Early noise-induced hearing loss in teenage boys

The Significance of Audiometric Notching in Individuals With a History of Noise Exposure: A Systematic Review

OBJECTIVES

The diagnosis of noise-induced hearing loss (NIHL) is reliant on the appraisal of audiometric data. A notch, dip or bulge, centered at the 4-kHz frequency is considered to be pathognomonic. However, guidelines applied to assist the diagnosis of NIHL often allow for a notch centered between the 3- and 6-kHz frequencies. The primary outcome of this review is to document the relationship between audiometric notching at particular frequencies and the populations in which they have been identified.

DESIGN

We included all population-based studies, cohort, cross-sectional, case-control, case-series, and case reports of adults and children, with exposure to noise and with a notch, dip or bulge. The review has been registered with Prospero (Registration: CRD42017079901) and prepared in line with the PRISMA guidelines.

RESULTS

We included 84 articles in the final systematic review. There were a total of 1,438,987 individuals, aged 7 to 80 years old. The studies were conducted in 26 different countries. Fourteen studies identified notching at 3 kHz, 63 studies identified notching at 4 kHz, and 47 studies identified notching at 6 kHz. The Newcastle-Ottawa risk assessment tool was performed on 82 of the studies emphasizing the high risk of bias in observational studies.

CONCLUSIONS

The overwhelming outcome of this systematic review demonstrates that the relationship between noise exposure and a 3- to 6-kHz audiometric notch is not straight-forward. A handful of articles have displayed a clear association between an individual's noise exposure and an audiometric notch. Unilateral notches, notches observed at 3 kHz and notches in the absence of continued high-intensity noise exposure must be scrutinized thoroughly. The ambiguous nature of NIHL directs its continued interest.

Epidemiology and Risk Factors for Leisure Noise-Induced Hearing Damage in Flemish Young Adults

CONTEXT

Young people regularly expose themselves to leisure noise and are at risk for acquiring hearing damage.

AIMS

The objective of this study was to compare young adults' hearing status in relation to sociodemographic variables, leisure noise exposure and attitudes and beliefs towards noise.

SETTINGS AND DESIGN

A self-administered questionnaire regarding hearing, the amount of leisure noise exposure and attitudes towards noise and hearing protection as well as an audiological test battery were completed. Five hundred and seventeen subjects between 18 and 30 years were included.

SUBJECT AND METHODS

Hearing was evaluated using conventional audiometry, transient evoked and distortion product otoacoustic emissions. On the basis of their hearing status, participants were categorised into normal hearing, sub-clinical or clinical hearing loss.

STATISTICAL ANALYSIS USED

Independent samples t-tests, chi-square tests and multiple regression models were used to evaluate the relation between groups based on hearing status, sociodemographics, leisure noise and attitudes towards noise.

RESULTS

Age was significantly related to hearing status. Although, the subjects in this study frequently participated in leisure activities, no significant associations between leisure noise exposure and hearing status could be detected. No relation with subjects' attitudes or the use of hearing protection devices was found.

CONCLUSIONS

This study could not demonstrate clinically significant leisure noise-induced hearing damage, which may lead to more non-protective behaviour. However, the effects of leisure noise may become noticeable over a long-term use since age was found to be related with sub-clinical hearing loss. Longitudinal studies are needed to evaluate the long-term effects of noise exposure.

Noise exposure and auditory thresholds of German airline pilots: a cross-sectional study

OBJECTIVE

The cockpit workplace of airline pilots is a noisy environment. This study examines the hearing thresholds of pilots with respect to ambient noise and communication sound.

METHODS

The hearing of 487 German pilots was analysed by audiometry in the frequency range of 125 Hz-16 kHz in varying age groups. Cockpit noise (free-field) data and communication sound (acoustic manikin) measurements were evaluated.

RESULTS

The ambient noise levels in cockpits were found to be between 74 and 80 dB(A), and the sound pressure levels under the headset were found to be between 84 and 88 dB(A).The left-right threshold differences at 3, 4 and 6 kHz show evidence of impaired hearing at the left ear, which worsens by age.In the age groups <40/≥40 years the mean differences at 3 kHz are 2/3 dB, at 4 kHz 2/4 dB and at 6 kHz 1/6 dB.In the pilot group which used mostly the left ear for communication tasks (43 of 45 are in the older age group) the mean difference at 3 kHz is 6 dB, at 4 kHz 7 dB and at 6 kHz 10 dB. The pilots who used the headset only at the right ear also show worse hearing at the left ear of 2 dB at 3 kHz, 3 dB at 4 kHz and at 6 kHz. The frequency-corrected exposure levels under the headset are 7-11 dB(A) higher than the ambient noise with an averaged signal-to-noise ratio for communication of about 10 dB(A).

CONCLUSIONS

The left ear seems to be more susceptible to hearing loss than the right ear. Active noise reduction systems allow for a reduced sound level for the communication signal below the upper exposure action value of 85 dB(A) and allow for a more relaxed working environment for pilots.

Hearing in young adults. Part II: The effects of recreational noise exposure

Great concern arises from recreational noise exposure, which might lead to noise-induced hearing loss in young adults. The objective of the current study was to evaluate the effects of recreational noise exposure on hearing function in young adults. A questionnaire concerning recreational noise exposures and an audiological test battery were completed by 163 subjects (aged 18-30 years). Based on the duration of exposure and self-estimated loudness of various leisure-time activities, the weekly and lifetime equivalent noise exposure were calculated. Subjects were categorized in groups with low, intermediate, and high recreational noise exposure based on these values. Hearing was evaluated using audiometry, transient-evoked otoacoustic emissions (TEOAEs), and distortion-product otoacoustic emissions (DPOAEs). Mean differences in hearing between groups with low, intermediate, and high recreational noise exposure were evaluated using one-way analysis of variance (ANOVA). There were no significant differences in hearing thresholds, TEOAE amplitudes, and DPOAE amplitudes between groups with low, intermediate, or high recreational noise exposure. Nevertheless, one-third of our subjects exceeded the weekly equivalent noise exposure for all activities of 75 dBA. Further, the highest equivalent sound pressure levels (SPLs) were calculated for the activities visiting nightclubs or pubs, attending concerts or festivals, and playing in a band or orchestra. Moreover, temporary tinnitus after recreational noise exposure was found in 86% of our subjects. There were no significant differences in hearing between groups with low, intermediate, and high recreational noise exposure. Nevertheless, a long-term assessment of young adults’ hearing in relation to recreational noise exposure is needed.

The prevention of noise induced hearing loss in children

Increasingly, our acoustic environment is filled with amplified sound sources (e.g., MP3 players, video game stations, and sports/entertainment venues). There is serious concern and also some controversy about the risks of acoustic trauma in children. This overview provides some basic information on the physiological mechanisms that lead to noise induced hearing loss, a survey of various studies that, on balance, indicates that there is cause for concern, and finally a discussion on measures that can help to prevent noise induced hearing loss in children. This paper is designed for public health and other healthcare professions (ENT, audiologists, family doctors, and pediatricians) who should understand the risks of noise induced hearing loss and its prevention.

Noise-induced hearing loss in children: A 'less than silent' environmental danger

A review of the problems of noise-induced hearing loss in children, especially related to recreational music and the use of personal entertainment devices. The pathophysiology of noise-induced hearing loss and its associated problems (eg, tinnitus) are discussed. The evidence for an increase in noise-induced hearing loss in children and young people is reviewed. Some practical advice (for clinicians, caregivers and children) on hearing loss prevention is provided.

Noise exposures of rural adolescents

PURPOSE

This project was conducted to characterize the noise exposure of adolescents living in rural and agricultural environments.

METHODS

From May to October, 25 adolescents ages 13 through 17, living either on a farm or a rural nonfarm, were enrolled in the study. Subjects received training on the correct operation and use of personal noise dosimeters and the proper way to record their daily tasks on activity cards. Subjects completed 4 days of self-monitoring noise dosimetry, 2 days in the first round (May-July) and 2 days in the second round (August-October). In addition to dosimetry, subjects completed activity logs of their daily tasks.

RESULTS

The mean daily noise exposures of adolescents living on farms and in nonfarm rural homes were between 55.4 dBA (A-weighted decibels) and 103.5 dBA, with 44% of the daily measurements greater than the National Institute of Occupational Safety and Health Recommended Exposure Level of 85 dBA. Task-based analysis of noise exposures found that activities involving mechanized equipment resulted in the highest exposures, while activities in the home resulted in the lowest exposure. No particular demographic group had a statistically higher noise exposure; therefore, specific factors apart from activities and noise sources could not be identified as risk factors for exposure to hazardous noise levels.

CONCLUSIONS

The results of this project indicate that rural adolescents complete a variety of activities and are exposed to noise sources with a broad range of decibel levels. While the exposures may change from day to day, there are occasions when exposure to noise exceeds the recommended levels.

Comparison of Audiometric Screening Criteria for the Identification of Noise-Induced Hearing Loss in Adolescents

Purpose

To ascertain whether current pure-tone school hearing screening criteria used across the United States are adequate for the early identification of noise-induced hearing loss (NIHL) in adolescents.

Method

School-based pure-tone hearing screening protocols were collected, reviewed, and consolidated from 46 state agencies. A retrospective categorical analysis of air-conduction audiometric thresholds from a computerized database of 9th-grade ( n = 376) and 12th-grade ( n = 265) students from a suburban high school was conducted. The database analysis was designed to determine whether each screening protocol would identify high-frequency notched audiometric configurations suggestive of NIHL when using the noise notch criteria described by A. S. Niskar et al. (2001).

Results

All of the school-based hearing screening criteria identified significantly ( p ≤ .05) fewer students with a high-frequency notch (HFN) than the noise notch protocol regardless of screening decibel level specified. Over half of the school-based hearing screening protocols used in the United States will identify only 22% of the students with an HFN and consequently would fail to detect a potential NIHL.

Conclusions

Currently implemented school-based hearing screening guidelines are nonstandardized and inadequate for the early identification of NIHL. This denies the majority of students the opportunity to receive early intervention and to prevent further progression of NIHL. It is necessary to identify, standardize, and implement effective and efficient screening or monitoring programs for the early detection and prevention of NIHL in adolescents.

Asymmetric hearing loss in a random population of patients with mild to moderate sensorineural hearing loss

OBJECTIVES

We evaluated the correlation of asymmetric hearing loss, in a random population of patients with mild to moderate sensorineural hearing loss, to several clinical factors such as age, sex, handedness, and noise exposure.

METHODS

We randomly selected, from 8 hearing institutes in Israel, 429 patients with sensorineural hearing loss of at least 30 dB at one frequency and a speech reception threshold not exceeding 30 dB. Patients with middle ear disease or retrocochlear disorders were excluded. The results of audiometric examinations were compared binaurally and in relation to the selected factors.

RESULTS

The left ear's hearing threshold level was significantly higher than that of the right ear at all frequencies except 1.0 kHz (p < .05). One hundred fifty patients (35%) had asymmetric hearing loss (more than 10 dB difference between ears). In most of the patients (85%) the binaural difference in hearing threshold level, at any frequency, was less than 20 dB.

CONCLUSIONS

Age, handedness, and sex were not found to be correlated to asymmetric hearing loss. Noise exposure was found to be correlated to asymmetric hearing loss.

Hearing ability according to screening at conscription; comparison with earlier reports and with previous screening results for individuals without known ear disease

OBJECTIVE

(1) To study if young, Swedish men have poorer or better hearing according to screening at conscription in 1988 compared to 1969-1977. (2) To study how the results of screening and audiometry vary across the teenage years for a group of boys without middle ear disease.

METHOD

A birth cohort has earlier been well documented regarding results in four general screenings with follow-up and examinations and treatment for middle ear disease at the ENT departments in the area. Their results when screened at conscription have been compared with those in earlier reports on screening of Swedish conscripts. We have also studied results in screenings and follow-up at 11 and 14 years of age with special focus on small losses at the frequencies of 3, 4, 6 and 8 kHz and describe how 611 boys without known ear disease performed in these examinations and in screening at the age of 18.

RESULTS

There is no obvious trend in the prevalence of hearing loss in Swedish conscripts. At 11 years of age 80.4% and at 14 years of age 64.6% of small high tone losses diagnosed by screening were not confirmed by audiometry. Approximately half of those who had confirmed losses had normal screening at conscription.

CONCLUSIONS

18-year-old Swedish boys did not have poorer hearing in 1998 than 29 years earlier. Information drawn from screenings must be interpreted with caution.

The association between short stature and sensorineural hearing loss

In order to test the Thrifty Phenotype Hypothesis on hearing, data from two cross-sectional studies on hearing were re-evaluated. The data sets comprised 500 18-year-old conscripts, and 483 noise-exposed male employees. Sensorineural hearing loss (SNHL) was over-represented among conscripts with a short stature (odds ratio=2.2) or hearing loss in the family (odds ration=4.2), but not among noise-exposed conscripts (odds ratio=0.9-1.3). Among noise-exposed short employees, hypertension and age exhibited a negative impact on high frequency hearing thresholds, while among tall employees hypertension had no effect on hearing and the influence of age was less pronounced (p<0.01 for body height; p<0.02 for age, hypertension and the interaction between body height and hypertension; p<0.05 for the interaction between body height and age). This suggests that mechanisms linked to fetal programming and growth retardation and/or insulin-like growth factor 1 levels during fetal life, such as a delayed cell cycle during the time window when the cochlea develops, may cause SNHL in adulthood.

Recreational noise exposure and its effects on the hearing of adolescents. Part II: development of hearing disorders

Part II, continuation of a previous paper, describes the significant hearing threshold shift found during the third year of the long-term study, which continued to be present in the fourth year, in a number of adolescents classified as Subgroup 2, who showed a higher mean HTL in the middle and especially in the high frequency ranges than the rest of the studied adolescents, classified as Subgroup 1. In both subgroups, the subjects showed high participation in recreational activities; nevertheless, the adolescents in Subgroup 2 showed higher participation in some of them in the last year of the study. From the beginning of the study, the mean HTL of the adolescents in Subgroup 2 was higher than the mean HTL of the adolescents in Subgroup 1. The exposure to high sound levels during leisure activities can be a cause of permanent hearing damage among young people with 'tender ears'.

Prevalence of hearing impairment in a population in Sweden

An epidemiological study was carried out, based on 590 randomly selected subjects, aged from 20 to 80 years, in the province of Ostergötland in Sweden. The results obtained were similar to published results from other countries, with an overall prevalence of subjects with average hearing threshold levels over the frequencies 0.5, 1, 2 and 4 kHz (M4) equal to or exceeding 25 dB HL for the better ear (BE) of 16.9% (95% CI: 13.819.9%). For M4 BE > or = 35 dB HL, the prevalence was 7.7% (95% CI: 5.5-9.8%), for M4 BE > or = 45 dB HL, the prevalence was 3.3% (95% CI: 1.9-4.8%), and for M4 BE > or = 65 dB HL, the prevalence was 0.2% (95% Cl: 0.0-0.6%). The overall prevalence of reported tinnitus was 13.2% (95% CI: 10.5-16.0%). In the population under study, 7.7% of the subjects were estimated to benefit from a hearing aid, while the prevalence of hearing aid users was 2.4%.

Characteristics of the audiometric notch as a clinical sign of noise exposure

This study investigated variability in audiometric notch recognition by asking three clinicians to identify notches in the audiograms of 634 noise-exposed employees. Agreement between the raters was assessed, and three notch characteristics, frequency, depth and shape (a wide or narrow notch), were investigated as recognition factors. The proportions of positive tests reported by each rater were 0.26, 0.49 and 0.68, respectively. The 'all rater' index of agreement was 0.45, and the range for pairwise comparisons was 0.14 to 0.52. With recognition factors, rater 1 was most strongly influenced by depth, rater 2 by shape and rater 3 by a possible combination of criteria. To reduce variability we suggest that narrow notches should be at least 15 dB in depth, and that broad notches should have a depth of 20 dB, with a recovery of at least 10 dB at the high end. Care should also be taken to elicit a sufficient history of noise exposure, and ensure that there are no other explanations for the notch.

Peripheral auditory asymmetry in infantile autism

Difficulty in filtering relevant auditory information in background noise is one of the features of autism. Auditory filtering processes can be investigated at the peripheral level as they are hypothesized to involve active cochlear mechanisms which are regulated by the efferent activity of the medial olivocochlear (MOC) system. The aim of the present work was therefore to assess these peripheral auditory processes in 22 children and adolescents with autism compared with age- and gender-matched normal controls. Active cochlear mechanisms were evaluated with transiently evoked otoacoustic emissions (TEOAEs) and MOC system efficiency was assessed via TEOAEs which are decreased when stimulating the contralateral ear with noise. The MOC system evaluation was performed on 18 of the 22 children. In both studies, results were analysed according to age (from 4 to 10 years and from 11 to 20 years). The main result concerns the asymmetry of the efferent system which differs in individuals with autism. Several neural processes might be hypothesized as involved in the results obtained as the MOC system which originates in the brainstem received regulating controls from upper brain structures including auditory cortex. Lateralization abnormalities at the auditory periphery may reflect indirectly a problem at a higher level of auditory processing. A second important result shows a decrease in TEOAE amplitude with age, in patients, that may correspond to a decrease in hearing sensitivity.

Audiometric notch as a sign of noise induced hearing loss

OBJECTIVES

To investigate the relation between different types of exposure to noise and a classic sign of noise induced hearing loss (NIHL), the audiometric notch.

METHODS

The study sample had exposure to both continuous and impulse noise and was drawn from a population of electrical transmission workers. Audiograms, taken as part of a hearing conservation programme, were read by three clinicians experienced in the assessment of NIHL. Working independently and using their clinical judgment, they were asked to identify localised increases in the threshold of hearing (audiometric notches) which they would attribute to noise, had a suitable history of exposure been elicited. Prevalent cases of NIHL were identified by the presence of a notch in either ear. Risk factors for NIHL were assessed by a questionnaire which sought information about exposure to air blast circuit breaker noise; firearms; explosions, and continuous noise. The odds of exposure to these factors in those with and without hearing loss were calculated, and odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated by logistic regression.

RESULTS

Of the 648 questionnaires sent out 357 were returned, a response rate of 55%. Of these, at least two out of the three assessors identified 175 (49%) people with a notch at any audiometric frequency. There was no association between these cases and the NIHL risk factors identified by the questionnaire, but a further frequency specific analysis showed a small proportion of people (15 (4%)) with notches at 4 kHz who had the expected associations with exposure to noise and a significant OR for firearms of 4.25 (95% CI 1.28 to 14.1). The much larger proportion of people with 6 kHz notches (110 (31%)) did not show these associations.

CONCLUSIONS

To diagnose NIHL it is important to elicit a detailed and accurate history of exposure to noise: although the notch at 4 kHz is a well established clinical sign and may be valuable in confirming the diagnosis, the 6 kHz notch is variable and of limited importance.

Tones disappear faster in the right ear than in the left

In order to gain further information on the characteristics and physiological correlates of tone decay in humans, the tone decay test was administered to 58 normal-hearing subjects, successively in the left and right ears and in absence and presence of a contralateral noise. The results revealed that tone decay was greater in the right than in the left ear and was increased by contralateral noise. The contralateral effect of this noise on cochlear biomechanisms was then estimated by measuring contralaterally induced variations in the amplitude of click-evoked otoacoustic emissions in the same subjects. In the right ear, the increase in tone decay and the decrease in otoacoustic emission amplitude--both induced by contralateral noise--were positively correlated (r = .315, p = .016). Furthermore, the contralateral changes in otoacoustic emission amplitude were found to be on average larger in the right than in the left ear, this asymmetry being correlated with that observed for the tone decay. These findings are discussed in relation to previous results on simple and induced loudness adaptation in the vicinity of threshold, on contralateral attenuation of otoacoustic emissions and on the influence of the auditory efferents on cochlear biomechanisms.

Do we know the real need for hearing rehabilitation at the population level? Hearing impairments in the 5- to 75-year-old cross-sectional Finnish population

The cross-sectional population sample studied here was randomly selected from the population register of northern Finland. The subjects comprised 10 different age groups between 2 and 75 years of age. Pure tone averages over the frequencies of both 0.5, 1 and 2 kHz and 0.5, 1, 2 and 4 kHz - i.e. better ear hearing levels (BEHL) of BEHL0.5-2kH and BEHL0.5-4kHz - were calculated. The prevalence of various grades of hearing impairment was investigated among the 3518 people who participated in audiometric measurements. Two different classifications were used to grade the hearing impairment. According to the World Health Organization (WHO) classification (1991), 94.3% of the subjects had normal hearing, whereas 3.8% had mild hearing impairment, 1.3% had moderate impairment, 0.4% severe impairment and 0.1% profound impairment. When the more recent EU definition (1996) was used, 85.3% of the subjects had normal hearing. Mild impairment was found in 11.5% of the subjects, moderate impairment in 2.8%, severe impairment in 0.3%, and profound in 0.1%. The difference between the two definitions mentioned above (resulting in different prevalence figures of hearing impairments) is clear. The WHO classification reveals the need for rehabilitation and can thus be used as a basis of resource allocation, whereas the EU proposal reveals even the mildest hearing impairments and hence better illustrates the real prevalence of impairment. The need for the current and future audiological services may be estimated from the prevalence rates of hearing impairments. The proportion of the Finnish elderly - the people most frequently using health services - is expected to increase from today's 15% to 23% within the next 20 years. The same phenomenon is to be expected in other Western societies.

Minimal, progressive, and fluctuating hearing losses in children. Characteristics, identification, and management

Referring to specific types of hearing loss as "minimal" or "mild" seems to imply that their effects are equally mild or negligible. A growing body of literature, however, supports the notion that such losses can have a significant impact on the communicative and educational development of young children. Although OME is considered a common childhood ailment, mounting evidence suggests that it is not always benign and may contribute to significant educational and communicative difficulties in some young children when accompanied by conductive hearing loss. Even very mild bilateral and unilateral SNHL seems to contribute to problems in the areas of social and emotional function, educational achievement, and communication in some children. Because these hearing losses are so mild, they may not be immediately recognized as the source of such difficulties. The purpose of this report is to heighten the general pediatrician's awareness of the significance of even very mild or minimal hearing losses in children. As the gatekeepers for children's health care, pediatricians are typically the primary recipients of parental expressions of concern and the initiators of evaluations or referrals to address such.

Click evoked otoacoustic emissions: inter-aural and gender differences in newborns

Click evoked otoacoustic emissions (CEOAEs) are an objective and reliable method of assessing cochlear status, particularly suitable for newborns. This study aimed to assess CEOAE inter-aural and gender differences. Other non-auditory factors, such as infant's head size and weight, were considered. Band averaged CEOAEs were analyzed for 120 healthy, full term newborns, 61 females and 59 males. The babies were randomly selected from the nursery and tested in a quiet room away from the ward, using an Otodynamic ILO 92 system. The CEOAEs of the females were significantly larger than those of the males. For the frequency bands 2, 3, and 4 kHz and for the overall response, the emissions were larger in the right ear, for both males and females. These inter-aural differences were more pronounced in male subjects than in female subjects. These findings may reflect the accumulating evidence that differences exist in efferent cochlear inhibition.

Estimated leisure noise exposure and hearing symptoms in Finnish teenagers

The aim of this study was to arrive at a theoretical statistical measure for the possible risk of future noise-induced hearing loss (NIHL) due to leisure time activities in teenagers. The subject's time consumed in noisy activities, the subject's self-evaluated loudness of the activities and estimated noise levels were used as the actual predictors in the risk analysis. Symptoms of hearing damage, i.e. tinnitus, pain in the ear and temporary hearing loss due to noise exposure, were also inquired about. No measurements of hearing loss were carried out in this study. Fifty-one percent of teenagers were estimated to be exposed to noise levels detrimental to hearing acuity. The incidence of hearing symptoms seemed to be correlated to increased noise dose. The noisiest leisure activities were: playing in a band, motor sport, discos and pop-concerts, and shooting. The results give indications of possibilities for NIHL among teenagers.

Screening for Hearing Loss in Adolescents

Three-hundred-forty-two adolescents between the ages of 10–20 years were administered an auditory screening protocol consisting of a: (a) noise history questionnaire, (b) otoscopic inspection, (c) tympanometry, and (d) pure-tone screening at 25 dB HL at 1000, 2000, 4000, and 6000 Hz. Results of this screening protocol suggest a high level of admitted noise exposure in the adolescent population. Overall failure rate was 25%. Pure-tone failure rate was 7% for the frequencies of 1000, 2000, and 4000 Hz, increasing to 17% when 6000 Hz was added. Significant correlations were found between firearm use and hearing loss at 6000 Hz. Recommendations for screening the adolescent population are made, and suggestions for educational intervention on the effects of firearm usage are provided.

The Effectiveness of an Interactive Hearing Conservation Program for Elementary School Children

An educational hearing conservation program (HCP) emphasizing student participation and supplemental in-class activities led by a teacher was presented in two 1-hour sessions to two classes of fourth-grade children enrolled in regular education programs. Questionnaires assessing their knowledge of hearing, noise-induced hearing loss, and hearing conservation practices were administered before and after the HCP. Significant increases in knowledge concerning noise-induced hearing loss and hearing conservation practices were seen in both classes, with greater gain seen among students receiving more extensive supplemental activities. Post-HCP responses revealed that the majority of the children intend to use ear protection when engaged in noisy activities. Teachers indicated they would increase coverage of hearing and hearing conservation in their classrooms and use hearing protection when exposed to loud noise.

Hearing loss associated with weapons noise exposure: when to investigate an asymmetrical loss

The air conduction thresholds in the right and left ears, and the interaural asymmetry of thresholds at 0.5, 1, 2, 3, 4 and 6 kHz were measured in a group of 225 soldiers exposed to a variety of weapon noise who were referred for assessment because of a deterioration in hearing on routine testing. At 0.5 and 1 kHz the threshold levels rarely exceeded 25 dB and the interaural asymmetry was 10 dB or less in 90 per cent of cases. The degree of hearing loss and interaural asymmetry increased as the frequency increased, with the average loss being significantly greater in the left ear at 2, 3, 4 and 6 kHz. Recommendations are made for the selection of cases of asymmetrical hearing loss exposed to weapon noise which require further investigation to exclude a retrocochlear cause or to define spurious hearing threshold levels.

Temporary threshold shift and otoacoustic emissions after industrial noise exposure

The objective of the present study was to investigate whether employees in a noise-exposed environment developed changes in cochlear function as manifested by elevation of pure-tone threshold and/or reduction in transient evoked otoacoustic emission (TEOAE) amplitude. Pure-tone air-conduction audiometry, otoacoustic emissions (OAEs) and tympanometry were recorded in 13 healthy employees on three consecutive days both before and after 7 h of noise exposure. Employees exposed to an industrial noise level of 85-90 dBA developed significant pure-tone air-conduction threshold elevation at 4 and 6 kHz. A significant reduction of the TEOAE amplitude was found. There was no correlation between temporary threshold shift (TTS) and TEOAE reduction.

Hearing in 18-year-old Swedish males

In modern work practice, occupational noise exposure appears to be diminishing. Conversely, leisure noise activities appear to increase exposure to both the occurrence and the level of sound. If increased exposure to noise results in deteriorating hearing, one would expect to discover this by audiometric tests in teenagers. In the present investigation, 500 randomly selected conscripts from military service were tested. The mean hearing level was mostly well within that expected by international standards. The individual analyses show that 14% had some hearing loss defined as more than 20 dBHL in either ear and in the frequency range 0.25-8 kHz. This figure is considerably lower than recent reports from Norway and Great Britain. We did not find any correlation between different health parameters and hearing loss, except that conscripts of short stature tended to have more hearing loss. Consequently, we could not confirm an increasing general prevalence of hearing loss in young male individuals.

A speculation about the parallel ear asymmetries and sex differences in hearing sensitivity and otoacoustic emissions

Hearing sensitivity and the prevalence of spontaneous otoacoustic emissions show parallel ear and sex differences in humans. Here it is proposed that these lateral asymmetries and sex differences may all result from differences in the 'strength' of the efferent inhibition delivered to individual cochleas. Specifically, it is proposed that the amount of efferent inhibition is relatively less in right ears and in females than in left ears and males. While it is unclear why or how ear asymmetries or sex differences would develop in the efferent system, by assuming that they do, one can begin to explain a number of basic facts of hearing. It is even possible that the lateral asymmetry in the efferent system may be related to the well-known cortical asymmetries that are believed to underlie speech perception, speech production, and other human abilities.

A Study of Noise Exposure and Hearing Sensitivity in a High School Woodworking Class

The purpose of this study was to determine if noise in a high school woodworking class could contribute to the incidence of hearing loss. Students in the woodworking class served as the experimental group, and students in a technical drawing class were the control group. Four separate experiments were conducted. Experiment 1 consisted of measuring and comparing the sound levels in the woodworking and the technical drawing class environments. In Experiment 2, dosimetry samples of the students in both classrooms were collected. In Experiment 3, the temporary threshold shifts (TTSs) were determined for students in both groups by assessing hearing thresholds at the beginning and end of a single class period. The focus of Experiment 4 was to determine if a threshold shift had occurred in the hearing of the students in the woodworking class over a semester.

Results of this study suggest that hazardous noise levels in the high school woodworking shop caused statistically significant TTS among the students. Relatively low noise doses were recorded, but no significant changes in hearing thresholds from the beginning to the end of the semester were noted. It was concluded that repeated noise exposure in a woodworking class may be a contributing factor to hearing loss among a student population and that a hearing conservation program should be instituted in these high school environments.

Noise levels from toys and recreational articles for children and teenagers

This study examined the noise level emitted by toys and recreational articles used by children and teenagers. The results indicate that many of the items tested emit sufficiently intense noise to be a source of noise induced hearing loss in school-age children. While the baby toys provided noise exposure within the limits of national regulations, they are most intense in a frequency range that corresponds to the resonance frequency of the external auditory canal of very young children. Hobby motors emit noise that may require protection depending upon the length of use. Fire-crackers and cap guns emit impulse noises that exceed even conservative standards for noise exposure.

Left-right asymmetries in hearing threshold levels in three age groups of a random population

The average asymmetry between the hearing threshold levels in the left and right ears was analyzed in a random population (n = 3487) representing a normal population. Males and females of age groups 5-10 years, 15-50 years and over 50 years were analyzed separately. A significant average inferiority of the hearing in the left ear was found at high frequencies, especially at 3-6 kHz, among adult males and females but not among children. A slight but statistically significant average superiority of the left ear at low frequencies was noted in all age groups. At corresponding hearing threshold levels at 4 kHz, the average inferiority of the left ear in the male population was significantly greater among subjects aged 15-50 years than among older subjects. In conclusion, the inferiority of hearing in the left ear at 4 kHz seems to be associated more with noise damage than with presbyacusis. The average interaural difference at 4 kHz was significantly more marked among subjects aged 15-50 years than among older subjects when analyzed at the corresponding threshold levels. These findings indicate a pathophysiological difference between noise damage and presbyacusis.

Left-right asymmetry in the human response to experimental noise exposure. II. Pre-exposure hearing threshold and temporary threshold shift at 4 kHz frequency

The repeatedly noted average inferiority of the left ear (or superiority of the right ear) in epidemiological surveys at frequencies most susceptible to noise damage has not been experimentally confirmed. Twenty-eight non-shooting young adults were exposed binaurally to broad-band noise for a maximum of 8 h in strictly symmetrical laboratory conditions. The left and right hearing thresholds of each individual were monitored during short interruptions in the exposure. The average interaural hearing threshold difference became statistically significant during the exposure, the left ear being worse than right. The negative correlation found between the pre-exposure threshold level and the temporary threshold shift (TTS) was more marked in the left than in the right ear. In conclusion a hypothesis is presented: a good hearing threshold level in the right ear seems to be better protected from noise-induced temporary threshold shift than a good hearing threshold in the left ear.

Hearing asymmetry among left-handed and right-handed persons in a random population

The possible effect of handedness on hearing threshold asymmetry was analysed in a large random population representing a normal population. The left ear was on an average slightly but significantly poorer than the right ear at high frequencies, especially at 4 kHz, while at low frequencies the right ear was on average poorer than the left ear. A matched control group of the right-handed subjects was formed for 211 left-handed subjects. Among the left-handed subjects the average ear asymmetry resembled the ear asymmetry of the whole population, the right-handed subpopulation, and of the matched control group. In conclusion, it seems that handedness cannot be responsible for the average inferiority of hearing in the left ear at 4-kHz or for the average slight superiority of the left ear at 0.125-0.5 kHz. However, this analysis does not rule out possible minor effects of handedness on ear asymmetry.

Left-right asymmetry in the human response to experimental noise exposure. I. Interaural correlation of the temporary threshold shift at 4 kHz frequency

Most epidemiological surveys concerning populations exposed to occupational noise or random populations have shown that the left ear is slightly but significantly poorer than the right ear, especially at frequencies most susceptible to noise damage. To experimentally study the possible left-right asymmetry in response to noise exposure, 28 non-shooting healthy young adults were exposed binaurally to symmetrical broad-band noise for a maximum of 8 h. 4 kHz hearing thresholds of each individual were monitored alternately in the left and right ears during short interruptions in the exposure. Considerable efforts were made to exclude any external factors that might influence the left-right asymmetry. A significant positive correlation between the temporary threshold shifts (TTS) in the left and in the right ear was found. The average TTS was higher in the left than in the right ear, the difference between ears being statistically indicative.

Hearing asymmetry among occupationally noise-exposed men and women under 60 years of age

Interaural asymmetry of hearing thresholds at 4 kHz was analysed in four populations exposed to occupational noise. The left ear was found to be on average significantly worse than the right ear, among both the male and female subjects. In the male population the left ear was twice as often the worse ear as the right one. In the female population the corresponding ratio was 1.5. The average inferiority of the left ear increased as a function of the hearing threshold level. Among subjects with abundant shooting (reindeer herders) the average inferiority of the left ear was close to the average of all male subjects. Interaural difference increased as a function of the hearing threshold level, both among subjects with the left ear and subjects with the right ear being the worse one. In the male population the interaural difference was significantly greater in the former than in the latter group of subjects.

Secretory otitis media and hearing loss

Hearing losses at 15 years of age were investigated in a material of 11,780 children born in Northern Finland in 1966 and followed-up since pregnancy. Two samples of the whole material, one representing a sample of 413 children with reported impaired hearing, and the other of 959 children with reported normal hearing were calculated to represent a total material of 11,748 cases. The correlation between the reported hearing and the audiometry results was very good. In the calculated material, 1,708 (14.6%) of the children exhibited a hearing loss exceeding 20 dB in at least one frequency in their school audiograms. The incidence of secretory otitis media as a risk diagnosis among those with impaired hearing was significantly higher than among those with normal hearing. Most of the hearing losses were found in the high frequencies.

Hearing loss in school children. A longitudinal study of sensorineural hearing impairment

In a longitudinal study, 2325 children were hearing tested at age 7, 10 and 13 with screening audiometry. The screening level was 20 dB HL. Approximately 75% of the children passed the screening level at all ages. Hearing loss was more frequent in boys than in girls at age 13 (16%:9%). The left ear was more commonly affected than the right ear. High frequency dips increased for boys with age, but not for girls. The increasing incidence of hearing loss for boys with age is probably due to noisy leisure time activities.

Audiological screening of Amerindians of the Suriname rainforest

Audiological screening tests were conducted among a remote, relatively noise-free population of Amerindians in the deep rainforests of Surinam, South America. These preliminary tests, the initial step in a planned long-term study, were the first such examinations on these people, and were intended to examine the overall audiological health of the population as a function of age and sex. Audiological testing of this non-technological population was more challenging than conventional test situations in modern industrial societies because the tests were hampered by a variety of extraneous factors. The results from a sample of the population showed a range of hearing impairments similar to that seen in modern industrial societies, including conductive, mixed, and sensorineural hearing losses. Also, hearing sensitivity was found to deteriorate with age in both females and males, particularly at the higher frequencies (2, 4, and 8 kHz). This deterioration was slightly greater for males, who as hunter-gatherers regularly use shotguns for hunting. Impact noise from hunting guns is the only source of intense noise to which the Amerindian population is exposed with any regularity. The diet of the Amerindians includes as the main carbohydrate staple the manioc cassava, which has also been linked to sensorineural hearing loss in some populations.

Prevalence of hearing loss at the age of 15 in a birth cohort of 12 000 children from northern Finland

Hearing losses at the age of 14 years were investigated in a questionnaire administered to 11 780 children born in northern Finland and followed up since pregnancy. The untraced cases numbered 20, or 1.7 per 1 000. Audiometry screening results from the schools were obtained from 97.2% of the 425 children who were reported to suffer from hearing loss and a random sample of 959 children with normal hearing. When the figures were calculated to represent the whole material of 11 748 cases, marked hearing loss, PTA greater than 25 dB in the better ear, was found in 64 children, 0.5%, minor loss, greater than 20 dB at 4 kHz but PTA less than 25 dB in the better ear, in 420 children, 3.6%, and slight abnormality, greater than 20 dB, at any frequency in 1 224, 10.4%. 17.6% of the boys and 11.8% of the girls had some kind of hearing loss. Eight children were deaf in both ears and 11 in one ear, and 16 children were severely impaired in at least one ear (PTA greater than or equal to 60; less than 90 dB).

Age-related changes in sensitivity of the postpubertal ear to acoustic trauma

Although the age of the postpubertal mammal is typically ignored in evaluating the damaging effects of noise on the ear, it was shown to account for over 65% of the variability in the mouse. 44 inbred CBA/J mice, ranging in age from 60 (early postpuberty) to 360 days (late middle age), were tested for cochlear AP thresholds at frequencies from 2 to 64 kHz. They were then subjected to 5 min of a 124 dB octave band (12-24 kHz) noise. Although all the mice had similar pre-exposure thresholds, the extent of noise-induced AP threshold elevation and the frequencies most severely affected depended upon the ages of the mice. The youngest subjects had the greatest threshold elevations, being most pronounced at, and 1 octave above, the center frequency of the noise exposure. With increasing age there was a progressively less severe effect. The oldest subjects had cochlear AP threshold elevations which were restricted to a frequency 2 octaves above the exposure frequency.