John R. Franks

Oxidative DNA damage is associated with intense noise exposure in the rat

Increasing evidence suggests that noise-induced hearing loss may be reduced or prevented with antioxidant therapy. Biochemical markers of reactive oxygen species (ROS)-induced damage can help elucidate possible treatment timing constraints. This study examined the time course of ROS damage following a 2-h, broad-band noise exposure resulting in permanent threshold shift in 35 Long-Evans rats. Cochlea, brain, liver, serum and urine were analyzed at 1, 3, 8, 72, and 672 h (28 days) after exposure. Oxidative DNA damage was assessed by measuring 8-hydroxy-2-deoxyguanosine (8OHdG) by high performance liquid chromatography with electrochemical detection. Lipid peroxidation was measured via the thiobarbituric acid-reactive substances (TBARS) colorimetric assay for detection of aldehydes (e.g., malondialdehyde). Auditory brainstem response and distortion product otoacoustic emission thresholds showed progressive elevation for the 3- and 8-h groups, then notable recovery for the 72-h group, and some worsening for the 672-h group. 8OHdG was significantly elevated in cochlea in the 8-h group, and in brain and liver for the 72-h group. TBARS were significantly elevated in serum for the 72-h group. Based upon oxidative DNA damage present in cochlea following intense noise, we postulate that the first 8 h following exposure might be a critical period for antioxidant treatment.

Audiometric findings in workers exposed to low levels of styrene and noise

Learning ObjectivesExplain whether and how exposure of workers to styrene in the course of making fiberglass products, and to high noise levels, interact to produce bilateral high-frequency hearing loss.Recall the personal and environmental factors that were significantly associated with hearing loss in this study.Discuss how these findings relate to past studies in animals and styrene-exposed workers, and take note of relevant public health considerations.Audiometry and exposure measurements were conducted on workers from fiberglass and metal products manufacturing plants and a mail distribution terminal (N = 313). Workers exposed to noise and styrene had significantly worse pure-tone thresholds at 2, 3, 4, and 6 kHz when compared with noise-exposed or nonexposed workers. Age, noise exposure, and urinary mandelic acid (a biologic marker for styrene) were the variables that met the significance level criterion in the multiple logistic regression. The odds ratios for hearing loss were 1.19 for each increment of 1 year of age (95% confidence interval [CI], 1.11–1.28), 1.18 for every decibel >85 dB(A) of noise exposure (95% CI, 1.01–1.34), and 2.44 for each millimole of mandelic acid per gram of creatinine in urine (95% CI, 1.01–5.89). Our findings suggest that exposure to styrene even below recommended values had a toxic effect on the auditory system.

Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part III. The validity of using subject-fit data

The mandate of ASA Working Group S12/WG11 has been to develop laboratory and/or field procedure(s) that yield useful estimates of field performance of hearing protection devices (HPDs). A real-ear attenuation at threshold procedure was selected, devised, tested via an interlaboratory study, and incorporated into a draft standard that was approved in 1997 [J. D. Royster et at., Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part I. Research of Working Group 11, Accredited Standards Committee S12, Noise, J. Acoust. Soc. Am. 99, 1506-1526 (1996); ANSI S12.6-1997, American National Standard Methods for Measuring Real-Ear Attenuation of Hearing Protectors (American National Standards Institute, New York, 1997)]. The real-world estimation procedure utilizes a subject-fit methodology with listeners who are audiometrically proficient, but inexperienced in the use of HPDs. A key factor in the decision to utilize the subject-fit method was an evaluation of the representativeness of the laboratory data vis-à-vis attenuation values achieved by workers in practice. Twenty-two field studies were reviewed to develop a data base for comparison purposes. Results indicated that laboratory subject-fit attenuation values were typically equivalent to or greater than the field attenuation values, and yielded a better estimate of those values than did experimenter-fit or experimenter-supervised fit types of results. Recent data which are discussed in the paper, but which were not available at the time of the original analyses, confirm the findings.

Detection of Tones in the Absence of External Masking Noise. I. Effects of Signal Intensity and Signal Frequency

Twelve highly trained listeners detected tonal signals in the absence of external masking noise. The signals were 150 msec long and ranged from 125 to 4000 Hz. Fitted psychometric functions were steeper at high than at low frequencies requiring between 3‐ and 8‐dB increase in signal level to raise performance from 60% to 95% correct. The signal levels that yield 76% correct detection in a two‐alternative, forced‐choice psychophysical procedure were in good agreement with the International Standards Organizations recommended values of audiometric zero. The results are consistent with a limitation imposed on auditory sensitivity by a “system noise” which is composed of the noise in the ear canal at low frequencies, and a low‐level (−11 dB SPL) component of unspecified origin at medium and high frequencies. No qualitative differences were observed between detection without external masking noise and previous data on the detection of tones masked by noise.

Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part I. Research of Working Group 11, Accredited Standards Committee S12, Noise

This paper describes research conducted by Working Group 11 of Accredited Standards Committee S12, Noise, to develop procedures to estimate the field performance of hearing protection devices (HPDs). Current standardized test methods overestimate the attenuation achieved by workers in everyday use on the job. The goal was to approximate the amount of attenuation that can be achieved by noise‐exposed populations in well‐managed real‐world hearing conservation programs, while maintaining acceptable interlaboratory measurement variability. S12/WG11 designed two new laboratory‐based protocols for measuring real‐ear attenuation at threshold, with explicit procedures for subject selection, training, supervision, and HPD fitting. After pilot‐testing, S12/WG11 conducted a full‐scale study of three types of earplugs and one earmuff tested by four independent laboratories using both protocols. The protocol designated as ‘‘subject‐fit’’ assessed the attenuation achieved by subjects who were experienced in threshold ...

Use of historical data and a novel metric in the evaluation of the effectiveness of hearing conservation program components

Objectives To evaluate the effectiveness of hearing conservation programs (HCP) and their specific components in reducing noise-induced hearing loss (NIHL). Methods This retrospective cohort study was conducted at one food-processing plant and two automotive plants. Audiometric and work-history databases were combined with historical noise monitoring data to develop a time-dependent exposure matrix for each plant. Historical changes in production and HCP implementation were collected from company records, employee interviews and focus groups. These data were used to develop time-dependent quality assessments for various HCP components. 5478 male (30u2008427 observations) and 1005 female (5816 observations) subjects were included in the analysis. Results Analyses were conducted separately for males and females. Females tended to have less NIHL at given exposure levels than males. Duration of noise exposure stratified by intensity (dBA) was a better predictor of NIHL than the standard equivalent continuous noise level (Leq) based upon a 3-dBA exchange. Within this cohort, efficient dBA strata for males were <95 versus ≥95, and for females <90 versus ≥90. The reported enforced use of hearing protection devices (HPDs) significantly reduced NIHL. The data did not have sufficient within-plant variation to determine the effectiveness of noise monitoring or worker training. An association between increased audiometric testing and NIHL was believed to be an artifact of increased participation in screening. Conclusions Historical audiometric data combined with noise monitoring data can be used to better understand the effectiveness of HCPs. Regular collection and maintenance of quality data should be encouraged and used to monitor the effectiveness of these interventions.

Alternative Field Methods for Measuring Hearing Protector Performance

In comparison with the mandatory noise reduction rating (NRR) testing of every hearing protector sold in the United States, real-world tests of hearing protector attenuation are scarce. This study evaluated data from three potential field-test methods as compared with the subject-fit data from Method B of ANSI S12.6-1997 for the E.A.R(R) Express trade mark Pod Plug trade mark. The new field-test methods were the FitCheck headphone (FCH) method, FitCheck in sound field (FCSF) method, and bone-conduction loudness balance (BCLB) method, all of which can be administered in small single-person audiometric booths such as are commonly found in industry. Twenty normal-hearing and audiometrically competent subjects naive to hearing protector use were tested with the laboratory and the three field-test methods in a repeated-measures design. Repeated-measures models with structured covariance matrices were used to analyze the data. Significant effects were found for method, frequency, and first-order frequency-by-gender and frequency-by-method interactions. These effects and interactions were expected given the different psychophysical tasks. The FCSF and BCLB methods provided attenuations that were not significantly different from those found with Method B. Although the attenuations measured for the FCH method were statistically different (greater) than the attenuations from the other methods, the differences were within the magnitude of acceptable test-retest audiometric variability. The results suggest that the FCH and FCSF methods were both feasible and reliable methods for field testing. The FCH method is limited to testing earplugs, and the FCSF requires additional equipment to outfit the test booth, but could be used for testing all types of protectors.

Development of a new standard laboratory protocol for estimation of the field attenuation of hearing protection devices: sample size necessary to provide acceptable reproducibility.

The mandate of ASA Working Group S12/WG11 has been to develop laboratory and/or field procedure(s) that yield useful estimates of field performance of hearing protection devices (HPDs). A real-ear attenuation at threshold procedure was selected, devised, tested for one earmuff and three earplugs via an interlaboratory study involving five laboratories and 147 subjects, and incorporated into a new standard that was approved in 1997 [Royster et al., Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part I. Research of Working Group 11, Accredited Standards Committee S 12, Noise, J. Acoust. Soc. Am. 99, 1506-1526; ANSI, S12.6-1997, American National Standard method for measuring real-ear attenuation of hearing protectors (American National Standards Institute, New York, 1997)]. The subject-fit methodology of ANSI S12.6-1997 relies upon listeners who are audiometrically proficient, but inexperienced in the use of HPDs. Whenever a new method is adopted, it is important to know the effects of variability on the power of the measurements. In evaluation of protector noise reduction determined by experimenter-fit, informed-user-fit, and subject-fit methods, interlaboratory reproducibility was found to be best for the subject-fit method. Formulas were derived for determining the minimum detectable difference between attenuation measurements and for determining the number of subjects necessary to achieve a selected level of precision. For a precision of 6 dB, the study found that the minimum number of subjects was 4 for the Bilsom UF-1 earmuff, 10 for the E.A.R Classic earplug, 31 for the Willson EP100 earplug, and 22 for the PlasMed V-51R earplug.

Detection of Tones in the Absence of External Masking Noise

Sound pressures required for various levels of detection performance, in the absence of external masking, are summarized in iso‐detectability contours. Each such contour shows, for frequencies from 125 to 4000 Hz, the SPL of 150‐msec tone pulses which yield a specific probability of correct decisions in a two‐alternative, temporal, forced‐choice psychophysical procedure (2ATFC). Detection in the absence of externally introduced masking noise is found to differ in no qualitative ways from that in the presence of noise. Additional results suggest a spectrum of “internal noise” which is essentially a critical ratio below the sound pressure level of low‐detectability (d′ = 1.0) tones in the quiet. Iso‐detectability contours for detection performance of 55% and 99% correct in the 2ATFC procedure are found to enclose the range of sound pressure levels currently accepted as audiometric zero (ISO). [Work supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education a...

Identification of synthetic /bdg/ by hearing‐impaired listeners under monotic and dichotic formant presentation

Individuals with sensorineural hearing losses of both flat and sloping configuration evidence difficulty in identifying stop consonant place of articulation. To assess whether upward spread of masking is responsible for this difficulty, we presented hearing-impaired listeners with stimuli from a /ba da ga/ continuum in both monotic and dichotic (F1 to one ear; F2/F3 to the other ear) listening conditions. In the monotic conditions, listeners with similar audiograms evidence great variability in identification performance. In the dichotic conditions performance did not generally improve. For a few listeners, however, the improvement was striking. At moderate levels of signal presentation, upward spread of masking does not appear to be responsible for the poor identification of place by the majority of listeners with moderate hearing losses.