RP310 - Using Body Height to Predict Adult RECD Measurement

Abstract: For 20 years, survey research has repeatedly shown that approximately two-thirds of audiologists program hearing aid amplification using “average” real-ear-to-coupler difference (RECD) values (based on chronological age), rather than directly measuring the patient’s RECD. Similarly, research on hearing aids programmed with “average” RECD values has repeatedly shown errors as large as 20 dB, resulting in under-amplification (poor audibility) or over-amplification (noise-induced hearing loss). In this ongoing 5-year longitudinal study, we test the hypothesis that the accuracy of “average” RECD values can be improved if they are normed using body height instead of chronological age.

Summary:

Background: The clinical gold standard for hearing aid programming includes the direct (not average) measurement of the adult patient’s real-ear-to-coupler difference (RECD), such that the patient’s natural, external-ear amplification is accounted for in the prescriptive amplification targets. Incorporating a patient’s measured RECD into hearing aid programming is known to improve hearing aid audibility, safety, and product satisfaction. However, the field of audiology faces a difficult reality in that - despite 25 years of gold standard recommendations to directly measure the patient’s RECD (ASHA, 1998) - one survey revealed that only 34% of U.S. audiologists actually do so (Beck, 2017), even lower than the 45% revealed by an ASHA survey (1991), 40% by Mueller (2005), and 40% by Mueller and Picou (2010). While the list of reasons audiologists may not use direct RECD measures in their practice is extensive and hotly debated, the reality is that the majority of audiologists quickly apply average-RECD adult values to the amplification prescription in the hearing aid. Average-RECD values are normed by chronological age, and can deviate as much as 20 dB from the patient’s true RECD (McCreery et al., 2015). This can lead to overamplification (noise-induced hearing loss) or under-amplification (poor hearing-aid audibility). Taken together, future efforts to improve hearing-aid safety and audibility would be best spent improving the current, average-RECD adult predictions used in automated hearing aid programming. An improved RECD estimate using a quick, low-tech, and cost-free “proxy” could not only be used in audiology offices, but also in over-the-counter hearing aids.

Rationale: The major error in the “one-size-fits-all” approach to the present-day “average adult RECD” values is that a very short/small adult patient and a very tall/large adult patient - with very different skull and ear sizes - would be fitted with the same “adult average” RECD prediction in their hearing aids. Specific

Aim: We hypothesized that average adult RECD predictions based on body height would yield significant improvement over the current “average adult” RECD prediction, which is a “one size fits all” RECD prescription used for every patient over the age of 15 years.

Design: From 271 adult participants, we collected data including chronological age, body height, pinna size, ear canal volume, and craniometry measurements in the following body height groups: < 5’3, 5’4-5’6, 5’7-5’9, 5’10-6’0, >6’1.

Results: Ear canal volume and body height are correlated with significant improvement in adult RECD prediction compared to the current “average-adult” RECD norm that is universally applied.

Discussion: The most precise hearing aid fitting would include direct measurement of the adult patient’s RECD. In the event that an audiologist does not or cannot directly measure RECD, applying a RECD-estimate based on the adult patient’s body height vs. the standard one-size-fits-all adult RECD average estimate may significantly improve the precision of the fitting.

Funding Acknowledgement: This project is part of a 5-yr ongoing study supported by the U.S. National Institutes of Health (1R01DC020699-01A1).

Brief Summary of Clinical Takeaways: The accuracy of the “one-size-fits-all” average-adult RECD values could be improved by norming RECD using body height. A proxy measurement, such as body height, is equally quick, accessible, and cost-free as the proxy measurement of chronological age.

Assumptions: This intermediate-level research presentation requires attendees to have a foundational knowledge of prescription targets and the influence of individually variable external-ear acoustics.