Physical treatment modalities

Pulsed electromagnetic (short-wave) energytherapyGeoffrey C. Goats, PhD, MCSP

Department of Physiotherapy, The Queen's College, 1 Park Drive, Glasgow G3 6LP

Therapy using pulsed electromagnetic energy is nowused widely in the UK and many claims are maderegarding its clinical effectiveness. The technique de-veloped about 40 years ago from that of continuousshort-wave diathermy, to which it is similar in manyrespects. There are, however, certain important dif-ferences between these therapies that influence sig-nificantly their clinical application.Continuous short-wave diathermy (SWD) is de-

scribed fully elsewhere' ' and relies principally for itstherapeutic effect upon the pattern of heating gener-ated deep within the tissues of the patient by a strongoscillating electromagnetic field. Heat is generated bythe movement of ions and distortion of molecules andcrystal lattices within the field, and by eddy currentsinduced within the tissues. The electromagnetic fieldoscillates at a frequency of 27.12 MHz. More energyenters the tissue than is transported away in the circu-lation and tissue easily achieves temperatures withinthe therapeutic range of 40-450C3. This technique isthus accurately described as diathermy.

Pulsed electromagnetic energy therapy (PEMET)cannot correctly be called a diathermy because little orno heating of the tissue occurs. The apparatus oper-ates at the same frequency as continuous SWD but theoutput is delivered as a train of pulses5. The intenseelectromagnetic field is thus established only briefly,and during the subsequent period of nil output, anyheat produced is dissipated by the circulation6.

This technique allows the use of a very high peakpower output without the risk of an undesirable in-crease in tissue temperature. Peak power output ap-pears to be more significant biologically than meanoutput . The therapeutic effects of PEMET appear todepend more upon subtle interactions between theelectric and magnetic field and biological tissue thanupon heating. These processes are as yet poorly un-derstood, although investigations are continuing.

This paper will attempt to describe the apparatus,biophysics and physiological and therapeutic effectsof PEMET with reference to the types of conditionencountered frequently in sports medicine.

ApparatusMany short-wave diathermy units are capable of deliv-ering either a pulsed or continuous output, althoughsome are manufactured to fulfil only one role. The

© 1989 Butterworth & Co (Publishers) Ltd0306-3674/89/040213-04 $03.00

specifications of units producing a pulsed output cur-rently used widely in the UK8 appear in Table 1. The de-sign of continuous SWD units is discussedelsewhere"', thus it is only the modifications requiredfor pulsed operation that will be considered here.A signal generator, operating at 27.12 MHz, is con-

structed to deliver brief pulses of energy. These pulsesusually have a duration of 20-400 Rus. Some machinesare capable of generating pulses of various lengthswhilst others operate at a single pulse duration. Pulsefrequency is similarly variable, usually within therange 100-600 pulses per second. This signal is thenamplified and fed to the tissues of the patient via atuned circuit and applicators. The applicators de-signed for use with continous SWD units may all beused safely to deliver a pulsed output, although cer-tain machines are constructed to accept only the'monode' type of applicator. This is essentially a coilencased within a cylindrical housing as seen in Figuire 1.

BiophysicsAlthough the oscillating electric and magnetic fieldsare usually pulsed to allow sufficient time for the circu-lation to dissipate the energy applied, thus preventinga cumulative heating effect, one should remember thatat a high output intensity, with a long duration pulseand rapid repetition rate, heating may occur6. This ismost likely in those tissues poorly supplied with bloodvessels or receiving a circulation that is otherwiseimpaired.The maximum mean output of most PEMET units is

usually in the region of 40W (compared to 400-450Wmaximum output for continuous short-wave dia-thermy), although the pulsing regime allows a peakoutput that often approaches 1 KW. The facility toapply a very strong electromagnetic field without therisk of a burn enhances those therapeutic processesmentioned earlier that are not a function of heating6'7'9.Some authors suggest that PEMET causes a redis-

tribution of ions across the cell membrane, thus mod-ifying resting membrane potential and certain cellularmetabolic processes, especially those active during in-flammation'0. Neurons may be depolarised directly,or as a result of neurotransmitters moving in theelectromagnetic field7.Others observe that ATPases are capable of absorb-

ing energy from oscillating electric fields of definedfrequency and amplitude and using this to performchemical work". Blood vessels may act as conductorswithin the time-varying magnetic field and thus haveinduced within them a weak electric current.

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Table 1. Specifications of pulsed output short-wave therapy units

Pulse Maximum PulsedPulse length Frequency Power Output

Manufacturer Model Mode ofOperation (4s) (pulses. s-') (W) Coupling Applicators

EMS (Greenham) Ltd. Megapulse Pulsed 20,40,65 100,200,400, 125 Manual Cable in drum100,200,400 600,800 case

Enraf-Nonius Delft Curapulse Pulsed/Continuous 400 15-200 1000 Automatic Rigid plates419 (10 steps) Flexible plates

Free cableCable in drumcaseCable inhinged case

Siemens Ltd. Ultratherm Pulsed/Continuous 400 20-180 900 Automatic Rigid plates808i Flexible plates

Free cableCable in drumcaseCable inhinged case

Diapulse Diapulse Pulsed 65 80,160,300 975 Manual Cable inDS104A 400,500,600 drum case

Some propose that these currents can initiate andco-ordinate repair processes, influence the rhythm ofelectrical activity in the brain, and alter directly vascularmuscle tone12. This direct effect of pulsing electro-magnetic fields upon blood vessels was seen experi-mentally when muscle, treated with PEMET at a meanoutput of 40 W, showed an increase of 308 per cent inthe rate of blood flow in the absence of measurableheating'3. This may, however, be a reflex pheno-menon. PEMET treatment of the epigastrum using aDiapulse unit delivering a mean power output of 16Wcaused an increase in blood flow to the lower limb

Figure 1. Pulsed electromagnetic energy therapy unit

with no increase in rectal temperature'. The authorproposes that this mechanism be harnessed in thetreatment of peripheral vascular disease.

Further explanation of these complex interactions isbeyond the scope of this work, and the interestedreader is directed, in the first instance, to morespecialized reviews"'9t. Much research is currentlydevoted to the investigation of frequencies other than27.12 MHz.

Physiological and therapeutic effects

Pain

Several manufacturers claim that PEMET is capable ofreducing pain'. Research substantiating this is de-scribed with injuries to the hand"8, vascular disorders'9,foot surgery20, and ankle sprains2'. Other investiga-tions have, however, failed to support thesefindings22'23, although a study of the effect of PEMETon post-surgical pain following repair herniae, inwhich no difference between treatment and controlgroups was reported24, used a machine that emitted aweak electromagnetic field (1W mean power output).

Soft tissue injuryInversion injuries of the ankle have been treated usingPEMET with varying degrees of success. Sprains re-ceiving therapy within 36 hours of injury usingDiapulse (38W mean power output) for one hour dailyon three successive days and graded subsequentlyfor swellin6, pain and disability are reported muchimproved2'-6. However, similar treatment and assess-ment criteria used by others failed to show any benefi-cial effect23 as have studies investigating PEMET atlower field intensities of 10 mW22 and 19.6 W21. Thislast investigation does, however, claim some improve-ment of swelling, pain and time taken to achieve fullweight bearing, although these improvements werenot statistically significant.

Trials using Diapulse to treat various lesions of thelower limb in a mixed population of subjects (38 W

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mean power output) report considerable therapeuticsuccess, particularly for conditions in which ischaemiawas a major factor'. Hand injuries treated with PEMETwithin 36 hours of injury for 30 minutes twice daily (30W mean power output) responded well with a markedreduction in swelling and some improvement in painand disability18.Experiments using animal models suggest that rab-

bit muscle injured artificially by the injection of a toxicagent and treated subsequently for 20 minutes twicedaily for eight or 16 days (38W mean power output in-itially rising to 143 W by the end of the experiment)was little improved by PEMET27. Haematomata in-duced experimentally in rabbits exposed subsequentlyto PEMET for 30 minutes twice daily (25 W meanpower output) showed a statistically significant accel-eration of the rate of healing after the sixth day of anine day treatment period28. Arthritis induced artifi-cially in the joints of rats by intra-articular injection offormaldehyde and treated using a Diapulse unit onceprior to damage and twice on the following day (25 Wmean power output) were markedly less swollen thanthose of the untreated control group29.

Wound healingStudies of the effect of PEMET on the rate of woundhealing have generally given encouraging results'. Adouble blind randomized trial in man studying thehealing of medium thickness split-skin grafts,evaluated the effect of a 30 minute preoperative expo-sure to PEMET followed by four 30 minute treatmentsdaily for seven days (25 W mean power output). Thestate of healing of the grafts at the end of this periodwas considerably advanced in the treated group whencompared with those in the control31. Similar studieson rat tissue failed to identify a beneficial therapeuticeffect, although in this study the period of exposure tothe electromagnetic field (25 W mean power output)was only 10 minutes twice daily32.The healing of surgical incisions was investigated in

a mixed population of patients undergoing surgeryand found to be influenced favourably by PEMETtreatment using Diapulse. Treatments were giventwice daily (25W mean output power) over a four dayperiod and lasted 20 minutes . This was combinedwith a coincidental application to the liver. Therationale given for this approach was based upon thehypothesis that this would elevate the level ofhaemopoitic activity. The acute lesions respondedparticularly well to PEMET.A similar double-blind study of patients receiving

surgery to the foot also incorporated a subsidiary treat-ment to the liver, although the main treatment was di-rected at the surgical incision for 15 minutes twicedaily (38 W mean power output). Swelling reducedmarkedly in the treated group, which also benefitedfrom an improvement in pain and erythema20.Other clinical studies have shown that the amount

of analgesia required by postoperative surgical pa-tients, and subsequent length of stay in hospital, wereboth reduced by Diapulse treatments'. The paralyticileus that often complicates abdominal surgery did notrespond favourably to PEMET35.

Nerve repairThere is growing evidence that PEMET assists therepair of both the peripheral and central nervoussystems. When the median ulnar nerve of rats was sec-tioned surgically and treated using a Diapulse unit for15 minutes within two hours of surgery, and thendaily for 15 minutes (11 W mean power output), thetreated wounds healed more quickly than those in thecontrol group. Nerve conduction studies indicatedthat function was restored to normal after 45 days intreated group compared to the 60 days that elapsedbefore the untreated nerves recovered .

Furthermore, sectioning of the common peronealnerve in rats, followed by a 15 minute treatment withPEMET within one hour of surgery, and then daily forup to eight days (15.5 W mean power output), de-monstrated that healthy nerves were unaffected andthat animals in the treated group recovered function inthe damaged limb more quickly. A statistically sig-nificant acceleration of the rate of degeneration, re-generation and maturation of myelinated axons alsooccurred37'38.A most interesting observation follows from experi-

ments with cats in which the animals suffered surgicalhemicordectomy in the upper lumber region and werethen treated using PEMET for 30 minutes daily for 30days (50 mW.cm-)39. After a three month postoperativeinterval, the spinal cords were examined histologic-ally. Those in the treated group showed less extensivescarring and a greater number of regeneratingneurons crossing the site of the lesion than controlanimals.

ConclusionPulsed electromagnetic energy therapy is a widelyused technique for which there exists considerable in-dustrial and paramedical enthusiasm. The researchsupporting the clinical effectiveness of PEMET isgrowing steadily although much work remains to becompleted. A considerable number of the existingstudies have been performed with the direct or in-direct sponsorship of the manufacturers of the equip-ment, notably the Diapulse Corporation of America,and whilst I suggest no bias, independent studieswould increase confidence in the information avail-able.Other factors militating against a definitive sum-

mary include the lack of experimental rigour that isevident in much previous work, and a failure to meas-ure or report details such as intensity of the elec-tromagnetic field applied to the tissues. Meaningfulcomparison between studies is sometimes difficult.The mechanisms responsible for the action of

PEMET have yet to be elucidated fully or reportedadequately in the West. A considerable amount ofwork has been done in the Eastern bloc countries towhich we have as yet limited access. I anticipate thatthe minimal heating effects produced by this equip-ment will be shown to exert only a marginal influencewhen compared to the direct effects of the interactionbetween the electromagnetic field and biologicaltissue.

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Certain conclusions may be drawn from the existingliterature. Laboratory experiments and clinical studiesindicate clearly that acute lesions in soft tissues,caused by accidental trauma or surgery, can be in-duced to heal more rapidly by the use of PEMET. Theeffects upon the skin and nervous system wouldappear particularly useful. Chronic lesions respondless well. Pulsed electromagentic energy therapyshould be regarded as a useful therapeutic tool likelyto become more effective clinically as further researchidentifies the conditions under which it is used mostappropriately.

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