Page Sixteen P H Y S I O T H E R A P Y January, 1957. ELECTRO THERAPY OF PARALYSES (BASIC PRINCIPLES AND METHODS OF APPLICATION) B y D r. Harold Thom Special reprint from the Zeitschrift Fur Orlhopadie und ihre Grenzgebieie Vol. 84, N o. 1, 1953. E d ito r: Prof. D r. M ax Lange, Bad Tolz Published by F erdinand Enke, Stuttgat W, Hasenbergstreige 3. IN recent years a great advance has been made in the field o f electro-therapy, in the treatm ent o f paralyses. This is due to th e fact th a t m odern electrical technology is now able to provide the means o f satisfying the demand for special apparatus which has long been m ade by physiolo­ gists. T here is, however, still no widespread knowledge o f either the physiological principles o f electric current application or the technique o f treatm ent which, especially in the case o f paralysis, is o f such vital im portance even though there are but few therapeutic agents which can look back on so long a history and which have been examined in such detail, both clinically and in the research field, in respect o f their possible applications. This is particularly true of the m odem methods o f electro-diagnosis and electro­ therapy which until quite recently were unknow n. A ccord­ ingly, it is the aim o f this paper, to present the basic physio­ logical principles o f m odern excitation current therapy and diagnosis, as well as the methods o f application, particularly in the treatm ent o f paralyses. U p till now, electric currents used in medicine have generally been divided into two classes: galvanic (or direct currents) and faradic (alternating currents) (Fig. 1). Experience, however, has made it increasingly clear th a t this division, adopted from electrical technology, no longer holds in the light of present physiological knowledge and the increased demands o f diagnostic and therapeutic work. I t is now possible to produce alm ost any form o f current by means o f electronically operated instrum ents; current forms which in their manifold variety cannot be covered by the term galvanic or faradic; so th a t in principle it has. become obvious th a t there is no distinction, either diag- nostically o r therapeutically, between a faradic current and a correspondingly interrupted direct current (Fig. 1). It is advisable, therefore, as k o w a r sc h ik 'has suggested, to find a com m on denom inator fo r both form s o f curernt and to com bine them under the term “excitation current.” This has th e effect of dividing electrotherapy (or low fre­ quency therapy) into (a) galvanization, i.e. application of constant direct current, and (b) application o f excitation currents. In spite o f their manifold variety, the various excitation currents can be easily and accurately defined by determining the com ponents or excitation param eters, such as duration of impulses and intervals, steepness o f the impulse gradient and the impulse intensity (Fig. 2). M odem electronic instrum ents can readily generate alm ost any excitation current defined by such com ponents, thus ensuring th a t the current can be constantly reproduced and th a t com parative examinations can be made. As a result o f extensive experiments on animals, the first o f which date from the middle o f the last century, and of the research work carried o u t in recent years, especially in America, there is no doubt as. to the value of. electro- therapeutical treatm ent o f paralysis. R ecent w ork has been aimed less a t obtaining p ro o f o f its value, as discovering the m ost favourable form o f current from the therapeutical point o f view. *) T h e f o u n d a tio n s o f all la ter clin ic a l ex p e rie n c e was ia id jn th e la st c g a lv a n o -th e ra p y . Fig. 1. (Fig. 1.) 1.—Galvanic current, constant D .C . 2.— Faradic current, original form , produced by an induction coil, entirely irregular, not measurable. 3.—T riangular im pulse sequence, corresponding to faradic cu rren t, exactly defined and m easurable. JL Fig. 2. (Fig. 2). I.— Intensity o f Impulse- o r peak intensity o f cu rren t 11.— Impulse d u ratio n . III.—Period o f rest. IV.—Increase o r gradient of impulse. T he oldest m ethod o f applying electric current is byi simple galvanization, meaning the application for thera­ peutical purposes of a constant direct current1). G alvanization produces in the body quite definite, characteristic reactions, which can be used to advantage for the m ost varied therapeutic purposes. Since most excitation currents can be derived from an interrupted, chopped, amplified o r otherwise modified direct current, they also have certain basic qualities in com m on with it. Hence a knowledge o f the effects o f direct current also forms th e com m on basis for an understanding o f the effects of excitation currents. These will be briefly examined, because o f the practical im portance o f simple galvanization. T he hum an body can be represented as a semi-conductor o f electric current, the current flows through it being effected by means o f ions. This is n o t so in the case o f metals, where current flow is effected by electron displacement. T hus a change in chemical structure o f a hum an body occurs when a current is passed through it. r by th e g re a t e le c tro th e r a p e u tis ts , chiefly by R e m a k , th e re a l fo u n d e r of R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) January, 1957. P H Y S I O T H E R A P Y Page Seventeen The ions responsible for conducting the current are e£j by the break-up (dissociation) o f the electrolytes • t o positively and negatively charged particles. T he oment a circuit is established, the positively charged 1 ctrolytic com ponents (or cations) sta rt moving towards the cathode, and those nagatively charged (anions) tow ards the anode. In addition to th e m igration of the dissociated ater and salt molecules, a movem ent o f actual liquid articles which occurs, takes place from the anode towards The cathode, i.e. in the so-called direction o f the current. This process is know n as cataphoresis, o r in general as e l e c t r o p h o r e s i s . I t involves the participation of the un­ d isin te g r a te d (i.e. non-dissociated) w ater and salt molecules, as well as the molecules o f colloids, lipoid substances, a lb u m e n , sugar, etc. suspended in the blood o r tissue fluid. There is no doubt th a t the com bined effect o f ionic migra­ tion o f the dissociated elements, together with electro­ p h o resis, play a leading p art in the curative effect o f galvanic cu rren ts, although the, actual degree o f cure achieved by either process is difficult to assess. The principal effect o f ionic m igration is to produce a change in the chemical concentration o f both the tissue fluid and cell substance. T he cause o f this change in con­ c en tr a tio n may be found mainly due to the varying con­ ditions o f permeability, m et with a t the cellular dividing walls, and wherever tw o media o f different kinds meet. A c ti v a t i o n and m obilisation of innum erable halogen and mineral ions results, which in tu rn brings ab o u t a strong stimulation o f all m etabolic and biological processes. T he vasomotor and trophic effects o f galvanic current are rendered visible, especially underneath the electrodes, as a bright reddening o f the skin which is h o t to the touch. By means of thermo-electric measurements, k o w a r s c h i k among others, was able to show th a t th e tem perature o f the skin could, by means o f galvanization, be increased by more than 2— 3° C. The ensuing hyperaem ia is stronger than after massage or even short wave treatm ent. This hyperaemia, however, extends not only to the skin b u t also to the more deep-seated tissue section, and moreover, it persists for a very long time. This increased tendency to vasodilation can often be detected for days afterwards. The persistent hyperaem ia reacts favourably o n the course o f the disease in m any ways, especially in the improved trophicity o f the tissues, which is nearly always strongly affected by paralyses, particularly poliomyelitis, and certain circulatory affections o f other origins. A further curative effect o f galvanic current, (the sedative and analgesic com ponent) is widely used in the treatm ent of neuralgic and neuritic ailments. F requent use is made, even now o f the soothing effect o f “descending galvanisa­ ti o n ” 1) in treating spastic paralytics, hemiplegia patients, etc., as introduced into electro-therapy by s c h e m i n z k y . The im portance o f galvanic current in the treatm ent o f paralysis, albeit only as an aid and a preparation for sub­ sequent electro-gymnastics, is still not always fully recog­ nised. Since a continuous direct current, a t th e intensities used in therapeutic treatm ent, produces no contraction of the muscles, it is sometimes assumed th a t it has no affect on paralytic disorders either. T hat this assum ption is wrong has been shown by num erous experiments on animals, some of them conducted in the middle o f last century (by r e id , d e j e r i n e , g o t z e , p i o n t k o w s k i , l e n o c h and others). Mention has already been m ade o f the great im portance of an increased and improved circulation in regenerating paralysed muscles. This does not, however, exhaust the effects of galvanic current. In fact, even after a galvanization of short duration (especially under th e cathode) the excita­ tion threshold is m aterially reduced. This reduction can be expressed as an easier susceptibility of th e nerv-muscle systems concerned, not only to electrical stimuli (reduction o f the chronaxy, etc.) b u t also to purely mechanical stimuli (testing o f the tendon reflexes). Thus a m uscular system pre-treated with constant galvanization not only shows an increased and stronger reaction in subsequent impulse or surge current therapy, but the responsiveness to self-created stimuli (i.e. em anating from the patient himself), is also increased. Hence, continuous galvanization (in the same way as a ho t bath or electro-therm al bath, etc.) is ju s t as suitable as a preparatory treatm ent fo r active movement exercises by the patient, as a subsequent course o f exercises under electro-stimulation. C onstant direct current has, however, only rarely been used in the electrical treatm ent o f paralysis. T he practice has rath er been to m ake use o f the abrupt rise and fall o f a direct current interrupted by means o f a hand key, resulting in the well-known closing and opening contrac­ tions. In addition to these galvanic current impulses o f varying length, faradic current was also used. How physiological science regards faradic current supplied by an induction coil, formerly the only m ethod used, is shown by the com ­ ments m ade by r e i n 2), which in view o f their im portance, are quoted verbatim , as follow s: “ N ow th at the effect o f the form and the frequency o f faradic current is well known, and its action on every individual nerve element has been established, it is tim e th a t this knowledge should be taken into account in medical practice. The m ost frequent source o f current used, incidentally a very bad one, is the induction coil which gives a current whose form and frequency cannot be defined. Because o f this, m otor, sensory, and a u to ­ nomic fibres in th e nerve tru n k are stim ulated indiscrimi­ nately. Thus the whole muscle is m ade to contract, yet a t th e sam e time the blood vessels are also contracted and the pain receptors stim ulated. This is certainly no t th e m ost appropriate m ethod of medical treatm ent. Such a procedure is called ‘faradization’ as opposed to ‘galvanization’. In view o f the present stage reached in physiology and electrical technology, we should discard these archaic terms and antiquated instruments, and replace them by m ore up-to-date ones.” There is no doubt, th a t the faradic, galvano-faradic or Leduc currents still extensively used in clinics and medical practice to-day, do not m eet the requirem ents o f excitation currents, especially for intelligent and selective treatm ent o f paralyses. T he reasons why the application of faradic and key-controlled electrical currents can no longer be regarded as up-to-date fo r this purpose, and the require­ ments for the intelligent application o f excitation currents will be dealt w ith below. The usual faradic current produced by an induction coil is unsuitable, especially for treatm ent of paralyses, not only because it does n o t m eet physological demands b u t also because it has o ther technical drawbacks which are manifested as irregular impulse duration, uneven pauses and variable current intensities. M oreover, the strength of the current can n o t be measured accurately; hence, in order to m ake a diagnosis, com parative tests have to be carried o u t on the corresponding healthy nerves and muscles. I f pathological conditions exist on both sides, as is frequently the case, such a procedure is obviously impossible. . ) The expression “ descending cu rren t,” originally coined by P flugkr to denote the perm eation by th e cu rren t o f a nerve in the direction o f the muscle, commonly understood, in a som ew hat modified form , to m ean th at the anode is applied proxim ally, i.e. at the head, an d the cath o d e distally, i.e. in the area o f the lum bar po rtio n o f the spine. T he assum ption in this case is that the cu rren t flows (only) from the plus to the minus pole. s) R ein , .Binfuhrung in die Physiologie des M enschen" (In tro d u ctio n to H um an Physiology), Springer 1948, p. 314. R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) Page Eighteen P H Y S I O T H E R A P Y January, 1957. T o illustrate th e following paragraphs m ore fully, certain physiological aspects m ust be discussed in some detail, necessitating a certain am ount o f generalization and simplifi­ cation. In doing so, the physiological data will be discussed from the standpoint o f the diagnostic and therapeutic conclusions which follow : 1. Current Strength Pulse Amplitude and Rheobase I t is self-evident that, in order to stim ulate a nerve or muscle, a certain minim um current strength, the so-called threshold value, is required, l a p i c q u e has called the current strength needed to produce a minim um twitch, the basic threshold o r the “ rheobase.” T he determ ination o f the minim um current strength which causes no stimulus reaction in a given period, is still the simplest m ethod used to-day for purposes o f diagnosis. 2. Duration of Current Flow and Effective Time T he m ere determ ination o f the current strength (“ R heo­ base”) necessary to produce a minim um twitch has proved inadequate in fixing the susceptibility o f a nerve, as no account is taken o f the time factor. T o produce a muscular contraction requires not only a minim um current strength, but also a fixed minim um duration o f current flow, related to the current intensity. Moreover, the practical determ ina­ tion o f the rheobase m ay give rise to considerable deviations and inaccuracies, largely because the (local) current density, which plays an im portant role, is no t taken into account. Similarly, the determ ination alone o f the minimum time o f current flow, (referred to as “ effective time” by l a p i c q u e and g i l d e r m e i s t e r ) , was bound from the outset to rem ain equally inadequate, as this again involves only one factor which is largely dependent on other values, i.e. current strength, and current impulse gradient. I t is to l a p i c q u e ’s m erit th a t he introduced, from such considera­ tions, the concept o f chronaxy. Its determ ination involves n o t the current strength needed to produce a minim um twitch, b u t the period for which a current o f a definite intensity, i.e. twice the rheobase intensity, m ust flow. 3. Excitation T im e/Stim ulus Intensity Curves a n d Rectangular Impulse Characteristics R heobase and effective tim e do n o t represent absolute values, b u t between the duration o f an impulse and its intensity a definite relationship exists, which was form ulated in the h o o r w e g - w e is s Law. If, for instance, the duration o f a (rectangular) impulse is reduced—within certain limits—the current strength m ust be correspondingly increased in order to produce a minim um twitch. O n the other hand, long current flow periods require lower in­ tensities. T o illustrate this principle m ore fully, we shall represent the relationship between impulse intensity and flow duration graphically, i.e. by using a system o f co­ ordinates and plotting intensity on the ordinate and the duration o f the current flow on th e abscissa. T his produces curves such as show n in Figs. 3a and 3b, which approxim ate to hyperbolae. R heobase and chronaxy represent therefore only two points on a curve. I t is obvious th a t a study o f the entire curve presents a m ore complete picture o f the con­ ditions o f susceptibility with which we are prim arily con­ cerned, th an is obtained by merely selecting tw o points from it. Such curves, showing the relationship between intensity (or voltage) and duration o f flow, required to produce a definite com parative reaction, are know n as excitation tim e/stim ulus intensity curves (or excitation tim e/stim ulus voltage curves) or, for short, “ I / t curves.” In order to illustrate the im portant section o f the curve (the ascending part), m ore clearly than w ould be possible with a linear scale, a logarithm ic scale is norm ally adopted for either ordinate o r abscissa, (i.e. intensity or time), or both. T he shape o f the curves show th a t the product o f intensity and time, i.e., the quantity o f electricity, is an im portant factor in producing a reaction. This product, however, is by no means constant ( I x t = constant) as might be concluded from the considerations mentioned a t the outset. The lack o f constancy can be traced to the counter-effects set up in the body, arising partly from the diffusion o f ions, which increases with the duration o f the concentration gradient brought ab o u t by the current; and partly from the change caused by the current, to the selective permeability o f the m em branes, which is the m ain cause of the change in concentration. In view o f these counter-effects it can be seen th a t lengthening the duration o f any given weak current will soon cease to produce further contraction stimuli. Similarly, even if very powerful currents are used, a certain minim um time o f current flow m ust be guaranteed. 4. Speed at which Current Rises and Accommodation T he contraction producing effect o f a current depends, however, no t only on its intensity and duration, b u t also on the speed with which it reaches its maximum intensity (i.e. peak value), d u b o is -r e y m o n d already realized that th e threshold value required to produce a minim um twitch in a sound voluntary muscle is smallest when the current rises to a peak value alm ost immediately, i.e. in a minimum o f time. In sound muscles, therefore, th e current is more effective, the m ore steeply it rises. If, however, the current rise is delayed, i.e. when current “ creeps” in, the peak current required to produce a stim ulus o f equal intensity must be considerably increased (see Fig. 3a). This pheno­ m enon can be explained by the counter-effects set up in the body, immediately an electrical stimulus is applied. The body is, as it were, “ surprised” by a m ore o r less sudden application o f the stim ulus and successful stimula­ tio n can only be produced by this means. O n the other hand, the tissue soon adapts itself to a stim ulus impulse of m oderate rise, in which case a m aterially stronger current is required to produce the same effect. J mi 80 N V—N \ V \ \ \ / \ N H 5 S --- 0,05 0,1 0,2 0,S 1,2 2 6 1 2 21 B0 100 200 400 1000 ms Fig. 3a. Fig. 3a. E xcitation tim e/stim ulus intensity curves o f a norm al nerve muscle system. I / t curve with rectangular impulses, rect-111 Li OW1W djdlvlll* / • w w w , an g u lar im pulse characteristic ( R P C ) . --------—#— I /t curve w it" *r]" an gular impulses, triangular im pulse characteristic (TPC). # O n the basis o f an im pulse d u ratio n o f 1000 ms, am perages o f 5.8 mA in th e case ot rectangular impulses an d 25 mA in th e case o f trian g u lar im pulses give 25 an accom m odability quotient A o f A = ---- -- 4,3. 5,8 T he quotient for norm al accom m odability is approxim ately = 3—6. R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) bnuarft 1957. ________________ P H Y S I O T H E R A P Y page Nineteen p o b o is -REYMo n d and n e r n s t have coined the expression “ a c c o m m o d a t i o n , ” t o . describe this process o f adaptation to the stimulus, and the capacity to accom m odate is know n as “accommodability” . I t is inherent to a high degree only in healthy cerebro-spinal nerves and sound voluntary m u scle . In a denervated muscle, the pow er o f accom­ modation is lost to a large extent, thus “creeping” , a pheno­ menon associated with healthy muscle, is i m p o s s i b l e , ■phis means th at a paralysed muscle can be m ade to contract even with a relatively low current rise, while adjoining m u sc le remains unaffected owing to its capacity o f accom­ modation (see Fig. 3b). This difference in the reaction o f healthy an d denervated muscle to stimuli, provides the key to the problem o f selective stim ulation o f paralysed muscle. As long ago as 1904 R E is s drew atten tio n to this decisive difference which yjs equally significant for both, diagnosis an d therapy. Later, w y s s , t u r r e l l , d u e n s i n g , k o w a r s c h i k and others have investigated the practical exploitation o f accom m od­ ability, or its loss, for diagnostic and therapeutical purposes. H05 0,1 0,2 0,5 1,2 2 6 12 21 50 100 200 100 1000 m s Fig. 3b. Excitation tim e /stim ulus intensity curves o f a denervated nerve muscle system. --------------- 1 /t curve with rectan g u lar impulses, Rectangular im pulse characteristic ( R P C ) ---------------I / t curve with CTiangular impulses, triangular impulse characteristic (TPC). Both ^curves are shifted distinctly upw ards and to the right. T he accommod- 18 ability has been almost entirely lost: A = ---- = 1.2. 14 According to s c h r i e v e r , a good m easure o f accom m oda­ bility is the so-called stim ulation quotient. This is found by dividing the threshold value for long triangular impulses (expressed in mA), by th e threshold value for rectangular impulses. In the case o f a current reaching its peak value gradually, the current strength required for a minimum response (the threshold for a long triangular impulse) is also called the galvano-tetanus threshold value. The current strength required to produce a minim um tw itch; the impulse beginning and ending abruptly, and having a duration of at least 1000 m s; has long been know n as the rheobase” (the threshold for a long rectangular impulse). T he stim ulation quotient, (or the galvano-tetanus quotient), is obtained from the ratio. galvano-tetanus threshold value in mA rheobase in mA. T he greater the quotient, i.el the higher th e galvano- tetanus threshold in relation to the rheobase, the better the accom modability, bu t as the tw o values approach each other, i.e. the ratio tends to unity, accom m odability decreases accordingly. A simple m ethod o f assessing accom m odability is to determ ine the rectangular and triangular threshold for impulses o f 1000 ms duration. T he quotient thus results from th e ratio T riangular impulse threshold in mA = accommo- R ectangular impulse threshold in mA dability(A ) N orm al values lie between 3 and 6, pathological values below 3; with a quotient o f 1, accom m odability ceases entirely. 5. Periods of Rest and R efractory or Recovery Period In nerve o r muscle stim ulation (using a single current impulse) th e effect o f the current depends largely on three factors, i.e. current intensity, time o f current flow and impulse gradient. However, as soon as we apply impulses in rapid succession, definition o f this impulse sequence requires a further factor which is physiologically no less ■mportant, viz. the period o f rest between th e individual impulses. T he im portance o f this factor, both, in diagnosis and fo r therapy, was recognized only com paratively recently. The time required by an individual cell o f excitable tissue to rebuild the reduced energy potential after excitation has ceased, is described as the refractory period. D uring this period the cell cannot be successfully stim ulated. T hus single muscle fibre cannot be m ade to perform full and continuous contractions, bu t will always respond even to continuous stim ulation, with small rhythm ic con­ tractions only. All the individual fibres in a complete muscle work on the same principle, except th a t a phase displacement occurs in such a manner, as to cause a large num ber o f fibres to be in a state o f refractory rest while others undergo contraction. Thus if a muscle is m ade to contract by a to o rapid succession- o f stimuli, regardless o f the refractory period, the contraction intensity rapidly falls, the stimulus intensity rem aining constant, since a n increasing num ber o f muscles fibres, which can no longer rise to their previous level o f energy, are eliminated from the next stimulus. In selecting the rest period these facts m ust therefore be taken into account, and the selection made according to the extended refractory o r recovery period. (To be concluded in n ext issue.) R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. )