above this region. Mild through severe threshold changes may be present. High frequency testing expands monitoring audiometry and has potential special application to hearing conservation programs.

Effects of Contralateral Masking on High-Frequency Bone-Conduction Thresholds

The present study reports effects of contralateral masking on high-frequency threshold force levels in 28 normal-hearing subjects. High-frequency air- and bone-conduction thresholds were measured with a high-frequency auditory evaluation system using matched Koss HV/1A earphones and the Pracitronic KH 70/5 bone vibrator. Measurements were made for both unmasked and masked bone-conduction thresholds at the ipsilateral mastoid of the better ear. The contralateral masked condition was performed using 30-dB-SL 400-Hz narrow-band masking noise centered at frequency of test tone. The results demonstrated that masked high-frequency bone-conduction thresholds were 1.5 to 3.4 dB poorer than the unmasked thresholds and that these differences were statistically significant at 0.01 level of confidence except at 12 kHz. ANSI and ISO standards for bone-conduction threshold force levels for frequencies below 8.0 kHz have been established with contralateral masking stimuli. This study supports the need to use effective contralateral masking to eliminate cross hearing in investigations of high-frequency bone-conduction threshold measurements.