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

Abstract

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.

Key Words::

• Hearing-aid safety
• threshold shift
• hearing-aid prescription
• children
• NAL-NL2
• DSLm[i/o]

Acknowledgements

The project described was supported by Award Number R01DC008080 from the National Institute On Deafness And Other Communication Disorders. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute On Deafness And Other Communication Disorders or the National Institutes of Health. We also acknowledge the financial support of the Commonwealth of Australia through the establishment of the HEARing CRC and the Cooperative Research Centres Program. This manuscript was supported by a Career Development Award-1 to the second author by the USA Department of Veterans Affairs Rehabilitation Research and Development Office. Disclaimer: The opinions expressed in this article are those of the authors and do not necessarily represent the official position of the U.S. Department of Veterans Affairs or the United States government or Australian government.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.