Depressive effects of segmental and heterotopic application of transcutaneous electrical nerve stimulation and piezo-electric current on lower limb nociceptive flexion reflex in human subjects

Clinical neurophysiology of neuropathic pain

Timely and accurate diagnosis of neuropathic pain is critical for optimizing therapeutic outcomes and minimizing treatment delays. According to current standards, the diagnosis of definite neuropathic pain requires objective confirmation of a lesion or disease affecting the somatosensory nervous system. This can be provided by specialized neurophysiological techniques as conventional methods like nerve conduction studies and somatosensory evoked potentials may not be sufficient as they do not assess pain pathways. These specialized techniques apply various stimuli, such as thermal, electrical, or mechanical, alongside assessments of spinal/cortical potential or electromyographic reflex recordings. The selection of techniques is guided by the patient's clinical history and examination. The most common neurophysiological tests used in clinical practice are pain-related evoked potentials (PREPs) providing an objective evaluation of nociceptive pathways. Four types of PREPs are employed: laser evoked potentials, contact-heat evoked potentials, intra-epidermal electrical stimulation evoked potentials, and pinprick evoked potentials, with the two former ones being the most robust and reliable ones. These techniques investigate small-diameter fibers, primarily Aδ-fibers, and spinothalamic tracts allowing the identification of peripheral or central nervous system lesions. Yet, they are limited in capturing neuronal mechanisms underlying neuropathic pain or in providing objective quantification of pain sensation. Two neurophysiological measures which investigate the pain system beyond its integrity are the nociceptive withdrawal reflex and the N13 component of somatosensory evoked potentials. Both of these methods are more commonly used in research than clinical practice, but they pose interesting approaches to quantify central sensitization, a key underlying mechanism of neuropathic pain. Future investigations in neuropathic pain are therefore warranted.

Modulation of the nociceptive flexion reflex by conservative therapy in patients and healthy people: a systematic review and meta-analysis

ABSTRACT

The nociceptive flexion reflex (NFR) is a spinally mediated withdrawal response and is used as an electrophysiological marker of descending modulation of spinal nociception. Chemical and pharmacological modulation of nociceptive neurotransmission at the spinal level has been evidenced by direct effects of neurotransmitters and pharmacological agents on the NFR. Largely unexplored are, however, the effects of nonpharmacological noninvasive conservative interventions on the NFR. Therefore, a systematic review and meta-analysis was performed and reported following the PRISMA guidelines to determine whether and to what extent spinal nociception measured through the assessment of the NFR is modulated by conservative therapy in patients and healthy individuals. Five electronic databases were searched to identify relevant articles. Retrieved articles were screened on eligibility using the predefined inclusion criteria. Risk of bias was investigated according to Version 2 of the Cochrane risk-of-bias assessment tool for randomized trials. The evidence synthesis for this review was conducted in accordance with the Grading of Recommendations Assessment, Development and Evaluation. Thirty-six articles were included. Meta-analyses provided low-quality evidence showing that conservative therapy decreases NFR area and NFR magnitude and moderate-quality evidence for increases in NFR latency. This suggests that conservative interventions can exert immediate central effects by activating descending inhibitory pathways to reduce spinal nociception. Such interventions may help prevent and treat chronic pain characterized by enhanced spinal nociception. Furthermore, given the responsiveness of the NFR to conservative interventions, the NFR assessment seems to be an appropriate tool in empirical evaluations of treatment strategies.PROSPERO registration number: CRD42020164495.

Remote Analgesic Effects Of Conventional Transcutaneous Electrical Nerve Stimulation: A Scientific And Clinical Review With A Focus On Chronic Pain

BACKGROUND

Transcutaneous electrical nerve stimulation (TENS) is a safe, noninvasive treatment for chronic pain that can be self-administered. Conventional TENS involves stimulation of peripheral sensory nerves at a strong, non-painful level. Following the original gate-control theory of pain, stimulation is typically near the target pain. As another option, remote stimulation may also be effective and offers potential advantages.

OBJECTIVE

This narrative review examines mechanisms underlying the remote analgesic effects of conventional TENS and appraises the clinical evidence.

METHODS

A literature search for English-language articles was performed on PubMed. Keywords included terms related to the location of TENS . Citations from primary references and textbooks were examined for additional articles.

RESULTS

Over 30 studies reported remote analgesic effects of conventional TENS. The evidence included studies using animal models of pain, experimental pain in humans, and clinical studies in subjects with chronic pain. Three types of remote analgesia were identified: at the contralateral homologous site, at sites distant from stimulation but innervated by overlapping spinal segments, and at unrelated extrasegmental sites.

CONCLUSION

There is scientific and clinical evidence that conventional TENS has remote analgesic effects. This may occur through modulation of pain processing at the level of the dorsal horn, in brainstem centers mediating descending inhibition, and within the pain matrix. A broadening of perspectives on how conventional TENS produces analgesia may encourage researchers, clinicians, and medical-device manufacturers to develop novel ways of using this safe, cost-effective neuromodulation technique for chronic pain.

The effect of heterotopic noxious conditioning stimulation on Aδ-, C- and Aβ-fibre brain responses in humans

Human studies have shown that heterotopic nociceptive conditioning stimulation (HNCS) applied to a given body location reduces the percept and brain responses elicited by noxious test stimuli delivered at a remote body location. It remains unclear to what extent this effect of HNCS relies on the spinal-bulbar-spinal loop mediating the effect of diffuse noxious inhibitory controls (DNICs) described in animals, and/or on top-down cortical mechanisms modulating nociception. Importantly, some studies have examined the effects of HNCS on the brain responses to nociceptive input conveyed by Aδ-fibres. In contrast, no studies have explored the effects of HNCS on the responses to selective nociceptive C-fibre input and non-nociceptive Aβ-fibre input. In this study, we measured the intensity of perception and event-related potentials (ERPs) to stimuli activating Aδ-, C- and Aβ-fibres, before, during and after HNCS, obtained by immersing one foot in painful cold water. We observed that (i) the perceived intensity of nociceptive Aδ- and C-stimuli was reduced during HNCS, and (ii) the ERPs elicited by Aδ- and Aβ- and C-stimuli were also reduced during HNCS. Importantly, because Aβ-ERPs are related to primary afferents that ascend directly through the dorsal columns without being relayed at spinal level, the modulation of these responses may not be explained by an influence of descending projections modulating the transmission of nociceptive input at spinal level. Therefore, our results indicate that, in humans, HNCS should be used with caution as a direct measure of DNIC-related mechanisms.

Effectiveness of High-Frequency Electrical Stimulation Following Sensitization With Capsaicin

Although nonnoxious, high-frequency electrical stimulation applied segmentally (ie, conventional transcutaneous electrical nerve stimulation [TENS]) has been proposed to modulate pain, the mechanisms underlying analgesia remain poorly understood. To further elucidate how TENS modulates pain, we examined evoked responses to noxious thermal stimuli after the induction of sensitization using capsaicin in healthy volunteers. We hypothesized that sensitization caused by capsaicin application would unmask TENS analgesia, which could not be detected in the absence of sensitization. Forty-nine healthy subjects took part in a series of experiments. The experiments comprised the application of topical capsaicin (.075%) on the left hand in the C6 dermatome, varying the location of TENS (segmental, left C6 dermatome, vs extrasegmental, right shoulder), and assessing rating of perception (numeric rating scale: 0-10) and evoked potentials to noxious contact heat stimuli. The extrasegmental site was included as a control condition because previous studies indicate no analgesic effect to remote conventional TENS. Conventional TENS had no significant effect on rating or sensory evoked potentials in subjects untreated with capsaicin. However, segmental TENS applied in conjunction with capsaicin significantly reduced sensation to noxious thermal stimuli following a 60-minute period of sensitization.

PERSPECTIVE

The study indicates that sensitization with capsaicin unmasks the analgesic effect of conventional TENS on perception of noxious contact heat stimuli. Our findings indicate that TENS may be interacting segmentally to modulate distinct aspects of sensitization, which in turn results in analgesia to thermal stimulation.

Facets and mechanisms of adaptive pain behavior: predictive regulation and action

Neural mechanisms underlying nociception and pain perception are considered to serve the ultimate goal of limiting tissue damage. However, since pain usually occurs in complex environments and situations that call for elaborate control over behavior, simple avoidance is insufficient to explain a range of mammalian pain responses, especially in the presence of competing goals. In this integrative review we propose a Predictive Regulation and Action (PRA) model of acute pain processing. It emphasizes evidence that the nervous system is organized to anticipate potential pain and to adjust behavior before the risk of tissue damage becomes critical. Regulatory processes occur on many levels, and can be dynamically influenced by local interactions or by modulation from other brain areas in the network. The PRA model centers on neural substrates supporting the predictive nature of pain processing, as well as on finely-calibrated yet versatile regulatory processes that ultimately affect behavior. We outline several operational categories of pain behavior, from spinally-mediated reflexes to adaptive voluntary action, situated at various neural levels. An implication is that neural processes that track potential tissue damage in terms of behavioral consequences are an integral part of pain perception.

Modulation of laser-evoked potentials and pain perception by transcutaneous electrical nerve stimulation (TENS): a placebo-controlled study in healthy volunteers

OBJECTIVE

To investigate the effects of transcutaneous electrical nerve stimulation (TENS) on brain nociceptive responses (laser-evoked potentials, LEPs) and pain perception.

METHODS

Twenty healthy subjects were included. Nociceptive CO(2)-laser pulses were sequentially delivered to the dorsum of both feet. The amplitude of LEPs and nociceptive thresholds were collected in three consecutive conditions: T1: "sham" TENS (2 Hz/low-intensity) positioned heterotopically, over the left thigh; T2: "active" TENS (120 Hz/low-intensity) applied homotopically, over the left common peroneal nerve; and T3: "sham" TENS (replication of condition T1).

RESULTS

Compared with "sham" TENS, "active" TENS significantly decreased the LEPs amplitude. This effect was observed exclusively when "active" TENS was applied ipsilaterally to the painful stimulus. Nociceptive thresholds increased with sessions in both limbs, but the increase observed during the "active" condition of TENS (T2) exceeded significantly that observed during the condition T3 only on the foot ipsilateral to TENS.

CONCLUSIONS

Compared with a credible placebo TENS, high-frequency TENS induced a significant attenuation of both the acute pain and LEPs induced by noxious stimuli applied on the same dermatome.

SIGNIFICANCE

This modulation of subjective and objective concomitants of pain processing reflects a real neurophysiological TENS-related effect on nociceptive transmission.

Pain modulation by meditation and electroacupuncture in experimental submaximum effort tourniquet technique (SETT)

CONTEXT

Although acupuncture and meditation are widely utilized in the clinical treatment of pain, trials to evaluate their efficacy and modes of action under experimental conditions have yielded equivocal results.

OBJECTIVE

This feasibility study investigated whether electroacupuncture (EA) and meditation effectively relieve pain within a well-established ischemic pain paradigm (submaximum effort tourniquet technique, SETT).

DESIGN

In this semirandomized trial, experienced meditators were compared with nonmeditators. The nonmeditating subjects were randomly assigned to either an EA group or a nontreatment group.

SETTING

The trial was conducted at the Department of Complementary and Integrative Medicine, University of Duisburg-Essen, Essen, Germany.

PARTICIPANTS

Eight Vipassana meditators (mean experience hours = 2,626.8 ± 1,602.3 hours SD) and 40 control subjects were enrolled.

INTERVENTIONS

SETT (250 mm Hg, time limit = 30 minutes, pain rating limit = 10) was applied twice (baseline vs treatment) on the nondominant arm; EA was applied to the contralateral acupoints LI4 and LI10 (stimulation 20 minutes prior to and throughout the SETT); meditators were asked to meditate throughout the whole experimental procedure.

MAIN OUTCOME MEASURE

Pain ratings were obtained every three minutes on a numerical rating scale (0-10). The ratio of the tolerated time to the ratings served as the pain tolerance index.

RESULTS

At baseline, meditators exhibited significantly greater pain tolerance than the other two groups. During the second or treatment session, pain sensitivity did not change significantly in the nontreatment group, whereas pain tolerance significantly increased and pain ratings decreased to the level of meditation-induced analgesia in the EA group. Electroacupuncture induced no additional pain control benefit for meditators.

An investigation into the hypoalgesic effects of transcutaneous piezoelectric current on experimentally induced thermal stimuli in healthy participants

OBJECTIVES

  To investigate the effects of transcutaneous piezoelectric currents on experimentally induced thermal pain in healthy human participants.

MATERIALS AND METHODS

  A repeated measure cross-over study recorded sensory detection and pain thresholds to contact thermal stimuli during active and placebo (no current) transcutaneous piezoelectric current in 15 pain-free healthy human volunteers. Active transcutaneous piezoelectric current (6 µA) was delivered as 35 high voltage single rectangular pulses (1 Hz) at the LI4 (Hegu) acupuncture point.

RESULTS

  Repeated measures ANOVA found that active and placebo transcutaneous piezoelectric current elevated thresholds for warm sensation, heat pain, and cold sensation. However, there were no statistically significant effects for active piezoelectric current compared with placebo for any outcome measure.

CONCLUSIONS

  Reductions in experimentally induced pain were not due to piezoelectric currents per se. These findings challenge claims about the efficacy of transcutaneous piezoelectric currents for pain relief. A clinical trial is needed.

Isolated and combined effects of electroacupuncture and meditation in reducing experimentally induced ischemic pain: a pilot study

Acupuncture and meditation are promising treatment options for clinical pain. However, studies investigating the effects of these methods on experimental pain conditions are equivocal. Here, the effects of electroacupuncture (EA) and meditation on the submaximum effort tourniquet technique (SETT), a well-established, opiate-sensitive pain paradigm in experimental placebo research were studied. Ten experienced meditators (6 male subjects) and 13 nonmeditators (6 male subjects) were subjected to SETT (250 mmHG) on one baseline (SETT only) and two treatment days (additional EA contralaterally to the SETT, either at the leg on ST36 and LV3 or at the arm on LI4 and LI10 in randomized order). Numeric Rating Scale (NRS) ratings (scale 0-10) were recorded every 3 min. During baseline, meditation induced significantly greater pain tolerance in meditators when compared with the control group. Both the EA conditions significantly increased pain tolerance and reduced pain ratings in controls. Furthermore, EA diminished the group difference in pain sensitivity, indicating that meditators had no additional benefit from acupuncture. The data suggest that EA as a presumable bottom-up process may be as effective as meditation in controlling experimental SETT pain. However, no combined effect of both the techniques could be observed.

Effects of simultaneous dual-site TENS stimulation on experimental pain

Transcutaneous electrical nerve stimulation (TENS) is commonly used for pain relief. However, little robust research exists regarding the combination of parameters required to provide effective doses. This study investigated the hypoalgesic effects of different parameter combinations, applied simultaneously at two sites (segmental and extrasegmental), on pressure pain threshold (PPT) in pain-free humans. Two-hundred and eight volunteers (median age 22 years, range 20-26) were randomized to eight groups: six active TENS groups, placebo and control. Parameter combinations were such that frequency always differed at each site (110 Hz or 4 Hz), but intensity could be either the same or different levels: high (to tolerance without pain) or low (strong but comfortable). TENS was administered to the forearm over the radial nerve and the ipsilateral leg below the fibular head for 30 min with monitoring for 30 further minutes. PPT measurements were taken bilaterally from the mid-point of first dorsal interosseous muscle, by an independent blinded rater, at baseline and at six subsequent 10-min intervals. Log-transformed data were analysed using repeated-measures analysis of covariance (baseline values and gender as covariates). Those groups using high-intensity stimulation at the segmental stimulation sites showed significantly greater hypoalgesia than placebo (p < 0.025 in each case). The largest hypoalgesic effect was for simultaneous high-intensity stimulation at segmental and extrasegmental sites, using different frequencies. These results reaffirm that high-intensity stimulation (regardless of frequency) is of fundamental importance in effective dosage.

Effects of a brief coping skills training intervention on nociceptive flexion reflex threshold in patients having osteoarthritic knee pain: a preliminary laboratory study of sex differences

Studies have documented the efficacy of coping skills training (CST) for managing pain, distress, and disability in persons with arthritis. However, no laboratory studies have examined the effects of CST on descending modulation of nociception. This study used the nociceptive flexion reflex (NFR) to document pain and nociceptive responding among 62 men and women with osteoarthritis of the knee (mean age=63.3+/-7.5 years). Before and after a 45-minute CST session, participants completed laboratory assessments of NFR threshold and questionnaires evaluating pain and state anxiety. Results indicated significantly increased NFR thresholds and decreased pain ratings following CST for men and women. A significant time by sex interaction was observed for state anxiety, with women reporting greater decreases in anxiety following CST than men. This is the first study to demonstrate effects of a CST protocol on a measure of descending inhibition of nociception among patients with osteoarthritic knee pain.

The lower limb flexion reflex in humans

The flexion or flexor reflex (FR) recorded in the lower limbs in humans (LLFR) is a widely investigated neurophysiological tool. It is a polysynaptic and multisegmental spinal response that produces a withdrawal of the stimulated limb and resembles (having several features in common) the hind-paw FR in animals. The FR, in both animals and humans, is mediated by a complex circuitry modulated at spinal and supraspinal level. At rest, the LLFR (usually obtained by stimulating the sural/tibial nerve and by recording from the biceps femoris/tibial anterior muscle) appears as a double burst composed of an early, inconstantly present component, called the RII reflex, and a late, larger and stable component, called the RIII reflex. Numerous studies have shown that the afferents mediating the RII reflex are conveyed by large-diameter, low-threshold, non-nociceptive A-beta fibers, and those mediating the RIII reflex by small-diameter, high-threshold nociceptive A-delta fibers. However, several afferents, including nociceptive and non-nociceptive fibers from skin and muscles, have been found to contribute to LLFR activation. Since the threshold of the RIII reflex has been shown to correspond to the pain threshold and the size of the reflex to be related to the level of pain perception, it has been suggested that the RIII reflex might constitute a useful tool to investigate pain processing at spinal and supraspinal level, pharmacological modulation and pathological pain conditions. As stated in EFNS guidelines, the RIII reflex is the most widely used of all the nociceptive reflexes, and appears to be the most reliable in the assessment of treatment efficacy. However, the RIII reflex use in the clinical evaluation of neuropathic pain is still limited. In addition to its nocifensive function, the LLFR seems to be linked to posture and locomotion. This may be explained by the fact that its neuronal circuitry, made up of a complex pool of interneurons, is interposed in motor control and, during movements, receives both peripheral afferents (flexion reflex afferents, FRAs) and descending commands, forming a multisensorial feedback mechanism and projecting the output to motoneurons. LLFR excitability, mediated by this complex circuitry, is finely modulated in a state- and phase-dependent manner, rather as we observe in the FR in animal models. Several studies have demonstrated that LLFR excitability may be influenced by numerous physiological conditions (menstrual cycle, stress, attention, sleep and so on) and pathological states (spinal lesions, spasticity, Wallenberg's syndrome, fibromyalgia, headaches and so on). Finally, the LLFR is modulated by several drugs and neurotransmitters. In summary, study of the LLFR in humans has proved to be an interesting functional window onto the spinal and supraspinal mechanisms of pain processing and onto the spinal neural control mechanisms operating during posture and locomotion.

Segmental noxious versus innocuous electrical stimulation for chronic pain relief and the effect of fading sensation during treatment

It is not clear whether segmental innocuous stimulation has a stronger analgesic effect than segmental noxious stimulation for chronic pain and whether the fading of current sensation during treatment interferes with the analgesic effect, as suggested by the gate control theory. Electrical stimulation (by way of Interferential Current) applied at the pain area (segmental) was administered to 4 groups of patients with osteoarthritis (OA) knee pain. Two groups were administered with noxious stimulation (30% above pain threshold) and two with innocuous stimulation (30% below pain threshold). In each group half of the patients received a fixed current intensity while the other half raised the intensity continuously during treatment whenever fading of sensation was perceived. Group 5 and 6 received sham stimulation and no treatment, respectively. The outcome measures were: chronic pain intensity, morning stiffness, range of motion (ROM), pain threshold and % pain reduction. Both noxious and innocuous stimulation significantly decreased chronic pain (P<0.001) and morning stiffness (P<0.01) and significantly increased pain threshold (P<0.001) and ROM (P<0.001) compared with the control groups. Nevertheless, noxious stimulation decreased pain intensity (P<0.05) and increased pain threshold (P<0.001) significantly more than innocuous stimulation. No differences in treatment outcomes were found between adjusted and unadjusted stimulation. (a) Interferential current is very effective for chronic OA knee pain, (b) segmental noxious stimulation produces a stronger analgesic effect than segmental innocuous stimulation, (c) the fading of sensation during treatment, does not decrease the analgesic effect. Possible mechanisms explaining the findings are discussed.

Agents physiques antalgiques

Analgesic electrotherapy is now based on more consistent scientific data; the biological action of the electric current, of the electromagnetic radiations and of the mechanical vibrations is better approached. But the randomized control trials still provide contradictory results concerning the analgesic efficiency of the cryotherapy, the TENS, the pulsed electro-magnetic fields, the ultrasound and laser therapy, the shock waves; iontophoresis, short waves, microwaves, infrasound vibrations are very few investigated. The analgesic electrotherapy cannot be recommended nor prohibited; physical agents represent only therapeutic options. On the basis of the scientific data and of their personal experience, the therapists can use them. More controlled clinical investigations of higher methodological levels are still required.

Sensory stimulation (TENS): effects of parameter manipulation on mechanical pain thresholds in healthy human subjects

Transcutaneous electrical nerve stimulation (TENS) is a popular form of electrostimulation. Despite an extensive research base, there remains no consensus regarding the parameter selection required to achieve maximal hypoalgesic effects. The aim of this double blind, sham-controlled study was to investigate the relative hypoalgesic effects of different TENS parameters (frequency, intensity and stimulation site) upon experimentally induced mechanical pain. Two hundred and forty participants were recruited in order to provide statistical analysis with 80% power at alpha = 0.05. Subjects were randomised to one of the six TENS groups, a control, and a sham TENS group (n = 30, 15 males, 15 females, per group). TENS groups differed in their combinations of stimulation; frequency (4 or 110 Hz), intensity ('to tolerance' or 'strong but comfortable') and stimulation site (segmental--over the distribution of the radial nerve or, extrasegmental--over acupuncture point 'gall bladder 34', or a combination of both segmental and extrasegmental). Pulse duration was fixed at 200 micros. Stimulation was delivered for 30 min and subjects were then monitored for a further 30 min. Mechanical pain threshold (MPT) was measured using a pressure algometer and taken from the first dorsal interosseous muscle of the dominant hand, ipsilateral to the stimulation site. MPT measures were taken, at baseline, and at 10-min intervals for 60 min. Difference scores were analysed using repeated measures and one-way ANOVA and relevant post hoc tests. Low frequency, high intensity, extrasegmental stimulation produced a rapid onset hypoalgesic effect, which increased during the stimulation period (P < 0.0005 control and sham) and was sustained for 30 min post-stimulation (P < 0.0005(control), P = 0.024(sham)). Whilst high frequency, 'strong but comfortable' intensity, segmental stimulation produced comparable hypoalgesic levels during stimulation, this effect was not sustained post-stimulation. Stimulation at a combination of the two sites did not produce any greater hypoalgesic effects. These results may have implications for the clinical use of sensory stimulation.

The nociceptive flexion reflex in humans -- review article

The nociceptive flexion reflex (NFR) is a physiological, polysynaptic reflex allowing for painful stimuli to activate an appropriate withdrawal response. NFR is easily measurable in clinical setting, and is a reliable and objective tool for measurement of an individual's pain experience. An exhaustive review of the literature, covering multiple search engines, indicates that the NFR method is valuable in studying the impact of diverse pharmacological and non-pharmacological interventions on the flexion reflex, in conditions of acute pain and in healthy volunteers. More recently, the NFR method has gained particular attention as a research tool in studies of central sensitization and persistent or chronic pain.

Electroanalgesia: its role in acute and chronic pain management

Interest in nonpharmacologic alternatives to conventional analgesic drugs for the management of acute and chronic pain has lead to an evaluation of the use of electroanalgesic therapies.

Study of the effects of various transcutaneous electrical nerve stimulation (TENS) parameters upon the RIII nociceptive and H-reflexes in humans

Despite over two decades of clinical use, the neurophysiological and anti-nociceptive effects of transcutaneous electrical nerve stimulation (TENS) have yet to be definitively described. The current study was designed to examine the effect of TENS on the RIII nociceptive reflex elicited in healthy human subjects; the H-reflex was measured concomitantly to monitor changes in alpha-motoneuron excitability. Following approval from the university's ethical committee, 50 healthy human volunteers (25 male and 25 female) participated in the study. The subjects ranged in age from 18 to 30 years (mean 22, SD 3). Subjects were randomly allocated equally to a control group or one of four TENS groups. In the TENS groups, stimulation was applied for a total of 15 min over the sural nerve in the left leg. Ipsilateral RIII and H-reflexes were recorded five times during the 45 min experimental period. In addition, subjects also rated pain associated with the RIII reflex using a computerized visual analogue scale (VAS). Statistical analysis using two-way repeated-measures ANOVA showed no differences between groups for H-reflex, RIII reflex nor VAS data. These results suggest that TENS does not significantly affect either of the two reflexes, at least using the parameters and application time in the current study.

Functional imaging and neurophysiological assessment of spinal and brain therapeutic modulation in humans

We summarize here our experience in the neurophysiological and neuroimaging assessment of spinal and brain neuromodulation for pain relief. Techniques reviewed include somatosensory evoked potentials (SEPs), nociceptive spinal (RIII) reflexes, and positron emission tomography (PET), which have been applied both to investigate the mechanisms and to optimize the application of neurostimulation procedures. SEPs are especially useful in the preoperative assessment of patients with neuropathic pain, as they allow the establishment of the functional state of the dorsal column system. Patients with strongly abnormal SEPs due to ganglionic or preganglionic pathology are not likely to benefit from spinal (SCS) or peripheral (TENS) neurostimulation, because ascending fibers disconnected from their soma will undergo rapid degeneration and not be excitable. In the postoperative period, nociceptive spinal reflexes yield objective data concerning the effects of neurostimulation on spinal circuitry. In our experience, the best clinical results are achieved in patients with preserved preoperative SEPs, in whom neurostimulation entails profound attenuation of nociceptive reflexes.PET-scan imaging techniques have recently been used to demonstrate changes in cerebral blood flow during new neuromodulation schemes such as motor cortex stimulation for pain control (MCS). PET studies highlight the thalamus as the key structure mediating functional MCS effects. Thalamic activation would trigger a cascade of synaptic events influencing activity in other pain-related structures including the anterior cingulate gyrus, insula, and upper brainstem. The combination of clinical electrophysiology and functional neuroimaging provides insight into the mechanisms of action of neuromodulation procedures, guides clinical decision, and contributes to optimize patient selection.

A controlled study on the effects of transcutaneous electrical nerve stimulation and interferential therapy upon the RIII nociceptive and H-reflexes in humans

OBJECTIVE

To study the effect of transcutaneous electrical nerve stimulation (TENS) and interferential therapy (IFT) upon the RIII nociceptive reflex and H-reflex.

DESIGN

Double-blind conditions.

PARTICIPANTS

Seventy healthy subjects were randomly allocated to one of seven groups (n = 10 per group): Control, TENS 1 (5 Hz), TENS 2 (100 Hz), TENS 3 (200 Hz), IFT 1 (5 Hz), IFT 2 (100 Hz), IFT 3 (200 Hz).

INTERVENTION

In the treatment groups, stimulation was applied over the right sural nerve for 15 minutes.

MAIN OUTCOME MEASURES

Ipsilateral RIII and H-reflexes were recorded before treatment, immediately after treatment, and subsequently at 25, 35, and 45 minutes. Subjects rated the pain associated with the RIII reflex using a computerized visual analogue scale (VAS).

RESULTS

Statistical analysis using ANOVA showed no significant differences between baseline and posttreatment measurement for RIII reflex, H-reflex, or VAS data.

CONCLUSION

These results suggest that neither type of electrical stimulation (TENS or IFT) affects the RIII or H-reflexes, at least using the parameters and application time in this study.