Question
In many clinical situations, audiometry is conducted using foam eartips coupled to insert earphones, and an RECD is required for the hearing aid fitting. The RECD is then measured using the child's personal earmold. What are the implications of this strategy?
Answer
RECDs are used in several stages of the hearing aid fitting process. One is to convert audiometry measured in dBHL or dBeHL to dBSPL at the eardrum. This provides a more accurate description of hearing thresholds, and the values are used to calculate the prescription in some formulae (i.e. DSL m[i/o] v5). Another use is in the verification stage. For the pediatric population, many times it is not feasible to conduct actual real-ear measures of the hearing instrument. With the RECD, clinicians can obtain a prediction of real-ear hearing instrument performance based on 2cc coupler measurements. Therefore, it would be ideal to apply RECD measures obtained with different coupling (i.e. foam eartip and earmold) for accuracy at all appropriate stages of the hearing aid fitting process.
If you measure the child's hearing with a foam eartip and the RECD with his/her personal earmold there will be some error in the dBSPL (ear canal) threshold measurements (by the amount that the real-ear measurement obtained with the foam eartip differs from the earmold). Accurate predictions of real-ear performance will be obtained if the earmold is coupled to the HA-1 (ITE) coupler for coupler-based measurements. Additional research needs to be conducted in this area. Manufacturers' implementation of RECD measurement procedures could be modified to allow end-users to choose from two couplers (HA-1 or HA-2) for the coupler part of the RECD procedure and from two real-ear coupling options (foam tip or earmold) to better accommodate the possible choices.
In the meantime, if the RECD was measured with the earmold and audiometry was conducted with a foam eartip, there will be some discrepancy in the high-frequency region in the converted SPL thresholds. Preliminary data analyses show that RECD values obtained using an eartip are approximately 5 dB larger in the high frequencies compared to RECDs measured with the child's earmold. This difference will transfer to the calculation of targets since they are calculated from the SPL thresholds. The discrepancy should only be present at the initial stages of the child's hearing aid use because subsequent audiometry can be conducted with the child's personal earmolds. Until the application of RECDs with different coupling is included in fitting approaches, an RECD with the child's personal earmold should be applied throughout the fitting process, even if the audiometry was conducted with foam eartips.
This Ask The Expert Question was taken from an article previous published on Audiology Online entitled, "Learning the Art to Apply the Science: Common Questions Related to Pediatric Hearing Instrument Fitting". See Bagatto and Moodie (2007) for additional information.
References:
Bagatto, M., Moodie, S., (2007, October 8). Learning the Art to Apply the Science: Common Questions Related to Pediatric Hearing Instrument Fitting. Audiology Online, Article 1886. Accessed from the Article Archives from www.audiologyonline.com/articles/
Marlene Bagatto, Au.D., is a Research Associate and Sheila T. F. Moodie, M.Cl.Sc., is a Research Audiologist at the National Centre for Audiology at the University of Western Ontario in London, Ontario, Canada.
