Control of inner ear blood flow

Relationship Between Serum ET-1, HDL-C, and sVCAM-1 and Hearing Loss in Patients with Sudden Deafness

Vascular causes are most commonly associated with sudden sensorineural hearing loss (SSHL). This study was performed to determine the relationship between serum endothelin-1 (ET-1), high-density lipoprotein cholesterol (HDL-C), soluble vascular cell adhesion molecule-1 (sVCAM-1) levels, and the degree of hearing loss in patients with SSHL. Firstly, 60 SSHL patients were admitted to The First Hospital of Shanxi Medical University. In the same period, 60 healthy subjects matching the age and gender of SSHL patients were selected as the control group. Then, serum levels of ET-1, HDL-C, and sVCAM-1 were measured by enzyme-linked immunosorbent assay (ELISA). Next, the relationship between serum levels of ET-1, HDL-C, and sVCAM-1 with clinicopathological factors and their diagnostic and prognostic values were analyzed and evaluated. Serum ET-1 and sVCAM-1 were increased, and HDL-C was decreased in patients with SSHL. Serum ET-1 and sVCAM-1 were higher and HDL-C was lower in patients aged ≥ 45 years, or severe hearing loss patients (P < 0.05). ROC analysis determined that ET-1 (AUC = 0.839), HDL-C (AUC = 0.830), and sVCAM-1 (AUC = 0.865) had excellent diagnostic values. In addition, patients with low levels of ET-1 and sVCAM-1 and high levels of HDL-C had better hearing prognosis (P < 0.05). Abnormal serum ET-1, HDL-C, and sVCAM-1 in patients with SSHL are closely related to age, and degree of hearing loss, and perform diagnostic and prognostic values.

Endothelial Dysfunction and Metabolic Disorders in Patients with Sudden Sensorineural Hearing Loss

Sudden sensorineural hearing loss (SSNHL) is defined as a sensorineural hearing loss of 30 dB or greater on at least three contiguous audiometric frequencies occurring within a 72 h period. Although SSNHL is commonly encountered in clinical audiology and otolaryngology practice, its etiopathogenesis continues to be poorly understood. Scientific investigations have highlighted the vulnerability of cochlear microcirculation to blood flow alterations. Even mild hypoperfusion can lead to immediate dysfunction in the organ of Corti, given the heightened susceptibility of cochlear hair cells to hypoxia and ischemic damage. The purpose of this review paper is to present evidence of endothelial and vascular involvement in SSNHL and the risk factors, such as metabolic syndrome, that may negatively impact the inner ear's vascular supply, influencing the onset pattern, incidence, and prognosis of SSNHL. By addressing these variables, we can deepen our comprehension of the mechanisms underlying SSNHL and potentially uncover strategies for prevention.

Dizziness, Falls, and Hearing Loss in Adults Living With Sickle Cell Disease

Objective:

The aim of this study was to assess the prevalence of reported dizziness/imbalance, frequency of falls, and hearing loss in adults with sickle cell disease (SCD) and determine the relationship of these self-reported problems both during and in the absence of an SCD crisis. Also, the impact of educational level and health insurance on seeking treatment services, as well as the relationship of falls to stroke, legal blindness, and other orthopedic problems, was assessed. Interrupted blood flow to shared vestibular and auditory arteries supports the notion of increased likelihood of balance deficits and increased falls in this population.

Design:

A cross-sectional survey study design was used. Adults living with SCD responded to a questionnaire that was distributed online and through traditional mail.

Study Sample:

Adults living with SCD ( N = 135) participated in the study.

Results:

Responses revealed 70% of participants with SCD experienced dizziness/imbalance and 23% reported hearing loss. Furthermore, 33% of participants reported falling one or more times in the last year. The prevalence of dizziness/imbalance, falling, and hearing loss in the respondents with SCD was much higher than that of the general population of the United States. Additionally, for dizziness and falling, the prevalence was higher not only than the national average but also for persons over 65 years of age. A significant association was demonstrated between dizziness/imbalance and hearing loss as well as dizziness/imbalance and falls for adults living with SCD. In fact, participants with self-reported hearing loss were 5.2 times more likely to also report dizziness/imbalance. They were 4.9 times more likely to fall if they also reported dizziness/imbalance. Numbness of the feet was revealed to significantly impact the likelihood of falling in this disease population and should be further studied. Regarding SCD crisis status, dizziness/imbalance and falls were more likely to occur outside of SCD crisis than during a crisis. Furthermore, pain levels were significantly associated with dizziness/imbalance only when respondents were in crisis and not in the absence of a crisis. In crisis, higher pain levels were reported from respondents who also reported dizziness/imbalance than from those who did not report dizziness. No significant relationship was revealed between hearing loss and falls.

Discussion:

These results provide justification for patient and health care provider education regarding appropriate referrals for vestibular/balance assessments and provision of fall prevention strategies. Future studies on balance and SCD are encouraged.

Association between meteorological factors and audiogram configurations in patients with sudden sensorineural hearing loss: a cross-sectional study

OBJECTIVE

We aimed to determine the association between meteorological factors and sudden sensorineural hearing loss (SSNHL) audiogram configurations.

DESIGN

Retrospective review of medical records from 1 October 2007 to 31 December 2018.

SETTING

A tertiary hospital.

PARTICIPANTS

510 patients with SSNHL who had data on the exact date of SSNHL onset and underwent audiological evaluation within 14 days were included.

PRIMARY AND SECONDARY OUTCOME MEASURES

Daily values of meteorological factors, including maximum and minimum temperature, mean temperature and its day-to-day change, diurnal temperature range, atmospheric pressure, mean and maximum wind speed and relative humidity, and seasonal distributions.

RESULTS

Among the 510 patients (259 women (50.8%); mean (SD) age, 46.4 (15.5) years), 108 (21.2%) displayed ascending patterns, 143 (28.0%) displayed descending patterns, 129 (25.3%) displayed flat patterns and 130 (25.5%) displayed profound patterns of audiograms. The diurnal temperature range on the day of SSNHL onset in patients with profound patterns was significantly higher than that in patient with ascending (mean difference (MD), 2.2°C; 95% CI, 0.7°C to 3.7°C; p=0.001) and descending (MD, 1.5°C; 95% CI, 0.1°C to 2.9°C; p=0.031) patterns. The relative humidity was the highest on the day of SSNHL onset in patients with ascending patterns and showed a significant difference compared with that in patients with profound patterns (MD, 8.0%; 95% CI, 0.7% to 15.3%; p=0.026). Seasonal distribution did not differ among patients with different audiogram configurations.

CONCLUSIONS

Profound audiogram patterns correlated with high diurnal temperature range, while ascending audiogram patterns correlated with high relative humidity in patients with SSNHL. No correlation was observed between seasons and audiogram configurations.

Sensorineural hearing loss in children with sickle cell disease

INTRODUCTION

Sensorineural hearing loss (SNHL) has been reported to occur at increased frequency in the pediatric sickle cell disease (SCD) population, likely secondary to ototoxic medication regimens and repeat sickling events that lead to end organ damage. Risk and protective factors of SNHL in this population are not fully characterized. The objective of this study was to describe audiology results in children with SCD and the prevalence and sequelae of SNHL.

METHODS

A comprehensive clinical database of 2600 pediatric SCD patients treated at 1 institution from 2010-16 was retrospectively reviewed to identify all patients who were referred for audiologic testing. Audiologic test results, patient characteristics, and SCD treatments were reviewed.

RESULTS

181 SCD children (97 male, 153 HbSS) underwent audiologic testing, with 276 total audiology encounters, ranging 1-9 per patient. Mean age at first audiogram was 8.9 ± 5.2 years. 29.8% had prior cerebrovascular infarct and an additional 25.4% had prior abnormal transcranial Doppler screens documented at time of first audiogram. Overall, 13.3% had documented hearing loss, with 6.6% SNHL. Mean pure tone average (PTA) among patients with SNHL ranged from mild to profound hearing loss (Right: 43.3 ± 28.9, Left: 40.8 ± 29.7), sloping to more severe hearing loss at higher frequencies.

CONCLUSIONS

Hearing loss was identified in a significant subset of children with SCD and the hearing loss ranged from normal to profound. Though the overall prevalence of SNHL in SCD patients was low, baseline audiology screening should be considered.

Endothelial Dysfunction in Idiopathic Sudden Sensorineural Hearing Loss: A Review

An endothelial dysfunction has been described in idiopathic sudden sensorineural hearing loss (ISSHL) patients. The purpose of our review was to: i) identify, evaluate and review recent research about cardiovascular risk factors involvement and signs of endothelial dysfunction in ISSHL; ii) implication of these discovering in clinical practice and future research. A Medline literature search was conducted to identify any study on the involvement of endothelial dysfunction in ISSHL, published in the English language in the last decade. The following MEDLINE search terms were used: sudden sensorineural hearing loss (SSHL) and endothelial dysfunction (text words). Additional studies were identified by hand searching the references of original articles and review articles. Studies were not excluded on the basis of the qualitative or quantitative definitions of SSHL, treatment regimens, or outcome measures. Data were extracted from included papers by a reviewer. Information on the patients, investigations, methods, interventions, and outcomes were systematically analyzed. Characteristics and results of all included studies were reviewed systematically. High levels of adhesion molecules, hyperhomocysteinemia and lower folate levels, unbalanced oxidative status, a lower value of flow-mediated dilatation of brachial artery and a reduced percentage of circulating endothelial progenitor cells in patients affected by ISSHL support the hypothesis that this syndrome should be considered as a microcirculation disorder based on endothelial dysfunction and drive clinicians to implement all the traditional strategies used for preventing cardiovascular events, to also reduce the likelihood of ISSHL occurrence.

Increased endothelial progenitor cell circulation and VEGF production in a rat model of noise-induced hearing loss

CONCLUSIONS

The vascular endothelial growth factor (VEGF)-mediated mechanism of endothelial progenitor cell (EPC) mobilization, migration, and differentiation may occur in response to noise-induced acoustic trauma of the cochlea, leading to the protection of cochlear function.

OBJECTIVE

The purpose of this study was to analyze changes in the cochlear vessel under an intensive noise environment.

METHODS

Sixty male Sprague-Dawley rats were randomly divided into six groups. Acoustic trauma was induced by 120 dB SPL white noise for 4 h. Auditory function was evaluated by the auditory brainstem response threshold. Morphological changes of the cochleae, the expression of VEGF, and the circulation of EPCs in the peripheral blood were studied by immunohistochemistry, Western blotting analysis, scanning electron microscopy, and flow cytometry.

RESULTS

Vascular recovery of the cochlea began after noise exposure. The change in the number of EPCs was consistent with the expression of VEGF at different time points after noise exposure. We propose that VEGF evokes specific permeable and chemotactic effects on the vascular endothelial cells. These effects can mobilize EPCs into the peripheral blood, leading the EPCs to target damaged sites and to exert a neoangiogenic effect.

Lipid profiles and obesity as potential risk factors of sudden sensorineural hearing loss

Objectives

The objective of our study was to establish whether increased lipid profiles and obesity affect the prevalence and prognosis of sudden sensorineural hearing loss (SSNHL).

Methods

This was a case-controlled study with a longitudinal design. According to our criteria, 324 patients with SSNHL were included in this study. To manage potential covariates, 972 subjects with normal hearing from the Korean National Health and Nutrition Examination Survey were matched as control group according to their propensity scores. Age, level of total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), and body mass index (BMI) were obtained from the clinical data. Multivariate logistic regression analysis was used to investigate the association between SSNHL and lipid profiles or obesity in the 1296 subjects. Multivariate Cox regression analysis was used to determine whether lipid profiles and obesity are prognostic factors in patients with SSNHL.

Results

Mean body weight, BMI, TC, and TG were significantly higher in patients with SSNHL compared with control subjects (p<0.05). However, LDL-C values did not differ significantly between the two groups. Subjects with elevated TC and TG levels had a 2.20- (95% CI 1.50–3.24) and 1.50-fold (95% CI 1.08–2.08) increased odds, respectively, of SSNHL compared with subjects with normal TC and TG levels. Subjects with grade III BMI had a 1.59-fold (95% CI 1.17–2.16) increased odds of SSNHL. Multivariate Cox regression analyses revealed that BMI was an independent risk factor of treatment outcome, as patients with BMI ≥27.5 were less likely to achieve complete recovery than those with BMI <27.5 (p<0.05).

Conclusions

The results of this study revealed that elevated TC and TG levels and increased BMI are significantly associated with the prevalence of SSNHL and its prognosis, indicating that vascular compromise may play an important role in the pathogenesis of SSNHL.

Two-photon microscopy allows imaging and characterization of cochlear microvasculature in vivo

Impairment of cochlear blood flow has been discussed as factor in the pathophysiology of various inner ear disorders. However, the microscopic study of cochlear microcirculation is limited due to small scale and anatomical constraints. Here, two-photon fluorescence microscopy is applied to visualize cochlear microvessels. Guinea pigs were injected with Fluorescein isothiocyanate- or Texas red-dextrane as plasma marker. Intravital microscopy was performed in four animals and explanted cochleae from four animals were studied. The vascular architecture of the cochlea was visualized up to a depth of 90.0±22.7 μm. Imaging yielded a mean contrast-to-noise ratio (CNR) of 3.3±1.7. Mean diameter in vivo was 16.5±6.0 μm for arterioles and 8.0±2.4 μm for capillaries. In explanted cochleae, the diameter of radiating arterioles and capillaries was measured with 12.2±1.6 μm and 6.6±1.0 μm, respectively. The difference between capillaries and arterioles was statistically significant in both experimental setups (P<0.001 and P=0.022, two-way ANOVA). Measured vessel diameters in vivo and ex vivo were in agreement with published data. We conclude that two-photon fluorescence microscopy allows the investigation of cochlear microvessels and is potentially a valuable tool for inner ear research.

Endothelial progenitor cells in patients with age-related hearing loss

OBJECTIVE

This study was conducted to determine the concentration of EPCs in patients with ARHL.

METHODS

Twenty patients with ARHL were evaluated. The number of EPCs was analyzed by flow cytometry analysis of peripheral blood CD34(+)/CD133(+) cells.

RESULTS

The concentration of circulating EPCs, both for CD34(+)/CD133(+) cells, was significantly lower in ARHL patients compared to controls (P<0.05). No statistically significant differences were found between these two groups in terms of the level of total cholesterol, LDL, HDL, triglycerides and GLU.

CONCLUSIONS

The possible role of circulating epithelial progenitor cells in the pathogenesis of age related hearing loss should be considered based on their significant reduction in patients with ARHL, although the association alone does not prove causality. Further studies were warranted to confirm the role of circulating EPCs in the pathogenesis of ARHL.

Thin and open vessel windows for intra-vital fluorescence imaging of murine cochlear blood flow

Normal microvessel structure and function in the cochlea is essential for maintaining the ionic and metabolic homeostasis required for hearing function. Abnormal cochlear microcirculation has long been considered an etiologic factor in hearing disorders. A better understanding of cochlear blood flow (CoBF) will enable more effective amelioration of hearing disorders that result from aberrant blood flow. However, establishing the direct relationship between CoBF and other cellular events in the lateral wall and response to physio-pathological stress remains a challenge due to the lack of feasible interrogation methods and difficulty in accessing the inner ear. Here we report on new methods for studying the CoBF in a mouse model using a thin or open vessel-window in combination with fluorescence intra-vital microscopy (IVM). An open vessel-window enables investigation of vascular cell biology and blood flow permeability, including pericyte (PC) contractility, bone marrow cell migration, and endothelial barrier leakage, in wild type and fluorescent protein-labeled transgenic mouse models with high spatial and temporal resolution. Alternatively, the thin vessel-window method minimizes disruption of the homeostatic balance in the lateral wall and enables study CoBF under relatively intact physiological conditions. A thin vessel-window method can also be used for time-based studies of physiological and pathological processes. Although the small size of the mouse cochlea makes surgery difficult, the methods are sufficiently developed for studying the structural and functional changes in CoBF under normal and pathological conditions.

Fibrinogen/LDL apheresis is a promising rescue therapy for sudden sensorineural hearing loss

BACKGROUND

Fibrinogen/LDL apheresis has been proven to be effective in treatment of sudden sensorineural hearing loss (SSNH). This study is aimed to investigate if reduction of fibrinogen and serum LDL is also effective in patients with SSNH non-responding toward treatment with corticosteroids and plasmaexpanders.

METHODS

Remission rates of 217 patients suffering from SSHL were investigated after treatment with apheresis. All patients were non-responders after other therapies such as high doses of steroids or plasmaexpanders.

RESULTS

Single apheresis resulted in complete or partial remissions in 61% of patients when given after other unsuccessful conducted therapies such as corticosteroids and plasmaexpanders.

CONCLUSION

Fibrinogen/LDL apheresis is a promising rescue therapy for sudden sensorineural hearing loss even after unsuccessful other therapies.

Sickle cell anemia and hearing loss among children and youngsters: literature review

Sickle cell anemia is still a significant public health issue in underdeveloped and developing countries. Sickle cell disease is one of the most common inherited diseases in Brazil. It affects mainly the mixed race population. Approximately 1 African-Brazilian child is affected with sickle cell disease for every 37,400 children born alive. Hearing loss has been considered one of the main clinical manifestations, especially in children. However, to date, there are just a hand full of studies in Brazil and the Brazilian state of Bahia has the largest African-descended population, attempting to establish the frequency of this event.

OBJECTIVES

To analyze the major studies associated with the subject, published in the last twenty years in the main indexed databases.

METHODS

To use MEDLINE to identify the main papers published in English in medical literature, between January of 1989 and January of 2009; associating sickle cell anemia and hearing loss, with its clinical outcomes.

CONCLUSION

Given that it is always possible to attempt to prevent disabilities, understanding hearing loss in children with sickle cell anemia enables to maximize quality of life and provides for a broader school attendance.

Physiopathology of the cochlear microcirculation

Normal blood supply to the cochlea is critically important for establishing the endocochlear potential and sustaining production of endolymph. Abnormal cochlear microcirculation has long been considered an etiologic factor in noise-induced hearing loss, age-related hearing loss (presbycusis), sudden hearing loss or vestibular function, and Meniere's disease. Knowledge of the mechanisms underlying the pathophysiology of cochlear microcirculation is of fundamental clinical importance. A better understanding of cochlear blood flow (CoBF) will enable more effective management of hearing disorders resulting from aberrant blood flow. This review focuses on recent discoveries and findings related to the physiopathology of the cochlear microvasculature.

Effect of Ginkgo biloba extract on endotoxin-induced labyrinthitis

OBJECTIVE

There are no reports on the therapeutic effect of Ginkgo biloba extract (GBE) on otitis media-induced labyrinthitis. The present study examined whether GBE can protect against cochlear damage induced by intratympanic instillation of lipopolysaccharide (LPS)-induced labyrinthitis.

MATERIALS AND METHODS

Experiments were performed in 20 healthy young male guinea pigs. The control group (n=10) received an intratympanic instillation of LPS (20 μl, 3mg/ml). The experimental group (n=10) received intratympanic instillation of LPS immediately after instillation of GBE (10mg/kg) and then experimental groups received GBE (100mg/kg) by intraperitoneal injection every day for 3 days. Instillation of LPS or LPS immediately after GBE was done in the right ear; the untreated left ear was considered normal. Physiological and morphological changes were evaluated.

RESULTS

Statistical analysis of treatment of GBE revealed significantly less hearing loss than LPS group (p<0.05). The ratio of the value of cochlear blood flow (CBF) compared to untreated left side was significantly higher in the GBE treated group than in the LPS-treated group (p<0.05). This result indicated the recovery of CBF in GBE treated group compared to LPS treated group. In the LPS group, scanning electron microscopy revealed hair cell damage with edema. Missing stereocilia in the third layer of the outer hair cell was revealed. However, both the inner hair cells and the outer hair cells had normal appearance in the GBE group. LPS group showed that cochlear Evans blue extravasation was increased strongly in the stria vascularis, spiral limbus, and in the spiral ligament compared with the GBE treated group.

CONCLUSION

GBE significantly minimizes cochlear damage against LPS-induced otitis media with labyrinthitis in a guinea pig model. GBE has potential as an adjunctive therapy to antibiotics in the treatment of acute otitis media with complicated labyrinthitis.

Fibro-vascular coupling in the control of cochlear blood flow

Background

Transduction of sound in the cochlea is metabolically demanding. The lateral wall and hair cells are critically vulnerable to hypoxia, especially at high sound levels, and tight control over cochlear blood flow (CBF) is a physiological necessity. Yet despite the importance of CBF for hearing, consensus on what mechanisms are involved has not been obtained.

Methodology/Principal Findings

We report on a local control mechanism for regulating inner ear blood flow involving fibrocyte signaling. Fibrocytes in the super-strial region are spatially distributed near pre-capillaries of the spiral ligament of the albino guinea pig cochlear lateral wall, as demonstrably shown in transmission electron microscope and confocal images. Immunohistochemical techniques reveal the inter-connected fibrocytes to be positive for Na+/K+ ATPase β1 and S100. The connected fibrocytes display more Ca²⁺ signaling than other cells in the cochlear lateral wall as indicated by fluorescence of a Ca²⁺ sensor, fluo-4. Elevation of Ca²⁺ in fibrocytes, induced by photolytic uncaging of the divalent ion chelator o-nitrophenyl EGTA, results in propagation of a Ca²⁺ signal to neighboring vascular cells and vasodilation in capillaries. Of more physiological significance, fibrocyte to vascular cell coupled signaling was found to mediate the sound stimulated increase in cochlear blood flow (CBF). Cyclooxygenase-1 (COX-1) was required for capillary dilation.

Conclusions/Significance

The findings provide the first evidence that signaling between fibrocytes and vascular cells modulates CBF and is a key mechanism for meeting the cellular metabolic demand of increased sound activity.

Endothelial progenitor cells in sudden sensorineural hearing loss

CONCLUSIONS

Endothelial progenitor cells (EPCs) are a unique subtype of circulating cells with properties similar to those of embryonal angioblasts. They have the potential to proliferate and to differentiate into mature endothelial cells. EPCs are reduced in patients with vascular risk factors due to a decreased mobilization, an increased consumption at the site of damage or a reduced half-life. The results of this study confirm the existence of an endothelial dysfunction in patients with sudden sensorineural hearing loss (SSHL) and support the vascular involvement in the pathogenesis of the disease.

OBJECTIVE

The aim of this study was to evaluate the concentration of EPCs in patients affected by SSHL.

METHODS

Twenty-one patients affected by SSHL were evaluated. The number of EPCs was analyzed by flow cytometry analysis of peripheral blood CD34+KDR+CD133+ cells.

RESULTS

Circulating levels of EPCs were significantly lower in SSHL patients compared with controls. In particular, CD34+KDR+ cells and CD34+CD133+KDR+ cells were significantly reduced (p < 0.05).

An animal model for the analysis of cochlear blood flow [corrected] disturbance and hearing threshold in vivo

Impairment of cochlear blood flow (CBF) is considered to be important in inner ear pathology. However, direct measurement of CBF is difficult and has not been investigated in combination with hearing function. Six guinea pigs were used to show feasibility of an animal model for the analysis of cochlear microcirculation by intravital microscopy in combination with investigation of the hearing threshold by brainstem response audiometry (ABR). By the application of sodium nitroprusside (SNP), CBF was increased over 30 min. Reproducibility of measurements was shown by retest measurements. Mean baseline velocity of CBF was 109 +/- 19 mum/s. Vessel diameters had a mean value of 9.4 +/- 2.7 mum. Mean hearing threshold was 19 +/- 6 dB. In response to SNP, CBF velocity increased significantly to 161 +/- 26 mum/s. Mean arterial pressure decreased significantly to 36 +/- 11 mmHg. After the end of the application, CBF velocity recovered to a minimum of 123 +/- 17 microm/s. Within the retest, CBF velocity significantly increased to a maximum of 160 +/- 31 microm/s. Second recovery of CBF velocity was 125 +/- 14 mum/s. Within the second retest, CBF increased significantly to 157 +/- 25 microm/s. ABR thresholds did not change significantly. The increase in blood flow velocity occurred in spite of substantial hypotension as induced by a vasodilator. This may explain the fact that ABR threshold remained unchanged reflecting a maintained blood supply in this part of the brain. This technique can be used to evaluate effects of treatments aimed at cochlear microcirculation in inner ear pathologies.

Soluble intercellular adhesion molecule 1 and soluble vascular cell adhesion molecule 1 in sudden hearing loss

HYPOTHESIS

The aim of the present study was to evaluate the concentration of soluble intercellular adhesion molecule 1 and soluble vascular cell adhesion molecule 1 in patients affected by sudden sensorineural hearing loss (SSHL).

STUDY DESIGN

Prospective study.

SETTING

Tertiary referral center.

PATIENTS

Patients affected by SSHL were evaluated. Inclusion criteria for this study were hearing loss of more than 30 dB hearing level affecting at least 3 contiguous frequencies, normal hearing on the contralateral ear, negative history of hearing loss or ear surgery in the affected ear, and magnetic resonance with gadolinium negative for VIII cranial nerve pathologic findings.

INTERVENTION

Circulating levels of soluble intercellular adhesion molecule 1 and soluble vascular cell adhesion molecule (VCAM) 1 were evaluated by means of enzyme-linked immunosorbent assay.

MAIN OUTCOME MEASURES

The levels of adhesion molecules in SSHL patients were compared with those of a control group.

RESULTS

Intercellular adhesion molecule 1 and VCAM-1 levels in sera of patients with SSHL were significantly higher than those of the matched control subjects (p < 0.001). Statistical analysis did not show significant differences between the 2 groups in terms of the known vascular risk factors such as total and fractionated cholesterol, triglycerides, fibrinogen, erythrocyte sedimentation rate smoking, and diabetes.

CONCLUSION

The results of this study show that in SSHL patients, there is an increased expression of circulating adhesion molecules confirming the existence of an endothelial dysfunction and supporting the vascular involvement in the pathogenesis of the disease. The identification of high levels of adhesion molecules and of the endothelial dysfunction open the way to selective pharmacologic treatments able to correct the activation of endothelial cells.

Does a Reduction of Adhesion Molecules by LDL-Apheresis Have a Role in the Treatment of Sudden Hearing Loss?

Sudden hearing loss (SHL) is a highly disabling affliction that can severely affect the subject's social and relational life. Although the etiology of the complaint is still debated, it is thought that microcirculation disturbances conditioned by an endothelial dysfunction might be the main pathogenetic mechanism. Adhesion molecules favoring interaction between leukocytes and endothelial cells are early markers of endothelial damage. In the present report, we describe a case of SHL that derived evident benefit from a single session of LDL/fibrinogen apheresis, with complete hearing recovery. In this patient, in addition to reducing LDL cholesterol and fibrinogen, the circulating adhesion molecules (sE-selectin, sVCAM-1 and sICAM-1), previously present in higher than normal concentrations, were reduced by the treatment.

The role of oxidative stress in noise-induced hearing loss

Modern research has provided new insights into the biological mechanisms of noise-induced hearing loss, and with these new insights comes hope for possible prevention or treatment. Underlying the classic set of cochlear pathologies that occur as a result of noise exposure are increased levels of reactive oxygen species (ROS) that play a significant role in noise-induced hair cell death. Both necrotic and apoptotic cell death have been identified in the cochlea. Included in the current review is a brief review of ROS, along with a description of sources of cochlear ROS generation and how ROS can damage cochlear tissue. The pathways of necrotic and apoptotic cell death are also reviewed. Interventions are discussed that target the prevention of noise-induced hair cell death: the use of antioxidants to scavenge and eliminate the damaging ROS, pharmacological interventions to limit the damage resulting from ROS, and new techniques aimed at interrupting the apoptotic biochemical cascade that results in the death of irreplaceable hair cells.

Acute effect of rheopheresis on peripheral endothelial dysfunction in patients suffering from sudden hearing loss

Single low density lipoprotein (LDL) fibrinogen apheresis has shown beneficial effects in the treatment of patients with sudden sensorineural hearing loss (SSHL). Pathophysiologically, a microcirculatory disorder of the inner ear, probably caused by disturbed endothelial function, is discussed as a final common pathway of a variety of SSHL etiologies. Thus, we carried out a prospective pilot study on the efficacy of Rheopheresis on vascular function in these patients, embedded into an ongoing randomized controlled multicenter trial investigating the efficacy of Rheopheresis for the treatment of SSHL. Potential modulation of systemic endothelial dysfunction by Rheopheresis was examined by measuring flow-associated vasodilatation of the brachial artery (according to the criteria of the American College of Cardiology) in a small group of patients suffering from SSHL (N=6, 5m/1f, mean age 56+/-11 years) within the last 3 days. At baseline, five of the six patients with acute hearing loss showed endothelial dysfunction as evidenced by diminished flow-mediated vasodilatation (FMD<5%). After a single Rheopheresis treatment, flow-mediated vasodilatation improved significantly (from 3.9+/-3.6% to 7.2+/-2.4%, P=0.05, mean+/-SD, two-sided paired T-test). This was paralleled by a reduction in fibrinogen (364+/-216 mg/dL to 142+/-96 mg/dL, P=0.03), total cholesterol (228+/-23 to 98+/-10, P<0.0001) and LDL cholesterol levels (153+/-8 mg/dL to 83+/-23 mg/dL, P<0.01). Based on this case series we conclude that single Rheopheresis treatment might have an acute beneficial effect on endothelial dysfunction in patients suffering from SSHL.

Hearing loss and auditory function in sickle cell disease

Sickle cell disease was first reported in 1910 by J. Herrick, and since then, various associated conditions and complications have been described. Sickle cell disease is a hereditary disorder characterized by abnormality of the hemoglobin in the red blood cell. During periods of decreased oxygen tension in the red blood cell's environment, the abnormal hemoglobin within the red blood cell polymerizes and causes it to assume its sickled shaped. This morphological change and its associated physiological changes drastically reduce the ability of red blood cells to navigate and deliver oxygen throughout the body. Sickle cell disease is a significant health problem affecting 1 in 400 African-Americans in the United States. One in 10 African-Americans in the United States has sickle cell trait. A variety of hemoglobinapathies are classified as sickle cell disease. Variants that simultaneously occur with hemoglobin S in high frequency are hemoglobins C and beta Thalassemia, and less frequently hemoglobin E. Sickle cell disease is characterized by chronic hemolytic anemia, end-organ damage, a heightened susceptibility to infections, and intermittent episodes of vascular occlusion causing both acute and chronic pain. Neurological symptoms are frequent in patients diagnosed with sickle cell disease. Considering the vaso-occlusive nature of sickle cell disease, the potential for auditory damage is not unexpected. However, the incidence of subjective hearing impairment among sickle cell anemia subjects is very low; therefore, the interest in hearing loss associated with the disease is not in its symptomatology, but in its pathogenesis. The relationship between sickle cell anemia and hearing loss is documented, but little is known about the relationship. Numerous investigations have assessed peripheral auditory sensitivity with a wide disparity of results. In the article, we will discuss: In view of the diversity of results and speculative etiology presented here and in the literature, the relationship between sickle cell anemia, auditory sensitivity, and auditory function warrants additional investigation.

LEARNING OUTCOMES

As a result of this activity, the participant will read descriptions of the genetic and pathophysiological characteristics of sickle cell disease. The participant will examine evidence of the prevalence of hearing loss and auditory dysfunction in the sickle cell population, as well as the overall hearing health risk for sickle cell patients in comparison to the risk for the normal hemoglobin population. The participant will examine a model for appropriate audiological assessment of treatment of patients with sickle cell disease.

Loss of alpha CGRP reduces sound-evoked activity in the cochlear nerve

alpha-Calcitonin gene-related peptide (alphaCGRP) is one of several neurotransmitters immunolocalized in the unmyelinated component of the cochlear efferent innervation, the lateral olivocochlear (OC) system, which makes axo-dendritic synapses with cochlear sensory neurons. In rodents, CGRP is also immunocolocalized in the myelinated medial OC system, which contacts cochlear outer hair cells (OHCs). To understand the role(s) of this neuropeptide in the OC system, we characterized the auditory phenotype of alphaCGRP-null mice. Cochlear threshold sensitivity was normal in mutant mice, both via a neural metric, the auditory brain stem response (ABR), and an OHC-based metric, distortion product otoacoustic emissions (DPOAEs). Medial OC function and resistance to acoustic injury were also unaffected by alphaCGRP deletion: the former was assessed by measuring cochlear response suppression with electrical stimulation of the OC bundle, the latter by measuring temporary threshold shifts after exposure to high level sound. However, significant abnormality in alphaCGRP-null mice was seen in the growth of cochlear neural responses with increasing stimulus level. This observation, contrasted with normal amplitude-versus-level functions for DPOAEs, is consistent with a selective, postsynaptic effect on cochlear neurons via alphaCGRP release from lateral OC terminals. This constitutes the most direct evidence to date for a functional role of the lateral OC system in the auditory periphery.

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.

Hyperfibrinogenemia as a risk factor for sudden hearing loss

OBJECTIVE

To clarify predisposing conditions for vascular events.

SETTING

Vascular events, immunologic processes, and viral infections have to be considered as pathomechanisms for most cases of sudden hearing loss.

STUDY DESIGN

Hemorrheologic parameters were studied in 53 patients with sudden hearing loss within 5 days of the onset.

PATIENTS

A control group of 53 normal-hearing people was matched pairwise according to age and gender.

RESULTS

Fibrinogen levels were significantly higher in patients with sudden hearing loss (343 +/- 98 mg/dl) than in control subjects (303 +/- 69 mg/dl). Erythrocyte aggregation (27.3 +/- 5.6 a.u. versus 20.9 +/- 8.5 a.u.) and plasma viscosity (1.31 +/- 0.13 mPa/s versus 1.26 +/- 0.08 mPa/s) in patients with SHL were also significantly higher than in control subjects. No significant difference could be found in the parameters of clinical chemistry, hematology, and hemostasias investigated.

CONCLUSION

Because elevated plasma fibrinogen plays a major role in cardiovascular diseases such as myocardial infarction and stroke, it is possible that this plasma protein is also involved in the pathogenesis of sudden hearing loss of vascular origin. More research is still required to determine the value of measuring plasma fibrinogen levels in clinical practice and identifying hyperfibrinogenemia in sudden hearing loss.

Co-existence of tyrosine hydroxylase and calcitonin gene-related peptide in cochlear spiral modiolar artery of guinea pigs

The distribution of tyrosine hydroxylase (TH) and calcitonin gene-related peptide (CGRP) on the cochlear spiral modiolar artery (SMA) was investigated in the guinea pig. The SMA was dissected from the modiolus so that the entire length of the vessel and many of its branches could be observed. Immunohistochemical labeling and double immunofluorescence were employed to localize each compound and to determine whether the TH and CGRP co-exist in neurons of the SMA. Microscopic examination of whole vessel preparations revealed numerous TH- and CGRP-positive neural networks innervating the SMA and its branches. The labeled neurons showed distinct arborization, varicosities and overlap, and were of different diameters. Confocal immunofluorescence microscopy of double-labeled TH and CGRP neurons showed that a number of the TH- and CGRP-positive neurons were co-labeled. Thus, TH and CGRP partially co-exist within the neuronal innervation of SMA. These findings support a hypothesis that specific neuropeptide and adrenergic neurons regulate cochlear blood flow.

The effect of blood flow promoting drugs on cochlear blood flow, perilymphatic pO(2) and auditory function in the normal and noise-damaged hypoxic and ischemic guinea pig inner ear

The effect of blood flow promoting drugs, such as hydroxyethyl starch (HES) either of low or high molecular weight (HES 70, HES 200), pentoxifylline, ginkgo biloba, naftidrofuryl and betahistine, and various combinations of the drugs was studied in unexposed and noise-exposed (broad-band noise, bandwidth 1-12 kHz, 106 dB SPL, 30 min) guinea pigs. The results were compared without therapy and placebo (isotonic saline, NaCl). The cochlear blood flow (CoBF) and the partial pressure of oxygen in the perilymph (PL-pO(2)) were continuously and simultaneously recorded over a period of 210 min. In addition, cochlear microphonics (CMs), compound action potentials of the auditory nerve (CAPs) and auditory brain stem responses (ABRs) were registered. Noise-induced hearing loss (NIHL) paralleled a decrease of PL-pO(2). Both were found to occur before evidence of reduced CoBF. PL-pO(2) and CoBF declined progressively post-exposure, while CMs, CAPs and ABRs showed no further deterioration or signs of recovery up to 180 min after cessation of noise. Treatment started 60 min post-exposure, respectively after 90 min, without manipulation in unexposed animals, and was then studied for a further 120 min. In unexposed animals, CoBF increased significantly during infusion of HES 70, HES 200, pentoxifylline and betahistine. NaCl, ginkgo biloba and naftidrofuryl did not alter CoBF. PL-pO(2) decreased significantly during infusion of all administered drugs and combinations, except for NaCl. CMs, CAPs and ABRs remained constant, with the exception of increased ABRs after infusion of HES 70 and HES 200. In noise-exposed animals, a sustained therapeutic effect on cochlear ischemia was achieved only by HES 200 and pentoxifylline. HES 70, betahistine and ginkgo biloba compensated cochlear ischemia only during infusion; however, 30-60 min after termination of therapy, no significant difference of values for CoBF was observed compared to the untreated noise-exposed groups. NaCl and naftidrofuryl showed no effect on CoBF. None of the applied drugs had a sustained compensatory effect on cochlear hypoxia. CMs, CAPs and ABRs improved significantly after HES 70, HES 200 and betahistine, resulting in partial recovery of CMs, and partial (betahistine) or even full (HES 70 and HES 200) recovery of CAPs and ABRs. In contrast, NaCl, pentoxifylline, ginkgo biloba and naftidrofuryl had no therapeutic effect on NIHL.

The influence of noise on blood flow in the basilar artery (BA) - measurements with transcranial color-coded duplex sonography (TCCD)

Acoustic stimuli are being reported as a cause of changes in resistance in the basilar artery (BA). It was the aim of this study to investigate this effect under standardized conditions dependent upon the intensity of the evoking stimulus. Twenty healthy subjects with normal hearing (male/female 14/6; mean age 26.4 years) were exposed to 'pink noise' for periods of 2 min at 75, 85 and 95 dB(A). Parallel to this, the Doppler spectrum of the BA and both the Pourcelot resistance index and the Gosling pulsatility index were measured by means of transcranial color-coded Doppler sonography. In comparison with the base value (at rest) a significant increase in resistance was noted during noise exposure. The noise-induced resistance changes could be interpreted as a consequence of changes in activity of the various centers of the auditory pathway and cerebral function. Further animal experiments may prove the connection between BA blood flow and resistance and their changes depending on different acoustic stimuli or different hearing pathophysiology.

Changes in serum osmolarity influence the function of outer hair cells

Fast motility of outer hair cells (OHC) is thought to be based on a hydromechanic principle. In vitro, the function of OHCs can be disturbed by a change in the osmolarity of the culture medium. Whether changes in the serum osmolarity in vivo can also interfere with OHC motility has not been investigated as yet. Serum osmolarity of New Zealand White rabbits (n = 18) was elevated by a continuous infusion of glucose 40%, decreased by an infusion of aqua dest, or kept constant by an infusion of saline. OHC function was monitored using distortion products of otoacoustic emissions (DPOAE). Input output curves were established between 2 and 5 kHz (geometric mean of f2) with primaries of levels between 35 and 55 dB SPL. Cochlear perfusion was measured using a fluorescence microsphere method. Elevation of the serum osmolarity from 306 +/- 17 mosm/l to 365 +/- 23 induced a decrease of DPOAE between 3 and 12 dB SPL. Cochlear blood flow increased from 0.11 +/- 0.09 to 0.15 +/- 0.10 ml/min/g. When decreasing the serum osmolarity from 303 +/- 9 to 281 +/- 8 mosm/l, only slight changes of the DPOAE could be verified. As in the control group, cochlear perfusion was almost unchanged. In the control group, neither serum osmolarity nor DPOAE changed. Comparable to findings in vitro, increasing the serum osmolarity can lead to a disturbance of OHC function. In patients suffering from sudden hearing loss. dehydration due to physical or mental stress is often observed. This new and promising pathophysiological concept needs further clinical evaluation.

Betahistine increases vestibular blood flow

Betahistine is used for treatment of several vestibular disorders. Despite the accepted use of this histamine-like substance, its mechanism of action is not well understood. The purpose of this study was to assess the possibility that one of the activities of betahistine is increasing blood flow in the peripheral vestibular end organs. Using a novel surgical approach, we identified the posterior semicircular canal ampulla of guinea pigs and placed a laser Doppler probe in position to obtain blood flow measurements from the posterior semicircular canal ampulla. Blood pressure, heart rate, and vestibular blood flow were continuously recorded. Concentration-response curves were obtained for betahistine (2.5, 5, 7.5, and 10 mg/kg) and control-vehicle (0.15 mol/L NaCl) infusions. A separate group of subjects was pretreated with the competitive selective H3 agonist, thioperimide maleate, before betahistine treatment. Increases in vestibular blood flow and decreases in blood pressure were observed in response to betahistine infusions. Pretreatment with thioperamide maleate abolished these changes at low doses of betahistine and attenuated the responses at higher doses of betahistine. These results show that betahistine administration induces increases in vestibular blood flow. These findings support the potential use of betahistine for treatment of vestibular disorders, which may be caused by compromised circulation.

Changes in cochlear blood flow due to intra-arterial infusions of angiotensin II (3-8) (angiotensin IV) in guinea pigs

The effects of a newly discovered form of angiotensin, angiotensin IV (ANGIV), on cochlear blood flow (CBF) have been investigated utilizing the laser Doppler flowmetry (LDF) technique. Two specific questions were addressed: What are the effects of anterior inferior cerebellar artery infusions (AICA) of ANGIV on CBF and do angiotensin fragments other than ANGIV influence CBF in mature male and female guinea pigs. Infusions of ANGIV, and C-terminal shortened fragments were accomplished via micropipette into the AICA and changes in CBF were observed using LDF. The results demonstrated that 10 and 100 pmol/min doses of ANGIV increased CBF 22% and 75% (n = 6; P < 0.01) from baseline, respectively, with little change in mean arterial blood pressure (MAP). Pretreatment with the ANGIV antagonist divalanal-ANGIV (1 nmole/min) blocked increases in CBF due to infusions of 100 pmol/min of ANGIV. The infusion of the C-terminal shortened fragment ANGIV(1-5) and saline had no significant effect on either CBF or MAP. These results provide the evidence for a new subtype of the angiotensin receptor and indicate the likely role of circulating hormones in blood flow regulation in the inner ear.

The effect of prednisolone and non-steroidal anti-inflammatory agents on the normal and noise-damaged guinea pig inner ear

The effect of anti-inflammatory agents, such as the synthetic glucocorticoid prednisolone, diclofenac sodium, and histamine H1-receptor antagonist, was studied in unexposed and noise-exposed (broad-band noise, bandwidth 1-12 kHz, 106 dB SPL, 30 min) guinea pigs. The results were compared with the results obtained from no treatment and with isotonic saline (placebo) therapy. The cochlear blood flow (CoBF) and the partial oxygen pressure in the perilymph (PL-pO2) were continuously and simultaneously recorded over a period of 210 min. In addition, cochlear microphonics (CMs), compound action potentials of the auditory nerve (CAPs), and auditory brain stem responses (ABRs) were registered. Noise-induced hearing loss paralleled a decrease of PL-pO2. Both were found to occur before evidence of reduced CoBF. PL-pO2 and CoBF progressively declined post-exposure, while CMs, CAPs, and ABRs did not further deteriorate nor showed signs of recovery up to 180 min after cessation of noise. Treatment started 60 min post-exposure, or after 90 min without manipulation and was then further studied for 120 min. In the unexposed animals, diclofenac sodium and prednisolone induced a significant decline of PL-pO2, while CoBF, CMs, CAPs, and ABRs revealed no change. Isotonic saline did not influence the measured parameters. After infusion of the histamine H1-receptor antagonist, a significant decrease of CoBF together with blood pressure and CMs was observed, while PL-pO2, CAPs, and ABRs showed no change. In the noise-exposed animals, diclofenac sodium induced partial restoration of CM and CAP amplitudes and full restoration of ABRs. Following a high dose of prednisolone (25 mg), partial restoration of CMs and full restoration of CAPs and ABRs were registered. This effect was significantly less pronounced following a low dose of prednisolone (2.5 mg). Restoration of CMs, CAPs, and ABRs was immediate (i.e. 50 min after infusion) and remained stable for another 60 min until the end of the recording period. The histamine H1-receptor antagonist and isotonic saline did not influence CMs, CAPs, and ABRs. None of the applied drugs resulted in relief of progressive noise-induced cochlear hypoxia and post-traumatic ischemia. These findings indicate direct cellular effects of prednisolone and diclofenac sodium in the cochlea taking into account no blood flow and oxygenation. The possible mechanisms involved are discussed.

Guinea pig vestibular blood flow in response to calcitonin-gene related peptide

Little is known about the physiologic regulation of the vestibular end organ blood flow. The purpose of the current study was to examine posterior semicircular canal ampulla blood flow in addition to systemic factors during intravenous infusions of calcitonin-gene related peptide (CGRP), a factor involved in the tonic regulation of blood flow. Receptors for this factor are known to be available to the vascular supply of the vestibular organs. Local blood flow using laser Doppler flowmetry and systemic parameters were monitored during infusion of CGRP. CGRP antagonists and control vehicle. The results show relatively stable vestibular blood flow (VBF), concentration-dependent decreases in systemic blood pressure, and elevations in heart rate. Pretreatment with CGRP(8-37), a specific receptor antagonist, attenuated these responses to subsequent CGRP infusions. These findings suggest a rigid regulation of VBF in the presence of a systemically active vasodilator.

Clinical observations on acute low-tone sensorineural hearing loss. Survey and analysis of 137 patients

We retrospectively analyzed the clinical records of 137 patients who were treated at our clinic for acute low-tone sensorineural hearing loss of unknown cause over a period of 8 years. The analyses of the clinical records indicated the following clinical characteristics: female preponderance; peak incidence during the fourth decade of life; frequent accompanying tinnitus, sensation of ear fullness, and/ or autophony; suspicion of bilateral involvement; and association with autonomic imbalance. The hearing in most of the patients completely recovered, but some selected patients experienced fluctuating hearing loss or progression to Meniere's disease. Our results suggest that a subgroup of patients with severe initial hearing loss should be carefully followed up, although it is difficult to predict the outcome of this disorder.

Can hypotension episodes cause cochlear damage in young subjects?

In the absence of a satisfactory interpretation, sudden sensorineural hearing loss is often attributed either to infective phenomena or to organic-type circulatory defects. This latter pathogenesis inevitably comes to mind in elderly patients or in the presence of signs of circulatory dysfunction. Nevertheless, the not-infrequent observation of sudden hearing loss in young persons lacking factors predictive of short-term vascular impairment makes us suppose the existence of etiopathogenetic mechanisms of a functional nature. A survey of our cases, matched with a control group, revealed the presence of lower mean blood pressure levels in the group of young patients with 'idiopathic' sudden hearing loss. This finding supports the hypothesis that a condition of haemodynamic imbalance linked to hypotension plays a role in the genesis of cochlear damage in young subjects. Such a mechanism would bear important therapeutic implications: should it be responsible for the damage in at least some cases, vasoactive drugs with a vasodilatative action could have adverse effects on the possibility of recovery.

The role of hypotension in the pathogenesis of sudden hearing loss

The generic term 'sudden hearing loss' indicates the lack of knowledge about the etiology and pathogenesis of this phenomenon. In most cases it would seem feasible to consider infections or organic circulatory defects, but there are cases, generally affecting young subjects in whom the damage is often reversible, in which a functional origin is possible. We therefore investigated the possible effect of systemic arterial pressure in a retrospective study in a group of 36 patients aged not more than 40 years, treated for sudden hearing loss, comparing the mean values of their arterial pressure with those of a control group of 25 subjects, of similar age, admitted for other disorders. The significantly lower mean values of arterial pressure in the group affected by sudden hearing loss and the easier reversibility of the damage in these patients suggests that, at least in some cases, the cochlear damage may be caused by a perfusion deficit due to the combined effect of hypotension and imperfect vasomotor regulation.

The vasculature of the peripheral portion of the human eighth cranial nerve

The vasculature of the peripheral portion of the human eighth cranial nerve (VIIIN) was investigated by light and transmission electron microscopy. Arterioles and venules running longitudinally around the VIIIN formed the extrinsic vascular system. The anatomical relationship between these extrinsic vessels and the VIIIN sheath was similar to that between blood vessels on the surface of the brain and the pia mater. In the endoneurium, postcapillary venules and large capillaries were sparsely distributed and longitudinally arranged, and these microvessels formed the intrinsic microvascular system, which was supported by the extrinsic vascular system via anastomosing vessels. The ultrastructural features of the internal auditory artery and its main branches were the same as those of other intracranial arteries. Ultrastructural study also revealed myo-endothelial junctions in anastomosing arterioles, and endothelio-pericytic junctions in extrinsic and anastomosing venules. Microvascular endothelial cells were connected by tight junctions in both the vestibular ganglion and the rest of the VIIIN. These features of the vasculature were considered to be effective for maintenance of the endoneurial fluid and regulation of the circulation in the peripheral portion of the human VIIIN.

Naloxone blockade of (-)pentazocine-induced changes in auditory function

OBJECTIVE

In a previous report, we found that intravenous (i.v.) (-)pentazocine improved auditory sensitivity and significantly altered compound action potential (CAP) amplitudes. Its sigma (sigma)-receptor-selective optical isomer (+)pentazocine administered at the same dose was without effect, suggesting that the observed auditory neural effects might be mediated by an opioid receptor. To directly test this hypothesis, in the present investigation we attempted to antagonize the auditory neural effects of (-)pentazocine using the pure, nonspecific drug antagonist naloxone.

DESIGN

In 25 normal-hearing, male, pigmented chinchillas, amplitude and latency changes in the click-evoked auditory nerve CAP (N1) and cochlear microphonic (CM) were tracked at six stimulus intensities during a baseline period and after the postbaseline administration of the opioid drug agonist (-)pentazocine (16 mg/kg; i.v.). In separate groups of chinchillas, (-)pentazocine was given alone or administered in combination with the standard opioid receptor antagonist naloxone administered at two doses.

RESULTS

Robust changes in CAP amplitudes after (-)pentazocine occurred in the absence of measurable alterations in CAP response latencies, CM amplitudes, or blood chemistries and were significantly antagonized when naloxone (5 mg/kg) was added to the i.v. infusion.

CONCLUSIONS

The observed blockade clearly indicates that the agonist effects of (-)pentazocine are opioid receptor-mediated and suggests a connection between opioid receptors and auditory neural function. Mechanisms of action and the connection between an opioid modulation of auditory function and stress, hyperacusis, and tinnitus are discussed.

Capsaicin-induced release of substance P increases cochlear blood flow in the guinea pig

Physiological evidence from several studies suggests that endogenous vasoactive peptides, such as substance P (SP), and their respective receptor populations may participate in the mechanisms that govern the autoregulatory capacity of the cochlear vascular system. However, these studies do not provide evidence regarding the origin or mechanism of action of SP. Capsaicin sensitivity has been used as a marker for sensory neurons, and the release of SP following capsaicin treatment suggests a sensory transmitter role for SP. The present investigation examines the relationship between the capsaicin-sensitive sensory neurons and SP in the regulation of cochlear blood flow (CBF). In 75 pigmented guinea pigs, the cochlea was surgically exposed and a laser Doppler flowmeter probe placed on the bony surface of the first turn to monitor CBF. Capsaicin solutions (2 microliters, 0.01%, 0.001% and 0.0001%) applied to the round-window membrane (RWM) resulted in a dose-related CBF increase, without change in the systemic blood pressure. This effect could be inhibited by application of a specific SP receptor antagonist, [D-Pro2,D-Trp7,9]-SP, after which none of the capsaicin concentrations used induced a change in CBF. Moreover, after RWM application of 50 nmol/2 microliters of SP there was a significant increase in CBF. No CBF change was observed with the lower concentrations of 10 nmol SP or 100 pmol SP. These results indicate a role of SP in CBF regulation and give indirect evidence that SP is released from capsaicin-sensitive primary sensory neurons.

Atrial natriuretic peptide participates in the regulation of vestibular blood flow

Atrial natriuretic peptide (ANP) is a cardiac hormone which exerts natriuretic, diuretic and vasorelaxant effects. Among the many organs and vascular beds populated with ANP receptors (Genest and Cantin, 1988) are the vestibular and auditory organs of the inner ear (Lamprecht and Meyer zum Gottesberge, 1988). The purpose of the current study was to assess the potential influence of ANP on vestibular blood flow in the guinea pig. The inner ear was exposed with a posterior-lateral approach medially through the mastoid cortex. The laser Doppler probe was placed adjacent to the ampulla of the posterior semicircular canal. Baseline measurements of mean blood pressure (BP), heart rate (HR) and vestibular blood flow were established. ANP dissolved in physiologic saline was infused intravenously at concentrations of 15, 150 or 300 ng/kg/min at 10 microliters/min for 30 min. Measurements were recorded during the infusion and for a recovery period of 65 min. The control group was treated equivalently and infused with 0.15 M NaCl. Baseline BP and HR for all animals were 40.1 +/- 6.67 and 190 +/- 15.7, respectively. BP, HR and vestibular blood flow remained stable during the baseline, control and recovery conditions of saline infused subjects. Infusion of ANP (15 ng/kg/min) induced a mild elevation of BP followed by a small decrease in pressure during the post-infusion period. Vestibular blood flow showed a decrease to approximately 20% below baseline during infusion and stabilized at this level during the recovery period. Infusion of higher concentrations of ANP (150 and 300 ng/kg/min) induced a similar pattern of BP change in a dose-dependent manner. Vestibular blood flow, however, evidenced significant elevations during the post-infusion periods for both concentrations. These increases (22% and 26%, for 150 and 300 ng/kg/min, respectively) were significantly different from vestibular blood flow changes in the saline and low dose groups. The HR remained stable for baseline, infusion and recovery periods for each of the ANP infused subjects. This investigation demonstrates the systemic and local effects of ANP suggest a possible role for ANP in local regulation of vestibular blood flow.

Effect of topical application of nitroglycerin on cochlear blood flow

PURPOSE

To investigate whether topical application of the vasodilator nitroglycerin would increase cochlear blood flow without adversely affecting inner ear function.

MATERIALS AND METHODS

The effect of topical application of nitroglycerin to the round window membrane on cochlear blood flow was measured in 33 guinea pigs with a laser Doppler flowmeter. Endocochlear potential, as an indicator of inner ear function, was recorded by a glass microelectrode inserted through the round window membrane in a second series of 27 guinea pigs. Blood pressure was also monitored in both experiments.

RESULTS

Low doses (0.0001 to 1 microgram) of nitroglycerin induced an increase in cochlear blood flow with no change in blood pressure. The cochlear blood flow was maximally increased by approximately 50%. A high dose (50 micrograms) of nitroglycerin induced a significant decrease in blood pressure but did not significantly affect endocochlear potential.

CONCLUSIONS

Topical application of nitroglycerin may be useful in increasing cochlear blood flow in various inner ear diseases.

Neuronal regulation of cochlear blood flow in the guinea-pig

1. Previous studies have shown that electrical stimulation (ES) of the guinea-pig cochlea causes a neurally mediated increase in cochlear blood flow (CBF). It is known that the centrifugal neuronal input to the cochlea comes through the perivascular sympathetic plexus from the cervical sympathetic chain and along the vestibular nerve (VN) from the periolivary area of the brainstem. Both of these neuronal systems are distributed topographically in the cochlea. 2. In order to study the neural origins of ES-evoked CBF increase, laser Doppler flowmetry was used to test the following hypotheses. (a) The response is regional, that is, limited to the area of the cochlea stimulated. To test this we performed differential ES of the cochlear turns. CBF was measured from either the third or the first turn. (b) The response is mediated via autonomic receptors within the cochlea. To study this, we applied atropine, succinylcholine and idazoxan locally to the cochlea. (c) The response is influenced by neuronal input via the sympathetic cervical chain (SC) and components of the VN. We stimulated and sectioned the SC, and sectioned the VN, to test this hypothesis. 3. We observed that the CBF response was topographically restricted to the stimulated region. Locally applied muscarinic or nicotinic antagonists (atropine and succinylcholine respectively) did not affect the response. However, local idazoxan (an alpha 2-blocker) eliminated the response. Locally applied adrenaline and SC stimulation modified the dynamic range of the response. SC sectioning enhanced the responsiveness of the cochlear vasculature to ES. The VN section caused a temporary decrease in CBF and elimination of the ES-evoked CBF response. 4. We conclude that the release of dilating agents is topographical with respect to ES current flow, the ES-evoked CBF increase is peripherally mediated via alpha 2-receptors, and the response is influenced by input via the SC. The elimination of the response by VN sectioning proximal to the brainstem indicated that fibres of the VN mediate the CBF increase during direct cochlear ES. The data suggest that these fibres may be the efferent limb of a neural loop involved with the regulation of CBF. Such a system could provide a mechanism for the rapid increase in CBF with organ stress.

Alterations of auditory nerve responses by hypoxia in normal and hydropic ears of awake guinea pigs

Total interruption of blood or oxygen supply to the inner ear produces very rapid and drastic effects, whereas moderate decreases can be well tolerated by normal ears. In experimental endolymphatic hydrops some moderate alterations of cochlear vasculature have been described which might affect cochlear adaptation to moderate blood or oxygen deficiencies. In order to test this hypothesis an hypoxia at 5% oxygen was imposed for 30 min in normal and hydropic ears of awake guinea pigs and cochlear function was monitored with an electrode at the round window. Electrophysiological recordings used measures of compound action potential (CAP) amplitudes evoked by high-intensity tones, and of CAP thresholds. In normal ears hypoxia induced threshold elevations at all frequencies and decreases of CAP amplitude only for high frequencies. Hydropic ears presented similar or smaller threshold elevations but showed CAP amplitude decreases extending to lower frequencies and showed a much slower recovery both for CAP thresholds and amplitudes. The data indicate that hypoxia had different effects on auditory nerve responses evoked by high versus low intensity tones. The deleterious effects of hypoxia were increased in hydropic ears. Hypoxia-induced alterations were measured twice at one week intervals during which an anti-ischemic drug was administered to the animals; some beneficial effects of the drug treatment were observed on normal but not on hydropic ears.