CA1238372A - Device for applying a high frequency electromagnetic field to living tissue to promote healing thereof - Google Patents

Abstract

Abstract Device for applying a high frequency electromagnetic field to living tissue to promote healing thereof A portable therapy device for attachment to a patient to promote tissue healing by exposure to an r.f.
field, comprises an oscillator (5) which energises an antenna having a transmitting element (1) the natural directive pattern of which is modified by a reflector (8) and a parasitic element (10) such that a major part of the r.f. field emitted by the antenna passes to the patient. In another embodiment the antenna is config-ured to produce a spatially substantially uniform field strength over the area of the patient being treated. The device subjects the tissue to r.f. power levels which produce no significant tissue heating.

Description

1~3~33~

Df~vi ce for applying a high fre~llerlc~
e~ectlc,lnag etic fiel_ to 1 V.7.11~
s~e to p~ ote _c.~ g t1lel-of il)is -inv~lltiorl rol~t~s to a 1c~ice l`or app1ying a high fLeqllency electro.lla~nel-ic rield to living ';issue to promote heali]lg thercof.
It has been kllown for many ycars that ;~nproved healing rates can be achieved by applying r~f. electro--magnetic fields to wounded tissue. The therapeutic effects were considered to be due to heating of the tissue by the field and prior therapy apparatus has been configured to produce r.f. energy levels for tissue heating either on the surface or deep into the tissue.
Thi heating technique is kno-~n as diathermy. It is known to pulse the r.f. field produced by diathermy apparatus. A specific example of the healing effects achieved with a pulsed field diathcrmy apparatus is given in "A Trial Involving the Use of Pulsed Electromagnetic Therapy on Children Undergoing Orchidopexy" R.H.C.
Bentall and H.B. Eckstein, Zeitschrift fur Kinderchirurgie und Grenzgebiete p. 380-398 November 1975.
HeretofOre the pulsed electromagetic field has been produced by hospital or laboratory based equip_ ment comprisisng an electrical signal generator which feeds an induction coil mounted on a stand, positioncd 1~383~X

adjacent an area of a ~)atient to he treated. This apparatus is bulky ~nd has t}-e disadvantage that a patient cannot be treated on a Co11ti~ 0Us intensive ~ sis without being 1~ocI~italis~d.
'lore ~ 3ltly, it h.ls 1~erl ~1pp ~ciated t1~at 11le theI-apy ~noduccd by an a~ lied r.f. f-ie]d is 7~0t ~1larac-terised solely ;n ter~ns o~ t]-e tics11e heati~1g eff~ct of ~he field. ~ dicc1Issioll of this sllbject is g ~cn in my paper e11titled ~1ealing by ~lectromdg1let;s1n ~ ct or Fiction" New Scientist 221ld April 1976.
I have devised lower po~-eI-ed ~ortable ~pp.lIa~us for producing the electrom~gnetic field, suit~b~e ~or bei11g attached to a ~atier1t. ~uch portable ~ trat1ls ;s dcscr;b~d in my 13ritish rate1-t nppli ~ ~lt i )n pllbl.i shed ~ der no. ~27594-1`his portab]e apparatus c~;-npIises a 1~attery d~ en r.f. osci]1ator a11d an antenna which is llex;ble to overlie an area of tissue to be treated. rhe i1pparatus thus can be attached to the patient and left running on a substantially continuous basis. The portable apparatus produces an electromagnetic field typically in the frequency range 3-30 MHz, the particular r.f. frequency not being of great significance as to the efficacy of the therapy. The r.f. field is pulsed in a manner to maximise the therapeutic effect. The field is of a strength which does not produce any s;gnificant tissue heating. The portable device thus operates at much lo~er~power levels than the bulky diathermy apparatus, typically to produce r.f. field of less than lOOmw cm as measured at the skin of the tissue, and utilising a fundamentally different premise as to the manner in which a r.f. field may be utilised to effect treatment, na,~ely that the field does not have to produce tissue heating in order to produce an improved healing rate.
A disadvantage of the portable device is that its ~Z;~8372 antenna transmits electramagnetic energy not only in a forward direction towards the tissue, but also in a rearward direction outwardly from the patient with the result that a substantial portion of the transmitted energy does not pass into the tissue. Also, the out-wardly passing energy may upset operation of laboratory or domestic electronic equipment. Furthermore, the prior flexible insulating substrate presents the un-desirable water and air impervious barrier over a wound which may impede healing in certain circumstances.
According to the present invention from a first aspect, which is described and claimed in parent Canadian aplication Serial No. 411,938, filed September 22, 1982, there is provided a device for applying a high frequency electromagnetic field to tissue of the patient to promote healing, comprising an antenna for directing the field to the patient, and an electrical oscillator circuit arranged to energise the antenna to propagate electromagnetic energy for promoting healing of the tissue but without producing any significant heating thereof, the antenna having a directive pattern so configured that a substantially greater proportion of said energy is propagated in a forward direction for treating the tissue than in an opposite rearward direction so as to minimise emission of said energy outwardly of the patient.
To this end, the antenna may comprise a transmit-ting element arranged to be energised by the oscillator circuit to propagate said energy, and reflector means for reflecting into said forward direction energy transmitted from said transmitting element in said rear-ward direction. Preferably the reflector means is so 1;~3~337~
arranged that the energy reflected thereby constructively adds to the energy propagated by the transmitting element in said forward direction.
The antenna may include additionally or alternatively to said reflector means, an absorber arranged to absorb said energy transmitted in the rearward direction.
The antenna may include a parasitic element for modifying the natural directive pattern of transmission of said energy from the transmitted element.
Preferably, the transmitting element comprises an electrical conductor arrangement formed as a loop encompassing a space permitting passage of fluids thereby allowing a wound in the tissue to breathe. If desired the space may include a wound dressing. The electrical conductor arrangement may comprise a loop of coaxial cable.
Other aspects of this invention herein are as follows:
A device for applying a high frequency electromagnetic field to tissue of a patient to promote healing, comprising an antenna for overlying tissue of a patient, said antenna encompassing a given area for treating a corresponding tissue area of the patient, an electrical oscillator means arranged to energize the antenna to propagate electromagnetic energy for promoting healing of the tissue but without producing any significant tissues heating thereof, wherein said antenna is arranged to produce said field with a ~0 spatially uniform field strength over at least a major portion of said given area, and said antenna presents an inductance to the r.f. energy produced by the oscillator means, and said inductance comprises a frequency determining circuit component of said oscillator means.
A device to be carried by a patient and for applying a r.f. electromagnetic field to tissue of the patient to promote healing thereof, comprising a flexible antenna for conforming to the shape of the patient, said antenna encompassing a given area for 4a ~3~3~

treating a corresponding tissue area of the patient, a battery, an electrical oscillator circuit arranged to energize the antenna to propagate electromagnetic energy for promoting healing of the tissue but without producing any significant tissue heating, wherein said antenna is arranged to produce said field with a spatially uniform field strength over at least a major portion of said given area, said antenna presenting an inductance to the r.f. energy produced by said oscillator, and said inductance comprising a frequency determining circuit component of said oscillator.
In accordance with this latter aspect of the invention it is possible to provide more predictable and quantifiable treatments than has been possible hitherto, because with the prior portable device the field strength to which the tissue is subjected varies across the spatial extent of the antenna and thus different tissue regions receive in effect different treatment conditions.

2(j Preferably the uniform field antenna is configured as a flexible sheet-like member to conform to a patient's body. For example, the antenna can comprise a flexible printed circuit which additionally carries components of a low voltage oscillator, typically powered by a battery.
In accordance with all aspects of the invention the inherent inductance of the antenna may be used as part of an L.C. circuit which defines the frequency of oscillation of the r.f. oscillator which energizes ~Z3837~

the antenna, in a mallner described in more detail in my British Patent Application l~ublished under no.
202759~.
In ord~r th~t the; ~ ltion may be IllOre fulLly und(l-stood ~ bodim-llts tE1~-~reof h'i Ll not~ be descri~J~d by l.ay of illustrative e~ plc with refcre11ce to the acco~ lyillg dr~ $s W1l~L'(' in:
ligllre 1 is a sch~lnatic plan v;ew of a device in Iccordlnce with the invention, Figure 2 is a sectional view of the de~-ice sho~ in Figure l taken ~long the line A' -A.
~ igure 3 is a scElelatic illllstration of .~notl1er I vice aecording to ~he i~ nti~n, for plodllling a spatially u1liforl-n field, and ~i~ure 4 is a schcmatic i~l1lstration of arlotl1er device L~ccording to the invention for ~rod~cing a uniform field.
Referring firstly to E~igures l and 2, the device includes a loop of coaxial cable l arranged in a suitable shape for overlying a wound~sore or like damaged area of tissue 2. The loop is flexible to conform to the surface of the patient's skin. At one end the cable l has its inner conductor 3 and its shielding sheath conductor 4 connected in an r.f. oscillator the major part of which comprises a circuit 5 shown schematically, the circuit 5 being mounted on a plastics support sub`~trate 6 which bridges the coaxial cable loop and is affixed thereto. ~le support substrate 6 also carries a battery power supply 7 for the oscillator~ The circuit 5 cooperates with the cable l to produce in the cable r.~. pulses at a predetermined repetition rate. The r.f. frequency may be in the range 3 to 30 MHz and desirably 27.12 MHz as this is a legally allowed frequency for medical uses E~owever the precise value of r.f. frequency does _ 6 - ~23~37X

not appear to be critical with regard to the efficacy of the treatment. rhe loop of coaxial cable 1 acts as the tr~nsmitting e]c~ent of .In clntenna ~nd propagates tlle r.f. en~gy ~ulscs. '`he Inlt~ al tran~ issi~
directive patt~rn in raclial section of the CO~lXi.ll cab1e 1 is substclntially uniform, .~nd +hus the r.f. ~nergy tetlds to be tr.lnsmitted by the .ab]e 1 both in a for~ d direction towards the tissue 2 to be t1e~ted ~nd a1so in a rearward direction away from the patient.
I-lowever~ in addition to the transmitting element 1, the antenna includes a reflector 8 which may co~prise a flexible metal mesh or a slleet of metal foil, ~-hich reflects the rcarwardly directed r.f. cnergy propdgated by the cable 1. l~le reflector 8 is sllitably spaced t5 from the coaxial c~lble 1 by rneans of a diclectric spacer layer 9, such that the r.f. energy reflected by t]le reflector 8 constructi~ely adds to the t-~nergy tr~ns-mitted by the cable 1 in the forward direction, thereby improving the r.f. energy density received by the tissue 2.
The antenna may include a parasitic element 10 comprising a loop formed of a plurality of turns of copper conductor wire 11 contained within a sheath 12. The effect of the parasitic element 9 is to modify the~natural directive pattern of r.f. propaga$ion from th ~ op of cable 1, such as to reduce emission in r~
~ transverse to the forward direction, and th~ff.~ovide the antenna with a main lobe in the forward direction.
Additionally, the antenna may include r.f.
absorbing material (not shown) for selectively absorbing rearward or sideways emitted r.f. radiation, so as to modify the directive pattern of the antenna as may be desirable in certain circumstances.
It is to be noted that the cable loop 1 surrounds _ 7 _ 123~3~

an open space 13 which may overlie a wound and which pcrmits the wound to breathe. ~e space may include a wound dressing (not shown).
The IJltel~a is lesilably driven to produce a r.f.
poh(r de~ y nieLls~ ed at the .~hin of tl)e ~ e 2 of l~ss ~h~n 100 mil]i~atts cm ;-~ld p~f~rably vf tbe or~ler of microwatts cm . ~liS locs not produce lny .si~nific.-lnt heating of the ti.ssue. l~le lepetition l'atC ~f 1lle r.f.
pulses is selected such to Inaxi~ll.ise the f~icl~y of the treatment. Typically~ the pulse repetition rate is ;.n the range 0.1 l~z to 10,000 }{z.
At r.f. frequencics, the coaxial cable pres(rlts an inductance bet~-een its -inner conlluctor 3 ~nd its shieldillg inductor 4. Fhis inductance is utili.s(d as a ~leqllel1cy determining component of the oscil.lator cileuit 5. This arrangement has the ad~ ntage that t.he circuit 5 need not include any inductors. I`lle oscillator essentially comprises-an L.C. ci.rcuit fed by a transistor, of which the L component is defined by the inductance of the coaxial cable wherein the oscillator components, apart from the L component are contained by the circuit 5. The circuit 5 can therefore be conveniently fabricated as a monolithic integrated circuit.
In a modification to the dcscribed device1 the support substrate 6 which carries the circuit 5 and th~ ~attery power supply 7, may be detachable from the antenna, for re-use with a new antenna over a different wound~.
The antenna may include on its front face a self adhesive material for attachment to the skin. The self adhesive material may extend outside of the perimeter define& by the cable loop 1.
It will be appreciated that the antenna described herein is flexible and can confor~ to the shape of the skin of a patient. Whilst as shown in Figure 1, the coaxial cable 1 is arranged in an elliptical loopg ~ 1;238372 it may be arranged in other shapes selected to co~form to contours of-p;lrticular p~rts of the anatomy, for example the jaw or the nose, the limbs or the trunk.
A p.~ir of the antcnn~s c.ln be c-nfigured i.n a ~n~lmer similar to a p.~ir of goy~lcs, for tLe;ltme1lt o~ ~he e~-eg.
AIso, more than o1le c~nte11na can be driven ~y a common oscillator circuit. rhe oscillator Cil~Uit m.ly be al~r~nged to dl~ive the ltl~n~ae in a predet-r~ d sequence.
In an alternative embod;ment~ the c~ndllctors ~f the traln~mitting element and the plrasitic e].~merlt may be formed in a loop on a flexib~e printed circuit board, cllld the reflector may be ~olmed ~y a ~lle~ 1is<ltion layer or pattcrn on the board. ~ref(~l~ably the i-lntellna is cvnfi~ured to present to the tissl1e a ~bst.-lti~lly uniform sp~tial r.f. power density at 1cast o~er a major portion of the area ~f the arl1enna facin~ the tissue.
Fhe devices shown in Figures 3 clnd 4 are illustrative of embodiments which achieve a spatially uniform electro-magnetic r.f. field for treating a patient~ the field being uniform over at least a major portion of the spatial extent of the antenna which in use faces the patient~ The teaching of the spatially uniform field given hereinafter with reference to Figures 3 or 4 may be used in combination with the teachings given in relation to Figure 1 and 2, or separately.
Referring to Figure 3 a flexible printed circuit substrate 15 carries an antenna comprising a metall-isation pattern 16 as shown, which is connected to anintegrated circuit 17 mounted on the substrate. The integrated circuit 17 is powered by a battery supply 18 also mounted on the substrate. It will be appreciated that the circuit 16 and battery 17 may correspond to the circuit 5 and battery 7 of Figure 2. In use, the 123~3372 _ 9 _ substrate 15 over~ics liviug tis~ue to be treated, ~nd typically is attachcd to a ~atient~s skin by adhesive means, not shown. 'Mle intcgrated circuit 17 co~nprises co~ oncllts of an osc,i11ator ~llld ti,lner cir~uit Irranged to cn~rgise the metll~isltio~l l)att~ l16 ~i,lh r.f. ~ lscs.
As dcscribed with referellce to Figllre 2, the i~ ctallce of the ~Intenna ll~ay be ll~cd as a frcquellcy de1,er~l;,7ling cornponent of the oscillator. 'I`l-e fr~ uellcy of ~he r.f.
energy typically lies within a range of 3-30~ " ~Ind is conveniently 27.12 ~illz. It will be seen that the mctallisation pattern 16 encompasses a given sllbstrate area alld will thus treat a c~rresponding area of the patiellt's tissue wllich ullderl;es the ~ubstrate 15. The -~ t.~ ation ~tt~rn 16 is ,o c<~ red th~t lll~re is ~mitted in tlle directi,l)n of the ti sue a pulsed r.f.
electromaglletic field hhich h~Y a substantially ~niform field strength at least over a major port;,on of the substrate 15. ;l~e field strellgth is desirably not ~reater than lOOmw cm and preferably is of the order of microuatts cm . This field strength does not produce any significant tissue heating. The metall-isation pattern includes a plurality of linear conductor portions 16a running parallel to one another transversely of the length of the substrate 15.
The r.f. pulse repetition rate is selected such as to maximise the efficacy of the treatment.
The flexible substrate15 has the advantage of being abl~,,to conform to the surface of the skin of a patient, and thus can wrap around a limb for example.
The device shown in Figure 4 is similar to that of Figure 3 but with the conductor portions 16a running longitudinally of the substrate 15.
~Sany modifications and variations within the scope of the invention will be apparent to those skilled in the-art. ~or example, rather than using a flexible ~Z3837~

printed circuit, tlle pattern of conductor portions defining tlle alltenrla can be formed from a serpentine conductor arranged in either of the patterns shown i.n ~'ig.s. 3 or 4, wi.th all electrical.ly ;.n.s~ ting co~-ering ho~di~lg tl-e conriuctor .i.n its serpe~lti.ne confi.guration.
.

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A device for applying a high frequency electromagnetic field to tissue of a patient to promote healing, comprising an antenna for overlying tissue of a patient, said antenna encompassing a given area for treating a corresponding tissue area of the patient, an electrical oscillator means arranged to energize the antenna to propagate electromagnetic energy for promoting healing of the tissue but without producing any significant tissues heating thereof, wherein said antenna is arranged to produce said field with a spatially uniform field strength over at least a major portion of said given area, and said antenna presents an inductance to the r.f. energy produced by the oscillator means, and said inductance comprises a frequency determining circuit component of said oscillator means.

2. A device to be carried by a patient and for applying a r.f. electromagnetic field to tissue of the patient to promote healing thereof, comprising a flexible antenna for conforming to the shape of the patient, said antenna encompassing a given area for treating a corresponding tissue area of the patient, a battery, an electrical oscillator circuit arranged to energize the antenna to propagate electromagnetic energy for promoting healing of the tissue but without producing any significant tissue heating, wherein said antenna is arranged to produce said field with a spatially uniform field strength over at least a major portion of said given area, said antenna presenting an inductance to the r.f. energy produced by said oscillator, and said inductance comprising a frequency determining circuit component of said oscillator.

3. A device according to claim 2 wherein said antenna comprises a flexible insulating substrate for overlying a patient's tissue, and a metallization pattern formed on the substrate.