Progressive hearing loss in children: hearing aids and other factors

Hearing-aid safety: a comparison of estimated threshold shifts for gains recommended by NAL-NL2 and DSL m[i/o] prescriptions for children

OBJECTIVE

To investigate the predicted threshold shift associated with the use of nonlinear hearing aids fitted to the NAL-NL2 or the DSL m[i/o] prescription for children with the same audiograms. For medium and high input levels, we asked: (1) How does predicted asymptotic threshold shifts (ATS) differ according to the choice of prescription? (2) How does predicted ATS vary with hearing level for gains prescribed by the two prescriptions?

DESIGN

A mathematical model consisting of the modified power law combined with equations for predicting temporary threshold shift (Macrae, 1994b) was used to predict ATS.

STUDY SAMPLE

Predicted threshold shift were determined for 57 audiograms at medium and high input levels.

RESULTS

For the 57 audiograms, DSL m[i/o] gains for high input levels were associated with increased risk relative to NAL-NL2. The variation of ATS with hearing level suggests that NAL-NL2 gains became unsafe when hearing loss > 90 dB HL. The gains prescribed by DSL m[i/o] became unsafe when hearing loss > 80 dB HL at a medium input level, and > 70 dB HL at a high input level.

CONCLUSION

There is a risk of damage to hearing for children using nonlinear amplification. Vigilant checking for threshold shift is recommended.

Noise exposure associated with hearing aid use in industry

Although noise may be innocuous in many vocational environments, there is a growing concern in industry that it can reach hazardous levels when amplified by hearing aids. This study examined the daily noise exposures associated with hearing aid use in industry. This was done by both laboratory and site measurements in which hearing aids were coupled to the microphone of an integrating sound level meter or dosimeter. The former method involved the use of recorded railroad and manufacturing noise and a Bruel and Kjaer 4128 Head and Torso simulator. In the latter procedure, a worker wore one of three hearing aids coupled to a dosimeter during 8-hour shifts in a manufacturing plant. Both methods demonstrated that even when amplified by mild-gain hearing aids, noise exposures rose from time-weighted averages near 80 dBA to well above the OSHA maximum of 90 dBA. The OSHA maximum was also exceeded when moderate and high gain instruments were worn in non-occupational listening environments. The results suggest that current OSHA regulations that limit noise exposure in sound field are inappropriate for hearing aid users.

Equivalent Noise Dose Obtained Through Hearing Aids in the Classrooms of Hearing-Impaired Children

A commercial noise dose meter was used to estimate the equivalent noise dose received through high-gain hearing aids worn in a school for deaf children. There were no significant differences among nominal SSPL settings and all SSPL settings produced very high equivalent noise doses, although these are within the parameters of previous projections.

Long-term effects of monaural, binaural and no amplification in subjects with bilateral hearing loss

This study expands upon our earlier work by comparing initial PB scores and audiometric thresholds with results obtained 4-17 years later for subjects with bilateral sensorineural hearing losses who were monaurally aided (n = 48), binaurally aided (n = 19), or unaided (n = 19). Thresholds decreased slightly for all groups, but aided and unaided ears did not differ significantly in this respect, revealing no acoustic trauma effect due to hearing aid use. PB scores decreased significantly only for the unaided ear of the monaurally aided subjects, but not for their aided ear, or for the binaurally aided or unaided groups. These findings suggest an auditory deprivation effect for the unaided ear of those wearing a monaural hearing aid. Changes in PB scores were not correlated with duration between the two test dates. Changes in PB scores were correlated with degree of hearing loss only for the unaided group.