Effect of different forms of transcutaneous electrical nerve stimulation on experimental pain

The purpose of this study was to compare the effects of five different types of transcutaneous electrical nerve stimulation on experimentally induced pain threshold and tolerance in healthy subjects. Fourteen subjects received the following treatments on different days: low frequency TENS, burst frequency TENS, hyperstimulation TENS, high frequency TENS with a low voltage galvanic stimulator, and high frequency TENS with a high voltage galvanic stimulator to the left upper extremity. Pain threshold and tolerance were tested with electric current on a fingertip of the left upper extremity before each treatment, immediately after each treatment, and 20 minutes after the end of each treatment. Data were analyzed using separate two-by-five analyses of variance with repeated measures for pain threshold and tolerance. No significant effects of treatment or time for pain threshold or tolerance were found. A significant interaction between treatment and time for pain threshold was found. Further study is needed to compare the effects of these treatments in patients with clinical pain.     

Comparison of effects of transcutaneous electrical nerve stimulation of auricular, somatic, and the combination of auricular and somatic acupuncture points on experimental pain threshold

This study compared the effects of high intensity, low frequency transcutaneous electrical nerve stimulation of auricular, somatic, and combined auricular and somatic acupuncture points on experimental pain threshold measured at the wrist. Sixty-seven healthy adults, aged 18 to 39 years, were assigned randomly to one of four groups: 1) the Auricular Group (n = 17) received TENS to auricular acupuncture points, 2) the Somatic Group (n = 17) received TENS to somatic acupuncture points, 3) the Combined Group (n = 17) received TENS to both auricular and somatic acupuncture points, and 4) the Control Group (n = 16) received no TENS and served as controls. Pain threshold was measured immediately before and after treatment or rest. Pain threshold significantly increased (p less than .05) in the Auricular, Somatic, and Combined Groups following treatment, with no statistically significant differences in mean pain threshold change scores among treatment groups. The Control Group demonstrated no statistically significant change in pain threshold. The results indicate that TENS applied to any of the three sets of acupuncture points equally increases pain threshold, thus possibly increasing options in choosing stimulation sites for treating patients with pain.     

Modulation of heat pain perception by high frequency transcutaneous electrical nerve stimulation (TENS).

Although many studies have indicated that high frequency nonpainful transcutaneous electrical nerve stimulation (TENS) reduces clinical pain, controlled studies of the modulation of experimental pain by TENS have produced conflicting results. This study evaluated the effect of high frequency nonpainful TENS on heat pain perception using a model that we have previously shown to be sensitive to other nonpharmacological analgesic treatments. We found that TENS significantly reduced subjects' ratings of painful and near painful heat stimuli (43-51 degrees C) (p = 0.01) and increased the pain threshold from 46.7 to 47.9 degrees C (p = 0.002). Placebo stimulation had no effect on the subjects' ratings or on their pain thresholds. Furthermore, TENS did not alter subjects' ratings of visual stimuli, indicating that the analgesic effect was not due to a nonspecific distraction. These data suggest that TENS alters the perception of experimentally produced natural pain stimuli. The TENS related modulation also appears to be comparable to that produced by other nonpharmacological analgesic manipulations such as counterirritation and changes in attention.     

Effects of unilateral and bilateral auricular transcutaneous electrical nerve stimulation on cutaneous pain threshold

This study compared the effects of unilateral and bilateral auricular transcutaneous electrical nerve stimulation on cutaneous pain threshold. Auricular acupuncture points were stimulated with low frequency, high intensity TENS for 45 seconds. Sixty healthy, adult subjects were assigned randomly to one of two treatment groups or to a control group. The two treatment groups received low frequency, high intensity TENS either unilaterally or bilaterally. The control group did not receive auricular stimulation. Experimental pain threshold at the left wrist was determined with a painful stimulus before and after auricular stimulation. Both unilateral and bilateral auricular stimulation groups exhibited a significant increase (p less than .05) in experimental pain threshold, but the control group did not. The mean change values between the unilateral and bilateral stimulation groups were not statistically different. These results suggest that both unilateral and bilateral auricular TENS can increase pain threshold.     

Treatment of Headache by Transcutaneous Electrical Stimulation

SYNOPSIS
Transcutaneous electrical stimulation (TENS) has been used extensively for many types of pain but only rarely for headache. The object of this study was to judge the efficacy of TENS against placebo. Contrary to popular use, TENS (and placebo) were applied in a rigid manner, probably prejudicial to maximum effectiveness.
62 patients with migraine or muscle contraction headache, or both, were studied using TENS equipment of low amperage and high frequency. One of three modalities was chosen at random for each patient: TENS just above the patient's ability to perceive the stimuli (perceived stimuli), TENS just below the perception threshold (subliminal stimuli), and electrodes applied without electrical stimulation (placebo). Degree of improvement was judged by the patient using a scale of pain from 1 to 10. Following treatment with TENS perceived by the patient, 55% of patients noted improvement as compared to 18% after application of placebo; a significant difference (p < .025 chi-square test). Subliminal TENS was not statistically better than placebo.     

Transcutaneous electrical nerve stimulation characteristics for altering pain perception

The purpose of this study was to determine the effect of conventional low-intensity transcutaneous electrical nerve stimulation (TENS) waveform and frequency characteristics on experimentally induced acute pain. Each of 28 male subjects received six forms of TENS and one control treatment during a single testing session. Treatments used one of two waveforms (monophasic or biphasic) and one of three frequencies (30, 60, or 85 Hz) administered to the forearm. Treatment effects were ascertained from alterations in pain-threshold and pain-tolerance responses induced by noxious electrical stimulation of the ipsilateral fifth digit. The TENS waveform and frequency had a negligible effect on pain threshold. The results indicated that waveform did not influence pain tolerance significantly. Pain tolerance, however, increased significantly at the frequency of 60 Hz but decreased significantly at both 30 and 85 Hz (p less than .05). We concluded that TENS frequency is an important factor in altering the subjects' perception of experimentally induced pain.     

Afferent stimulation induced pain relief in acute oro-facial pain and its failure to induce sufficient pain reduction in dental and oral surgery

In the present paper it is demonstrated that transcutaneous electrical nerve stimulation (TENS) and vibratory stimulation can reduce pathological pain but give insufficient pain reduction to allow dental and oral surgery. Thirty-seven patients were assigned to one of 4 groups receiving either TENS of high (100 Hz) or low (2 Hz) frequency, vibration at 100 Hz or placebo stimulation. Pain intensity was continuously assessed. A crude assessment of pinprick threshold, paraesthesia and anaesthesia was made prior to the clinical treatment. After 30 min of afferent stimulation the surgical treatment was started, aiming at pulp surgery, abscess incision or tooth extraction. However, all patients experienced intolerable pain at these attempts although about half of the patients experienced relief of their pathological pain, increase in pinprick threshold, paraesthesia as well as anaesthesia during the stimulation period. All patients were thus given conventional local anaesthesia and were all painlessly treated.     

Effect of transcutaneous electrical nerve stimulation on human blood beta-endorphin levels

We randomly assigned 42 subjects for treatment with transcutaneous electrical nerve stimulation (TENS) to one of three groups: conventional TENS--80 Hz; low frequency TENS--2 Hz; and a control group--TENS without batteries. Pain threshold measurements and blood beta-endorphin levels were obtained at regular intervals before, during, and for 17 hours after TENS application. We found no significant difference in blood beta-endorphin levels between the groups before, during, or immediately after TENS application. The differences in pain threshold and beta-endorphin levels appeared to be a function of the patient-selection process and not the application of TENS. The results indicated that TENS, with the stimulation characteristics used in this study, did not significantly change the measured plasma levels of beta-endorphin. The blind administration of naloxone hydrochloride, an opiate antagonist, did not significantly alter the perceived experimental pain of these subjects. We could find no evidence that TENS altered experimental pain threshold or plasma beta-endorphin levels.     

Effect of transcutaneous electrical nerve stimulation at auricular points on experimental cutaneous pain threshold

The purposes of this study were 1) to examine the effect of high intensity, low frequency transcutaneous electrical nerve stimulation at auricular acupuncture points on experimental pain threshold measured at the wrist and 2) to determine the changes in effect over time. Forty-four healthy adult men and women were assigned randomly to one of three treatment groups. Group 1 (n = 15) received TENS to appropriate auricular points for wrist pain, Group 2 (n = 14) received TENS to inappropriate (placebo) auricular points, and Group 3 (n = 15) received no TENS. We measured experimental pain threshold at the wrist after an electrical stimulus during one pretreatment and three posttreatment time periods. Group 1 was the only group that had a statistically significant increase (p less than .05) in pain threshold after testing. This increase remained significant for all posttreatment measurements for Group 1. These results suggest that high intensity, low frequency TENS applied to appropriate auricular acupuncture points can increase pain threshold.     

Analgesic effects of different frequencies of transcutaneous electrical nerve stimulation on cold-induced pain in normal subjects

The efficacy of transcutaneous electrical nerve stimulation (TENS) in producing analgesia in cold-induced pain was assessed using a range of 5 stimulating frequencies (10 Hz, 20 Hz, 40 Hz, 80 Hz and 160 Hz) in 83 normal healthy subjects. TENS significantly elevated ice pain threshold when compared with sham and control groups. TENS frequencies between 20 and 80 Hz produced greatest analgesia, while frequencies below and above this level (10 Hz and 160 Hz), although significantly elevating ice pain threshold, produced effects of a lesser magnitude. The frequency of pulse delivery was the governing factor as no significant differences in stimulus intensity were observed across the treatment groups. Measurement of ice pain tolerance was found to be unreliable under the present conditions. No significant relationships were observed between personality variables as measured by Eysenck Personality Questionnaires and the degree of TENS response.     

Transcutaneous electrical nerve stimulation and the reaction to experimental pain in human subjects

The effect of peripheral transcutaneous electrical nerve stimulation (TENS) on the reaction to experimental pain in human volunteers has been assessed. Placebo stimulation and electrical stimulation at moderate intensities failed to modify the response to the pain produced by conducted thermal stimuli. TENS at very high intensities did however elevate both the thermal pain threshold and the tolerance temperature. TENS at moderate intensities failed completely to alter the response to graded mechanical stimuli. The subjective pain assessment and the maximum pain tolerance produced by ischaemic pain after a submaximal effort tourniquet test were significantly modified by peripheral electrical stimulation at non-noxious intensities. The response to experimental pain can therefore be altered in man by peripheral electrical stimulation in a manner partly dependent on the sensory modality used for producing the experimental pain and on the intensity of the electrical stimulation.     

Effects of auricular transcutaneous electrical nerve stimulation on experimental pain threshold

This study was conducted to examine the effects of high intensity transcutaneous electrical nerve stimulation at auricular acupuncture points on experimental pain threshold. Forty-five healthy adult male and female subjects were assigned randomly to one of two treatment groups or to a control group. Subjects in the two treatment groups received high intensity TENS to either appropriate or inappropriate (placebo) acupuncture points on one ear. Experimental pain threshold at the ipsilateral wrist was determined with a painful electrical stimulus before and after ear stimulation. Only the group receiving stimulation of appropriate ear acupuncture points exhibited a significant increase (p less than .01) in experimental pain threshold after ear stimulation. The comparable placebo and control groups, again, did not exhibit significant pretest-posttest differences in experimental pain threshold. The results suggest that, if applied accurately, auricular TENS can increase pain threshold. Further research is needed to assess the effects of this technique on patient groups.     

Effect of transcutaneous electrical nerve stimulation characteristics on clinical pain

We compared the effects of four treatment variables on the pain reduction produced by transcutaneous electrical nerve stimulation and attempted to establish indications for TENS based on patient history and pain evaluation items. Treatment variables were the therapist and the three TENS stimulus characteristics--pulse width, frequency, and amplitude. We randomly assigned 192 consecutive adult patients suffering from painful conditions to one of four physical therapists and one of 12 stimulus characteristic combinations. We used a standard evaluation form that included a visual analog scale (VAS) to evaluate pain. Patients were given a 30-minute trial using TENS, followed by reevaluation. The VAS line length change after treatment was the criterion score for comparison of stimulus characteristic effectiveness. Although pain was reduced greatly with TENS (p = .01), a four-way analysis of variance (pulse width, frequency, amplitude, and therapist) attributed little of the treatment effect to the treatment variables or their interactions (r2 = .101). The amplitude effect, however, was borderline (p = .056), and subthreshold stimulation proved more effective than stimulation to tolerance (p = .05). Extensive multiple linear regression analyses failed to provide indications for TENS based on patient information and pain evaluation items. Therefore, pain remains the only indication for TENS, and we recommend subthreshold rather than higher amplitude stimulation on the initial TENS trial.     

Auricular transcutaneous electrical nerve stimulation (TENS) reduces phantom limb pain

The present paper evaluates the efficacy of low frequency, high intensity auricular transcutaneous electrical nerve stimulation (TENS) for the relief of phantom limb pain. Auricular TENS was compared with a no-stimulation placebo condition using a controlled crossover design in a group of amputees with (1) phantom limb pain (Group PLP), (2) nonpainful phantom limb sensations (Group PLS), and (3) no phantom limb at all (Group No PL). Small, but significant, reductions in the intensity of nonpainful phantom limb sensations were found for Group PLS during the TENS but not the placebo condition. In addition, 10 min after receiving auricular TENS, Group PLP demonstrated a modest, yet statistically significant decrease in pain as measured by the McGill Pain Questionnaire. Ratings of mood, sleepiness, and anxiety remained virtually unchanged across test occasions and sessions, indicating that the decrease in pain was not mediated by emotional factors. Further placebo-controlled trials of auricular TENS in patients with phantom limb pain are recommended in order to evaluate the importance of electrical stimulation parameters such as pulse width and rate, and to establish the duration of pain relief.     

Comparison of stochastic vs. conventional transcutaneous electrical stimulation for pain modulation in patients with electromyographically documented radiculopathy

OBJECTIVE: To determine if a transcutaneous electrical stimulation (TENS) unit modified to deliver electrical impulses at random (R) or stochastic frequency, called TENS-R, provided better pain relief than conventional TENS. DESIGN: A prospective, randomized, double-blinded, placebo-controlled study at an urban teaching hospital. A total of 13 adult subjects with radiculopathy on electromyogram and chronic radicular pain rated pain before and after walking 100 feet with proximal (axial) placement of TENS leads with randomized settings on conventional TENS, placebo, or TENS-R and, subsequently, with distal (limb) placement of TENS leads with randomized settings, all on the same day. The pain measures used were the McGill Pain Questionnaire, parts 1 and 2, and the Visual Analog Scale. The functional measure was speed of walking. RESULTS: Four men and seven women completed the study pain scores, measured by McGill Pain Questionnaire part 2, significantly improved when the patient used TENS-R vs. conventional TENS (P = 0.006, analysis of variance). Placement of TENS electrodes on the back significantly decreased pain compared with lead placement on the legs for McGill Pain Questionnaire part 1 (P = 0.007), McGill Pain Questionnaire part 2 (P = 0.042), and the Visual Analog Scale (P = 0.026) measures. CONCLUSIONS: Qualitative pain scores significantly improved when the patient used TENS-R vs. conventional TENS. Lead placement of any TENS modality over the back vs. over the leg improved all pain scores.     

The effects of auricular transcutaneous electrical nerve stimulation (TENS) on experimental pain threshold and autonomic function in healthy subjects.

The present study examines the effects of auricular transcutaneous electrical nerve stimulation (TENS) on electrical pain threshold measured at the ipsilateral wrist and autonomic functions including skin temperature, blood pressure and pulse rate in 24 healthy subjects. TENS was administered as low frequency trains of pulses delivered at a 'strong but comfortable' intensity to 1 of 3 auricular points to be examined: (i) autonomic effects (autonomic point), (ii) pain threshold effects (wrist point), and (iii) placebo effects at an unrelated point (face point). A fourth untreated group was designated as a situation control. The main finding of the study was that auricular TENS produced no significant overall effects on experimental pain threshold or autonomic functions recorded under the present conditions. However, pain threshold was found to increase by over 50% of its pretreatment baseline in 4 subjects and by 30% in 6 subjects. This rise was not dependent upon the site of auricular TENS. The possible mechanisms of such changes are discussed.     

The effects of unilateral transcutaneous electrical nerve stimulation of the median nerve on bilateral somatosensory thresholds

Transcutaneous electrical nerve stimulation (TENS) is used to relieve acute and chronic pain. TENS electrodes are applied at the site of pain or in segments related to the pain, although there is limited research to support either approach. This study investigated the effects of unilateral TENS on mechanical and thermal thresholds at ipsilateral and contralateral sites in healthy human participants. Sensory perception thresholds were measured on the ipsilateral and contralateral thenar eminence of 16 volunteers for von Frey filaments, sharpness, warm, cold and heat pain. TENS was administered over the right median nerve for 10 min at 100 pulses per second (pps) and an intensity which elicited mild tingling in the hand. During TENS, ipsilateral threshold was greater than contralateral threshold for all sensory modalities, although differences were less marked for thermal stimuli. TENS effects had disappeared 30 min after TENS had been switched off although there was a tendency for thermal thresholds to remain elevated. We conclude that during stimulation, TENS elevates somatosensory thresholds within the distribution of the stimulated nerve. The rapid and short-lived ipsilateral effect is consistent with findings from animal studies and suggests a central segmental mechanism.     

The effect of temporal parameters on subjective sensations evoked by electrical tooth stimulation

The effect of stimulus duration and frequency on subjective sensations evoked by electrical tooth stimulation was studied in 12 subjects. The sensory responses were classified using 5 equi-sensation categories (perception threshold, prepain, pain threshold, moderate pain, intense pain). Both continuously increasing and randomised stimuli were applied. A comparison was made with the activation thresholds of intradental A- and C-fibres in the cat.

The mean threshold of intradental A-fibres was lower than the perception threshold at all pulse durations. Perception threshold decreased with increasing stimulus frequency. Current intensities which evoked prepain at a stimulus frequency of 1 Hz were rated as pain at 20 Hz. At supraliminal pain levels the effects of summation were more marked. High-frequency stimulation produced intense pain sensations at intensities well below the activation thresholds of pulpal C-fibres in the cat.

We conclude that both perception and pain thresholds and supraliminal pain are modified by temporal summation, and that activation of different pulpal fibre populations is not responsible for production of prepain and pain sensations.     

Effects of transcutaneous electrical nerve stimulation on pain in patients with spinal cord injury: a randomized controlled trial

[Purpose] To investigate the effects of transcutaneous electrical nerve stimulation (TENS) on pain in patients with spinal cord injury. [Subjects and Methods] Fifty-two spinal cord injury patients with central pain were randomly allocated into two groups TENS and control with 26 subjects per group. The patients in TENS and control groups were treated with TENS and sham TENS for 20 min (three times a week) for 12 consecutive weeks, respectively. The two group’s pain was assessed using visual analog scale (VAS) and the McGill Pain Questionnaire (including pain rating index-total, pain rating index-affective, pain rating index-sensory, present pain intensity, and number of words chosen) before and after the treatment. [Results] After the intervention, we found significant differences in VAS, pain rating index-total, pain rating index-affective, pain rating index-sensory, present pain intensity, and number of words chosen between the TENS group and the control group. [Conclusion] Our results suggest that TENS effectively decreases pain in patients with spinal cord injury.Key words: Transcutaneous electrical nerve stimulation, Pain, Spinal cord injury     

The effects of non-painful transcutaneous electrical nerve stimulation on cutaneous pain threshold and muscular reflexes in normal men and in subjects with chronic pain

In healthy subjects and in subjects with chronic myofascial pain of one lower limb, the following was measured in both lower limbs: (i) sequential Hoffman (H) reflex, (ii) sequential Achilles tendon (T) reflex, (iii) cutaneous pain threshold determined with electrical stimuli, before, during and after transcutaneous electrical nerve stimulation (TENS).In healthy subjects no significant differences were observed between the pain thresholds of the two limbs. During and after TENS, changes of the reflexes were related to the pain thresholds.In the pathological subjects a significant difference of pain threshold was present between the affected limb and the contralateral one. An important difference between healthy and pathological subjects is not the quality but the quantity of the changes induced by TENS, in the sense that the levels of inhibition and facilitation of the reflexes are more evident in patients with pain. Indeed, TENS induces a reset of sensory and of motor system and a parallel long lasting effect both on sensory and on muscular function, with concomitant pain relief in the pathological subjects.