Effect of transcutaneous electrical nerve stimulation on the pressor response to static handgrip exercise

Forebrain Network Associated with Cardiovascular Control in Exercising Humans

ABSTRACT

This article describes the forebrain neurocircuitry associated with rapid heart rate response at the exercise onset with attention to ascending somatosensory information from the Type I and II afferents from the contracting muscle and potential influence of sensory information related to blood pressure and changes in heart rate.

A scoping review of the contralateral effects of unilateral peripheral stimulation on neuromuscular function

It is known that resistance exercise using one limb can affect motor function of both the exercised limb and the unexercised contralateral limb, a phenomenon termed cross-education. It has been suggested that cross-education has clinical implications, e.g. in rehabilitation for orthopaedic conditions or post-stroke paresis. Much of the research on the contralateral effect of unilateral intervention on motor output is based on voluntary exercise. This scoping review aimed to map the characteristics of current literature on the cross-education caused by three most frequently utilised peripheral neuromuscular stimulation modalities in this context: electrical stimulation, mechanical vibration and percutaneous needling, that may direct future research and translate to clinical practice. A systematic search of relevant databases (Ebsco, ProQuest, PubMed, Scopus, Web of Science) through to the end of 2020 was conducted following the PRISMA Extension for Scoping Review. Empirical studies on human participants that applied a unilateral peripheral neuromuscular stimulation and assessed neuromuscular function of the stimulated and/or the unstimulated side were selected. By reading the full text, the demographic characteristics, context, design, methods and major findings of the studies were synthesised. The results found that 83 studies were eligible for the review, with the majority (53) utilised electrical stimulation whilst those applied vibration (18) or needling (12) were emerging. Although the contralateral effects appeared to be robust, only 31 studies claimed to be in the context of cross-education, and 25 investigated on clinical patients. The underlying mechanism for the contralateral effects induced by unilateral peripheral stimulation remains unclear. The findings suggest a need to enhance the awareness of cross-education caused by peripheral stimulation, to help improve the translation of theoretical concepts to clinical practice, and aid in developing well-designed clinical trials to determine the efficacy of cross-education therapies.

Cutaneous warmth, but not touch, increases muscle sympathetic nerve activity during a muscle fatigue hand-grip task

In homeostasis, somatosensory C fibre afferents are hypothesised to mediate input to the brain about interactions with external stimuli and sympathetic efference provides the output that regulates bodily functions. We aimed to test this hypothesis and whether different types of innocuous somatosensory input have differential effects. Healthy volunteers performed a muscle fatigue (hand-grip) task to exhaustion, which produces increased muscle sympathetic nerve activity (MSNA), as measured through microneurography. Participants completed the muscle fatigue task without concurrent cutaneous sensory stimulation (control) or we applied skin warming (heat pack) as a C fibre stimulation, slow brush stroking as C and Aβ fibre stimulation, or vibration as Aβ fibre stimulation, to the participant’s forearm. We also measured heart rate, the duration of the hand-grip task, and ratings of pain at the end of the task. Concurrent skin warming showed increased MSNA compared to the other conditions. Tactile stimuli (brushing, vibration) were not significantly different to the control (no intervention) condition. Warming increased the pain from the muscle contraction, whereas the tactile stimuli did not. We interpret the effect of warming on MSNA as providing relevant afferent information during muscle contraction, which needed to be counteracted via vasoconstriction to maintain homeostasis. Brushing and vibration were less homeostatically relevant stimuli for the muscle contraction and hence had no significant effect. The findings add sensory specificity to our current understanding of homeostatic regulation through somatosensory afferent and sympathetic efferent pathways.

Cardiovascular responses during isometric exercise following lengthening and shortening contractions

The present study investigated the effects of prior lengthening or shortening contractions on cardiovascular responses during isometric exercise. We utilized the history dependence of skeletal muscle, where active 2-s lengthening or shortening before an isometric contraction can increase [residual force enhancement (RFE)] or decrease [force depression (FD)] force production. Matching torque output between RFE and FD conditions yields lower and higher electromyography (EMG) values, respectively. In study 1, heart rate and perceived exertion (PE; Borg10) were measured in 20 participants during 20-s isometric plantar flexion contractions at low (16 ± 4% MVC)-, moderate (50 ± 5% MVC)-, and high (88 ± 7% MVC)-intensity. In study 2, heart rate and blood pressure were measured in 14 participants during 2-min isometric plantar flexion contractions (40% MVC). In both studies, torque output was held constant between FD and RFE conditions resulting in differences in soleus EMG activity ( P < 0.05). In study 1, PE was lower during the RFE condition ( P < 0.01), while increases in heart rate were similar between FD and RFE at low (∆2 ± 8 vs. 3 ± 6 beats/min, P > 0.99) and moderate (∆14 ± 9 vs. 14 ± 9 beats/min, P > 0.99) intensity but smaller during RFE at high intensity (∆35 ± 13 vs. 29 ± 13 beats/min, P = 0.004). In study 2, heart rate responses were smaller in the RFE condition following the initial 20-s period; diastolic blood pressure responses were smaller during the last 80 s. A 2-s active change in muscle length before an isometric contraction can influence heart rate and blood pressure responses; however, these differences appear to be modulated by both intensity and duration of the contraction. NEW & NOTEWORTHY Using the history dependence of isometric force to alter maximal torque production and motor unit activation between residual force enhancement and force depression conditions, we observed that heart rate responses were different between conditions during a subsequent 20-s high-, but not low- or moderate-, intensity isometric contraction. A 2-min moderate-intensity contraction revealed time-dependent effects on heart rate and diastolic blood pressure. Active 2-s shortening and lengthening before an isometric contraction can influence the cardiovascular responses.

Does transcutaneous nerve stimulation have effect on sympathetic skin response?

OBJECTIVE

This study examined the effects of transcutaneous electrical nerve stimulation (TENS) on the sympathetic nerve system by sympathetic skin response test.

METHODS

Fifty-five healthy volunteers received either: (i) 30minutes TENS (25 participants) (ii) 30minutes sham TENS (30 participants) and SSR test was performed pre- and post-TENS. The mean values of latency and peak-to-peak amplitude of five consecutive SSRs were calculated.

RESULTS

A significant amplitude difference was found between TENS and sham TENS group both in right and left hand (p=0.04, p=0.01, respectively). However there was no significant latancy difference between two groups (p>0.05 ).

CONCLUSION

TENS has an inhibitory effect on elicited SNS responses when compared with sham TENS control group.

Cutaneous Mechanoreceptor Feedback from the Hand and Foot Can Modulate Muscle Sympathetic Nerve Activity

Stimulation of high threshold mechanical nociceptors on the skin can modulate efferent sympathetic outflow. Whether low threshold mechanoreceptors from glabrous skin are similarly capable of modulating autonomic outflow is unclear. Therefore, the purpose of this study was to examine the effects of cutaneous afferent feedback from the hand palm and foot sole on efferent muscle sympathetic nerve activity (MSNA). Fifteen healthy young participants (9 male; 25 ± 3 years [range: 22-29]) underwent microneurographic recording of multi-unit MSNA from the right fibular nerve during 2 min of baseline and 2 min of mechanical vibration (150 Hz, 220 μm peak-to-peak) applied to the left hand or foot. Each participant completed three trials of both hand and foot stimulation, each separated by 5 min. MSNA burst frequency decreased similarly during the 2 min of both hand (20.8 ± 8.9 vs. 19.3 ± 8.6 bursts/minute [Δ -8%], p = 0.035) and foot (21.0 ± 8.3 vs. 19.5 ± 8.3 bursts/minute [Δ -8%], p = 0.048) vibration but did not alter normalized mean burst amplitude or area (All p > 0.05). Larger reductions in burst frequency were observed during the first 10 s (onset) of both hand (20.8 ± 8.9 vs. 17.0 ± 10.4 [Δ -25%], p < 0.001) and foot (21.0 ± 8.3 vs. 18.3 ± 9.4 [Δ -16%], p = 0.035) vibration, in parallel with decreases in normalized mean burst amplitude (hand: 0.45 ± 0.06 vs. 0.36 ± 0.14% [Δ -19%], p = 0.03; foot: 0.47 ± 0.07 vs. 0.34 ± 0.19% [Δ -27%], p = 0.02) and normalized mean burst area (hand: 0.42 ± 0.05 vs. 0.32 ± 0.12% [Δ -25%], p = 0.003; foot: 0.47 ± 0.05 vs. 0.34 ± 0.16% [Δ -28%], p = 0.01). These results demonstrate that tactile feedback from the hands and feet can influence efferent sympathetic outflow to skeletal muscle.

Hemodynamic Effects Induced by Transcutaneous Electrical Nerve Stimulation in Apparently Healthy Individuals: A Systematic Review With Meta-Analysis

OBJECTIVE

To determine the immediate effects of transcutaneous electrical nerve stimulation (TENS) on heart rate, systolic blood pressure (SBP), and diastolic blood pressure (DBP) in apparently healthy adults (age ≥18y).

DATA SOURCES

The Cochrane Library (online version 2014), PubMed (1962-2014), EMBASE (1980-2014), and LILACS (1980-2014) electronic databases were searched.

STUDY SELECTION

Randomized controlled trials were included when TENS was administered noninvasively with surface electrodes during rest, and the effect of TENS was compared with that of control or placebo TENS. A sensitive search strategy for identifying randomized controlled trials was used by 2 independent reviewers. The initial search led to the identification of 432 studies, of which 5 articles met the eligibility criteria.

DATA EXTRACTION

Two independent reviewers extracted data from the selected studies. Quality was evaluated using the PEDro scale. Mean differences or standardized mean differences in outcomes were calculated.

DATA SYNTHESIS

Five eligible articles involved a total of 142 apparently healthy individuals. Four studies used high-frequency TENS and 3 used low-frequency TENS and evaluated the effect on SBP. Three studies using high-frequency TENS and 2 using low-frequency TENS evaluated the effect on DBP. Three studies using high-frequency TENS and 1 study using low-frequency TENS evaluated the effect on heart rate. A statistically significant reduction in SBP (-3.00mmHg; 95% confidence interval [CI], -5.02 to -0.98; P=.004) was found using low-frequency TENS. A statistically significant reduction in DBP (-1.04mmHg; 95% CI, -2.77 to -0.03; I(2)=61%; P=.04) and in heart rate (-2.55beats/min; 95% CI, -4.31 to -0.78; I(2)=86%; P=.005]) was found using both frequencies. The median value on the PEDro scale was 7 (range, 4-8).

CONCLUSIONS

TENS seems to promote a discrete reduction in SBP, DBP, and heart rate in apparently healthy individuals.

Forebrain neurocircuitry associated with human reflex cardiovascular control

Physiological homeostasis depends upon adequate integration and responsiveness of sensory information with the autonomic nervous system to affect rapid and effective adjustments in end organ control. Dysregulation of the autonomic nervous system leads to cardiovascular disability with consequences as severe as sudden death. The neural pathways involved in reflexive autonomic control are dependent upon brainstem nuclei but these receive modulatory inputs from higher centers in the midbrain and cortex. Neuroimaging technologies have allowed closer study of the cortical circuitry related to autonomic cardiovascular adjustments to many stressors in awake humans and have exposed many forebrain sites that associate strongly with cardiovascular arousal during stress including the medial prefrontal cortex, insula cortex, anterior cingulate, amygdala and hippocampus. Using a comparative approach, this review will consider the cortical autonomic circuitry in rodents and primates with a major emphasis on more recent neuroimaging studies in awake humans. A challenge with neuroimaging studies is their interpretation in view of multiple sensory, perceptual, emotive and/or reflexive components of autonomic responses. This review will focus on those responses related to non-volitional baroreflex control of blood pressure and also on the coordinated responses to non-fatiguing, non-painful volitional exercise with particular emphasis on the medial prefrontal cortex and the insula cortex.

Effect of transcutaneous electrical nerve stimulation on peripheral to central blood pressure ratio in healthy subjects

PURPOSE

To investigate the effect of transcutaneous electrical nerve stimulation (TENS) on the arterial stiffness in healthy young adult and middle-aged men using the augmentation index (AI-x) and hemodynamic measures.

METHODS

Twenty-four men (12 aged 27·25 ± 5·53 years and 12 aged 54·83 ± 5·10 years) were randomly allocated to two subgroups: TENS or placebo in ganglion region for 45 min. The AI-x and hemodynamic measures [late systolic blood pressure (SBP), central blood pressure (CBP), difference between P1 and P2 (ΔP) and tension time index (TTI)] were determined before and after protocols.

RESULTS

TENS resulted in reduction of SBP in younger adults (TENSpre: 111 ± 2; post: 105 ± 2·2 mm Hg; PLACEBOpre: 113 ± 1·8; post: 114 ± 2·5 mm Hg; GEE, P<0·01), whereas no difference was found in middle-aged group. TENS also resulted in reduction of AI-x younger adults group (TENSpre: 56 ± 2·8; post: 53 ± 2%; PLACEBOpre: 55 ± 3; post: 58 ± 2·5%; GEE, P<0·01). ΔP and TTI were significantly decreased after the application of TENS in both groups, but significantly greater reductions in TTI and the SBP/CBP ratio were found in the group of younger adults.

CONCLUSIONS

The acute application of ganglion TENS attenuated arterial stiffness in younger adults as well as hemodynamic measures in the middle-aged group. This method could emerge as effective therapy for the management of arterial blood pressure.

Sympathetic ganglion transcutaneous electrical nerve stimulation after coronary artery bypass graft surgery improves femoral blood flow and exercise tolerance

We tested the hypothesis that transcutaneous electrical nerve stimulation (TENS) over the stellate ganglion region would reduce sympathetic overstimulation and improve femoral blood flow (FBF) after coronary artery bypass graft surgery. Thirty-eight patients (20 men, 24 New York Heart Association class III-IV) were randomized to 5-day postoperative TENS (n = 20; 4 times/day; 30 min/session) or sham TENS (n = 18) applied to the posterior cervical region (C7-T4). Sympathetic nervous system was stimulated by the cold pressor test, with FBF being measured by ultrasound Doppler. Femoral vascular conductance (FVC) was calculated as FBF/mean arterial pressure (MAP). Six-min walking distance established patients' functional capacity. Before and after the intervention periods, pain scores, opiate requirements, and circulating β-endorphin levels were determined. As expected, preoperative MAP increased and FBF and FVC decreased during the cold pressor test. Sham TENS had no significant effect on these variables (P > 0.05). In contrast, MAP decreased in the TENS group (125 ± 12 vs. 112 ± 10 mmHg). This finding, in association with a consistent increase in FBF (95 ± 5 vs. 145 ± 14 ml/min), led to significant improvements in FVC (P < 0.01). Moreover, 6-min walking distance improved only with TENS (postsurgery-presurgery = 35 ± 12 vs. 6 ± 10 m; P < 0.01). TENS was associated with lesser postoperative pain and opiate requirements but greater circulating β-endorphin levels (P < 0.05). In conclusion, stellate ganglion TENS after coronary artery bypass graft surgery positively impacted on limb blood flow during a sympathetic stimulation maneuver, a beneficial effect associated with improved clinical and functional outcomes.

Forebrain organization representing baroreceptor gating of somatosensory afferents within the cortical autonomic network

Somatosensory afferents are represented within the cortical autonomic network (CAN). However, the representation of somatosensory afferents, and the consequent cardiovascular effects, may be modified by levels of baroreceptor input. Thus, we examined the cortical regions involved with processing somatosensory inputs during baroreceptor unloading. Neuroimaging sessions (functional magnetic resonance imaging [fMRI]) recorded brain activity during 30 mmHg lower-body negative pressure (LBNP) alone and combined with somatosensory stimulation (LBNP+SS) of the forearm (n = 14). Somatosensory processing was also assessed during increased sympathetic outflow via end-expiratory apnea. Heart rate (HR), blood pressure (BP), cardiac output (Q), and muscle sympathetic nerve activity (MSNA) were recorded during the same protocols in a separate laboratory session. SS alone had no effect on any cardiovascular or MSNA variable at rest. Measures of HR, BP, and Q during LBNP were not different compared with LBNP+SS. The rise in MSNA burst frequency was attenuated during LBNP+SS versus LBNP alone (8 vs. 12 bursts/min, respectively, P < 0.05). SS did not affect the change in MSNA during apnea. Activations within the insula and dorsal anterior cingulate cortex (ACC) observed during LBNP were not seen during LBNP+SS. Anterior insula and ACC activations occurring during apnea were not modified by SS. Thus, the absence of insular and dorsal ACC activity during LBNP+SS along with an attenuation of MSNA burst frequency suggest sympathoinhibitory effects of sensory stimulation during decreased baroreceptor input by a mechanism that includes conjoint insula-dorsal ACC regulation. These findings reveal that the level of baroreceptor input influences the forebrain organization of somatosensory afferents.

Representation of somatosensory inputs within the cortical autonomic network

Regions of the cortical autonomic network (CAN) are activated during muscle contraction. However, it is not known to what extent CAN activation patterns reflect muscle sensory inputs, top-down signals from the motor cortex, and/or motor drive to cardiovascular structures. The present study explored the functional representation of somatosensory afferent input within the CAN with an a priori interest in the insula and ventral medial prefrontal cortex (vMPFC) (n=12). Heart rate (HR) and functional MRI data were acquired during 1) 30s periods of electrical stimulation of the wrist flexors at sub-motor (SUB; Type I,II afferents) and 2) motor thresholds (MOT; Type I,II,III afferents), 3) volitional wrist flexion at 5% maximal voluntary contraction (MVC) to match the MOT tension (VOL5%), and 4) volitional handgrip at 35% MVC to elicit tachycardia (VOL35%). Compared with rest, HR did not change during SUB, MOT, or VOL5% but increased during VOL35% (p<0.001). High frequency HR variability was 29.42±18.87 ms(2) (mean±S.D.) at rest and 39.85±27.60 ms(2) during SUB (p=0.06). High frequency HR variability was decreased during VOL35% compared to rest (p≤0.005). SUB increased activity in the bilateral posterior insula, vMPFC, subgenual anterior cingulate cortex (ACC), mid-cingulate cortex (MCC), and posterior cingulate cortex. MOT increased activity in the left posterior insula and MCC. During VOL5%, activity increased in the right anterior-mid insula. VOL35% was associated with activity in the bilateral insula as well as vMPFC and subgenual ACC deactivation. These data suggest that the left posterior insula processes sensory input from muscle during passive conditions and specifically that Type I and/or II muscle afferent stimulation during SUB impacts the vMPFC and/or subgenual ACC, regions believed to be involved in brain default mode and parasympathetic activity.

A New Analgesic Method, Two-minute Sciatic Nerve Press, for Immediate Pain Relief: A Randomized Trial

BACKGROUND

Current analgesics have drawbacks such as delays in acquisition, lag-times for effect, and side effects. We recently presented a preliminary report of a new analgesic method involving a two-minute sciatic nerve press, which resulted in immediate short-term relief of pain associated with dental and renal diseases. The present study investigated whether this technique was effective for pain associated with other disease types, and whether the relief was effective for up to one hour.

METHODS

This randomized, placebo-controlled, parallel-group trial was conducted in four hospitals in Anhui Province, China. Patients with pain were sequentially recruited by participating physicians during clinic visits, and 135 patients aged 15 - 80 years were enrolled. Dental disease patients included those with acute pulpitis and periapical abscesses. Renal disease patients included those with kidney infections and/or stones. Tumor patients included those with nose, breast, stomach and liver cancers, while Emergency Room patients had various pathologies. Patients were randomly assigned to receive a "sciatic nerve press" in which pressure was applied simultaneously to the sciatic nerves at the back of both thighs, or a "placebo press" in which pressure was applied to a parallel region on the front of the thighs. Each fist applied a pressure of 11 - 20 kg for 2 minutes. Patients rated their level of pain before and after the procedure.

RESULTS

The "sciatic nerve press" produced immediate relief of pain in all patient groups. Emergency patients reported a 43.5% reduction in pain (p < 0.001). Significant pain relief for dental, renal and tumor patients lasted for 60 minutes (p < 0.001). The peak pain relief occurred at the 10 - 20th minutes, and the relief decreased 47% by the 60th minutes.

CONCLUSION

Two minutes of pressure on both sciatic nerves produced immediate significant short-term conduction analgesia. This technique is a convenient, safe and powerful method for the short-term treatment of clinical pain associated with a diverse range of pathologies.

TRIAL REGISTRATION

Current Controlled Trials ACTRN012606000439549.

Immediate and short-term pain relief by acute sciatic nerve press: a randomized controlled trial

BACKGROUND

Despite much research, an immediately available, instantly effective and harmless pain relief technique has not been discovered. This study describes a new manipulation: a "2-minute sciatic nerve press", for rapid short-term relief of pain brought on by various dental and renal diseases.

METHODS

This randomized, single-blind, placebo-controlled trial ran in three hospitals in Anhui Province, China, with an enrollment of 66 out of 111 solicited patients aged 16 to 74 years. Patients were recruited sequentially, by specific participating physicians at their clinic visits to three independent hospitals. The diseases in enrolled dental patients included dental caries, periodontal diseases and dental trauma. Renal diseases in recruits included kidney infections, stones and some other conditions. Patients were randomly assigned to receive the "2-minute sciatic nerve press" or the "placebo press". For the "2-minute sciatic nerve press", pressure was applied simultaneously to the sciatic nerves at the back of the thighs, using the fists while patients lay prone. For the "placebo press", pressure was applied simultaneously to a parallel spot on the front of the thighs, using the fists while patients lay supine. Each fist applied a pressure of 11 to 20 kg for 2 minutes, after which, patients arose to rate pain.

RESULTS

The "2-minute sciatic nerve press" produced greater pain relief than the "placebo press". Within the first 10 minutes after sciatic pressure, immediate pain relief ratings averaged 66.4% (p < 0.001) for the dental patients, versus pain relief of 20% for the placebo press, and, 52.2% (p < 0.01) for the renal patients, versus relief of 14% for the placebo press, in median. The method worked excellently for dental caries and periodontal diseases, but poorly for dental trauma. Forty percent of renal patients with renal colic did not report any pain relief after the treatment.

CONCLUSION

Two minutes of pressure on both sciatic nerves can produce immediate significant conduction analgesia, providing a convenient, safe and powerful way to overcome clinical pain brought on by dental diseases and renal diseases for short term purposes.

TRIAL REGISTRATION

ACTR 12606000439549.

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.

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.

Transcutaneous electric nerve stimulation: the effect of intensity on local and distal cutaneous blood flow and skin temperature in healthy subjects

OBJECTIVE

To determine what effect transcutaneous electric nerve stimulation (TENS) intensity has on local and distal cutaneous blood flow and skin temperature.

DESIGN

Double-blind conditions.

SETTING

University research laboratory.

PARTICIPANTS

Forty subjects (20 men, 20 women) randomly assigned to 1 of 4 groups (10 per group): control, above-motor-threshold TENS, below-motor-threshold TENS, or perception-threshold TENS.

INTERVENTION

TENS (4Hz, 200micros) was applied over the median nerve of the right forearm for 15 minutes.

MAIN OUTCOME MEASURES

Blood flow measured by laser Doppler flowmeter and skin temperature measured by skin thermistor were recorded during TENS and for 15 minutes after it.

RESULTS

Significant differences occurred between groups for forearm (P <.0001; repeated-measures analysis of variance) but not fingertip cutaneous blood flow. Post hoc Fisher tests showed a significant increase in forearm blood flow during TENS application in the above-motor-threshold TENS group compared with the other 3 groups. No significant differences between groups for skin temperature data were observed.

CONCLUSIONS

The effect of TENS on cutaneous blood flow depends on whether muscle activity is induced. Low-frequency TENS applied above the motor threshold significantly increases local cutaneous blood flow. There were no significant differences between groups for skin temperature.

Nonpharmacological treatments for musculoskeletal pain

BACKGROUND

Several types of physical therapy are used in the management of painful musculoskeletal disorders. These treatment modalities can be broadly categorized as electrotherapy modalities (e.g., transcutaneous electrical nerve stimulation), acupuncture, thermal modalities (e.g., moist heat, ultrasound), manual therapies (e.g., manipulation or massage), or exercise. Within each of these broad categories significant variations in treatment parameters are possible.

OBJECTIVE

To consider the evidence base for each of these main categories of physical therapy in the management of musculoskeletal pain.

METHOD

To consider the available evidence related to clinical effectiveness and then to review evidence from basic science studies evaluating potentially therapeutic effects of the various therapies.

RESULTS

There seems to be evidence from basic science research to suggest that many of the therapies could have potentially therapeutic effects. However, there appears to be limited high-quality evidence from randomized clinical trials to support the therapeutic effectiveness of several of the therapies.

CONCLUSIONS

There is some preliminary evidence to support the use of manual therapies, exercise, and acupuncture in the management of some categories of musculoskeletal pain. Limitations of the existing research base are discussed and recommendations for areas of future research are provided.

Significant changes in systolic blood pressure post vectored upper cervical adjustment vs resting control groups: a possible effect of the cervicosympathetic and/or pressor reflex

OBJECTIVE

To determine whether a vectored adjustment of the atlas in patients identified as demonstrating signs of upper cervical joint dysfunction would cause lowering of blood pressure in comparison with resting controls.

DESIGN

Test 1: controlled clinical trial with a treatment (adjustment) group and a control (resting) group. Test 2: controlled clinical trial with subjects serving as their own controls.

SETTING

Private chiropractic practice.

PARTICIPANTS

Test 1: Forty established patients demonstrating signs of upper cervical subluxation/joint dysfunction and 40 established patients without such signs. Test 2: Thirty established patients demonstrating signs of upper cervical subluxation/joint dysfunction.

INTERVENTION

Specific, vectored upper cervical (atlas) adjustment or similarly positioned resting.

MAIN OUTCOME MEASURES

Prerest, postrest, and postadjustment systolic, diastolic, and pulse rates as recorded through use of a digital oscillometric sphygmomanometer.

RESULTS

In test 1, subjects receiving adjustment had a significant (P <.001) decrease in systolic blood pressure whereas resting subjects did not. Intergroup comparison of the treatment (adjustment) and control (resting) groups demonstrated a significant difference (P <.001). A greater pre/post drop in systolic pressure was associated with greater age and higher initial systolic pressure. In test 2, the pre/postrest change in systolic blood pressure was not significant. The systolic blood pressure changed significantly (P <.001) from postrest readings to postadjustment readings.

CONCLUSION

The results indicate that palpation and vectored atlas adjustment causes a significant decrease in systolic blood pressure in patients with putative upper cervical subluxation/joint dysfunction in comparison with resting controls. Similar results were also demonstrated when subjects acted as their own controls. The lack of randomization, blinding, and a manipulated control group are factors that weaken these findings. The sudden drop in systolic pressure is proposed to be due to stimulation of the cervicosympathetic reflex or moderation of muscle tone and elimination of the effects of the pressor reflex.

The effect of high- and low-frequency transcutaneous electrical nerve stimulation upon cutaneous blood flow and skin temperature in healthy subjects

The reported non-analgesic effects of transcutaneous electrical nerve stimulation (TENS) include alterations to the local circulation; however, research in this area has produced equivocal findings. In the present study, the effect of low- (4 Hz) and high-frequency (110 Hz) TENS on forearm skin blood perfusion was assessed using laser Doppler flowmetry. The effect on skin temperature was also assessed using a skin thermistor. Thirty healthy human volunteers were recruited and randomly assigned to a control or one of the two treatment groups. TENS was applied to the skin overlying the median nerve under double-blind conditions for 15 min. Blood flow and skin temperature readings were recorded pre-TENS, during TENS application and continued for 15 min post-TENS application. Analysis of results showed significant increases in blood perfusion during the treatment period in the low-frequency group when compared to the other two groups (P = 0.0106; ANOVA). No significant changes in skin temperature were observed. The results of this study demonstrate that low-frequency TENS produces a local increase in cutaneous blood flow.