Acoustic impedance studies of the normal ear

Otoacoustic emissions and tympanometry in a general adult population in Sweden: Emisiones otoacústicas y timpanometría en la población general adulta de Suecia

The present study concerns a general adult population in Sweden, not exposed to hazardous occupational noise. Tympanometry and spontaneous (SOAE), transient evoked (TEOAE) and distortion-product (DPOAE) otoacoustic emissions were investigated in 493 randomly selected men and women aged from 20 to 79 years. Effects of gender, age, ear side and middle ear state were determined, with and without adjusting for hearing threshold level. No statistically significant effects on middle ear pressure or compliance were present. For TEOAEs and DPOAEs, the effect of gender and age was statistically significant (p < 0.01), with larger signal levels for female subjects and young subjects, even after adjusting for hearing threshold level. No effect of middle ear pressure on otoacoustic emissions was present, but high middle ear compliance was associated with low emission levels (p < 0.01). Reference data for middle ear compliance and pressure and prevalence data on SOAEs, TEOAEs and DPOAEs for male and female subjects in different age groups were determined. Mean signal levels of TEOAEs and DPOAEs are presented.

Neurochemistry of identified motoneurons of the tensor tympani muscle in rat middle ear

The objective of the present study was to identify efferent and afferent transmitters of motoneurons of the tensor tympani muscle (MoTTM) to gain more insight into the neuronal regulation of the muscle. To identify MoTTM, we injected the fluorescent neuronal tracer Fluoro-Gold (FG) into the muscle after preparation of the middle ear in adult rats. Upon terminal uptake and retrograde neuronal transport, we observed FG in neurons located lateral and ventrolateral to the motor trigeminal nucleus ipsilateral to the injection site. Immunohistochemical studies of these motoneurons showed that apparently all contained choline acetyltransferase, demonstrating their motoneuronal character. Different portions of these cell bodies were immunoreactive to bombesin (33%), cholecystokinin (37%), endorphin (100%), leu-enkephalin (25%) or neuronal nitric oxide synthase (32%). MoTTM containing calcitonin gene-related peptide, tyrosine hydroxylase, substance P, neuropeptide Y or serotonin were not found. While calcitonin gene-related peptide was not detected in the region under study, nerve fibers immunoreactive to tyrosine hydroxylase, substance P, neuropeptide Y or serotonin were observed in close spatial relationship to MoTTM, suggesting that these neurons are under aminergic and neuropeptidergic influence. Our results demonstrating the neurochemistry of motoneuron input and output of the rat tensor tympany muscle may prove useful also for the general understanding of motoneuron function and regulation.

Submucous resection

The combination of nasal septal deviation and Eustachian tube dysfunction, in the absence of any other pathology, constitutes the Nose–Ear Distress Syndrome.

We have undertaken a clinical assessment of the relationship between uncomplicated deviation of the nasal septum and Eustachian tube dysfunction in Naval Personnel who are serving in environments of primarily increased barometric pressure.

120 candidates to the Submarine, Diving and Aircrew branches of the Royal Navy who presented with the Nose–Ear distress syndrome were initially surveyed. None were able to equilibrate their middle ear pressures at an increased ambient pressure of 3 metres of water. Submucous resection was performed on 116, of whom 110 (94·83 per cent) were able to equilibrate their middle ear pressures at an increased ambient pressure of 9 metres of water post-operatively.

Xenon 133 Scintigraphy was performed on a further 25 recruits to delineate the post-nasal airflow. This investigation was performed pre- and post-operatively. Pre-operatively, Scintigraphy showed the presence of turbulence in the post-nasal space, while post-operatively the turbulence was absent. All the candidates were unable to equilibrate their middle ear pressures pre-operatively, but after submucous resection 24 (96 per cent) were able to equilibrate their middle ear pressures at an increased barometric pressure of 9 metres of water.

A specialized innervation of the tensor tympani muscle in Macaca fascicularis

The innervation of the tensor tympani muscle of the middle ear in Macaca fascicularis (cynomolgus monkey) was studied using the horseradish peroxidase (HRP) neural tracing technique. A compact column of small trigeminal motoneurons was labeled ipsilaterally following intramuscular application of HRP to the tensor tympani muscle. This column is located ventral and lateral to the dorsolateral division of the trigeminal motor nucleus, and just medial to the descending trigeminal nerve rootlets. No labeled neurons were present in the trigeminal mesencephalic nucleus or any other brainstem nucleus. Results are compared with those previously reported in several non-primate mammalian species, and in detail with that of the cat. A possible differential role of the tensor tympani muscle in acoustic modulation/middle ear aeration between primate and non-primate mammals is discussed.