Topical application of betahistine improves eustachian tube function in an animal model.

CONCLUSION: Betahistine dihydrochloride, a drug used widely in the systemic treatment of balance disorders such as Ménière's disease, was found to improve eustachian tube function when applied topically in the nasopharynx of rats. OBJECTIVES: The study tested the effect of betahistine, a histamine receptor agonist, on eustachian tube function and tested the involvement of H1 and H3 histamine receptors. METHODS: Eustachian tube function was measured in anaesthetized rats while middle ear pressure was increased and then monitored during induced swallowing. Betahistine and other drugs were applied topically in the nasopharynx, bulla and epipharynx, and administered intraperitoneally. RESULTS: Systemic application of betahistine hardly changed eustachian tube function, but topical application significantly improved it. The action of topical betahistine was unaffected by the HI receptor antagonist mepyramine and was mimicked by the H3 agonist, ciproxifan.

Effect of static middle-ear and intracranial pressure changes on differential electrocochleographic response.

In an animal model, we examined the extratympanic electrocochleographic response to static pressure changes (middle-ear pressure and intracranial pressure [ICP]) with attention to the summating potential (SP), action potential (AP), and the SP/AP ratio. With a closed middle ear, raised or lowered middle-ear pressure and raised or lowered ICP resulted in congruent increases of the SP and the SP/AP ratio, while the AP remained at a steady voltage. With a closed middle ear, raising or lowering ICP by positioning also had the effect of raising or lowering middle-ear pressure. With an open middle ear, raising or lowering middle-ear pressure resulted in congruent increases of the SP and the SP/AP ratio and, though the AP remained steady, it showed much higher voltage values. With an open middle ear, the baseline SP and baseline SP/AP ratio were reduced, but the reduction of the SP/AP ratio was mainly due to an increased AP. With an open middle ear, the SP, the SP/AP ratio, and the AP did not change appreciably during positioning-induced ICP changes. This suggests that ICP changes by positioning are not very effective in the rat when the middle ear is open. Thus, the effect of ICP changes with the middle ear closed are mainly due to positioning-induced pressure changes in the middle ear. Our findings confirm that static middle-ear pressure is critical for the cochlea and that good eustachian tube function is essential to keeping the pressure gradient across the round-window membrane as small as possible, the latter possibly assisted by a Windkessel function of the round-window membrane. However, relatively small pressure changes in the middle ear can overwhelm it, which suggests a very limited Windkessel function. In Ménière's disease, sensitivity to static pressure changes is possibly exaggerated. The insertion of a middle-ear ventilation tube, as practiced in treating selected cases of Ménière's disease, could restore Windkessel function. It has a stabilizing effect, as the inner ear appears less pressure-sensitive. This effect decreases Ménière's disease symptoms, but it is not without consequences. After the insertion of a middle-ear ventilation tube, a reduced SP/AP ratio is no evidence of improved inner-ear function. Its consequences are enlarged AP voltages, very likely loss of middle-ear dampening, and possible increased ringing.

The effect of the sympathetic and sensory nervous system on active eustachian tube function in the rat.

CONCLUSION: We propose that simultaneous activation of the sensory and sympathetic nervous system may adversely affect eustachian tube function, which may have a role in the genesis of Ménière's disease. OBJECTIVE: We have determined the distribution of sympathetic and nociceptive sensory axons in the mucosa of the rat eustachian tube and investigated whether sympathetic or nociceptive neurons influence the function of the eustachian tube. MATERIALS AND METHODS: We tested whether the ability of a rat to equalize air pressure in the middle ear during evoked swallowing was altered by activation or blockade of the local sympathetic nervous system, or by stimulation of nociceptive neurons with capsaicin. RESULTS: Sympathetic axons were sparse, but CGRP-immunoreactive, nociceptive axons formed a dense subepithelial plexus beneath the eustachian tube epithelium. Neither the adrenergic blocking drug, bretylium, nor electrical stimulation of the superior cervical ganglion significantly altered eustachian tube function. Capsaicin alone did not affect eustachian tube function but capsaicin applied with an alpha adrenoceptor agonist impaired the function of the eustachian tube. Capsaicin applied to the bulla also increased spontaneous swallowing in anaesthetized rats and this effect was enhanced by addition of an alpha adrenoceptor agonist and by stimulation of the superior cervical ganglion.

The potential role of joint injury and eustachian tube dysfunction in the genesis of secondary Ménière's disease.

Ménière's diseasenot only includes the symptom complex consisting of attacks of vertigo, low-frequency hearing loss, and tinnitus but comprises symptoms related to the eustachian tube, the upper cervical spine, the temporomandibular joints, and the autonomic nervous system. Quantifiable experience shows that the insertion of a middle-ear ventilation tube can alleviate Ménière's disease symptoms, suggesting that eustachian tube dysfunction is a contributing feature. Clinical practice also shows that treating disorders of the upper cervical spine and temporomandibular joints can lessen Ménière's disease symptoms, suggesting a relationship. Similarly, stellate ganglion blocks can be beneficial in controlling Ménière's disease symptoms, highlighting the influence of the autonomic nervous system. Thus, contrasting symptoms associated with the eustachian tube, the upper cervical spine, the temporomandibular joints, and the autonomic nervous system relate to Ménière's disease, but the possible reflex pathway by which a link is established is unclear. We made an attempt in this study to describe a hypothetical reflex pathway that links joint injury and the autonomic nervous system, where eustachian tube function is under their influence and is the critical link. In this hypothetical reflex pathway, irritation of facet joints can first lead to an activated anterior cervical sympathetic system via an independent pathway in the mediolateral cell column; it can simultaneously lead to an axon reflex involving nociceptive neurons, resulting in neurogenic inflammation and the prospect of a eustachian tube dysfunction. The eustachian tube dysfunction is responsible for a disturbed middle ear-inner ear pressure relationship, circumstances that have the potential to develop into secondary Ménière's disease. This reflex pathway is supported by recent animal experiments.

Amplitude range analysis of otolithic organ responses.

Benign paroxysmal positioning vertigo is easily diagnosed with the Dix-Hallpike maneuver. It is an ideal clinical condition in which to study the electrical response of the inner ear with electrocochleography techniques. Responses can be recorded during head tilt in roll and in pitch. With this technique we found that the amplitude range and scaling behavior of recorded raw data for the baseline resting position versus the stimulus position was statistically different in both patients and normal subjects. This can be demonstrated in the visual format of box plots. This technique promises to become a valuable addition to electrical examination techniques of the inner ear.

P-100 in the treatment of Ménière's disease: a clinical study.

Patients suffering from Ménière's disease are particularly sensitive to negative pressure in the middle ear. For example, attacks of vertigo can be triggered by a descent in an aircraft when ventilation of the middle ear can become critical. Positive-pressure pulse treatment has been shown to have a beneficial effect on the symptomatology and is now a true alternative in the treatment of Ménière's disease. In this study, we compared two devices that produced positive-pressure pulses delivered to the inner ear via the external ear canal and after the insertion of a middle-ear ventilation tube. Both devices (Meniett and P-100) were equally successful and confirmed that positive-pressure pulse treatment is a true alternative to current treatment modalities. However, the P-100 is the preferred device, particularly for its convenience of use and its cost, which is considerably lower.

Electro-otolithography: new insight into benign paroxysmal positioning vertigo.

Early vestibular evoked potentials were recorded with an extratympanic electrode. The recording principle was adding responses that were phase-locked to a recording frequency. The recording frequency was empirically determined to match harmonically an individual response frequency, thus allowing averaging. This new technique was evaluated in benign paroxysmal positioning vertigo. Normal data were obtained from 12 patients without vestibulocochlear symptoms and were compared with data from 18 symptomatic patients with diagnoses of benign paroxysmal positioning vertigo. All symptomatic patients were treated with a canalith repositioning maneuver, and all responded, in that they no longer had attacks of vertigo. Of the five patients who could be reassessed, all five no longer had attacks of vertigo, but three complained of persisting postural imbalance. Repeat electro-otolithography results continued to be abnormal in these patients, whereas in the remaining two patients responses were normal, consistent with the treatment outcome. The results suggest that electro-otolithography is a valuable addition to the otoneurological test battery. Successful canalith repositioning can abolish attacks of vertigo, although not necessarily a persisting imbalance, which patients frequently describe as a temporary and momentary instability. This is most likely related to a remaining otolithic deficit.

Tinnitus suppression with threshold and subthreshold sound stimuli.

In this preliminary report, we present the results from our investigation of 34 tinnitus patients for tinnitus suppression with frequency-specific sound stimuli within the auditory spectrum. Of this number, 22 (64.7%) experienced suppression, 5 (14.7%) had partial suppression, and 7 (20.6%) were nonresponders. Suppression of peripheral tinnitus may result when mechanosensitive outer hair cells are recruited by sound stimuli that can remain at subthreshold level. The suppression mechanism is possibly explained by the electromodel of the auditory system. This physiological model could be the basis of tinnitus suppression therapy in which a low-intensity, frequency-specific and tinnitus-suppressing sound stimulus is introduced instead of a wide-band masking noise.

A model of active Eustachian tube function in the rat: effect of modulating parasympathetic innervation.

The effect of altering secretion into the Eustachian tube by modulating cholinergic innervation was studied in the anaesthetized rat. Active properties of the Eustachian tube were determined by measuring the ability of reflex-induced swallowing to equalize against an increased pressure level in the bulla. Reflex-induced swallowing was initiated by electrically stimulating the superior laryngeal nerve. Passive properties of the Eustachian tube were determined by increasing middle ear pressure until the Eustachian tube spontaneously opened. Blocking cholinergic neurotransmission with atropine had no effect on active or passive properties of the Eustachian tube. Potentiating cholinergic neurotransmission with neostigmine significantly impaired the ability of active swallowing to equilibrate middle ear pressure, but had no effect on passive properties of the Eustachian tube. The findings show that cholinergic nerve transmission, most likely from the parasympathetic division of the autonomic nervous system, can influence Eustachian tube function. We hypothesize that this effect is due to changes in surface tension in the Eustachian tube as a result of changes in secretion.