Chih-Chung Chen

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.

UNLABELLED 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. PERSPECTIVE 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.

An investigation into the effects of frequency-modulated transcutaneous electrical nerve stimulation (TENS) on experimentally-induced pressure pain in healthy human participants.

UNLABELLED Frequency-modulated transcutaneous electrical nerve stimulation (TENS) delivers currents that fluctuate between preset boundaries over a fixed period of time. This study compared the effects of constant-frequency TENS and frequency-modulated TENS on blunt pressure pain in healthy human volunteers. Thirty-six participants received constant-frequency TENS (80 pps), frequency-modulated TENS (20 to 100 pps), and placebo (no current) TENS at a strong nonpainful intensity in a randomized cross-over manner. Pain threshold was taken from the forearm using pressure algometry. There were no statistical differences between constant-frequency TENS and frequency-modulated TENS after 20 minutes (OR = 1.54; CI, 0.29, 8.23, P = 1.0). Both constant-frequency TENS and frequency-modulated TENS were superior to placebo TENS (OR = 59.5, P < .001 and OR = 38.5, P < .001, respectively). Frequency-modulated TENS does not influence hypoalgesia to any greater extent than constant-frequency TENS when currents generate a strong nonpainful paraesthesia at the site of pain. The finding that frequency-modulated TENS and constant-frequency TENS were superior to placebo TENS provides further evidence that a strong yet nonpainful TENS intensity is a prerequisite for hypoalgesia. PERSPECTIVE This study provides evidence that TENS, delivered at a strong nonpainful intensity, increases pain threshold to pressure algometry in healthy participants over and above that seen with placebo (no current) TENS. Frequency-modulated TENS does not increase hypoalgesia to any appreciable extent to that seen with constant-frequency TENS.

The traction angle and cervical intervertebral separation

Seventeen normal young adults were evaluated for cervical intervertebral separation under different traction angles through motorized intermittent traction in the supine position. In all cases, the anterior and posterior intervertebral spaces were increased by traction at neutral position and in 30°flexion, but not in 15° extension. The effects of separation were 1) neutral position: anterior intervertebral separation C4–5 (12%) > C3–4 (8%), posterior intervertebral separation C6–7 (37%) > C3–4 (22%) > C4–5 (19%); and 2) 30° flexion: anterior intervertebral separation C2–3 (21 %) > C4–5 (16%) > C5–6 (15%) > C3–4 (10%), posterior intervertebral separation C6–7 (20%) > C5–6 (19%) > C4–5 (17%). There was a significant decrease in intervertebral separation posteriorly in extension traction, especially at C6–7 (−50%), C5–6 (−37%), C4–5 (−26%), and C3–4 (−14%). The separation of facet joint surfaces was found after traction at 15° extension, but not in the neutral or flexion positions.

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 μs), or High frequency TENS (110 Hz/200 μs). 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.

Differential Frequency Effects of Strong Nonpainful Transcutaneous Electrical Nerve Stimulation on Experimentally Induced Ischemic Pain in Healthy Human Participants

IntroductionElectrophysiological studies show frequency-dependent effects of transcutaneous electrical nerve stimulation (TENS) in animal models of hyperalgesia. Evidence of frequency-dependent effects of TENS in humans is conflicting. ObjectiveTo assess the effects of low-frequency and high-frequency TENS at a strong nonpainful intensity on experimentally induced ischemic pain. MethodsSubmaximal effort tourniquet tests were carried out on 48 healthy human participants before (baseline) and during TENS at 3 pulsed currents per second (pps), 80 pps, and no current (placebo). TENS was switched on for 20 minutes and a submaximal effort tourniquet test was carried out during the final 5 minutes of the intervention. There was a 30-minute washout, with TENS switched off, between the interventions. ResultsRepeated measure analysis of variance detected significant effects for pain intensity [100 mm Visual Analog Scale (VAS)] for condition (P<0.001), time (P<0.001), and time×condition (P=0.039). When compared with pre-TENS lower VAS scores were detected for placebo TENS (P=0.026) and 80 pps (P<0.001), but not for 3 pps (P=0.19). There were lower VAS scores for 80 pps than placebo (mean difference, 13.29 mm; 95% CI, 9.71, 16.87; P<0.001) and 3 pps (mean difference, 19.88 mm; 95% CI, 17.20-22.55; P<0.001), yet 3 pps scores were higher than placebo (mean difference, 6.58 mm; 95% CI 3.45, 9.72; P<0.001). There were significantly lower scores for sensory dimensions of the short-form McGill Pain Questionnaire for both 3 pps and 80 pps when compared with the placebo (P<0.001; P=0.005, respectively), but no significant differences between TENS at 80 and 3 pps (P=1.0). There were no significant effects detected for condition (P=0.217) or for condition×sequence interaction (P=0.800) for affective dimensions. ConclusionsStrong nonpainful TENS delivered at 80 pps reduced experimentally induced ischemic pain when compared with TENS delivered at 3 pps.

A comparison of transcutaneous electrical nerve stimulation (TENS) at 3 and 80 pulses per second on cold-pressor pain in healthy human participants.

Electrophysiological studies suggest that there are differential frequency effects during TENS. The aim of this experimental study was to assess the effects of strong non‐painful TENS administered at 3 pulses per second (pps) and 80 pps on cold‐pressor pain in healthy human participants. A repeated measure design was used with participants receiving TENS at 3 pps and 80 pps in the same experiment. There were six cold‐pressor pain tests conducted on the hand with each type of TENS delivered via four electrodes on the ipsilateral forearm for 20 min. Outcomes were differences in pain threshold (s) and intensity (VAS) after 5 and 15 min of TENS. A 2 × 3 factorial repeated measure ANOVA was performed on data. Thirty‐five participants completed the experiment. Statistically significant effects were detected for condition, time and interactions between time × condition for both threshold and intensity. There were statistically higher pain thresholds and lower pain intensities for 3 pps when compared to 80 pps after 5 and 15 min of TENS. The differences after 15 min of TENS were 1·70 s to 3·70 s (95% CI) for threshold and 6·63–15·5 mm (95% CI) for pain intensity. In conclusion, strong non‐painful TENS at 3 pps was superior to 80 pps at reducing experimentally induced cold‐pressor pain. The implications of these findings are discussed.

Neuromuscular electrical stimulation of the median nerve facilitates low motor cortex excitability in patients with spinocerebellar ataxia.

The neuromodulation of motor excitability has been shown to improve functional movement in people with central nervous system damage. This study aimed to investigate the mechanism of peripheral neuromuscular electrical stimulation (NMES) in motor excitability and its effects in people with spinocerebellar ataxia (SCA). This single-blind case-control study was conducted on young control (n=9), age-matched control (n=9), and SCA participants (n=9; 7 SCAIII and 2 sporadic). All participants received an accumulated 30 min of NMES (25 Hz, 800 ms on/800 ms off) of the median nerve. The central motor excitability, measured by motor evoked potential (MEP) and silent period, and the peripheral motor excitability, measured by the H-reflex and M-wave, were recorded in flexor carpi radialis (FCR) muscle before, during, and after the NMES was applied. The results showed that NMES significantly enhanced the MEP in all 3 groups. The silent period, H-reflex and maximum M-wave were not changed by NMES. We conclude that NMES enhances low motor excitability in patients with SCA and that the mechanism of the neuromodulation was supra-segmental. These findings are potentially relevant to the utilization of NMES for preparation of motor excitability. The protocol was registered at Clinicaltrials.gov (NCT02103075).

Gender differences in the effects of presynaptic and postsynaptic dopamine agonists on latent inhibition in rats

The present study investigated gender differences in the effects of presynaptic and postsynaptic DA agonists on latent inhibition in the passive avoidance paradigm. During the preexposure phase, 32 male and 32 female Wistar rats were exposed to a passive avoidance box (or a different context) and received drug injections in three trials: the control group received an injection of 10% ascorbic acid in a different context. The experimental groups received injections of 10% ascorbic acid (latent inhibition [LI] group), 1mg/kg of the postsynaptic DA D(1)/D(2) agonist apomorphine (APO group), and 1.5mg/kg of the presynaptic DA agonist methamphetamine (METH group) in a passive avoidance box. All experimental groups were placed in the light compartment of the passive avoidance box and were allowed to enter into the dark compartment to receive a footshock (1mA, 2s) in five trials over 5 days. The latency to enter into the dark compartment was recorded in these five trials. The latent inhibition occurred in the female LI group but not in the male LI group. Regardless of gender, the APO group exhibited an increase in latent inhibition. Male rats in the METH group exhibited a decrease in latent inhibition, but female rats in the METH group exhibited an increase in latent inhibition, indicating that the METH group exhibited sexual dimorphism. The gender factor interacted only with the METH group and not the LI or APO group. The present paper discusses whether gender, the postsynaptic DA D(1)/D(2) agonist APO, and presynaptic DA agonist METH may be related to schizophrenia.

The antalgic effects of non-invasive physical modalities on central post-stroke pain: a systematic review.

[Purpose] This study systematically reviewed the antalgic effects of non-invasive physical modalities (NIPMs) on central post-stroke pain (CPSP). [Subjects and Methods] Clinical studies were sought on September 2015 in 10 electronic databases, including Medline and Scopus. The searching strings were “central pain and stroke” and “treatment, and physical or non-pharmacological”. The inclusion and exclusion criteria were set for screening the clinical articles by two reviewers. Pain scores on visual analog scale in an article were used as the outcome measure for resulting judgment. The NIPMs intervention summarized from the eligible articles was rated from Levels A to C according to Evidence Classification Scheme for Therapeutic Interventions. [Results] Over 1200 articles were identified in the initial searches and 85 studies were retrieved. Sixteen studies were eligible and judged. Caloric vestibular stimulation (n=3), heterotopic noxious conditioning stimulation (n=1), and transcutaneous electrical stimulation (n=1) were rated below Level C. Transcranial direct current stimulation (TDCS; n=2) and transcranial magnetic stimulation (TMS; n=9) were rated as Level B. [Conclusion] The findings suggest that TMS and TDCS were better than other treatments for CPSP relief but the studies were of insufficient quality.

An examination of the roles of glutamate and sex in latent inhibition: Relevance to the glutamate hypothesis of schizophrenia?

The present study examined the effects of the glutamate receptor antagonist MK-801, the glutamate receptor agonist N-methyl-D-aspartate (NMDA), and sexual dimorphism on latent inhibition to elucidate the glutamate hypothesis of schizophrenia. During the pre-exposure phase, 56 male and 65 female Wistar rats were intracerebroventricularly administered normal saline, MK-801 or NMDA, in the left ventricle and then exposed to a passive avoidance box (or a different context) in three trials over 3 days. Then, all of the rats were placed in the light compartment of the passive avoidance box and were allowed to enter the dark compartment, where they each received a footshock (1mA, 2s) in five trials over 5 days. Injections of the glutamate drugs NMDA and MK-801 did not affect latent inhibition. Sexual dimorphism did not occur in latent inhibition. The present data on the male rats indicated that the glutamate system did not affect latent inhibition, indicating that the glutamate system was not like the dopamine system in terms of mediating the positive symptoms of schizophrenia. The glutamate system might be involved in the negative and cognitive symptoms of schizophrenia. The results may provide information for novel treatments of the negative and cognitive symptoms of schizophrenia.