An Examination of Asymmetry in Adult Tympanometric Measures

During audiologic evaluations, an examination of interaural asymmetry is commonly evaluated. To date, however, interaural differences for tympanometric indices have not been reported for adults. Without documented tympanometric right-left differences, one cannot determine if asymmetries are normal or are indicative of significant clinical asymmetries.

The purpose of this study was to investigate interaural asymmetries in peak compensated static acoustic admittance (Y_tm), equivalent ear canal volume (V_ea), tympanometric peak pressure (TPP), and tympanometric width (TW) in normal adults.

Descriptive, correlational, and inferential measures designs were employed.

Participants were 188 otologically normal Caucasian young adults (i.e., 77 females and 111 males; M = 23.0 years, standard deviation [SD] = 2.7, range = 18-30 years).

Y_tm, V_ea, TPP, and TW measures were obtained bilaterally from an admittance tympanogram using a 226 Hz probe tone. Separate two-factor mixed measures analysis of variance examined the effect of ear and sex for each tympanometric index. Correlation analyses examined the association between right and left ear indices. Interaural differences in tympanometric indices were examined with independent t-tests. Critical differences, for deciding if two tympanometric indices are different between ears, were computed from the standard deviations of the right-left ear difference for statistical confidence levels of 85, 90, 95, and 99%.

The effect of ear was not statistically significant (p > 0.05) on any tympanometric index. Females had significantly lower Y_tm and smaller V_ea measures than males (p < 0.05). Correlations between all right and left tympanometric indices were positive and statistically significant (p < 0.05). There were no statistically significant differences in interaural differences for any of the tympanometric indices as a function of sex (p > 0.05). Critical differences, for confidence levels for 85% to 99% confidence ranged from ± 0.20-0.36 mmhos for Y_tm, ± 0.23-0.41 cm³ for V_ea, ± 11.1-19.8 daPa for TPP, and ± 27.2-48.7 daPa for TW.

A clinician can use these critical differences to determine if tympanometric index interaural differences in ears of young normal Caucasian adults are statistically significant.