Frequency Transcutaneous Electrical Nerve Stimulation Research Articles

Effect of transcutaneous electrical stimulation on nociception and edema induced by peripheral serotonin

Transcutaneous electrical nerve stimulation (TENS) is defined as the application of an electrical current to the skin through surface electrodes for pain relief. Various theories have been proposed in order to explain the analgesic mechanism of TENS. Recent studies have demonstrated that part of this analgesia is mediated through neurotransmitters acting at peripheral sites. The aim of this study was to investigate the effects of low frequency (LF: 10 HZ) TENS and high frequency (HF: 130 HZ) TENS on hyperalgesia and edema when applied before the serotonin (5-HT) administered into the rat paw. LF and HF TENS were applied to the right paw for 20 min, and 5-HT was administered immediately after TENS. The Hargreaves method was used to measure nociception, while the hydroplethysmometer (Ugo Basile®) was used to measure edema. Neither HF nor LF TENS inhibited 5-HT-induced edema. However, LF TENS, but not HF TENS, completely reduced 5-HT-induced hyperalgesia. Pre-treatment of the paw with naltrexone, prior to application of TENS, (Nx: 50μg; I.pl.) showed a complete blockade of the analgesic effect induced by low frequency TENS. Thus, our results confirmed the lack of an anti-inflammatory effect through the use of TENS as well as the participation of peripheral endogenous opioid receptors in LF TENS analgesia in addition to its central action.

Comparative evaluation of the direct analgesic efficacy of selected physiotherapeutic methods in subjects with knee joint degenerative disease – preliminary report.

The goals of the study were to evaluate the efficacy of two physiotherapeutic procedures: low energy laser therapy and low frequency transcutaneous electric nerve stimulation (TENS) and to compare these modalities with regard to their therapeutic effects in patients with knee osteoarthritis. Fifty (50) subjects were enrolled into the study and divided into two groups of 25 subjects. Group A received 10 MLS laser therapy sessions with a synchronised laser beam at doses of 12 J per treated site. Group B received ten sessions of low frequency TENS. The procedures were carried out every day for two weeks (5 times a week). All patients completed a personal data questionnaire and underwent an examination of knee joint motion range and circumference. Subjective pain intensity was assessed using the VAS pain scale and the modified Laitinen questionnaire. An analysis of the results of the treatment demonstrated statistically significant pain reduction in both groups. This improvement was significantly higher in the two-phase laser therapy group vs. the LF-TENS group. No statistically significant improvement was noted in either of the groups regarding the knee joint range of motion. 1. Synchronised laser beam (MLS) therapy and low-frequency TENS contribute to direct pain relief effects in subjects with knee osteoarthritis. 2. The study confirmed better analgesic effects of two-phase laser therapy vs. LF-TENS.

Increase intensity in TENS prevent tolerance in rats

Transcutaneous electrical nerve stimulation (TENS) reduces hyperalgesia and pain through release of endogenous opioids in the central nervous system. Both low frequency (LF) and high frequency (HF) TENS, delivered at the same intensity (90% motor threshold (MT)) daily, results in analgesic tolerance with repeated use by the 5th day of treatment. Animals with TENS tolerance show a cross tolerance to opioid agonists in the spinal cord. The current study tested if 1) increasing intensity by 10% per day prevents the development of tolerance to repeated TENS, and 2) if lower intensity TENS produces an equivalent reduction in hyperalgesia when compared to 90% MT TENS.

TENS de alta e baixa frequência para dismenorreia primária: estudo preliminar

Introdução: Dismenorreia primária é conceituada como dor menstrual sem associação de patologias. Objetivo: Avaliar o efeito da eletroestimulação nervosa transcutânea (TENS) de alta e baixa frequência na redução do quadro álgico de mulheres com dismenorreia primária. Métodos: Realizou-se ensaio clínico preliminar, randomizado, controlado e duplo cego com 15 voluntárias com dismenorreia primária, divididas em três grupos: TENS alta frequência (TAF), TENS baixa frequência (TBF) e TENS placebo (TP). Na avaliação da dor e da limitação nas atividades diárias, utilizou-se a escala de categoria numérica. A avaliação da dor foi realizada antes e após a aplicação da TENS, que teve duração de 30 minutos. Foram utilizados testes estatísticos não paramétricos. O nível de significância foi p

Effects of Repetitive High Frequency Transcutaneous Electrical Nerve Stimulation (HF-TENS) on Spasticity and Motor Function following Spinal Cord Injury in Rats

[Purpose] The aim of this study was to determine whether high frequency transcutaneous electrical nerve stimulation (HF-TENS) influences spasticity and motor function recovery after spinal cord injury (SCI). [Subjects] Thirty six male Sprague-Dawley rats (200-250 g) were received contusive SCI at T10 level. One week after SCI, 20 rats with SCI showed increased spasticity. Rats with spasticity after SCI were randomly assigned into two groups: the HF-TENS group (n=10) and the control group (n=10). [Methods] HF-TENS stimulation (100 Hz, 200 μs) was applied to anterior tubercle of the tibia near the knee joint and ankle joint in front of the achilles tendon. To test the effects of HF-TENS on spasticity and motor function recovery, we assessed BBB, combined behavioral score and Modified Ashworth scale for 9 days, at 1 hour after HF-TENS application on hindlimb. [Results] Rats with HF-TENS showed a significant decrease in spasticity 7 days after the HF-TENS application and a prominent improvement in functional outcome 5 days after the HF-TENS application compared to the control group. [Conclusion] Our results suggest that HF-TENS may help relieve spasticity and improve recovery of motor function after SCI.

Transcutaneous electrical nerve stimulation at different frequencies on heart rate variability in healthy subjects

Sympathetic and parasympathetic nervous system imbalance has been strongly associated to sudden cardiac death. Among the non-pharmacological treatment, transcutaneous electrical nerve stimulation (TENS) represents a possible therapeutic intervention to reduce sympathetic excitation and improve the sympatho-vagal balance in different clinical conditions. We aimed to verify acute effects of high and low transcutaneous electrical nerve stimulation (TENS) frequencies by the evaluation of heart rate variability. Seven healthy volunteers received an application of low frequency (10-Hz) and high frequency (100-Hz) TENS. After 10-Hz, there was decrease of LF normalized units (n.u.) component (32.7±5.9 vs 18.3±3.4, p<0.002) and increase of HF n.u. (60.9±4.3 vs 72.6±8.9, p<0.016). In contrast, after 100-Hz there was increase of LF n.u. (31.5±16.1 vs 41.6±12.2, p<0.019) and reduction of HF n.u. (63.9±15.3 vs 53.7±12.3, p<0.031). In conclusion, TENS modulates sympathetic and parasympathetic activity in a frequency dependent manner.

Electrical stimulation reduces secondary mechanical hyperalgesia in a non-inflammatory pain model in rats

Fibromyalgia is a musculoskeletal disease characterized by widespread pain. Its physiological mechanisms are not clear yet, which directly interferes on the quality of pain management. Electrical therapeutic approaches such as interferential current (IFC) and transcutaneous electrical nerve stimulation (TENS) have been used in several pain conditions. To our knowledge this is the first study investigating the effects of both IFC and TENS on reduction of secondary mechanical hyperalgesia in a non-inflammatory muscle pain models in rats. Double intramuscular injection of acid saline (Ph 4.0) was performed five days apart on the left gastrocnemius muscle. Twenty male Wistar rats were divided in four groups: high frequency TENS (100Hz), low frequency TENS (5Hz), interferential current-IFC (modulated frequency of 100Hz) and sham stimulation. Control animals received the same treatment but with no delivery of electrical stimulation. A pair of round electrodes were placed at the lateral and medial aspects of the left gastrocnemius muscle. Animals were lightly anesthetized (5%-2%) with isoflurane and received a single stimulation for 20 minutes. Sensorial intensity was set for starting stimulation. Mechanical hyperalgesia was assessed through von Frey filaments with increasing bending forces before both first and second acid saline injections, 24 h after second injection and following the treatment. All animals showed significant reduction of the mechanical hyperalgesia 24 h after the second injection (p< 0.05). There was a significant reduction of the mechanical hyperalgesia in IFC-treated (p< 0.01) and both high and low frequency TENS-treated animals (p<0,03) compared to sham animals. Thus we suggest that both IFC and TENS at both high and low frequencies promote antinociceptive effect on muscle pain model. Fibromyalgia is a musculoskeletal disease characterized by widespread pain. Its physiological mechanisms are not clear yet, which directly interferes on the quality of pain management. Electrical therapeutic approaches such as interferential current (IFC) and transcutaneous electrical nerve stimulation (TENS) have been used in several pain conditions. To our knowledge this is the first study investigating the effects of both IFC and TENS on reduction of secondary mechanical hyperalgesia in a non-inflammatory muscle pain models in rats. Double intramuscular injection of acid saline (Ph 4.0) was performed five days apart on the left gastrocnemius muscle. Twenty male Wistar rats were divided in four groups: high frequency TENS (100Hz), low frequency TENS (5Hz), interferential current-IFC (modulated frequency of 100Hz) and sham stimulation. Control animals received the same treatment but with no delivery of electrical stimulation. A pair of round electrodes were placed at the lateral and medial aspects of the left gastrocnemius muscle. Animals were lightly anesthetized (5%-2%) with isoflurane and received a single stimulation for 20 minutes. Sensorial intensity was set for starting stimulation. Mechanical hyperalgesia was assessed through von Frey filaments with increasing bending forces before both first and second acid saline injections, 24 h after second injection and following the treatment. All animals showed significant reduction of the mechanical hyperalgesia 24 h after the second injection (p< 0.05). There was a significant reduction of the mechanical hyperalgesia in IFC-treated (p< 0.01) and both high and low frequency TENS-treated animals (p<0,03) compared to sham animals. Thus we suggest that both IFC and TENS at both high and low frequencies promote antinociceptive effect on muscle pain model.

The Influence of ULF-TENS on Electroencephalographic Tracings

The purpose of this study was to evaluate and quantify the effects of Ultra-Low Frequency Transcutaneous Electrical Nerve Stimulation (ULF-TENS) on the Central Nervous System, using electroencephalography. The research was conducted on a study group of twelve patients, and a control group of six. Patients were chosen between the ages of twenty and thirty years old, and all had occlusal flags without pain. The electroencephalography patterns were registered, for each patient in the study group, before and after the application of 60’ of the ULF-TENS. In nine of the twelve cases studied, a diminution of the cerebral rhythm was registered along with the appearance of a sedative effect caused by an increment in Alfa waves and a state of hypo-alertness caused by an increment in the theta rhythm. An identical effect was registered in one subject of the control group while another subject had an increased cerebral rhythm, and in the remaining four subjects, all values remained invariable. The study demonstrated two important points. First, it confirmed the utility of the EEG as a noninvasive useful method in order to study the central effects of the ULF-TENS, and second, also positive, it revealed the sedative effects on the central nervous system registered by the EEG.

Reduced Analgesic Effect of Acupuncture-like TENS but Not Conventional TENS in Opioid-Treated Patients

Evidence from recent animal studies indicates that the analgesic effect of low-frequency transcutaneous electrical nerve stimulation (TENS) is reduced in opioid-tolerant animals. The aim of the present study was to compare the analgesic effect of conventional (high frequency) and acupuncture-like (low frequency) TENS between a group of opioid-treated patients and a group of opioid-naive patients in order to determine if this cross-tolerance effect is also present in humans. Twenty-three chronic pain patients (11 who took opioids and 12 who did not) participated in the study. Participants were assigned in a randomized crossover design to receive alternately conventional and acupuncture-like TENS. There was a significant reduction in pain during and after conventional TENS when compared to baseline for both the opioid and nonopioid group (P < .01). For acupuncture-like TENS however, the analgesic effect of TENS was only observed in the nonopioid group (P < .01), with opioid-treated patients showing no change in pain scores during and after TENS when compared to baseline (P > .09). The reduced analgesic effect of acupuncture-like TENS in opioid-treated patients is coherent with previous animal studies and suggests that conventional TENS should be preferred in patients taking opioids on a regular basis. This study shows that patients taking opioids on a regular basis are less susceptible to benefit from acupuncture-like TENS. This phenomenon is probably attributable to the fact that the analgesia induced by acupuncture-like TENS and opioids are mediated by the same receptors (ie, μ opioid receptors).

Cholecystokinin receptors mediate tolerance to the analgesic effect of TENS in arthritic rats

Transcutaneous electrical nerve stimulation (TENS) is a treatment for pain that involves placement of electrical stimulation through the skin for pain relief. Previous work from our laboratory shows that repeated application of TENS produces analgesic tolerance by the fourth day and a concomitant cross-tolerance at spinal opioid receptors. Prior pharmacological studies show that blockade of cholecystokinin (CCK) receptors systemically and spinally prevents the development of analgesic tolerance to repeated doses of opioid agonists. We therefore hypothesized that systemic and intrathecal blockade of CCK receptors would prevent the development of analgesic tolerance to TENS, and cross-tolerance at spinal opioid receptors. In animals with knee joint inflammation (3% kaolin/carrageenan), high (100 Hz) or low frequency (4 Hz) TENS was applied daily and the mechanical withdrawal thresholds of the muscle and paw were examined. We tested thresholds before and after inflammation, and before and after TENS. Animals treated systemically, prior to TENS, with the CCK antagonist, proglumide, did not develop tolerance to repeated application of TENS on the fourth day. Spinal blockade of CCK-A or CCK-B receptors blocked the development of tolerance to high and low frequency TENS, respectively. In the same animals we show that spinal blockade of CCK-A receptors prevents cross-tolerance at spinal delta-opioid receptors that normally occurs with high frequency TENS; and blockade of CCK-B receptors prevents cross-tolerance at spinal mu-opioid receptors that normally occurs with low frequency TENS. Thus, we conclude that blockade of CCK receptors prevents the development of analgesic tolerance to repeated application of TENS in a frequency-dependent manner.

An Investigation Into the Hypoalgesic Effects of High- and Low-Frequency Transcutaneous Electrical Nerve Stimulation (TENS) on Experimentally-Induced Blunt Pressure Pain in Healthy Human Participants

Transcutaneous electrical nerve stimulation (TENS) is a noninvasive technique used to reduce pain. It is claimed that TENS frequency is a key determinant of outcome. This study compared TENS delivered at 3 pulses per second (pps) and 80 pps on blunt pressure pain in human participants when TENS intensity was standardized at a strong nonpainful level. Thirty-two pain-free participants completed an experiment in which they received TENS at 3 pps and 80 pps in a crossover fashion. An algometer was used to measure pain threshold for each frequency before and during 20 minutes of TENS. A statistically significant elevation in pain threshold relative to baseline was found for 80 pps when compared to 3 pps after 10 and 20 minutes of TENS (P = .001 and P < .001, respectively). After 20 minutes of TENS, 30 of 32 participants had exceeded a 10N elevation in threshold relative to baseline during 80 pps compared to 19 participants during 3 pps (odds ratio 10.3 (CI, 2.28, 44.78), P = .002). We suggest that the higher rates of impulse generation by TENS at 80 pps resulted in a stronger afferent input to the central nervous system, resulting in stronger segmental inhibition of nociceptive transmission of second-order neurones, in line with the gate control theory of pain. In conclusion, strong nonpainful TENS at 80 pps was superior to 3 pps at increasing pressure-pain threshold in healthy volunteers. We recommend a follow-up study using pain patients. This study provides evidence that high frequency TENS at 80 pulses per second increases pain threshold to pressure algometry in healthy participants over and above that seen with low frequency TENS at 3 pulses per second when a strong nonpainful TENS sensation is experienced within the site of experimental pain.

Transcutaneous electrical nerve stimulation at both high and low frequencies activates ventrolateral periaqueductal grey to decrease mechanical hyperalgesia in arthritic rats

Transcutaneous electric nerve stimulation (TENS) is widely used for the treatment of pain. TENS produces an opioid-mediated antinociception that utilizes the rostroventromedial medulla (RVM). Similarly, antinociception evoked from the periaqueductal grey (PAG) is opioid-mediated and includes a relay in the RVM. Therefore, we investigated whether the ventrolateral or dorsolateral PAG mediates antinociception produced by TENS in rats. Paw and knee joint mechanical withdrawal thresholds were assessed before and after knee joint inflammation (3% kaolin/carrageenan), and after TENS stimulation (active or sham). Cobalt chloride (CoCl2; 5 mM) or vehicle was microinjected into the ventrolateral periaqueductal grey (vlPAG) or dorsolateral periaqueductal grey (dlPAG) prior to treatment with TENS. Either high (100 Hz) or low (4 Hz) frequency TENS was then applied to the inflamed knee for 20 min. Active TENS significantly increased withdrawal thresholds of the paw and knee joint in the group microinjected with vehicle when compared to thresholds prior to TENS (P<0.001) or to sham TENS (P<0.001). The increases in withdrawal thresholds normally observed after TENS were prevented by microinjection of CoCl2 into the vlPAG, but not the dlPAG prior to TENS and were significantly lower than controls treated with TENS (P<0.001). In a separate group of animals, microinjection of CoCl2 into the vlPAG temporarily reversed the decreased mechanical withdrawal threshold suggesting a role for the vlPAG in the facilitation of joint pain. No significant difference was observed for dlPAG. We hypothesize that the effects of TENS are mediated through the vlPAG that sends projections through the RVM to the spinal cord to produce an opioid-mediated analgesia.

The effect of transcutaneous electrical nerve stimulation on postmastectomy skin flap necrosis

Transcutaneous electrical nerve stimulation (TENS) is primarily used for pain reduction and is thought to activate neural fibers modifying vascular resistance and local blood flow influencing flap necrosis. This study aimed to delineate the effects of TENS on the viability of skin flaps created during mastectomy in breast cancer patients. Patients treated with modified radical mastectomy were prospectively randomized to receive either TENS or no further local treatment postoperatively. High frequency (70 Hz) and low intensity (2 mA) TENS was applied and areas of flap ecchymosis and necrosis were measured after the completion of TENS application and compared between the two groups. Patients were also compared according to age, comorbid diseases, duration of anesthesia, flap area, amount of wound drainage and seroma, presence of wound infection and abscess. In addition, local and systemic complications related to TENS were recorded. About 173 patients with a median age of 49 (range 25-87) were included in the study. About 87 patients received TENS whereas 86 patients formed the control group. Patients' characteristics were comparable between the two groups. Number of patients with skin flap necrosis was higher in the control group compared to TENS group (P < 0.0001). Mean area of flap necrosis was significantly lower in TENS group (85.2 +/- 35.9) compared to control group (252.5 +/- 64.1; P = 0.024). Similarly, number of patients with skin flap ecchymosis was higher in the control group compared to TENS group (P = 0.002). However, although mean area of flap ecchymosis was lower in TENS group (105.5 +/- 49.8) compared to control group (172.9 +/- 49.9), this difference did not reach statistical significance (P = 0.34). In addition, there were no local or systemic complications related to TENS application in patients. TENS can be safely used to decrease the amount of skin flap necrosis after mastectomy in breast cancer patients without any additional complication.

High and Low Frequency TENS Reduce Postoperative Pain Intensity After Laparoscopic Tubal Ligation

Transcutaneous electrical nerve stimulation (TENS) is an effective adjunctive therapy for postoperative pain; however, effects of different frequencies of stimulation have not been systematically investigated. Laparoscopic sterilization (LS) causes significant pain in the early postoperative period and requires substantial postoperative medication. Therefore, we studied the effects of TENS on postoperative pain after LS through placement of Yoon fallopian rings in a prospective, randomized, double-blinded, and placebo-controlled study.Sixty-four patients undergoing LS for uterine tube ligation were randomly allocated to receive either active TENS or placebo TENS. Postoperative pain was evaluated using a standard 11-point numeric rating scale and the McGill Pain Questionnaire (MPQ)-pain rating index and number of words chosen. Both high frequency (100 Hz) and low frequency (4 Hz) TENS, at strong, but comfortable sensory intensity, were applied for 20 minutes through 4 electrodes placed around the surgical incision immediately after surgery. Pain was assessed before and after application of TENS when patients were at postanesthesia care unit (PACU).Both high and low frequency TENS significantly decreased postoperative pain intensity when compared with before administration of TENS using the numeric rating scale (P=0.001), pain rating index (P=0.001), and number of words chosen (P=0.001) compared with placebo TENS (P=0.001). TENS in combination with standard pharmacologic analgesic treatment was efficacious for postoperative pain relief after LS.We recommend regular use of multimodal therapy with TENS and analgesic drugs after LS with placement of Yoon rings.

Contralateral High or a Combination of High- and Low-Frequency Transcutaneous Electrical Nerve Stimulation Reduces Mechanical Allodynia and Alters Dorsal Horn Neurotransmitter Content in Neuropathic Rats

The purpose of the study was to examine the effect of 3 different application strategies for transcutaneous electrical nerve stimulation (TENS) on neuropathy-induced allodynia and dorsal horn neurotransmitter content. Rats were treated with high-frequency, low-frequency, or a combination of high and low-frequency stimulation. TENS was delivered through self-adhesive electrodes daily for 1 hour to rats with a right-sided chronic constriction injury (CCI). Stimulation was delivered to skin or acupuncture points on the left and mechanical and thermal pain thresholds were assessed in the right hind paw. Neurotransmitter content was assessed bilaterally in the dorsal horn of the spinal cord. Daily, high-frequency or a combination of high- and low-frequency TENS reduced mechanical (P < .001), but not thermal allodynia in the right hind paw when compared with untreated CCI rats. Daily high frequency TENS elevated the dorsal horn synaptosomal content of GABA bilaterally (P < .014) and a combination of high- and low-frequency TENS elevated the dorsal horn content of aspartate (P < .001), glutamate (P < .001) and glycine (P < .001) bilaterally over that seen in untreated CCI rats. The present findings support a contralateral approach to the application of TENS and suggest that distinct strategies for TENS application may differentially alter neurotransmission in the central nervous system. Because CCI rats are reminiscent of humans with neuropathy, daily high or a combination of high- and low-frequency TENS may reduce mechanical allodynia in humans with neuropathic pain. Because the 2 intervention strategies produce distinctive alterations in spinal cord neurotransmitter content, each may represent a distinctive option for treatment.

Modulation Between High- and Low-Frequency Transcutaneous Electric Nerve Stimulation Delays the Development of Analgesic Tolerance in Arthritic Rats

DeSantana JM, Santana-Filho VJ, Sluka KA. Modulation between high- and low-frequency transcutaneous electric nerve stimulation delays the development of analgesic tolerance in arthritic rats. Objective To investigate whether repeated administration of modulating frequency transcutaneous electric nerve stimulation (TENS) prevents development of analgesic tolerance. Design Knee joint inflammation (3% carrageenan and kaolin) was induced in rats. Either mixed or alternating frequency was administered daily (20min) for 2 weeks to the inflamed knee under light halothane anesthesia (1%–2%). Setting Laboratory. Animals Adult male Sprague-Dawley rats (N=36). Intervention Mixed- (4Hz and 100Hz) or alternating- (4Hz on 1 day; 100Hz on the next day) frequency TENS at sensory intensity and 100μs pulse duration. Main Outcome Measures Paw and joint withdrawal thresholds to mechanical stimuli were assessed before induction of inflammation, and before and after daily application of TENS. Results The reduced paw and joint withdrawal thresholds that occur 24 hours after the induction of inflammation were significantly reversed by the first administration of TENS when compared with sham treatment or to the condition before TENS treatment, which was observed through day 9. By the tenth day, repeated daily administration of either mixed- or alternating-frequency TENS did not reverse the decreased paw and joint withdrawal thresholds. Conclusions These data suggest that repeated administration of modulating frequency TENS leads to a development of opioid tolerance. However, this tolerance effect is delayed by approximately 5 days compared with administration of low- or high-frequency TENS independently. Clinically, we can infer that a treatment schedule of repeated daily TENS administration will result in a tolerance effect. Moreover, modulating low and high frequency TENS seems to produce a better analgesic effect and tolerance is slower to develop.

High‐ and low‐frequency transcutaneous electrical nerve stimulation delay sciatic nerve regeneration after crush lesion in the mouse

The stimulation of peripheral nerve regeneration has been studied in different ways, including the use of electrical fields. The capacity of this modality to enhance nerve regeneration is influenced by the parameters used, including current type, frequency, intensity, and means of administration. Transcutaneous electrical nerve stimulation (TENS) is a frequently used form of administering electrical current to the body, but its effects on peripheral nerve regeneration are not known. This study assessed the influence of TENS on sciatic nerve regeneration, using a model of crush lesion in the mouse. Mice were stimulated 30 min a day, 5 days a week, for 5 weeks with both high- (100 Hz) and low- (4 Hz) frequency TENS. Control animals had the sciatic nerve crushed but were not stimulated. Assessment was performed weekly by functional analysis using the Static Sciatic Index for the mouse and at the end of the experiment by light and electron microscopy. The results showed that although there were no differences between the groups regarding the Static Sciatic Index values, TENS led to nerves with morphological signs of impaired regeneration. At light microscopy level, TENS nerves presented more axons with dark axoplasm, signs of edema, and a less organized cytoarchitecture. Electronmicrographs showed fewer and thinner thick myelinated fibers and increased number of Schwann cell nuclei. Myelinated axon diameters and density and diameter of nonmyelinated fibers were not affected by TENS, leading to the conclusion that this regimen of electrical stimulation leads to a delayed regeneration after a crush lesion of the sciatic nerve in the mouse. All these effects were more pronounced on high-frequency TENS nerves.

Alternating Frequencies of Transcutaneous Electric Nerve Stimulation: Does it Produce Greater Analgesic Effects on Mechanical and Thermal Pain Thresholds?

Tong KC, Lo SK, Cheing GL. Alternating frequencies of transcutanenous electric nerve stimulation: does it produce greater analgesic effects on mechanical and thermal pain thresholds? Objective To determine whether alternating frequency transcutaneous electric nerve stimulation (TENS) at 2 and 100Hz (2/100Hz) has a more potent hypoalgesic effect than a fixed frequency at 2 or 100Hz in healthy participants. Design A single-blind randomized controlled trial with a convenience sample. Setting University physiotherapy department. Participants Sixty-four healthy volunteers (32 men [mean age, 28.1±5.9y], 32 women [mean age, 27.7±5.6y]) were recruited and randomly divided into 4 groups. Interventions The 4 groups received TENS delivered at (1) 2Hz; (2) 100Hz; (3) 2/100Hz alternating frequency; and (4) no treatment (control group), respectively. Electric stimulation was applied over the anterior aspect of the dominant forearm for 30 minutes. Main Outcome Measures Mechanical pain thresholds (MPTs) and heat pain thresholds (HPTs) were recorded before, during, and after TENS stimulation. The data were analyzed using linear mixed models, with group treated as a between-subject factor and time a within-subject factor. Results During and shortly after electric stimulation, HPT increased significantly in the alternating frequency stimulation group ( P=.024). MPT increased significantly in both the 100Hz ( P=.008) and the alternating frequency groups ( P=.012), but the increase was substantially larger in the 100Hz group. Conclusions Alternating frequency stimulation produced a greater elevation in the HPT, but a greater increase in the MPT was achieved using 100Hz stimulation.

Predicting outcome of TENS in chronic pain: A prospective, randomized, placebo controlled trial

Transcutaneous electrical nerve stimulation (TENS) is an easy to use non-invasive analgesic intervention applied for diverse pain states. However, effects in man are still inconclusive, especially for chronic pain. Therefore, to explore the factors predicting result of TENS treatment in chronic pain we conducted a prospective, randomized, placebo-controlled trial ( n = 163), comparing high frequency TENS ( n = 81) with sham TENS ( n = 82). Patients’ satisfaction (willingness to continue treatment; yes or no) and pain intensity (VAS) were used as outcome measures. The origin of pain and cognitive coping strategies were evaluated as possible predictors for result of TENS treatment. Results: Fifty-eight percent of the patients in the TENS group and 42.7% of the sham-TENS group were satisfied with treatment result (chi square = 3.8, p = 0.05). No differences were found for pain intensity. Patients diagnosed with osteoarthritis and related disorders (especially of the vertebral column) or peripheral neuropathic pain were less satisfied with high frequency TENS (OR = 0.12 (95% CI 0.04–0.43) and 0.06 (95% CI 0.006–0.67), respectively). Injury of bone and soft tissue (especially postsurgical pain disorder) provided the best results. Treatment modality or interactions with treatment modality did not predict intensity of pain as a result of treatment. We conclude, that predicting the effect of high frequency TENS in chronic pain depends on the choice of outcome measure. Predicting patients’ satisfaction with treatment result is related to the origin of pain. Predicting pain intensity reflects mechanisms of pain behavior and perceived control of pain, independent of treatment modality. Pain catastrophizing did not predict TENS treatment outcome.

The effect of transcutaneous electrical nerve stimulation on local and distal cutaneous blood flow following a prolonged heat stimulus in healthy subjects

The aim of this study was to investigate the effects of transcutaneous electrical nerve stimulation (TENS) on blood flow and skin temperature following an elevation of baseline blood flow using infrared preheating. A randomized controlled approach was used whereby 66 healthy human subjects (33 male, 33 female) were allocated to one of three intervention groups (n=22 per group, equal male and female): Control, Low frequency TENS (4 Hz/200 micros), or High frequency TENS (110 Hz/200 micros). TENS was applied just below motor threshold over the median nerve of the right forearm for 15 min immediately following an infrared preheating. Cutaneous blood flow and skin temperature were recorded at 3-min intervals from the forearm and fingertips during TENS and for 15 min following TENS. Analysis of data revealed no significant differences between High and Low frequency TENS for cutaneous blood flow or skin temperature at the forearm. A small and short lived increase in cutaneous blood flow at the index finger was observed on TENS groups compared with control when TENS was switched off. TENS reduced skin temperature when compared to control during the first 9 min of the 15-min stimulation period at the middle finger but not at the index finger. It was concluded that the effects of high and low frequency TENS when applied below motor threshold produced changes in blood flow and skin temperature that were transient and small.