해외산업간호정보 - 미국 산업안전보건연구원(National Institute for Occupational Safety and Health) 소개

Impaired speech perception in noise with a normal audiogram: No evidence for cochlear synaptopathy and no relation to lifetime noise exposure.

This study tested hypothesized relationships between noise exposure and auditory deficits. Retrospective assessment of potential associations between noise exposure history and performance on an audiologic test battery and prospective assessment of potential changes in performance after new recreational noise exposure were completed. METHODS: 32 participants (13M, 19F) with normal hearing (25-dB HL or better,0.25-8 kHz) were asked to participate in 3 pre- and post-exposure sessions including: otoscopy, tympanometry, distortion product otoacoustic emissions (DPOAEs) (f2 frequencies 1-8 kHz), pure-tone audiometry (0.25-8 kHz), Words-in-Noise (WIN) test, and electrocochleography (eCochG) measurements at 70, 80, and 90-dB nHL (click, and 1-4 kHz tone-bursts). The first session was used to collect baseline data, the second session was collected the day after a loud recreational event, and the third session was collected 1-week later. Of the 32 participants, 26 completed all 3 sessions. RESULTS: The retrospective analysis did not reveal statistically significant relationships between noise exposure history and any auditory deficits. The day after new exposure, there was a statistically significant correlation between noise “dose” and WIN performance overall, and within the 4-dB signal-to-babble ratio. In contrast, there were no statistically significant correlations between noise dose and changes in threshold, DPOAE amplitude, or AP amplitude the day after new noise exposure. Additional analyses revealed a statistically significant relationship between TTS and DPOAE amplitude at 6 kHz, with temporarily decreased DPOAE amplitude observed with increasing TTS. CONCLUSIONS: There was no evidence of auditory deficits as a function of previous noise exposure history, and no permanent change in audiometric, electrophysiologic, or functional measures after new recreational noise exposure. There were very few participants with TTS the day after exposure - a test time selected to be consistent with previous animal studies. The largest observed TTS was approximately 20-dB. The observed pattern of small TTS suggests little risk of synaptopathy from common, recreational noise exposure, and that we should not expect to observe changes in evoked potentials for this reason. No such changes were observed in this study. These data do not support suggestions that common, recreational noise exposure is likely to result in “hidden hearing loss”.

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Hidden Hearing Loss? No Effect of Common Recreational Noise Exposure on Cochlear Nerve Response Amplitude in Humans.

OBJECTIVES Recent animal studies suggest that noise-induced synaptopathy may underlie a phenomenon that has been labeled hidden hearing loss (HHL). Noise exposure preferentially damages low spontaneous-rate auditory nerve fibers, which are involved in the processing of moderate- to high-level sounds and are more resistant to masking by background noise. Therefore, the effect of synaptopathy may be more evident in suprathreshold measures of auditory function, especially in the presence of background noise. The purpose of this study was to develop a statistical model for estimating HHL in humans using thresholds in noise as the outcome variable and measures that reflect the integrity of sites along the auditory pathway as explanatory variables. Our working hypothesis is that HHL is evident in the portion of the variance observed in thresholds in noise that is not dependent on thresholds in quiet, because this residual variance retains statistical dependence on other measures of suprathreshold function. DESIGN Study participants included 13 adults with normal hearing (≤15 dB HL) and 20 adults with normal hearing at 1 kHz and sensorineural hearing loss at 4 kHz (>15 dB HL). Thresholds in noise were measured, and the residual of the correlation between thresholds in noise and thresholds in quiet, which we refer to as thresholds-in-noise residual, was used as the outcome measure for the model. Explanatory measures were as follows: (1) auditory brainstem response (ABR) waves I and V amplitudes; (2) electrocochleographic action potential and summating potential amplitudes; (3) distortion product otoacoustic emissions level; and (4) categorical loudness scaling. All measurements were made at two frequencies (1 and 4 kHz). ABR and electrocochleographic measurements were made at 80 and 100 dB peak equivalent sound pressure level, while wider ranges of levels were tested during distortion product otoacoustic emission and categorical loudness scaling measurements. A model relating the thresholds-in-noise residual and the explanatory measures was created using multiple linear regression analysis. RESULTS Predictions of thresholds-in-noise residual using the model accounted for 61% (p < 0.01) and 48% (p < 0.01) of the variance in the measured thresholds-in-noise residual at 1 and 4 kHz, respectively. CONCLUSIONS Measures of thresholds in noise, the summating potential to action potential ratio, and ABR waves I and V amplitudes may be useful for the prediction of HHL in humans. With further development, our approach of quantifying HHL by the variance that remains in suprathreshold measures of auditory function after removing the variance due to thresholds in quiet, together with our statistical modeling, may provide a quantifiable and verifiable estimate of HHL in humans with normal hearing and with hearing loss. The current results are consistent with the view that inner hair cell and auditory nerve pathology may underlie suprathreshold auditory performance.

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Using Thresholds in Noise to Identify Hidden Hearing Loss in Humans.

Lifetime noise exposure is generally quantified by self report. The accuracy of retrospective self report is limited by respondent recall, but is also bound to be influenced by reporting procedures. Such procedures are of variable quality in current measures of lifetime noise exposure, and off-the-shelf instruments are not readily available. The Noise Exposure Structured Interview (NESI) represents an attempt to draw together some of the stronger elements of existing procedures and to provide solutions to their outstanding limitations. Reporting is not restricted to pre-specified exposure activities, and instead encompasses all activities that the respondent has experienced as noisy (defined based on sound level estimated from vocal effort). Changing exposure habits over time are reported by dividing the lifespan into discrete periods in which exposure habits were approximately stable, with life milestones used to aid recall. Exposure duration, sound level, and use of hearing protection are reported for each life period separately. Simple-to-follow methods are provided for the estimation of free-field sound level, the sound level emitted by personal listening devices, and the attenuation provided by hearing protective equipment. An energy-based means of combining the resulting data is supplied, along with a primarily energy-based method for incorporating firearm-noise exposure. Finally, the NESI acknowledges the need of some users to tailor the procedures; this flexibility is afforded and reasonable modifications are described. Competency needs of new users are addressed through detailed interview instructions (including troubleshooting tips) and a demonstration video. Limited evaluation data are available and future efforts at evaluation are proposed.

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The Noise Exposure Structured Interview (NESI): An Instrument for the Comprehensive Estimation of Lifetime Noise Exposure

Exposure to both occupational and nonoccupational noise is recognized as a risk factor for noise-induced hearing loss (NIHL). Although audiologists routinely inquire regarding history of noise exposure, there are limited tools available for quantifying this history or for identifying those individuals who are at highest risk for NIHL. Identifying those at highest risk would allow hearing conservation activities to be focused on those individuals. To develop a detailed, task-based questionnaire for quantifying an individual’s annual noise exposure (ANE) arising from both occupational and nonoccupational sources (aim 1) and to develop a short screening tool that could be used to identify individuals at high risk of NIHL (aim 2). Review of relevant literature for questionnaire development followed by a cross-sectional descriptive and correlational investigation of the newly developed questionnaire and screening tool. One hundred fourteen college freshmen completed the detailed questionnaire for estimating ANE (aim 1) and answered the potential screening questions (aim 2). An additional 59 adults participated in data collection where the accuracy of the screening tool was evaluated (aim 2). In study aim 1, all participants completed the detailed questionnaire and the potential screening questions. Descriptive statistics were used to quantify participant participation in various noisy activities and their associated ANE estimates. In study aim 2, linear regression techniques were used to identify screening questions that could be used to predict a participant’s estimated ANE. Clinical decision theory was then used to assess the accuracy with which the screening tool predicted high and low risk of NIHL in a new group of participants. Responses on the detailed questionnaire indicated that our sample of college freshmen reported high rates of participation in a variety of occupational and nonoccupational activities associated with high sound levels. Although participation rates were high, ANE estimates were below highest-risk levels for many participants because the frequency of participation in these activities was low in many cases. These data illustrate how the Noise Exposure Questionnaire (NEQ) could be used to provide detailed and specific information regarding an individual’s exposure to noise. The results of aim 2 suggest that the screening tool, the 1-Minute Noise Screen, can be used to identify those participants with high- and low-risk noise exposure, allowing more in-depth assessment of noise exposure history to be targeted at those most at risk. The NEQ can be used to estimate an individual’s ANE and the 1-Minute Noise Screen can be used to identify those participants at highest risk of NIHL. These tools allow audiologists to focus hearing conservation efforts on those individuals who are most in need of those services.

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Susan Cooper

Papers

Noise Exposure Questionnaire: A Tool for Quantifying Annual Noise Exposure.

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