Wideband acoustic-reflex test in a test battery to predict middle-ear dysfunction

Abstract

A wideband (WB) aural acoustical test battery of middle-ear status, including acoustic-reflex thresholds (ARTs) and acoustic-transfer functions (ATFs, i.e., absorbance and admittance) was hypothesized to be more accurate than 1-kHz tympanometry in classifying ears that pass or refer on a newborn hearing screening (NHS) protocol based on otoacoustic emissions. Assessment of middle-ear status may improve NHS programs by identifying conductive dysfunction and cases in which auditory neuropathy exists. Ipsilateral ARTs were assessed with a stimulus including four broadband-noise or tonal activator pulses alternating with five clicks presented before, between and after the pulses. The reflex shift was defined as the difference between final and initial click responses. ARTs were measured using maximum likelihood both at low frequencies (0.8-2.8 kHz) and high (2.8-8 kHz). The median low-frequency ART was elevated by 24 dB in NHS refers compared to passes. An optimal combination of ATF and ART tests performed better than either test alone in predicting NHS outcomes, and WB tests performed better than 1-kHz tympanometry. Medial olivocochlear efferent shifts in cochlear function may influence ARs, but their presence would also be consistent with normal conductive function. Baseline clinical and WB ARTs were also compared in ipsilateral and contralateral measurements in adults.

Fig. 1

[grey-scale, EPS]. The stimulus waveform of 5 clicks, which are output by a first probe receiver, is shown in the top panel. The stimulus waveform of 4 pulsed activators, which are output by a second probe receiver, is shown in the middle panel. The duration of each pulse is 116 ms. The stimulus waveform shown in the bottom panel is the linear combination of clicks and pulsed activators from each receiver. Each pair of dashed lines shows a 46.4 ms analysis buffer surrounding each click response. Each buffer is temporally separated from any pulse activator.

Fig. 2

[grey-scale, EPS]. The waveform response in an ear of an adult to the initial click is shown in the top panel, for which the peSPL in the ear was 91 dB. Time t=0 ms is located at the maximum amplitude of the click stimulus. The click difference waveform response (final click minus initial click) is shown in the bottom panel at each of the 10 BBN activator levels, with increasing line thickness corresponding to increasing activator level. The click differences for the 5 lower-level activators are plotted with dashed lines, and those for the 5 high-level activators are plotted with solid lines. Each click difference response is the average across the two repetitions at each activator level.

Fig. 3

[grey-scale, EPS]. The waveform response in the ear of a newborn to the initial click is shown in the top panel, for which the peSPL in the ear was 98 dB. The format of the figure is otherwise similar to that in Fig. 2. A reflex response above baseline was observed in each trace.

Fig. 4

[grey-scale, EPS]. The AR status as determined for a BBN activator is plotted for a newborn test ear for AR-L. The ART for this ear was θ_L =60 dB SPL.

Fig. 5

[grey-scale, EPS]. The relative AR levels are plotted for AR-L (solid line) and AR-H (dashed line) for a newborn ear as a function of the BBN activator SPL. The ARTs for this ear were the lowest activator test level, θ_L =θ_H =40 dB SPL.

Fig. 6

[grey-scale, TIF]. Left panel: The relative AR spectral levels (ΔL_AR (f)) are plotted for a newborn test ear with separate line styles for each of the 10 BBN activator SPLs. These spectra were calculated from the windowed click-difference signals in Fig. 3. SPLs and line styles are listed in the legend. The nominal noise spectral level is plotted as a black dotted line. Right: The relative AR spectral levels are plotted with a similar format as in the left panel, except that these spectra were calculated from the windowed click-difference signals after removing the response energy that occurred 2 ms or later (relative to the time axis in Fig. 3).

Fig. 7

[grey-scale, EPS]. The median ARTs (in dB SPL) measured in 80 normal-hearing adult ears are plotted for each activator type for clinical [left bar] and WB tests (θ_L and θ_H) [middle and right bars, respectively]. The associated IQRs are shown by the vertical error bars. The ipsilateral activator types include tonal activators (0.5, 1, 2 and 4 kHz) and BBN. The contralateral activators include tonal activators (0.5_C at 0.5 kHz, and 1_C at 1 kHz). The upper error bar extends above the plotting range for the clinical activator at 0.5_C because the 75^th percentile was an absent AR at every activator level. The upper or lower bar value is plotted at the median value for those conditions in which the 75^th or 25^th percentile, respectively, of the ART was numerically equal to the median ART.

Fig. 8

[grey-scale, EPS]. The median ARTs (in dB SPL) measured in the Day-1 newborn group of pass and refer ears are plotted as bars for each activator type for θ_L (top panel) and θ_H (bottom panel). The associated IQRs are shown by the error bars. The ipsilateral activator types include the 1 kHz tonal activator at the reference click level and at a level 6 dB higher than the reference (denoted 1 kHz and 1 kHz (+6 dB), respectively), the 2 kHz tonal activator at a level 6 dB higher than the reference (denoted 2 kHz (+6 dB)), and BBN. The upper error bar extends above the plotting range for θ_L in the refer group at 1 kHz and BBN because the 75^th percentile was an absent AR at every activator level.

Fig. 9

[color, EPS]. Left panel: The proportions of infants in the DP1-Pass (dashed line) and DP1-Refer (solid line) group are plotted as a function of each possible value of θ_L, in which the right-most category NR represents no response, i.e., the AR was absent at every activator level. Right panel: the ROC curve is plotted for θ_L predicting sound-conduction status as DP1-Pass or DP1-Refer. In each panel, green symbols representing a test result of pass are defined by activator levels with a test sensitivity > 0.90; red symbols representing a test result of refer are defined by activator levels with a test specificity > 0.90; yellow symbols representing a test result of borderline are defined by any activator levels not in either of the other groups.

Fig. 10

[grey-scale, EPS]. For predicting sound-conduction status in newborn infants, the ROC summary measures for 1-kHz tympanometry, WB ATF test, AR-L, AR-H and a test battery combining the WB ATF and AR-L tests are plotted, with AROC results in the left column, SYM results in the right column, Day-1 results in the top row, and Day-2 results in the bottom row. The black error bars show the 95% confidence intervals of each ROC summary measure. The dashed black line at 0.5 represents chance performance.

Fig. 11

[grey-scale, EPS]. The click-difference waveforms are plotted that were generated by a time-domain simple-harmonic oscillator model of middle-ear response, including the round-trip travel time in an ear canal with cylindrical dimensions, based on an input signal with the same impulse strength as the measured click stimulus. Top: results modeling the measured adult-ear response in Fig. 2 (bottom). Bottom: results modeling the measured infant-ear response in Fig. 3 (bottom). Modeling results are shown for three stiffnesses, with the thickest solid line corresponding to the largest stiffness.