Humans can perceive electric currents through sensory nerve activation
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Multiple peer-reviewed scientific studies report that humans can perceive electric currents through sensory nerve and neural pathway activation, establishing quantifiable perception thresholds.
<h4>Objective</h4>To investigate the efficacy and safety of transcutaneous electrical nerve stimulation (TENS) for relief of pain in adults.<h4>Design</h4>Systematic review and meta-analysis.<h4>Data sources</h4>Medline, Cochrane Central, Embase (and others) from inception to July 2019 and updated on 17 May 2020.<h4>Eligibility criteria for study selection</h4>Randomised controlled trials (RCTs) comparing strong non-painful TENS at or close to the site of pain versus placebo or other treatments in adults with pain, irrespective of diagnosis.<h4>Data extraction and synthesis</h4>Reviewers independently screened, extracted data and assessed risk of bias (RoB, Cochrane tool) and certainty of evidence (Grading and Recommendations, Assessment, Development and Evaluation). Mean pain intensity and proportions of participants achieving reductions of pain intensity (≥30% or <u>></u>50%) during or immediately after TENS. Random effect models were used to calculate standardised mean differences (SMD) and risk ratios. Subgroup analyses were related to trial methodology and characteristics of pain.<h4>Results</h4>The review included 381 RCTs (24 532 participants). Pain intensity was lower during or immediately after TENS compared with placebo (91 RCTs, 92 samples, n=4841, SMD=-0·96 (95% CI -1·14 to -0·78), moderate-certainty evidence). Methodological (eg, RoB, sample size) and pain characteristics (eg, acute vs chronic, diagnosis) did not modify the effect. Pain intensity was lower during or immediately after TENS compared with pharmacological and non-pharmacological treatments used as part of standard of care (61 RCTs, 61 samples, n=3155, SMD = -0·72 (95% CI -0·95 to -0·50], low-certainty evidence). Levels of evidence were downgraded because of small-sized trials contributing to imprecision in magnitude estimates. Data were limited for other outcomes including adverse events which were poorly reported, generally mild and not different to comparators.<h4>Conclusion</h4>There was moderate-certainty evidence that pain intensity is lower during or immediately after TENS compared with placebo and without serious adverse events.<h4>Prospero registration number</h4>CRD42019125054.
ABSTRACT
It remains unknown why some people with diabetes develop painful neuropathies while others experience no pain. This study aimed to validate a novel method for assessing the function of small sensory nerves in diabetes to further elucidate this phenomenon.The function of large and small nerves was assessed using a novel perception threshold tracking technique in three well-characterized groups (n=60) with type 1 diabetes and 1) painful diabetic peripheral neuropathy (T1DM+PDPN), 2) painless diabetic peripheral neuropathy (T1DM+DPN), 3) no neuropathy (T1DM-DPN), and 4) healthy controls (n=20). Electrical currents with different shapes, duration, and intensities were applied by two different skin electrodes activating large- and small fibers, respectively. The minimal current needed to activate the fibers were analyzed as the rheobase of the stimulus-response function. Nerve fiber selectivity was measured by accommodation properties of stimulated nerves.The rheobase of both fiber types were highest for T1DM+PDPN, followed by T1DM+DPN, T1DM-DPN and healthy controls, indicating that the nerve properties are specific in individuals with diabetes and pain. There was an overall significant difference between the groups (p<0.01). The accommodation properties of stimulated fibers were different between the two electrodes (p<0.05) apart from in the group with T1DM+PDPN, where both electrodes stimulated nerves displaying properties similar to large fibers.Perception threshold tracking reveals differences in large- and small nerve fiber function between groups with and without diabetes, DPN, and pain. This indicates that the methods have potential applications in screening DPN and explore further the features differentiating painful from non-painful DPN.
Abstract Introduction Pain is one of the main symptoms prevalent in most pathologies. Transcutaneous Electrical Nerve Stimulation (TENS) represents not only a therapeutic measure, but also a mean to quantify the neurosensory and pain perception in patients with chronic pain. Objective To evaluate the relationship between sex and age with neurosensory thresholds (sensory threshold and tolerance threshold) in the application of therapeutic current in patients with chronic pain. Methods Forty-five patients with chronic pain (30 women and 15 men) aged between 24 and 87 years were selected. Each patient answered the Individual Questionnaire, McGill Pain Questionnaire (MPQ) and Beck Depression Inventory (BDI). Subsequently, the electric current was applied, through which the sensory and pain thresholds were analyzed, as well as the perception of activation of the neurosensory pathways for each individual. Data were analyzed using the SPSS 24.0 for Windows. Results There was no significant correlation (p > 0.05) between a possible depressive diagnosis and the perception of current by the sensory and pain thresholds. Regarding sex, there was a significant difference in sensory thresholds (p = 0.003) between men and women, while no statistical differences were observed between sexes for pain complaint and pain threshold (p > 0.05). For the correlational analysis, a significant correlation (p = 0.05) was identified between the variables BMI and pain tolerance threshold (r = 0.68) for females and age and sensory threshold (r = 0.65) for males. Conclusion The sex and age variables are important in the measurement of TENS parameters because they lead to significant differences in sensory and pain thresholds.
Objectives. Transcutaneous Electrical Nerve Stimulation (TENS) to the lower back is an established electrical therapy for acute and chronic back pain. The efficacy and mechanisms of lower back TENS depend on the penetration depth of electrical current. We compare the intensity and spatial extent (depth) of current flow in the body during TENS with varied electrode positions/shapes on the human back. Materials and Methods. A high-resolution MRI-derived anatomical model of the back was developed, considering major tissue compartments, including skin and muscles. TENS with upper and lower back electrode positions and varied electrode shapes (square, circular, rectangular) were simulated. An exemplary 50 mA current was applied under quasistatic approximation and quasi-uniform electric field assumption of 6.15 V m−1 (low), 12.3 V m−1 (mid), and 24.6 V m−1 (high) neuromuscular activation thresholds were considered. Results. Under all simulated TENS conditions (50 mA), electric fields at the skin exceed the high threshold (consistent with peripheral nerve activation) and at least some muscle regions exceed the mid threshold. Muscle activation was influenced by the anatomy of muscle in the medial-lateral direction and upper-lower back. The electrode shape had minimal effect on deep tissue current penetration. Conclusions. Our simulations indicate significant current penetration into back tissue (electric fields above low threshold) to >8 cm in all TENS conditions simulated, consistent with nerve and muscle activation. Significance. Anatomically precise models of upper and lower back TENS show current penetration to deep muscle, supporting direct muscle stimulation driving clinical benefits.
Radiofrequency contact current occurs when a human touches objects with different electrical potentials. For emerging wireless power transfer systems, this type of exposure is potentially more restrictive than direct exposure. The limits for contact current are prescribed in the international guidelines for human protection from electromagnetic fields, but its rationale is limited compared with that for direct field exposure. In this article, the perceptional threshold for electrostimulation and heating was evaluated based on computational dosimetry from 10 kHz to 10 MHz. First, the time course of the temperature rise was calculated until each subject perceived the contact current. Second, the perception of current was estimated considering the nerve activation modeling. The computationally estimated current threshold for nerve activation was consistent with the measured data at 100 kHz and increased linearly with increasing frequency, which was contrary to the measured threshold for perception above 300 kHz. By contrast, the estimated perceptual temperature increase was smaller at 100 kHz than at 300 kHz and above. These results indicate that the transient frequency of the threshold for stimulation and heating lies between 100 and 300 kHz, supporting the transition frequency of contact current in the international guidelines.
Abstract : A survey was made of all available information about electric shock to humans, including children, at power-transmission frequencies of 50 and 60 Hz. Reliable quantitative data at these frequencies are available for three measurable physiological responses to electrical stimulation: (1) the perception of electric current flow, (2) uncontrollable muscular contraction, and (3) death. Relevant threshold conditions for response to minimum currents include the size and resistance of the body and the duration and pathway of current flow. One percent of the general populace can perceive from 0.1 to 0.5 mA of 50-60 Hz current, depending upon the type of hand contact made with an electrically-energized circuit. A safety threshold of 5 mA, recommended for the general population including children, is based upon the conclusion that any 50-60 Hz current in excess of the release threshold of an individual should be regarded as hazardous and potentially lethal. Ninety-nine percent of adult male workers should be able to release 9 mA of 50-60 Hz current. Voltages calculated from reliable experimental data on effective currents and expected resistances are lower than voltages generally recommended to be safe.
The volumes at which these sensations are perceived are recorded. Three sensory thresholds are usually defined: constant sensation of fullness, urge to defecate, and maximum tolerated volume. The modalities of anal sensation can be precisely defined. Touch, pain and temperature sensation exist in normal subjects. There is profuse innervation of the anal canal with a variety of specialized sensory nerve endings: Meissner's corpuscles which record touch sensation, Krause end-bulbs which respond to thermal stimuli, Golgi-Mazzoni bodies and pacinian corpuscles which respond to changes in tension and pressure, and genital corpuscles which respond to friction. In addition, there are large diameter free nerve endings within the epithelium. The nerve pathway for anal canal sensation is via the inferior haemorrhoidal branches of the pudendal nerve to the sacral roots of S2, S3 and S4. Anal sensation may be quantitatively measured in response to electrical stimulation. The technique involves the use of a specialized constant current generator and bipolar electrode probe inserted in the anal canal.
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