Implications of Tympanometry Results on RECD and Hearing Aid Fitting Across Populations
2Doctor of Audiology Program, Department of Communication Sciences & Disorders, MGH Institute of Health Professions, United States of America
3Department of Audiology, Federal University of Rio Grande do Norte, Brazil
4University of Sao Paulo, Bauru (FOB), Brazil
5Doctor of Audiology Program, Department of Communication Sciences & Disorders, California State University Los Angeles, United States of America
6Federal University of Jaoa Pessoa, Brazil
Mobility of the eardrum and ear canal volume (ECV) are two of the parameters measured by tympanometry and they are reported to affect Real-Ear-to-Coupler Difference (RECD), which represents the difference between sound levels in an individual’s ear and a standard coupler. RECD is used in three conversions in the hearing aid fitting process: 1) to convert the hearing thresholds from dB HL to dB SPL, 2) to generate the hearing aid targets, and 3) to convert the loudness discomfort levels from dB HL to dB SPL. When real ear measurements and RECDs cannot be performed, audiologists often rely on the average RECD values to estimate the sound pressure levels at the hearing aid users’ ear drum. As the sound pressure levels at the eardrum are highly dependent on the ear canal volume, hearing aid fitting prescriptions have norms on average RECDs by age to account for age-related ear canal changes in children and adults. Additionally, the sounds heard by an individual depends on their eardrum compliance. However, the average RECDs used in the common hearing aid prescriptions (i.e., NAL, DSL) are both based on Caucasians. The purpose of this study was to examine the population/ethnic differences in ear canal volumes and eardrum compliance of children at different ages. The ear canal volume and eardrum compliance of children aged 4-18 years old were measured as a part of clinical testing of the middle ear status using tympanometry. As both Type B and C reflected abnormal eardrum compliance, only ears with Type A tympanometry were included in the analyses. A total of 5702 ears were analyzed, including Brazil (N=2263 ears), Cambodia (N=764), Poland (N=1028), and the United States (N=1050). There were no statistically significant differences in the ear canal volume or eardrum compliance among the Brazilian, Polish, and US children. Cambodian children, however, had significantly lower ear canal volume and eardrum compliance. We, therefore, recommend professionals to always measure RECDs for non-Caucasian children and to generate population-based average RECDs so that the sound pressure level in the ear canal can be predicted more accurately.