Tinnitus in noise-induced hearing loss

Tinnitus was analysed in 94 patients with noise-induced hearing loss. Tinnitus of a pure tone character was most common followed by narrow-band noises, and a combination of these. A broad-band noise type of tinnitus was the least common finding. Tinnitus was most common at high frequencies. The suggested mean tinnitus level (in dBHL) corresponded well with the mean audiometric threshold for these patients. Most patients characterized their tinnitus as moderate to severe. Subjective tinnitus grading showed poor correlation to the audiometric threshold or to sensation level e.g. patients with a suggested tinnitus threshold corresponding to the hearing threshold could consider their tinnitus severe. The most common subjective discomforts were concentration difficulties, insomnia and decreased speech discrimination. In most cases residual inhibition was limited to 60 seconds.     

Glutathione limits noise-induced hearing loss

The generation of reactive oxygen species (ROS) is thought to be part of the mechanism underlying noise-induced hearing loss (NIHL). Glutathione (GSH) is an important cellular antioxidant that limits cell damage by ROS. In this study, we investigated the effectiveness of a GSH supplement to protect GSH-deficient animals from NIHL. Pigmented guinea pigs were exposed to a 4 kHz octave band noise, 115 dB SPL, for 5 h. Group 1 had a normal diet, while groups 2, 3 and 4 were fed a 7% low protein diet (leading to lowered tissue levels of GSH) for 10 days prior to noise exposure. One hour before, immediately after and 5 h after noise exposure, subjects received either an intraperitoneal injection of 5 ml/kg body weight of 0.9% NaCl (groups 1 and 2), 0.4 M glutathione monoethyl ester (GSHE; group 3) or 0.8 M GSHE (group 4). Auditory thresholds were measured by evoked brain stem response at 2, 4, 8, 12, 16 and 20 kHz before and after noise exposure. Ten days post exposure, group 1 showed noise-induced threshold shifts of approximately 20 dB at 2, 16 and 20 kHz and 35 to 40 dB at other frequencies. Threshold shifts in group 2 were significantly greater than baseline at 2, 4, 16 and 20 kHz. GSHE supplementation in a dose-dependent fashion attenuated the threshold shifts in the low protein diet animals. Hair cell loss, as evaluated with cytocochleograms, was consistent with the auditory-evoked brainstem response results. Group 2 exhibited significantly more hair cell loss than any of the other groups; hair cell loss in group 3 was similar to that seen in group 1; group 4 showed less loss than group 1. These results indicate that GSH is a significant factor in limiting noise-induced cochlear damage. This is compatible with the notion that ROS generation plays a role in NIHL and that antioxidant treatment may be an effective prophylactic intervention.     

Presbycusis and noise-induced hearing loss

In a longitudinal and an age cohort comparing study the influence of aging and occupational noise exposure on hearing sensitivity was studied. The participants of the longitudinal study were studied at 70, 75, and 79 years of age. Seventy year old men exposed to occupational noise had 10 to 15 dB poorer hearing in the high frequency range than nonexposed men. The difference in hearing acuity decreased with increasing age. The differences between exposed and nonexposed older persons was no longer significant at age 79. In women there were no differences in hearing sensitivity between those exposed to noise and those not exposed to noise. Men not exposed to noise had 10 to 15 dB poorer hearing at 4 kHz compared with women of the same age also not exposed to noise.     

Age and noise-induced hearing loss

The purpose of the study was to evaluate the effect of noise, age and confounders in noise-induced hearing loss (NIHL). Information about work exposure, the use of hearing protective devices, audiogram, environmental and biological factors was collected from 406 paper mill workers exposed to noise levels of 91-94 dB(A), 124 forest workers exposed to noise levels of 96-99 dB(A) and 176 shipyard workers exposed to noise levels 95-97 dB(A). In addition to noise exposure, we collected the following confounders: smoking habits, serum cholesterol, systolic or diastolic blood pressure and use of analgesics. Subjects were classified based on median values, into high- and low-risk groups. The confounders were a significant source of hearing loss (HL) in younger and elderly groups of subjects, serum cholesterol level being the most important. In risk analysis the confounders partly masked the effects of noise in the development of HL. For subjects with less than two confounders, occupational noise exposure determined the development of NIHL. As the number of confounders increased, the noise exposure was overruled by these factors in the development of HL. In analysis where the subjects were matched with pairs by age, exposure, blood pressure and serum cholesterol level, the elderly subjects were more susceptible to NIHL than younger subjects. Factors independently but causally related to age were important in the development of NIHL among workers exposed to noise levels below 98 dB(A).     

Epidemiology of professional noise-induced hearing loss

Denmark has a population of 4.9 million inhabitants, who are carefully registered from birth until death. Every Danish citizen with a permanent hearing impairment may have a complete evaluation free of charge, including being able to select one or two hearing aids from the current market. Therefore, very few people buy a hearing aid themselves, and thus the group of hearing handicapted persons passing through the hearing clinics indicate the morbidity nearly 100%. 92 367 persons applied for hearing revalidation in a 5-year period, and of those 7 108 (7.7%) were registered under the diagnosis professional noise-induced hearing loss, i.e. an incidence of about 1 400 per year = 28 per 100 000. 40% were below 65 years of age, and only 6% were women. In a sample of 1 108 noise-induced hearing losses, the severity of the loss was related to the exposure time, but so far the nature of the noise has not been examined nor been related to the single cases.     

噪音致隐匿性耳聋的研究进展

噪音致听力损伤(noise-induced hearing loss,NIHL) 一直受到广泛的关注,但噪音致隐匿性耳聋(noise-induced hearing hidden loss,NIHHL)的研究尚少,本文就NIHHL的发病特点,防治的现状和进展进行综述。     

依达拉奉对噪声性聋防治作用

目的探讨依达拉奉(Edaravone,Ed)对豚鼠声损伤的保护作用。方法清洁级豚鼠30只,雌雄不限,体重200²50g。随机分3组,正常对照组10只,生理盐水组10只,依达拉奉组10只。予白噪声120dB SPL,每天4h,连续4天。噪声前半小时腹腔注射依达拉奉溶液,8.0mg/kg,每天一次,持续给药到噪声完毕后一周。噪声前,噪声后即刻,第3天,第7天行听性脑干反应(ABR)检测,第8天琥珀酸脱氢酶,免疫组化,扫描电镜检测。结果噪声前,3组豚鼠ABR阈值无明显差异(P>0.05),噪声后即刻生理盐水及依达拉奉组ABR阈值均高于正常对照组,依达拉奉组ABR阈值低于生理盐水组,差异有统计学意义(P<0.05),3天后,依达拉奉组ABR阈值明显降低,7天后接近正常对照组,而生理盐水组则明显高于正常对照组,差异有统计学意义(P<0.05)。正常对照组外毛细胞胞质琥珀酸脱氢酶(SDH)着色深,胞核、纤毛排列整齐;光镜下观察生理盐水组底转毛细胞中SDH着色浅,细胞肿胀不规则,依达拉奉组较生理盐水组外毛细胞胞质着色深,细胞形态规则,免疫组化及扫描电镜检测显示正常对照组细胞核纤毛排列整齐,未见缺失,而生理盐水组和依达拉奉组底转毛细胞出现缺失,依达拉奉组较生理盐水组细胞核及纤毛缺失明显减轻。结论结合之前的实验研究,初步推测依达拉奉对噪声性耳聋中产生的自由基具有清除作用。     

High-frequency audiometry and noise-induced hearing loss

A group of noise-exposed male subjects with an audiogram that is characteristic for noise trauma were submitted to high-frequency audiometry (HFA) up to 20 000 HZ. The results were compared with those obtained in a group of normally hearing persons with no history of noise exposure. Conserved high frequency hearing was found. Very strict selection criteria were applied in both groups in order to avoid hereditary diseases and to ensure normal middle ear function. The findings are in good overall agreement with histological findings in noise-exposed animals and also with high-frequency studies in the older literature. Two illustrative case stories from patients with severe 4--6 kHz dips are reported, one with preserved high-frequency hearing in spite of a considerable acoustic trauma and one with extreme sensitivity towards noise and with no hearing at all in the high frequencies. It is concluded that 1) HFA cannot be used as an early indicator of the traumatic effect of high intensity noise; 2) presbycusis and noise damage may be additive elements in the older age groups (above 50 years); 3) persons with abnormal high-frequency hearing are possibly hypersensitive towards excessive noise and HFA might be useful in the routine audiological evaluation of workers before these are exposed to noise.     

Temporal bone histopathology of noise-induced hearing loss

To examine the relationship between hearing and changes in the inner ear, we investigated human temporal bone specimens from 2 patients with noise-induced hearing loss and prepared audio-cytocochleograms as described by Schuknecht et al. Patient 1 was a 50-year-old male who died of thyroid cancer and had worked at a printing house for 38 years. Patient 2 was a 58-year old male who died of maxillary sinus cancer and had worked in construction for 22 years. A pure-tone audiogram showed high-tone sensorineural hearing loss with c5-dip-type hearing disorder in both ears in Patient 1, and a high-tone abrupt form of sensorineural hearing loss in Patient 2. Pathological examination of the temporal bone revealed degeneration and disappearance of the organ of Corti at the basal turn and disappearance of cochlear neurons in both patients. Audio-cytocochleograms revealed hearing disorder consistent with the changes in the inner ear in both patients. Marked degeneration and disappearance of the organ of Corti and stria vascularis were present in patient 1. It is generally known that disorders of the organ of Corti for a long period is involved in the etiology of noise-induced hearing loss. This degeneration of the organ of Corti is produced at a basilar membrane with the maximum amplitude related to exposure to noise according to a physical and mechanical factors. Moreover, animal experiments have shown that exposure to noise decrease cochlear blood flow. In Patient 1 both the organ of Corti and the stria vascularis exhibited degeneration, suggesting that not only physical and mechanical factors but a cochlear circulatory disorder related to exposure to noise was involved in the etiology of the pathological changes in the temporal bone related to noise-induced hearing loss.     

Prevalence of noise-induced hearing loss in student musicians

Abstract

This study describes the prevalence and characteristics of noise-induced hearing loss (NIHL) in student musicians (N = 329) aged 18–25 years. Students completed a questionnaire regarding exposures before a hearing assessment. NIHL was defined by the presence of a notch 15 dB in depth at 4000 or 6000 Hz relative to the best preceding threshold. Overall prevalence of NIHL was 45%, with 78% of notches occurring at 6000 Hz. The proportion of the total population with bilateral notching at any frequency was 11.5%, mostly occurring at 6000 Hz. There was a significant increase in the frequency of notching in students who reported more than two hours per day of personal practice. There were no significant associations for instrument group or other noise exposures. The data suggest that susceptibility to NIHL among students of music is not uniform and cannot be ascribed solely to the instrument played and other exposures. Students with bilateral losses tend to have deeper notches and may represent a group that has an inherent predisposition to NIHL.

Sumario

Este estudio describe la prevalencia y las características de la hipoacusia inducida por ruido (NIHL) en estudiantes de música (N = 329) con edades entre 18 y 25 años. Los estudiantes completaron un cuestionario sobre exposición a ruido antes de la evaluación auditiva. Se definió NIHL como la presencia de una muesca de 15dB en 4000 o 6000Hz con relación al mejor umbral precedente. La prevalencia general de NIHL fue de 44%, con 78% de las muescas en 6,000 Hz. La proporción de la población total con muescas bilaterales en cualquier frecuencia fue de 11.5%, en su mayoría a 6,000 Hz. Hubo un incremento significativo en la frecuencia de la muescas en los estudiantes que reportaban más de dos horas al día de práctica profesional. No hubo una asociación significativa con grupos de instrumentos u otra exposición a ruido. Los datos sugieren que la susceptibilidad a NIHL entre los estudiantes de música no es uniforme y no puede atribuirse solamente al instrumento tocado o a otras exposiciones. Los estudiantes con pérdida bilateral tienden a tener muescas más profundas y pueden representar un grupo que tenga una predisposición inherente a la NIHL.     

Audiologic profile of noise-induced hearing loss.

Audiologic results for 450 ears presumed to have uncomplicated noise induced hearing loss were analyzed to describe their typical profile and to quantify the characteristic audiometric notch. Data consisted of tonal and speech thresholds, speech discrimination scores, Bekesy tracings, and short increment sensitivity index scores, and tone decay at 4,000 hertz. In each case, the pattern of results indicated a cochlear site of lesion, although the only uniformly cochlear sign was the absence of a pattern of abnormal adaptation in Bekesy tracings. In each case, the audiogram could be approximated by a quartic equation. The mean difference between actual thresholds and those predicted by the best-fit quartic did not exceed 7.72 dB and was less than 5 dB for eight of the 11 frequencies for which comparisons were made. We propose the application of this characteristic to clinical practice and to automated hearing conservation programs.     

助听器的声场验配法

在声场测听条件下，对17名儿童（33耳）进行助听前和助听后的声场听阈测试。以助听后听阈值能否进入言语香蕉图范围来评价助听效果，为使助听效果满意，在测试时可调节助听器的各种调节使扭；测试结果显示，该法不失为助听器验配的有效方法之一。本文亦对影响本方法的一些因素做了讨论。     

Auditory brainstem responses in noise-induced permanent hearing loss

Fifty-four patients (108 ears) with presumed noise-induced hearing loss, were subjected to tonal and speech audiometry, impedance tests and measurements of auditory brainstem responses (ABR), in order to check for possible retrocochlear involvement. ABR data indicated that latency values of waves I, III and V, as well as III-I, V-III and V-I intervals fell within the normal range in all cases (M +/- 2 SD), even for fast repetition rates (51 stim/s). Poor waveform resolution of early components, particularly of wave I, was found in 12 ears (11.1%) and a total absence of evoked potentials not always related to the hearing loss, occurred in 5 ears (4.6%).     

Race difference in susceptibility to noise-induced hearing loss

Pure-tone audiometric thresholds were compared in 28 black and 28 matched white male Emergency Medical Service firefighters exposed to high levels of ambulance siren noise. Groups were matched on the basis of chronologic age, duration of firefighter employment, and prevalence of nonjob-related noise exposure. Results suggested that whites are more susceptible to the damaging effects of high-level noise than blacks. In both the mid- and high-frequency regions of the audiogram, blacks showed significantly better sensitivity than whites on the poorer ear. On the better ear, the sensitivity difference between blacks and whites widened as employment duration and, therefore, duration of noise exposure, increased.     

Acoustic reflex amplitude and noise-induced hearing loss

Acoustic reflex maximum amplitude measurements elicited both contralaterally and ipsilaterally were obtained from subjects with noise-induced hearing loss and compared with those obtained from normal-hearing subjects. The eliciting signal was a pure tone of 1 kHz presented for 1,000 ms. The groups were matched on age, sex, static immittance and ear canal volume. Acoustic reflex amplitudes were clearly reduced in noise-impaired subjects compared with normal-hearing subjects at a frequency where their hearing thresholds were normal.