Audiometric findings of printing press workers exposed to noise and organic solvents.

OBJECTIVE: To determine if exposure to organic solvents and noise is associated with audiometric results among workers from a printing press in Mexico City. DESIGN: Cross-sectional study. STUDY SAMPLE: One hundred and seventy-six male workers at a printing press in Mexico City exposed to noise and organic solvents, including xylene, and 103 non-exposed male workers as reference group. Hearing thresholds were assessed with pure-tone audiometry. RESULTS: Poorer hearing thresholds were observed among printing workers than non-exposed controls, particularly among groups with over 5 years of exposure. Hearing thresholds differences were observed in the frequencies above 500 Hz, especially in 4000 Hz in all exposure groups compared to the reference. Adjusted models for age and previous exposure to noise and organic solvents showed worse hearing thresholds as years of seniority increased -ß coefficients (95% CI): ≤5 years: 3.06 dB (0.01, 6.10); >5-10 years: 4.51 dB (1.13, 7.89); >10 years: 4.58 dB (1.20, 7.96). Further analyses showed no interaction between noise and organic solvents on hearing thresholds, considering both current and previous occupational exposures. CONCLUSION: Exposure to noise levels that were below recommended exposure limits and organic solvents were associated with poorer hearing thresholds than those observed among non-exposed study participants. This suggests that workers exposed to solvents should be included in hearing conservation programmes, even when noise exposures are below 85 dB. If only noise levels were taken into consideration in the risk assessment of this worker population, the risk of hearing effects could have been overlooked.

Commute times and audiometric findings among adult population in Mexico City.

INTRODUCTION: Long commute times are common in big cities. OBJECTIVE: To determine hearing thresholds and their association with commute time in Mexico City. METHODS: Cross-sectional study that included 177 healthy adults from 2009 to 2011. Demographic information and commute times were recorded. Hearing was assessed by audiometry. Regression models were constructed to determine the predictors of hearing thresholds. RESULTS: There were 101 men (53%) and 76 women (43%). Mean commute time was 43 minutes (1-150 minutes). A hearing threshold drop was observed at 4000 Hz, with recovery at 8000 Hz in both ears when patients were stratified by gender and age groups. A commute time > 40 min/day increased the hearing threshold at 4000 Hz (ß = 2.96 dB HL, p < 0.01). Men had higher thresholds (ß = 2.6 dB HL), as older subjects also did: 25-34 years, ß = 2.2 dB HL; 35-44 years, ß = 5.2 dB HL; and ≥ 45 years, ß = 8.3 dB HL. CONCLUSION: The hearing pattern, although normal, resembled that of noise-induced hearing loss, associated with long commute times.

INTRODUCCIÓN: Los tiempos prolongados de traslado son comunes en las ciudades grandes. OBJETIVO: Determinar los umbrales auditivos y su asociación con el tiempo de traslado al trabajo en la Ciudad de México. MÉTODOS: Estudio transversal que incluyó a 177 adultos sanos de 2009 a 2011. Se registró información demográfica y tiempo de traslado al trabajo. La audición se evaluó mediante audiometría. Se realizaron modelos de regresión para determinar los predictores de los umbrales auditivos. RESULTADOS: Se trató de 101 hombres (53 %) y 76 mujeres (43 %). El tiempo promedio de traslado fue 43 minutos (1 a 150 minutos). Se observó una caída del umbral auditivo en 4000 Hz, con recuperación en 8000 Hz en ambos oídos al estratificar por sexo y grupos de edad. Un tiempo de traslado > 40 minutos/día incrementó el umbral auditivo en 4000 Hz (b = 2.96 dB HL, p < 0.01). Los hombres presentaron umbrales mayores (b = 2.6 dB HL), al igual que los sujetos de edad más avanzada: 25 a 34 años, b = 2.2 dB HL; 35 a 44 años, b = 5.2 dB HL y ≥ 45 años, b = 8.3 dB HL. CONCLUSIÓN: El patrón auditivo, aunque normal, se asemejó a la pérdida auditiva por ruido asociada a tiempo prolongado de traslado al trabajo.

Prevalence, Incidence Proportion, and Heritability for Tinnitus: A Longitudinal Twin Study.

OBJECTIVES: The purpose of this longitudinal twin study was to explore the effect of tinnitus on hearing thresholds and threshold shifts over two decades and to investigate the genetic contribution to tinnitus in a male twin cohort (n = 1114 at baseline and 583 at follow-up). The hypothesis was that participants with faster hearing deterioration had a higher risk for developing tinnitus and there is an underlying role of genetic influences on tinnitus. DESIGN: Male mono- and dizygotic twin pairs, born between 1914 and 1958 were included. Mixed models were used for comparison of hearing threshold shifts, adjusted for age. A co-twin comparison was made within pairs discordant for tinnitus. The relative influence of genetic and environmental factors was estimated by genetic modeling. RESULTS: The overall prevalence of tinnitus was 13.5% at baseline ((Equation is included in full-text article.)age 50) and 34.4% at follow-up ((Equation is included in full-text article.)age 67). The overall incidence proportion was 27.8%. Participants who reported tinnitus at baseline or at both time points were older. At baseline, the hearing thresholds differed between tinnitus cases and controls at all frequencies. New tinnitus cases at follow-up had the greatest hearing threshold shift at the high-frequency area compared with the control group. Within pairs, the tinnitus twin had poorer hearing than his unaffected co-twin, more so for dizygotic than monozygotic twin pairs. The relative proportion of additive genetic factors was approximately 0.40 at both time points, and the influence of individual-specific environment was 0.56 to 0.61. The influence of genetic factors on tinnitus was largely independent of genetic factors for hearing thresholds. CONCLUSIONS: Our hypotheses were confirmed: The fastest hearing deterioration occurred for new tinnitus cases. A moderate genetic influence for tinnitus was confirmed.

Influence of well-known risk factors for hearing loss in a longitudinal twin study.

OBJECTIVE: The aim was to investigate the influence of environmental exposures on hearing loss in a twin cohort. STUDY SAMPLE: Male twins born 1914-1958, representing an unscreened population, were tested for hearing loss at two occasions, 18 years apart. DESIGN: Clinical audiometry and a questionnaire were performed at both time points in this longitudinal study. Noise and solvent exposure were assessed using occupational work codes and a job exposure matrix. Hearing impairment was investigated using two different pure tone averages: PTA4 (0.5, 1, 2, and 4 kHz) and HPTA4 (3, 4, 6, and 8 kHz). RESULTS: Age affected all outcome measures. Noise exposure between time point one and two affected the threshold shifts of PTA4 and HPTA4 more in participants with a pre-existing hearing loss at time point one. Lifetime occupational noise exposure was a risk factor especially for the low-frequency hearing threshold PTA4. Firearm use was a statistically significant risk factor for all outcome measures. CONCLUSIONS: Pre-existing hearing loss can increase the risk of hearing impairment due to occupational noise exposure. An increased risk for NIHL was also seen in the group with exposures below 85 dB(A), a result that indicates awareness of NIHL should be raised even for those working in environments where sound levels are below 85 dB(A).

Combined severe-to-profound hearing and vision impairment-Experiences of daily life and need of support, an interview study.

OBJECTIVES: The purpose of the present study was to describe experiences of disabilities and factors affecting daily life from the perspective of adult persons with severe-to-profound hearing impairment in combination with severe vision impairment. Furthermore, the study also investigated which kind of support individuals with dual sensory loss received, and their experiences as citizens in the society. METHODS: Semi-structured qualitative interviews were performed, analyzed, and categorized using content analysis. RESULTS: Fourteen interviews were performed, with equal number of both sexes. Mean age was 70.1 years (47-81 years). Analysis of the data resulted in 22 categories, six sub-themes and two main themes. Two main themes emerged as Isolation and The Ability to control one's own daily life. Surprisingly, most of the participants did not think of their vision and hearing impairment as a combined disability. The interviews showed various kind of strategies to handle daily life. The Deafblind-team unit was reported to offer excellent health care. Companion services for persons with disabilities proved to have become more difficult to get support from and created lack of independence and control over their own lives. However, it was also obvious that the participants felt a positive outlook on life and were more solution-oriented in order to adjust their everyday life to their life-situation. CONCLUSIONS: The combination of vision and hearing impairment demonstrated isolation, and the respondents in the study have a need of support in everyday lives. At the same time, they struggle to have the ability to control their own lives.

Sensitivity and Specificity of Automated Audiometry in Subjects with Normal Hearing or Hearing Impairment.

OBJECTIVE: To investigate the sensitivity and specificity in an automatic computer-controlled audiometric set-up, used for screening purposes. DESIGN: Comparison between standardized audiometry and automated audiometry performed in the same participants. STUDY SAMPLE: In total, 100 participants (51 females and 49 males) were recruited to take part of this study the same day they visited the hearing clinic for clinical audiometry. Ages varied between 18 and 84 years (mean 45.9 in females, 52.3 in males). RESULTS: The participants were divided into groups, dependent of type of hearing. A total of 23 had normal hearing, 40 had sensorineural hearing loss, 19 had conductive hearing loss and 18 showed asymmetric hearing loss. The sensitivity for the automated audiometry was 86%-100% and the specificity 56%-100%. The group with conductive hearing loss showed the poorest sensitivity (86 %) and specificity (56 %). The group with sensorineural hearing loss showed the smallest variation in difference between the two methods. CONCLUSIONS: The results show that automated audiometry is a method suitable to screen for hearing loss. Screening levels need to be selected with respect to cause of screening and environmental factors. For patients with asymmetric hearing thresholds it is necessary to consider the effect of transcranial routing of signals.

Augmented ototoxic effect of cisplatin in heterozygotes of the German waltzing guinea pig.

It has previously been demonstrated that the carriers of the German waltzing guinea pig are less susceptible to noise trauma. To explore whether this represents a general resistance to inner ear trauma, carriers of the German waltzing guinea pig were exposed to the ototoxic agent cisplatin. Two doses of cisplatin were injected intravenously into anesthetized carriers and weight-matched control animals. Prior to and 96 h after the injections hearing thresholds were established by recording the auditory brainstem responses at 3.5, 7, 14, and 28 kHz. The cochleae were harvested to estimate hair cell loss and to analyze total platinum content. The carriers of the German waltzing guinea pig strain suffered from a more pronounced cisplatin-induced hearing loss compared to the control animals. The results suggest that mechanisms responsible for the protection against acoustic stress do not provide any protection against cisplatin in carriers of the German waltzing guinea pig.

Exploring efferent-mediated DPOAE adaptation in three different guinea pig strains.

The aims of this study were to explore the correlation between DPOAE adaptation magnitude in three different guinea pig strains to examine if the genetic component affects the DPOAE adaptation magnitude. It was also to investigate the correlation between strains with certain characteristics i.e. reduced susceptibility to noise, and early onset of age-dependent hearing loss and the DPOAE adaptation magnitude. The animals were anaesthetized and the 2f1-f2 DPOAE (f1=8k Hz, and f2/f1=1.2) adaptation was established with a minimum of 144 combinations of f1; f2 where f1 was held fixed and f2 was varied in 1 dB or 0.4 dB steps. The DPOAE adaptation magnitude was defined as the difference between maximum positive level and the maximum negative level. ABRs were conducted at different age-groups (at 4, 6.3, and 12.5k Hz) to evaluate the progress of hearing thresholds by age. There was a significant difference between strains regarding the hearing loss at one year of age. There was no significant difference in DPOAE adaptation magnitude between strains included in this study and from this we conclude that the DPOAE adaptation magnitude is not a predictor for the susceptibility to noise trauma, or early onset of age-dependent hearing loss, using the methods described in this paper.

Auditory function and cochlear morphology in the German waltzing guinea pig.

The German waltzing guinea pig is a new strain of animals with a recessively inherited inner ear defect resulting in deafness and severe vestibular dysfunction. Measurements of auditory brainstem responses (ABRs) demonstrated that the homozygotes (gw/gw) are deaf while the heterozygotes (gw/+) have normal hearing. In the gw/gw cochlea, a collapse of Reissner's membrane leads to the absence of scala media. Melanin pigment accumulation was clearly observed in the gw/gw stria vascularis, and both the height and width of stria vascularis were significantly reduced. Ultrastructural observations further detailed the disorganization of stria vascularis in the gw/gw animals: marginal cells lacked basolateral infoldings; intermediate cells (melanocytes) were scarce and degenerated; and basal cells were difficult to identify. The level of degeneration of the organ of Corti varied between individual gw/gw animals. The density of spiral ganglion neurons was significantly decreased in old (1-2 years of age) gw/gw animals. In contrast, no pathological changes were observed in the cochleae of gw/+ animals. Our data suggest that the degeneration originates in the stria vascularis (most likely in the melanocytes), and that this is the primary cause for inner ear defects in the German waltzing guinea pig. Here, we describe the auditory function and cochlear morphology in this spontaneously mutated guinea pig strain.

Efferent-mediated adaptation of the DPOAE as a predictor of aminoglycoside toxicity.

Rapid efferent adaptation of the distortion product otoacoustic emission (DPOAE) predicts susceptibility to noise-induced damage, and is linked to the concentration of the efferent receptor (alpha9). Maximum adaptation occurs at intense primary levels, rapidly switching from positive to negative orientation in a very narrow (2 dB) range of F1 and F2 levels. Aminoglycosides are commonly used antibiotics, with the undesirable side-effect of ototoxicity. Susceptibility to hair cell damage from the aminoglycoside gentamicin can be quite variable, even within a single strain and species of animal. Since one of gentamicin's first sites of action in the outer hair cell (OHC) is at the efferent receptor, it is possible that efferent activity could be a predictor of susceptibility to gentamicin induced damage. Significant sex-related differences were found in two strains of guinea pigs when treated with gentamicin. Female guinea pigs were more susceptible both to systemic effects and to specific ototoxic effects. Efferent-mediated DPOAE adaptation served as a predictor of sensitivity to aminoglycoside damage, predicting both number of days before onset of deafness in male animals, and predicting final threshold shifts from gentamicin doses which produced variable results.

Reduced noise susceptibility in littermate offspring from heterozygous animals of the German waltzing guinea pig.

The German waltzing guinea pig is a spontaneously mutated strain with severe auditory and vestibular impairment caused by a so far unknown genetic mutation. The animals are born deaf and show a circling behavior. The heterozygote animals of this guinea pig strain have functionally normal hearing and balance. However, these animals have, in earlier studies, shown an increased resistance to noise compared with normal wild-type guinea pigs. In the present study, we explored the functional hearing with auditory brainstem response thresholds before and at different time points after noise exposure. Symptom-free littermates from heterozygote couples of the German waltzing guinea pigs were exclusively used for the study, which, after the hearing test, were sent back for breeding to confirm their genotype (i.e. heterozygote or normal). The aim of this paper was to ascertain that the previously shown reduced susceptibility to noise trauma in the heterozygote animals of the German waltzing guinea pig was also evident when littermates were used as control animals. The findings are important for further analysis of the heterozygote animals of this strain and for future investigations of the underlying mechanisms behind the diverse susceptibility to exposures of loud sound.

The role of genetic factors for hearing deterioration across 20 years: a twin study.

BACKGROUND: Hearing deterioration at advanced ages is associated with environmental exposures (eg, to noise and solvents) and genetic influences may also be important. Little is known about the role of genetic influences on hearing when evaluated longitudinally. We sought to investigate longitudinal hearing loss in a cohort of adult male twins to evaluate the importance of genetic and environmental factors for hearing deterioration over time. METHODS: Hearing using conventional clinical audiometry was assessed in 583 male twins (128 monozygotic twin pairs and 111 dizygotic twin pairs) aged 34-79 at baseline and again two decades later. The hearing thresholds at two time points were compared at each frequency and in two different frequency regions. Genetic analyses were based on structural equation models. Bivariate Cholesky decomposition was used for longitudinal analysis. RESULTS: The prevalence of hearing loss increased over time in better and worse ear. The hearing threshold shift was more pronounced in the high-frequency region, especially at 8000 Hz. Genetic influences were moderate (heritability: 53%-65%) for pure-tone averages at both lower and higher frequencies, and were of equal magnitude at baseline and follow-up. In contrast, environmental influences were of substantial importance (55%-88%) for rate of change of the hearing threshold over the 18-year period. CONCLUSIONS: Genetic factors are of considerable importance for level of hearing acuity, but environmental factors are more important for rate of change over an 18-year period.

Imaging of the guinea pig cochlea following round window gadolinium application.

Precise, non-invasive determination of the aetiology and site of pathology of inner ear disorders is difficult. The aim of this study was to describe an alternative method for inner ear visualization, based on local application of the paramagnetic contrast agent gadolinium. Using a 4.7 T MRI scanner, high contrast images of all four cochlear turns were obtained 3.5 h after placing gadolinium on the round window membrane. Gadolinium cleared from the cochlea within 96 h. Auditory brainstem response measurements performed on a separate group of animals showed no significant threshold shifts after the application, indicating that gadolinium is non-toxic to the guinea pig cochlea.

A guinea pig strain with recessive heredity of deafness, producing normal-hearing heterozygotes with resistance to noise trauma.

A new strain of waltzing guinea pigs arose spontaneously in a guinea pig breeding facility in Germany in 1996. In addition to obvious vestibular dysfunction, the waltzing animals appear deaf already at birth. Histological analysis revealed that the waltzers lack an open scala media due to the collapse of Reissner's membrane onto the surface of the hearing organ. Subsequent breeding has shown that this strain has a recessive mode of inheritance. The homozygotes are deaf and display a waltzing behaviour throughout their lives while the heterozygotes show no significant signs of inner ear injury despite being carriers of this specific mutated gene of hearing impairment. However, the heterozygous animals offer the opportunity to study how hereditary factors interact with auditory stress. In the present study, the susceptibility of the carriers to noise was investigated. Auditory brainstem responses were obtained prior to and after noise exposure (4 kHz, 110 dB, 6 h). The carriers were significantly less affected by the noise as compared to control animals. This difference was still significant at 4 weeks following noise exposure. It is suggested that the heterozygous animals have an endogenous resistance to auditory stress.