Biomedical subjects

M Hildesheimer

Publications and source records attributed to M Hildesheimer.

44 records · Page 3Linked to original sources

PubMed1984

Influence of catecholamines on perilymph Po2.

In a previous study, a special rheological model of intra-arterial perfusion was used to examine the existence and effectiveness of vasomotor control of the cochlear vessels in guinea pigs. Catecholamines were injected intra-arterially into this animal model and the changes induced in the cochlear action potentials were examined. In this investigation, we used the same animal model and technique to measure the perilymph Po2 after perfusion of the cochlea with catecholamines. In addition, the effect of drainage of the CSF before infusion was examined. The results indicated that opening the labyrinth allows the escape of CSF through the patent cochlear duct. This may modify the concentration of the substance under study in the perilymph and cause inaccuracies in the data obtained.

Animals↗

PubMed1983

Influence of catecholamines on cochlear action potentials.

Catecholamines were injected intra-arterially in guinea pigs using a rheological model described elsewhere. With this method, apart from the ear, only a relatively restricted area was perfused with catecholamines, and the amount eventually entering the general circulation was insufficient to change the normal BP. The induced vasoconstriction of the labyrinthine vessels affected the cochlear blood flow and caused an increase of 11.34 dB in the mean action potential threshold. When the rate of catecholamine infusion was increased, associating vasoconstriction of the cochlear vessels with increased BP, deterioration of the action potential threshold was limited to only 2 dB. However, decrease in the normal BP under the same experimental conditions raised the threshold by 21.67 dB.

Animals↗

PubMed1983

A model for research on cochlear hypoxia.

The vessels emerging from one side of the basilar artery are supplied exclusively by the homolateral vertebral artery. Since blood flow is laminar through the vertebrobasilar system, mixing between two sides does not normally occur. Based on this fact, an experimental model for research on cochlear hypoxia is proposed and described. The animal's own blood flow in the vertebral artery is completely replaced by a stream of poorly oxygenated blood injected retrogradely through the ipsilateral axillary artery. In this way, the territory supplied by the vessels emerging from this side of the basilar artery, including the ear, is rendered hypoxic. The changes in the cochlear action potentials induced by the reduced oxygen supply are recorded by a chronically implanted electrode and analyzed.

Animals↗

PubMed1982

Influence of blood viscosity on cochlear action potentials and oxygenation.

Impairment of the cochlear blood supply of guinea pigs was induced in order to study the effects of hypoxia on the cochlear action potentials. The oxygenation of the cochlear structures was decreased by perfusing the ears with polycythemic hyperviscous blood. The validity of using this model of cochlear blood flow was based on the propensity of the blood to flow in a laminar way. Because of the streamlined flow pattern, the blood supplied by the two vertebral arteries does not mix within the common trunk of the basilar artery. The retrograde injection of polycythemic hyperviscous blood into one vertebral artery will affect the ear on the injected side only. The high viscosity of the polycythemic blood decreases the rate of flow of blood through the cochlear vessels; the high oxygen content of this blood, however, avoids hypoxia of the cochlea. Therefore, in order to make the slowdown in the blood flow evident, its oxygen content was reduced to a 'precritical level' before it was infused. Injecting normoviscous blood with a 'precritical level' of oxygen caused a mild reduction in the scala media pO2 of 15.2% for the whole group of twenty animals. The hyperviscous blood with the same level of oxygenation, however, reduced the pO2 in the scala media to 53.3% of normal. These findings explain the difference in the altered click-evoked action potentials in the two groups of animals.

Action Potentials↗

PubMed1980

Effect of emotional stress on hearing.

An experimental model for emotional stress is described. Emotional stress can affect hearing if severe enough or if it lasts long enough. The noxious effect on the ear can be explained by the high level of blood catecholamines and exaggerated activity of the cochlear sympathetic innervation.

Animals↗

PubMed1979

Long-term electrode implantation for recording cochlear electrical activity in guinea pigs.

Comparative measurements of the cochlear electrical activity over prolonged periods require long-term implantation of electrodes. During this time, changes in the electrode recording ability and/or impairment of the sound-conducting system, could erroneously be attributed to the experiment. To avoid this risk, an easy and reliable technique is described. The procedure uses the Fallopian canal as a route by which to approach the cochlear potentials' generators, while leaving the middle ear untouched.

Action Potentials↗

PubMed1977

Chronic cardiovascular pathology and hearing loss in the aged.

With the objective of studying a possible correlation between chronic cardiovascular disturbances and hearing loss in aged people, two groups were compared. The first was composed of apparently healthy subjects and the second, of subjects suffering from clinically evident chronic cardiovascular pathology. All the subjects were submitted to a pure tone audiometry, discrimination test, SISI test and TDT. The results showed a significant difference in pure tone threshold audiometry between the apparently healthy subjects and those presenting cardiovascular symptoms; the discrimination and the TDT were comparable in the two groups.

Aged↗

PubMed1975

Cochlear action potentials in experimentally induced hypothyroidism in guinea pigs.

Hypothyroidism was induced in guinea pigs by various methods. Using a new technique, electrodes were permanently implanted and action potentials aroused by different sound stimuli recorded and measured. The results obtained before and during the hypometabolic state were analysed and compared with those obtained after replacement therapy. A tentative attempt was made to extrapolate the changes in pattern and magnitude of the action potentials caused by the experimentally induced hypothyroidism, to the hearing disorders observed in patients with thyroid deficiency.

Acoustic Stimulation↗