Using a combination of click- and tone burst-evoked auditory brain stem response measurements to estimate pure-tone thresholds

Abstract

Design: A retrospective medical record review of evoked potential and audiometric data were used to determine the accuracy with which click-evoked and tone burst-evoked auditory brain stem response (ABR) thresholds predict pure-tone audiometric thresholds.

Methods: The medical records were reviewed of a consecutive group of patients who were referred for ABR testing for audiometric purposes over the past 4 yrs. ABR thresholds were measured for clicks and for several tone bursts, including a single-cycle, Blackman-windowed, 250-Hz tone burst, which has a broad spectrum with little energy above 600 Hz. Typically, the ABR data were collected because the patients were unable to provide reliable estimates of hearing sensitivity, based on behavioral test techniques, due to developmental level. Data were included only if subsequently obtained behavioral audiometric data were available to which the ABR data could be compared. Almost invariably, the behavioral data were collected after the ABR results were obtained. Because of this, data were included on only those ears for which middle ear tests (tympanometry, otoscopic examination, pure-tone air- and bone-conduction thresholds) indicated that middle ear status was similar at the times of both tests. With these inclusion criteria, data were available on 140 ears of 77 subjects.

Results: Correlation was 0.94 between click-evoked ABR thresholds and the average pure-tone threshold at 2 and 4 kHz. Correlations exceeded 0.92 between ABR thresholds for the 250-Hz tone burst and low-frequency behavioral thresholds (250 Hz, 500 Hz, and the average pure-tone thresholds at 250 and 500 Hz). Similar or higher correlations were observed when ABR thresholds at other frequencies were compared with the pure-tone thresholds at corresponding frequencies. Differences between ABR and behavioral threshold depended on behavioral threshold, with ABR thresholds overestimating behavioral threshold in cases of normal hearing and underestimating behavioral threshold in cases of hearing loss.

Conclusions: These results suggest that ABR thresholds can be used to predict pure-tone behavioral thresholds for a wide range of frequencies. Although controversial, the data reviewed in this paper suggest that click-evoked ABR thresholds result in reasonable predictions of the average behavioral thresholds at 2 and 4 kHz. However, there were cases for which click-evoked ABR thresholds underestimated hearing loss at these frequencies. There are several other reasons why click-evoked ABR measurements were made, including that they (1) generally result in well-formed responses, (2) assist in determining whether auditory neuropathy exists, and (3) can be obtained in a relatively brief amount of time. Low-frequency thresholds were predicted well by ABR thresholds to a single-cycle, 250-Hz tone burst. In combination, click-evoked and low-frequency tone burst-evoked ABR threshold measurements might be used to quickly provide important clinical information for both ends of the audiogram. These measurements could be supplemented by ABR threshold measurements at other frequencies, if time permits. However, it may be possible to plan initial intervention strategies based on data for these two stimuli.

Figure 1

ABR waveforms for toneburst stimuli (left column) and clicks (right column) in a patient with normal hearing. For toneburst stimuli, responses are only shown at the minimum response level (20 dB nHL). For clicks, responses are shown at several levels, including the minimum response level. The time base varied, depending on stimulus. Thus, one cannot directly compare response latencies based on these plots. For tonebursts (left column), the response window was 25 ms in length. For clicks (right column), the response epoch was 15 ms.

Figure 2

ABR waveforms in a patient with moderate-to-severe hearing loss, following the convention used in Fig. 1. In this case, however, waveforms are shown at the lowest level at which a response was evident and then at the next lower level. Response epochs for toneburst (left column) and click (right column) responses were 25 ms and 15 ms, respectively.

Figure 3

Average pure-tone behavioral thresholds at 2 and 4 kHz (dB HL) as a function of click-evoked ABR threshold (dB nHL). Horizontal and vertical dashed lines represent cases for which no response was measured. The heavy diagonal line serves as a point of reference, representing the case when there was one-to-one correspondence between pure-tone and ABR thresholds. The thinner, near-diagonal solid line represents a least-squares, linear fit to the data. The equation describing the best-fit line is provided within the panel, along with correlation (r), and the number of cases for which data were available.

Figure 4

Pure-tone behavioral thresholds (dB HL) at 250 Hz (top), 500 Hz (middle) and the average of 250 and 500 Hz (bottom) as a function of ABR threshold (dB nHL) to a 250-Hz toneburst. Dashed horizontal and vertical lines, and the solid diagonal line serve the same purpose here as in Fig. 1. The best-fit line, correlation, and number of cases are shown in each panel.

Figure 5

Pure-tone behavioral thresholds at 1 kHz (dB HL) as a function of ABR thresholds (dB nHL) to a 1-kHz toneburst, following the conventions used in previous figures.

Figure 6

Pure-tone behavioral thresholds (dB HL) at either 1 or 2 kHz as a function of ABR thresholds (dB nHL) for either 2 or 4 kHz tonebursts, following the same conventions as used in previous figures. Open circles represent data for 2 kHz, while filled circles represent data for 4 kHz.

Figure 7

Differences between pure-tone audiometric thresholds (in dB HL) and ABR thresholds (measured in dB nHL) as a function of pure-tone audiometric threshold. Cases in which no response was measured are excluded. Each panel represents results for a different comparison, as indicated within each panel. Also shown within each panel is the grand mean and standard deviation of the differences.

Figure 8

Case examples in which click-evoked and toneburst evoked ABR thresholds are compared to the pure-tone audiogram. Open squares represent ABR thresholds; filled circles represent audiometric thresholds. Thresholds refer to dB HL (re: ANSI, 1996) for pure-tone audiometry and dB nHL (locally determined) for ABR measurements.