RSS Stimulation with high frequency electric pulses

Sham RSS Stimulation (no pulses are transmitted)

RSS is a high frequency electrical stimulation protocol delivered to the peripheral nerves (median and ulnar nerve) of the hand. The signals are generated by a TENS-stimulator and are conveyed to each finger of the hand via a custom-made hand-shaped device with conductive contacts at each fingertip and at the palmar base.

In case of the sham-stimulation no pulses are transmitted.

Thresholds on the tip of the index finger of both hands are assessed using the method of constant stimuli. One single needle and seven pairs of needles with different spacings are tested in randomized order. After each presentation, the subject has to report the sensation of one or two needles by answering immediately "one" or "two." Each distance is presented eight times resulting in 64 single decisions. The summed responses are plotted against distance as a psychometric function for absolute threshold and get fitted by a binary logistic regression. Threshold are taken from the fit at the distance at which 50% correct answers are given.

Pain intensity is rated by the patient on a 11-point numerical rating scale (NRS). Pain intensity is rated before the start of the 5 day stimulation phase (baseline,pre) and at the end (post, in combination with the other outcome measures). Additionally pain intensity is rated directly before the start of each daily stimulation session and immediately after each session of 45 minute duration.

Somatosensory evoked potentials after electrical paired pulse median nerve stimulation are recorded. The median nerve is stimulated by innocuous paired electrical pulses conveyed to the nerve by a block electrode placed on the wrist. For correct positioning the subject has to report a prickling sensation in thumb, index and middle finger. Stimulation intensity is choosen to induce a small muscular twich at the thenar muscles. SEP recordings are done with a 3-electrode array. Two electrodes are fixed on the scalp over the left and right somatosensory cortex. The third (reference) electrode is fixed over the midfront. SEP signals get amplified and filtered and digitized in a PC.