^{1,a)}, Judi A. Lapsley Miller

^{1}, Laurie M. Heller

^{1,b)}, Keith S. Wolgemuth

^{2,c)}, Linda M. Hughes

^{3}, Shelley D. Smith

^{4}and Richard D. Kopke

^{5,d)}

### Abstract

Audiometric thresholds and otoacoustic emissions (OAEs) were measured in 285 U.S. Marine Corps recruits before and three weeks after exposure to impulse-noise sources from weapons’ fire and simulated artillery, and in 32 non-noise-exposed controls. At pre-test, audiometric thresholds for all ears were HL from and HL at . Ears with low-level or absent OAEs at pre-test were more likely to be classified with significant threshold shifts (STSs) at post-test. A subgroup of 60 noise-exposed volunteers with complete data sets for both ears showed significant decreases in OAE amplitude but no change in audiometric thresholds. STSs and significant emission shifts (SESs) between 2 and in individual ears were identified using criteria based on the standard error of measurement from the control group. There was essentially no association between the occurrence of STS and SES. There were more SESs than STSs, and the group of SES ears had more STS ears than the group of no-SES ears. The increased sensitivity of OAEs in comparison to audiometric thresholds was shown in all analyses, and low-level OAEs indicate an increased risk of future hearing loss by as much as ninefold.

Thanks to Linda Westhusin, Michael McFadden, Denise Cline, Jackie Adler, Joy Houston, and Brian Ferris for their assistance with data collection. A special thanks to the staff and recruits of the Marine Corps Recruit Depot (MCRD) San Diego and Charles Jackson of the Naval Medical Center San Diego Occupational Audiology Department. Thanks to Tom Taggart for his input into the overall experimental design, help with logistics, and feedback on preliminary analyses. Thanks to Chris Shera for helpful discussions on the theoretical aspects. Thanks to the two anonymous reviewers whose considered opinions substantively improved the manuscript. This research was supported primarily by grants from the Office of Naval Research. The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Navy, the Department of Defense, or the United States Government.

I. INTRODUCTION

II. METHOD

A. Participants

B. Noise exposures

C. Audiometric equipment, stimuli, and testing

D. Tympanometry equipment, stimuli, and testing

E. Otoacoustic emission equipment, stimuli, and testing

F. Data definitions, cleaning, and reduction

III. RESULTS

A. Changes in group OAE and audiometric thresholds after noise exposure

B. Significant threshold shift (STS) and significant emission shift (SES) criteria

C. STSs detected in the noise-exposed group

D. SESs detected in the noise-exposed group

E. Comparison of STS and SES

F. OAE predictors of susceptibility to NIHL

G. Susceptibility to NIHL for volunteers rather than ears using “worst ear” as a predictor

IV. DISCUSSION

A. OAEs are more sensitive than audiometric thresholds to noise exposure

B. STS and SES criteria

C. Susceptibility to NIHL from impulse noise

D. Susceptibility to NIHL from impulse noise compared with continuous noise

E. Concluding remarks

## Figures

Average pre-test and post-test audiometric thresholds for the noise-exposed group by STS status. Average pre-test thresholds for the 42 STS ears (21 left and 21 right ears) were essentially the same as for the 528 no-STS ears (286 left ears and 286 right ears). Post-test audiograms show that the average thresholds for the STS ears increased up to (left ears, ), while the no-STS ears stayed essentially the same. The error bars are 95% confidence intervals.

Average pre-test and post-test audiometric thresholds for the noise-exposed group by STS status. Average pre-test thresholds for the 42 STS ears (21 left and 21 right ears) were essentially the same as for the 528 no-STS ears (286 left ears and 286 right ears). Post-test audiograms show that the average thresholds for the STS ears increased up to (left ears, ), while the no-STS ears stayed essentially the same. The error bars are 95% confidence intervals.

Average pre-test and post-test TEOAE amplitudes for the noise-exposed group by significant TEOAE shift (SES) status. Average pre-test amplitudes for the SES ears (22–27 left ears and 14–21 right ears) were slightly higher than for the no-SES ears (112–118 left ears and 129–138 right ears). Average post-test TEOAE amplitudes decreased by approximately from pre-test for the SES ears, while the post-test average for the no-SES ears stayed essentially the same. The error bars are 95% confidence intervals. The number of ears contributing to the average at each frequency varied because of some unusable data.

Average pre-test and post-test TEOAE amplitudes for the noise-exposed group by significant TEOAE shift (SES) status. Average pre-test amplitudes for the SES ears (22–27 left ears and 14–21 right ears) were slightly higher than for the no-SES ears (112–118 left ears and 129–138 right ears). Average post-test TEOAE amplitudes decreased by approximately from pre-test for the SES ears, while the post-test average for the no-SES ears stayed essentially the same. The error bars are 95% confidence intervals. The number of ears contributing to the average at each frequency varied because of some unusable data.

Average pre-test and post-test amplitudes for the noise-exposed group by significant shift (SES) status. Average pre-test amplitudes for the SES ears (16–17 left ears and 25–26 right ears) were slightly higher than the average for the no-SES ears (180–185 left ears and 166–172 right ears). Average post-test amplitudes decreased by approximately from pre-test for the SES ears, while the post-test average for the no-SES ears stayed essentially the same. The error bars are 95% confidence intervals. The number of ears contributing to the average at each frequency varied because of some unusable data.

Average pre-test and post-test amplitudes for the noise-exposed group by significant shift (SES) status. Average pre-test amplitudes for the SES ears (16–17 left ears and 25–26 right ears) were slightly higher than the average for the no-SES ears (180–185 left ears and 166–172 right ears). Average post-test amplitudes decreased by approximately from pre-test for the SES ears, while the post-test average for the no-SES ears stayed essentially the same. The error bars are 95% confidence intervals. The number of ears contributing to the average at each frequency varied because of some unusable data.

Average pre-test and post-test amplitudes for the noise-exposed group by significant shift (SES) status. Average pre-test amplitudes for the SES ears (15–16 left ears and 24–26 right ears) were slightly higher than the average for the no-SES ears (201–206 left ears and 188–192 right ears). Average post-test amplitudes decreased by approximately from pre-test for the SES ears, while the post-test average for the no-SES ears stayed essentially the same. The error bars are 95% confidence intervals. The number of ears contributing to the average at each frequency varied because of some unusable data.

Average pre-test and post-test amplitudes for the noise-exposed group by significant shift (SES) status. Average pre-test amplitudes for the SES ears (15–16 left ears and 24–26 right ears) were slightly higher than the average for the no-SES ears (201–206 left ears and 188–192 right ears). Average post-test amplitudes decreased by approximately from pre-test for the SES ears, while the post-test average for the no-SES ears stayed essentially the same. The error bars are 95% confidence intervals. The number of ears contributing to the average at each frequency varied because of some unusable data.

PPV, for the left and right ears separately, as a function of the PPV criterion, which is OAE amplitude (in dB SPL). PPV is the probability that an ear was classified with a STS given an OAE amplitude less than the criterion. As the OAE amplitude decreased, PPV tended to increase for the higher-frequency bands, but not for all OAE types and frequencies. [(a) and (b)] ,[(c) and (d)] , and [(e) and (f)] TEOAEs. The thin solid horizontal line represents the prior probability of a STS averaged over the displayed frequencies.

PPV, for the left and right ears separately, as a function of the PPV criterion, which is OAE amplitude (in dB SPL). PPV is the probability that an ear was classified with a STS given an OAE amplitude less than the criterion. As the OAE amplitude decreased, PPV tended to increase for the higher-frequency bands, but not for all OAE types and frequencies. [(a) and (b)] ,[(c) and (d)] , and [(e) and (f)] TEOAEs. The thin solid horizontal line represents the prior probability of a STS averaged over the displayed frequencies.

PPV at (from Fig. 5 ). for the left and right ears separately, for each OAE type replotted as a function of OAE amplitude in percentiles.

PPV at (from Fig. 5 ). for the left and right ears separately, for each OAE type replotted as a function of OAE amplitude in percentiles.

PPVs as a function of PPV criterion, which in this case is OAE amplitude for the worst ear, which is the way it would be implemented in occupational audiology programs. For each volunteer, the ear with the lowest OAE amplitude was used as the predictor. (a) at 3.6 and , (b) at 3.6 and and (c) TEOAEs at 2, 2.8, and . The thin solid horizontal line represents the prior probability of a STS averaged over the displayed frequencies.

PPVs as a function of PPV criterion, which in this case is OAE amplitude for the worst ear, which is the way it would be implemented in occupational audiology programs. For each volunteer, the ear with the lowest OAE amplitude was used as the predictor. (a) at 3.6 and , (b) at 3.6 and and (c) TEOAEs at 2, 2.8, and . The thin solid horizontal line represents the prior probability of a STS averaged over the displayed frequencies.

PPV as a function of OAE amplitude in percentiles for TEOAEs at for the left ears from Fig. 6 (solid line) compared with the same data after excluding ears with audiometric thresholds HL (dashed line).

PPV as a function of OAE amplitude in percentiles for TEOAEs at for the left ears from Fig. 6 (solid line) compared with the same data after excluding ears with audiometric thresholds HL (dashed line).

Comparisons of likelihood ratio as a function of OAE amplitude (in dB SPL), indicating susceptibility to noise-induced hearing loss, between the current study (Marine recruits exposed to impulse noise, solid line) and ^{ Lapsley Miller et al. (2006) } (deployed aircraft carrier sailors exposed to continuous noise overlaid with impact noise, dashed line) for the OAE test frequencies where there were no large differences in the amplitude distributions between the ears: (a) TEOAEs at (half-octave band), (b) at , (c) at , (d) at , and (e) at .

Comparisons of likelihood ratio as a function of OAE amplitude (in dB SPL), indicating susceptibility to noise-induced hearing loss, between the current study (Marine recruits exposed to impulse noise, solid line) and ^{ Lapsley Miller et al. (2006) } (deployed aircraft carrier sailors exposed to continuous noise overlaid with impact noise, dashed line) for the OAE test frequencies where there were no large differences in the amplitude distributions between the ears: (a) TEOAEs at (half-octave band), (b) at , (c) at , (d) at , and (e) at .

## Tables

The number of ears and the total number of volunteers in each group that contributed to each analysis, listed by the section. The numbers varied at each test frequency, OAE level, and OAE type, because only valid data were used. The exception was for the ANOVAs where volunteers were required to have complete OAE data sets for both ears.

The number of ears and the total number of volunteers in each group that contributed to each analysis, listed by the section. The numbers varied at each test frequency, OAE level, and OAE type, because only valid data were used. The exception was for the ANOVAs where volunteers were required to have complete OAE data sets for both ears.

STS criteria based on the standard error of measurement from the control group (32 volunteers/64 ears) for individual audiometric-threshold frequencies and for averaged frequencies. Shown is the frequency, mean shift between post-testing and pre-testing, , and the resulting STS criteria (see footnote 7). Note that although the STS criteria were calculated for all frequencies, only frequencies from and the averaged frequency bands were used to determine the STS status.

STS criteria based on the standard error of measurement from the control group (32 volunteers/64 ears) for individual audiometric-threshold frequencies and for averaged frequencies. Shown is the frequency, mean shift between post-testing and pre-testing, , and the resulting STS criteria (see footnote 7). Note that although the STS criteria were calculated for all frequencies, only frequencies from and the averaged frequency bands were used to determine the STS status.

SES criteria based on the standard error of measurement from the control group (32 volunteers/64 ears). Shown are the OAE type, frequency for DPOAEs or half-octave frequency band for TEOAEs, the number of ears contributing to the calculation, , and the resulting SES criteria (see footnote 7). Note that although the SES criteria were calculated for all valid frequencies, only some frequencies were used to determine the SES status (2.5, 3.2, and for DPOAEs, and 2, 2.8, and for TEOAEs).

SES criteria based on the standard error of measurement from the control group (32 volunteers/64 ears). Shown are the OAE type, frequency for DPOAEs or half-octave frequency band for TEOAEs, the number of ears contributing to the calculation, , and the resulting SES criteria (see footnote 7). Note that although the SES criteria were calculated for all valid frequencies, only some frequencies were used to determine the SES status (2.5, 3.2, and for DPOAEs, and 2, 2.8, and for TEOAEs).

Breakdown of the 285 volunteers in the noise-exposed group by STS status and SES status for the left/right ear and the measurement type. The first number is the count, and the number in parentheses is the overall percentage. The Unknown category represents those ears for which a SES determination could not be made, usually due to unusable data. See text for summaries of STS and SES rates for volunteers and ears.

Breakdown of the 285 volunteers in the noise-exposed group by STS status and SES status for the left/right ear and the measurement type. The first number is the count, and the number in parentheses is the overall percentage. The Unknown category represents those ears for which a SES determination could not be made, usually due to unusable data. See text for summaries of STS and SES rates for volunteers and ears.

STS vs SES matrices. The first number is the count, and the number in parentheses is the overall percentage. For the left and right ears separately, ears were grouped by whether they were classified as STS and/or SES ears. The unknown-SES category is for those ears where there were unusable data; these ears were not used in the analysis of the matrices.

STS vs SES matrices. The first number is the count, and the number in parentheses is the overall percentage. For the left and right ears separately, ears were grouped by whether they were classified as STS and/or SES ears. The unknown-SES category is for those ears where there were unusable data; these ears were not used in the analysis of the matrices.

STS ears are over-represented in the group of SES ears, compared with the probability of a STS in general. Likewise SES ears are over-represented in the group of STS ears, compared with the probability of a SES in general. This finding holds over the left and right ears and for all three OAE types, except for in the right ears, where representation was proportional, and where OAEs had the highest variability. The pooled category represents the results pooled over the ear and the OAE type. The true SES rate is underestimated because there are likely to be some unidentified SES ears in the large group of unknown-SES ears, where SES status could not be determined at all three frequencies. (For the underlying cell counts, see Table V .)

STS ears are over-represented in the group of SES ears, compared with the probability of a STS in general. Likewise SES ears are over-represented in the group of STS ears, compared with the probability of a SES in general. This finding holds over the left and right ears and for all three OAE types, except for in the right ears, where representation was proportional, and where OAEs had the highest variability. The pooled category represents the results pooled over the ear and the OAE type. The true SES rate is underestimated because there are likely to be some unidentified SES ears in the large group of unknown-SES ears, where SES status could not be determined at all three frequencies. (For the underlying cell counts, see Table V .)

Maximum increased risk for STS (PPV/base-rate) for each OAE type and frequency, by ear. Each number represents how many times more likely a STS is given a low pre-test OAE result relative to the base rate.

Maximum increased risk for STS (PPV/base-rate) for each OAE type and frequency, by ear. Each number represents how many times more likely a STS is given a low pre-test OAE result relative to the base rate.

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