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Biomedical subjects

K Maurer

Publications and source records attributed to K Maurer.

At least 163 records · Page 9Linked to original sources
PubMed1985

Uncertainties of topodiagnosis of auditory nerve and brain-stem auditory evoked potentials due to rarefaction and condensation stimuli.

Auditory nerve and brain-stem auditory evoked potentials (AN and BAEP) were elicited after separate stimulation with rarefaction and condensation stimuli. There were only few persons with identical patterns in the two opposite phases. Rarefaction stimuli showed a tendency to evoke AN and BAEP with shorter latencies and better synchronization. In diseases of the auditory nerve and brain-stem the phase-dependent differences were even more prominent, indicating different topodiagnostic levels of lesions. The results point to the need for stimulus presentation with rarefaction and condensation stimuli separately and an evaluation of both curves. The alternating mode is the result of summating rarefaction and condensation stimuli.

Brain Stem↗
PubMed1985

Isolation and characterization of Paracoccus denitrificans mutants with defects in the metabolism of one-carbon compounds.

Mutants deficient in the metabolism of one-carbon compounds have been obtained by treating Paracoccus denitrificans with the mutagen N-methyl-N'-nitro-N-nitrosoguanidine. Mutants were selected without enrichment procedures by newly developed plate screening tests. The obtained mutants were characterized by their growth responses, cytochrome composition, enzyme activities, and immunogenic reaction with antisera against methanol dehydrogenase. By these criteria five mutant classes could be distinguished. Class I mutants are involved in the expression of methanol dehydrogenase. Three mutants of this class have a defect in the structural gene. A double mutant was found with defects in the expression of both methanol dehydrogenase and hydrogenase. Class II mutants have a defect in a regulatory gene involved in the regulation of both methanol dehydrogenase and methylamine dehydrogenase. Class III mutants are deficient in formaldehyde metabolism. A defect may exist in the expression of a second non-NAD-linked formaldehyde dehydrogenase which was postulated to be involved in C1 metabolism. Class IV mutants are deficient in cytochrome c. Mutants of class V have a defect in synthesis of the molybdenum cofactor essential for the function of formate dehydrogenase.

Alcohol Oxidoreductases↗
PubMed1985

Isometric muscle contraction in endocrine myopathies.

Isometric contraction of the adductor pollicis muscle of the thumb was evoked by stimulating the ulnar nerve in 20 normal adults and 58 patients with endocrine disorders. We evaluated mechanical latency, electromechanical latency, contraction time, half relaxation time, isometric twitch force, compound muscle action potential, nerve conduction velocity, and relative refractory period. Mechanical characteristics were altered in diseases of the pituitary, thyroid, and parathyroid glands. The close relationship between thyroid hormone and contractile properties discriminated between hypo- and hyperthyroidism.

Adrenal Gland Diseases↗
PubMed1985

[Acoustic evoked potentials and topical diagnosis in the central nervous system].

Acoustic stimulation evokes about 15 waves, the so-called auditory evoked potentials (AEP). According to their appearance in time there are three groups: early auditory evoked potentials, middle latency AEP and late latency AEP. The shorter the latency of a wave, the more precise the coordination to a definable structure in the CNS. Therefore only EAEP allow besides an evaluation of hearing threshold a differential diagnosis between peripheral, neural and central hearing disturbances. Still unclear are questions such as exact origin of waves II to V and the difference of response due to rarefaction and condensation stimuli. The test, however, is a sensitive indicator to evaluate hearing disturbances and brainstem disorders.

Brain Diseases↗
PubMed1985

[Rarefaction-pressure problem of acoustic stimuli from the neuro-otologic viewpoint].

The differences in response pattern of early auditory evoked potentials (EAEP) depending on the two phases (rarefaction & condensation) are well accepted. There are, however, intricacies when EAEP are applied in the otological and neurological fields. Wave V guarantees a fairly good threshold determination. Rarefaction stimuli, however, tend to indicate the threshold more precisely than condensation stimuli. In neurological application, there are different patterns of waves II to V according to the phase, so that different sites of lesions may result. The responses due to rarefaction and condensation stimuli have to be known in the otological and neurological application of the test.

Auditory Perception↗
PubMed1984

Early auditory evoked potentials: developmental aspects and validity in neuropaediatric and audiologic disorders.

Auditory evoked potentials and in this context especially five waves in the first 10 ms (early auditory evoked potentials = EAEP) are a diagnostic aid in topodiagnosis of posterior fossa diseases. This is due to waves I to V which arise along the acoustic nerve and in brain stem structures such as medulla, pons and mid-brain. Besides an indication about the site of a lesion in the posterior fossa, wave V allows an objective threshold determination. The present results were gained in normal children aged 1-3 years and in children with neuropaediatric and audiologic disorders.

Adolescent↗
PubMed1984

Programmable auditory stimulus generator and electro-acoustic transducers--measurements of sound pressure in an artificial ear and human ear canal.

The measurement of sound pressure wave forms of different headphones resulted in considerable differences in an artificial ear and in the external auditory canal in man. This concerns, in particular, the pattern of stimuli used to elicit the auditory nerve and brain-stem auditory evoked potentials. By varying the electrical input to the headphones by means of a programmable stimulus generator, it can be shown that the sound pressure wave form can be influenced considerably.

Brain Stem↗
PubMed1983

Wave I of early auditory evoked potentials in multiple sclerosis.

Early auditory evoked potentials (EAEPs) were recorded in a series of 71 consecutively examined patients suffering from clinically definite or probable multiple sclerosis (MS). Wave I abnormalities, i.e., delayed latency, with or without reduced amplitude, were observed in 15 such patients and were interpreted as due to MS in 8 of them. As EAEP wave I is identical with the potential N1 in electrocochleography and corresponds to activity of the most distal part of the acoustic nerve or the spiral ganglion, it is concluded that the peripheral part of the acoustic nerve is involved in about 10% of MS patients. In two cases normalization of initially delayed wave I latencies were demonstrated during follow-up recording. The pattern of a late wave I but normal hearing in 3 patients is interpreted in terms of a desynchronized compound nerve activity with fully preserved conductivity, segmental demyelination of a considerable number of acoustic nerve fibres being the most likely cause.

Auditory Perception↗
PubMed1983

Early auditory evoked potentials (EAEPs) in the rabbit. Normative data and effects of lesions in the cerebello-pontine angle.

Early auditory evoked potentials (EAEPs) were measured in rabbits. After establishing normative data an operative method was developed to expose the cerebello-pontine angle. Compression of the VIIIth nerve and a reduction of blood supply to the cochlea via the labyrinthine artery altered the EAEP systematically. In all cases of an VIIIth nerve lesion wave 1 continued to be elicited whereas waves 2-5 disappeared. Circulatory disturbances had an effect upon wave 1. The results indicate that the generator of wave 1 is the unit cochlea/acoustic nerve and of waves 2-5 the auditory pathway within the brain stem. The resultant data help to understand wave alterations in patients with acoustic neuromas.

Animals↗
PubMed1983

[Early auditory evoked potentials (EAEP) following cochlear nerve lesions in the cerebellopontile angle. An animal experiment study].

After exposure of the cerebello-pontine angle, various lesions were applied to the cochlear nerve in 20 rabbits. Changes of the EAEP were registered at the same time. Lesions proximal to the internal auditory meatus hardly exercised any influence on wave I. Waves II-V disappeared immediately after the trauma, Partial or complete recovery was observed, depending on the extension of the nerve lesion. Dissection or crushing of the cochlear nerve resulted in permanent disappearance of the waves II-V. Wave I often showed a slight reduction of amplitude, combined with a broadening of its duration and increase in latency. Lesions of minor intensity produced a transient disappearance of waves II-V. Recovery of these waves occurred within the following 2-3 days.

Animals↗
PubMed1982

Acoustic tumour detection with early auditory evoked potentials and neuroradiological methods.

A total of 43 patients with surgically identified acoustic neuromas were tested. Results of early auditory evoked potentials (EAEP) and of neuroradiological methods were analysed. Abnormal EAEPs were observed in all patients. In 73% of the cases the EAEP indicated the retrocochlear site of the lesion; in 27%, however, the results did not localize the exact site of the lesion owing to a lack of waves I, II and III due to a pronounced hearing loss. Neuroradiological procedures provided an indication of the site and extent of the tumour. The number of true positives was 21 of 29 cases with polytomography of the petrous bone, 23 of 28 with computed tomography and in all cases when pontine angle cisternography and computed tomography combined with gas cisternography were performed. The EAEPs provide a screening-test for acoustic tumour detection at an early stage. Wave abnormalities indicative of a lesion at the acoustic nerve should lead to a neuroradiological investigation and are particularly valuable in cases with small intracanalicular tumours.

Adult↗
PubMed1982

[Wave-length changes of the early auditory evoked potentials in acoustic neuroma].

In 37 patients with a surgically proven unilateral acoustic neuroma early auditory evoked potentials (EAEP) were studied. The waves showed alterations, which allowed classification of the patients into groups with special potential characteristics. In Group A, waves I to V were normal; Group B showed a normal wave I whereas waves II to V were altered. In Group C wave I was altered, too, whereas Group D showed only a delayed wave V. In Group E it was not possible to detect waves at all. Classification into Groups A to E facilitates differentiation between a cochlear and retrocochlear lesion. The waves of the contralateral side allow an assessment of the size of the tumour. Large neuromas compress the brain stem and produce a deterioration of the midbrain answer by herniation of the midbrain in the tentorium gap.

Audiometry, Evoked Response↗
PubMed1981

[Mechanomyography - results in a normal population and in patients with thyroid dysfunction (author's transl)].

Isometric contraction of the adductor pollicis by stimulating the ulnar nerve was determined in 20 normal adult subjects. We measured mechanical latency, electro-mechanical latency, contraction time, time to half relaxation and isometric twitch force. Besides that we registered the compound muscle action potential and the nerve conduction velocity. The median nerve was used to elicit the nerve action potential and to determine conduction velocity and relative refractory period. In 6 pat. with hypothyroidism and in 7 pat. with hyperthyroidism the above mentioned parameters were measured. There was a significant change concerning contractile properties, i.e. muscular contraction became slower in hypothyroidism and faster in hyperthyroidism as compared to values obtained in the control group. The isometric twitch force was reduced in both conditions. To assure the close relationship between thyroid hormone (L-thyroxin) and muscle contraction a group of patients who have undergone thyroidectomy was investigated in the same way. Muscle and nerve parameters were determined during a levothyroxin-therapy and in a period without any treatment. The same phenomenon was observed, i.e. reduction of twitch velocity in the hypothyroid state. The twitch force was not reduced in this group. The close relationship between thyroid hormone and contractile properties allows a discrimination between hypo-and hyperthyroid state and a control of thyroxin substitution.

Electric Stimulation↗
PubMed1981

[The effect of rarefaction and condensation tone pips on early auditory evoked potentials (EAEP) (author's transl)].

Tone pips of suprathreshold intensity were used to elicit 7 potentials in the nanovolt range. The acoustic nerve response (I) and 4 brainstem potentials (II-V) were studied in 8 normal listeners in regard to varying acoustic polarity (rarefaction vs condensation). Rarefaction and condensation stimuli produced different responses. In the alternating mode, which helps to suppress stimulus related artifacts, waves may be generated solely as a function of the averaging process if the responses of the two types of tone pips are almost out of phase. Rarefaction tone pips exhibited a better synchronizing effect on auditory unites in the periphery and in brainstem areas. The different responses evoked by stimuli of different polarity must be recognized and controlled in neurologic application of the test.

Evoked Potentials, Auditory↗