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Biomedical subjects

B Conrad

Publications and source records attributed to B Conrad.

At least 217 records · Page 12Linked to original sources
PubMed1978

[The problem of early diagnosis in discrete peripheral nerve lesions. Comparative study of F-wave latency and conventional motor nerve conduction velocity in healthy persons and diabetics (author's transl)].

In 71 healthy subjects and in 38 diabetics the shortest F-wave latencies were evaluated for the n.medianus, n.ulnaris, n.tibialis and n.peronaeus. The motor nerve conduction velocities calculated hereby for the upper and lower extremities were compared with the corresponding distal motor conduction velocities measured in the conventional manner. The comparison of the 2 differently defined motor conduction velocities in healthy and diabetic subjects yielded a better separation between the normal and pathological range in all 4 nerves with the method based on the F-wave latency. For the group of healthy subjects the statistical basis of a preliminary normal range of the F-wave latency was established and nomograms were provided on the basis of the 99% confidence limits which--knowing the length of the arm or leg--open the possibility to derive the corresponding motor conduction velocity.

Adolescent↗
PubMed1977

Effects of voluntary isometric and isotonic activity on late transcortical reflex components in normal subjects and hemiparetic patients.

When the median nerve is stimulated at the wrist during voluntary contraction of m. abductor pollicis brevis (APB) EMG activity of this muscle contains different distinct responses: a direct muscular response (M response), a spinal reflex response (S response) and a third late reflex response, first described by Upton et al. (1971) as a second volitional reflex response (V2). Comparison of this very likely long-loop reflex involving pathways to and from the cortical level (therefore labelled C response) under isometric (hold) and isotonic (move) contraction revealed a strong facilitation of the response under the latter condition. Repetitive trains of stimuli had stronger facilitatory effect on the occurrence of this late reflex response than single stimuli. Cutaneous stimuli of the median nerve afferents did not exhibit M and S responses but definite late excitatory responses with similar latencies to the C responses. In cases of hemiparesis (mild to severe loss of sensorimotor control of finger movements) the C response was diminished, delayed or absent. These findings together with recent primate and human experimental work support the hypothesis of a transcortical stretch reflex. On the premise that muscular as well as cutaneous afferents contribute to the afferent cortical input the late C response can be interpreted as the efferent component. The C response may be a valuable aid in the diagnosis of small lesions of the sensorimotor cortex and internal capsule.

Adult↗
PubMed1975

[The diagnostic value of the F wave latency (author's transl)].

The N. medianus was stimulated electrically in 44 healthy persons and in 30 unselected diabetics. Latencies of the F wave were measured, corrected for different lengths of the upper extremity, and used for computation of nerve conduction velocity. In comparison with conventional motor nerve conduction velocities the F wave latencies showed a more pronounced difference between the normal and the pathological (diabetic) range. The F wave nerve conduction velocities also varied less than conventional nerve conduction velocities. The explanation for this might be that the F wave recordings are the result of a full anti- and orthodromic impulse propagation which travels 5 to 6 times further than the impulse measured with conventional nerve conduction velocity methods. Therefore small delays of nerve conduction will be amplified and can be better recognized by F wave latency measurements. The present findings suggest that F wave latencies may be more sensitive than conventional nerve conduction velocities in evaluating mild cases and in identifying the initial phases of neuropathies.

Adolescent↗
PubMed1975

Precentral unit activity following torque pulse injections into elbow movements.

(1) Precentral neural activity was studied in relation to transient load changes on self-paced elbow movements. Four Cebus monkeys were trained to turn a freely moving handle back and forth between two targets by alternating self-paced elbow flexions and extensions. Torque pulses (of 10 or 100 msec) injected randomly to load or unload the movements stretched or slackened the appropiate prime movers: biceps or triceps. Perturbed movements oscillated at about 5.5 Hz but were completed successfully in about the same time as unperturbed movements. (2) Torque pulses evoked distinct "early" responses with latencies of 20-40 msec in 134 out of 153 precenteral neurons. Oppositely directed torque pulses evoked reciprocal (i.e. increased or decreased) early responses in 61 neurons, and uniform responses in 27 neurons. (3) Early responses were followed by "late" responses with peaks succeeding one another at about 5.5 Hz in 111 neurons, but another 16 exhibited late responses only. (4) Timing of both early and late cortical responses was tightly coupled to peripheral changes. Early responses were timed by the initial torque-induced passive elbow jerk. Timing of late responses was best related to subsequent peak decelerations of accelerations. Intensity of the early but not of all late precentral responses was tightly coupled to peripheral events. (5) Torque pulses that impeded flexions or extensions evoked spinal stretch reflexes in biceps or triceps with EMG latencies of about 15 msec, leading to an acceleration peak about 25 msec later. A second EMG burst followed the first in about 30 msec. The second burst occurred about 20 msec after onset of the early precentral response, which is thought to have caused it, as well as a second acceleration peak that was seen about 60 msec after precentral response (for flexion load pulses). Peaks of late precentral responses were followed by acceleration peaks within about 70 msec. (6) An interaction akin to the spinal stretch reflex is thus revealed between elbow perturbations, early responses of precentral neurons and subsequent elbow movements: discharges of neurons that usually fire in relation to an intended movement can be altered by sudden load changes so that the neurons tend to reduce mismatch between intended and actual movements (cortical load compensation), created by the perturbation. An analagous interaction may also occur with late cortical responses.

Adaptation, Physiological↗
PubMed1975

Effects of dentate cooling on precentral unit activity following torque pulse injections into elbow movements.

(1) The effects were studied of brief, reversible cooling of the dentate nucleus of two Cebus monkeys on the activity of 69 precentral neurons that were related to self-paced elbow flexions or extensions. Sixty-two neurons were studied when movements were randomly perturbed by transient load changes. (2) During unperturbed movements dentate cooling altered precentral activity and movement parameters in the same direction. Extension movements and extension-related precentral neurons developed oscillations and rhythmical activity at about 4 Hz with increased peak values of acceleration and discharge intensity. Flexion peak accelerations and dynamic properties of flexion-related precentral neurons decreased. (3) Dentate cooling had no major effects on the "early" precentral responses to torque pulses and on the initial rapid movement adjustment. (4) Dentate cooling decreased intensity of "late" precentral responses and slowed their frequency together with associated movement oscillations from 5-6 Hz to 3-4 Hz. EMG bursts of biceps and triceps were prolonged accordingly. (5) It is concluded that the tightly coupled interaction between precentral motor cortex and the evolving movement was independent of dentate function in the early stage of the cortical load compensation. The dentate nucleus was involved, however, in adjusting intensity and frequency of subsequent late precentral responses and of movement oscillations.

Adaptation, Physiological↗
PubMed1975

[Cerebellar movement disorders in monkeys. Comparison of rapidly alternating and slower target movements during cooling of the dentate nucleus (author's transl)].

The effects of short reversible cooling of the dentate nucleus in two groups of 3 and 4 cebus monkeys, with two different types of ipsilateral elbow movements, have been studied. One group was trained to turn a moving handle back and forth rapidly between two mechanical stops, while the second group was trained to move the handle between two target zones. Brief blocking of the dentate nucleus caused a delayed termination of contraction of the agonistic muscles (hypermetria) near the mechanical stop for very rapid, ballistic, alternating arm movements and, consequently, delayed initiation of the antagonistic return movement. The resulting increase of the duration of a single movement was not caused by a reduction of the peak acceleration of the movement. For the slower target movements, dentate nucleus cooling caused shortening of agonistic muscular contraction (hypometria) with corresponding, saccadic movement corrections. The frequency of the "movement tremor" lay between 3 and 5 Hz. The average velocity maxima during dentate cooling did not change. The findings indicate that different types of movements exhibit different disturbances of the movement pattern during the period of functional elimination of the same anatomical structure. The results indicate that the dentate nucleus and cerebellar hemispheres take part in preprogramming movement duration (Kornhuber) for rapid ballistic movements. In slower target movements, the dentate nucleus may be involved in sectional preprogramming of step movements.

Animals↗
PubMed1974

Acquired pendular nystagmus with oscillopsia in multiple sclerosis: a sign of cerebellar nuclei disease.

In an unselected series of 644 cases of multiple sclerosis, 25 cases with acquired pendular nystagmus were found. Ten additional cases of pendular nystagmus in multiple sclerosis were investigated, and four cases from the literature are analysed. Acquired pendular nystagmus is purely sinusoidal in form, ceases with eye closure, is accompanied by oscillopsia, often monocular and vertical in direction, and never accompanied by optokinetic inversion. This is different from congenital nystagmus. Acquired pendular nystagmus in multiple sclerosis shows a high correlation with holding tremor of head and arm and with trunk ataxia, and must therefore be viewed as a result of lesions of cerebellar nuclei or their fibre connections with the brain-stem. Supporting evidence is discussed. The results fit into a theory of cerebellar function according to which the cerebellar nuclei are involved in the maintenance of positions.

Adult↗
PubMed1972

Interval analysis of repetitive denervation potentials of human skeletal muscle.

Interval analyses of denervation potentials (fibrillation-potentials and positive sharp waves) in human skeletal muscles were performed using a DEC PDP-12 computer. Extremely small differences between consecutive intervals (usually less than 1%) and slow up and down drifts in the spontaneous discharge frequency were found to be characteristic of repetitive denervation potentials. These two findings are safe criteria for the clinical diagnosis of denervation and they may be superior to the more commonly used criteria based upon the shapes, amplitudes, and durations of the potentials. Physiological data from the literature as well as hypotheses relating to spontaneous activity are reviewed. Generator potentials across the muscle fibre membrane, lowered firing threshold, and constant-sized after-potentials are considered the basic factors relevant to spontaneous and rhythmical firing and to the slow drift observed in the firing frequency.

Action Potentials↗