Transcutaneous electrical nerve stimulation and conditioned pain modulation influence the perception of pain in humans

Effectiveness of high-intensity laser therapy in the treatment of patients with frozen shoulder: a systematic review and meta-analysis

The purpose of this study is to evaluate the effects of high-intensity laser therapy (HILT) in patients with frozen shoulder. PRISMA guidelines were adhered to, and a systematic search was conducted in the PubMed, Web of Science, Scopus, CINAHL, Science Direct, and PEDro databases (last update: September 4, 2023; search period: December 2022-September 2023). The inclusion criteria encompassed RCTs comparing HILT with other physical therapy interventions in frozen patients with frozen shoulders, with or without sham HILT, assessing pain intensity, shoulder ROM, and disability outcomes. The quality of the RCTs was assessed with the Cochrane Risk of Bias tool, and evidence was assessed using the GRADE approach. Five trials met the eligibility criteria and were included in the review and meta-analysis, which pooled results from the visual analog scale (VAS), goniometry, and the shoulder pain and disability index (SPADI). Mean differences (MDs) for pain intensity and disability show a pooled effect in favor of HILT both for VAS (MD =  - 2.23 cm, 95% CI: - 3.25, - 1.22) and SPADI (MD =  - 10.1% (95% CI =  - 16.5, - 3.7), changes that are statistical (p < 0.01) and clinical. The MD for flexion (MD = 9.0°; 95% CI: - 2.36°, 20.3°; p = 0.12), abduction (MD = 3.4°; 95% CI: - 6.9°, 13.7°; p = 0.51), and external rotation (MD =  - 0.95°; 95% CI: - 5.36°, 3.5°; p = 0.67) does not show statistical and clinical differences between groups after treatment. PI and disability changes were graded as important due to their clinical and statistical results. HILT into a physical therapy plan reduce pain and disability, but it does not outperform conventional physical therapy in improving shoulder ROM. It is suggested that future RCTs compare the effects of HILT and LLLT to assess their possible differences in their analgesic effects.

Effects of Percutaneous Electrolysis on Endogenous Pain Modulation: A Randomized Controlled Trial Study Protocol

Percutaneous electrolysis consists of the application of a galvanic electrical current throughout an acupuncture needle. It has been previously hypothesized that needling procedures' neurophysiological effects may be related to endogenous pain modulation (EPM). This protocol study describes the design of a double-blind (participant, assessor) randomized controlled trial with the aim to investigate whether percutaneous electrolysis is able to enhance EPM and whether the effect is different between two applications depending on the dosage of the galvanic electrical current. Seventy-two asymptomatic subjects not reporting the presence of pain symptoms the previous 6 months before the study, aged 18-40 years, are randomized into one of four groups: a control group who does not receive any intervention, a needling group who receives a needling intervention without electrical current, a low-intensity percutaneous electrolysis group (0.3 mA × 90 s), and a high-intensity percutaneous electrolysis group (three bouts of 3 mA × 3 s). Needling intervention consists of ultrasound-guided insertion of the needle on the common extensor tendon of the lateral epicondyle. The primary outcome is conditioned pain modulation (CPM), and secondary outcomes include widespread pressure pain sensitivity (pressure pain thresholds (PPT) over the lateral epicondyle, the cervical spine, and the tibialis anterior muscle) and temporal summation (TS). We expected that percutaneous electrolysis would have a greater influence on CPM than an isolated needling procedure and no intervention. In addition, we also postulated that there might be differences in outcome measures depending on the intensity of the electrical current during the percutaneous electrolysis application. This study makes a new contribution to the field of neurophysiological effects of percutaneous electrolysis and needling interventions.

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.

New method for postoperative pain relief using a combination of noxious and non-noxious stimuli after impacted wisdom tooth extraction

Although in clinical dentistry the major method used for pain relief is oral administration of analgesics, alternative methods are available, such as transcutaneous electrical nerve stimulation (TENS), acupuncture, vibration and conditioned pain modulation (CPM), formerly termed diffuse noxious inhibitory control. The aim of the present study was to investigate the combined effects of non-noxious (TENS) and noxious (CPM) stimuli on postoperative pain after extraction of an impacted wisdom tooth. The study involved 44 patients who were scheduled to undergo impacted wisdom tooth extraction. The patients were randomly allocated into four groups: noxious stimuli, non-noxious stimuli, combined noxious and non-noxious stimuli, and a sham group. On the day after tooth extraction, stimulation procedures for pain relief were performed and changes in the level of perceived pain were scored using a visual analog scale (VAS). The combination of non-noxious and noxious stimuli decreased the VAS scores by 63.7%, indicating a more potent analgesic effect than that in the non-noxious, noxious, and sham groups. This method of analgesia using a combination of non-noxious and noxious stimuli can be applied to patients who are unable to tolerate analgesics, such as those with allergy, hypersensitivity or digestive disorders, and those who are pregnant.

Immediate effects of transcutaneous electrical nerve stimulation (TENS) administered during resistance exercise on pain intensity and physical performance of healthy subjects: a randomized clinical trial

PURPOSE

Exercise-induced muscle pain is a self-limiting condition which impacts physical activity habits. Transcutaneous electrical nerve stimulation (TENS) promotes pain reduction and functional improvement in different pain conditions. We propose that applying TENS during exercise might reduce pain and improve physical performance. Thus, we aimed to investigate immediate effects of TENS applied during resistance exercise.

METHODS

Healthy subjects of both sexes, irregularly active or sedentary were assigned into two groups: active (n = 24) or placebo (n = 22) TENS. The study was conducted over five moments: on day 0, subjects were recruited, on day 1 subjects performed the one-repetition maximum test (1RM); 72 h later, on day 2, 1RM was retested; 48 h later, on day 3, TENS was applied during a functional-resisted exercise protocol for upper limbs (bench press and rowing), with an intensity of 80% of 1RM; and 24 h after, on day 4, subjects were reevaluated. Assessment included pain intensity at rest and with movement, pressure pain thresholds, and muscle fatigue.

RESULTS

TENS did not reduce pain intensity when compared to placebo (p > 0.05). TENS reduce PPT in the latissmus dorsi: p = 0.02 and anterior tibialis: p = 0.04 in immediate reassessment. Immediate effects of TENS were significant for fatigue perception at rest (p = 0.01) and number of maximum repetitions during exercise sets, starting from the 5th set of rowing exercise (p = 0.002).

CONCLUSION

Our results show that TENS did not reduce pain perception in healthy individuals, but its use induced increased muscle action, contributing to a greater fatigue perception.

Effects of Noxious Electrical Stimulation and Eccentric Exercise on Pain Sensitivity in Asymptomatic Individuals

BACKGROUND

Achilles tendinopathy is a common overuse injury in running and jumping athletes. Currently, we do not understand why some conservative interventions (eg, noxious electrical stimulation and eccentric training) may reduce the pain associated with tendinopathy.

OBJECTIVE

To determine whether noxious electrical stimulation (NES) or eccentric contractions would alter pain sensitivity around the asymptomatic Achilles tendon.

DESIGN

A double-blind trial with block-randomization by gender into 3 intervention arms: NES, eccentric contractions, or low-intensity cycling.

PARTICIPANTS

A total of 40 volunteers with no current pain conditions started the study, and 39 completed follow-up testing.

METHODS

Participants underwent 2 baseline sessions to assess pain sensitivity response stability of pressure pain threshold (PPT), heat pain threshold (HPT), and heat temporal summation (HTS) over the Achilles tendon. Immediately after the second baseline session, participants performed 1 session of an intervention and were tested immediately postintervention and the next morning. Eccentric-only plantarflexor exercise was performed (4 sets of 15 repetitions) using full bodyweight and slow, 5-second contractions. Noxious electrical stimulation was applied to the Achilles for 20 minutes and dosed to the subjects' pain tolerance. Low-intensity cycling was dosed (60-70 W for 20 minutes) to minimize occurrence of exercise-induced hypoalgesia. The PPT was the primary outcome measure.

RESULTS

For PPT, both NES (P < .001) and eccentric (P = .003) groups were less sensitive to pressure immediately posttreatment, and the eccentric group maintained this effect through the next morning (P = .043). No group differences were seen for HPT, but the NES (P = .031) and eccentric (P = .036) groups had less HTS the next morning.

CONCLUSIONS

A single session of eccentric exercise and NES can produce immediate and next-day reductions in pain sensitivity in asymptomatic adults. The immediacy of these effects points toward a neurophysiologic mechanism. Future research needs to be performed in clinical populations and to assess any cumulative effects to repetitive intervention.

Central sensitization and changes in conditioned pain modulation in people with chronic nonspecific low back pain: a case-control study

Quantitative sensory testing is widely used in human research to investigate the state of the peripheral and central nervous system contributions in pain processing. It is a valuable tool to help identify central sensitization and may be important in the treatment of low back pain. The aim of this study was to evaluate changes in local and segmental hypersensitivity and endogenous pain inhibition in people with chronic nonspecific low back pain. Thirty patients with chronic low back pain and thirty healthy subjects were studied. Pressure pain thresholds (PPTs) were measured from the lumbar region and over the tibialis anterior muscle (TA). A cold pressor test was used to assess the activation of conditioned pain modulation (CPM), and PPTs in the lumbar region were recorded 30 s after immersion of participant's foot in a bucket with cold water. People with chronic low back pain have significantly lower PPT than controls at both the lumbar region [89.5 kPa (mean difference) 95 % CI 40.9-131.1 kPa] and TA [59.45 kPa (mean difference) 95 % CI 13.49-105.42 kPa]. During CPM, people with chronic low back pain have significantly lower PPT than controls in lumbar region [118.6 kPa (mean difference) 95 % CI 77.9-159.2 kPa]. Women had significantly lower PPTs than men in both lumbar region [101.7 kPa (mean difference) 95 % CI 37.9-165.7 kPa] and over the TA [189.7 kPa (mean difference) 95 % CI 14.2-145.2 kPa]. There was no significant difference in PPTs in men between healthy controls and those with low back pain, suggesting the significant differences are mediated primarily by difference between women.

Transcutaneous electrical nerve stimulation regulates organ blood flow and apoptosis during controlled hypotension in dogs

Transcutaneous electrical nerve stimulation (TENS) is commonly used in clinical practice for alleviating pains and physiological disorders. It has been reported that TENS could counteract the ischemic injury happened in some vital organs. To determine the protective effect of TENS on internal organs during CH in dogs, target hypotension was maintained for 60 min at 50% of the baseline mean arterial pressure (MAP). The perfusion to the brain, liver, stomach, and kidney was recorded and apoptosis within these organs was observed. Results showed that when arriving at the target MAP, and during the maintaining stage for 10 min, perfusion to the stomach and liver in the CH+TENS group was much higher than in the CH group (P<0.05). Perfusion to the cerebral cortex greatly declined in both the controlled pressure groups when compared with the general anesthesia (GA) group (P<0.05). After withdrawing CH, the hepatic blood flow in both the CH and CH+TENS groups, and the gastric and cerebral cortical blood flow in the CH+TENS group, were rapidly increased. By the end of MAP restoration, gastric blood flow in the CH group was still low. At 72 h after applying CH, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL)-positive cells in stomach and kidney tissue from the CH group were significantly increased compared with those in the GA group (P<0.05). There was no significant difference in TUNEL-positive cells in the liver and hippocampus among the three groups. Our results demonstrated that CH with a 50% MAP level could cause lower perfusion to the liver, stomach, cerebral cortex, and kidney, with apoptosis subsequently occurring in the stomach and kidney. TENS combined GA is able to improve the blood flow to the liver, stomach, and reduce the apoptosis in the stomach and kidney.