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Biomedical subjects

R Benecke

Publications and source records attributed to R Benecke.

At least 145 records · Page 8Linked to original sources
PubMed1986

[Residues of organochlorine compounds in plant drugs. 1. Gas chromatographic determination of residues of organochlorine insecticides].

A method for the identification and determination of HCH-and DDT-isomers and their respective metabolites in vegetable drugs is presented. The plant material is extracted with hexane in a Soxhlet apparatus in the presence of silicagel and sodium sulfate. For removing interfering endogenous plant constituents a Celite oleum column cleanup and usually and acetonitrile partitioning to follow are necessary. A mixed stationary phase OV-17/QF-1 has proved effective for the gc separation on packed columns. 3H-ECD is used for detection. For the quantitative determination by using an external standard the peak height measurement is recommended. Recoveries of all insecticides were in the order of 70-105% with coefficients of variation between 6 and 20%. To ensure the results the alkaline treatment and oxidation of extracts are proposed.

Chromatography, Gas↗
PubMed1986

[Plant drugs with residues of organochlorine compounds. 2. Identification of residues of DDT and its analogs by comparison of gas chromatography on packed and capillary columns and GC/MS coupling].

For the GC analysis of DDT isomers and metabolites in extracts of Flores Chamomillae end Radix Valerianae the separation on a packed QF-1/OV-17 column was compared with various capillary columns of the CP-Sil type. Identification of the individual compounds could be achieved by comparing the retention behavior, chemical transformation of DDT and DDE, as well as by capillary GC-MS using single ion monitoring of substance-characteristic ion mass. In this way, residues of p,p'-DDT, o,p'-DDE and p,p'-TDE could be identified.

Chromatography, Gas↗
PubMed1985

Increase of the Bereitschaftspotential in simultaneous and sequential movements.

The amplitude and duration of the Bereitschaftspotential were analysed in 9 normal subjects prior to four different motor tasks: (1) simple isotonic elbow flexion ('flex'), (2) simple isometric finger flexion ('squeeze'), (3) simultaneous performance of 'flex' and 'squeeze', and (4) sequential performance of 'flex' then 'squeeze'. The Bereitschaftspotential was much larger and slightly longer in the simultaneous and sequential movements than in the same movements performed separately. The amplitudes of the Bereitschaftspotential were measured 150 and 75 ms prior to electromyographic (EMG) onset of the prime mover, and at the time of EMG onset. Changes in size were seen in all leads (FCz, Cz, C3', C4') and at all time points. It is suggested that the increase of the Bereitschaftspotential prior to complex arm movements reflects a greater activation of the supplementary motor area before simultaneous and sequential movements.

Adult↗
PubMed1985

Rapid goal-directed elbow flexion movements: limitations of the speed control system due to neural constraints.

In rapid goal-directed elbow flexion movements the influence of both movement amplitude and inertial load on the three-burst pattern and the consequences on movement time were studied. Subjects performed visually guided, self-paced movements as rapidly and as accurately as possible. An increase of both the movement amplitude and the inertial load were found to be interacting factors for the modulation of the three-burst-pattern and movement time. The first biceps burst progressively increased in duration and amplitude for larger movements, resulting in prolonged movement times. Surplus inertial loads further prolonged the agonist burst for large, but not for small movement amplitudes. The activity of the antagonist burst, in contrast, was largest in small movements and successively decreased at increasing movement amplitudes. Its duration, however, remained fairly constant. As was similarly observed for the agonist burst, surplus inertial loads lead to a prolongation of antagonist burst duration and an small movement amplitudes. It is suggested that in elbow flexion movements the programming of fastest goal-directed movements must take into account neural constraints and biomechanical characteristics of the agonist muscle and the antagonist muscle. Due to neural constraints of the biceps muscle, in contrast to finger movements, the concept of movement time invariance does not hold for elbow movements. Furthermore, neural constraints of the antagonist muscle lead to a limited force production of the agonist muscle at small movement amplitudes in order to avoid an overload of the braking process.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

The flexor reflex--influence of stimulus parameters on the reflex response.

The flexor reflex evoked in the tibialis anterior muscle by stimulation of the medial plantar nerve was investigated in 54 normal subjects. Three main reflex components were identified (excitation--inhibition-- excitation), the early excitation being composed of two subcomponents. Occasionally, a fourth (excitatory) reflex component was seen breaking through EMG inhibition. The individual reflex components were differentially susceptible to facilitatory influences which suggested transmission via a central multichannel system. Methodological experiments showed that the amplitudes and to some degree also the latencies of the individual reflex components were modified by both the parameters of the stimulus as well as by the degree of pre-innervation. However, the patterning of the reflex response was basically independent from methodological permutations.

Adult↗
PubMed1984

Changes of somatosensory evoked potentials in man as correlates of transcortical reflex mediation?

Somatosensory evoked potentials (SSEP) from the scalp of the sensori-motor cortex were recorded together with long latency reflexes in the EMG of the contralateral biceps muscle in 17 human subjects, who were instructed to compensate a sudden biceps stretch. In this 'compensate' condition the earliest deviation from the shape of the SSEP obtained in a 'let go' situation (exhibiting only short latency reflexes) occurred as early as 35-40 ms. The results indicate that SSEP changes associated with the occurrence of long latency reflexes might be compatible with a transcortically mediated reflex activity.

Adult↗
PubMed1984

Human ballistic finger flexion: uncoupling of the three-burst pattern.

In isotonic and isometric goal-directed index finger movements made as fast as possible, the "braking hypothesis" ascribed to the antagonist burst was tested. Under isotonic conditions, the extensor burst often failed to occur in small angle movements with low inertial load. It regularly occurred, however, in small angle movements with high inertial load and in wide angle movements with both low and high inertial loads. Such features suggest, indeed, the antagonist burst as being part of braking strategies. Under isometric conditions, the antagonist burst - if it occurred - exhibited characteristics which suggested a rapidly alternating movement rather than a braking strategy.

Electromyography↗
PubMed1983

Premovement silent period in fast movement initiation.

Premovement inhibitory processes were studied in human subjects performing ballistic elbow movements in a self-paced or reaction time situation. The experiments were designed to test the hypothesis that there is an interdependence between a preparatory disfacilitatory process at the motoneurone level and an impending phasic motoneurone activation. The results indicate that in ballistic movements there is a positive relation between extent of premovement depression of tonic activity and subsequent phasic innervation. The results suggest that in high speed movements where a maximal number of motor units have to be recruited, those motoneurones which are already tonically active have to be released from tonic activity for optimal synchrony.

Acoustic Stimulation↗
PubMed1983

Denervation activity in the EMG of patients with upper motor neuron lesions: time course, local distribution and pathogenetic aspects.

EMG denervation activity was studied in patients without peripheral neuron disorder but with upper motor neuron lesions. The time course of such central denervation activity, the local distribution and the quantitative relationship between denervation activity and the degree of paresis and spasticity were also studied. A total of 101 patients, who had developed hemiplegia or hemiparesis as a result of a cerebral vascular accident, underwent needle electromyographic examination at regular intervals in proximal and distal muscle groups. The maximum observation time was 1 year. Denervation activity in cases of central paresis first occurred 2-3 weeks after stroke. This could be observed most frequently in the distal arm and hand muscles. In the course of weeks and months the frequency of the denervation activity decreased in parallel with the development of spasticity and the increasing voluntary innervation. The occurrence and the dynamic properties of the denervation activity in cases of central paresis support the assumption of a trans-synaptic degeneration of alpha-motoneurons and of a compensating segmental "sprouting" of afferents.

Cerebral Infarction↗
PubMed1983

Visual evoked potentials in neurosyphilis.

The visual evoked potential (VEP) to pattern reversal was recorded in 79 patients with neurosyphilis. Sixteen patients (20%) had abnormal VEP latencies with a predominance of pathological VEP values in the group of tabes dorsalis (50%) as compared to general paresis (18%) or meningovascular forms (13%). A comparison of the frequency of abnormal VEPs with that of other ophthalmological tests (visual acuity, visual field, central campimetry, pupillary reactions, dark adaptation, optic fundus) yielded no diagnostic superiority of VEP.

Adult↗
PubMed1982

[Psychogenic visual disturbances in children and adults. Ophthalmological, neurological and psychodynamic findings].

In large series of ophthalmic patients there may occasionally be some in whom the reduction of visual acuity cannot be explained by organic findings. In such patients simulation is suspected. However, simulation is not the only cause of decreased visual acuity and a lack of organic pathologic findings. It is obvious that all efforts must be made to exclude organic changes as the cause of decreased visual acuity. With modern diagnostic modalities this is possible to a large extent. If there are no organic pathologic findings, a psychiatric exploration is indicated. In the eight patients presented in this paper the reduction of visual acuity was the expression of a psychologic conflict situation. The cases are described in detail and the difference between simulation and a psychogenic decrease of visual acuity is pointed out.

Adolescent↗
PubMed1982

[Lesions of the peripheral nervous system in the treatment of breast cancer].

On the basis of our own patients, the anamnestic data and the neurological constellation in late radiogenic paresis (the most frequent peripheral nervous condition in treatment of mammary carcinoma) are described. A comparison with the situation in metastatic infiltration of the brachial plexus shows the great difficulties in differential diagnosis. Pain can be observed more frequently in metastatic plexus infiltration. The presence of a Horner syndrome can be regarded as decisive evidence for recurrent growth of a carcinoma. If a Horner syndrome is absent, tumor growth can be demonstrated conclusively only by biopsy or surgical exploration. The most frequent condition which is not connected with mammary carcinoma and its followup treatment, but which can stimulate a late radiogenic paresis of the brachial plexus is the carpal tunnel syndrome. Whereas a certain differentiation is not always possible on the basis of the anamnesis and clinical findings, a clear discrimination is possible by means of electrophysiological investigation techniques.

Brachial Plexus↗