Sensations and reaction times evoked by electrical sinusoidal stimulation.

OBJECTIVE: To determine whether 5 Hz and 2000 Hz sinusoidal electric currents evoke different sensations and to indirectly evaluate which peripheral nerve fibers are stimulated by these different frequencies. METHODS: One hundred and fifty subjects chose three among eight descriptors of sensations evoked by 5 Hz and 2000 Hz currents and the results were submitted to factor analysis. In 20 subjects, reaction times to 5, 250 and 2000 Hz currents were determined at 1.1 x ST and reaction times to 5 Hz currents were also determined at 2 x ST. RESULTS: Responses were grouped in four factors: Factor 1, which loaded mainly in descriptors related to tweezers stimulation, was higher than the other factors during 2000 Hz stimulation at 1.5 x ST. Factor 2, which loaded mainly in descriptors related to needle stimulation, was higher than the other factors during 5 Hz stimulation. Factor 1 increased and Factor 2 decreased with an increase in 5 Hz intensity from 1.5 to 4x ST. Reaction times measured from the fastest responses were significantly different: 0.57 s (0.16 to 1.60), 0.34 s (0.12 to 0.71) and 0.22s (0.08 to 0.35) for 5, 250 and 2000 Hz, respectively, and 0.22s (0.11 to 0.34) for 5 Hz at 2 x ST. CONCLUSIONS: Sinusoidal electrical stimulation of 5 Hz and 2000 Hz evoke different sensations. At juxta-threshold intensities, RT measurements suggest that 2000 Hz stimulates Abeta-fibers, 250 Hz Abeta- or A partial differential-fibers, 5 Hz Abeta-, A partial differential- or C-fibers. The fiber type, which was initially stimulated by the lower frequencies, depended on inter-individual differences.

The relationship between symptoms and electrophysiological detected compression of the median nerve at the wrist.

OBJECTIVE: The aim of this study was to evaluate the relationship between carpal tunnel syndrome symptoms and compression of the median nerve at the wrist in symptomatic patients. METHODS: A total of 250 patients were selected among those referred for electrodiagnostic evaluation with complaints involving hand or wrist. Primary and secondary symptoms were extracted from the answers to the instrument proposed by Levine et al. [J Bone Joint Surg Am 1993;75:1585]. The association of symptoms and the presence of compression of the median nerve at the wrist were ascertained through a multiple logistic regression test. RESULTS: Secondary symptoms (pain and weakness) were inversely associated with the presence of median nerve compression. Furthermore, primary symptoms (paresthesia, disability and nocturnal symptom) occurred similarly in patients with and without electrophysiologic findings of median nerve compression at the wrist.

Potencial evocado por estimulaçäo do nervo mediano (PESS): componentes subcorticais / Evoked potentials by median nerve stimulation (SSEP): subcortical components

Este estudo constitui uma revisäo de literatura realizada com a finalidade de se relacionar a designaçäo, as características dos campos de potencial e os geradores implicados, para os componentes subcorticais do potencial evocado somatossensorial por estimulaçäo do nervo mediano no punho

Potencial evocado por estimulaçäo do nervo mediano: comparaçäo do tempo de conduçäo central definido por diferentes pontos de medida / Evoked potentials by median nerve stimulation: comparation of central conduction time defined by different measure points

Neste estudo é feita comparaçäo entre a latência interpicos N13-N20 e entre inícios N11-N20. É evidenciada diferença significante entre essas medidas. Os achados sugerem ainda que as montagens usualmente utilizadas para a medida interpicos podem ser utilizadas para determinaçäo das latências de inícios das ondas, bem como para determinaçäo do ponto de fracionamento da medida entre inícios. É salientado o diferente signficado fisiológico das duas medidas

Observaçöes relacionadas à utilizaçäo de montagens entre a face posterior do pescoço e o couro cabeludo no potencial evocado por estimulaçäo do nervo mediano / Related observations for the use of mounting between neck posterior and scalp in evoked potentials by median nerve stimulation

Foram realizados potenciais evocados por estimulaçäo do nervo mediano no punho, em grupo de voluntários normais. Foram avaliados os componentes que ocorreram entre 12 e 22 ms. Os registros foram feitos com referências cefálicas e näo cefálicas. Foi evidenciada maior contribuiçäo do complexo P13-14 na amplitude do componente N13 registrado entre C6 e Fz. Näo foram detectadas diferenças significativas na amplitude e latência dos componentes N18 e P22 quando avaliados nas montagens FZ-näo cefálico e C6-FZ. Säo discutidas as implicaçöes desses achados para a interpretaçäo clínica dessas respostas

Median nerve sep after a high medullary lesion: preserved N18 and absent P14 components. Case report

Median nerve SEPs recorded from patient with a high medullary lesion are described. The lesion involved the anteromedial and anterolateral right upper third of the medulla, as documented by MRI. Forty one days after the lesion, left median nerve SEP showed preserved N18 and absent P14 and N20 components; stimulation of the right median nerve evoked normal responses. These findings agree with the proposition that low medullary levels are involved in the generation of the N18 component of the median nerve SEP.