|Year : 2020 | Volume
| Issue : 3 | Page : 135-140
Influence of cardiovascular risk factors on cochlear dysfunction
Nemanja Radivojevic1, Nenad Arsovic2, Zoran Dudvarski2, Vladimir Nesic2, Ljiljana Cvorovic2, Snezana Babac3, Aleksandra Radivojevic4
1 Clinic for Otorhinolaryngology and Maxillofacial surgery, Clinical Center of Serbia, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
2 Clinic for Otorhinolaryngology and Maxillofacial Surgery, Clinical Center of Serbia, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
3 ENT Clinic, Clinical and Hospital Centre Zvezdara, Faculty for Special Education and Rehabilitation, University of Belgrade, Belgrade, Serbia
4 Clinic for Neurology, Clinical Center of Serbia, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
|Date of Submission||15-Nov-2019|
|Date of Acceptance||03-Mar-2020|
|Date of Web Publication||22-Dec-2020|
Dr. Nemanja Radivojevic
Clinic for Otorhinolaryngology and Maxillofacial Surgery, Clinical Center of Serbia, Pasterova 2, 11000 Belgrade
Source of Support: None, Conflict of Interest: None
Background: Cochlear dysfunction can arise not only from various factors such as ear diseases but also from systemic disorders of the body. The occurrence of otologic symptoms such as hearing loss, dizziness, and tinnitus can be due to cardiovascular disorders. Therefore, current understandings in the field of the diagnosis and therapy of cardiovascular diseases (CVDs) should include, among others, evidence of otologic disorders. Objective: The aim of this study is to determine the association between risk factors for CVD and cochlear dysfunction. Methods: The cross-sectional study included 128 participants with major CVD risk factors who underwent auditory function examination (pure tone audiometry). Results: There were 52 women (40.6%) and 76 men (59.4%) in total. The mean age of the participants was 58 years (a range of 28–83 years). The mean age among participants with hearing loss was 60 (±10.88), whereas the mean age among participants that had normal hearing thresholds was 54 (±12.18). Sensorineural hearing loss (SNHL) was measured in 59% of participants, of most frequent mild degree hearing loss. The prevalence of SNHL was higher in participants with arterial hypertension (P < 0.001, OR = 5.881, 95% CI 2.694–12.837) and the most common among them was moderate degree hearing impairment (38%). There is also a statistically significant association of SNHL with dyslipidemia and elevated body mass index (P < 0.001, [OR]: 4.118, 95% [CI]: 1.873–9.053 and P< 0.001, [OR]: 1.517, 95% [CI]: 1.237–1.859 ) with moderate and profound hearing loss. Conclusion: Based on the data obtained, it seems that the presence of major cardiovascular risk factors was a significant predictor for cochlear dysfunction.
Keywords: Arterial hypertension, diabetes mellitus, dyslipidemia, sensorineural hearing loss
|How to cite this article:|
Radivojevic N, Arsovic N, Dudvarski Z, Nesic V, Cvorovic L, Babac S, Radivojevic A. Influence of cardiovascular risk factors on cochlear dysfunction. Indian J Otol 2020;26:135-40
|How to cite this URL:|
Radivojevic N, Arsovic N, Dudvarski Z, Nesic V, Cvorovic L, Babac S, Radivojevic A. Influence of cardiovascular risk factors on cochlear dysfunction. Indian J Otol [serial online] 2020 [cited 2021 Mar 7];26:135-40. Available from: https://www.indianjotol.org/text.asp?2020/26/3/135/304280
| Introduction|| |
Cochleovestibular dysfunction can arise not only from various factors such as ear diseases but also from general disorders of the body. In etiological terms, more considerable attention is paid today to the impact of systemic diseases on the occurrence of otologic disorders. These cause-and-effect relationships are based on data from fundamental, clinical, laboratory, and other studies. The occurrence of otologic symptoms such as hearing loss, dizziness, and tinnitus can be due to cardiovascular disorders. Data from the literature indicate that this topic is represented and that research in this field is on the rise. Therefore, current understandings in the field of diagnosis and therapy of cardiovascular diseases (CVDs) should include, among others, evidence of otologic disorders. Initial otologic symptomatology is significant in detecting cardiovascular disorders as well as in assessing the development of the disease. CVDs are the number 1 cause of death globally. An estimated 17.9 million people died from CVDs in 2012, representing 34% of all global deaths under 70 years of age. Early intervention and treatment of these disorders and their risk factors have led to a drop in the incidence, but further work thereon is needed. Simple, repeatable, and sensitive screening for CVDs and risk factors that lead to these diseases could improve detection and lead to early intervention before significant organ damage begins. Hypertensive organ damage defined by current guidelines can develop in the heart, arteries, brain, kidneys, or eyes. Hearing impairment, or any form of damage to the auditory system, has not been recognized as evidence of organ damage due to vascular disease.
The association between hearing loss and coronary heart disease was first published by Rosen and Olin in 1965. They conducted an age-based case–control study comparing members of the Maban tribe with urban populations in the United States, Europe, and Egypt and found a clear link between hearing loss and coronary disease. Nearly 50 years since the study, other associations have been reported between hearing loss, elevated blood lipids, CVD, and various therapeutic interventions.,
The emergence of atherosclerosis as a major pathophysiological process for the onset of CVD was first explained by the presence of the following risk factors: cigarette smoking, elevated blood pressure, increased serum total (and low-density lipoprotein) cholesterol, low high-density lipoprotein cholesterol, diabetes mellitus, men over 55 years of age, postmenopausal women and women over 65 years of age, older age, obesity, abdominal obesity, low physical activity, sedentary lifestyle, positive family history for ischemic heart disease in early life (<55 in men; <65 years in women), ethnic characteristics, and psychosocial factors. We have tried to relate some of these risk factors to cochlear damage.
| Methods|| |
The cross-sectional descriptive study included 140 participants with cardiovascular risk factors attending the department of general medicine. Auditory function examination was carried out between December 2015 and December 2016 in our audiology department. The study was approved by the institutional ethics committee. Informed consent was obtained, where appropriate. Ethical approval for this study (Ethical Committee N0 12-70/19) was provided by the Ethical Committee of University in Belgrade, Faculty of Medicine, Belgrade, Serbia, in october 2019.
All participants with normal and sensorineural hearing loss (SNHL) and normal tympanometry test results (Type A) were included in the study. Exclusion criteria were a history of acute and chronic middle ear inflammation, history of head trauma, and possible exposure to risk factors for hearing disorders (ototoxic drugs, noise, and vibration). Furthermore, we excluded patients with neurological diseases, mental disorders, congenital ear disorders, people with conductive hearing impairment, and functional middle ear disorder based on tympanogram results (Type B and Type C), participants who rejected the proposed testing, participants with incomplete medical records.
Data on 128 participants who met the above criteria were collected from the enclosed medical documentation, diagnostic methods performed, and clinical examination of an otolaryngologist, including a hearing test.
The analyzed parameters are gender, age at the time of study, body weight, body height, body mass index (BMI), cigarette smoking habit (active smoking, years of smoking, average number of cigarettes smoked per day), arterial blood pressure, diabetes mellitus, dyslipidemia (hypertriglyceridemia and hypercholesterolemia), cochlear dysfunction (impaired auditory function, tinnitus).
High blood pressure (hypertension) is defined as a measured value of arterial blood pressure >140/90 mmHg. Based on the measured value, arterial hypertension can be classified into three categories (Grade 1 (mild) - 140–159/90–99 mmHg, Grade 2 (moderate) - 169–179/100–109 mmHg, and Grade 3 (severe) - ≥180/110) according to the ESH/ESC. In the group of participants with diabetes mellitus type II, we classified all patients with measured fasting blood sugar ≥7 mmol/l (126 mg/dl), and dyslipidemia was defined based on the therapy used by the subject and based on laboratory blood examination (triglycerides ≥150 mg/dL, total cholesterol ≥200 mg/dL (NCEP-ATP III)). According to the World Health Organization guideline, overweight was defined as a BMI ≥25.0 kg/m2.
We categorized participants with tinnitus based on a subjective sensation of tinnitus, ringing, or rustling in the ears over the last year, which is of higher intensity and prevents continuous sleep. The calculation of hearing impairment is performed based on the tonal audiometric curve for airborne conductance and is defined by hearing loss >25 dB at specific frequencies in at least one ear. Based on the current guidelines, SNHL is classified into the following categories: normal hearing <25 dB, mild 25–40 dB, moderate 41–60 dB, severe 61–90 dB, and profound hearing loss >90 dB.
All the results were analyzed in the IBM SPSS Statistics for Windows, version 21.0 (IBM Corp., Armonk, NY, USA). Absolute numbers and percentages describe the data. Numerically, continuous data are expressed by mean ± standard deviation. Comparison of categorical variables was performed by using the Chi-squared test and the Fisher test. Univariate and multivariate logistic regression analysis was performed. The value of P < 0.05 was considered statistically significant, and the confidence interval (CI) was 95%.
| Results|| |
Risk factors for cardiovascular disease and otologic manifestations
There were 52 women (40.6%) and 76 men (59.4%) in total. The mean age of the participants was 58 years (a range of 28–83 years). The mean age among participants with hearing loss was 60 (±10.88), whereas the mean age among participants that had normal hearing thresholds was 54 (±12.18). Hearing impairment of varying degrees was measured in 76 participants. The most prevalent was a mild degree of hearing impairment (38%) with a mean age of 57 years ± 10.9 [Figure 1].
|Figure 1: Distribution of degree of hearing impaired subjects by age (mean)|
Click here to view
Major or independent CVD risk factors were found in 80% of the participants. Most participants had only one risk factor (31%), two risk factors were found in 15% of the participants, and three or more risk factors were identified in 32% of the participants.
A BMI >25 kg/m2 was found in 42/128 (33%). The number of cigarette smokers was 46/128 (36%). The total number of smokers with over 5 years of smoking was 34. The elevated arterial pressure was measured in 66/128. The highest-incidence hypertensive participants were of the first grade 29/66 (40%). Dyslipidemia was reported in 42% and type 2 diabetes in 25% of the participant [Table 1]. Distribution of all our participants with tinnitus and hearing impairment in terms of the presence of individual risk factors for CVD is shown in [Table 2].
|Table 2: Distribution of subjects with tinnitus and hearing impairment based on the presence of individual risk factors|
Click here to view
Risk factors for developing CVD sporadically correlate with otologic manifestations. Of the 76 hearing-impaired participants, 67 were diagnosed with at least one risk factor (P = 0.05, odds ratio [OR] =3.616; 95% CI: 1.462–8.942). The chances of hearing impairment increase with each additional risk factor (P < 0.001, OR = 2.679, 95% CI: 1.695–4.236).
As shown in [Table 2], the prevalence of hearing impairment was higher in participant with arterial hypertension. Of the total number of patients with arterial hypertension (66), 52 were diagnosed with impairment of the auditory function of varying degrees, whereas 14 patients had a normal auditory function (P < 0.001, OR = 5.881, 95% CI 2.694–12.837). We found a statistically significant correlation between hearing impairment and second-grade arterial hypertension (P = 0.006, OR 4,889 [95% CI: 1.573–15.196]). As far as the degree of hearing impairment is concerned, in the group of participants with arterial hypertension, it was highest in the group of moderate hearing impairment (20/52). Furthermore, controlling for gender, we have a statistically significant correlation between these two variables.
The prevalence of hearing impairment was highest in participant with a BMI over 25 kg/m2 (P < 0.001), with 47% of them who had moderate SNHL.
[Table 2] shows the distribution of smokers and nonsmokers in relation to the occurrence of otologic manifestations, as well as the distribution of all subjects in relation to years of smoking and the occurrence of otologic manifestations. 35% of cigarette smokers had a moderate impaired auditory function and most of them had smoked longer than 5 years. There were 25% of diabetic participant who had a profound hearing impairment and 38% with normal hearing function.
The highest percentage of patients with dyslipidemia had SNHL (55.3%), and this correlation was statistically significant (P < 0.001). The majority of participant had moderate and profound impairment of auditory function.
To avoid as much as possible the impact of presbycusis on the results obtained, we categorized the participant into three age groups, striving to have a similar number of subjects in each group, and hence, we obtained 40 participant or 31% in the category between 28 and 51 years, and 34% in the categories 52–62 and 64–83 years [Figure 2]. In the middle group, almost all risk factors were statistically significantly associated with impairment of auditory function except for diabetes.
|Figure 2: Cardiovascular disease risk factors relative to the severity of hearing loss by age groups|
Click here to view
Results of multivariate logistic regression analysis
In the multivariate logistic model, we included all risk factors which we have analyzed in previous data. The independent risk factors for hearing impairment based on the results of multivariate analysis [Table 3], were hypertension (P = 0.031), dyslipidemia (P = 0.036), and BMI >25 kg/m2 (P = 0.004), respectively. The chance of developing hearing impairment increases several times in hypertensive and dyslipidemic patients (OR = 2.9, 95% CI 1.1–7.6 and OR = 2.7, 95% CI 1.0–6.8, respectively).
|Table 3: Multivariate logistic regression model and independent risk factors for hearing loss|
Click here to view
| Discussion|| |
Presbycusis and microvascular changes
As one of the most common chronic conditions in adults over 65 years old, hearing loss is generally considered a normal aging process.,
Studies on animals have shown age-related degeneration of stria vascularis, possibly related to microvascular changes such as a reduction in capillary density and blood vessel diameter. An association between stria atrophy and age has also been found in a study of the temporal bone in humans. Reduction of blood flow to stria vascularis may contribute to the loss of endolymph, which potentially reduces cochlear function and endocochlear potential. Reduction in blood flow may also be associated with histopathological changes in the Corti organ. Some studies suggest that changes in the inner ear causing tinnitus, vertigo, and hearing impairment may be related to microcirculatory insufficiency resulting from vascular occlusion caused by embolism, hemorrhage, or vasospasm, which may again be the result of hyperviscosity or microangiopathic syndrome in patients with diabetes or hypertension. Thus, the precise etiology of presbycusis is unknown, but multiple factors are likely involved.
We have shown that the age of the participant associated with the presence of arterial hypertension or dyslipidemia may be responsible for accelerating cochlear damage.
Cochlear dysfunction and cardiovascular disease risk factors
Atherosclerosis is associated with a 5-year incidence of hearing loss in a cohort study predominated by middle-aged patients. Interventions involving the prevention of atherosclerosis can help prevent or delay the onset of impaired hearing. In the Framingham Heart Study, hearing impairment was associated with cardiovascular events.,
Rosen et al. hypothesized that low rates of CVD, diabetes, and hypertension, together with increased physical activity with the low rate of smoking and exposure to noise, as well as high intake of fruit and fibers, contributed to maintaining good hearing function in the older age. In a series of environmental studies, poorer hearing was found in a population of people living in areas with a high CVD rate compared to the population in areas with a lower rate of these diseases. Socioeconomic status, BMI, and waist circumference as CVD risk factors were also associated with the incidence of hearing loss in longitudinal studies. Other risk factors (hypertension, type 2 diabetes, cigarette smoking habit, alcohol consumption) were associated with hearing loss in some but not all cohort and cross-sectional studies.,, The chances of hearing impairment increase with each additional risk factor according to our results.
Although there is no agreed definition of tinnitus for the research purpose, numerous population studies have attempted to estimate the prevalence of this condition. The prevalence estimate ranges generally between 7 and 20%.
Clinical conditions associated with tinnitus such as vascular diseases, middle ear diseases, diabetes, hypertension, autoimmune disorders, and degenerative nerve disorders with or without hearing loss may be associated with disorders of the peripheral circulation. Nearly all clinical conditions that lead to a reduction in systemic or regional circulation at the ear level can be a trigger for the development of tinnitus or exacerbate in patients who already have this disorder. The prevalence of tinnitus is higher in patients with BMI ≥30 kg/m2 who are smokers and in those diagnosed with hypertension, diabetes, or dyslipidemia.
Cochlear dysfunction and diabetes
The relationship between diabetes and hearing impairment was discovered many years ago. In 1857, Jordao published a case report of a diabetic patient with hearing loss. Edgar was the first to report high-frequency hearing loss in diabetic patients in 1915.
Today, most authors conclude that patients with diabetes have worse hearing; however, several authors, for example, Harner and Schuknecht, rejected this correlation. Axelsson et al. stated that when hearing in patients with diabetes is analyzed, in correlation with age, the results are generally normal., As a contribution to these claims, our findings have shown 25% of diabetic patients with profound hearing impairment but no statistical significance between those two variables.
Relating of hearing loss to diabetes alone is often difficult because of other vascular diseases in these patients and due to associated variables such as presbycusis. Duck et al. studied the interaction of hypertension in patients with insulin-dependent diabetes mellitus and hearing loss. They observed that hypertension and diabetes have a synergistic effect on high-frequency SN hearing impairment. The microvascular effects of hypertension are similar to those of diabetes, making this data credible. This concept is important because the prevalence of hypertension in patients with diabetes varies between 10% and 80%, according to various reports. Furthermore, patients with retinopathy should have more pronounced hearing loss given the similarity of blood supply to the ear and eye structures. Jorgensen supported these claims, and report that hearing loss is twice as common in diabetic patients with retinopathy. The pathogenetic effects of diabetes on the ear can be broadly grouped into neuropathic, angiopathic, and a combination of the two. Makishima and Tanaka observed severe spiral ganglion atrophy in the basal and middle parts of the cochlea in diabetic patients with SNHL. They also noted that atherosclerosis, a well-documented consequence of diabetes and hypertension, was responsible for neuron degeneration in the inner ear. Jorgensen first studied the histopathological features of the temporal bone in patients with diabetes and hearing loss, and noted wall thickening of the cranial nerve VIII, leading to acoustic neuropathy. Jorgensen also noted microangiopathic changes in the stria vascularis and basilar membrane.
Cochlear dysfunction and dyslipidemia
Evidence from experimental studies demonstrates the impact of hyperlipidemia on auditory function. Experimental hypercholesterolemia metabolically stretches inner ear tissue, inducing glycogen accumulation in the cochlea and edema in the stria vascularis and external auditory cells. Vascular occlusion is also mentioned as a possible mechanism by which hyperlipidemia contributes to an increased risk of cochleovestibular pathology.
The chance of developing SNHL increases several times in our patients with dyslipidemia.
| Conclusion|| |
Based on the results of the study, a statistically significant association of arterial hypertension, dyslipidemia, and BMI with cochlear dysfunction was observed, which was especially pronounced in the elderly population.
These findings cannot conclusively confirm that cochleovestibular manifestations and particular risk factors for CVD have a cause-effect relationship. However, the connection is high enough to justify further research. Furthermore, we must distance ourselves and say that this study has its limitation-a small study group. Further analysis on a larger sample may contribute to the validation of these results as well as the application of additional diagnostic procedures for the sake of greater objectivity.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
World Health Organization. Global Health Estimates: Deaths by Cause, Age, Sex and Country, 2000-2012. Geneva: World Health Organization; 2014.
Mozaffarian D, Benjamin EJ, Go AS, Arnett DK, Blaha MJ, Cushman M, et al
. Heart disease and stroke statistics-2015 update: A report from the American Heart Association. Circulation 2015;131:e29-322.
Rosen S, Olin P. Hearing loss and coronary heart disease. Arch Otolaryngol 1965;82:236-43.
Simpson AN, Matthews LJ, Dubno JR. Lipid and C-reactive protein levels as risk factors for hearing loss in older adults. Otolaryngol Head Neck Surg 2013;148:664-70.
Gopinath B, Flood VM, Teber E, McMahon CM, Mitchell P. Dietary intake of cholesterol is positively associated and use of cholesterol-lowering medication is negatively associated with prevalent age-related hearing loss. J Nutr 2011;141:1355-61.
Ašanin M, Beleslin B, Dobrić M, Dikić AĐ Kovačević V, Nedeljković M, et al
. The National Guide to Good Clinical Practice For Diagnosis and Treatment Of Ischemic Heart Disease. Ministry of Health of the Republic of Serbia, Belgrade; 2012.
Williams B, Mancia G, Spiering W, Agabiti Rosei E, Azizi M, Burnier M, et al
. 2018 ESC/ESH guidelines for the management of arterial hypertension: The task force for the management of arterial hypertension of the European Society of Cardiology and the European Society of Hypertension: The task force for the management of arterial hypertension of the European Society of Cardiology and the European Society of Hypertension. J Hypertens 2018;36:1953-2041.
Nondahl DM, Cruickshanks KJ, Wiley TL, Klein R, Klein BE, Tweed TS. Prevalence and 5-year incidence of tinnitus among older adults: The epidemiology of hearing loss study. J Am Acad Audiol 2002;13:323-31.
Jerger J, Chmiel R, Wilson N, Luchi R. Hearing impairment in older adults: New concepts. J Am Geriatr Soc 1995;43:928-35.
Spiess AC, Lang H, Schulte BA, Spicer SS, Schmiedt RA. Effects of gap junction uncoupling in the gerbil cochlea. Laryngoscope 2002;112:1635-41.
Morizane I, Hakuba N, Shimizu Y, Shinomori Y, Fujita K, Yoshida T, et al
. Transient cochlear ischemia and its effects on the stria vascularis. Neuroreport 2005;16:799-802.
Fischer ME, Schubert CR, Nondahl DM, Dalton DS, Huang GH, Keating BJ, et al
. Subclinical atherosclerosis and increased risk of hearing impairment. Atherosclerosis 2015;238:344-9.
Gates GA, Cobb JL, D'Agostino RB, Wolf PA. The relation of hearing in the elderly to the presence of cardiovascular disease and cardiovascular risk factors. Arch Otolaryngol Head Neck Surg 1993;119:156-61.
Culleton BF, Larson MG, Evans JC, Wilson PW, Barrett BJ, Parfrey PS, et al
. Prevalence and correlates of elevated serum creatinine levels: The Framingham heart study. Arch Intern Med 1999;159:1785-90.
Ros S, Preobrajensky N, Khechinashvili S, Glazunov I, Kipshidze N, Rosen HV. Epidemiologic hearing studies in the USSR. Arch Otolaryngol 1970;91:424-8.
Brant LJ, Gordon-Salant S, Pearson JD, Klein LL, Morrell CH, Metter EJ, et al
. Risk factors related to age-associated hearing loss in the speech frequencies. J Am Acad Audiol 1996;7:152-60.
Cruickshanks KJ, Klein R, Klein BE, Wiley TL, Nondahl DM, Tweed TS. Cigarette smoking and hearing loss: The epidemiology of hearing loss study. JAMA 1998;279:1715-9.
Dalton DS, Cruickshanks KJ, Klein R, Klein BE, Wiley TL. Association of NIDDM and hearing loss. Diabetes Care 1998;21:1540-4.
Popelka MM, Cruickshanks KJ, Wiley TL, Tweed TS, Klein BE, Klein R, et al
. Moderate alcohol consumption and hearing loss: A protective effect. J Am Geriatr Soc 2000;48:1273-8.
Bainbridge KE, Hoffman HJ, Cowie CC. Diabetes and hearing impairment in the United States: Audiometric evidence from the National Health and Nutrition Examination Survey, 1999 to 2004. Ann Intern Med 2008;149:1-0.
Fransen E, Topsakal V, Hendrickx JJ, Van Laer L, Huyghe JR, Van Eyken E, et al
. Occupational noise, smoking, and a high body mass index are risk factors for age-related hearing impairment and moderate alcohol consumption is protective: A European population-based multicenter study. J Assoc Res Otolaryngol 2008;9:264-76.
Cullen JR, Cinnamond MJ. Hearing loss in diabetics. J Laryngol Otol 1993;107:179-82.
Axelsson A, Sigorth K, Vertes D. Hearing in diabetics. Acta Otolaryngol 1978;356:3-21.
Jordao AM. Consideration on a case of diabetes. Un Med Paris 1857;11:446.
Edgar TO. Clinical studies of auditory organ diseases in diabetes mellitus. Mschr Ohrenheilk 1915;49:215-60.
Harner SG. Hearing in adult-onset diabetes mellitus. Otolaryngol Head Neck Surg 1981;89:322-7.
Schuknecht HF. Pathology of the Ear. Cambridge, Mass: Harvard University Press; 1974. p. 386-8.
Duck SW, Prazma J, Bennett PS, Pillsbury HC. Interaction between hypertension and diabetes mellitus in the pathogenesis of sensorineural hearing loss. Laryngoscope 1997;107:1596-605.
Jorgensen MB. The inner ear in diabetes mellitus. Histological studies. Arch Otolaryngol 1961;74:373-81.
Makishima K, Tanaka K. Pathological changes of the inner ear and central auditory pathway in diabetics. Ann Otol Rhinol Laryngol 1971;80:218-28.
Preyer S, Baisch A, Bless D, Gummer AW. Distortion product otoacoustic emissions in human hypercholesterolemia. Hear Res 2001;152:139-51.
Gratton MA, Wright CG. Alterations of inner ear morphology in experimental hypercholesterolemia. Hear Res 1992;61:97-105.
Rudack C, Langer C, Stoll W, Rust S, Walter M. Vascular risk factors in sudden hearing loss. Thromb Haemost 2006;95:454-61.
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]