Investigating longitudinal changes in real-ear to coupler difference measurements in infants

Abstract

The real-ear-to-coupler difference (RECD) measurement is a commonly-used clinical procedure that quantifies the difference in sound-pressure level between a 2-cc coupler and an individual's ear canal. The SPL levels in infant ears are highly variable and significantly higher than the SPL levels present in average adult ears, which makes the quantification of SPL levels in infant ears extremely important for threshold determination and the fitting of amplification. The purpose of this study was to examine longitudinal changes in RECD values in newborn infants, over a 1 -month interval, to determine whether a significant decrease in RECD values takes place, and whether that decrease is predictable from either the infant's corrected age or their initial RECD values. Using standard (226Hz) and high frequency (1000 Hz) tympanometry, measures of static admittance and ear canal volume were also evaluated to determine their predictive ability regarding frequency specific RECD values. Measurement error associated with the RECD was quantified and then compared to the magnitude of RECD changes over a 1 month interval. A multi-variate analysis of variance (MANOVA) was performed and revealed an overall significant change in RECD values over a 1 month interval. Forward regression analysis further revealed corrected age as a predictor of RECD values at 3 frequencies and initial RECD values as a predictor at 1 frequency. Static admittance was a larger predictor of RECD values when compared to E C V , with the exception of the lowest and highest frequencies (0.25 and 6 kHz). Magnitude of the test-retest variability associated with the RECD measurement was not large but variability was large enough to obscure longitudinal RECD changes over a 1-month period. Consequently, it may be clinically unnecessary to re-measure an RECD within an infant's first month of life, to account for changes in ear canal acoustics between initial screening tests and follow-up assessments. The best measures of static admittance and ear canal volume in infants remains undetermined and a strong need exists for further longitudinal data in infant populations. iv Table of