Effect of isobaric oxygen versus hyperbaric oxygen on the normal and noise-damaged hypoxic and ischemic guinea pig inner ear

Is repetitive systemic corticosteroid therapy effective for idiopathic sudden sensorineural hearing loss? a retrospective study

Introduction

Some idiopathic sudden sensorineural hearing loss (ISSHL) cases experience repetitive systemic corticosteroid treatment, but studies focusing on repetitive systemic corticosteroid administration have not been reported. Thus, we investigated the clinical characteristics and usefulness of repetitive systemic corticosteroid treatment in ISSHL cases.

Methods

We reviewed the medical records of 103 patients who received corticosteroids only in our hospital (single-treatment group), and 46 patients who presented at our hospital after receiving corticosteroids in a nearby clinic and were subsequently treated with corticosteroids again in our hospital (repetitive-treatment group). Clinical backgrounds, hearing thresholds, and hearing prognosis were assessed.

Results

The final hearing outcomes were not different between the two groups. Further, in the repetitive-treatment group, statistical differences were found between the good and poor prognosis groups in the number of days to start corticosteroid administration (p = 0.03), the dose of corticosteroid (p = 0.02), and the duration of corticosteroid administration (p = 0.02) at the previous facility. Multivariate analysis revealed a significant difference in the dose of corticosteroids administered by the previous clinic (p = 0.004).

Conclusion

The repetitive systemic corticosteroid administration might play a supplementary role in hearing improvement, and initial sufficient corticosteroid administration would lead to good hearing outcomes in an early phase of ISSHL.

Prevention and Treatment of Life-Threatening COVID-19 May Be Possible with Oxygen Treatment

Most SARS CoV-2 infections probably occur unnoticed or cause only cause a mild common cold that does not require medical intervention. A significant proportion of more severe cases is characterized by early neurological symptoms such as headache, fatigue, and impaired consciousness, including respiratory distress. These symptoms suggest hypoxia, specifically affecting the brain. The condition is best explained by primary replication of the virus in the nasal respiratory and/or the olfactory epithelia, followed by an invasion of the virus into the central nervous system, including the respiratory centers, either along a transneural route, through disruption of the blood-brain barrier, or both. In patients, presenting with early dyspnea, the primary goal of therapy should be the reversal of brain hypoxia as efficiently as possible. The first approach should be intermittent treatment with 100% oxygen using a tight oronasal mask or a hood. If this does not help within a few hours, an enclosure is needed to increase the ambient pressure. This management approach is well established in the hypoxia-related diseases in diving and aerospace medicine and preserves the patient’s spontaneous breathing. Preliminary research evidence indicates that even a small elevation of the ambient pressure might be lifesaving. Other neurological symptoms, presenting particularly in long COVID-19, suggest imbalance of the autonomous nervous system, i.e., dysautonomia. These patients could benefit from vagal nerve stimulation.

Intratympanic steroid injection versus hyperbaric oxygen therapy in refractory sudden sensorineural hearing loss: a meta-analysis

OBJECTIVE

The present meta-analysis aims to compare the efficacy of intratympanic steroid (ITS) injection and hyperbaric oxygen (HBO) therapy as salvage treatments for refractory sudden sensorineural hearing loss (SSNHL).

DATA SOURCES

Comprehensive searches were performed in PubMed, EMBASE and the Cochrane Library from the date of the database inception to June 2020. All studies reporting the use of salvage ITS and HBO treatments in refractory SSNHL patients were included. Subsequently, the full texts of the eligible studies were evaluated.

METHODS

The quality and bias of the studies were assessed using the Newcastle-Ottawa Scale and Cochrane's risk of bias tools for nonrandomized and randomized studies, respectively. The data were analyzed using Comprehensive Meta-Analysis software (Version 3; Biostat, Englewood, NJ).

RESULTS

Three hundred and fourteen subjects in 3 observational studies and 1 randomized controlled trial met our inclusion criteria. The pooled results demonstrated that there were no significant differences in the mean posttreatment hearing gain between the ITS and HBO groups. The changes in word discrimination and hearing gain at 250, 500, 1000, 2000, 4000 and 8000 Hz were also comparable between the two salvage treatment groups.

CONCLUSIONS

The pooled results demonstrated that there were no significant differences in hearing improvements between salvage ITS injection and salvage HBO therapy after failed primary systemic steroid treatment in patients with SSNHL. However, spontaneous recovery could bias the treatment outcomes, and these results should be interpreted with caution. Clinicians may choose these salvage treatments according to personal experience and treatment availability. In cases in which specialized HBO facilities are difficult to access, salvage ITS injection can be provided with comparable responses.

Association between Vitamin D Supplements, Oxidative Stress Biomarkers, and Hyperbaric Therapy in Patients with Sudden Sensorineural Hearing Loss

The effect of vitamin D supplementation to patients with sudden sensorineural hearing loss (SSNHL), treated with hyperbaric oxygen (HBO) therapy, on the markers of the oxidant-antioxidant equilibrium was investigated. Patients were divided into two groups: those who did and did not receive vitamin D (cholecalciferol at 4000 IU/24 h). Concentrations of the following compounds, thiobarbituric acid reactive substances (TBARS), malondialdehyde (MDA), conjugated dienes (CD) in plasma and erythrocytes and activities of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) in erythrocytes, were determined. Haemoglobin (HGB) and haematocrit (HCT) were measured. Blood for analyses was collected from the basilic vein at three time points: before the first HBO procedure, up to 5 min after the first procedure, and after 14 procedures. No statistically significant differences in parameters tested were found between patients who did and did not receive vitamin D. In patients without supplementation, an increase of 53.2% (P ≤ 0.05) in erythrocyte TBARS was observed after the first HBO treatment. In patients receiving vitamin D, a reduction of 27.6% (P ≤ 0.05) was observed in erythrocyte MDA after 14 HBO treatments vs. that after the first treatment. In both groups, a decrease of 33.3% in plasma CD was observed after 14 treatments vs. that after the first treatment (P ≤ 0.05 and P ≤ 0.01, respectively). No statistically significant changes were observed in the erythrocyte SOD, GPx, and CAT activities and in HCT. A reduction of HGB concentration of 10.9% (P ≤ 0.05) was demonstrated in nonsupplemented patients after 14 treatments compared with baseline. The results confirm that the effect of HBO therapy on oxidative stress markers is inconclusive and complex. Repeated HBO procedures can induce adaptive changes which protect against disruption of the oxidant-antioxidant equilibrium. It is possible that vitamin D supplementation inhibits the process of lipid peroxidation in erythrocytes.

Comparison of Therapeutic Results with/without Additional Hyperbaric Oxygen Therapy in Idiopathic Sudden Sensorineural Hearing Loss: A Randomized Prospective Study

OBJECTIVE

To assess the efficacy of the combination of hyperbaric oxygen (HBO) and pharmacological treatment in patients with idiopathic sudden sensorineural hearing loss (ISSNHL) and define patients amenable for HBO therapy.

METHODS

Prospective, randomized, trial involving 136 cases with unilateral ISSNHL that were randomly divided into 2 groups: the pharmacological treatment (P) group and HBO + pharmacological treatment (HBO+P) group, which received additional HBO for 14 days besides the pharmacological treatments. Pure tone audiometry gain larger than 15 dBHL was defined as success, and the success rate of each group was calculated.

RESULTS

The overall success rate of the HBO+P group and the P group is 60.6% (40/66) and 42.9% (30/70), respectively (p < 0.05). Furthermore, patients with mild-moderate baseline hearing loss, aged ≤50 years, receiving treatment in ≤14 days, or without accompanied dizziness/vertigo in the HBO+P group had higher success rate than the P group (p < 0.05).

CONCLUSIONS

HBO combined with pharmacological treatments leads to better hearing recovery than pharmacological treatments alone.

Use of Gases to Treat Cochlear Conditions

Although the cochlear vascular supply (stria vascularis) is designed to block to certain compounds and molecules, it must enable gas exchange to survive. The inner ear capillaries must deliver oxygen and remove carbon dioxide for the cochlea to function. These gases diffuse through tissues across a concentration gradient to reach the desired target. Tight junctions or the endothelial basement membrane do not impede them. Therefore, gases that can diffuse into the inner ear are attractive as therapeutic agents. The two gases most often used in this way are oxygen and hydrogen, although carbon dioxide, ozone, and argon have also been investigated. Typically, oxygen is delivered as hyperbaric oxygen (HBO) (oxygen at pressure higher than atmospheric) to provide increased oxygen levels to the inner ear. This not only relieves hypoxia, but also has anti-inflammatory and other biochemical effects. HBO is used clinically to treat idiopathic sudden sensorineural hearing loss, and both animal and human studies suggest it may also assist recovery after acute acoustic trauma. Laboratory studies suggest hydrogen works as a free radical scavenger and reduces the strong oxidants hydroxyl radicals and peroxynitrite. It also has anti-apoptotic effects. Because of its anti-oxidant and anti-inflammatory effects, it has been studied as a treatment for ototoxicity and shows benefit in an animal model of cisplatinum toxicity. Gas diffusion offers an effective way to provide therapy to the inner ear, particularly since some gases (oxygen, hydrogen, carbon dioxide, ozone, argon) have important therapeutic effects for minimizing cochlear damage.

Comparison of Different Treatment Methods for Idiopathic Sudden Sensorineural Hearing Loss

Objective

To evaluate the effectiveness of different therapies for idiopathic sudden sensorineural hearing loss and prognostic factors, and determine the most successful treatment according to the audiogram type and time from onset to treatment.

Methods

A total of 90 cases from February 2009 to January 2015 were classified under Group I oral treatment (methylprednisolone, acyclovir, betahistine-dihydrochloride, and vitamin B12); Group II oral treatment + intratympanic steroids (ITS); Group III oral treatment + hyperbaric oxygen; and Group IV only ITS. A pure tone average (PTA) improvement of less than 10 dB was assessed as "no improvement," a PTA of 10 dB or more or a 10% or more increase in the speech discrimination score (SDS) as "partial improvement," and a hearing threshold within 10 dB and SDS within 5%-10% of the unaffected ear as "full improvement."

Results

Overall, 32.2% patients showed full and 28.9% showed partial improvement, whereas 38.9% showed no improvement. There was no significant difference in terms of mean hearing gain between the different treatment methods. As the degree of hearing loss and time from onset to treatment increased, improvement worsened (p<0.05). Descending audiogram had lower mean hearing gains compared to other groups (p=0.014). There was no significant effect of age, sex, tinnitus and/or vertigo, and systemic disease on treatment success (p>0.05).

Conclusion

The most important factors affecting prognosis were the time from onset to treatment, hearing loss severity, and audiogram type. Only ITS avoided side effects and reduced hospitalization. ITS in the first two weeks, followed by hyperbaric oxygen were considered as the treatment priority.

The effectiveness of hyperbaric oxygen in patients with idiopathic sudden sensorineural hearing loss: a systematic review

Objective

To evaluate the effectiveness of hyperbaric oxygen in the treatment of patients with idiopathic sudden sensorineural hearing loss (ISSHL).

Data sources

An Embase, MEDLINE and Cochrane search were utilised to identify various clinical trials on the treatment of ISSHL. Studies that were published between 2002 and 2018 and written in the English, Dutch or German language were included. Search terms included synonyms for idiopathic sudden hearing loss.

Data synthesis

A total of 16 articles were identified regarding hyperbaric oxygen therapy. All patients were evaluated with pure-tone audiometry. A major part of the cases presented with unilateral hearing loss(bilateral hearing loss less than 5%). In several studies, the average of the mean hearing gain at five contiguous frequencies was significantly higher in the hyperbaric oxygen (HBO) therapy and systemic steroid (SS) group in patients with severe or profound hearing impairment. They recorded a significant treatment effect (p = 0.005) of HBO + SS therapy on patients with an initial hearing loss of ≥ 81 dB.

Conclusions

On the whole group of ISSHL patients, no significant difference was demonstrated between the intervention and control group. However, in severe or profound hearing-impaired ISSHL patients, significant benefit was observed in the intervention group. These results likely indicate that adding HBO to steroid therapies might be of benefit in cases of severe and profound hearing impairment.

Effect of hyperbaric oxygen on BDNF-release and neuroprotection: Investigations with human mesenchymal stem cells and genetically modified NIH3T3 fibroblasts as putative cell therapeutics

Hyperbaric oxygen therapy (HBOT) is a noninvasive widely applied treatment that increases the oxygen pressure in tissues. In cochlear implant (CI) research, intracochlear application of neurotrophic factors (NTFs) is able to improve survival of spiral ganglion neurons (SGN) after deafness. Cell-based delivery of NTFs such as brain-derived neurotrophic factor (BDNF) may be realized by cell-coating of the surface of the CI electrode. Human mesenchymal stem cells (MSC) secrete a variety of different neurotrophic factors and may be used for the development of a biohybrid electrode in order to release endogenously-derived neuroprotective factors for the protection of residual SGN and for a guided outgrowth of dendrites in the direction of the CI electrode. HBOT could be used to influence cell behaviour after transplantation to the inner ear. The aim of this study was to investigate the effect of HBOT on the proliferation, BDNF-release and secretion of neuroprotective factors. Thus, model cells (an immortalized fibroblast cell line (NIH3T3)–native and genetically modified) and MSCs were repeatedly (3 x – 10 x) exposed to 100% oxygen at different pressures. The effects of HBO on cell proliferation were investigated in relation to normoxic and normobaric conditions (NOR). Moreover, the neuroprotective and neuroregenerative effects of HBO-treated cells were analysed by cultivation of SGN in conditioned medium. Both, the genetically modified NIH3T3/BDNF and native NIH3T3 fibroblasts, showed a highly significant increased proliferation after five days of HBOT in comparison to normoxic controls. By contrast, the number of MSCs was decreased in MSCs treated with 2.0 bar of HBO. Treating SGN cultures with supernatants of fibroblasts and MSCs significantly increased the survival rate of SGN. HBO treatment did not influence (increase / reduce) this effect. Secretome analysis showed that HBO treatment altered the protein expression pattern in MSCs.

Concurrent hyperbaric oxygen therapy and intratympanic steroid application as salvage therapy after severe sudden sensorineural hearing loss

Concurrent hyperbaric oxygen therapy (HBOT) and intratympanic steroid application (ITS) are beneficial as salvage therapy for therapy‐refractory sudden sensorineural hearing loss (SSNHL). The findings encourage further research on the treatment of noise‐induced and idiopathic SSNHL with concurrent use of HBOT and ITS respecting also patients with long‐term or therapy‐refractory SSNHL.

Comparison of two different steroid treatments with hyperbaric oxygen for idiopathic sudden sensorineural hearing loss

The purpose of the study was to assess the efficacy of the association of intratympanic (IT) steroid and hyperbaric oxygen (HBO) therapy in patients presenting with idiopathic sudden sensorineural hearing loss (ISSNHL), and to compare this protocol with another consisting of intravenous (IV) steroid administration and HBO therapy. A total of 80 patients diagnosed with ISSNHL were included in this prospective trial. Patients were divided into three categories: a mild-to-moderate ISSNHL group with a pure-tone average (PTA) ≤60 decibels (dB), a severe ISSNHL group with a PTA of 60-80 dB, and a profound ISSNHL group with a PTA ≥81 dB. The first protocol consisted of 20 sessions of HBO therapy together with IV methylprednisolone 1 mg/kg body weight and a 10 mg taper every 3 days for 10 days. The second protocol consisted of HBO therapy for 20 sessions, together with an IT injection of dexamethasone at a dose of 4 mg/mL, 0.5-0.7 mL once a day for 7 consecutive days, performed 3 h before the HBO therapy. In the mild-to-moderate ISSNHL patients, the mean hearing gain and successful treatment rate was 19 (0-27) dB and 78.9 %, respectively in the IT + HBO treatment group, and 18 (3-44) dB and 70.5 % in the IV + HBO therapy group. In the severe ISSNHL patients, the mean hearing gain and successful treatment rate was 33 (1-54) dB and 81.8 %, respectively in the IT + HBO treatment group and 33.5 (7-57) dB and 58.2 % in the IV + HBO group. In the profound ISSNHL patients, the mean hearing gain and successful treatment rate was 36 (4-69) dB and 40 %, respectively in the IT + HBO therapy group, and 39.5 (0-92) dB and 72.7 % in the IV + HBO treatment group. The results demonstrated that patients with severe hearing loss success rate was superior in the group submitted to IT + HBO treatment, conversely IV + HBO therapy may be benefit for patients with profound hearing loss. Nevertheless, these clinical results were not statistically significant.

Hyperbaric oxygen upregulates cochlear constitutive nitric oxide synthase

Background

Hyperbaric oxygen therapy (HBOT) is a known adjuvant for treating ischemia-related inner ear diseases. Controversies still exist in the role of HBOT in cochlear diseases. Few studies to date have investigated the cellular changes that occur in inner ears after HBOT. Nitric oxide, which is synthesized by nitric oxide synthase (NOS), is an important signaling molecule in cochlear physiology and pathology. Here we investigated the effects of hyperbaric oxygen on eardrum morphology, cochlear function and expression of NOS isoforms in cochlear substructures after repetitive HBOT in guinea pigs.

Results

Minor changes in the eardrum were observed after repetitive HBOT, which did not result in a significant hearing threshold shift by tone burst auditory brainstem responses. A differential effect of HBOT on the expression of NOS isoforms was identified. Upregulation of constitutive NOS (nNOS and eNOS) was found in the substructures of the cochlea after HBOT, but inducible NOS was not found in normal or HBOT animals, as shown by immunohistochemistry. There was no obvious DNA fragmentation present in this HBOT animal model.

Conclusions

The present evidence indicates that the customary HBOT protocol may increase constitutive NOS expression but such upregulation did not cause cell death in the treated cochlea. The cochlear morphology and auditory function are consequently not changed through the protocol.

Factors influencing the outcome of idiopathic sudden sensorineural hearing loss treated with hyperbaric oxygen therapy

Idiopathic sudden sensorineural hearing loss (ISSNHL) is an otologic emergency with an incidence of about 5-20 per 100,000 of the population per year. There is no universally accepted standard protocol for the treatment of patients with ISSNHL. Hyperbaric oxygen therapy (HBOT), was first reported to improve the outcome following acute inner ear disorders during the late 1960s by both French and German authors. The increase in perilymph oxygenation produced by HBOT provides logical basis for the use of this treatment modality in ISSNHL. We reviewed the records of 97 cases that received HBOT for SSNHL to identify the factors that may affect the treatment outcomes. The effects of age, gender, affected ear, status of the contralateral ear, symptoms associated with hearing loss, presence of a cardiovascular disease, dyslipidemia, history of diabetes mellitus, seasonal factor, smoking, degree of hearing loss, audiogram type, medical treatments provided prior to HBOT, onset time, and number of HBOT sessions were evaluated. The mean hearing gain in all cases after the HBOT was 29.5 dB. The gains were statistically significant in the following cases: early onset of HBOT (p = 0.016), higher number of HBOT sessions (p < 0.01), steroid usage (p = 0.009), low frequency-ascending and total audiogram configuration (p < 0.01) and profound hearing loss (p = 0.011). The success rate was significantly lower in cases with high frequency-descending audiogram configuration (p < 0.001). The most important factor affected the prognosis favorably was found as steroid therapy. This retrospective study and our clinical experience suggest that HBOT has beneficial effects when administered in the early phase of the disease together with steroids. HBOT is a safe practice when used properly by an experienced hyperbaric team. In the treatment of ISSNHL, 20 sessions of HBOT at 2.5 ATA can be tolerated well besides some minor side effects. HBOT should be considered for the cases especially with total or profound hearing loss.

[Inner ear damage due to leisure and broadband noise. An experimental study on initial and permanent functional and morphological damage]

The initial and permanent effects of leisure noise (toy pistols, rock music) compared to broadband noise were examined in 68 guinea pigs. Auditory threshold shifts at 1.5, 2, 3, 4, 6, 8, 12 und 16 kHz were registered before and immediately after exposure as well as on days 1, 2, 3, 5,7 and 21 post-exposure using the auditory brain stem response (ABR) technique. In order to examine cilia and hair cell damage in eight cochlear frequency regions (<0,4 kHz, 0,4-0,8 kHz, 0,8-1.5 kHz, 1.5-3 kHz, 3-5 kHz, 5-11.5 kHz, 11.5-26 kHz und >26 kHz), cytocochleograms were performed immediately after exposure and on days 1, 7 and 21.Frequency dependent functional or morphological damage was found which depended on the type of trauma tested. All results were highly significant ( P<0.001). The results show that partial recovery of hearing occurred within 3 days of acute acoustic trauma induced by toy pistols and within 1 day after exposure to rock music or broadband noise. There was no further recovery of hearing within the following 18 and 20 days, respectively. Furthermore, permanent threshold shifts after exposure to rock music or broadband noise were not associated with cilia and/or hair cell damage.

Should hyperbaric oxygen be added to treatment in idiopathic sudden sensorineural hearing loss?

At present, there is still no agreement about the therapy of idiopathic sudden sensorineural hearing loss (ISSHL). Hyperbaric oxygen (HBO) is used in the therapy of ISSHL to increase the partial oxygen pressure and the oxygen concentration in the inner ear and also to improve the blood profile and the microcirculation. In our prospective randomized study, we aimed to investigate the therapeutic effects of HBO therapy in the 1st 2 weeks of the onset of ISSHL. Fifty-one hospitalized patients with confirmed ISSHL who had received therapy were grouped randomly into two groups. Twenty-one patients (group I) received steroids, plasma expander dextrans (rheomacrodex), diazepam, pentoxiphylline and salt restriction, and 30 patients (group II) received the same basic treatment with the addition of HBO therapy. Audiological assessments of the patients were performed before and after the treatment. The hearing gains at frequencies of 250, 500, 1,000, 2,000 and 4,000 Hz were calculated separately. The level of hearing loss at the five frequencies was assessed in three groups at the first visit: equal or below 60 dB, between 61-80 dB and equal or above 81 dB. The average of the mean hearing gains at the five frequencies of the patients according to the age groups in group II was compared. The mean hearing gains at the five frequencies were compared between the two groups, and statistically significant improvement was detected in all the frequencies except at 2,000 Hz in group II. The mean hearing gains in group II were found to be significantly high in patients with initial hearing levels up to 60 dB in comparison to patients with initial hearing levels below 60 dB. When age groups and mean hearing gains were compared, there was no statistically significant difference in group I. In group II, the mean hearing gains were 39.1+/-18.3 dB in patients younger than 50 years and 22.7+/-11.3 dB in patients older than 50 years ( P=0.044). In conclusion, the addition of HBO therapy to conventional treatment modalities significantly improves the outcome of ISSHL, especially at the frequencies of 250, 500, 1,000 and 4,000 Hz and in hearing loss of above 61 dB. Furthermore, HBO therapy was found to be more effective in patients younger than 50 years.

Sudden Hypoacusis Treated with Hyperbaric Oxygen Therapy: A Controlled Study

The term sudden hypoacusis describes a hearing loss of rapid onset and unknown origin that can progress to severe deafness. Of the many therapeutic protocols that have been proposed for treating sudden hypoacusis, hyperbaric oxygen therapy (HOT) plays a leading role. We studied 50 patients who had been referred to our ENT unit within 48 hours of the onset of sudden hypoacusis. We randomly assigned 30 of these patients to undergo once-daily administration of HOT for 10 days; the other 20 patients were treated for 10 days with an intravenous vasodilator. Response to therapy in all patients was evaluated by calculating the mean hearing threshold at frequencies between 500 and 4, 000 Hz and by assessing liminal tonal audiometry results recorded at baseline and 10 days after the cessation of treatment. These results, plus the findings of other audiologic and otoneurologic examinations, revealed that the patients in the HOT group experienced a significantly greater response to treatment than did those in the vasodilator group, regardless of age and sex variables. Significantly more patients in the HOT group experienced a good or significant response. In both groups, patients with pantonal hypoacusis responded significantly better than did those with a milder condition. Based on our findings, coupled with the fact that oxygen therapy is well tolerated and produces no side effects, we conclude that HOT should be considered the preferred treatment for patients with sudden hypoacusis.

Treatment of acoustic trauma

The aim of this study is to determine the actual efficiency of the present medical treatments of acoustic trauma. Untreated and treated groups of guinea pigs are exposed to a traumatic noise exposure, inducing up to 60-dB threshold shift. The recovery is followed for up to 14 days. The first results indicate that in some animals the recovery of the threshold shifts are complete despite the fact that significant areas of hair cells are damaged. The most widely used medical treatments of acoustic trauma (oxygenotherapy, carbogen, hyperbaric oxygen, vasoactive agents, and corticotherapy) have been tested. Preliminary results indicate that pure oxygen and carbogen seem ineffective, hyperbaric oxygen used alone is dangerous, and corticoids and combined corticoid/hyperbaric oxygen seem to improve functional and morphological recovery. This study will be taken as a reference to look for new treatments that will be applied directly to the cochlea by means of an implanted osmotic micropump.

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.