The distribution of hearing threshold levels in the general population aged 18-30 years

Guidelines for Diagnosing and Quantifying Noise-Induced Hearing Loss

This paper makes recommendations for the diagnosis and quantification of noise-induced hearing loss (NIHL) in a medico-legal context. A distinction is made between NIHL produced by: steady broadband noise, as occurs in some factories; more impulsive factory sounds, such as hammering; noise exposure during military service, which can involve very high peak sound levels; and exposure to very intense tones. It is argued that existing diagnostic methods, which were primarily developed to deal with NIHL produced by steady broadband noise, are not adequate for the diagnosis of NIHL produced by different types of exposures. Furthermore, some existing diagnostic methods are based on now-obsolete standards, and make unrealistic assumptions. Diagnostic methods are proposed for each of the types of noise exposure considered. It is recommended that quantification of NIHL for all types of exposures is based on comparison of the measured hearing threshold levels with the age-associated hearing levels (AAHLs) for a non-noise exposed population, as specified in ISO 7029 (2017), usually using the 50^th percentile, but using another percentile if there are good reasons for doing so. When audiograms are available both soon after the end of military service and some time afterwards, the most recent audiogram should be used for diagnosis and quantification, since this reflects any effect of the noise exposure on the subsequent progression of hearing loss. It is recommended that the overall NIHL for each ear be quantified as the average NIHL across the frequencies 1, 2, and 4 kHz.

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.

Hearing threshold levels of Australian coal mine workers: a retrospective cross-sectional study of 64196 audiograms

OBJECTIVE

This study examined the hearing threshold levels (HTL) of workers commencing employment in Australian coal mines in the State of New South Wales (NSW). The aim was to establish if some degree of hearing loss was identifiable in the mandatory pre-employment audiograms of workers.

DESIGN

This was an observational, retrospective, repeated cross-sectional study.

STUDY SAMPLE

De-identified audiometric records of 64196 employees entering NSW coal mining in three representative five-year periods between 1991-2015 were utilised.

RESULTS

Although HTLs were lower (better) in more recent years, the results showed clinically significant hearing loss (≥25dBHL) for older workers, 45-60 years. Pure tone average (PTA) hearing losses were greater at the higher frequencies associated with excessive noise exposure (3-6 kHz), than at the speech frequencies (0.5-4 kHz). Hearing loss in the left ears were higher compared to the right ears, with higher prevalence of audiometric notches in males.

CONCLUSION

Almost a fifth (14.8-20.1%) of male workers commencing work in NSW coal mines presented with an audiometric notch at 4 kHz. Further research is required to determine if these notches represent true NIHL, and how the residual hearing of workers may be conserved.

Better Hearing in Norway: A Comparison of Two HUNT Cohorts 20 Years Apart

OBJECTIVE

To obtain updated robust data on a age-specific prevalence of hearing loss in Norway and determine whether more recent birth cohorts have better hearing compared with earlier birth cohorts.

DESIGN

Cross-sectional analyzes of Norwegian representative demographic and audiometric data from the Nord-Trøndelag Health Study (HUNT)-HUNT2 Hearing (1996-1998) and HUNT4 Hearing (2017-2019), with the following distribution: HUNT2 Hearing (N=50,277, 53% women, aged 20 to 101 years, mean = 50.1, standard deviation = 16.9); HUNT4 Hearing (N=28,339, 56% women, aged 19 to 100 years, mean = 53.2, standard deviation = 16.9). Pure-tone hearing thresholds were estimated using linear and quantile regressions with age and cohort as explanatory variables. Prevalences were estimated using logistic regression models for different severities of hearing loss averaged over 0.5, 1, 2, and 4 kHz in the better ear (BE PTA4). We also estimated prevalences at the population-level of Norway in 1997 and 2018.

RESULTS

Disabling hearing loss (BE PTA4 ≥ 35 dB) was less prevalent in the more recent born cohort at all ages in both men and women (p < 0.0001), with the largest absolute decrease at age 75 in men and at age 85 in women. The age- and sex-adjusted prevalence of disabling hearing loss was 7.7% (95% confidence interval [CI] 7.5 to 7.9) and 5.3% (95% CI 5.0 to 5.5) in HUNT2 and HUNT4, respectively. Hearing thresholds were better in the more recent born cohorts at all frequencies for both men and women (p < 0.0001), with the largest improvement at high frequencies in more recent born 60- to 70-year old men (10 to 11 dB at 3 to 4 kHz), and at low frequencies among the oldest.

CONCLUSIONS

The age- and sex-specific prevalence of hearing impairment has decreased in Norway from 1996-1998 to 2017-2019.

Hearing in Adults: A Digital Reprint of the Main Report From the MRC National Study of Hearing

The 1011-page book, Hearing in Adults, published in 1995, contains the fullest report of the United Kingdom’s Medical Research Council National Study of Hearing. It was designed to determine the prevalence and distribution in Great Britain of audiometrically measured hearing loss as a function of age, gender, occupation, and noise exposure. The study’s size, quality, and breadth made it unique when it was done in the 1980s. These qualities remain, and its data are still the primary U.K. source for the prevalence of auditory problems. However, only 550 copies were printed, and the book is essentially unobtainable today. We describe here a fully searchable, open-access, digital (PDF) “reprinting” of Hearing in Adults, summarizing the study’s design and the book’s contents, together with a brief commentary in the light of subsequent developments.

Hearing Tests Based on Biologically Calibrated Mobile Devices: Comparison With Pure-Tone Audiometry

BACKGROUND

Hearing screening tests based on pure-tone audiometry may be conducted on mobile devices, provided that the devices are specially calibrated for the purpose. Calibration consists of determining the reference sound level and can be performed in relation to the hearing threshold of normal-hearing persons. In the case of devices provided by the manufacturer, together with bundled headphones, the reference sound level can be calculated once for all devices of the same model.

OBJECTIVE

This study aimed to compare the hearing threshold measured by a mobile device that was calibrated using a model-specific, biologically determined reference sound level with the hearing threshold obtained in pure-tone audiometry.

METHODS

Trial participants were recruited offline using face-to-face prompting from among Otolaryngology Clinic patients, who own Android-based mobile devices with bundled headphones. The hearing threshold was obtained on a mobile device by means of an open access app, Hearing Test, with incorporated model-specific reference sound levels. These reference sound levels were previously determined in uncontrolled conditions in relation to the hearing threshold of normal-hearing persons. An audiologist-assisted self-measurement was conducted by the participants in a sound booth, and it involved determining the lowest audible sound generated by the device within the frequency range of 250 Hz to 8 kHz. The results were compared with pure-tone audiometry.

RESULTS

A total of 70 subjects, 34 men and 36 women, aged 18-71 years (mean 36, standard deviation [SD] 11) participated in the trial. The hearing threshold obtained on mobile devices was significantly different from the one determined by pure-tone audiometry with a mean difference of 2.6 dB (95% CI 2.0-3.1) and SD of 8.3 dB (95% CI 7.9-8.7). The number of differences not greater than 10 dB reached 89% (95% CI 88-91), whereas the mean absolute difference was obtained at 6.5 dB (95% CI 6.2-6.9). Sensitivity and specificity for a mobile-based screening method were calculated at 98% (95% CI 93-100.0) and 79% (95% CI 71-87), respectively.

CONCLUSIONS

The method of hearing self-test carried out on mobile devices with bundled headphones demonstrates high compatibility with pure-tone audiometry, which confirms its potential application in hearing monitoring, screening tests, or epidemiological examinations on a large scale.

Transient evoked otoacoustic emissions in rock musicians

OBJECTIVE

Our focus in this study was the assessment of transient evoked otoacoustic emissions (TEOAEs) in a large group of rock musicians. A further objective was to analyse tinnitus among rock musicians as related to TEOAEs.

DESIGN

The study was a cross-sectional survey of rock musicians selected at random. A control group was included at random for comparison.

STUDY SAMPLE

We recruited 111 musicians and a control group of 40 non-musicians. Testing was conducted by using clinical examination, pure tone audiometry, TEOAEs and a questionnaire.

RESULTS

TEOAE SNR in the half-octave frequency band centred on 4 kHz was significantly lower bilaterally in musicians than controls. This effect was strongly predicted by age and pure-tone hearing threshold levels in the 3-6 kHz range. Bilateral hearing thresholds were significantly higher at 6 kHz in musicians. Twenty percent of the musicians had permanent tinnitus. There was no association between the TEOAE parameters and permanent tinnitus.

CONCLUSIONS

Our results suggest an incipient hearing loss at 6 kHz in rock musicians. Loss of TEOAE SNR in the 4 kHz half-octave frequency band was observed, but it was related to higher mean 3-6 kHz hearing thresholds and age. A large proportion of rock musicians have permanent tinnitus.

Hearing in middle age: a population snapshot of 40- to 69-year olds in the United Kingdom

OBJECTIVES

To report population-based prevalence of hearing impairment based on speech recognition in noise testing in a large and inclusive sample of U.K. adults aged 40 to 69 years. The present study is the first to report such data. Prevalence of tinnitus and use of hearing aids is also reported.

DESIGN

The research was conducted using the UK Biobank resource. The better-ear unaided speech reception threshold was measured adaptively using the Digit Triplet Test (n = 164,770). Self-report data on tinnitus, hearing aid use, noise exposure, as well as demographic variables were collected.

RESULTS

Overall, 10.7% of adults (95% confidence interval [CI] 10.5-10.9%) had significant hearing impairment. Prevalence of tinnitus was 16.9% (95%CI 16.6-17.1%) and hearing aid use was 2.0% (95%CI 1.9-2.1%). Odds of hearing impairment increased with age, with a history of work- and music-related noise exposure, for lower socioeconomic background and for ethnic minority backgrounds. Males were at no higher risk of hearing impairment than females.

CONCLUSIONS

Around 1 in 10 adults aged 40 to 69 years have substantial hearing impairment. The reasons for excess risk of hearing impairment particularly for those from low socioeconomic and ethnic minority backgrounds require identification, as this represents a serious health inequality. The underuse of hearing aids has altered little since the 1980s, and is a major cause for concern.

Biological calibration for web-based hearing tests: evaluation of the methods

Background

Online hearing tests conducted in home settings on a personal computer (PC) require prior calibration. Biological calibration consists of approximating the reference sound level via the hearing threshold of a person with normal hearing.

Objective

The objective of this study was to identify the error of the proposed methods of biological calibration, their duration, and the subjective difficulty in conducting these tests via PC.

Methods

Seven methods have been proposed for measuring the calibration coefficients. All measurements were performed in reference to the hearing threshold of a normal-hearing person. Three methods were proposed for determining the reference sound level on the basis of these calibration coefficients. Methods were compared for the estimated error, duration, and difficulty of the calibration. Web-based self-assessed measurements of the calibration coefficients were carried out in 3 series: (1) at a otolaryngology clinic, (2) at the participant’s home, and (3) again at the clinic. Additionally, in series 1 and 3, pure-tone audiometry was conducted and series 3 was followed by an offline questionnaire concerning the difficulty of the calibration. Participants were recruited offline from coworkers of the Department and Clinic of Otolaryngology, Wroclaw Medical University, Poland.

Results

All 25 participants, aged 22-35 years (median 27) completed all tests and filled in the questionnaire. The smallest standard deviation of the calibration coefficient in the test-retest measurement was obtained at the level of 3.87 dB (95% CI 3.52-4.29) for the modulated signal presented in accordance with the rules of Bekesy’s audiometry. The method is characterized by moderate duration time and a relatively simple procedure. The simplest and shortest method was the method of self-adjustment of the sound volume to the barely audible level. In the test-retest measurement, the deviation of this method equaled 4.97 dB (95% CI 4.53-5.51). Among methods determining the reference sound level, the levels determined independently for each frequency revealed the smallest error. The estimated standard deviations of the difference in the hearing threshold between the examination conducted on a biologically calibrated PC and pure-tone audiometry varied from 7.27 dB (95% CI 6.71-7.93) to 10.38 dB (95% CI 9.11-12.03), depending on the calibration method.

Conclusions

In this study, an analysis of biological calibration was performed and the presented results included calibration error, calibration time, and calibration difficulty. These values determine potential applications of Web-based hearing tests conducted in home settings and are decisive factors when selecting the calibration method. If there are no substantial time limitations, it is advisable to use Bekesy method and determine the reference sound level independently at each frequency because this approach is characterized by the lowest error.

Aminoglycoside antibiotics cochleotoxicity in paediatric cystic fibrosis (CF) patients: A study using extended high-frequency audiometry and distortion product otoacoustic emissions

Despite known ototoxic effects of aminoglycoside (AG) antibiotics, audiological assessment is not routinely undertaken in UK CF patients. Consequently, the incidence of hearing loss is not well established.

OBJECTIVE

To document the incidence of hearing loss in cystic fibrosis (CF) children.

DESIGN

Hearing function of 45 children from Great Ormond Street Hospital was assessed using pure-tone audiometry up to 20kHz and DPOAEs up to 8kHz.

STUDY SAMPLE

39/45 of participants had received intravenous (IV) AGs, 23 of which received repeated IV AGs every 3 months.

RESULTS

In this high exposure group, 8 (21%) had clear signs of ototoxicity; average 8-20kHz thresholds were elevated by ∼50dB and DPOAE amplitudes were >10dB lower at f2 3.2-6.3 kHz. The remaining 31/39 (79%) of AG exposed patients had normal, even exceptionally good hearing. The 21% incidence of ototoxicity we observed is substantial and higher than previously reported. However, our finding of normal hearing in children with equal AG exposure strongly suggests that other unknown factors, possibly genetic susceptibility, influence this outcome.

CONCLUSIONS

We recommend comparable auditory testing in all CF patients with high AG exposures. Genetic analysis may help explain the dichotomy in response to AGs found.

Screened and unscreened hearing threshold levels for the adult population: Results from the Nord-Trøndelag Hearing Loss Study Niveles de umbrales auditivos tamizados y no tamizados en la población adulta. Resultados del estudio Nord-TrøndeIag sobre hipoacusias

This paper presents normative data of hearing threshold levels of a population screened with various criteria, as compared to unscreened population data. Computer-controlled pure-tone audiometry was administered to the adult population in Nord-Trøndelag County, Norway, during 1995-1997. The 51975 participants also provided questionnaire information about occupational and leisure noise exposure, previous ear infections, and head injury. While screening had little effect on the median hearing threshold levels of young adults, there was a substantial effect when screening men above 40 years of age for a history of noise exposure. Screening for known ear-related disorders and diseases resulted in small effects on the mean hearing threshold levels The median hearing thresholds of both the screened and the unscreened sample exceeded the age and sex specific thresholds specified by the ISO 7029.

Variation of young normal-hearing thresholds measured using different audiometric earphones: Implications for the acoustic coupler and the ear simulator

This paper questions the necessity for two calibration devices to measure the acoustic output from different types of audiometric earphones. International standards give the audiometric zero for TDH39 earphones on the IEC 60318-3 acoustic coupler; the IEC 60318-1 ear simulator is intended for other supra-aural earphone types. If hearing threshold samples from young, healthy ears were found to be more variable using TDH39 earphones, then that earphone and its coupler might be taken out of service. The audiological literature yielded threshold survey results for over 5100 otologically normal ears of subjects aged 31 years or less. These independent samples showed smaller variation for TDH39 samples than for samples using other earphones; this finding does not support abandoning the TDH39 and its coupler. Nevertheless, benefits accrue from calibrating TDH39 output to the audiometric zero as measured on the ear simulator.

Occupational noise, smoking, and a high body mass index are risk factors for age-related hearing impairment and moderate alcohol consumption is protective: a European population-based multicenter study

A multicenter study was set up to elucidate the environmental and medical risk factors contributing to age-related hearing impairment (ARHI). Nine subsamples, collected by nine audiological centers across Europe, added up to a total of 4,083 subjects between 53 and 67 years. Audiometric data (pure-tone average [PTA]) were collected and the participants filled out a questionnaire on environmental risk factors and medical history. People with a history of disease that could affect hearing were excluded. PTAs were adjusted for age and sex and tested for association with exposure to risk factors. Noise exposure was associated with a significant loss of hearing at high sound frequencies (>1 kHz). Smoking significantly increased high-frequency hearing loss, and the effect was dose-dependent. The effect of smoking remained significant when accounting for cardiovascular disease events. Taller people had better hearing on average with a more pronounced effect at low sound frequencies (<2 kHz). A high body mass index (BMI) correlated with hearing loss across the frequency range tested. Moderate alcohol consumption was inversely correlated with hearing loss. Significant associations were found in the high as well as in the low frequencies. The results suggest that a healthy lifestyle can protect against age-related hearing impairment.

Is the relation of social class to change in hearing threshold levels from childhood to middle age explained by noise, smoking, and drinking behaviour?

Recent work shows that variation in adult hearing function is related both to social class of origin and current social class. This study examines how much of this relationship after adjustment for childhood hearing impairment is explicable by occupational noise, current smoking, and alcohol consumption. A cohort of 9023 persons born in the UK during one week in 1958 was followed periodically, and hearing threshold levels (HTLs) were measured at 1 kHz and 4 kHz at age 45 years. Most (71% and 68%, at 1 kHz and 4 kHz respectively) of the relation to social class of origin of adult HTLs remains after adjustment for these other factors. For the relation to current social class, corresponding values are 64% and 44% (though varying by gender). The magnitude of social class effect is comparable to that of occupational noise. Susceptibility to hearing impairment is likely to be appreciably determined in early childhood.

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.

Noise-Induced Permanent Threshold Shifts in the Occupational Noise and Hearing Survey: An Explanation for Elevated Risk Estimates

OBJECTIVES

To (1) estimate noise-induced permanent threshold shift (NIPTS) values from the data of the 1968-1972 Occupational Noise and Hearing Survey (ONHS); (2) compare these NIPTS estimates to NIPTS predictions from an international standard (ISO-1999); (3) determine why excess risk estimates based on the ONHS are so much higher than those based on ISO-1999.

DESIGN

The ONHS raw data were acquired from the National Institute for Occupational Safety and Health. Binaural average thresholds from 0.5 to 6 kHz were calculated for each of 1291 noise-exposed subjects (80 to 94 dBA, for up to 30 yr, all tested just before their shifts) and 665 non-noise-exposed control subjects (mostly office workers, tested throughout the work day). "Screened" subjects had had no prior significant noise exposure and had no evidence of other ear disease, whereas "excluded" subjects had failed one or more screening criteria. Twenty exposure groups were created (based on exposure level, exposure duration, and screened versus excluded status) and compared with 20 age-matched control groups. The median difference statistic estimated median NIPTS.

RESULTS

Median NIPTS estimates in the 3 to 6 kHz region were generally consistent with the NIPTS predictions of ISO-1999. At lower frequencies, especially at 0.5 and 1 kHz, the ONHS estimates were significantly larger than the ISO-1999 predictions, even for exposures below 90 dBA, but these differences did not increase systematically with exposure level and duration.

CONCLUSIONS

High-frequency median NIPTS estimates from ONHS data are consistent with the predictions of ISO-1999. Differences between exposed and control low-frequency thresholds in the ONHS are higher than predicted by ISO-1999, but these differences probably are related more to socioeconomic or test procedure effects than to occupational noise exposure. These low-frequency effects explain why excess risk estimates from the ONHS are higher than those based on ISO-1999.

Hemispheric differences in processing dichotic meaningful and non-meaningful words

Classic dichotic-listening paradigms reveal a right-ear advantage (REA) for speech sounds as compared to non-speech sounds. This REA is assumed to be associated with a left-hemisphere dominance for meaningful speech processing. This study objectively probed the relationship between ear advantage and hemispheric dominance in a dichotic-listening situation, using event-related potentials (ERPs). The mismatch negativity (MMN) and a late negativity (LN) were measured for bisyllabic meaningful words and non-meaningful pseudowords, which differed in their second syllable. Eighteen normal-hearing listeners were presented with a repeating diotic standard ([beI-gi:] or [leI-gi:]) and an occasional dichotic deviant (a standard presented to one ear and a deviant [beI-bi:], [beI-di:], [leI-bi:] or [leI-di:] presented to the opposite ear). As predicted there was a REA for meaningful words compared to non-meaningful words. Also, dipole source analysis suggested that dipole strength was stronger in the left than the right cortical region for meaningful words. However, there were differences in response within meaningful words as well as between meaningful and non-meaningful words which may be explained by the characteristics of embedded words and the position-specific probability of phoneme occurrence in words.

Methodological Issues When Comparing Hearing Thresholds of a Group With Population Standards: The Case of the Ferry Engineers

OBJECTIVES

To discuss appropriate and inappropriate methods for comparing distributions of hearing thresholds of a study group with distributions in population standards and to determine whether the thresholds of Washington State Ferries engineers are different from those of men in the general population, using both frequency-by-frequency comparisons and analysis of audiometric shape.

DESIGN

The most recent hearing conservation program audiograms of 321 noise-exposed engineers, ages 35 to 64, were compared with the predictions of Annexes A, B, and C from ANSI S3.44. There was no screening by history or otoscopy; all audiograms were included. 95% confidence intervals (95% CIs) were calculated for the engineers' median thresholds for each ear, for the better ear (defined two ways), and for the binaural average. For Annex B, where 95% CIs are also available, it was possible to calculate z scores for the differences between Annex B and the engineers' better ears. Bulge depth, an audiometric shape statistic, measured curvature between 1 and 6 kHz.

RESULTS

Engineers' better-ear median thresholds were worse than those in Annex A but (except at 1 kHz) were as good as or better than those in Annexes B and C, which are more appropriate for comparison to an unscreened noise-exposed group like the engineers. Average bulge depth for the engineers was similar to that of the Annex B standard (no added occupational noise) and was much less than that of audiograms created by using the standard with added occupational noise between 90 and 100 dBA.

CONCLUSIONS

Audiograms from groups that have been selected for a particular exposure, but, without regard to severity, can appropriately be compared with population standards, if certain pitfalls are avoided. For unscreened study groups with large age-sex subgroups, a simple method to assess statistical significance, taking into consideration uncertainties in both the study group and the comparison standard, is the calculation of z scores for the proportion of better-ear thresholds above the Annex B median. A less powerful method combines small age-sex subgroups after age correction. Small threshold differences, even if statistically significant, may not be due to genuine differences in hearing sensitivity between study group and standard. Audiometric shape analysis offers an independent dimension of comparison between the study group and audiograms predicted from the ANSI S3.44 standard, with and without occupational noise exposure. Important pitfalls in comparison to population standards include nonrandom selection of study groups, inappropriate choice of population standard, use of the right and left ear thresholds instead of the better-ear threshold for comparison to Annex B, and comparing means with medians. The thresholds of the engineers in this study were similar to published standards for an unscreened population.

Absence of cochleotoxicity measured by standard and high-frequency pure tone audiometry in a trial of once- versus three-times-daily tobramycin in cystic fibrosis patients

We undertook assessment of hearing in patients with cystic fibrosis who were taking part in a large randomized controlled trial of once- versus three-times-daily tobramycin for pulmonary exacerbations of cystic fibrosis (the TOPIC study). All patients were eligible to have standard pure tone audiometry performed across the frequency range of 0.25 to 8 kHz. High-frequency pure tone audiometry over 10 to 16 kHz was also performed with a subset of patients. Audiometry was undertaken at the start of tobramycin treatment, at the end of a 14-day course of treatment, and at follow-up 6 to 8 weeks later. We enrolled 244 patients, of whom 219 (125 children and 94 adults) completed treatment. Nineteen patients were excluded from analysis due to abnormal baseline audiometry. Complete pre- and posttreatment standard audiological data were obtained for 168/219 patients. We found no significant differences in hearing thresholds when they were assessed at the baseline, at the end of treatment, and at follow-up 6 to 8 weeks later were compared. In addition, no significant differences in hearing thresholds were detected between treatment regimens. Similar results were obtained for the subset of 63/168 patients who underwent high-frequency audiometry. We conclude that for a single 14-day course of tobramycin treatment in patients with cystic fibrosis with no preexisiting auditory deficit, no measurable effect on hearing was apparent with either once- or three-times-daily treatment. Estimation of the cumulative cochleotoxic risk in cystic fibrosis patients due to repeated aminoglycoside therapy, as evidenced by the patients excluded from this study due to hearing loss, also requires further characterization.

Hearing threshold levels and speech recognition in noise in 7-year-olds

International standards define normal hearing threshold levels (HTLs) and many studies describe speech recognition in noise (SRN) for adults. Less has been published on these characteristics for children. This study aims to establish ranges of HTLs and SRN for otologically normal 7-year-olds. Air conduction HTLs were measured in 189 7-year-olds within an audiometric booth. Speech recognition was measured adaptively for BKB sentences in noise presented binaurally through headphones, determining the speech-to-noise ratio (SNR) required to score 71% correct. The mean HTLs of otologically normal 7-year-olds were significantly lower (better) than those published for young adults at 1 and 2 kHz. Speech recognition in noise was unrelated to HTLs and was higher (worse) for 7-year-olds (SNR = -4 dB) than has been found for young otologically normal adults (SNR = -6 dB). It is concluded that although the HTLs of 7-year-old children are generally better than those of young adults, their speech recognition in noise is worse. This confirms that their ability to recognise speech in noise is not fully developed at this age.

Estimating Noise-Induced Permanent Threshold Shift from Audiometric Shape: The ISO-1999 Model

OBJECTIVE

To describe the relation between audiometric shape and noise-induced permanent threshold shift averaged across the speech frequencies (N5123).

DESIGN

Using an international standard (ISO-1999), 270 audiograms were created, representing both sexes and a variety of ages, exposure levels, and percentiles. Bulge depth (BD) was defined as the difference between pure-tone average for 2, 3, and 4 kHz and PTA for 1 and 6 kHz.

RESULTS

N5123 was well-predicted by quadratic functions of BD, which accounted for 72 to 95% of the variance in N5123.

CONCLUSIONS

Estimates of N5123, based on BD, can be helpful in medical-legal diagnosis and allocation of hearing loss.

Once versus three-times daily regimens of tobramycin treatment for pulmonary exacerbations of cystic fibrosis--the TOPIC study: a randomised controlled trial

BACKGROUND

Intravenous tobramycin (three-times daily) is widely used for pulmonary exacerbations in patients with cystic fibrosis who have chronic Pseudomonas aeruginosa infection. We undertook a double-blind, randomised controlled trial to assess the safety and efficacy of once versus three-times daily tobramycin in these patients.

METHODS

244 patients from 21 cystic-fibrosis centres in the UK were randomly assigned to once or three-times daily tobramycin (with ceftazidime) for 14 days. Treatment was given as 30-min infusions of tobramycin in 0.9% saline. Primary outcome measure was change in forced expiratory volume in 1s (FEV1), over the 14 days of treatment, expressed as a percentage of the predicted normal value for age, sex, and height. We also measured the change in FEV1 expressed as a percentage of baseline. Secondary outcomes included change in serum creatinine. The study was powered for equivalence, and primary analysis was per protocol.

FINDINGS

219 patients (107 once daily, 112 three-times daily) completed the study per protocol. None was lost to follow-up, although 20 discontinued intervention. Of 122 patients assigned to once daily treatment, three did not receive the study regimen. The mean change in FEV1 (% predicted) over 14 days was similar on the two regimens (10.4% [once daily] vs 10.0% [three-times daily]; adjusted mean difference 0.4% [95% CI -3.3 to 4.1]). Mean% change in FEV1 from baseline was also similar in both treatments (21.9% vs 22.1%; -0.1% [-8.0 to 7.9]). There was no significant difference in% change in creatinine from baseline (-1.5% [once daily] vs 1.7% [three-times daily]). However, in children, once daily treatment was significantly less nephrotoxic than was thrice daily (mean% change in creatine -4.5% [once daily] vs 3.7% [thrice daily]; adjusted mean difference -8.0%, 95% CI -15.7 to -0.4). No patients developed hearing loss during the study, although two reported acute dizziness and were withdrawn from the study.

INTERPRETATION

Intravenous tobramycin has equal efficacy if given once or three-times daily (with ceftazidime) for pulmonary exacerbations of cystic fibrosis. The once daily regimen might be less nephrotoxic in children.

Evidence of Subtle Auditory Deficit in a Group of Patients Recovered from Bacterial Meningitis

OBJECTIVES

Sensorineural hearing loss of greater than 30 dB hearing loss occurs in up to 30% of patients after acute bacterial meningitis. This study investigated whether postbacterial meningitic patients with no apparent clinical sensorineural hearing loss had any evidence of more subtle subclinical cochlear deficit.

DESIGN

Prospective case-controlled clinical trial.

SETTING

Departments of Otolaryngology in Leicester and Nottingham, England, UK.

PATIENTS

Fifty-eight controls and 20 postbacterial meningitic patients aged between 18 and 38 years were screened by a questionnaire and tympanometry to exclude hearing loss attributable to other causes. All participants fell below the 90th percentile pure-tone audiometry threshold of the Lutman and Davis UK data sets.

MAIN OUTCOME MEASURES

In both ears, standard (0.25-8 kHz) pure-tone audiometry, high-frequency pure-tone audiometry (10-16 kHz), and distortion product otoacoustic emissions at 2, 4, and 6 kHz were measured.

RESULTS

Mean thresholds over the range of standard pure-tone audiometry (analyzed independently) for the postbacterial meningitic patients were significantly elevated at most frequencies (p < 0.05-p < 0.001) between 4 and 7 dB in both ears above control group values. There was no evidence of significant high-frequency threshold elevation (10-16 kHz). The mean iso-distortion product values at 2, 4, and 6 kHz were elevated in both ears in the meningitis group; significantly so (p < 0.05-p < 0.01) at all three frequencies in the right ear and at 4 kHz in the left.

CONCLUSIONS

Postbacterial meningitic patients with hearing below the 90th percentile range had a slight but significant subclinical threshold elevation over the standard pure-tone audiometry. This may reflect a real effect of the infection at the level of the cochlea, or it may be attributable to a mild residual cognitive defect. The moderate increases in iso-distortion product values are more likely to be real and reflect an effect on outer hair cell function in response to lower stimulus intensities.

The acute effects of tetrahydrocannabinol on auditory threshold and frequency resolution in human subjects

AIMS

The study was designed to investigate the acute effects of ingested tetrahydrocannabinol (THC) on auditory function.

METHODS

Eight male subjects (aged 22-30 years), who had previous experience of cannabis use, took part in this study. They performed air conduction pure tone audiometry in both ears over 0.5-8 kHz. A simple test of frequency selectivity by detecting a 4-kHz tone under two masking noise conditions was also carried out in one ear. Three test sessions at weekly intervals were carried out, at the start of which they ingested a capsule containing either placebo, or 7.5 or 15 mg of THC. These were administered in a randomized cross-over, double-blind manner. Auditory testing as described above was carried out 2 hours after ingestion. Blood samples were also obtained at this time point and assayed for delta 9- and 11-OH-THC levels.

RESULTS

No significant changes in threshold or frequency resolution were seen with the dosages employed in this study.

CONCLUSIONS

This suggests that THC at the plasma levels attained in this study does not have profound effect on the processing of elementary stimuli by the auditory pathway.

Hearing threshold levels for an otologically unscreened, non-occupationally noise-exposed population in Sweden

The aim of this study was to investigate the hearing threshold levels (HTL) of an otologically unscreened population in Sweden. The results are compared to other studies of otologically unscreened populations, and a new mathematical model of hearing threshold levels as a function of age is presented. The subjects were males and females aged from 19 to 81 years, selected from the province of Ostergötland in Sweden. The test battery included otoscopy, tympanometry, pure-tone audiometry, and a questionnaire. Subjects exposed to occupational noise were excluded, and in total 603 persons were included in the analysis. The regression analysis resulted in different hyperbolic tangent functions with four parameters: HTL=A+B x tanh(C x age+D).

Occurrence and risk of cochleotoxicity in cystic fibrosis patients receiving repeated high-dose aminoglycoside therapy

Cystic fibrosis (CF) patients receive repeated courses of aminoglycoside therapy. These patients would consequently be expected to be more susceptible to cochleotoxicity, a recognized side effect with single courses of aminoglycoside therapy. The primary aim of this retrospective study was to establish the incidence and severity of auditory deficit in CF patients. Standard (0.25- to 8-kHz) and high-frequency (10- to 16-kHz) pure-tone audiometry was carried out in 70 CF patients, and the results were compared with the results from 91 control subjects. These subjects were further divided into pediatric and adult groups. Of 70 CF patients, 12 (1 pediatric) displayed hearing loss considered to be caused by repeated exposure to aminoglycosides. There was a nonlinear relationship between the courses of therapy received and the incidence of hearing loss. The severity of the loss did not appear to be related to the number of courses received. Assuming the risk of loss to be independent for each course, preliminary estimates of per course risk of hearing loss were less than 2%. Upon comparison with previous clinical studies and experimental work, these findings suggest that the incidence of cochleotoxicity in CF patients is considerably lower than would be expected, suggesting that the CF condition may confer protection against aminoglycoside cochleotoxicity.

A longitudinal study of the association between tooth loss and age-related hearing loss

The purpose of this study was to investigate cross-sectional and longitudinal associations between hearing acuity and tooth loss in 1156 US veterans taking part in the Veterans Affairs' Normative Aging (NAS) and Dental Longitudinal (DLS) Studies in the Boston, MA, area. The mean age was 48 years (SD = 8.9), 5.3% were edentulous, and 15.4% had < 17 teeth at baseline. Hearing acuity was determined by puretone, air- and bone-conduction audiometry, and speech discrimination tests at triennial examinations over a 20-year follow-up period. Hearing decline was defined as a change from baseline in the average puretone air-conduction thresholds of > or = 20 dB at 0.25, 0.5, 1, 2, 3, 4, 6, and 8 kHz. The explanatory variables of interest were change since baseline in dentate status (cut points at < 1, < 17, and < 20 teeth), and in the number of teeth lost (linear). Linear and logistic regression models--which controlled for baseline audiological status, age, air-bone gap, and otoscopic examination at current visit--showed that subjects who went from having > or = 17 to < 17 teeth had 1.64 times (95% CI, 1.24-2.17) as high odds of having hearing decline as those with no change in their dentate status. For every tooth lost since baseline, there was a 1.04 times as high odds (95% CI, 1.02-1.06) for hearing decline, when additional baseline and time-varying covariates were taken into account in the model.

Guidelines on the diagnosis of noise-induced hearing loss for medicolegal purposes

These guidelines aim to assist in the diagnosis of noise-induced hearing loss (NIHL) in medicolegal settings. The task is to distinguish between possibility and probability, the legal criterion being 'more probable than not'. It is argued that the amount of NIHL needed to qualify for that diagnosis is that which is reliably measurable and identifiable on the audiogram. The three main requirements for the diagnosis of NIHL are defined: R1, high-frequency hearing impairment; R2, potentially hazardous amount of noise exposure; R3, identifiable high-frequency audiometric notch or bulge. Four modifying factors also need consideration: MF1, the clinical picture; MF2, compatibility with age and noise exposure; MF3, Robinson's criteria for other causation; MF4, complications such as asymmetry, mixed disorder and conductive hearing impairment.

Abnormal audiograms and elevated acoustic reflex thresholds in obligate carriers of autosomal recessive non-syndromic hearing loss

Pure-tone audiograms and acoustic reflex thresholds were obtained in 24 presumed obligate carriers of autosomal recessive non-syndromic hearing loss and 30 sex and age appropriate control subjects, with a view to evaluating the prevalence of abnormalities on these tests in the two groups, and a possible link between the findings on the two tests, which may help to localize threshold deficits and/or abnormal configurations to different sections of the reflex arc. Six (25%) of the carriers and one control subject had abnormal audiograms, inferred to be of genetic aetiology through careful exclusion of environmental risk factors. Four additional carriers had acoustic reflex threshold abnormalities. None of the carriers had an abnormality on both tests. The audiometric configurations and acoustic reflex patterns of abnormality were diverse, and may be a reflection of the genetic heterogeneity in ARNSHL.