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Biomedical subjects

J Gybels

Publications and source records attributed to J Gybels.

At least 55 records · Page 3Linked to original sources
PubMed1984

Nociceptor discharges and sensations due to prolonged noxious mechanical stimulation--a paradox.

Forceps were used to induce controlled squeeze stimuli to small skin folds of the dorsal surface of the hand of human volunteers. Psychophysical and microneurographic experiments were performed to characterize sensations and afferent input induced by stimuli exerting a constant force during a period of 120 s. The psychophysical data showed that forces greater than 4 N exerted on forceps faces of 30 mm2 elicited pain, which had two main characteristics: (a) stronger stimuli evoked a stronger pain response, (b) pain had a tendency to increase throughout the 120-s stimulus duration. In contrast, discharges of polymodal C-fibre nociceptors showed an initial high frequency dynamic discharge followed by adaptation. It was found that the ratio of C-fibre activity to activity in myelinated SA-fibres provided a better correlate of the time course of the stimulus-induced pain sensations than C-fibre activity alone. Possible reasons for the mismatch between nociceptor input and pain sensations are discussed.

Afferent Pathways↗
PubMed1981

C nociceptor activity in human nerve during painful and non painful skin stimulation.

Percutaneous recordings from more than one hundred single C fibres have been performed in the radial nerve of conscious human subjects. All these fibres belong to the poly-modal C nociceptor group, being excited by mechanical and thermal and also by chemical stimulation. Conduction velocities showed a monophasic distribution with a mean value of 0.86 m/s (SD: 0.17). The mechanical threshold, measured with von Frey hairs, varied between 2.3 and 13.1 g. The receptive field was circular or elliptical; for 33 units the mean axes were 6 mm and 7 mm. Mechanically evoked C fibre discharge even up to more than 10 spikes/s was not necessarily accompanied by pain sensation. Nettle sting evoked an irregular C fibre discharge (maximum 10 spikes/s) accompanied by a pricking and burning sensation; the sensation of itch which was sometimes reported, was not correlated with the discharge frequency. C fibre activation by a chemical irritant (paint remover) also evoked an irregular discharge (maximum 3 to 6 spikes/s), accompanied by pricking and burning pain sensation. The C threshold for radiant heat usually lay below the subject's pain threshold. Increasing skin temperature produced increasing neural firing rate. The mean spike frequency rarely exceeded two spikes/s even with stimuli evoking strong heat pain. The occurrence of subjective heat pain response could be as well predicted from th C fibre spike frequency as from the skin temperature. It is concluded that nociceptive C input provoked by thermal or chemical stimuli correlates well with pain sensation. However, similar C input provided by mechanical stimulation which activates also A beta mechanoreceptors, did not necessarily produce pain sensation.

Adult↗
PubMed1980

Latencies of chemically evoked discharges in human cutaneous nociceptors and of the concurrent subjective sensations.

Percutaneous recordings from single nociceptive A delta- and C-fibers have been performed from the superficial radial nerves of conscious human subjects. Nociceptors were tested with a chemical irritant substance, which induced a burning sensation when applied to the intact skin. A comparison of the onset of spike discharges in nociceptors and the onset of the subjective burning sensation indicated that under the conditions of our experiments summation of input from nociceptors is needed in order to induce pain sensations. In particular, our results indicate spatial summation.

Adult↗
PubMed1980

Electrical stimulation of the central gray for pain relief in human: autopsy data.

Anatomopathological studies are reported of 5 brains in which electrical stimulation of the periventricular--periaqueductal gray was applied for the treatment of chronic pain. It was found that the recommended target was reached in 4 cases (only 1 case out of 5 was successful as far as a pain relief is concerned). PtIr electrodes caused little tissue reaction. The chronic stimulation had not provoked lesions observable by light-microscopy.

Brain↗
PubMed1980

Reconstruction of an arbitrary cross section from the serial drawings of a stereotaxic brain atlas.

A method is described for the reconstruction of arbitrary cross section from the serial line drawings of a stereotaxic brain atlas. Mathematically, the problem reduces to the intersection of a plane with a line pattern lying in another plane. However, the calculation yields a cloud of points, often confusing and unusable for the surgeon. Because it is impossible to link correctly all the calculated points in all cases [1,2], we propose a method where the number of points is drastically reduced: only regions of interest are depicted, i.e., the area where the electrode point is situated and the neighbouring regions. Instead of points, symbols are displayed, each symbol representing a different region. The efficiency of the method is shown using an atlas simulation of four intersecting spheres in the three dimensional space, Although the procedure is useful for all stereotaxic brain atlasses, a practical example is given where the poor quality of the reconstructed images does not allow good interpretation.

Analog-Digital Conversion↗
PubMed1980

[Cerebellar tumours in the child. Technic and operative results (author's transl)].

The authors present a series of 95 cerebellar tumours in the child. They discuss the relationship between the clinical syndrome and the histological nature on the one hand and the site of the tumour on the other hand. Favourable operative results, characterised by a very low mortality and by the absence of grave postoperative complications, are attributed to as complete an excision as possible of the tumour and preoperative normalisation of intracranial pressure by the installation of ventriculo-subcutaneous drainage.

Adolescent↗
PubMed1979

Percutaneous epidural dorsal cord stimulation in multiple sclerosis.

The effectiveness of percutaneous epidural stimulation has been evaluated in 11 patients with multiple sclerosis. Trial stimulation was performed at the thoracic level and lasted for 4 to 10 days. Evaluation was accomplished before the start and at regular intervals during and after the treatment. The scoring systems of the Standard Neurological Examination and of the Disability Status Scale of Kurtzke were used for evaluation of the neurological status. In addition, functionally useful changes were assessed by a physical therapist using a disability scoring technique designed at the National Multiple Sclerosis Centre at Melsbroek. Visual and somatosensory evoked potentials were also recorded at regular intervals. Six out of 11 patients claimed a subjective improvement following stimulation. But only four patients had better scoring results in the quantitative neurological testing, and for only two patients was this objective improvements functionally useful.

Activities of Daily Living↗
PubMed1979

A comparison between the discharges of human nociceptive nerve fibres and the subject's ratings of his sensations.

1. Impulses in cutaneous nerve fibres were recorded percutaneously with tungsten micro-electrodes from the superficial radial nerve of adult human subjects. 2. Eight units studied had conduction velocities below 1.5 m/sec, and thus belong to the class of C fibres. On the basis of their responsiveness to mechanical and to thermal stimuli the units were classified as 'polymodal nociceptors'. 3. Units were tested with 12 sec heat pulses starting from a base line temperature of 43.0-43.5 degrees C. Heat stimuli reaching three different maximal levels were applied in randomized order, the subjects being blind with respect to stimulus size. Each of the eight units studied was tested with more tha 20 stimuli and with four of them were 80-125 stimulus repetitions. 4. After each stimulus the subjects had to rate his sensations on a six-point rating scale extending from 'just noticeable' to 'very hot, painful'. 5. Discrimination between the three stimulus levels by the integtated spike discharges and by the ratings of the subject was compared using the P(A) measure of the Signal Detection Theory. It was found that both the neurophysiological and the psychophysical measurements provided about equal discrimination. 6. In addition it has been found that spike discharges and ratings share a common variance beyond their common dependence on the stimulus level. Among the factors contributing to this interdependence a 'temporal position effect' was the most significant. 7. In spite of this interdependence between discharge rates and subjective ratings, the latter gave a better estimation of the stimulus size than of the discharge rates of the individual C fibre under study. 8. It was concluded that the polymodal C-nociceptors might be instrumental for the quantitative aspects of heat pain sensation. The hypothesis was derived from the present results that, under the conditions of cour experiments, the loss of information in the course of central processing might be about equal to the gain by the parallel processing in a population of nociceptors excited by a stimulus.

Action Potentials↗