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

Bioelectric medicine: unveiling the therapeutic potential of micro-current stimulation

Bioelectric medicine (BEM) refers to the use of electrical signals to modulate the electrical activity of cells and tissues in the body for therapeutic purposes. In this review, we particularly focused on the microcurrent stimulation (MCS), because, this can take place at the cellular level with sub-sensory application unlike other stimuli. These extremely low-level currents mimic the body's natural electrical activity and are believed to promote various physiological processes. To date, MCS has limited use in the field of BEM with applications in several therapeutic purposes. However, recent studies provide hopeful signs that MCS is more scalable and widely applicable than what has been used so far. Therefore, this review delves into the landscape of MCS, shedding light on the multifaceted applications and untapped potential of MCS in the realm of healthcare. Particularly, we summarized the hierarchical mediation from cell to whole body responses by MCS including its physiological applications. Our final objective of this review is to contribute to the growing body of literature that unveils the captivating potential of BEM, with MCS poised at the intersection of technological innovation and the intricacies of the human body.

Effect of Transcutaneous Electrical Nerve Stimulation on Pain-related Quantitative Sensory Tests in Chronic Musculoskeletal Pain and Acute Experimental Pain: Systematic Review and Meta-analysis

This report provides a systematic review of the literature to analyze the effects of transcutaneous electrical nerve stimulation (TENS) on analgesia on sensitization measures, in studies with chronic musculoskeletal pain and in studies with acute experimental pain. The protocol was registered at PROSPERO (CRD42020213473). The authors searched Cochrane Central Register of Controlled Trials, Cumulative Index to Nursing and Allied Health Literature, EMBASE, Latin American and Caribbean Health Sciences Literature via Biblioteca Virtual de Saúde, Physiotherapy Evidence Database, PubMed, ScienceDirect, Web of Science, Google Scholar, and hand-searched reference lists were also conducted. Among 22,252 manuscripts found, 58 studies were included in the systematic review and 35 in the meta-analysis. Thirty-four studies assessed pain intensity; 24 studies investigated hyperalgesia; temporal summation was only evaluated in 2 studies; and conditioned pain modulation was not observed in the included studies. Meta-analyses favored TENS, despite its limitations and heterogeneity. Primary hyperalgesia in studies with musculoskeletal pain presented a high level of evidence, while other outcomes presented moderate evidence in the studies that were included. It is not possible to infer results about both temporal summation and conditioned pain modulation. Moderate evidence suggests that TENS promotes analgesia by reducing both central and peripheral sensitization, as shown by the reduction in primary and secondary hyperalgesia, pain intensity at rest, and during movement in experimental acute pain and chronic musculoskeletal pain. Overall, both types of studies analyzed in this review presented meta-analyses favorable to the use of TENS (compared to placebo TENS), showing reductions in both primary and secondary hyperalgesia, as well as decreases in pain intensity at rest and in motion. PERSPECTIVE: This article presents data from the literature on the effect of TENS through sensitization assessments in individuals with chronic musculoskeletal pain, or acute experimental pain. These data contribute to knowledge about pain neuroscience research, using TENS technology.

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.

Repeated and patterned stimulation of cutaneous reflex pathways amplifies spinal cord excitability

Priming with patterned stimulation of antagonist muscle afferents induces modulation of spinal cord excitability as evidenced by changes in group Ia reciprocal inhibition. When assessed transiently with a condition-test pulse paradigm, stimulating cutaneous afferents innervating the foot reduces Ia presynaptic inhibition and facilitates soleus Hoffmann (H)-reflex amplitudes. Modulatory effects (i.e., priming) of longer lasting sensory stimulation of cutaneous afferents innervating the foot have yet to be examined. As a first step, we examined how priming with 20 min of patterned and alternating stimulation between the left and right foot affects spinal cord excitability. During priming, stimulus trains (550 ms; consisting of twenty-eight 1-ms pulses at 51 Hz, 1.2 times the radiating threshold) were applied simultaneously to the sural and plantar nerves of the ankle. Stimulation to the left and right ankle was out of phase by 500 ms. We evoked soleus H-reflexes and muscle compound action potentials (M waves) before and following priming stimulation to provide a proxy measure of spinal cord excitability. H-reflex and M-wave recruitment curves were recorded at rest, during brief (<2 min) arm cycling, and with sural conditioning [train of five 1-ms pulses at 2 times the radiating threshold (RT) with a condition-test interval (C-T) = 80 ms]. Data indicate an increase in H-reflex excitability following priming via patterned sensory stimulation. Transient sural conditioning was less effective following priming, indicating that the increased excitability of the H-reflex is partially attributable to reductions in group Ia presynaptic inhibition. Sensory stimulation to cutaneous afferents, which enhances spinal cord excitability, may prove useful in both rehabilitation and performance settings.NEW & NOTEWORTHY Priming via patterned stimulation of the nervous system induces neuroplasticity. Yet, accessing previously known cutaneous reflex pathways to alter muscle reflex excitability has not yet been examined. Here, we show that sensory stimulation of the cutaneous afferents that innervate the foot sole can amplify spinal cord excitability, which, in this case, is attributed to reductions in presynaptic inhibition.

Evaluation of Percutaneous Electrical Nerve Stimulation of the Auricle for Relief of Postoperative Pain Following Cesarean Section

Objective: Percutaneous electrical nerve stimulation is a nonpharmacologic modality of analgesia. This study was conducted to evaluate such a technology (ANSiStim™, DyAnsys Inc., San Mateo, CA) prospectively, in conjunction with standard analgesia per patient demand, for managing postoperative pain following lower-segment cesarean section. Materials and Methods: One hundred parturients were randomized into 2 equal groups (controls and study cases). The latter cohort consisted of parturients for whom nerve stimulation was exerted on the pinna. Pain scores were compared across subjects at corresponding time points with 17 intervals in 48 hours, and, in totality, using estimated area under the curves of numerical scores. Conditional inference analysis was also performed. Results: Ninety-six parturients were finally included. The device was well-tolerated by a majority of parturients. Pain scores were significantly lower in the study group, both at corresponding time intervals and in totality. (H - 15)*(0.74 - H)*(H² - 17H + 110)/440, where H was the corresponding hour, fit the pain scores in the control group. Controls could be detected at the 11 hour with greater pain scores (≥ 4), whereas smaller scores (≤ 2) at the 42nd hour mostly revealed that electrical stimulation was performed (p < 0.001). Requirements for supplementary analgesics were lower for subjects who were given the electroanalgesia. Conclusions: Neurostimulation via the ANSiStim™ is a safe and reasonably effective ambulatory analgesic adjuvant following abdominal delivery. There are no serious adverse effects.

Contralateral segmental transcutaneous electrical nerve stimulation inhibits nociceptive flexion reflex in healthy participants

BACKGROUND

Transcutaneous electrical nerve stimulation (TENS) is a non-invasive treatment to relieve pain. Contralateral TENS (i.e. TENS administered to the contralateral side of a painful body part) is beneficial when TENS cannot be directly applied to pain site, such as in cases of trauma. Although TENS produces segmental analgesia in an ipsilateral limb, it has been unclear whether TENS produces higher analgesic effects in the contralateral segmental area. The aim of the present study was to investigate the analgesic effects of TENS in contralateral segmental or extra-segmental areas on physiological and subjective pain outcomes, using a nociceptive flexion reflex (NFR) method.

METHODS

We randomly allocated 60 healthy participants to three groups: contralateral segmental TENS (CS-TENS); contralateral extra-segmental TENS (CE-TENS); and contralateral placebo TENS (CP-TENS). CS-TENS was applied to right superficial sural nerve and CE-TENS was applied to the right superficial femoral nerve, each for 30 minutes. The magnitude of the NFR elicited by electrical stimulation of the left sural nerve was measured at baseline and at three subsequent 10-minute intervals. Subjective pain intensity was measured simultaneously with a visual analogue scale (VAS).

RESULTS

At 30 min, the NFR magnitude of CS-TENS group was significantly lower than that of the CP-TENS group (p = 0.021). There were no significant differences in VAS scores among the groups at any time point.

CONCLUSIONS

Our findings suggest that CS-TENS inhibited NFR. Although there was no significant between-group difference in subjective pain intensity, factors such as a placebo effect probably impacted it.

SIGNIFICANCE

Our findings provide support for the contralateral approach at stimulation sites when TENS cannot be directly administered to a pain site (e.g. due to disease or trauma).

Intensity matters: Therapist-dependent dose of spinal transcutaneous electrical nerve stimulation

The intensity used during transcutaneous electrical nerve stimulation (TENS) in both, clinical practice and research studies, is often based on subjective commands such as “strong but comfortable sensation”. There is no consensus regarding the effectiveness dose of TENS. The objective was to determine the difference in the effect of spinal TENS on soleus H-reflex modulation when applied by two therapists instructed to apply the stimulation at a “strong but comfortable” intensity. Twenty healthy volunteers divided into two groups: Therapist 1 (n = 10) and Therapist 2 (n = 10). Both therapist applied spinal TENS and sham stimulation at the T10–12 spinal level for 40min in random order to each subject, at an intensity designed to produce a “strong but comfortable” sensation. To avoid habituation, the intensity was adjusted every 2min. Soleus H-reflex was recorded before, during, and 10min after TENS by an observer blinded to the stimulus applied. Despite the instruction to apply TENS at a “strong comfortable” level, a significant difference in current density was identified: Therapist 1 (0.67mA/cm², SD 0.54) applied more than Therapist 2 (0.53mA/cm², SD 0.57; p<0.001) at the onset of the intervention. Maximal peak-to-peak H-reflex amplitude was inhibited significantly more 10min following TENS applied by Therapist 1 (-0.15mV, SD 0.16) compared with Therapist 2 (0.04mV, SD 0.16; p = 0.03). Furthermore, current density significantly correlated with the inhibitory effect on peak-to-peak Soleus H-reflex amplitude 10 min after stimulation (Rho = -0.38; p = 0.04). TENS intensity dosage by the therapist based on the subjective perception of the participants alone is unreliable and requires objective standardization. In addition, higher current density TENS produced greater inhibition of the Soleus H-reflex.

Beep tones attenuate pain following Pavlovian conditioning of an endogenous pain control mechanism

Heterotopic noxious counter-stimulation (HNCS) is commonly used to study endogenous pain control systems. The resulting pain inhibition is primarily based on spinal cord-brainstem loops. Recently, functional imaging studies have shown that limbic structures like the anterior cingulate cortex and amygdala are also implicated. Since these structures are involved in learning processes, it is possible that the HNCS-induced pain inhibition may depend on specific cues from the environment that have been associated with pain reduction through associative learning. We investigated the influence of Pavlovian conditioning on HNCS-induced pain inhibition in 32 healthy subjects by using a differential conditioning paradigm in which two different acoustic stimuli were either repeatedly paired or unpaired with HNCS. Series of noxious electrical pulse trains delivered to the non-dominant foot served as test stimuli. Diffuse noxious inhibitory control (DNIC)-like effects were induced by concurrent application of tonic HNCS (immersion of the contralateral hand in ice water). Subjective pain intensity and pain unpleasantness ratings and electromyographic recordings of the facial corrugator muscle and the nocifensive RIII flexion reflex were used to measure changes in pain sensitivity. HNCS induced significant pain and reflex inhibitions. In the post-conditioning phase, only the paired auditory cue was able to significantly reduce pain perceptions and corrugator muscle activity. No conditioned effect could be observed in RIII reflex responses. Our results indicate that the functional state of endogenous pain control systems may depend on associative learning processes that, like in the present study, may lead to an attenuation of pain perception. Similar albeit opposite conditioning of pain control mechanisms may significantly be involved in the exacerbation and chronification of pain states.

Pain relief by transcutaneous electric nerve stimulation with bidirectional modulated sine waves in patients with chronic back pain: a randomized, double-blind, sham-controlled study

Objectives.  Newly developed bidirectional modulated sine waves (BMW) might provide some derived benefit to patients with low back pain. Pain relief by transcutaneous electric nerve stimulation (TENS) with BMWs was tested. Materials and Methods.  Analgesic effects of BMWs and conventional bidirectional pulsed waves on chronic back pain in 28 patients were compared, and effects of repeated TENS using BMWs on chronic back pain were investigated in 21 patients by means of a randomized double-blind, sham-controlled, parallel-group method. Pain intensity was assessed using numerical rating scale (NRS). Results.  There was significant immediate reduction in NRS in patients receiving BMWs, and 60 min after treatment compared to sham TENS. Weekly repeated treatments using massage and TENS with BMWs for 5 weeks resulted in a decrease of NRS, but there were no significant differences between the TENS plus massage and sham TENS plus massage groups. Conclusions.  This study shows that TENS with BMWs significantly inhibits chronic back pain, and treatment effects are attained within a day. The results also suggest that there were no statistically significant long-term effects of TENS with BMW in the repeated treatment.

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.

Penetration and spread of interferential current in cutaneous, subcutaneous and muscle tissues

OBJECTIVES

To investigate the penetration depth of interferential current (IFC) through soft tissue and the area over which it spreads during clinical application.

DESIGN

A laboratory-based study of healthy participants.

SETTING

A university research laboratory.

PARTICIPANTS

Twelve healthy subjects.

INTERVENTIONS

Premodulated IFC at 90 Hz and 'true' IFC at frequencies of 4, 40 and 90 Hz were applied via four electrodes, in a quadrant setting, to the distal medial thigh of each participant on separate occasions.

MAIN OUTCOME MEASURE

Voltage induced by tested currents was measured at three locations (middle of the four electrodes, in line with one circuit and outside the four electrodes) and three depths (skin, subcutaneous and muscle tissues) using three Teflon-coated needle electrodes connected to a Cambridge Electronic Design data acquisition system.

RESULTS

All voltages were greater at all depths and locations compared with baseline (P<0.001): premodulated IFC [mean difference 0.112, 95% confidence interval (CI) 0.065 to 0.160], 4 Hz (mean difference 0.168, 95% CI 0.106 to 0.229), 40 Hz (mean difference 0.165, 95% CI 0.107 to 0.223) and 90 Hz (mean difference 0.162, 95% CI 0.102 to 0.221). Voltages decreased with depth. Lower voltages of all currents were recorded in the middle of the four electrodes, with the highest voltage for 'true' IFC being recorded outside the four electrodes (mean difference 0.04, 95% CI 0.01 to 0.029; P=0.011). The premodulated IFC had the highest voltage in line with one circuit.

CONCLUSIONS

IFC passed through soft tissues, with the highest voltages recorded in superficial tissue and the lowest voltages recorded in muscle. For 'true' IFC, the current spread outside the electrodes at higher voltages compared with the intersection of the four electrodes. The premodulated IFC had the highest voltage in line with one circuit. In terms of higher recorded voltages, 'true' IFCs were more efficient than the premodulated IFC when targeting deeper tissues. However, further studies with larger samples are required to confirm the results of this study.

Effects of transcutaneous electrical nerve stimulation (TENS) and interferential currents (IFC) in patients with nonspecific chronic low back pain: randomized clinical trial

CONTEXT AND OBJECTIVE

Transcutaneous electrical nerve stimulation (TENS) and interferential current are the most used electrotherapy methods, although there is little scientific evidence to support their use. The aim of this study was to compare the effects of TENS and interferential current among patients with nonspecific chronic low back pain.

DESIGN AND SETTING

Single-blind randomized controlled trial in the Department of Physiotherapy, Centro Universitário de Maringá.

METHODS

One hundred and fifty patients were randomly divided into three groups: TENS (group 1), interferential current (group 2) and controls (group 3). The patients designated for electrotherapy received ten 30-minute sessions, while the control group remained untreated. All patients and controls were evaluated before and after treatment using a visual analog scale and the McGill Pain and Roland Morris questionnaires, and regarding their use of additional medications.

RESULTS

There was a mean reduction on the visual analog scale of 39.18 mm with TENS, 44.86 mm with interferential current and 8.53 mm among the controls. In the Roland Morris questionnaire, group 1 had a mean reduction of 6.59; group 2, 7.20; and group 3, 0.70 points. In group 1, 84% of the patients stopped using medications after the treatment; in group 2, 75%; and in group 3, 34%. There was no statistically significant difference between the TENS and interferential current groups (P > 0.05); a difference was only found between these groups and the controls (P < 0.0001).

CONCLUSION

There was no difference between TENS and interferential current for chronic low back pain treatment.

CLINICAL TRIAL REGISTRATION

NCT01017913.

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.

Effectiveness of interferential current therapy in the management of musculoskeletal pain: a systematic review and meta-analysis

BACKGROUND

Interferential current (IFC) is a common electrotherapeutic modality used to treat pain. Although IFC is widely used, the available information regarding its clinical efficacy is debatable.

PURPOSE

The aim of this systematic review and meta-analysis was to analyze the available information regarding the efficacy of IFC in the management of musculoskeletal pain.

DATA SOURCES

Randomized controlled trials were obtained through a computerized search of bibliographic databases (ie, CINAHL, Cochrane Library, EMBASE, MEDLINE, PEDro, Scopus, and Web of Science) from 1950 to February 8, 2010.

DATA EXTRACTION

Two independent reviewers screened the abstracts found in the databases. Methodological quality was assessed using a compilation of items included in different scales related to rehabilitation research. The mean difference, with 95% confidence interval, was used to quantify the pooled effect. A chi-square test for heterogeneity was performed.

DATA SYNTHESIS

A total of 2,235 articles were found. Twenty studies fulfilled the inclusion criteria. Seven articles assessed the use of IFC on joint pain; 9 articles evaluated the use of IFC on muscle pain; 3 articles evaluated its use on soft tissue shoulder pain; and 1 article examined its use on postoperative pain. Three of the 20 studies were considered to be of high methodological quality, 14 studies were considered to be of moderate methodological quality, and 3 studies were considered to be of poor methodological quality. Fourteen studies were included in the meta-analysis.

CONCLUSION

Interferential current as a supplement to another intervention seems to be more effective for reducing pain than a control treatment at discharge and more effective than a placebo treatment at the 3-month follow-up. However, it is unknown whether the analgesic effect of IFC is superior to that of the concomitant interventions. Interferential current alone was not significantly better than placebo or other therapy at discharge or follow-up. Results must be considered with caution due to the low number of studies that used IFC alone. In addition, the heterogeneity across studies and methodological limitations prevent conclusive statements regarding analgesic efficacy.

Postoperative pain: acupuncture versus percutaneous electrical nerve stimulation

The purpose of this study was to examine the effect of traditional acupuncture compared with acupuncture with percutaneous electrical nerve stimulation (PENS) on postoperative surgical pain relief in gynecologic oncology patients. Twenty postoperative gynecologic oncology patients were randomly assigned into the two groups, and the intervention was initiated within 24 hours after surgery. The patients in each group received four treatments in the subsequent 48 hours, with 12 hours between each treatment. Either traditional acupuncture needles or acupuncture needles with a pulsed electric current were applied to stimulate the area of points Sp6 and Sp8 near the saphenous nerve. Pain measurement instruments included a visual analog scale and the McGill Pain Questionnaire. Although the PENS treatment group demonstrated a consistent decrease in pain with each treatment application compared with the traditional acupuncture group, after 48 hours both groups experienced equivalent pain relief.

Physical agents used in the management of chronic pain by physical therapists

Evidence supporting the use of specific physical agents in the management of chronic pain conditions is not definitive; it is largely incomplete and sometimes contradictory. However, the use of agents in chronic pain management programs is common. Within the broad use of physical agents, they are rarely the sole modality of treatment. A 1995 American Physical Therapy Association position statement asserts that "Without documentation which justifies the necessity of the exclusive use of physical agents/modalities, the use of physical agents/modalities, in the absence of other skilled therapeutic or educational intervention, should not be considered physical therapy". Physical agents may serve as useful adjunctive modalities of pain relief or to enhance the effectiveness of other elements in therapy geared toward resolution of movement impairments and restoration of physical function. Given that a conclusive aggregate of findings is unlikely to exist for all permutations of patient conditions, combined with interacting therapeutic modalities, an evidence-based approach to pain management is not always possible or beneficial to the patient. In the face of inconclusive evidence, a theory-based approach may help determine if the therapeutic effect ofa given physical agent has the possibility of being a useful clinical tool in the context of treating a particular patient's mechanism of pain generation. Until controlled efficacy findings are definitive, careful individual patient response monitoring of thoughtful theoretical application of adjunctive physical agents may be a prudent approach to the management of chronic 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.

Effects of electric stimulation on C and A delta fiber-mediated thermal perception thresholds 11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated

OBJECTIVE

To determine if interferential current (IFC) or transcutaneous electric nerve stimulation (TENS) alters C and A delta fiber-mediated thermal perception thresholds.

DESIGN

Single-blind, randomized controlled trial.

SETTING

Laboratory.

PARTICIPANTS

One hundred forty healthy women volunteers (mean age +/- standard deviation, 20.6+/-2.7 y).

INTERVENTIONS

Subjects were randomly and exclusively assigned to 1 of 7 groups (n=20 in each): 0, 5, and 100 Hz of IFC; 5 and 100 Hz of TENS; placebo and control stimulation. Stimulation was applied through 2 electrodes placed over the median nerve. Warm sensation, cold sensation, hot pain, and cold pain perception thresholds were measured from the thenar eminence by using a quantitative sensory testing device and a method of limits algorithm.

MAIN OUTCOME MEASURES

Warm sensation, cold sensation, hot pain, and cold pain thresholds (degrees C) before, during, and after stimulation.

RESULTS

There was a statistically significant effect of time for all 4 thermal perception thresholds (separate 2-way analyses of variance with repeated measures, all P<.001). There were no statistically significant differences between experimental groups, nor any interaction effects (all P>.05).

CONCLUSIONS

Neither IFC nor TENS altered C and A delta fiber-mediated thermal perception thresholds. The results suggest that any analgesic mechanisms with these modalities are likely to be complex.

An investigation into the analgesic effects of different frequencies of the amplitude-modulated wave of interferential current therapy on cold-induced pain in normal subjects 11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or any organization with which the authors are associated

OBJECTIVE

To investigate the analgesic effects of different amplitude-modulated frequencies of interferential current therapy (IFT) on cold-induced pain in healthy subjects.

DESIGN

Single-blind parallel group methodology was used. Subjects completed 6 cycles of the cold-induced pain test (2 pretreatment, 2 during treatment, 2 posttreatment). During each cycle, subjects plunged their hand into iced water and the time taken to reach pain threshold was recorded. The hand remained immersed in the iced water for a further 30 seconds, after which the self-reports of pain intensity and pain unpleasantness were recorded.

SETTING

Laboratory in the United Kingdom.

PARTICIPANTS

Sixty unpaid, pain-free volunteers without a known pathology that could cause pain.

INTERVENTIONS

IFT delivered on the nondominant arm at a "strong but comfortable" intensity without visible muscle twitches, using a quadripolar application technique at 1 of 6 possible amplitude modulated "beat" frequencies (20, 60, 100, 140, 180, 220Hz).

MAIN OUTCOME MEASURES

The percentage change in pain threshold, pain intensity, and pain unpleasantness from the pretreatment baseline.

RESULTS

Two-way repeated-measures analyses of variance found no effects for groups for pain threshold (P=.11) or pain ratings (P>.05). There were no effects for cycle for any of the outcome measures. Effects for group by cycle interaction were noted for pain intensity and unpleasantness ratings (P<.05), although post hoc analysis failed to determine the nature of this interaction.

CONCLUSIONS

Experimentally induced cold pain was not influenced by IFT frequencies.

Contribution of individual spa therapies in the treatment of chronic pain

OBJECTIVES

The aim of the present study was to evaluate the contribution of individual spa therapies administered during a period of 3 weeks on measures of well being and pain in a sample of patients with chronic back pain.

DESIGN

One hundred fifty-three patients with chronic back pain undergoing inpatient spa therapy in Bad Tatzmannsdorf, Austria, participated in the study. According to the prescription of their spa physician, patients underwent two or more of the following treatments: mud packs, carbon dioxide baths, massages, exercise therapies, spinal traction, and electrotherapy. The outcome measures were general pain, back pain, negative mood, and health satisfaction. Regression analyses were conducted to predict the 4 outcome measures at the end of spa therapy and at 6 weeks' follow-up for all therapies applied. The pretreatment outcome measure, age, and sex were controlled for by entering them into the analysis.

RESULTS

Patients showed significant improvements in all 4 outcome measures. The prediction of improvement was generally small: only 1% to 11% of the change of the outcome measures could be explained by the type and number of therapies received. On a short-term basis, mud packs and exercise were found to be associated with a greater improvement in mood, whereas a greater frequency of massage therapy and carbon dioxide baths was associated with a smaller improvement in health satisfaction. On a long-term basis, exercise therapy and spinal traction were associated with a greater reduction in back pain.

CONCLUSIONS

The results indicate that, in addition to the individual therapies, other factors relating to spa therapy as a whole must contribute to overall treatment outcome. In addition, the results support the efficacy of exercise therapy for chronic back pain.

Altered central nervous system processing of noxious stimuli contributes to decreased nociceptive responding in individuals at risk for hypertension

Previous evidence indicates that individuals with hypertension and those at increased risk for the disorder exhibit decreased pain perception. To test the hypothesis that attenuation of nociceptive processing in individuals at genetic risk for hypertension is related to differential central modulation of nociceptive transmission, the present study examined descending modulation, alpha-motoneuron excitability, and temporal summation of nociceptive input in young adults with and without a parental history of hypertension. Nociceptive flexion (NFR) and non-nociceptive Hoffman reflexes were assessed at rest and during performance of a mental arithmetic task. Temporal summation was assessed by examining NFR threshold in response to a series of five electrical pulses delivered at 2 Hz. Compared to participants without a parental history of hypertension, offspring of individuals with hypertension exhibited significantly higher NFR thresholds, suggesting that risk for hypertension may be associated with enhanced activation of central pain inhibition pathways.

A single-blind placebo-controlled investigation into the analgesic effects of interferential currents on experimentally induced ischaemic pain in healthy subjects

The aim of this single-blind placebo-controlled study was to examine the analgesic effects of interferential currents (IFC) on experimentally induced ischaemic pain. Ischaemic pain was induced using the submaximal effort tourniquet technique (SETT) and pain intensity was recorded using a visual analogue scale at 1-min intervals was used as the primary outcome measure. Following baseline recordings 30 healthy volunteers received either active IFC, sham IFC, or no treatment (10 subjects per group). Data were analysed by calculating the mean change in pain intensity at each 1-min interval by subtracting data during treatment from the baseline data. IFC was administered throughout the duration of the ischaemic pain test via four electrodes (quadripolar application) on the forearm. Active IFC delivered electrical currents at a 'strong but comfortable' intensity. A 'dummy' stimulator that delivered no current was used as sham IFC. Subjects in the no treatment control group were informed that the IFC device was not switched on. There were significant effects for Groups (P=0.04) which were attributed to a significant reduction in pain intensity for the IFC group when compared with sham and no-treatment control (P< or =0.05). There were no significant effects for Time (P=0.69) or Group-Time interaction (P=0.45). In conclusion, IFC produced significantly greater analgesia than sham and no-treatment control groups under the present experimental conditions.

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.