Remote Effects of Electromagnetic Millimeter Waves on Experimentally Induced Cold Pain: A Double-Blinded Crossover Investigation in Healthy Volunteers.

BACKGROUND: The hypoalgesic effect of electromagnetic millimeter waves (MW) is well studied in animal model; however, the results of human research are controversial. The aim of this study was to evaluate the effects of various frequency ranges of MW on hypoalgesia using the cold pressor test (CPT). METHODS: Experimental pain was induced using standardized CPT protocols in 20 healthy male volunteers. The skin of the lower part of sternum was exposed to MW with a frequency of 42.25 GHz (active generator); MW within 50-75 GHz frequency range (noise generator); or an inactive MW device (placebo generator) in a random crossover double-blinded manner. Pain threshold, measured using the CPT, was the primary outcome. Other CPT parameters, heart rate, blood pressure, incidence of subjective sensations (paresthesia) during exposure, as well as quality of volunteers' blinding were also recorded. The end points of the condition with exposure to 42.25 GHz, were compared with baseline; exposure to noise 50-75 GHz; and placebo generators. RESULTS: Pain threshold increased during exposure to the 42.25 GHz generator when compared with baseline: median difference (MD), 1.97 seconds (95% confidence interval [CI], 0.35-3.73) and noise generator: MD, 1.27 seconds (95% CI, 0.05-2.33) but not compared with the placebo generator. Time to onset of cold and increasing pain sensations as well as diastolic blood pressure increased under the exposure to the 42.25 GHz generator when compared with baseline and noise generator. Other outcome measures were comparable among the study conditions. CONCLUSIONS: We were able to partially confirm the previously suggested hypoalgesic effects of low-intensity electromagnetic MW. However, the effect was indistinguishable from the placebo condition in our investigation.

Preliminary findings of cerebral responses on transcutaneous vagal nerve stimulation on experimental heat pain.

Transcutaneous vagal nerve stimulation (TVNS) is a promising complementary method of pain relief. However, the neural networks associated with its analgesic effects are still to be elucidated. Therefore, we conducted two functional magnetic resonance imaging (fMRI) sessions, in a randomized order, with twenty healthy subjects who were exposed to experimental heat pain stimulation applied to the right forearm using a Contact Heat-Evoked Potential Stimulator. While in one session TVNS was administered bilaterally to the concha auriculae with maximal, non-painful intensity, the stimulation device was switched off in the other session (placebo condition). Pain thresholds were measured before and after each session. Heat stimulation elicited fMRI activation in cerebral pain processing regions. Activation magnitude in the secondary somatosensory cortex, posterior insula, anterior cingulate and caudate nucleus was associated with heat stimulation without TVNS. During TVNS, this association was only seen for the right anterior insula. TVNS decreased fMRI signals in the anterior cingulate cortex in comparison with the placebo condition; however, there was no relevant pain reducing effect over the group as a whole. In contrast, TVNS compared to the placebo condition showed an increased activation in the primary motor cortex, contralateral to the site of heat stimulation, and in the right amygdala. In conclusion, in the protocol used here, TVNS specifically modulated the cerebral response to heat pain, without having a direct effect on pain thresholds.

Transcutaneous vagal nerve stimulation may elicit anti- and pro-nociceptive effects under experimentally-induced pain - a crossover placebo-controlled investigation.

Vagal nerve stimulation is a promising method for the treatment of pain. The aim was to investigate the effect of non-invasive transcutaneous vagal nerve stimulation (TVNS) on the experimental pain threshold (PT) and to compare it with placebo. PT of standardized electrical stimulation was measured in 22 healthy male volunteers during two study sessions. TVNS was applied to the auricular concha bilaterally for 35min using 2Hz/100Hz bursts with the intensity, which was individually maximal but non-painful. During the placebo session, the volunteers received no stimulation. PT, heart rate and blood pressure were registered as outcome measures. There were no differences in PT values between TVNS and placebo conditions in the group analysis. Fifteen volunteers (responders) reacted with an increase in PT during TVNS (p<0.01 vs. baseline) but not during the placebo session. Another six participants reported decreased PT during and after TVNS (p<0.05 vs. baseline), but not during the placebo session. Heart rate and blood pressure did not change during the study. Transcutaneous vagal nerve stimulation may produce both anti- and pro-nociceptive effects in healthy volunteers. The individual sensitivity and TVNS parameters might play a role.

Vagal sensory evoked potentials disappear under the neuromuscular block - an experimental study.

BACKGROUND: Transcutaneous vagal nerve stimulation is a promising treatment modality in patients suffering mood disorders and chronic pain, however, the mechanisms are still to be elucidated. A recently developed technique of EEG responses to electrical stimulation of the inner side of the tragus suggests that these responses are far field potentials, generated in the vagal system - Vagal Sensory Evoked Potentials (VSEP). OBJECTIVE: To reproduce the VSEP technique free from myogenic artifacts. METHODS: Fourteen ASA I-II patients scheduled for elective surgery in standardized Total Intravenous Anesthesia (TIVA) were enrolled. Transcutaneous electrical stimulation was applied to the inner side of the right tragus. Averaged EEG responses were recorded from the electrode positions C4-F4 and T4-O2 before and after induction of TIVA, during the maximal effect of the non-depolarizing muscle relaxing agent, cis-atracurium (C-AR) and after recovery from C-AR under TIVA. RESULTS: Typical response curves with P1, N1 and P2 peaks could be reproduced in all patients before and after anesthesia induction. The response curves disappeared during the C-AR action and re-appeared after recovery from C-AR under TIVA. CONCLUSION: The disappearance of the scalp responses to electrical tragus stimulation under the neuromuscular block suggests a muscular origin of these potentials.