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Biomedical subjects

B Conrad

Publications and source records attributed to B Conrad.

At least 145 records · Page 8Linked to original sources
PubMed1989

The role of short-term visuo-spatial memory in control of rapid multi-joint prehensive movements.

How memorized visuo-spatial information influences motor control and whether this information is able to replace the feedback processing in cases of visual deprivation was studied using an unrestrained finger- and hand-movement paradigm. Nineteen right-handed subjects were asked to grasp and lift a small block with the index finger and thumb of the right hand, as quickly as possible. The efficiency of motor performance was analysed by measuring the grasping time derived from tangential velocity profiles of the fingertips. The data revealed significantly shorter grasping times under continuous visual guidance than during blind grasping. Grasping times increased under conditions with stepwise prolongation of visual deprivation time prior to the movement onset. The results support the general concept that within the first seconds of visual deprivation, stored visuo-spatial information can partly compensate for the lack of continuous visual feedback.

Adult↗
PubMed1989

[Botulinum toxin in therapy of craniocervical dystonia].

Craniocervical dystonias are a major therapeutic problem, since in the majority of cases various drug regimens as well as surgical interventions either fail or are accompanied by serious side effects. Botulinum toxin, well known as a biological toxin which blocks the cholinergic neuromuscular synapse, proved to be a new and successful concept in the treatment of these disorders. In the present study, mechanisms of action, clinical indications and practical use of botulinum toxin are described.

Botulinum Toxins↗
PubMed1988

Transcranial magnetic stimulation of the human brain: responses in muscles supplied by cranial nerves.

The present investigation demonstrates that time-varying magnetic fields induced over the skull elicit distinct types of responses in muscles supplied by the cranial nerves both on the ipsilateral and the contralateral side. When the center of the copper coil was positioned 4 cm lateral to the vertex on a line from the vertex to the external auditory meatus, bilateral responses in the masseter, orbicularis oculi, mentalis, and sternocleidomastoideus muscles with a delay of about 10 to 14 ms after the stimulus occurred. Similar to the transcranially evoked muscle responses in hand muscles, the responses in the cranial muscles can be influenced in latency and amplitude by background excitation. It is concluded that these responses are induced by excitation of the face-associated motor cortex followed by multiple I-waves in the corticonuclear tract with both ipsilateral and contralateral projections to the corresponding motoneurones. Additionally, at higher stimulation strengths "short-latency" ipsilateral responses in muscles supplied by the trigeminal, facial, and accessory nerves occurred which we suggest are induced by direct stimulation of the peripheral cranial nerves in their intracisternal course. The present study confirms the bilateral projection of corticonuclear tracts in awake unanesthetised human subjects which has been observed by electrical stimulation on the exposed cortex during surgical procedures already decades ago. The present investigation will serve as a basis for the assessment of pathophysiological mechanisms involving the corticonuclear system or the peripheral cranial nerves in their proximal parts in awake humans.

Adult↗
PubMed1988

Evaluation of intracranial pressure from transcranial Doppler studies in cerebral disease.

The extent to which estimations of intracranial pressure can be derived from intracranial flow patterns was studied. The blood flow velocity in the middle cerebral artery was recorded with the EME TC 2-64 transcranial Doppler (TCD) device in 26 patients suffering from various severe cerebral diseases. Simultaneously the mean intracranial pressure (ICP) was measured by means of an epidural device. Arterial carbon-dioxide tensions were monitored by blood gas analysis. In all patients it was observed that the middle cerebral artery flow patterns changed distinctly when the ICP increased; these changes were distinguished by a decrease of the mean flow velocity and an increase of the Pourcelot index. A good correlation between the ICP and the flow parameters (especially the product mean systemic arterial pressure x Pourcelot index/mean flow velocity) was found in a select group of 13 patients, in whom comparable initial conditions existed and in whom additional parameters influencing the TCD recordings could be kept constant (r = 0.873; P less than 0.001).

Adult↗
PubMed1988

Complex repetitive discharges in the iliopsoas muscle.

A prospective electromyographic investigation of lower limb muscles in patients with different neurogenic disorders showed that complex repetitive discharges (CRD) were observed predominantly and often only in the iliopsoas muscle. Analysis of the EMG findings in acute and chronic lesions shows that CRD are a feature of a chronic proximal motor axon lesion. Furthermore, the frequently focal occurrence of CRD in the iliopsoas muscle in clinically distal diabetic polyneuropathies suggests that this muscle and its nerves represent a locus minoris resistentiae.

Acute Disease↗
PubMed1988

Analysis of muscle responses elicited by transcranial stimulation of the cortico-spinal system in man.

Anodal stimulation of the central area of the scalp can produce visible twitches of various contralateral muscles. In a number of recent reports the technique of transcranial motor stimulation in man has been used to demonstrate abnormal evoked muscle responses in various diseases affecting descending motor pathways. The present paper deals with the systematic study of physiological influences and wave forms of these motor responses in normal subjects. It is demonstrated that they depend strongly on the stimulus strength, the placement of stimulating electrodes and the amount of background voluntary innervation. The presented normal values obtained under standardized conditions may serve as a basis for the decision on whether responses in an individual subject are abnormal or not.

Action Potentials↗
PubMed1988

Successful treatment of tardive and spontaneous dyskinesias with corticosteroids.

Three patients, 2 with tardive dyskinesia and 1 with senile chorea, were successfully treated with corticosteroids during an observation period of up to 5 months. Permanent complete relief or pronounced improvement of the dyskinesias was observed at a dosage of 5 mg prednisolone/day. Possible interactions between the putatively hyperactive dopaminergic system and corticosteroids are discussed.

Adrenal Cortex Hormones↗
PubMed1988

Transcranial Doppler ultrasonography of carotid-basilar collateral circulation in subclavian steal.

The combination of a carotid-basilar and a vertebro-vertebral collateral circulation was verified directly in a patient with a complete subclavian steal by means of transcranial Doppler ultrasonography. The patient showed permanently reversed blood flow in the basilar artery. The subclavian steal influenced the hemodynamics of the circle of Willis at rest and during functional tests of the collaterally supplied arm. Our investigation provides the first direct experimental evidence of increased blood flow velocity in the carotid artery after decompressing the collaterally supplied arm.

Arm↗
PubMed1988

[Thoraco-abdominal manifestation of diabetic neuropathy].

The differential diagnostic importance of the thoraco-abdominal manifestation of diabetic neuropathy, with special reference to the neurophysiological findings is underlined. The cases of six patients are described who suffered from severe, burning pain of varying location (area of the lower thoracic aperture, lower abdomen, scapulae, back). In all six patients pathological spontaneous activity of different location and intensity could be found bilaterally in the paravertebral muscles. Their segmental location correlated with the individual experience of pain.

Abdomen↗
PubMed1988

[Fractionated determination of central motor conduction times using stimulation of the cortex, spinal tract and spinal nerve roots: possibilities and limits].

Two different approaches of determining central motor conduction times were investigated. Both methods were based on calculations of latency differences of muscle compound action potentials. First, using multilocal stimulation of the descending motor system at different levels (motor cortex, motor tracts at spinal level, motor roots) and recording from one reference muscle (Figs. 1 and 2). Second, using unilocal stimulation over the motor cortex and recording from a number of paravertebral muscles at levels from C7 to L5 (Figs. 3 and 4). With multilocal stimulation of the motor pathways, muscle response potentials are observed which differ in amplitude, duration and configuration depending on the site of stimulation (Figs. 1 and 2). This finding points to the incongruency of excited fibres within the descending motor pathways. The causes underlying this phenomenon and the resulting limitations for determining central motor conduction times are discussed. The new approach using recordings of cortically evoked responses on different levels in paravertebral muscles does not suffer from the methodical limitations of the multilocal stimulation and may be of higher clinical validity for the localization of circumscript spinal processes.

Adult↗
PubMed1988

[Changes in multi-locally recorded muscle responses following cortex stimulation in patients with multiple sclerosis].

The application of transcranial brain stimulation widens the range of neurophysiological tools available for the diagnostic evaluation of impaired function in central conduction pathways. A standardized examination of 25 patients with multiple sclerosis (diagnoses of different certainties using the classification by Bauer) was performed with electrical brain stimulation and EMG recordings from 3 muscles in each of the upper and lower extremities (Fig. 2). The occurrence and the change (amplitude, latency) of abnormal cortically evoked muscle responses correlated with the distribution and the severity of the clinical motor deficits respectively (Fig. 1 to 4 and Tab. 1). Furthermore, in some cases, abnormal responses were found in clinically unaffected limbs. Non-invasive stimulation of the motor cortex may reveal lesions affecting the function of the fast conducting component of the corticospinal tract even when there is no pathological clinical finding. In patients suspected of having multiple sclerosis the use of this technique may allow greater diagnostic certainty or even an early diagnosis.

Electric Stimulation↗
PubMed1988

[The role of magnetic stimulation in diagnosis of the peripheral nervous system].

Magnetic stimulation has recently been introduced as a new method for stimulation of neuronal tissues. Up to now most investigators were emphasized the advantages of this method for the investigation of the central nervous system. With this paper we want to show that magnetic stimulation may also be useful for the examination of the peripheral nervous system. Both, magnetic and electrical stimulation, seem to employ the same stimulation mechanisms in the nervous tissue. The results obtained with both methods should therefore be comparable. By measuring EMG-latencies after electrical and magnetic stimulation (Fig. 1) the exact site of magnetic stimulation can be determined. Magnetic stimulation offers major advantages over electrical stimulation: 1) Magnetic stimulation is a painless method even when high stimulus intensities are used. 2) Magnetic stimulation can reach deep neuronal structures that are not easily accessible using electrical stimulation (Fig. 2, Fig. 3). 3) Using a wide range of stimulus intensities (Fig. 4, Fig. 5) magnetic stimulation provides a much better descrimination of different components of the compound muscle action potential than electrical stimulation. Magnetic stimulation seems to be a promising new method for the electrodiagnostic examination of pain- sensitive patients, especially when deep-lying peripheral nerves have to be investigated.

Electric Stimulation↗
PubMed1988

[Transcranial brain stimulation. Methods and results].

Since the end of last century direct electric brain stimulations have produced remarkable neurophysiological results. Unfortunately, this method can be used only during neurosurgical operations. With the introduction of transcranial electric brain stimulation in 1980, for the first time, it became possible to perform brain stimulations on non-anaesthetized subjects. Magnetic brain stimulation, available since 1985, allows brain stimulation without any discomfort of the subject. This paper is dealing with methodological aspects of both methods and presents first results of neurophysiological and clinical applications.

Brain↗
PubMed1988

[Assessment of motor cranial nerve functions using transcranial magnetic stimulation].

Transcranial magnetic stimulation applied over one cerebral hemisphere evokes bilateral responses in the muscles supplied by cranial nerves (masseter, mentalis, sternomastoid, genioglossus) (Tabl. 1). The relatively long latencies of these responses and the influence that preactivation of the muscle has on them, suggests that they are cortically evoked. Shorter latency and exclusively ipsilateral responses can be obtained if the position of the stimulating coil over the head is more lateral. These responses are uninfluenced by pre-activation of the muscle which suggests that they arise from stimulation of the peripheral nerve itself. By considering the conduction velocity of the nerve and the response latency such stimulation probably occurs in the proximal intracisternal segment (Fig. 2). The results obtained using magnetic stimulation of the cortex in patients with unilateral cerebral hemisphere lesions lend support to the idea of a bilateral projection from each cerebral hemisphere to the motor nuclei of the facial and hypoglossal nerves on both sides: stimulations over the intact hemisphere produces bilateral responses, whereas stimulations over the damaged hemisphere produce no responses (Fig. 1). In patients with idiopathic facial palsy no short latency responses were obtained on the affected side either during the acute (less than 10 days) or during the chronic phase (greater than 3 months) of the illness-despite clinical improvement during the chronic stage (Fig. 3, 4). However cortically evoked responses were obtainable in patients seen during the chronic phase indicating that facial motoneurones could be excited transsynaptically (Fig. 3).(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral Infarction↗
PubMed1988

[Form of manifestations and course of brachial plexus lesions following medial sternotomy].

A prospective study is reported of the prevalence, the clinical picture and the course of plexus brachialis lesions following median sternotomy during heart operations. The study comprises 1,585 patients. In 22 patients (1.39%) a lesion of the lower plexus brachialis was found postoperatively. In 12 patients the plexus lesion was combined with an ipsilateral Horner syndrome. The present study suggests that in spite of cautious use of the sternal retractor, the appearance of a postoperative plexus lesion cannot be completely avoided. In contrast to a cranial incision of the retractor, which can be associated with a posterior fracture of the first rib, a caudal placement of the retractor seems to induce a superior luxation of the first rib and local hematoma without concurrent fracture. Re-examinations of the patients demonstrated a good prognosis of these plexus lesions, the Horner syndromes, however, may remain for a longer time period. It is advisable that patients who have to undergo a heart operation with median sternotomy should be informed beforehand about the possible side-effects described here.

Aortic Valve↗