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LITERATURE REVIEW

Dosage of Some Pulsed Shortwave Clinical Trials John Low

Key Words

Pulsed shortwave, pulsed electromagnetic energy, dinical trlals, analysis, meta-analysis. dosage, energy dose, cliniucal eff icacy, therapeutic effects.

sUtYlt?l8v

The mechanisms by which pulsed shortwave might be thera- peutically effective are discussed. The dosages applied during treatment in nine dinical trials are considered and the total applied energy per 24 hours calculated, showing successtUl outcomes are associated with longer treatment times and higher energy applications. Trials on sprained ankles are compared, suggesting an approximate correlation between success and the energy applied per 24 hours. Four other clinical trials are also discussed. Comment is made on unquantified factors which may affect dosage. It is concluded that successful treatment has largely resulted from the application of quantities of energy (in kJ per 24 hours) at the higher end of the scale of energies used and associated with the longer treatment times.

Introduction Pulsed shortwave has become a popular physie therapy modality over the past twenty years or so yet there is no agreement about appropriate dosages or, indeed, whether it is efficacious. There have been a number of clinical trials over the years but not all of them have demonstrated benefit. This paper is an attempt to analyse some of the features of comparable trials to determine which characteristics are associated with effec- tiveness. Previous reviews of this therapy, eg Kitchen and Partridge (1992), have concluded that there is considerable uncertainty of efficacy and little consistency of dosage. Other reviews, notably from the USA, conclude that there is insufficient evidence to support the therapeutic value of low intensity pulsed shortwave, eg Kloth (1986). Apart from the manufacturers’ literature, some dosage suggestions have been provided by Hayne (1984).

Pulsed shortwave involves the application of discrete pulses of high fresuncy (27.12 MHz) elec- trical oscillations to the tissues. The length of these pulses varies but they are usually of tens or hundreds of microseconds. Pulse frequencies are of a few hundred Hz. The pulsing paramebm can be varied in different ways on different machines. Due to the long pulse intervals, high

(peak) energy can be applied at each pulse while keeping the average energy - hence tiesue heating - very low indeed. The energy can be introduced into the tissues either inductively or capacita- tively - see Low and Reed (1994a) and Oliver (1984) for further descriptions.

Mechanisms Pulsed shortwave has been considered to act by accelerating the tissue healing processes, in particular the rapid resolution of early oedema (Nicolle and Bentall, 1982). Several mechanisms have been proposed. The simplest, and perhaps intuitively most appealing, is the suggestion that the additional energy simply ‘stirs’ ions, mole- cules, membranes and metabolic activity of cells; thus increasing the overall rates of phagocytoeie, transport across membranes, enzymic activity and so forth (Evans, 1980; Low and Reed, 1994a). This would account for the acceleration of both inflammatory and healing processes leading to the earlier resolution of injury.

More complex mechanisms have also beem proposed. These include the unidirectional motion of asymmetrical bodies in tissue fluids due to the electromotive effects of currents (Collier, 1993, cited by Hayne, 1984) and the idea that the elec- tromagnetic field is able to alter the cell membrane potential, repolarising the cell. This latter ie an attractive suggestion since the normal cell membrane polarity tends to be reduced in damaged cells and it is involved in the control of cell division and proliferation, and hence in healing (Hayne, 1984; Low, 1978). What is not evident about this suggestion is why evenly oecil- lating currents applied in small bursts should have this effect. It might be expected that a unidi- rectional current would be appropriate, and there is evidence of the good therapeutic effects of low intensity direct current on wound healing (Weiss et al, 1990) and on un-united fractures (Bassett, 1984). For a thorough and valuable review of these and related matters see Charman (1990). An underlying theoretical idea is that the elec- trical pulse needs to be specific to provoke a particular cell response. This specific nature of the pulse depends on its amplitude, rise time, frequency or other parameters. This leads to the concept of ‘frequency windows’ or ‘amplitude windows’ meaning that cells will absorb energy

812

only a t a particular narrow range of frequencies or amplitudes. The absorbed energy then provokes or enhances some particular cellular activity (Tsong, 1989; Charman, 1990).

As well as these possible mechanisms, there is the ‘heat’ controversy. It is the view of some, such as Lehmann and de Lateur (19821, that any benefi- cial eEects of pulsed shortwave are due to very low intensity heating denying specific effects. Others emphasise that where short pulses at low frequency are applied there would be no rise in temperature. This is to some extent anunjustified dichotomy because heat is simply kinetic energy in the microstructure of matter (Low and Reed, 1994b). However trivial the additional electro- magnetic energy, it adds to the total heat; a point noted previously (Adey, 1981; Low and Reed, 1994a). Thus, high or low intensity electromag- netic energy delivered a t whatever frequencies or pulse lengths will ultimately end as heat what- ever other energy conversions may also occur. Clearly the term ‘athermic’ is inappropriate to describe these treatments. It simply indicates that beating is below the detection threshold.

So the effects could be due to mechanical or elec- trical changes affecting the tissues before the energy is randomised, ie becomes heat, perhaps requiring specific frequencies or pulse shapes. On the other hand, the effect could be due to random particle motion - ie low-level heating - the conse- quence of any combination of pulse frequency, length, and intensity which gave a suitable average quantity of additional energy. This latter case would fit the simple ’particle stirring‘ mech- anism noted above. In all cases, a dose-response relationship would be expected such that small amounts of energy had no effect, increasing energy produced an increasingly beneficial effect, and large quantities produced no further benefit or perhaps had a deleterious effect. If particular pulse parameters were necessary then the dose- response relationship would obtain only when those specific pulse parameters were being applied.

C M d T r i a l S Do the results of clinical trials support any of these suggestions and indeed do they support the eficacy of pulsed shortwave? There are no clear answers to these questions due to the paucity of comparable clinical trials and because the full parameters of treament are not always available, a point noted by Kitchen and Partridge (1992). However, from the published accounts, it is possible to provide some comparisons on the basis of the information given and a few reasonable assumptions. Almost all the claims for the euecessful uae of pulsed shortwave have involved

acute tissue injury of some kind; the treatment being applied during the early stages of recovery from accidental injury o r surgery. Nine trials using similar methods are listed in the table. These all fulfilled the following criteria:

1. The purpose was to assess effects of pulsed shortwave. 2. The treatment was applied to acute injuries. 3.27.12 MHz oscillations in pulses of either 65 or 400 microseconds were used. 4. Treatment was started within a day or so of injury, applied at least once per day, and continued for more than one day. 5. Selection was randomised and a control group was used. 6. Treatment was applied to at least 18 patients and a similar or larger number of controls. 7. There was some objectivity in the measure- ments used to determine outcome.

Parameters of Treatment Published descriptions of these studies do not always give all the details of applied dosage but from information known relating to the machines used it is possible to calculate or predict some of the missing measurements. Some of these assumptions may not be entirely accurate. The following measures of the applied treatments are provided and the values shown in the table.

1. The length of time for which treatment was applied per %hours (minutes). 2. Pulse frequency (Hz). 3. Pulse length (microseconds). 4. Peak power (watts). 5. Average power (watts). 6. Energy applied per 24hour period in kilojoules.

Power, in watts, is energy per second, 1 watt = 1 joule per second. Peak power is thus the rate at which energy is being applied to the tissues during the pulse of high frequency. For example during a 65 ps pulse, 1,000 W might be applied. (This is not strictly true in real sources because the pulse power may not be uniform). However, the average power depends on the length of time for which the energy is applied in each second. Thus 100 pulses per second (100 Hz) of 65 ps each of 1,OOO W would give a mean or average power of

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6.5 W. If this mean power were to be applied to Trials on Sprained Ankles the tissues for a 10-minute treatment the total six treated acute sprains ,$the lateral liga- enerfD would be 3-9 kJ (6.5 w x 600 set). Simi- ment ofthe ankle in a similar way (Wilson, 1972, larlY a 500 peak power 65 pulse at 1974; Pasila et al, 1978 (Curapuls and Diapulse); loo HZ for 2o Barker et al, 1985; McGill, 1988). By comparing Grant et al (lW9) in the the results of objective measures, swelling, enem per 24 hours can be in disability, etc, given in these papers, an average the differing regimes* percentage improvement can be found. Thus, if tissues cannot be known, it is simply assumed the swelling diminished twice as much in the

amount of energy applied. as loo%, and so forth. When the average ‘improvement’ figure for each trial is plotted

Analysis and Discussion against the energy applied per 24 hours, an approximate positive correlation results (fig 2). The data are shown in the table and figure 1.

It is not possible to quantify the precise degree

wave to be effective. It is, however, possible to

.“hose that found a clear beneficial effect.

.Those that found a weak or slight beneficial e5&. .Those that found no beneficial effect a t all.

It might be s u r p r i s i i to find these three groups fitting neatly into some satisfyingly simple pattern in figure 1, but they do. Studies A to E on the left all considered the treatment clearly ef€i- cacious, the next two (Paaila et al, 19781, found a weak effect. The three studies H to J on the right (McGill, 1988; Grant et al, 1987; and Barker et al, 1986) all found pulsed shortwave treatment in- effective. Looking at the individual treatment parametera in the table, none stand out as being clearly related to treatment success. Of course all of them - frequency, peak power, average power, and length of treatment - contribute to the total daily energy application. This pattern conforma with the simple ‘stirring‘ mechanisms in that low intemity energy (low average wattage) is ineffective if it is either too low or applied for too little time.

The study by Pasila et al(1978) needs further comment. It has been described (Kitchen and partri*’ lm2) as showing p*d shortwave to be ineffective and the authors themselves say they ‘found little significant difference between recovery in the placebo group paients and those given shortwave treamtent by either of the devices used‘. They did, however, note a distinct trend favouring pulsed shortwave treatment. They made some 20 objective comparisons of which 16 showed benefit for the treated group over the placebo but only two of these were statis- tically significant. This study was composed of two trials, one with a Curapuls and the other with a Diapdse machine. Hence they are shown meparately in the table.

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While this may suggest that increasing amounta of energy are associated with a better result it must be emphasid that it is b a d on some very tenuous assumptions since the studies are not comparable - it is rather overstretching these data. Of course, all these studies are using low average energies, well below the threshold of detectable heating. Increasing the average power - more heat - is likely to be deleterious. I t is well recognised that heating acute injuries too much can be unhelpful.

It might be wondered how other studies of pulsed shortwave not included in the table conform to this picture. Wagstaff et ul (19861, treating chronic backache, found the treatment effective when applying about 21 W per 24 horn. Duma- Drzewineka and Buczynski (1978), treating chronic pressure sores (no controls), found accel- erated healing using some 45.6 kJ per 24 hours

61 6

over the lesions. Aronofsky (1971) treated patients recovering from dental surgery and found a clear advantage (assessed subjectively) in the treated subjects over the controls while applying some 22.8 KJ per 24 hours to the affected area. Thus, all three found treatment to be effective using doses near the lower end of the scale. Amnofsky (1971) and Bentall and Eckstein (1975) applied pulsed shortwave pre-operatively as well as post-operatively. They, and Duma- Drzewinska and Buczynski (1978) also applied pulsed shortwave to the adrenal or liver region in the belief that this would provoke a beneficial systemic effect. These applications to un-injured tissue and the pre-operative treatments have not been included in any of the energy estimations. One other study involved a somewhat different source. A small device emitting 100 ps length pulses of 27.12 MHz oscillations with pulse frequencies of 1,000 Hz has been built with the applicator in the form of a pair of wire loops, like the frame of a pair of spectacles. These were applied during the post-opkrative 24 hours following bi-lateral blepharoplasty with one active loop. The post-operative reaction in each eye was assessed in 21 patients and it was found that oedema and brusing were markedly less on the treated side of 11 of these patients (Nicolle and Bentall, 1982). It seems that this device might produce up to about 1 mW which applied for 24 hours would give about 86 J. Reports of the success of this and other extremely low power sources do not, of course, support the contention that low total energy applications are ineffective. They do, though, support the view that low power and prolonged application are needed for success.

Treatment andksage Characteristics It is possible to argue the superiority of some treatment parameters simply because there are no available comparisons. Thus, almost all the successful outcomes involve 65 ps pulses delivered by Diapulse machiens at 400,500 or 600 pulses per second. The only study to compare one source with another using different pulse lengths (Pasila et d, 1978) found little difference; if anything the 400 ps Curapuls did trivially better. Overall, the ‘successful’ trials tend to have somewhat higher peak and mean powers. They also applied much longer daily treatmenh, 60 minutes or more. Thie is the most distinct difference between the ‘successful’ group and the others. It is the main reason why greater total daily eneqy ie applied in this group. It must be added that three of the studies noted as successful but not included in the table do not conform to this generalisation. The actual amount of energy introduced into the

tissues is entirely unknown, as already noted. It would depend on such variables 88 the method of application, the shape and mass of surrounding tissues, the depth of the w e t ’ tissue ae well as the way in which the energy was distributed in the tissues. This, then, is a further confounding factor. It might be expected that more deeply placed lesions would receive proportionally less energy than superficial; and most of the studies considered have involved lesions close to the surface.

Another variable considered important by some writers is the w e of the E-field (electric field) or the H-field (magnetic field). Normally energy would be transmitted to the tissues by both the electric (or capacitative) field and the magnetic field, the latter provoking currents in the tieeuee by induction. Placing a metal mesh (Faradic screen) between the induction coil applicator and the tissues eliminates the E-field. This leaves only the magnetic component which passes readily through tissue. (For discussion on electromagnetic waves, see Low and Reed, 1994b). Such a Bereen would significantly reduce the applied energy. The only study indicating the use of this device was McGill(1988).

All the published clinical studies claiming effectiveness considered here, except that of Wagstaff et a2 (19861, have treated resolving tissue injury. There are, as yet unpublished, studies showing ineffectiveness in the treat- ment of degenerative and other conditions. There are, of course, numerous accounta of the BU- ful treatment of many conditions such as arthritis, phantom limb pain, and oeteopomeis. On the basis of some well-supported experimental findings, the use of pulsed &ortwave in the treab ment of recovering peripheral nerve leaions has been recommended. For further amounts, see Kitchen and Partridge (1992) and Low and- (1994a).

Conclusions and Implications for Treatment Reported successful treatment with pulsed short- wave has been largely confined to the treatment of acute tissue injury with the application of upwards of 40 kJ of energy in each %hour period. This has been given with high peak pulses (around 900 W) at a few hundred pulses per second over periods of 60 minutes or so per 24 hours. This length of treatment time appears tobeimportant.

The evidence is at least consistent with the simple ‘stirring up’ mechanism model. Thus, high wattage brief pulses provoke activity while the long interpuke intervals ensure that the average

m

rate of energy addition - the mean power - is not too great. Insufficient energy, either because it is too little or because it is applied for too little time, is ineffktive. Were the average wattage to be too high - ie at or claee to the thmshold of detectable heating - then no benefit ensues. There seems to be no clear evidence from these clinical studies of the value of particular pulsing parameters but this may be due to the lack of evidence. In making the customary call for further research in this area of treatment, two points are stressed. One is the importance of providing information of the energy and the way it is applied. The other is the great importance of this work. If tissue healing can be accelerated, even to a trivial degree, the benefits would be enormous in both pereonal and economic terms.

mbfmGa Moy, W R (1981). 'Electromgnetk field effects on tissue'. phvskkorclJ w, 6l, 3.4364514. &wmwy, 0 H ( 1 ~ 1 ) . 9~bductkn ddentaf post-surgical - u d n g - p h e d ~ ~ d e c b o m a Q w l b c ~ * o r J s u p y , ~ 5 * g e e - g s s .

- w w ~ ~ - w . ~ w Y , w, V. cda. R J d- A (1983). 7- Ol-

69,6.186-188. Barker, A T. Barlow. P S, Porter, J. Smlth. M E, Cllfton. S, Andrews. L and O'Dowd, W J (1985). 'A double-blind clinical trieldbw-powwpui8e(jshortwsvetherapy in the treatment of a w r t t k u e ~ w u r y ' . ~ , n , 1 2 . 5 0 0 6 0 4 . Bassett, C A L (1984). Tho development and appllcation of prla4debdmmpktblds(mFB)kruMnitedfraLtwesand arthrodeses', Ofihupaedk Cllnks of North Ametfca. 15, 10, 61-89. M. R H C and EdutJn. H 6 (1975). 'Atrial hvoMnuIhe use ol pulsed --on children undergoing Orchi- dapexy'. -. 17.4, W. chsmun, R A (1saO). 'Exogcwua CU- and fields - Experi- mental and dhkal appUccrtion'. (part 5 of 'Bloelectrkity and ebddmmy-TomvQa new paradigm?') Fttpmmapy, 76, 12,743-750.

Duma-Onewinska. A and Buczynski, A 2 (1978). 'Pulsed high frequency cumnk (Diepulse) epplied in treatment of bed-sores', POW Tygodnik L e M , T. X)(XIII, nr 22. Evans, P (1980). The healing process at a cellular level: A review', Phmw, 6!5,8,256-259. W i n , J H, Broadbent, N R G. Nancarrow, J D and Marshall. T (1981). 'The effects of Diapulse on the healing of wounds: A doubleblind randomii controlled triat in man', British Joumal

Grant, A. Sleep, J. Mclntosh, J and Ashurst, H (1989). 'Ultra- sound and pulsed elechomagnetic energy tntatment for perineal trauma. A randomised placebocontrolled trial', British Journal 0farMrK.s ' andGyneeoology.%,434439. Hem, C R (1984). 'Pulsed h i frequency energy - Its piece in physiotherapy'. Phpiothempy. 7 0 , 1 2 , 4 5 W . Kitchen. S and Partrldge, C (1992). 'Review of shortwave dialhermy continuous and pulsed patterns'. PhysioUmmpy, 18.4, 243-252. Kloth, L (1986). 'Shortwave and microwave diathermy', in: Michlovitt, S (ed) Thennel Agents in Rehabilitation, F A Davis

Lehmann, J F and debteur, 6 J (1982). 'Therapeutic heat' in: Lehmann, J F (ed) Therapeutic Heat and Gold, Williams and Wilkins. BeltimoreRondon, 3rd edn, pages 406-562. Low, J L (1978). The nature and effects of pulsed electro- magnetic radiations', New Zealand Journal of Physiotherapy, 6.4.18-22.

p k and practice, Butterworttr-Heinemann. Oxford. 2nd edn. Low, J L and Reed, A (1994b). Physical Principles Explained, Butternorth-Heinemann, Oxford. Will, S N (1988). 'The effect of pulsed shortwave therapy on lateral ligament sprain of the ankle', New Zealand Journal of

Nicolle, F V and Elentall, R M (1982). 'Use of radio-frequency pulsed energy in the control of post-operative reaction in blepkaroplasty', Aesthek Was& Suqry, 6,169-1 71.

Oliver, D E (1984). 'Pulsed electromagnetic energy -What is It?' PhyskHf?ewy* 70,12,458-459. Pasila, M, Viri, T and Sundholm, A (1978). 'Pulsating shortwave diathermy: Value in treatment of recent ankle and foot sprains', Archives of Physical Medicine and Rehebilltetkm, 59,383-386.

Tsong, T Y (1 989). 'Deciphering the language of cells', Trends in the Bidogical Sdences, 14, 92.

Wagstaff, P, Wagstaff, S and Downie, M (1986). 'A pilot study to compare the efficacy of continuous and pulsed magnetic energy (shortwave diathermy) on the relief of low back pain',

WeiSS, D S. Kirsner, R and Eaglstein. W H (1990). 'Electrical stimulation and wound healing', Archives of Dermatology, 126,222-225.

Wilson, D H (1972). 'Treatment of soft tissue injuries by pulsed elechical energy', Brirish Whl Jouma~ 2.269-270.

Wilson, D H (1974). 'Comparison of shortwave diathermy and pulsed elechomagnetic energy in treatment of soft tissue injuries', Physiotheqy, 60,10,83-85.

d plestic Surgery, 34,267-270.

Compeny. Phhdelphle, pages 177-21 6.

Low. J L and Reed. A (1994a). € m f h e w y €@ti&: Prim'-

PhysWwapy , lo , 21-24.

mMfhempy, n, i 1, sum.