2003; 83:208-223. PHYS THER. Mark I Johnson and Ghazala Tabasam Ischemic Pain in Otherwise Pain-Free Volunteers Nerve Stimulation on Experimentally Induced Electrical Interferential Currents and Transcutaneous An Investigation Into the Analgesic Effects of http://ptjournal.apta.org/content/83/3/208 found online at: The online version of this article, along with updated information and services, can be Collections Pain Elect rotherapy in the following collection(s): This article, along with others on similar topics, appears e-Letters "Responses" in the online version of this article. "Submit a response" in the right-hand menu under or click on here To submit an e-Letter on this article, clickE-mail alerts to receive free e-mail alerts here Sign up by guest on April 23, 2014 http://ptjournal.apta.org/Downloaded fromby guest on April 23, 2014 http://ptjournal.apta.org/Downloaded from
Mark I Johnson and Ghazala TabasamIschemic Pain in Otherwise Pain-Free VolunteersNerve Stimulation on Experimentally Induced
ElectricalInterferential Currents and TranscutaneousAn Investigation Into the Analgesic Effects of
http://ptjournal.apta.org/content/83/3/208found online at:The online version of this article, along with updated information and services, can be
Collections
Pain Electrotherapy
in the following collection(s):This article, along with others on similar topics, appears
e-Letters"Responses" in the online version of this article."Submit a response" in the right-hand menu underor click onhereTo submit an e-Letter on this article, click
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Transcutaneous electrical nerve stimulation(TENS) and interferential currents (IFC) arenoninvasive, analgesic techniques that areclaimed to have an effect.1–5 There is wide-
spread use of TENS throughout health care, and somepatients report satisfaction with treatment outcome.1–5
There is an extensive but confusing body of literature onTENS, and systematic reviews have questioned its effec-tiveness for postoperative pain and labor pain.6–9 Thereis some evidence that TENS is beneficial for some formsof chronic pain.9,10 Inadequacies in systematic reviewsand in the quality of and appropriateness of randomizedcontrolled trials (RCTs) included in reviews may havecontributed, in part, to the negative findings.11–13
Interferential currents are similar to TENS, although theuse of IFC appears to be primarily by physical therapists.
Surveys have shown that physical therapists report that they use TENS and IFC regularly.14–16 The most com-mon use of IFC, we believe, is to relieve pain, althoughsome therapists also report using IFC for the reductionof swelling, the healing of wounds and fractures, and therestoration of function associated with muscle weak-ness.17,18 These indications mirror information providedin key textbooks on the clinical use of IFC.19–21 Accep-
tance of IFC into practice is not based on evidence of effects. Literature on IFC is anecdotal, and someresearchers, including ourselves, have questioned theeffects of IFC.22–24
Some authors, in nonrefereed publications,19–21 claimthat the mechanism of action is different between IFCand TENS. The active element of TENS is biphasicpulsed currents.25–28 In its conventional form, TENS hasbeen shown to selectively activate large-diameter A fibers without concurrently activating small-diameter A and C-fibers or muscle efferents, which leads to inhibi-tion of ongoing activity in second-order nociceptiveneurons.25,26,29,30 In theory, high-frequency (1–250pulses per second [pps]), low-intensity (non-noxious)pulsed currents should be most efficient at the selectiveactivation of large-diameter fibers.26 In practice, how-
ever, a trial-and-error approach is used to determineTENS settings. The TENS settings are based on thepatients’ titration of current amplitude, frequency, andduration to produce a strong but comfortable electricalparesthesia, because this sensation indicates activity inlarge-diameter afferents.31 The trial-and-error approach,using patients’ self-reports of sensations produced by electrical currents, in our view is justified because we
MI Johnson, PhD, is Principal Lecturer in Human Physiology, School of Health Sciences, Faculty of Health and Environment, Leeds Metropolitan
University, Calverly St, Leeds LS1 3HE, United Kingdom ([email protected]). Address all correspondence to Dr Johnson.
G Tabasam, PhD, is Lecturer in Human Physiology, School of Health Sciences, Faculty of Health and Environment, Leeds Metropolitan University.
Both authors provided concept/research design, writing, data analysis, institutional liaisons, clerical support, and consultation (including review
of manuscript before submission). Dr Tabasam provided data collection and subjects. Dr Johnson provided project management, fund
procurement, and facilities/equipment.
Ethical approval for this experiment was obtained from Leeds Metropolitan University.
This work was funded by National Health Service Executive PhD studentship grant no. RAC733.
Preliminary findings of this work were presented at the International Association of Pain Ninth World Congress; Vienna, Austria; August 22–27,
1999.
This article was submitted April 5, 2002, and was accepted October 24, 2002 .
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whom pain can be induced in the laboratory to monitorinterventions and side effects.34 Studies on subjects usingcold-induced pain in our laboratory showed that IFCdelivered at a strong but comfortable level elevated painthreshold when compared with sham or “mock” electro-therapy where no electrical current was delivered.35,36
However, there were no differences in the analgesic
effects of IFC and TENS, suggesting that the output characteristics of the devices did not influence themagnitude of analgesic effects.35,36 These findings raisequestions about the continued use of both IFC andTENS for relief of pain.
We believe it is important to replicate these findingsusing a different pain model because the analgesicresponse to TENS has been shown to be dependent onthe sensory modality used to induce pain experimental-ly.37 Experimentally induced ischemic pain using thesubmaximal-effort tourniquet test (SETT) has been usedfor the assessment of analgesic efficacy of drugs38–44 andelectrotherapy.37,45–48 Blood flow is arrested in the armby a tourniquet, and the subject exercises the hand by isometric or isotonic contraction. The resulting deepaching pain closely simulates the sensation of pain dueto some pathologies.49–52 Pain with this technique isbelieved to be caused by the accumulation of algesicmetabolites (pain-producing chemicals such as potas-sium, histamine, acetylcholine, bradykinin, serotonin,and adenosine) resulting from occlusion of blood vesselsbelow the inflated cuff and from the mechanical pres-sure of the cuff, which, theoretically, directly activatesmechano-sensitive nociceptors.53 This physiological
mechanism differs from that of cold-induced pain wheredirect activation of high-threshold thermo-sensitive noci-ceptors produces the pain. The aim of our single-blindsham-controlled study was to compare the analgesiceffects of IFC and TENS on experimentally inducedischemic pain using the SETT. The change in subjects’ratings of pain during intervention from the pretreat-ment baseline will be used as a measure of response.Effects associated with the delivery of electrical currents will be isolated by comparing the pain measured for theactive treatment (TENS and IFC) groups and the shamelectrotherapy group. Effects of the electrical currents
generated by the devices will be determined by compar-ing TENS and IFC pain ratings.
Methods
SubjectsThe subjects were 30 university student volunteers (18male, 12 female) without known pathology that couldcause pain who were recruited via notice board adver-tisements. Their mean age was 33.5 years (SD9.9,range21–54). All potential subjects who expressedinterest in participating in the study were briefed on the
experimental procedure (both verbally and in writtenform) and were screened for contraindications to theexperimental procedure or electrotherapy. These con-traindications included any illness or pathology such asperipheral vascular abnormalities, hypertension andhypotension, peripheral neuropathies, recent trauma,and menstruation problems.54,55 Subjects who were tak-
ing any medication or who were likely to take any medication during the period of study were excluded.
Staff or students at the university who had not previously used a TENS-like device and had not reported having apainful medical condition within the previous 2 weeks were included in the study. Subjects who had previously heard of the use of TENS devices in health care and forpain relief were allowed to participate in the study provided that they did not express definite beliefs about how TENS worked or whether different types of TENShad different treatment effects. This was ascertainedthrough a dialogue between the investigator (GT) andthe subjects prompted by a series of standard questions.The investigator also checked each subject ’s nondomi-nant arm for signs of previous trauma and recordedblood pressure from the nondominant arm (because theeffectiveness of TENS and IFC is dependent on normally functioning nerves in the skin) using a sphygmomanom-eter. Outcome measurements were recorded from thenondominant arm so that subjects could use the domi-nant arm when completing visual analog scales (VASs). All subjects who expressed an interest in the study met the criteria and subsequently agreed to participate.Subjects were required to sign a consent form and were
reminded that they had the right to withdraw from theexperiment at any time.
Procedure Each subject attended our research laboratory on 2separate occasions with a 24- to 48-hour interval betweenthe 2 visits. The first visit was used to record pretreat-ment data, and the second visit was used to record datafrom 1 of 3 treatments: (1) IFC, (2) TENS, or (3) shamelectrotherapy. During each visit, ischemic pain wasinduced over a 12-minute period using the SETT(Fig. 2). The self report of pain intensity was recorded at
1-minute intervals during the ischemic pain test using a VAS where 0 cm represented “no pain” and 10 cmrepresented “ worst pain imaginable.”34,35
A posttest short-form McGill Pain Questionnaire (MPQ) was completed by all subjects, because it has been shownto provide sensitive measurements of change in painbrought about by TENS.56 At the end of the ischemicpain test, subjects ranked 15 MPQ descriptors accordingto intensity (ie, 0“none,” 1“mild,” 2“moderate,” or3“severe”). Pain scores were derived for sensory com-ponents, affective components, Pain Rating Index (PRI),
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and Pain Intensity Index (PPI) using the sum of theintensity rank values of the words chosen. The change inMPQ scores during treatment was calculated by subtract-ing scores for visit 2 (during treatment) from the scores
for visit 1 (pretreatment) and used as the outcomemeasure for the intervention.
Ischemic Pain Test During the SETT, a sphygmomanometer cuff is usually applied above the subject ’s elbow and inflated to 200mm Hg. During pilot studies in our laboratory, we foundthat most subjects experienced widespread paresthesia within the arm rather than pain. Thus, we modified theSETT by applying the sphygmomanometer cuff to theforearm 5 cm below the elbow crease, because thisplacement of the sphygmomanometer cuff produced a
dull aching pain that was localized to the area of the cuff in all subjects (Fig. 3).
Before the start of the experiment, maximal grip force was determined using a dynamometer (Martin Vigorim-eter*) fitted with a medium bulb. Seventy-five percent of maximal grip force was calculated and identified on thedynamometer scale. Ischemic pain was induced in thefollowing manner. Subjects raised their nondominant arm vertically above their head for 1 minute to desan-
guinate the limb. The sphygmomanometer cuff (15 cmin length) was then inflated to above 200 mm Hg at arate of 40 mm Hg per second. Full cuff inflation wastaken as time 0, and subjects rated the intensity of the
pain in their raised arm using the VAS. The forearm wasthen returned to rest in the horizontal position on apolystyrene box that was designed to support the fore-arm and hand without applying pressure on the sphyg-momanometer cuff. This was done in an effort to ensurethat there was an even distribution of pressure through-out the cuff. Subjects then performed 20 hand-grippingexercises at 75% of their maximal grip force for a periodof 1 minute (squeeze for 2 seconds and rest for 2seconds). Pain intensity was recorded on completion of these exercises and at 1-minute intervals for the remain-der of the experiment. The cuff was deflated over a
period of 2 minutes to allow the limb to resanguinate,and the final pain intensity rating was taken 1 minuteafter cuff deflation. No signs of any trauma wereobserved in the arms of any subjects following theischemic pain test.
Treatment GroupsOn the second visit to the laboratory, subjects wererandomly allocated to one of 3 treatment groups:(1) IFC, (2) TENS, or (3) sham electrotherapy. Allsubjects received 22 minutes of uninterrupted treat-ment, and a single-blind experimental approach was
* Nomeq, Worcestershire, United Kingdom.
Figure 2.Experimental procedure. The subjects raise their arm above their head for 1 minute, and the first pain intensity rating (VAS 1) is taken. Thesphygmomanometer cuff is inflated over a period of 20 seconds, and the second pain intensity rating (VAS 2) is taken. The subjects lower their armto the horizontal position and perform 20 handgrip exercises over a 1-minute period, after which the third pain intensity rating (VAS 3) is taken. Thearm remains rested in the horizontal position, and pain intensity ratings are taken at 1-minute intervals (VAS 4–9). The cuff is then deflated over a2-minute period after the pain intensity rating at 7 minutes (VAS 9) has been taken. VASvisual analog scale.
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used whereby the subjects were not aware of whichtreatment they were being given. Four self-adhesiveelectrodes (each electrode4.5 cm2) were applied to allsubjects before the start of the experiment, and treat-ment was switched on 10 minutes 40 seconds before the
arm was raised above the head (Fig. 2). Electrode sites were chosen to target afferents emerging from theischemic area. We were concerned that afferents underthe cuff might be unable to fire due to pressure blockfrom the cuff. However, all subjects in the IFC and TENSgroups reported that they experienced a strong but comfortable electrical paresthesia, suggesting to us that afferents remained active. Electrodes were attached toan EMS model 70 interferential therapy machine,†
which could deliver either IFC or TENS.
IFC. Electrodes were applied in a quadripolar mannerto the anterior and posterior aspects of the subjects’forearm so that electrical currents would intersect at themidpoint of the cuff. The distal electrode for channel A was attached to the anterior surface of the forearm 5 cm
proximal to the first wrist crease. The distal electrode forchannel B was attached to the posterior surface of theforearm directly beneath the distal electrode for channel A. Proximal electrodes were applied directly above thecuff. Subjects in the IFC group were told that in order toproduce an effect, the intensity of the stimulator must bemaintained at a “strong but comfortable level” at alltimes. Initially, when the IFC device was switched on forthe first time, the “strong but comfortable level” wasobtained by increasing current amplitude so that thesubjects reported either that the currents were uncom-fortable or that motor threshold had been reached
† Electro Medical Supplies, Greenwich, United Kingdom.
Figure 3.The experimental setup. An oscilloscope displayed the electrical output for both active treatment groups and the sham electrotherapy group. Theoutput from the interferential current device was gated enroute to the subjects using the electronic circuit shown so that subjects in the shamelectrotherapy group did not receive any current.
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(determined by the experimenter observing visible mus-cle contractions). Current amplitude was then reduceduntil the subjects reported that they experienced acomfortable level of stimulation with no visible musclecontractions. The subjects were then informed that thesensation produced by the IFC device may fade away during the ischemic pain test and that they should adjust
current amplitude to try to maintain a strong but com-fortable sensation without concurrent muscle contrac-tion. Mean current amplitude for the IFC grouprecorded as the maximum amplitude reached at any time during the test was 19.2 mA (SD10.2, range4.0–29.0). The IFC was an amplitude-modulated frequency of 100 Hz generated by 4-kHz sinusoidal waves. Thesettings we used, in our view, are commonly used by therapists and were used in our previous studies oncold-induced pain.35,36
TENS. Transcutaneous electrical nerve stimulation isusually applied using a single-channel device via 2 elec-trodes. The TENS in our study was delivered via 4electrodes using a dual-channel device in order tostandardize the amount of current administered by the 2modalities. Electrodes were applied to the anterior andposterior aspects of the subjects’ forearm in an identicalmanner to that for IFC. To minimize interference of currents from the 2 channels, both distal electrodes wereattached to channel A of the TENS device and bothproximal electrodes were attached to channel B. Sub- jects were told that the intensity of the stimulator must be maintained at a “strong but comfortable level” at alltimes. The “strong but comfortable level” was obtained
using the same procedure as that described for IFC.Mean current amplitude for the TENS group recordedas the maximum amplitude reached at any time duringthe test was 11.3 mA (SD2.7, range8.0–17.0). Sub- jects were told that the sensation produced by thecurrent might fade away and that they should adjust thestimulator to maintain a strong but comfortable sensa-tion. The electrical characteristics of TENS were set todeliver 200-microsecond biphasic pulsed currents at apulse frequency of 100 pps and a “continuous” pulsepattern. These settings were chosen because we believedthat they were similar to those used for IFC and that they
were consistent with those used in our previous studieson cold-induced pain.35,36
Sham electrotherapy. Subjects in the sham electro-therapy group received no current output from the IFCdevice or the TENS device (TENS, IFC, and shamelectrotherapy were all delivered using the same electro-therapy machine). This was achieved using a circuit that prevented currents from reaching subjects in the shamelectrotherapy group but that allowed currents to reachsubjects in the active IFC group without altering theelectrical characteristics (Fig. 3). The output from the
IFC device was displayed on a cathode ray oscilloscopeduring the treatment cycles for both the active treatment groups and the sham electrotherapy group to give theimpression to subjects that electrical currents were beingdelivered to the electrodes. Subjects in the sham elec-trotherapy group also were told that “the electrothera-peutic device may have effects at subthreshold levels,
which you may not be able to feel” and “this means that you may or may not feel a slight tingling sensationbeneath the electrodes.” Previous workers57–59 havefound that this technique can reduce sham electro-analgesia. No subjects questioned this procedure, andtheir responses to a posttest question revealed that allsubjects in the sham electrotherapy group believed that they were receiving currents.
Data AnalysisData were analyzed by calculating the change in painintensity rating and MPQ scores during the intervention when compared with the pretreatment measurements.Pretreatment VAS recordings for pain intensity rating were subtracted from the corresponding recordingsobtained during treatment for each subject and dis-played as the mean change in pain intensity rating foreach treatment group. Because the aim of this experi-ment was to compare the effects of interventions onpain, data points taken during cuff inflation and handgrip exercises (VAS units 1–3) and cuff deflation (VASunits 10 –12) when pain was either absent in the pretreat-ment readings or fluctuating greatly were not used in theanalyses (Figs. 2 and 4). The absence of pain in thepretreatment VAS scores would prevent the detection of
pain reduction, and subjects would find estimating painintensity difficult during marked fluctuations, as experi-enced when the cuff was being inflated and deflated. Wedefined a meaningful analgesic effect as a reduction of 1 VAS unit or more for the active treatment groups whencompared with the sham electrotherapy group. Treat-ment effects were determined by a 2-way repeated-measures analysis of variance (ANOVA) on the changein pain intensity during treatment for VAS units 4through 9. The change in MPQ scores were calculated by subtracting the pretreatment measurement from themeasurement obtained during treatment for each sub-
ject and displayed as the mean change in MPQ for eachtreatment group. A 1-way ANOVA on the change inMPQ scores was used to determine effects among thetreatment groups.
Results
Pain Intensity The pain intensity ratings are summarized in Table 1.Pretreatment pain intensity ratings were similar to thosepreviously reported by other groups using the sametechnique to induce pain.45,47 The repeated-measures
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ANOVA on the pretreatment data for the entire VASdata set (ie, VAS units 1–12) indicated there was noeffect of treatment group or group time interaction.These findings suggest to us that subjects in different treatment groups were matched in pretreatment VASscores. There was an effect of time (P .01), which weattributed to the onset of pain that occurs during cuff inflation and hand grip exercises (VAS units 1–3) and tothe decrease in pain that occurs upon cuff deflation(VAS units 10 –12) (Tab. 1).
The repeated-measures ANOVA on the change in painintensity during treatment for VAS units 4 through 9there was no effect of time or group time interaction(Tab. 2). Effects for treatment groups failed to reachstatistical significance. Unpaired t tests on the averagechange in pain intensity during cuff inflation were usedto isolate potential effects among the 3 treatment groups(Fig. 5). The unpaired t tests revealed that IFC reducedpain intensity when compared with the sham treatment
(P .05). The apparent reduction in pain intensity dur-ing TENS (Figs. 4 and 5) did not reach statisticalsignificance when compared with the sham treatment (P .06). There were no changes in pain intensity between IFC and TENS.
MPQ ScoresMcGill Pain Questionnaire sensory, affective, PRI, andPPI scores were calculated for pretreatment data anddata obtained during treatment. One-way analysis of thepretreatment data showed that there were no differencesamong the groups for any of these measures. Thechange in each of the MPQ scores during treatment wasused as the outcome measure and was calculated foreach individual by subtracting the pretreatment valuesfrom the corresponding values obtained during treat-ment (Fig. 6). There were no differences among thegroups for any MPQ scores (1-way ANOVA). However,scores for affect suggested that there might have beendifferences between active treatment groups and the
Figure 4.Mean (SD) (n10 per group) change in pain intensity rating during the intervention when compared with the pretreatment baseline value. Unitsare centimeters on a 0 –10 visual analog scale, where 0“no pain” and 10“worst pain imaginable.” Negative values represent a reduction in painintensity during treatment.
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P a i n I n t e n s i t y R a t i n g f o r T r a n s c u t a n e o u s E l e c t r i c a l N e r v e S t i m u l a t i o n ( T E N S ) , I n t e r f e r e n t i a l C u r r e n t s ( I F C ) , a n d S h a m
E l e c t r o t h e r a p y D u r i n g t h e I s c h e m i c P a i n T e s t a
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D e f l a t i n g
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C u f f
D e f l a t e d
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V A S 1
0 m i n
V A S 2
1 m i n
V A S 3
2 m i n
V A S 4
3 m i n
V A S 5
4 m i n
V A S 6
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V A S 7
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V A S 8
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V A S 1 0
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P r e t r e a t m e n t s e s s i o n
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1 . 2 –
9 . 4
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1 . 1 –
9 . 7
1 . 2 –
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1 . 3 –
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2 . 7
4 . 5 –
2 . 5
3 . 5 –
1 . 8
3 . 3 –
1 . 3
4 . 6 –
0 . 9
4 . 7 –
1 . 5
5 . 6 –
1 . 2
6 . 1 –
1 . 0
8 . 9 –
2 . 7
1 . 2 –
2 . 5
S h a m
e l e c t r o t h e r a p y
X
0 . 3
0 . 6
0 . 0
0 . 1
0 . 1
0 . 0
0 . 1
0 . 0
0 . 1
0 . 0
0 . 7
0 . 6
S D
1 . 1
1 . 1
0 . 9
0 . 9
1 . 2
1 . 1
1 . 6
1 . 3
1 . 1
0 . 7
1 . 3
1 . 3
R a n g e
0 . 9 –
3 . 2
0 . 9 –
3 . 3
1 . 4 –
1 . 5
1 . 9 –
1 . 3
2 . 0 –
2 . 1
1 . 6 –
1 . 7
2 . 6 –
1 . 8
1 . 9 –
1 . 7
2 . 0 –
1 . 5
1 . 4 –
0 . 9
0 . 4 –
3 . 9
0 . 5 –
4 . 1
a
P a i n i n t e n s i t y r a t i n g s w e r e s c o r e d o n a 0 -
t o
1 0 - c m
v i s u a l a n a l o g s c a l e ( V A S )
, w h e r e 0 “ n o p a i n ”
a n d 1 0 “ w o r s t p a i n i m a g i n a b l e
. ”
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sham electrotherapy group. The 1-way ANOVA was usedto reveal differences across all 3 treatment groups. Weset levels of significance at .05. However, we wanted toreveal potential differences among groups (ie, TENS versus sham electrotherapy, IFC versus sham electro-therapy, TENS versus IFC). When the probability valuefrom the 1-way ANOVA for the MPQ scores (and fromthe 2-way ANOVA for VAS scores) fell between 0.1 and.05, we decided to explore the relationship among
groups further. Post hoc analysis revealed a reduction inthe score for affect during intervention for the IFCgroup when compared with the sham electrotherapy group (P .03, unpaired t test). However, there were nodifferences in the change in scores for affect duringintervention between the TENS and sham electrother-apy groups or between the IFC and TENS groups.
DiscussionPhysical therapists need information about the absoluteand relative effects of TENS-like devices. In our single-blind, sham-controlled investigation into the analgesic
effects of IFC and TENS in pain-free volunteers who hadischemic pain induced, we found that IFC reduced theintensity of experimentally induced ischemic pain whencompared with sham electrotherapy. However, the anal-gesic effects produced by IFC were similar in magnitudeto those observed for TENS. The IFC, but not TENS,produced a reduction in the affective components of pain when compared with sham electrotherapy.
Our findings for TENS are similar to the results of previous studies by other workers using comparablemethods.37,46,47,60 Transcutaneous electrical nerve stimu-lation at non-noxious intensities has been found toreduce ischemic pain to a greater extent that shamTENS in otherwise pain-free subjects using SETT.37
Roche et al46 reported that TENS produced a greaterresponse to induced ischemic pain in otherwise pain-free volunteers when compared with no stimulation andthat the effect was dependent on the time course of thepain and the intensity and time duration of TENS.High-intensity continuous TENS increased endurance of pain, whereas low-intensity trains of stimulation raisedpain thresholds but did not increase endurance. Greaterreductions in pain intensity have been found for TENS when compared with sham TENS on experimentally
induced ischemic pain under double-blind, sham-controlled conditions in 32 otherwise pain-free volun-teers,47 although those researchers were unable to rep-licate their findings in a subsequent study using similarmethods.45 In addition, researchers60 have reported that TENS did not influence the duration of ischemia toler-ated or the intensity of pain when delivered proximal to
the tourniquet.
One reason for the conflicting results may be that TENSeffects depend on the sensory modality used for toinduce pain experimentally.37 We have repeatedly dem-onstrated in otherwise pain-free volunteers that TENSelevates cold-induced pain threshold when compared with sham TENS.36,58,61,62 In these studies, TENS wasadministered in a conventional manner by deliveringcurrents at a strong but comfortable intensity within orimmediately proximal to the site of pain. Trancutaneouselectrical nerve stimulation has also been shown toproduce analgesic effects in otherwise pain-free subjects when pain was induced thermally,63–65 althoughresearchers using other experimental pain models havefound conflicting results. Some researchers66 havereported that TENS increases the mechanical painthreshold in otherwise pain-free subjects, whereas otherresearchers37 have reported that TENS has no effect onmechanical pain threshold in otherwise pain-free sub- jects. Reports that TENS reduces delayed-onset musclesoreness (DOMS)67,68 or electrically induced pain69,70
are countered by reports that it does not.71,72 There arereports that TENS does not alter pain associated withRIII nociceptive reflexes in otherwise pain-free sub-
jects.73,74 Inconsistencies in findings may be due to variations in TENS application procedures, inadequatedoses of TENS, and outcome measurements taken at inappropriate times.75 Our findings add to the conflict-ing nature of existing evidence because the apparent reduction in experimentally induced pain by TENS didnot reach statistical significance (P .06) when levels were set at .05.
Experimental work on the analgesic effects of IFC issparse. We have previously reported that IFC delivered at a “strong but comfortable” level produced a greater
reduction in pain intensity ratings for experimentally induced ischemic pain than sham electrotherapy and notreatment control in volunteers who were pain-free.76
We have reported that IFC elevates pain threshold whencompared with no treatment and with sham electro-therapy using cold-induced pain in otherwise pain-freesubjects.36,77 However, the analgesic effects of IFC onpain induced experimentally under placebo-controlledconditions is yet to be confirmed by other researchers.
Proving that technique-based interventions such asTENS and IFC produce effects that are greater than
Table 2.Two-Way Repeated-Measures Analysis of Variance on the Change inPain Intensity Rating During the Intervention When Compared Withthe Pretreatment Value for Visual Analog Scale Readings 4 –9
those produced by placebo, in our view, is difficult.There is disagreement on what constitutes a TENSplacebo, due in part to difficulties in defining the activeelement of the technique. Because some authors57,78
believe that electrical currents are the critical variable of all electrotherapeutic devices, they have used devicesthat deliver no current (ie, sham electrotherapy) asplacebo controls because they enable researchers toisolate effects associated with the electrical currentsthemselves. In our study, sham electrotherapy was
achieved using an electronic circuit to gate the output of the stimulator so that no current was delivered to thesubjects. This ensured that there were no differences inthe appearance of the stimulator to subjects in different treatment groups. We also used the verbal suggestionthat “IFC may have effects at subthreshold levels, which you may not be able to feel” and a waveform displayedon a cathode ray oscilloscope. Subjects were instructedto alter the intensity of the currents using a dial on thestimulator in order to “prevent the body from adaptingto the currents,” and this was accompanied by changes inthe size of the electrical wave on the cathode ray
oscilloscope. No subjects questioned the lack of sensa-tion from the stimulating device.
Despite confidence in the authenticity of our shamintervention, this type of control does not establish thenature of the effects. Thus, we cannot discount thepossibility that treatment effects were produced by dis-traction associated with sensations generated by theelectrical currents. Researchers63 have attempted toaccount for nonspecific distraction effects produced by
TENS currents by monitoring the effect of TENS on visual stimuli. In order to isolate the effects of electricalcurrents on specific physiological processes such assegmental inhibition of antinociceptive transmission, which could be considered the critical element of TENSfrom a physiological perspective, researchers wouldneed to compare the effects of currents delivered at segmental and remote body sites.64 This was beyond thescope of our study.
Despite our confidence in sham electrotherapy, thereare still problems in achieving and maintaining blinding
Figure 5.Mean (SD) (n10 per group) change in pain intensity rating averaged across all cycles when the cuff was fully inflated (eg, 2 min–7 min, visualanalog scale [VAS] readings 4 –9). Units are centimeters on a 0 –10 VAS, where 0“no pain” and 10“worst pain imaginable.” Note: positivevalues represent a reduction in pain intensity.
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in studies of technique-based interventions.79,80 Treat-ment effects due to the use of placebos may be up to17%.81 Double blinding is considered the “gold stan-dard” in clinical trials for isolating this effect. Reports onTENS that claim to have achieved double blinding rarely provide details on how blinding was maintained ormonitored throughout the trial.47,82–85 In drug trials, theinvestigator can administer the treatment and recordoutcome measurements while remaining blinded. Intechnique-based interventions, such as many of theinterventions used in physical therapy, including TENSand IFC, this is not necessarily possible because theinvestigator (or therapist) needs to be aware of thetreatment in order to administer treatment appropri-ately. Investigators (or therapists) who administer treat-ments are likely to have prior knowledge and expecta-tions about treatment outcome, and this may influencethe way in which treatment is given and thus bias theoutcome.
In studies of technique-based interventions, we believe what we consider a triple-blind method should be the“gold-standard.” Subject membership in a treatment group is concealed from the subject, the investigatorrecording outcomes, and the investigator (or therapist)administering the treatment. Blinding the investigator(or therapist) administering the treatment is problem-atic, if not impossible. One approach could be to trainan investigator who was naive to the therapeutic strategy and outcome to administer treatment using a standardprotocol. We used a single-blind experimental approachin our study because of the lack of additional investiga-tors. We attempted to reduce bias associated with theexperimenter’s expectation of treatment outcome by using standardized cue cards. In summary, our findingssuggest that electrical currents produced changes inpain intensity, but it was not possible to determine whether the effects were due to distraction or to asegmental inhibition of nociceptive input.
Figure 6.Mean (SD) (n10 per group) change in McGill Pain Questionnaire (MPQ) scores during the treatment intervention when compared with thepretreatment value for sensory and affective dimensions and for Pain Rating Index (PRI) and Present Pain Intensity (PPI). Probability values represent1-way analysis of variance across groups.
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With a variety of electroanalgesic devices available, webelieve it is important for the therapist to know whetherone electroanalgesic device can be used to deliver anintervention that is more effective than another. Thecomparison between TENS and IFC could provide someevidence of the treatment effects of each modality. By standardizing current intensity across subjects using the
report of a strong but comfortable intensity, we contendthat we were able to discount putative effects associated with differences in the subjects’ perceptions of thestrength of stimulation. The finding that there were nodifferences in pain relief between TENS and IFC sug-gests that the different output characteristics had noeffect on the magnitude of pain relief. This finding isconsistent with our previous work.36 We reported that there were no differences in the magnitude of theincrease in pain threshold or ratings between IFC andTENS on cold-induced pain.36 Another group74 alsoreported no differences in the effects of TENS or IFC onthe rating of pain associated with RIII nociceptivereflexes. However, their findings differ from oursbecause they did not find TENS and IFC effects whencompared with sham electrotherapy, although they didnot record outcome measurements during stimulation.
Because TENS effects are believed to be maximal whilethe stimulator is switched on and are short-lived whenthe device is switched off, it is possible that treatment effects were missed.36,58,62,86 Work in our laboratory suggests that IFC also has short post-stimulation effects when delivered at non-noxious intensities.35,36 Most ther-apists, we believe, deliver IFC at non-noxious levels when
managing people with painful conditions.18 Interferen-tial current machines are relatively expensive andrequire an electrical supply other than batteries, sotreatment usually takes place in a clinic under therapist supervision. Treatment sessions generally last no morethan 30 minutes, and patients are often required toattend the clinic for a course of treatments. If theanalgesic effects of IFC are no different than those of TENS, then the practice of short-duration treatment sessions may be of little value. Most TENS machines areportable, and patients can self-administer treatment throughout the day. Thus, the use of TENS may be a
more appropriate treatment strategy to control an ongo-ing pain problem.
The continued use of both IFC and TENS is justified by some therapists who claim that the mechanism of actionand analgesic profile of TENS and IFC differ. They lackdata, however, to support this and related assumptions(eg, whether TENS or IFC is effective). It is believed that IFC excites deep tissue and TENS excites superficialtissue,19–21 although this remains to proven experimen-tally. To our knowledge, there is no experimental evi-dence available to determine whether TENS and IFC
stimulate fiber populations at different depths, resultingin different analgesic profiles. The IFC modulationpatterns described in textbooks are unlikely to be faith-fully reproduced in biological tissue. Measurements of voltage patterns of IFC within biological tissue (pork)and an isotropic medium (water) have shown that modulation patterns produced in biological tissue are
complex and unpredictable.87,88
Measurements of sen-sory, motor, and pain thresholds to IFC under single-blind conditions have shown no differences in thepresence and absence (eg, pure 4-kHz currents) of amplitude-modulated waves, suggesting that pure 4-kHz waves are the main variable in stimulation.89 The only suggestion that there may have been may be differencesin the analgesic profiles in our study were found inchanges in affective scores of the MPQ following treat-ment. Interferential currents but not TENS reducedaffective components of the pain experience. We foundno differences in any MPQ scores between TENS andsham electrotherapy or between IFC and TENS. Otherauthors47 using similar methods also have reported alack of difference in MPQ scores between TENS andsham electrotherapy. Further work in this area is neededto confirm the possibility that reductions in effect con-tribute to pain relief obtained with IFC.
Laboratory studies are often viewed with suspicion by clinical investigators. However, we argue that laboratory studies serve as an essential precursor to clinical trials,providing data from which to determine dose relation-ships and treatment regimens.34,38–44 Because laboratory studies can be conducted in an environment in which
variables can be controlled and modified in a systematicmanner, they overcome many of the logistical problemsassociated with clinical trials. These problems includestaff and patient recruitment, nonadherence and with-drawal, ethical considerations associated with placebointervention, and constraints of time and cost of execut-ing a clinical trial. Models of experimentally inducedpain enable investigators to quantify the duration andintensity of the noxious stimulus, which is difficult tocontrol in clinical settings due to larger fluctuations inthe intensity and quantity of pain across time. In ourstudy, the deep aching pain associated with SETT
remained stable in its intensity during pretreatment recordings once the cuff had been fully inflated, and thisenabled measurement of effects on pain sensations that were similar among subjects and repeatable over time.
There are clear differences between experimentally induced pain and clinical pain. Experimentally inducedpain produces minimal tissue damage and can be termi-nated at any point during the test. Consequently, it is lesslikely to be influenced by affective and cognitive ele-ments that may contribute to the overall report of painin patient populations. Experimentally inducing pain
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also has been criticized because it elicits only one type of pain sensation, whereas a patient ’s pain often is morecomplex. Some models of experimentally induced painalso produce painful sensations that are not normally experienced by patients, such as electrically inducedpain. We chose the ischemic model of experimentally induced pain because it produces a deep aching pain
sensation that has similar qualities to those found inclinical conditions. In addition, SETT has similarities toischemia of soft tissue leading to pain, including that experienced by people with angina. Transcutaneouselectrical nerve stimulation and TENS-like devices suchas IFC have been used in the symptomatic management of ischemic pain.19–21,27 Despite our argument about theimportance of laboratory-based research, we note that only clinical trials can document an intervention’seffectiveness.
ConclusionInterferential currents reduced the intensity of experi-mentally induced ischemic pain, although there were nodifferences in the magnitude of response between TENSand IFC. Comparisons of effects between treatments canprovide information about relative effectiveness and caninform decisions about treatment selection. The find-ings of our study, if they can be replicated in a clinicaltrial, suggest that IFC is at least as effective as TENS whendelivered to produce a strong but comfortable electricalparesthesia within the site of pain, as is most likely usedin clinical practice. However, the lack of difference inthe analgesic effects of TENS and IFC bring into ques-tion the continued use of both modalities when admin-
istered in this way. The small amount of experimentalevidence that has compared IFC and TENS suggests that it may be more cost-effective to use TENS rather thanIFC when therapy is administered at a strong but com-fortable level for the symptomatic relief of pain. As it isthe output characteristics of electrotherapeutic devicessuch as TENS and IFC that gives them their identity,and ultimately their place in the commercial market,it is crucial that more well-designed clinical andexperimental studies be performed to assess theirrelative usefulness.
References1 Reeve J, Menon D, Corabian P. Transcutaneous electrical nervestimulation (TENS): a technology assessment. Int J Technol Assess Health
Care. 1996;12:299 –324.
2 Fishbain DA, Chabal C, Abbott A, et al. Transcutaneous electricalnerve stimulation (TENS) treatment outcome in long-term users. Clin
J Pain. 1996;12:201–214.
3 Chabal C, Fishbain DA, Weaver M, Heine LW. Long-term transcuta-neous electrical nerve stimulation (TENS) use: impact on medicationutilization and physical therapy costs. Clin J Pain. 1998;14:66 –73.
4 Johnson MI, Ashton CH, Thompson JW. Long term use of transcu-taneous electrical nerve stimulation at Newcastle Pain Relief Clinic.
J Royal Soc Med. 1992;85:267–268.
5 Johnson MI. Transcutaneous electrical nerve stimulation (TENS) inthe management of labour pain: the experience of over ten thousand women. Br J Midwifery. 1997;5:400 – 405.
6 Carroll D, Tramer M, McQuay H, et al. Randomization is important in studies with pain outcomes: systematic review of transcutaneouselectrical nerve stimulation in acute postoperative pain. Br J Anaesth.
1996;77:798– 803.
7 Carroll D, Tramer M, McQuay H, et al. Transcutaneous electrical
nerve stimulation in labour pain: a systematic review. Br J Obstet Gynaecol. 1997;104:169 –175.
8 Carroll D, Moore A, Tramer M, McQuay H. Transcutaneous electri-cal nerve stimulation does not relieve in labour pain: updated system-atic review. Contemp Rev Obstet Gynecol. September 1997:195–205.
9 McQuay H, Moore A. TENS in chronic pain. In: McQuay H, Moore A, eds. An Evidence-Based Resource for Pain Relief . Oxford, UnitedKingdom: Oxford University Press; 1998:207–211.
10 Gadsby JG, Flowerdew MW. Transcutaneous electrical nerve stimu-lation and acupuncture-like transcutaneous electrical nerve stimula-tion for chronic low back pain. Cochrane Database System Reviews.
2000:CD000210.
11 Bjordal J, Greve G. What may alter the conclusions of systematicreviews? Physical Therapy Review. 1998;3:121–132.
12 Johnson MI. The clinical effectiveness of TENS in pain manage-ment. Critical Reviews in Physical Therapy Rehabilitation. 2000;12:131–149.
13 Johnson MI. Does TENS work? Clin Effect Nurs. 1998;2:111–121.
14 Pope GD, Mockett SP, Wright JP. A survey of electrotherapeuticmodalities: ownership and use in the NHS in England. Physiotherapy.
1995;81:82–91.
15 Robertson VJ, Spurritt D. Electrophysical agents: implications of their availability and use in undergraduate clinical placements. Physio-
therapy. 1998;84:335–344.
16 Foster NE, Thompson KA, Baxter GD, Allen JM. Management of nonspecific low back pain by physiotherapists in Britain and Ireland: a
descriptive questionnaire of current clinical practice. Spine. 1999;24:1332–1342.
17 Mantle J, Versi E. Physiotherapy for stress urinary incontinence: anational survey. BMJ. 1991;302:753–755.
18 Johnson MI, Tabasam G. A questionnaire survey on the clinical useof interferential currents (IFC) by physiotherapists. In: The Pain Society
of Great Britain Annual Conference Abstracts . Leicester, United Kingdom:Pain Society of Great Britain; 1998.
19 DeDomenico G. New Dimensions in Interferential Therapy: A Theoretical
and Clinical Guide . Linfield: Reid Medical Books; 1987.
20 Nikolova L. Treatment With Interferential Current . Edinburgh, Scot-land: Churchill Livingstone; 1987.
21 Savage B. Interferential Therapy . London, United Kingdom: WolfePublishing Ltd; 1992.
22 Martin D. Interferential for pain control. In: Kitchen S, Bazin S, eds.Clayton’s Electrotherapy 10E . 10th ed. London, United Kingdom: WBSaunders Co Ltd; 1994:306 –315.
23 Johnson MI. The mystique of interferential currents. Physiotherapy.
1999;85:294–297.
24 Low J, Reed A, eds. Electrotherapy Explained: Principles and Practice .2nd ed. Oxford, United Kingdom: Butterworth-Heinemann Ltd; 1994.
25 Sjolund B, Eriksson M, Loeser J. Transcutaneous and implantedelectric stimulation of peripheral nerves. In: Bonica J, ed. The Manage-
ment of Pain . Vol 2. Philadelphia: Lea & Febiger; 1990:l852–1861.
Physical Therapy . Volume 83 . Number 3 . March 2003 Johnson and Tabasam . 221
by guest on April 23, 2014http://ptjournal.apta.org/ Downloaded from
30 Garrison DW, Foreman RD. Effects of transcutaneous electricalnerve stimulation (TENS) on spontaneous and noxiously evokeddorsal horn cell activity in cats with transected spinal cords. Neurosci
Lett. 1996;216:125–128.
31 Johnson MI, Ashton CH, Thompson JW. An in-depth study of long-term users of transcutaneous electrical nerve stimulation (TENS):implications for clinical use of TENS. Pain. 1991;44:221–229.
32 Kloth LC. Interference current. In: Nelson RM, Currier DP, eds.Clinical Electrotherapy . 2nd ed. Norwalk, Conn: Appleton and Lange;1991:221–260.
33 Nelson B. Interferential therapy. Australian Journal of Physiotherapy.
1981;27:53–56.
34 Gracely R. Methods of testing pain mechanisms in normal man.In: Wall PD, Melzack R, eds. Textbook of Pain . Edinburgh, Scotland:Churchill Livingstone; 1989:257–268.
35 Tabasam G, Johnson MI. Electrotherapy for pain relief: Does it work? A laboratory based study to examine the analgesic effects of electrotherapy on cold-induced pain in healthy individuals. Clin Effect
Nurs. 1999;3:14 –24.
36 Johnson M,I Tabasam G. A double-blind placebo-controlled inves-tigation into the analgesic effects of interferential currents (IFC) andtranscutaneous electrical nerve stimulation (TENS) on cold inducedpain in healthy subjects. Physiotherapy Theory and Practice. 1999;15:217–233.
37 Woolf CJ. Transcutaneous electrical nerve stimulation and thereaction to experimental pain in human subjects. Pain. 1979;7:115–127.
38 Parry JW. The evaluation of analgesic drugs: the case for experi-mental methods. Anaesthesia. 1979;34:468– 475.
39 Clements JA, Nimmo WS. Pharmacokinetics and analgesic effect of ketamine in man. Br J Anaesth. 1981;53:27–30.
40 Grant IS, Nimmo WS, Clements JA. Pharmacokinetics and analgesiceffects of i.m. and oral ketamine. Br J Anaesth. 1981;53:805– 810.
41 Neal MJ, Murray BR. The analgesic effect of anaesthetic mixtures:
the effect of nitrous oxide with trichlorethylene or halothane onexperimental ischaemic pain. Guys Hospital Reports. 1966;115:19 –26.
42 Sacchetti G, Lampugnani R, Battistini C, Mandelli V. Response of pathological ischaemic muscle pain to analgesics. Br J Clin Pharm.
1980;9:165–169.
43 Rae CP, Mansfield MD, Dryden C, Kinsella J. Analgesic effect of adenosine on ischaemic pain in human volunteers. Br J Anaesth.
1999;82:427– 428.
44 Jonzon B, Sylven C, Kaijser L. Theophylline decreases pain in theischaemic forearm test. Cardiovasc Res. 1989;23:807– 809.
45 Foster N, Baxter F, Walsh D, et al. Manipulation of transcutaneouselectrical nerve stimulation variables has no effect on two models of experimental pain in humans. Clin J Pain. 1996;12:301–310.
46 Roche P, Gijsbers K, Belch J, Forbes C. Modification of inducedischaemic pain by transcutaneous electrical nerve stimulation. Pain.
1984;20:45–52.
47 Walsh DM, Liggett C, Baxter D, Allen JM. A double-blind investiga-tion of the hypoalgesic effects of transcutaneous electrical nerve
stimulation upon experimentally induced ischaemic pain. Pain. 1995;61:39– 45.
48 McDowell BC, Lowe AS, Walsh DM, et al. The lack of hypoalgesicefficacy of H-wave therapy on experimental ischaemic pain. Pain.
1995;61:27–32.
49 Lahuerta Dal Re J, Campbell J, Dewshi F. Ischemic muscular pain,II: its evaluation by the McGill Pain Questionnaire in the repeatedperformance of an experimental test. Revista De Medicina De La
Universidad De Navarra. 1984;28:36 – 40.
50 Elton D, Quarry PR, Burrows GD, Stanley GV. A new test of painreactivity. Percept Mot Skills. 1978;47:125–126.
51 von Graffenried B, Adler R, Abt K, et al. The influence of anxiety and pain sensitivity on experimental pain in man. Pain. 1978;4:253–263.
52 Smith G, Egbert L, Markowitz R, et al. An experimental painmethod sensitive to morphine in man: the submaximal effort tourni-quet technique. J Pharm Exp Ther. 1966;154:234–332.
53 Pertovaara A, Nurmikko T, Pontinen PJ. Two separate componentsof pain produced by the submaximal effort tourniquet test. Pain.
1984;20:53–58.
54 Electrotherapeutic Terminology in Physical Therapy: Report by the Electro-
therapy Standards Committee of the Section on Clinical Electrophysiology of the
American Physical Therapy Association . Alexandria, Va: American PhysicalTherapy Association; 1990.
55 The Chartered Society of Physiotherapy (CSP) Standards for the Use of
Electrophysical Modalities . London, United Kingdom: Chartered Society of Physiotherapy.
56 Melzack R. The short-form McGill Pain Questionnaire. Pain. 1987;30:191–197.
57 Petrie I, Hazelman B. Credibility of placebo transcutaneous electri-cal nerve stimulation and acupuncture. Clin Exp Rheum. 1985;2:285–287.
58 Johnson M, Ashton C, Bousfield D, Thompson J. Analgesic effects of different frequencies of transcutaneous electrical nerve stimulation oncold-induced pain in normal subjects. Pain. 1989;39:231–236.
59 Deyo R, Walsh N, Martin D, et al. A controlled trial of transcutane-ous electrical nerve stimulation (TENS) and exercise for chronic low back pain. N Engl J Med. 1990;322:1627–1634.
60 Rosenblatt R, Hetherington A. Failure of transcutaneous electricalstimulation to alleviate experimental tourniquet pain. Anesth Analg.
1981;60:720–722.
61 Ashton H, Ebenezer I, Golding J, Thompson J. Effects of acupunc-ture and transcutaneous electrical nerve stimulation on cold-inducedpain in normal subjects. J Psychosom Res. 1984;28:301–308.
62 Johnson MI, Ashton CH, Thompson JW. Analgesic effects of acupuncture-like TENS on cold pressor pain in normal subjects. Eur J
Pain. 1992;13:101–108.
63 Marchand S, Bushnell MC, Duncan GH. Modulation of heat painperception by high frequency transcutaneous electrical nerve stimula-tion (TENS). Clin J Pain. 1991;7:122–129.
222 . Johnson and Tabasam Physical Therapy . Volume 83 . Number 3 . March 2003by guest on April 23, 2014http://ptjournal.apta.org/ Downloaded from
64 Eriksson MB, Rosen I, Sjolund B. Thermal sensitivity in healthy subjects is decreased by a central mechanism after TNS. Pain. 1985;22:235–242.
65 Pertovaara A. Experimental pain and transcutaneous electricalnerve stimulation at high frequency. Appl Neurophysiol. 1980;43:290–297.
66 Walsh DM, Lowe AS, McCormack K, et al. Transcutaneous electricalnerve stimulation: effect on peripheral nerve conduction, mechanical
pain threshold, and tactile threshold in humans. Arch Phys Med Rehabil.1998;79:1051–1058.
67 Denegar C, Huff C. High and low frequency TENS in the treatment of induced musculoskeletal pain: a comparison study. Athletic Training.
1988;23:235–237.
68 Denegar C, Perrin D, Rogol A, Rutt R. Influence of transcutaneouselectrical nerve stimulation on pain, range of motion, and serumcortisol concentration in females experiencing delayed onset musclesoreness. J Orthop Sports Phys Ther. 1989;11:100 –103.
69 Oliveri A, Clelland J, Jackson J, Knowles C. Effects of auriculartranscutaneous electrical nerve stimulation on experimental painthreshold. Phys Ther. 1986;66:12–16.
70 Noling L, Clelland J, Jackson J, Knowles C. Effect of transcutaneouselectrical nerve stimulation at auricular points on experimental cuta-neous pain threshold. Phys Ther. 1988;68:328 –332.
71 Craig JA, Cunningham MB, Walsh DM, et al. Lack of effect of transcutaneous electrical nerve stimulation upon experimentally induced delayed onset muscle soreness in humans. Pain. 1996;67:285–289.
72 Johnson M, Hajela V, Ashton C, Thompson J. The effects of auricular transcutaneous electrical nerve stimulation (TENS) onexperimental pain threshold and autonomic function in healthy subjects. Pain. 1991;46:337–342.
73 Walsh DM, Noble G, Baxter GD, Allen JM. Study of the effects of various transcutaneous electrical nerve stimulation (TENS) parametersupon the RIII nociceptive and H-reflexes in humans. Clin Physiol.
2000;20:191–199.
74 Cramp FL, Noble G, Lowe AS, et al. A controlled study on theeffects of transcutaneous electrical nerve stimulation and interferentialtherapy upon the RIII nociceptive and H-reflexes in humans. Arch Phys
Med Rehabil. 2000;81:324 –333.
75 Johnson MI. Comments on: Craig JA, Cunningham MB, Walsh DM,et al. Lack of effect of transcutaneous electrical nerve stimulation uponexperimentally induced delayed onset muscle soreness in humans[Pain. 1996;67:285–289]. Pain. 1997;71:208 –209.
76 Johnson MI, Tabasam G. A single-blind placebo-controlled investi-gation into the analgesic effects of interferential currents (IFC) onexperimentally induced ischaemic pain in healthy subjects. Clin Physiol
Funct Imagery . 2002;22:187–196.
77 Stephenson R, Johnson MI. The analgesic effects of interferentialtherapy on cold-induced pain in healthy subjects: a preliminary report.Physiotherapy Theory and Practice. 1995;11:89 –95.
78 Wood R, Lewith G. The credibility of placebo controls in acupunc-ture studies. Complement Ther Med. 1998;6:79– 82.
79 Thorsteinsson G. Comments on: Deyo R, Walsh N, Schoenfeld L,Ramamurthy S. Can trials of physical treatments be blinded? Theexample of transcutaneous electrical nerve stimulation for chronic
pain [Am J Phys Med Rehabil. 1990;69:6 –10]. Am J Phys Med Rehabil.1990;69:219–220.
80 Deyo R, Walsh N, Schoenfeld L, Ramamurthy S. Can trials of physical treatments be blinded? The example of transcutaneous elec-trical nerve stimulation for chronic pain. Am J Phys Med Rehabil.
1990;69:6–10.
81 Schultz KF, Chalmers I, Hayes RJ, Altman DG. Empirical evidenceof bias: dimensions of methodological quality associated with estimatesof treatment effects in controlled trials. JAMA. 1995;273:408 – 412.
82 Langley GB, Sheppeard H, Johnson M, Wigley RD. The analgesiceffects of transcutaneous electrical nerve stimulation and placebo inchronic pain patients: a double-blind non-crossover comparison. Rheu-
matol Int. 1984;4:119–123.
83 Modaresi A, Lindsay S, Gould A, Smith P. A partial double-blind,placebo-controlled study of electronic dental anaesthesia in children.Int J Paediatr Dent. 1996;6:245–251.
84 Fargas-Babjak A, Rooney P, Gerecz E. Randomised control trial of Codetron for pain control in osteoarthritis of the hip/knee. Clin J Pain.
1989;5:137–141.
85 Gemignani G, Olivieri I, Ruju G, Pasero G. Transcutaneous electri-cal nerve stimulation in ankylosing spondylitis: a double-blind study.Arthritis Rheum. 1991;34:788 –789.
86 Johnson MI, Ashton CH, Bousfield DR, Thompson JW. Analgesiceffects of different pulse patterns of transcutaneous electrical nervestimulation on cold-induced pain in normal subjects. J Psychosom Res.
1991;35:313–321.
87 Demmink J. The Degree of Modulation in Interferential Current Stimula-
tion as Used in Physiotherapy: The Effect of a Biological Conducting Medium
on the Pattern of Modulation in a Two-Circuit Static Interferential Field [MScthesis]. Bergen, Norway: University of Bergen; 1993.
88 Demmink J. The effect of a biological conducting medium on thepattern of modulation and distribution in a two-circuit static interfer-ential field [abstract]. In: 12th International Congress of the World
Confederation for Physical Therapy . Alexandria, Va: American PhysicalTherapy Association; 1995:583.
89 Palmer ST, Martin DJ, Steedman WM, Ravey J. Alteration of interferential current and transcutaneous electrical nerve stimulationfrequency: effects on nerve excitation. Arch Phys Med Rehabil.
1999;80:1065–1071.
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