Antidromic Sensory Nerve Action Potentials Research Articles

Effect of percutaneous electrical stimulation with high-frequency alternating currents at 30 kHz on the sensory-motor system.

Unmodulated high-frequency alternating currents (HFAC) are employed for producing peripheral nerves block. HFAC have been applied in humans with frequencies up to 20 kHz, whether transcutaneously, percutaneously, or via surgically-implanted electrodes. The aim of this study was to assess the effect of percutaneous HFAC, applied with ultrasound-guided needles at 30 kHz, on the sensory-motor nerve conduction of healthy volunteers. A parallel, double-blind, randomized clinical trial with a placebo control was conducted. Percutaneous HFAC at 30 kHz or sham stimulation was applied via ultrasound-guided needles in 48 healthy volunteers (n = 24 in each group) for 20 min. The assessed outcome variables were pressure pain threshold (PPT), mechanical detection threshold (MDT), maximal finger flexion strength (MFFS), antidromic sensory nerve action potential (SNAP), hand temperature, and subjective sensations by the participants. The measurements were recorded pre-intervention, during the stimulation (at 15 min), immediately post-intervention (at 20 min), and 15 min after the end of treatment. The PPT increased in the active group compared with sham stimulation, both during the intervention [14.7%; 95% confidence interval (CI): 4.4-25.0], immediately post-intervention (16.9%; 95% CI: -7.2-26.5), and 15 min after the end of the stimulation (14.3%; 95% CI: 4.4-24.3) (p < 0.01). The proportion of participants who reported feelings of numbness and heaviness was significantly higher in the active group (46 and 50%, respectively) than in the sham group (8 and 18%, respectively) (p < 0.05). No intergroup differences were observed in the remaining outcome variables. No unexpected adverse effects derived from the electrical stimulation were reported. Percutaneous stimulation with HFAC at 30 kHz applied to the median nerve increased the PPT and subjective perception of numbness and heaviness. Future research should evaluate its potential therapeutic effect in people with pain. https://clinicaltrials.gov/ct2/show/NCT04884932, identifier NCT04884932.

Spread to the dorsal ulnar cutaneous branch: A pitfall during the routine antidromic sensory nerve conduction study of the ulnar nerve

ObjectiveTo document the incidence and effects of a previously unreported pitfall during routine antidromic sensory nerve conduction study (SCS) of the ulnar nerve: the spread of the wrist stimulation to the dorsal ulnar cutaneous (DUC) branch. MethodsThe subjects consisted of 20 healthy volunteers. An antidromic sensory nerve action potential (SNAP) was recorded over the proximal interphalangeal joint of the little finger, and the DUC response was monitored over the dorsum of hand to check for the occurrence of this spread. ResultsThe spread occurred in all subjects, which caused a 4–87% increase in the SNAP amplitude. The likelihood that this spread may occur during routine SCS varied among the subjects, and also within an individual subject depending on minute shifts of the stimulating site. Selective stimulation of the ulnar main trunk up to maximal intensity without spread to the DUC was not achieved despite every effort in two subjects. ConclusionsThis spread phenomenon may occur frequently during routine antidromic SCS, but would not be recognized without monitoring the DUC response. SignificanceThis pitfall may interfere with the reproducibility of the SNAP amplitude, and also with the diagnosis of ulnar neuropathy at the wrist.

Effect of maximal voluntary contraction on the amplitude of the compound muscle action potential: Implications for the interpolated twitch technique

The compound muscle action potential (M(MAX)) during a maximal voluntary contraction (MVC) may be measured to determine if the motor nerve has been supramaximally stimulated during the interpolated twitch technique (ITT). Ten males performed isometric knee extension MVCs. M(MAX) for the vastus medialis was recorded during MVC and rest. To examine the effect of stimulating electrode movement, the M(MAX) of the thenar group and antidromic sensory nerve action potentials (SNAPs) to the third digit were recorded in a separate experiment. M(MAX) during MVC was reduced by 18% (P < 0.0001) and 43% (p < 0.0001) for the quadriceps and thenar group, respectively. The SNAP amplitude was not different between rest and MVC (P = 0.18). Reduction of M(MAX) during MVC suggests that some motor axons are refractory and unable to respond to a superimposed maximal stimulus. These results have implications for the sensitivity of the interpolated twitch technique.

The consequences of stimulus intensity on sensory nerve action potentials

Although clinical references recommend evoking sensory nerve action potentials (SNAPs) using supramaximal stimulation, many patients and research subjects report that the maximal and supramaximal stimulation is uncomfortable. The purpose of this study was to determine whether using stimulation intensities at maximal and submaximal levels results in differences in SNAP latency or amplitude outcomes relative to SNAPs recorded using supramaximal stimulation. Twenty healthy male and female subjects participated. Antidromic SNAPs were evoked at two separate sites along the course of the median nerve: (1) just proximal to the wrist and (2) just proximal to the antecubital fossa in each subject. All evoked potentials were recorded from the second digit. The stimulation current that resulted in a maximal amplitude SNAP was determined and 10 SNAPs were ensemble averaged using this stimulation level. Ten SNAPs were then evoked at each of four other stimulation intensities (20% and 10% both above and below that which generated a maximal amplitude SNAP) and were ensemble averaged. For each stimulation intensity and stimulation site, SNAP amplitude and latency determined for each ensemble average. SNAP amplitudes and latencies were compared among stimulus levels and between sexes using a repeated measures analyses of variance. The results of this study suggest that stimulus intensities used to generate SNAPs at the median nerve do not need to be supramaximal in order to generate valid and reliable SNAP data, with stimulation intensities as low as 20% below maximal proving to be sufficient, particularly for the measurement of SNAP latency.

Decreased sensory cortical excitability after 1 Hz rTMS over the ipsilateral primary motor cortex

Objectives: To study changes in the excitability of the sensory cortex by repetitive transcranial magnetic stimulation (rTMS) in humans. Methods: Somatosensory evoked potentials (SEPs) and antidromic sensory nerve action potentials (SNAPs) were elicited by right median nerve stimulation at the wrist before and after low frequency (1 Hz) rTMS over the left motor cortex, lateral premotor cortex, sensory cortex, and also after sham stimulation. The intensity of rTMS was fixed at 1.1 times the active motor threshold at the hand area of motor cortex. Results: N20 peak (N20p)-P25 and P25-N33 amplitudes were suppressed after rTMS over the motor cortex, whereas the N20 onset (N20o)-N20p and SNAP amplitudes were not affected. They recovered to the baseline about 100 min after the rTMS. rTMS over the premotor cortex or sensory cortex or sham stimulation had no suppressive effect on SEPs. Conclusions: The reduction of N20p-P25 and P25-N33 components without any changes of N20o-N20p amplitude suggests that the suppression occurs in the sensory cortex. rTMS (1 Hz) of the motor cortex induces a long-lasting suppression of the ipsilateral sensory cortex even at an intensity as low as 1.1 times the active motor threshold, probably via cortico-cortical pathways between motor and sensory cortex.

Conduction block and segmental velocities in carpal tunnel syndrome

In carpal tunnel syndrome (CTS) standard measurement of median distal motor latency and sensory conduction does not distinguish whether low amplitude responses are due to axonal degeneration or demyelination. In 88 control and 294 CTS hands we recorded amplitude and duration of compound muscle action potential (CMAP) and of antidromic sensory nerve action potential (SNAP) after palm and wrist stimulation to determine wrist to palm amplitude, duration ratios and segmental conduction velocities. In 16% of CTS hands there was an abnormal amplitude reduction without increased duration of CMAP or SNAP from wrist stimulation indicating partial conduction block. In 148 hands distal motor latency to abductor pollicis brevis and/or sensory conduction to digit 2 were abnormal. In the remaining 146 hands wrist to palm motor conduction was less than 35 m/s in 22.6% and wrist to palm sensory conduction was less than 45 m/s in 13%. At least one segmental conduction was abnormal in 27% of hands. Segmental studies allow the discrimination between conduction block and axonal degeneration, increase diagnostic yield in CTS, and might be useful in addressing treatment and predicting outcome.

Characteristics of the F response: a single motor unit study.

Trains of 100 to 200 stimuli result in F discharges from less than one half of motor units of hand muscles. The maximum observed F discharge frequency was 10%. There was no relation between the surface voltage of motor unit potentials and the frequency of F discharge. The motor unit potentials of larger surface voltage were recruited at higher stimulus intensity levels, usually supramaximal for the antidromic sensory nerve action potential. No correlation was observed between F latency and the surface voltage of the motor unit potentials. In only one pathological example was a clear interaction observed between the frequency of F discharge in motor unit potentials and the recruitment of other single motor unit potentials by increments in the stimulus intensity. The observations suggested that caution should be exercised before the F discharge is accepted as a method for measuring proximal conduction times in human motor nerves.