Wideband acoustic transfer functions predict middle-ear effusion

Abstract

Objectives/hypothesis: Compare the accuracy of wideband acoustic transfer functions (WATFs) measured in the ear canal at ambient pressure to methods currently recommended by clinical guidelines for predicting middle-ear effusion (MEE).

Study design: Cross-sectional validating diagnostic study among young children with and without MEE to investigate the ability of WATFs to predict MEE.

Methods: WATF measures were obtained in an MEE group of 44 children (53 ears; median age, 1.3 years) scheduled for middle-ear ventilation tube placement and a normal age-matched control group of 44 children (59 ears; median age, 1.2 years) with normal pneumatic otoscopic findings and no history of ear disease or middle-ear surgery. An otolaryngologist judged whether MEE was present or absent and rated tympanic-membrane (TM) mobility via pneumatic otoscopy. A likelihood-ratio classifier reduced WATF data (absorbance, admittance magnitude and phase) from 0.25 to 8 kHz to a single predictor of MEE status. Absorbance was compared to pneumatic otoscopy classifications of TM mobility.

Results: Absorbance was reduced in ears with MEE compared to ears from the control group. Absorbance and admittance magnitude were the best single WATF predictors of MEE, but a predictor combining absorbance, admittance magnitude, and phase was the most accurate. Absorbance varied systematically with TM mobility based on data from pneumatic otoscopy.

Conclusions: Results showed that absorbance is sensitive to middle-ear stiffness and MEE, and WATF predictions of MEE in young children are as accurate as those reported for methods recommended by the clinical guidelines.

Figure 1

The solid and dotted lines represent the median absorbance for the normal and middle-ear effusion (MEE) group, respectively. The light gray fill represents the inter-quartile range (IQR) for the normal group, and the dark gray fill for the MEE group. The medium gray fill at each frequency represents the absorbance range over which the group interquartile ranges (IQRs) overlap.

Figure 2

Median absorbance is plotted (black lines) across frequency for each of the subgroups of ears with the same TM stiffness classification (1 through 5) obtained via pneumatic otoscopy. Stiffness classifications are defined as follows: (1) Normal (N+), (2) Slightly stiff (SS), (3) Moderately stiff (MS), (4) Very stiff (VS), and (5) No movement (i.e., immobile; IM). The absorbance for the middle-ear effusion (MEE) group is plotted for comparison (gray dotted line).

Figure 3

Absorbance (AB) responses averaged from 0.8 to 2 kHz are plotted as box and whiskers plots for each otoscopic subgroup and the middle-ear effusion (MEE) group. For each box, the center horizontal line represents the median AB, and the top and bottom horizontal lines represent the interquartile range (IQR) of AB. Each whisker length denotes the lesser of the full range of the data or 1.5 times the IQR. The notch is used with a nonparametric test to evaluate if two medians are significantly different at the 0.05 level. If notches are non-overlapping across tympanic membrane stiffness classifications, then the medians are significantly different. The notch for a box and whiskers plot can be wider than the IQR if the number of ears is small, such as is the case for the Moderately stiff, Very stiff, and No movement subgroups.