Alterations in electrical pain thresholds by use of acupuncture-like transcutaneous electrical nerve stimulation in pain-free subjects

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

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

Gender differences in electrical pain threshold responses to transcutaneous electrical nerve stimulation (TENS)

Gender differences in pain perception have been frequently discussed, but the documented gender-related pain-alleviating effects of non-pharmacological methods are sparse. In this study we aimed to investigate changes in electrical sensory thresholds and electrical pain thresholds, in response to high frequency transcutaneous electrical nerve stimulation, TENS, for 20 min in healthy women (n=29) and men (n=29). The thresholds were assessed pre-, during-, and post-TENS. The pattern of change in thresholds was evaluated with a rank-based statistical method regarding the level of systematic change, expressed as relative position (RP) and additional individual changes, expressed as relative rank variance (RV), with its 95% confidence intervals. Equal levels of systematic changes towards increased electrical sensory thresholds were seen in women and men post-TENS (RP, 0.35; 95% CI, 0.07, 0.63, and RP, 0.36; 95% CI, 0.17, 0.53, respectively). At the same point of time, systematic changes towards increased electrical pain thresholds were only seen in women (RP, 0.43; 95% CI, 0.27, 0.60), while they were unchanged in men (RP, -0.01; 95% CI, -0.13, 0.10). Significant additional individual variations were found in the women's responses of assessed electrical sensory and pain thresholds but not in the men's. It is concluded that both women and men responded with a significant increase of the electrical sensory threshold to high frequency TENS, but only women responded with increase of the electrical pain thresholds. The individual variation of the responses was greater in the women than in the men.

The effects of transcutaneous electrical nerve stimulation on experimental pain and sympathetic nervous system response

OBJECTIVE

Transcutaneous electrical nerve stimulation (TENS) is a technique widely used in clinical practice to control pain, although its clinical efficacy remains controversial. Though many mechanisms have been proposed for its analgesic effects, there is a conspicuous lack of experimentally controlled research investigating whether TENS analgesia is related to its effects on the sympathetic nervous system (SNS).

METHODS

Using an established psychophysiological paradigm, the present study investigated the effects of high-frequency/low-intensity TENS, low-frequency/high-intensity TENS, and sham TENS on the perception of experimental pain and SNS function in healthy volunteers. Measures of heart rate, digital pulse volume, and skin conductance were recorded during a 20-minute TENS stimulation period and in anticipation of a series of painful electric shocks prior to and following TENS stimulation. Healthy volunteers rated the intensity of the shocks using a 0-10-point verbal pain rating scale.

RESULTS

The three TENS conditions failed to differentially effect SNS responses during either the 20-minute TENS treatment period or the shock anticipation periods, and TENS did not affect ratings of pain intensity to the shock stimuli.

CONCLUSIONS

While these results may not generalize to acute or chronic pain patients, within the limitations of the present experimental paradigm, no support was found for TENS affecting either SNS function or acute experimental pain perception.

Electrical stimulation: a reflection on current clinical practices

This paper briefly reviews the basic principles of several clinical applications of electrical stimulation for therapeutic purposes. It is intended to facilitate the integration of electrical stimulation into routine clinical practice by clarifying the terminology and standard conventions of the field, explaining the delivery capabilities of common electrical stimulators commercially available for clinical use, summarizing several examples of evidence-based therapeutic applications, and providing guidelines for selection of most commonly used treatment parameters. Rather than an exhaustive survey of the field, the presentation touches broadly on guidelines for use of transcutaneous electrical stimulation employing surface electrodes for the purposes of analgesia (TENS), drug delivery (iontophoresis), or neuromuscular rehabilitation (NMES), as well as other selected clinical applications. The paper is a general review of common clinical practices of electrotherapy and should serve as an introduction to the important factors for clinicians to consider when contemplating electrical stimulation as a treatment option.

Alteration of interferential current and transcutaneous electrical nerve stimulation frequency: effects on nerve excitation

OBJECTIVES

To investigate the effects of different interferential current (IC) and transcutaneous electrical nerve stimulation (TENS) frequencies on sensory, motor, and pain thresholds.

STUDY DESIGN

Single blind, repeated measures design.

SETTING

Laboratory.

PARTICIPANTS

Women students 18 to 30 years old (n = 24).

INTERVENTIONS

Premodulated IC and square-wave TENS pulses (125micros phase duration) were applied over the median nerve at a range of frequencies in all subjects.

MAIN OUTCOME MEASURES

The peak current (in milliamperes) was recorded twice at each threshold for each frequency, and averaged.

RESULTS

Both IC and TENS displayed a statistically significant effect of frequency for each threshold. However, frequency effects with IC were not well defined and were of small magnitude. Pure 4kHz current (0Hz amplitude modulated frequency) with IC did not produce effects different from those produced when an amplitude modulated frequency was included. With TENS, frequency effects were very clearly observed, with a distinct increase in the current intensity at each threshold as frequency decreased.

CONCLUSIONS

It is postulated that the medium frequency component of IC is the main parameter in stimulation, contrary to traditional claims of the amplitude modulated frequency being important. TENS was shown to be a more adaptable method of stimulating these nerve pathways than IC.