Résumé :
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Communication n° 231. INTRODUCTION : Following an action potential, peripheral nerve axons become first totally unexcitable: absolute refractory period (ARP) then partially unexcitable: relative refractory period (RRP). OBJECTIVE : To compare various techniques of stimulation to estimate ARP and RRP in motor nerve trunks of healthy subjects to establish normative values. METHODS : Double collision (DC) technique and two types of paired pulse (PP) technique, with test stimulation of supramaximal (PPsupra) or submaximal (PPsub) intensity, were applied to 32 healthy subjects. The ulnar nerve was stimulated either at a single site (wrist) for PP techniques or at two sites (wrist and elbow) for DC technique, with various distal interstimuli intervals (ISIs). The elicited compound muscle action potentials (CMAPs) were recorded from the abductor digitorum minimi muscle. The DC technique provided estimates of minimal and maximal ARPs, whereas maximal RRP values were obtained with the PP techniques. Pain induced by each technique was assessed on a visual analogue scale. RESULTS : RP estimates varied depending on stimulation technique. The DC technique was more painful than the PP techniques, but provided shorter and more accurate ARP values (1.21 ms Æ 0.46), whereas the PPsub technique provided longer, but valid RRP values. DISCUSSION : Once normative values were determined and the application field of each technique defined, PP techniques have been applied in 10 patients suffering from neuropathy and radiculopathy. The PR values increase in patients was not correlated with neural conduction velocity abnormalities. CONCLUSIONS : Compared to the PP techniques, the DC technique allowed the evaluation of the whole distribution of ARP estimates, not distorted by muscle fiber RPs. For RRP estimation, the PPsub technique can be preferred to the PPsupra technique. The evaluation of PR can be easily and reliably assessed in whole motor nerve trunks of humans, providing valuable complementary information to classical conduction velocity studies in order to assess peripheral nerve excitability. Acknowledgements: This work was supported by the Association Française contre les Myopathies (AFM).
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