Audiometric predictions using stimulus-frequency otoacoustic emissions and middle ear measurements

Abstract

Objective: The goals of the study are to determine how well stimulus-frequency otoacoustic emissions (SFOAEs) identify hearing loss, classify hearing loss as mild or moderate-severe, and correlate with pure-tone thresholds in a population of adults with normal middle ear function. Other goals are to determine if middle ear function as assessed by wideband acoustic transfer function (ATF) measurements in the ear canal account for the variability in normal thresholds, and if the inclusion of ATFs improves the ability of SFOAEs to identify hearing loss and predict pure-tone thresholds.

Design: The total suppressed SFOAE signal and its corresponding noise were recorded in 85 ears (22 normal ears and 63 ears with sensorineural hearing loss) at octave frequencies from 0.5 to 8 kHz, using a nonlinear residual method. SFOAEs were recorded a second time in three impaired ears to assess repeatability. Ambient-pressure ATFs were obtained in all but one of these 85 ears and were also obtained from an additional 31 normal-hearing subjects in whom SFOAE data were not obtained. Pure-tone air and bone conduction thresholds and 226-Hz tympanograms were obtained on all subjects. Normal tympanometry and the absence of air-bone gaps were used to screen subjects for normal middle ear function. Clinical decision theory was used to assess the performance of SFOAE and ATF predictors in classifying ears as normal or impaired, and linear regression analysis was used to test the ability of SFOAE and ATF variables to predict the air conduction audiogram.

Results: The ability of SFOAEs to classify ears as normal or hearing impaired was significant at all test frequencies. The ability of SFOAEs to classify impaired ears as either mild or moderate-severe was significant at test frequencies from 0.5 to 4 kHz. SFOAEs were present in cases of severe hearing loss. SFOAEs were also significantly correlated with air conduction thresholds from 0.5 to 8 kHz. The best performance occurred with the use of the SFOAE signal-to-noise ratio as the predictor, and the overall best performance was at 2 kHz. The SFOAE signal-to-noise measures were repeatable to within 3.5 dB in impaired ears. The ATF measures explained up to 25% of the variance in the normal audiogram; however, ATF measures did not improve SFOAEs predictors of hearing loss except at 4 kHz.

Conclusions: In common with other OAE types, SFOAEs are capable of identifying the presence of hearing loss. In particular, SFOAEs performed better than distortion-product and click-evoked OAEs in predicting auditory status at 0.5 kHz; SFOAE performance was similar to that of other OAE types at higher frequencies except for a slight performance reduction at 4 kHz. Because SFOAEs were detected in ears with mild to severe cases of hearing loss, they may also provide an estimate of the classification of hearing loss. Although SFOAEs were significantly correlated with hearing threshold, they do not appear to have clinical utility in predicting a specific behavioral threshold. Information on middle ear status as assessed by ATF measures offered minimal improvement in SFOAE predictions of auditory status in a population of normal and impaired ears with normal middle ear function. However, ATF variables did explain a significant fraction of the variability in the audiograms of normal ears, suggesting that audiometric thresholds in normal ears are partially constrained by middle ear function as assessed by ATF tests.

Figure 1

Multiple suppression input-output functions obtained using a 1-kHz probe (L_p = 60 dB SPL) as a function of increasing suppressor level. Each solid line represents a suppressed emission from a single suppressor frequency, and each dashed line at the bottom of the figure represents the corresponding noise. The broad dashed line marked as ‘Level’ represents the SFOAE level, the dotted line marked as ‘Noise’ represents the SFOAE noise, and the vertical solid line represents the SFOAE S/N.

Figure 2

The ROC areas for SFOAE S/N (left panel) and SFOAE level (right panel) are plotted as predictors of the presence or absence of hearing loss for octave frequencies 0.5 to 8 kHz. The parameter is the L_p used to elicit an SFOAE response. Standard error bars are provided for conditions when L_p = 60 dB SPL. Filled symbols represent a non-significant effect in predicting hearing loss.

Figure 3

The percentage of ears correctly identified by the SFOAE S/N response as having normal hearing, a mild hearing loss, or a moderate-severe hearing loss at octave frequencies 0.5 to 8 kHz. The parameter is the category of auditory status that was correctly identified. The dashed horizontal line (33%) represents chance level performance.

Figure 4

AC thresholds (dB HL) up to 95 dB HL are plotted as a function of SFOAE S/N (dB). Each panel represents one octave frequency 0.5 to 8 kHz. In each panel the number of ears is provided as well as the variance (R²) accounted for in each analysis. Solid lines represents the least-mean-square linear fit for all data points in each panel. Using the same format, the bottom right panel shows the data at 8 kHz when restricted to hearing losses ≤ 50 dB HL.

Figure 5

The SFOAE level, noise, and S/N from two sessions are plotted at octave frequencies 0.5 to 8 kHz for three hearing impaired subjects. The L_p used to elicit an SFOAE response equaled 60 dB SPL. Open symbols represent data from the first session and filled symbols represent data from the second session.

Figure 6

AC thresholds (dB HL) in 53 normal ears at 1 kHz are plotted as a function of tympanometric ear-canal volume (ml) in the left panel and as a function of the acoustic transfer function (ATF) admittance magnitude (dB) at 1 kHz in the right panel. In each panel R2 values are provided. Solid lines in each panel represent the least-means-square fit for all the data.

Figure 7

The ROC areas for univariate S/N models are plotted as predictors of the presence or absence of hearing loss for octave frequencies 0.5 to 8 kHz. SFOAE data are compared to DPOAE (0.5 kHz from Gorga et al., 1993a; 1 to 8 kHz from Gorga et al., 1997) and TEOAE data (Prieve et al., 1993). SFOAE values represent the L_p condition that resulted in the largest ROC area (see Figure 2). Data at each frequency represent the f₂ primary used to obtain DPOAEs, the center frequency of the one-octave wide TEOAE band, or the SFOAE f_s.