Is there a relationship between hypercholesterolaemia and noise-induced hearing loss?

Sensorineural hearing loss among type 2 diabetic patients and its association with peripheral neuropathy: a cross-sectional study from a lower middle-income country

INTRODUCTION

Despite potential links between diabetes and sensorineural hearing loss (SNHL), routine hearing assessments for diabetic patients are not standard practice. Our study aimed to investigate the prevalence of SNHL and its association with diabetes-related factors among patients with type 2 diabetes mellitus (T2DM).

RESEARCH DESIGN AND METHODS

This cross-sectional study was conducted at the Diabetes Clinic, Jinnah Postgraduate Medical Centre, Karachi, Pakistan, from May to September 2021. A total of 396 patients fulfilling the inclusion criteria participated after informed consent. Data collection involved a sociodemographic profile, Michigan Neuropathy Screening Instrument examination followed by pure-tone audiometry and laboratory tests including haemoglobin A1C (HbA1c). HL was defined using better ear four-frequency pure-tone average of ≥26 dB HL and graded as per WHO criteria. Statistical analyses were performed using SPSS. χ2, independent t-test and multinomial logistic regression analyses were applied. P<0.05 at 95% CI was considered significant.

RESULTS

Our study revealed a high prevalence of SNHL among patients with T2DM. Mild HL was seen in 55.8%, while 18.7% suffered from moderate HL. Common audiological symptoms included difficulty understanding speech in noisy surroundings (44.2%), balance problems (42.9%), sentence repetition (35.9%), tinnitus (32.3%) and differentiating consonants (31.1%). Hearing impairment predominantly affected low (0.25-0.5 kHz) and high (4-8 kHz) frequencies with a significant difference at 4 kHz among both sexes (t (394)=2.8, p=0.004). Peripheral neuropathy was significantly associated with SNHL on multinomial logistic regression after adjusting with age, sex, body mass index and the presence of any comorbidities. Diabetes duration, HbA1c or family history of diabetes was found unrelated to SNHL severity.

CONCLUSIONS

The study highlights the substantial prevalence of SNHL among patients with T2DM and emphasises the importance of targeted audiological care as part of a holistic approach to diabetes management. Addressing HL early may significantly improve communication and overall quality of life.

Association between Serum Lipid Levels and Sensorineural Hearing Loss in Korean Adult Population

Background

Hearing loss (HL) has been suggested to be associated with impaired microcirculation of the inner ear. This cross-sectional study aimed to evaluate an association between HL and serum lipid levels.

Methods

The study comprised 10,356 Korean adults who participated in the fifth Korea National Health and Nutrition Examination Survey (2010–2012). We defined HL as the average hearing thresholds exceeding 25 dB at predetermined frequency levels by pure tone audiometry. Serum lipid levels were measured using an enzymatic assay. The associations between lipid levels and HL were evaluated using a multiple logistic regression model after adjusting for covariates including age, sex, hypertension, diabetes, smoking status, alcohol, physical activity, educational level, household income, and noise exposure. Stratified analyses were performed to examine the effect of the covariates on the association between lipid levels and HL.

Results

The high-density lipoprotein cholesterol (HDL-C) level was inversely associated with high-frequency (HF)-HL, with an odds ratio (95% confidence interval) of 0.78 (0.64–0.96) for 1-mmol/L increase in the HDL-C level. Neither the triglyceride nor the low-density lipoprotein cholesterol level was associated with HF-HL. For low-frequency HL, association with any of the serum lipid components was absent. A stratified analysis showed that the inverse association between HDL-C levels and HF-HL was evident (P trend <0.05) in some subjects with specific characteristics such as older age (≥65 years), female sex, non-hypertensive state, and non-regular physical activity. However, a significant interaction between HDL-C levels and all of the stratified variables was absent (P for interaction >0.05).

Conclusion

The HDL-C level has a linear inverse association with the risk of HF-HL. Given the known protective role of HDL-C against atherosclerotic changes, this finding seems to support the concept of impaired microcirculation in the inner ear as a mechanism for HF-HL.

The effects of dyslipidemia on noise-induced hearing loss in a petrochemical workers in the Southwest of Iran

BACKGROUND

Research has shown that the decrease in the inner diameter of vessels caused by hyperlipidemia lowers the capacity for blood oxygen delivery to the cochlea. This leads to impaired cochlear metabolism and causes hearing problems.

OBJECTIVE

The effects of dyslipidemia on noise-induced hearing loss in workers were examined.

METHODS

This descriptive cross-sectional study was performed on 692 male employees in a petrochemical industry in the southwest of Iran exposed to 85 dB noise. Clinical audiometry and blood sample tests were used to evaluate the hearing and prevalence indices of dyslipidemia (cholesterol, triglyceride, HDL and LDL). The data were analyzed using SPSS software version 25 (p = 0.05).

RESULTS

The results showed that the prevalence of dyslipidemia was 24.5%with abnormal relative triglyceride frequency of 49.5%, HDL of 28%, LDL of 33%, and total blood cholesterol level of 37.8%. There was no significant relationship between NIHL and dyslipidemia (p >  0.09). However, the major NIHL drops at different frequencies were in the individuals with dyslipidemia. The parameters age and dyslipidemia increased NIHL odds ratio (95%C.I.). by 1.130 (1.160-1.100) and 1.618 (2.418-1.082) respectivelyCONCLUSION:The rate of hearing loss in individuals with dyslipidemia increases at different frequencies and it leads to an increase of the OR of NIHL in individuals with dyslipidemia. We can control dyslipidemia and its effective factors. The NIHL is more common in people exposed to noise.

Effects of co-exposure to 900 MHz radiofrequency electromagnetic fields and high-level noise on sleep, weight, and food intake parameters in juvenile rats

OBJECTIVE

Electrohypersensitive people attribute various symptoms to exposure of radiofrequency electromagnetic fields (RF-EMF); sleep disturbance is the most frequently cited. However, laboratory experiments have yielded conflicting results regarding sleep alterations. Our hypothesis was that exposure to RF-EMF alone would lead to slight or non-significant effects but that co-exposure to RF-EMFs and other environmental constraints (such as noise) would lead to significant effects.

METHODS

3-week-old male Wistar rats (4 groups, n = 12 per group) were exposed for 5 weeks to continuous RF-EMF (900 MHz, 1.8 V/m, SAR = 30 mW/kg) in the presence or absence of high-level noise (87.5 dB, 50-20000 Hz) during the rest period. After 5 weeks of exposure, sleep (24 h recording), food and water intakes, and body weight were recorded with or without RF-EMF and/or noise. At the end of this recording period, sleep was scored during the 1 h resttime in the absence of noise and of RF-EMF exposure.

RESULTS

Exposure to RF-EMF and/or noise was associated with body weight gain, with hyperphagia in the noise-only and RF-EMF + noise groups and hypophagia in the RF-EMF-only group. Sleep parameters recording over 24 h highlighted a higher frequency of active wakefulness in the RF-EMF-only group and a lower non-rapid eye movement/rapid eye movement sleep ratio during the active period in the noise-only group. There were no differences in sleep duration in either group. During the 1-h, constraint-free sleep recording, sleep rebound was observed in the noise-only group but not in the RF-EMF-only and RF-EMF + noise groups.

CONCLUSION

Our study showed effects of RF-EMF, regardless of whether or not the animals were also exposed to noise. However, the RF-EMF + noise group presented no exacerbation of those effects. Our results did not support the hypothesis whereby the effects of RF-EMF on physiological functions studied are only visible in animals exposed to both noise and RF-EMF.

Research and Discussion on the Relationships between Noise-Induced Hearing Loss and ATP2B2 Gene Polymorphism

Long-term and continuous noise exposure can result in noise-induced hearing loss (NIHL), which is a worldwide problem resulting from the interaction of environmental and genetic factors. The ATP2B2 gene polymorphism can destroy cochlear hair cells and increase the risk of NIHL. A case-control study of 760 Chinese textile workers was conducted to investigate the relationship between ATP2B2 polymorphisms and NIHL susceptibility. Venous blood was collected and questionnaires were conducted by professional physicians. A case group and a control group which were typed by individuals' pure-tone audiometry test results were set. Three polymorphism sites of ATP2B2 were genotyped by using the PCR technique. Analysis results revealed that the C allele of rs3209637 (95%CI = 1.08-2.58, odds ratio (OR) = 1.67, P = 0.027) was a dangerous factor and could add to risks of NIHL in the Chinese employees. The data of stratified analysis revealed that individuals who are exposed to noise > 95 dB with the rs3209637 C genotype have a higher susceptibility to NIHL (OR = 1.34, 95%CI = 1.07-1.68). Multifactor dimensionality reduction analysis revealed that the interaction between rs14154 and rs3209637 is linked to increased NIHL risk, and for the interaction among rs14154, smoking and drinking had the same function (OR = 1.54 and 1.77, 95%CI = 1.15-2.07, 1.33-2.37, and P = 0.0037 and P < 0.0001, respectively). Our results suggest that genetic polymorphism rs3209637 C within ATP2B2 is a risk factor for NIHL among Chinese employees and rs3209637 C could be a potential biomarker for NIHL patients.

Impacts of Subchronic, High-Level Noise Exposure on Sleep and Metabolic Parameters: A Juvenile Rodent Model

BACKGROUND

Noise is an environmental factor that has been associated with metabolic and sleep disorders. Sleep is a vital function, since it underpins physiologic processes and cognitive recovery and development. However, the effects of chronic noise exposure on the developing organism are still subject to debate.

OBJECTIVE

The objective of the present study was to assess the effects of subchronic, high-level noise exposure on sleep, apnea, and homeostasis in juvenile rats.

METHODS

Twenty-four 3-wk-old male Wistar rats were exposed to noise [[Formula: see text], [Formula: see text]] for 5 wk and 2 d during the 12-h rest period. Data on sleep stages, food and water intake, apnea, and body and organ weight were recorded.

RESULTS

Five weeks of high-level noise exposure were associated with hyperphagia ([Formula: see text]), body weight gain ([Formula: see text]), a heavier thymus ([Formula: see text]), and heavier adrenal glands ([Formula: see text]). A sleep analysis highlighted microstructural differences in the active period: in particular, the mean daily amount of rapid eye movement (REM) sleep as a proportion of total sleep time (TST) was higher. The mean daily amount of non-REM (NREM) sleep was lower in the exposed group, meaning that the intergroup difference in the TST was not significant. During a 1-h, noise-free plethysmographic recording during the rest period, the mean total amount of active wakefulness (AW) was lower in the exposed group (by 9.1 min), whereas the mean duration of an episode of REM sleep was higher (by 1.8 min), and the TST was higher (by 10.7 min).

DISCUSSION

Subchronic exposure of juvenile rats to high-intensity noise during the rest period was associated with some small but significant sleep disturbances, greater food and water intakes, greater body weight gain, and greater thymus and adrenal gland weights. The main effects of noise exposure on sleep were also observed in the 1-h plethysmography session after 5 wk of exposure. https://doi.org/10.1289/EHP4045.

Utility of otoacoustic emissions and olivocochlear reflex in predicting vulnerability to noise-induced inner ear damage

Aim:

The aim of the present study was to explore the possible utility of otoacoustic emissions (OAEs) and efferent system strength to determine vulnerability to noise exposure in a clinical setting.

Materials and Methods:

The study group comprised 344 volunteers who had just begun mandatory basic training as Hellenic Corps Officers Military Academy cadets. Pure-tone audiograms were obtained on both ears. Participants were also subjected to diagnostic transient-evoked otoacoustic emissions (TEOAEs). Finally, they were all tested for efferent function through the suppression of TEOAEs with contralateral noise. Following baseline evaluation, all cadets fired 10 rounds using a 7.62 mm Heckler & Koch G3A3 assault rifle while lying down in prone position. Immediately after exposure to gunfire noise and no later than 10 h, all participants completed an identical protocol for a second time, which was then repeated a third time, 30 days later.

Results:

The data showed that after the firing drill, 280 participants suffered a temporary threshold shift (TTS) (468 ears), while in the third evaluation conducted 30 days after exposure, 142 of these ears still presented a threshold shift compared to the baseline evaluation [permanent threshold shift (PTS) ears]. A receiver operating characteristics curve analysis showed that OAEs amplitude is predictive of future TTS and PTS. The results were slightly different for the suppression of OAEs showing only a slight trend toward significance. The curves were used to determine cut points to evaluate the likelihood of TTS/PTS for OAEs amplitude in the baseline evaluation. Decision limits yielding 71.6% sensitivity were 12.45 dB SPL with 63.8% specificity for PTS, and 50% sensitivity were 12.35 dB SPL with 68.2% specificity for TTS.

Conclusions:

Interestingly, the above data yielded tentative evidence to suggest that OAEs amplitude is both sensitive and specific enough to efficiently identify participants who are particularly susceptible to hearing loss caused by impulse noise generated by firearms. Hearing conservation programs may therefore want to consider including such tests in their routine. As far as efferent strength is concerned, we feel that further research is due, before implementing the suppression of OAEs in hearing conservations programs in a similar manner.

Comparisons of hearing threshold changes in male workers with unilateral conductive hearing loss exposed to workplace noise: a retrospective cohort study for 8 years

BACKGROUND

The purpose of this study was to investigate hearing threshold changes of workers with unilateral conductive hearing loss who were exposed to workplace noise for 8-years.

METHODS

Among 1819 workers at a shipyard in Ulsan, 78 subjects with an air-bone gap ≥10 dBHL in unilateral ears were selected. Factors that could affect hearing were acquired from questionnaires, physical examinations, and biochemistry examinations. Paired t-test was conducted to compare the hearing threshold changes over time between conductive hearing loss (CHL) ear and sensorineural hearing loss (SNHL) ear.

RESULTS

The study included male subjects aged 48.7 ± 2.9, having worked for 29.8 ± 2.7 years. Hearing thresholds increased significantly in CHL ears and SNHL ears at all frequencies (0.5-6 kHz) during follow-up period (p < 0.05). The threshold change at 4 kHz was 3.2 dBHL higher in SNHL ears which was statistically significant (p < 0.05). When workers were exposed to noise levels of 85 dBA and above, threshold change at 4 kHz was 5.6 dBHL higher in SNHL ears which was statistically significant (p < 0.05). Among workers aged below 50, the threshold change values were lower in low-frequency (0.5-2 kHz) in SNHL ears, with a small range of changes, whereas in high-frequency (3-6 kHz), the range of changes was greater SNHL ears (p < 0.05). Among workers aged 50 and above, SNHL ears showed a wider range of changes in both high- and low-frequency areas (p < 0.05).

CONCLUSIONS

At high-frequencies, particularly at 4 kHz, the range of hearing threshold changes was lower in ears with conductive hearing loss than in contralateral ears. This is suggested as a protective effect against noise exposure.

QTL Mapping of Endocochlear Potential Differences between C57BL/6J and BALB/cJ mice

We reported earlier that the endocochlear potential (EP) differs between C57BL/6J (B6) and BALB/cJ (BALB) mice, being lower in BALBs by about 10 mV (Ohlemiller et al. Hear Res 220: 10-26, 2006). This difference corresponds to strain differences with respect to the density of marginal cells in cochlear stria vascularis. After about 1 year of age, BALB mice also tend toward EP reduction that correlates with further marginal cell loss. We therefore suggested that early sub-clinical features of the BALB stria vascularis may predispose these mice to a condition modeling Schuknecht's strial presbycusis. We further reported (Ohlemiller et al. J Assoc Res Otolaryngol 12: 45-58, 2011) that the acute effects of a 2-h 110 dB SPL noise exposure differ between B6 and BALB mice, such that the EP remains unchanged in B6 mice, but is reduced by 40-50 mV in BALBs. In about 25 % of BALBs, the EP does not completely recover, so that permanent EP reduction may contribute to noise-induced permanent threshold shifts in BALBs. To identify genes and alleles that may promote natural EP variation as well as noise-related EP reduction in BALB mice, we have mapped related quantitative trait loci (QTLs) using 12 recombinant inbred (RI) strains formed from B6 and BALB (CxB1-CxB12). EP and strial marginal cell density were measured in B6 mice, BALB mice, their F1 hybrids, and RI mice without noise exposure, and 1-3 h after broadband noise (4-45 kHz, 110 dB SPL, 2 h). For unexposed mice, the strain distribution patterns for EP and marginal cell density were used to generate preliminary QTL maps for both EP and marginal cell density. Six QTL regions were at least statistically suggestive, including a significant QTL for marginal cell density on chromosome 12 that overlapped a weak QTL for EP variation. This region, termed Maced (Marginal cell density QTL) supports the notion of marginal cell density as a genetically influenced contributor to natural EP variation. Candidate genes for Maced notably include Foxg1, Foxa1, Akap6, Nkx2-1, and Pax9. Noise exposure produced significant EP reductions in two RI strains as well as significant EP increases in two RI strains. QTL mapping of the EP in noise-exposed RI mice yielded four suggestive regions. Two of these overlapped with QTL regions we previously identified for noise-related EP reduction in CBA/J mice (Ohlemiller et al. Hear Res 260: 47-53, 2010) on chromosomes 5 and 18 (Nirep). The present map may narrow the Nirep interval to a ~10-Mb region of proximal Chr. 18 that includes Zeb1, Arhgap12, Mpp7, and Gjd4. This study marks the first exploration of natural gene variants that modulate the EP. Their orthologs may underlie some human hearing loss that originates in the lateral wall.

Lutein and zeaxanthin status and auditory thresholds in a sample of young healthy adults

OBJECTIVES

Dietary carotenoids lutein (L) and zeaxanthin (Z) have been linked to improved visual and cognitive function. These effects are thought to be mediated by the presence of these pigments in critical regions of the retina and brain. There, it has been postulated that L and Z mediate improved performance by enhancing neural efficiency. The auditory system also relies on efficient segregating of signals and noise and LZ are also found in the auditory cortex. The purpose of the present study was to investigate the influence of LZ status (as assessed by the measuring levels in retina) on auditory thresholds in young non-smokers (N = 32, M = 20.72 ± 3.28 years).

DESIGN

LZ status was determined by measuring macular pigment (MP) optical density using a standardized psychophysical technique (customized heterochromatic flicker photometry). Auditory thresholds were assessed with puretone thresholds and puretone auditory thresholds in white noise.

RESULTS

MP density was related to many, but not all, of the puretone thresholds we tested: 250 Hz (F(6,32) = 4.36, P < 0.01), 500 Hz (F(6,32) = 2.25, P < 0.05), 1000 Hz (F(6,32) = 3.22, P < 0.05), and 6000 Hz (F(6,32) = 2.56, P < 0.05).

CONCLUSION

The overall pattern of results is consistent with a role for L and Z in maintaining optimal auditory function.

Metabolic Syndrome Is not an Independent Risk Factor for Hearing Impairment

OBJECTIVE

We aimed to investigate the association between metabolic syndrome (MS) and hearing impairment (HI) using nationally representative data from Korean adults.

DESIGN, SETTING AND PARTICIPANTS

A total of 16,799 subjects (≥19 years old; 7,170 men and 9,629 women) who underwent pure tone audiometry testing were included in the analysis. Data were obtained from the fifth Korea National Health and Nutrition Examination Survey (2010-2012). Subjects were divided into two groups according to the presence of MS.

RESULTS

Among the subjects with MS, 47% had HI. Logistic regression analysis revealed that MS was not an independent risk factor for HI, although increased fasting plasma glucose (OR 1·4, 95% CI: 1·1-1·8) was independently associated with HI. In addition, older age, male sex, very low body mass index (≤17·5 kg/m2), lower education level, smoking history, and occupational noise exposure were independently associated with HI. For low-frequency HI, independent risk factors included older age, lower educational level, lower economic status, and very low BMI (≤17·5 kg/m2). For high-frequency HI, independent risk factors included older age, male sex, lower educational level, lower economic status, increased blood pressure, lower high-density lipoprotein cholesterol, and smoking history.

CONCLUSIONS

MS itself was not an independent risk factor for HI, and, among the individual metabolic components, only increased fasting plasma glucose was independently associated with HI.

Cardiovascular risk factors and hearing loss: The HUNT study

OBJECTIVE

The purpose of the present paper was to examine the association between prospectively and cross-sectionally assessed cardiovascular risk factors and hearing loss.

DESIGN

Hearing was assessed by pure-tone average thresholds at low (0.25-0.5 kHz), middle (1-2 kHz), and high (3-8 kHz) frequencies. Self-reported or measured cardiovascular risk factors were assessed both 11 years before and simultaneously with the audiometric assessment. Cardiovascular risk factors were smoking, alcohol use, physical inactivity, waist circumference, body mass index, resting heart rate, blood pressure, triglycerides, total serum cholesterol, LDL cholesterol, HDL cholesterol, and diabetes.

STUDY SAMPLE

A population-based cohort of 31 547 subjects.

RESULTS

After adjustment for age, sex, level of education, income, recurrent ear infections, and noise exposure, risk factors associated with poorer hearing sensitivity were smoking, diabetes, physical inactivity, resting heart rate, and waist circumference. Smoking was only associated with hearing loss at high frequencies. The effects were very small, in combination explaining only 0.2-0.4% of the variance in addition to the component explained by age and the other cofactors.

CONCLUSION

This cohort study indicates that, although many cardiovascular risk factors are associated with hearing loss, the effects are small and of doubtful clinical relevance.

Occupational noise exposure and hearing: a systematic review

Purpose

To give a systematic review of the development of noise-induced hearing loss (NIHL) in working life.

Methods

A literature search in MEDLINE, Embase, Web of Science, Scopus, and Health and Safety Abstracts, with appropriate keywords on noise in the workplace and health, revealed 22,413 articles which were screened by six researchers. A total of 698 articles were reviewed in full text and scored with a checklist, and 187 articles were found to be relevant and of sufficient quality for further analysis.

Results

Occupational noise exposure causes between 7 and 21 % of the hearing loss among workers, lowest in the industrialized countries, where the incidence is going down, and highest in the developing countries. It is difficult to distinguish between NIHL and age-related hearing loss at an individual level. Most of the hearing loss is age related. Men lose hearing more than women do. Heredity also plays a part. Socioeconomic position, ethnicity and other factors, such as smoking, high blood pressure, diabetes, vibration and chemical substances, may also affect hearing. The use of firearms may be harmful to hearing, whereas most other sources of leisure-time noise seem to be less important. Impulse noise seems to be more deleterious to hearing than continuous noise. Occupational groups at high risk of NIHL are the military, construction workers, agriculture and others with high noise exposure.

Conclusion

The prevalence of NIHL is declining in most industrialized countries, probably due to preventive measures. Hearing loss is mainly related to increasing age.

Electronic supplementary material

The online version of this article (doi:10.1007/s00420-015-1083-5) contains supplementary material, which is available to authorized users.

Lipid Profile among Patients with Sudden Sensorineural Hearing Loss

Associations between hearing and blood lipids have been the focus of scientific inquiry for more than 50 years. The aim of the present study is to evaluate the association between hyperlipidaemia among patients presented with sudden sensorineural hearing loss compared to normal controls. A case control study concerned with 22 patients presented with sudden sensorineural hearing loss who underwent lipid profile evaluation. The lipid profile of these patients was compared with corresponding results of 55 age matched persons (volunteers) with normal hearing. These patients were collected from the Out Patient Department of ENT at Al-Jamhory Teaching Hospital, Mosul/Iraq and private clinic of the author for the period from February 2011 to July 2013. The average age of patients was 44.7 years with a range of 26-65 years. The peak age incidence was in the 5(th) decade of life. The study included 11 male patients (50 %) and 11 females (50 %). Meanwhile, the average age of the control group was 41.7 years with 25 (45.5 %) males and 30 (54.5 %) females. Statistical analysis showed that there was significant difference between the means of lipid profile and blood sugar of the patients and the control group apart from HDL where there was no significant difference. In conclusion, hyperlipidemia seems to be significantly associated with the occurrence of sudden sensorineural hearing loss according to this study.

Association between paraoxonase 2 gene polymorphisms and noise-induced hearing loss in the Chinese population

OBJECTIVES

The aim of the present study was to investigate whether PON2 gene polymorphisms (rs7493, rs12026, rs12704796, rs7785846 and rs7786401) are associated with susceptibility to noise-induced hearing loss (NIHL) in the Chinese population.

METHODS

A case-control study was conducted using 615 cases selected without any restriction in age or sex and 644 controls who were matched with the cases in terms of age, gender and the intensity and duration of exposure to noise. Information on these subjects was gathered by questionnaires that were administered through face-to-face interviews by trained interviewers.

RESULTS

We found that the rs7493 CG + GG genotype (OR=1.36, 95% CI, 1.08-1.72), rs12026 CG + GG genotype (OR=1.34, 95% CI, 1.06-1.70), rs7785846 CT + TT genotype (OR=1.36, 95% CI, 1.07-1.71) and rs7786401 GT + TT genotype (OR=1.33, 95% CI, 1.05-1.68) were risk factors for NIHL.

CONCLUSIONS

PON2 gene polymorphisms may be associated with susceptibility to NIHL in the Chinese population

Auditory brainstem evoked responses in hyperlipidaemia: effect of various lipid fractions on auditory function

OBJECTIVE

To evaluate the effect of different lipid fractions on auditory brainstem evoked responses in hyperlipidaemia.

METHOD

We conducted a single institution (medical college), prospective, cross-sectional study of 25 hyperlipidaemic patients and 25 normolipidaemic controls, all with a normal hearing threshold on pure tone audiometry. Brainstem evoked response audiometry results were recorded in both groups. The hyperlipidaemic group were further divided into two subgroups, based on the serum value of each lipid fraction: those with less than and those with greater than the mean serum value. These two subgroups were further compared with the control group.

RESULTS

The hyperlipidaemic and normolipidaemic groups had statistically significant differences for all audiometry waves apart from the wave I and the III-V interpeak latencies. The subgroups had a statistically significant difference in brainstem evoked responses. We found a statistically significant association between low-density lipoproteins and many waveforms in the hyperlipidaemic group.

CONCLUSION

We found that low-density lipoproteins were significantly associated with many waveforms in hyperlipidaemic patients. Thus, low-density lipoproteins may be important in auditory dysfunction.

Cochlear dysfunction in hyperuricemia: otoacoustic emission analysis

PURPOSE

The objective of this study is to provide evidence that primary hyperuricemia is associated with cochlear dysfunction as other metabolic diseases that interfere with cell metabolism.

MATERIALS AND METHODS

Cochlear function was evaluated in 25 subjects with asymptomatic hyperuricemia using routine diagnostic audiometry along with transient evoked and distortion product otoacoustic emissions (TEOAE and DPOAE, respectively). To support the notion that vascular compromise was a significant underlying factor for such cochlear dysfunction, we assessed vascular anatomical and functional states through measuring the common carotid artery intima-media thickness and flow velocity of the basal intracranial vessels.

RESULTS

Compared with control subjects, reduced response levels of TEOAEs (P < .01) and amplitudes of DPOAEs (P < .001) were detected at higher frequencies. The reduced DPOAE levels at 5 kHz and TEOAEs at 4 kHz correlated significantly with uric acid (P < .05; P < .01), patients' age (P < .06; P < .05), duration since diagnosis of hyperuricemia (P < .05; P < .001), common carotid artery intima-media thickness (P < .05), mean flow velocities of middle cerebral arteries (P < .05), and vertebral arteries (P < .01). Multivariate analysis showed that the abnormalities at higher frequencies were significantly correlated with the duration and degree of hyperuricemia.

CONCLUSIONS

These data suggest that subclinical changes in cochlear function are associated with hyperuricemia. They support the usefulness of otoacoustic emissions in early detection of cochlear dysfunction. It is possible that hyperuricemia could be accompanied by increased stiffness and/or compromise of blood supply of the outer hair cells, which will impair their electromotile response.

Association between cardiovascular health and hearing function: pure-tone and distortion product otoacoustic emission measures

PURPOSE

A reduction in hearing sensitivity is often considered to be a normal age-related change. Recent studies have revisited prior ways of thinking about sensory changes over time, uncovering health variables other than age that play a significant role in sensory changes.

METHOD

In this cross-sectional study, cardiovascular (CV) health, pure-tone thresholds at 1000 to 4000 Hz, and distortion product otoacoustic emissions (DPOAEs), with and without contralateral noise, were measured in 101 participants age 10-78 years.

RESULTS

Persons in the "old" age category (49-78 years) had worse pure-tone hearing sensitivity and DPOAEs than persons in the younger age categories (p < .05), affirming an age effect. Although hearing decline occurred in all persons in all CV fitness categories of every age group, those with low CV fitness in the old age group had significantly worse pure-tone hearing at 2000 and 4000 Hz (p <.05). Otoacoustic emission measurements were better for the old high-fit group but not significantly influenced by CV fitness level across age groups.

CONCLUSIONS

Results of the current study elucidate the potentially positive impact of CV health on hearing sensitivity over time. This finding was particularly robust among older adults.

Smoking and height as risk factors for prevalence and 5-year incidence of hearing loss. A questionnaire-based follow-up study of employees in Denmark aged 18–59 years exposed and unexposed to noise

This paper investigated whether smoking and short stature in adulthood were independent risk factors for hearing loss. We reanalyzed data from the Danish Work Environment Cohort Study (an existing cohort study), on prevalence of self-reported hearing loss among 7,221 employees and on five-year incidence among 4,610 employees. We found that smoking predicted hearing loss incidence and prevalence. Smoking did not predict incidence at noise exposure during half or more of a worker's hours. Very short stature predicted prevalence in the total adult population only weakly, but strongly among employees born before 1951. These prospective findings indicate that smoking is an independent risk factor for incidence of hearing loss. Very short stature predicted prevalence of hearing loss only in a subpopulation.

Hyperlipidemia in noise-induced hearing loss

OBJECTIVES

To assess the influence of hyperlipidemia on the development of noise-induced hearing loss (NIHL).

STUDY DESIGN

This case-control study analyzed data from the Department of Preventive Medicine at one academic medical center in southern Taiwan.

SUBJECTS AND METHODS

We collected the laboratory data from routine health examinations administered to workers who were exposed to noise greater than 85 dBA over a one-year period. We analyzed the relationships of cholesterol and triglyceride levels with NIHL.

RESULTS

A total of 4071 cases were analyzed. After adjusting for age and gender, hypertriglyceridemia was found to be related to NIHL (aOR = 1.281; 95% CI, 1.088-1.507), but hypercholesterolemia was not (aOR = 0.951; 95% CI, 0.795-1.138).

CONCLUSIONS

This study, one of the largest to date to study the relationship between hyperlipidemia and NIHL, found that individuals with hypertriglyceridemia are at greater risk of NIHL. On the basis of this finding, workers exposed to high noise levels should be educated on control of triglyceride levels to help reduce their risk of NIHL.

WITHDRAWN: [Effects of atorvastatin on presbyacusis and tinnitus : A prospective, randomized, double-blind clinical trial.]

Ahead of Print article withdrawn by publisher

Effect of atorvastatin on progression of sensorineural hearing loss and tinnitus in the elderly: results of a prospective, randomized, double-blind clinical trial

OBJECTIVE

To test whether the 3-hydroxy-3-methylglutaryl- coenzyme A reductase inhibitor atorvastatin can slow down the progression of presbycusis.

PATIENTS

Fifty patients 60- to 75-years-old with presbycusis and moderately elevated serum cholesterol.

INTERVENTION(S)

In a double-blind design, patients were randomly assigned to treatment with either atorvastatin (40 mg/d orally) or placebo.

MAIN OUTCOME MEASURE(S)

Pure-tone audiometry and tinnitus evaluation at enrolment and after 7 and 13 months.

RESULTS

Development of hearing thresholds after 7 and 13 months showed no significant differences between the groups. Tinnitus score continuously improved in the atorvastatin group (34.8 at 7 and 27.6 at 13 mo), whereas it slightly deteriorated in the placebo group (24.8 at 7 and 26.8 at 13 mo). The effect on tinnitus was a tendency without statistic significance (p = 0.0833).

CONCLUSION

Atorvastatin had no effect on the development of hearing thresholds, but resulted in a trend toward a relief of tinnitus.

Dyslipidemia and auditory function

The relationship between dyslipidemia and hearing is unclear. This study was conducted to investigate whether elevated serum lipid levels impact auditory function in humans and in guinea pigs. In the human study, a cross-sectional study of 40 volunteers with dyslipidemia was conducted. Pure tone thresholds, distortion product otoacoustic emissions, and lipid profiles were analyzed. When controlled for patient age and sex, we found that elevated triglycerides were associated with reduced hearing. In the guinea pig study, a prospective study of animals fed a high-fat diet for 14 weeks was conducted. Although the high-fat diet led to a dramatic elevation in the average weight and total cholesterol in all animals (from 61 to 589 mg/dl), there were no meaningful changes in distortion product otoacoustic emission magnitudes. These results suggest that whereas chronic dyslipidemia associated with elevated triglycerides may reduce auditory function, short-term dietary changes may not.

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.

Morphological and functional alterations of the cochlea in apolipoprotein E gene deficient mice

The relationship between hyperlipidemia and sensorineural hearing loss remains obscure. In this study, we elucidate for the first time the cochlear morphological and auditory alterations and their relationships with hyperlipidemia, atherosclerosis, and endothelial dysfunction in apolipoprotein-E knockout (ApoE-KO) mice. Ten-week-old ApoE-KO mice were fed either atherosclerotic diet (1.25% cholesterol) or normal diet. Wild type mice (C57BL/6J) served as normal controls. Fourteen weeks later, marked hyperlipidemia, atherosclerosis, endothelial dysfunction, and hearing impairment, especially in the high frequencies, had developed in ApoE-KO mice as compared with C57BL/6J mice (P<0.001). A high positive correlation between hearing loss and the extent of atherosclerosis and plasma total cholesterol levels was found. Hearing loss, especially at high frequencies, was detected in all ApoE-KO mice. Hair cell loss mainly at the base turn, thickening of vascular intima, and lumen stenosis of the spiral modiolar artery (SMA) in cochlea were also found; these histological changes were exacerbated by the atherosclerotic diet. Furthermore, endothelial nitric oxide synthase (eNOS) in aortic wall and cochlea was distinctly reduced in ApoE-KO mice. These results demonstrate that hyperlipidemia and atherosclerosis can induce alterations in cochlear morphology and function. The stenosis of SMA, which may cause cochlear ischemia and hypoxia, endothelial dysfunction, and low eNOS activity, may contribute to hearing loss.

Fibrinogen and LDL apheresis in treatment of sudden hearing loss: a randomised multicentre trial

BACKGROUND

Sudden sensorineural hearing loss (SSHL) is thought to have many different origins, including disturbances of microcirculation, autoimmune pathology, and viral infection. We aimed to determine whether acute reduction of plasma fibrinogen and serum LDL is effective for treatment of SSHL of suspected vascular origin.

METHODS

Between January, 2000, and June, 2001, we recruited 201 patients with sudden hearing loss from four otorhinolaryngology clinics in Germany. Patients were randomly allocated to single fibrinogen/LDL apheresis or standard treatment (250 mg prednisolone reduced by 25 mg per day, 500 mL 6% hydroxyethyl starch, 400 mg pentoxifylline per day). The primary outcome was recovery of hearing as measured by pure-tone audiometry 48 h after the start of treatment. Secondary outcomes were recovery of hearing 6 weeks after treatment, improvement of speech audiometry, tinnitus, and frequency of side-effects. Analysis was done per protocol.

FINDINGS

Overall improvement of pure-tone thresholds was slightly but not significantly better in patients given apheresis than in those given standard treatment (difference 7.7, 95% CI -8.2 to 23.6). However, the mean sound level at which 50% of recorded digits were recognised was significantly lower after 48 h in the apheresis group (21.6 dB, SD 20.8) than in the standard group (29.3 dB, 29.4; p=0.034). After 6 weeks, the mean 50% speech perception was at 13.6 dB (SD 14.3) in the apheresis group and at 20.8 dB (25.4) in those on standard treatment (p=0.059). At 48 h, in patients with plasma fibrinogen concentrations of more than 295 mg/dL, speech perception was improved much more in those on apheresis (15.3 dB, 17.3) than in those on standard treatment (6.1 dB, 10.4; p=0.005).

INTERPRETATION

A single fibrinogen/LDL apheresis lasting for 2 h could be used as an alternative to conventional infusion treatment and prednisolone for 10 days. Patients with a plasma fibrinogen of more than 8.68 micromol/L improve much better when treated with apheresis, especially if serum LDL concentrations are also raised.

Ultrastructural effects of hypercholesterolemia on the cochlea

HYPOTHESIS

The goals of this study were to identify the effects of hypercholesterolemia on the cochlea and to find out where the pathologic changes first occur.

BACKGROUND

Some authors have stated that hypercholesterolemia alone does not produce auditory dysfunction. Others propose that auditory dysfunction is caused by glycogen accumulation and other alterations on cochlear ultrastructure.

METHODS

Twenty guinea pigs were classified as a control group fed with a normal diet, and a cholesterol group of 24 animals was given a diet composed of 1 g cholesterol per day for 4 months. The hearing acuity of the animals before the diets was compared with that after the diets by means of auditory brainstem responses. The basal and apical turns of the cochleas were examined by light microscopy and transmission electron microscopy.

RESULTS

The control group showed normal cochlear ultrastructures consistent with normal hearing thresholds, whereas the cholesterol group had profound edema in the strial marginal layer and slight edema in the outer hair cells, in line with data from auditory brainstem responses revealing changes in hearing sensitivity in various degrees. The pathologic changes in the basal turn and the stria vascularis were qualitatively prominent in comparison with those of the apical turn and the outer hair cell.

CONCLUSIONS

These observations confirm that hypercholesterolemia alone may cause auditory dysfunction if dietary cholesterol is kept at a high level for a long time. Alterations attributed to hypercholesterolemia begin in the stria vascularis and then spread over the outer hair cells, mainly in the basal turn.

A prospective case-control study of 50 consecutive patients presenting with hyperlipidaemia

The literature contains many references which refer to a causal relationship between hyperlipidaemia and hearing loss, but the majority of reports lack adequate controls, or are based on a series of cases which may represent incidental findings. This prospective case-control study compared a restricted population of 50 consecutive hyperlipidaemic patients attending a lipid clinic whose fasting lipid levels were > 2 SDs above the population mean with a control population recruited from patients undergoing nasal surgery for structural abnormalities (n = 159). The National Study of Hearing data was also compared with both groups in order to provide external validity to the control group. This study showed no consistent differences in the hearing thresholds of the hyperlipidaemic group compared with either control group. The Null hypothesis that sensorineural hearing loss is no greater in a population whose fasting blood lipids are raised > 2 SDs above the population mean level than in a control population cannot be refuted given the variability of the data.

Distortion product otoacoustic emissions in human hypercholesterolemia

Epidemiological and experimental studies suggest that hypercholesterolemia promotes the development of sensorineural hearing loss; however, the underlying cellular pathomechanism remains obscure. In the present study, 20 healthy subjects and 20 patients with familial hypercholesterolemia were compared with respect to their hearing function. None of the 40 persons reported any history of hearing disorder. In accordance with this subjective impression, mean hearing thresholds were within the normal, age-dependent ranges in both groups. In contrast, the single-generator distortion product otoacoustic emissions (sgDPOAE) were reduced at and above 4 kHz. Input-output functions of DPOAE could be subdivided into three groups: (i) normal, with unity slope at low intensities and slope less than unity (0.24+/-0.07 dB/dB at higher intensities; (ii) pathologic, described by a single straight line; (iii) ill-defined, with data usually indistinguishable from the background noise level. The ill-defined DPOAE behavior was only found in patients with hypercholesterolemia; namely, for 25% of patients at f(2)=1.5 kHz and for 50% at f(2)=4 kHz. Patients belonging to the pathologic and ill-defined DPOAE groups had significantly (P<0.05) higher total serum cholesterol and LDL-cholesterol levels compared with subjects from the normal DPOAE group. While hearing thresholds of patients with ill-defined growth functions were not statistically different from those of normal subjects, speech scores were significantly reduced in these cases. The data imply that nonlinear mechanical processes in the cochlea are compromised in hypercholesterolemic patients.

A retrospective case-controlled study of 1490 consecutive patients presenting to a neuro-otology clinic to examine the relationship between blood lipid levels and sensorineural hearing loss

This study set out to test the null hypothesis that the distribution of blood lipid levels is the same in a population with a sensorineural hearing loss (SNHL) as in a control population. Hyperlipidaemia has been implicated as an aetiological factor in SNHL; however, the majority of reports are retrospective, lack adequate controls, or are based on a series of cases which may represent incidental findings and not a true causal relationship. In all, 1490 consecutive patients who presented to a neuro-otology clinic were studied retrospectively. This group is exceptional in that all patients had had fasting lipid profiles done regardless of their presenting problem. Those with a mean SNHL > 25 dB (0.5, 1, 2 and 4 kHz) were compared with those with hearing thresholds < or = 25 dB. An analysis of variance was also done. The study group was also compared with the National Study of Hearing data set to add external validity. Simple correlations were found between hearing thresholds and many parameters such as blood pressure, fasting glucose, triglyceride or fasting cholesterol. Analysis of variance of the neuro-otology group, controlling for variables such as age and sex, showed no significant association between hearing and blood pressure, packed cell volume, mean corpuscular volume, fasting glucose, triglyceride or fasting cholesterol. However, when general linear interactive modelling was used to analyse hearing thresholds, raised total fasting cholesterol was associated with significantly better hearing threshold levels. This study leads to a rejection of the Null hypothesis that the distribution of lipid levels is the same in a population with a hearing loss as in a control population, as hearing thresholds were found to be significantly better in those with raised cholesterol levels.

Cigarette smoking and risk for hearing impairment: a longitudinal study in Japanese male office workers

The association of cigarette smoking with development of hearing impairment (loss of 30 dB at 1000 Hz and 40 dB at 4000 Hz) over a 5-year follow-up was studied in 1554 non-hearing-impaired Japanese male office workers who ranged in age from 30 to 59 years. After controlling for potential predictors of hearing impairment, the relative risk for low-frequency hearing impairment compared with never smokers was 1.12 (95% confidence interval [CI], 0.57 to 2.17) for ever-smokers, 1.21 (95% CI, 0.65 to 2.25) for current smokers of 1 to 20 cigarettes/day, 1.35 (95% CI, 0.70 to 2.61) for current smokers of 21 to 30 cigarettes/day, and 1.82 (95% CI, 0.98 to 3.38) for current smokers of 31 or more cigarettes/day (P for trend = 0.063). The respective multivariate-adjusted relative risks for high-frequency hearing impairment compared with never smokers were 1.70 (95% CI, 0.85 to 3.40), 1.82 (95% CI, 0.92 to 3.59), 2.00 (95% CI, 0.98 to 4.08), and 2.20 (95% CI, 1.09 to 4.42) (P for trend = 0.025). As the number of pack-years of exposure increased, the risk for high-frequency hearing impairment increased in a dose-dependent manner (P for trend = 0.011), but the risk for low-frequency hearing impairment did not (P for trend = 0.172). Our results indicate that cigarette smoking is highly associated with development of high-frequency hearing impairment in Japanese male office workers.

Efficacy of serologic testing in asymmetric sensorineural hearing loss

PURPOSE

The goal of this study was to determine the efficacy of a detailed questionnaire, auditory brain stem response testing (ABR), MRI, and an extensive battery of serologic tests in diagnosing asymmetric sensorineural hearing loss (ASNHL).

METHODS AND MATERIAL

Patients with audiograms demonstrating ASNHL of 10 dB or greater in 2 consecutive frequencies or 15 dB in any 1 frequency between 250 and 6000 Hz were asked to participate. Patients underwent MRI scanning of the cerebellopontine angle, internal auditory canals, and posterior fossa with gadolinium contrast, ABR, and an extensive battery of tests. The causative diagnosis was made by the individual clinician based on each patient's history, physical examination, and test results.

RESULTS

Forty-five patients completed the study. A review of the data confirmed the utility of a detailed history and physical examination, MRI, and fluorescent treponemal antibody test in all cases. Erythrocyte sedimentation rate, glycosylated hemoglobin, Lyme antibody titers, and total hemolytic component (CH50) were helpful in selected cases. Thyroid function testing, complete blood count, Sequential Multiple Analysis-7, prothrombin time/partial thromboplastin time, lipid profile, and ABR were of no value in these patients.

CONCLUSION

A careful history and physical examination, MRI, and fluorescent treponemal antibody test should be performed for the evaluation of all patients with ASNHL; however, more extensive serologic testing, including sedimentation rate, glycosylated hemoglobin, Lyme antibody titers, and CH50, should be selectively performed, based on a suggestive history or suspicious physical findings.

A prospective case-controlled study of patients presenting with idiopathic sensorineural hearing loss to examine the relationship between hyperlipidaemia and sensorineural hearing loss

The prevalence of hyperlipidaemia in the normal population means that hyperlipidaemia is often found in patients who have a hearing loss of unknown aetiology. We prospectively undertook a case-controlled study of 85 patients presenting consecutively with a sensorineural hearing loss of unknown aetiology to see if the prevalence of hyperlipidaemia differed between the group with an idiopathic sensorineural hearing loss and a control population. Control subjects were recruited from patients undergoing nasal surgery for structural abnormalities. Both the study and control groups were also compared with the National Study of Hearing data. Hyperlipidaemia was no more prevalent in a population with idiopathic sensorineural hearing loss than a control population. No consistent association between hyperlipidaemia and hearing loss was found.

A prospective case-controlled study of 197 men, 50-60 years old, selected at random from a population at risk from hyperlipidaemia to examine the relationship between hyperlipidaemia and sensorineural hearing loss

Hyperlipidaemia has been reported as an aetiological factor in sensorineural hearing loss. Reports on this subject have been retrospective, lacked adequate controls, or have been based on a series of cases which may represent incidental findings as hyperlipidaemia is prevalent in the normal population. The published evidence that hyperlipidaemia causes hearing problems is contradictory and warrants further controlled trials: A prospective case-controlled study was conducted of 197 men between 50 and 60 years old selected at random from a population at risk from ischaemic heart disease or hyperlipidaemia. Hearing thresholds, relevant variables and--on two occasions--their fasting cholesterol levels, were recorded. The control subjects were recruited from patients undergoing nasal surgery for either internal or external structural abnormalities. All study and control groups were also compared with the National Study of Hearing (NSH) data. When hearing thresholds were grouped together as 0.5, 1, 2 and 4 kHz, 0.5, 1, 2 kHz or 4, 6 and 8 kHz there were no statistically significant differences except at 4, 6 and 8 kHz in the worse hearing ear where the at risk group had better hearing thresholds, P = 0.0475. However, the differences which existed became reduced across all frequencies when the subgroup with fasting lipids > 6.5 mmol/l was compared with the at risk group as a whole against the NSH data.

Contribution of membrane cholesterol to outer hair cell lateral wall stiffness

The outer hair cell can be divided into three domains: the apex, the base, and the lateral wall. With the use of filipin, a polyene fluorescent antibiotic that binds to cholesterol, we found under fluorescence microscopy that the lateral wall membranes were less intensely stained than the apical and basal membranes. This difference in filipin fluorescence between the lateral walls and the ends diminished when cells were incubated in water-soluble cholesterol before staining, suggesting that exogenous cholesterol enters the lateral wall. Under confocal microscopy, we studied the incorporation pattern of a fluorescent cholesterol analogue, NBD-cholesterol. NBD-cholesterol did not stain the apical membranes whereas it intensely labeled the lateral wall. The micropipette aspiration technique was used to assess the effect of cholesterol on lateral wall stiffness. The lateral wall stiffness parameter of cells treated with water-soluble cholesterol (n = 23) was significantly higher than that of controls (n = 27): 0.76+/-0.24 (mean +/- SD) versus 0.46+/-0.10 (Student's t-test, p < 0.001). In conclusion, cholesterol has different distributions among outer hair cell membranes, and when water-soluble cholesterol is incorporated into the cells, the outer hair cell lateral wall stiffness parameter increases.

Multiplicative effect of smoking and age on hearing impairment

PURPOSE

To determine the combined effect of smoking and age on hearing impairment.

MATERIALS AND METHODS

Pure tone audiometry test was conducted on 263 residents of a rural village who were not exposed to noise. The pack-years of smoking were computed from the subjects' smoking history. The association between pack-years and hearing impairment was assessed. The combined effect of smoking and age on hearing impairment was determined based on prevalence rate ratio.

RESULTS

There was a statistically significant trend in the number of pack-years of smoking and age as risk factors for hearing impairment. The prevalence rates of hearing impairment for nonsmokers aged 40 years and younger, smokers aged 40 years and younger, nonsmokers older than 40 years of age, and smokers older than 40 years of age were 6.9%, 11.9%, 29.7%, and 51.3%, respectively. The prevalence rate ratio for nonsmokers aged 40 years and younger, smokers aged 40 years and younger, nonsmokers older than 40 years of age, and smokers older than 40 years of age (nonsmokers aged 40 years and younger as a reference group) was 1, 1.7, 4.3, and 7.5, respectively. The prevalence rate ratios showed a multiplicative effect of smoking and age on hearing impairment.

CONCLUSION

Age and smoking are risk factors for hearing impairment. It is clear that smoking and age have multiplicative adverse effects on hearing impairment.

Analysis of blood chemistry and hearing levels in a sample of older persons

OBJECTIVE

As part of an ongoing study of presbyacusis, the relationship between blood chemistry levels and hearing levels was investigated. Previous reports often used small sets of blood chemistry measures, and results were inconclusive. This experiment examined hearing levels and 27 measures of blood chemistry using various univariate and multivariate statistical procedures.

DESIGN

Blood from 89 female and 128 male human subjects was collected. Subjects' ages ranged from 60 to 82 yr, and hearing levels ranged from normal to moderate/severe. Subjects with a history of middle ear disease were excluded. Electrolyte panel (Na, K, Cl, CO2, Ca, urea nitrogen, glucose, creatinine, and Mg), hematology panel (WBC, RBC, Hgb, hematocrit, platelet, etc.), serum lipids (total cholesterol, low-density lipoprotein [LDL], and high-density lipoprotein [HDL]), immunoglobulins (IgG, IgA, IgM, and IgE), and thyroxine were analyzed using univariate and multivariate statistical procedures.

RESULTS

Blood chemistry levels of most subjects were within normal ranges as defined by our laboratory. Correlation between blood chemistry measures and pure-tone averages (PTAs) ranged from minimal to low. Results of factor analysis, discriminant analysis, and canonical analysis showed that combining blood chemistry measures from the same panel still could not predict PTA effectively. One exception to this was a gender-specific effect of cholesterol. Hearing levels of women with high LDL/HDL ratios were 5 dB better than those of women with low LDL/HDL ratios. The comparable difference in men was only 1 dB.

CONCLUSION

Results suggest that blood chemistry measures that are primarily within the normal range have very little value in predicting pure-tone thresholds in older subjects.

Dose-response relationship between smoking and impairment of hearing acuity in workers exposed to noise

The study included an inquiry and clinical examination of 443 reindeer herders (mean age 43 years) who frequently used noisy tools and vehicles, in particular snowmobiles and chain-saws. Age-adjusted hearing thresholds at 3 and 4 kHz deteriorated significantly with increased exposure to noise. There was the dose-response relationship between the amount of smoking and the impairment of hearing acuity when exposure time to noise was used as covariance. The amount of smoking was not significant until very heavy smoking (more than 144,000 cigarettes, i.e. 20 cigarettes/day for more than 20 years), and no smoking effect could be seen using the classification of current smoking habits. The results support the practice that screening of hearing acuity should be repeated more often in smokers than in non-smokers in noisy work so that hearing damage can be found in an incipient stage and noise-induced hearing loss effectively prevented.

Epidemiology of hearing disorders. Some factors affecting hearing. The Copenhagen Male Study

This epidemiological investigation reports on the results from a 10-year follow-up examination concerning hearing and factors known to cause hearing problems. In addition, an evaluation concerning the possible association between hearing impairment and factors affecting the state of health is reported. The original sample comprised 5,050 subjects, and at the present examination 3,387 (67%) males at a median age of 63 years (range 53-75) participated. An increasing prevalence of 30-40% of hearing problems was demonstrated with increasing age. A prevalence of 17% of tinnitus of more than 5 min duration was found; 3% indicated that their tinnitus was so annoying that it interfered with sleep, reading and/or concentration. The prevalence of tinnitus increased up to the age of 70, and seemed to remain constant thereafter. A significant correlation between experienced hearing problems and environmental factors causing damage to the hearing organ was found. Furthermore, a correlation between hearing problems and C3-S complement was found, but no correlations could be established between hearing problems and other blood groups. No correlation was found between cardiovascular disease and hearing problems except for minor circulatory problems, nor between hearing problems and hormonal diseases. It is concluded that the present study supports previous epidemiological investigations concerning the prevalence of hearing problems and factors affecting hearing. The association between hearing problems and C3-S complement, which to the authors' knowledge has not previously been reported, should be further evaluated. No association was found between hearing problems and other blood groups.

Alterations of inner ear morphology in experimental hypercholesterolemia

Previous clinical and experimental studies have indicated that auditory function may be compromised by hypercholesterolemia. In this investigation, inner ear tissue from chinchillas maintained on a cholesterol-supplemented diet for 3 months was examined for morphological alterations which might underlie the physiological changes observed with this condition in earlier studies. Ultrastructural analysis of cochleas from 16 hypercholesterolemic chinchillas revealed alterations in both the stria vascularis and outer hair cells. Strial marginal cells throughout the cochlea and outer hair cells of the apical turn, contained electron-lucent patches of an amorphous material. These patches had the morphological characteristics and histochemical properties of glycogen. Mild extracellular edema and increased numbers of lysosomes were also noted in the stria vascularis of experimental animals. These alterations suggest that chronic hypercholesterolemia metabolically stresses inner ear tissue. It is hypothesized that such changes could increase susceptibility of the cochlea to ototraumatic agents.

Changes in pure-tone thresholds in individuals aged 70-81: results from a longitudinal study

The results of audiometric evaluation of 376 randomly selected men and women, 70 years old and born in 1901, are reported. The investigation is part of a large study on a gerontological population in which the original participants were tested again with pure-tone and speech audiometry at ages 75, 79 and 81. We also report audiometric results obtained at ages 70 and 75 from a second group, consisting of 297 men and women born in 1906. Hearing loss was most pronounced at higher frequencies for both sexes, and men had an average of 10 dB greater hearing loss at 8 kHz than women. The decrease in hearing threshold in men between the ages of 70 and 81 was more pronounced at 2 kHz (27 dB) than at 4 and 8 kHz (15 and 20 dB, respectively). The average hearing loss in women increased at a constant rate between the ages of 70 and 79 (15 dB), while between the ages of 79 and 81 the changes in pure-tone threshold was minimal. There were no significant differences in pure-tone thresholds for women born in 1901 when compared to those born in 1906 at the ages of 70 and 75. However, men born in 1906 had a more pronounced hearing loss at the age of 75 than those born in 1901.