CA1314941C - Flexible coil construction for electromagnetic treatment of an afflicted body region - Google Patents

Abstract

F.6105 FLEXIBLE COIL CONSTRUCTION FOR ELECTROMAGNETIC
TREATMENT OF AN AFFLICTED BODY REGION

ABSTRACT OF THE DISCLOSURE

The invention provides a thin, flexible, comfortably wearable coil for use in electromagnetic therapy of body tissue. The coil comprises plural turns of a single coil in radially spiralling adjacency and by forming all turns from the same single length of bunched multiple strands of flexible insulated conductors of equal gauge. First and second connections for lead-cable connection to a signal generator are each made to all strands at the respective ends of the coil, and axially flexible means retains the radial adjacency of the turns of the coil.

Description

~ :~31~9~

FLEXIBLE COIL CONSTRUCTION FOR ELECTROMAGNETIC
TREATMENT OF AN AFFLICTED BODY REGION

BACKGROUND OF THE INVENTION

This invention relates to the treatment of living tissues and/or cells by altering their interaction with charged species in their environment. ~ore particularly, the invention relates to an electromagnetic body treatment device for surgically non-invasive modi~ication of the growth, repair and maintenance behavior of living tissues and cells by a specific and selective change in electrical environment.
Ryaby, et al U.S. Patent Nos. 4,105,017, 4,266,~32 and 4,266,533 describe means for effecting surgically non-invasive direct inductive coupling to an afflicted body region, whereby one or more electric voltage and concomitant current signals conform to a highly specific pattern and have been found to develop therapeutically beneficial treatment of the afflicted region, as for example in the enhancemènt of repair of bone fractures, non-unions, and the like. In general, the involved treatment head or heads have involved one or more large coils, which have served well for the treatment of large-member bones, as in leg regions. And various speciaI-purpose coil and head configurations have been disclosed for specific treatments. In general, it may be said that it has been preferred practice to employ a treatment-head configuration in which two like coils are electrically connected in flux-aiding relation and have 24 flexibly articulated connection to enable strapped application Ib 13:~4941 on opposite sides of an afflicted llmb, and with the coils on a common axis of magnetic-flux development through the afflicted region; in this situation, as in the vast majority of bone-treating uses of such treatment heads, they are removably applied to the outside of a plaster cast or other means of immobilizing the site to be repaired. The coils are therefore bulky and awkward, and they limit freedom of movement while in use.
Pescatore, U.S. Patent No. 4,501,265, describes a coil configuration wherein bulk is reduced and use is simplified, in that the configuration is unit-handling, does not require strapping, and yet achieves the effect of two spaced coils driven in flux-aiding direction; this effect results from the par-ticular twisting of a single large coil into a figure-8 pattern, to establish two loops which are then folded to establish these loops in spaced parallel relation on a common axis, and the body member to be treated is interposed between the folded loops.
Talish, et al U.S. Patent No. 4,550,714 recognizes the desirability of reducing the bulk and awkwardness of conventional coil-head configurat:ions by designing them for castability, i.e., for embedment within an immobilizing cast.
But to achieve assurance of adequate in-depth flux development in a given body member, the coils of said application~rely upon the recognized effectiveness of two spaced coils, connected in flu~-aiding relation.
Moore, U.S. Patent No. 4,616,629, recognizes the desirability of further reducing the bulk and complexity of castable coils b~ disclosing a single-coil configuration, wherein an otherwise flat circular multi-turn coil is so permanently deformed as to establish a first generally U-shaped projection of the coil in a first viewing aspect which is normal to the coil a~is, and in which the deformation is also such as to establish a second generally U-shaped projection of the coil in a second viewing aspect which is normal to the coil axis, these two viewing aspects being orthogonally related.
The depth of the deformation is common to each of the U-shapes 13t~L9~

and is approximately one fourth of the combined span of the two U-shapes. The net result is to enable one of the U-shapes to be selected for general conformance with curvature of the limb to be treated, whereby a substantial development of magne-tic-flux density-of relatively uniform intensity is available at the in-depth situs of -tissue that is subjected to osteogenic therapy.
The kind of treatment for which coils of the foregoing nature are best suited involves afflictions to a limb, in which case immobilization of the treated region is important. But any attempt to use such stiff and bulky coils for electro-magnetic field therapy of the back or hips can be a source of real discomEort, due, for example, to the patient lying on the rigid form of the wire coil, which often is as much as 12 inches (30-cm) in diameter. Even if the coil is preformed to the approximately desired local curvature of the human body, it is still not comfortable over many hours of daily treatment.
~oreover, to hold such a coil in place on the body requires a garment in the nature of a large belt or sash, elasticized trunks, or the like. But a large rigid form still has a propensity to move relative to the body when the wearer turns or lies in different positions, thus introducing possibly undesirable changes in the field at the target site.
BRIEF__TATEMENT OF THE INVENTION
It is an object of the invention to provide an improved coil configuration for surgically non-invasive magnetic-field treatment of an afflicted body region.
A specific object is to provide an improved coil construction which will provide relief from the discomfort and other difficulties inherent in using conventional constructions for the treatment of the back or hips.
Another specific object is to meet the above objects with a flexible single-coil configuration, i.e., with a coil (a) which is 1exibly adaptable to an afflicted part of the body/ (b) which does not require the cooperative concurrent action of another coil in order to establish a substantial in-depth distribution of relatively uniform magnetic flu~, and (c) which, in a mode of use which does not involve a cast, will adapt to ar~iculating changes in locally involved curvature o~ the body.
A further speciflc o~ect is to meet the above ob~ects with a coil construction which is so thin and flexible as to be comfortably wearable on or wlthin a body-fitting garment or ~o be retainable to the body as by tape, bandage or the llke means.
The lnven~ion achieves the foregoing objects and provides further features, using plural turns of a single coil in radially spiralling adjacency and by forming all turns from the same single length of bunched multiple strands of flexible insulated conductors of equal gauge. First and second connections for lead-cable connection to a signal generator are each made to all strands at the respective ends of the coil, and axially flexible means retains the radial adjacency of ~he turns of the coil.
DETAILED D~ESCRIPTION OF THE INVENTION
The invention will be illustratively described in detail ln conjunction with the accompanying ~rawings, ln which:
Flgure 1 ls a perspective view of a co~l configuration of the invention, applied to an a~flicted shoulder regionr with connections for electromagnetlc treatment of the region;
Figure 2 is a plan view o~ the coil of Flgure 1, in flattened conditlon, to permit identification of features and pxoportions;
Figure 3 is an enlarged fragmentary se~tional view ta~en at 3-3 of Figure 2; and Figure 4 is a view similar to Figure 3 to show a :~ .
,,~ ~,., 131~g~ 71010-4 modification.
Figures Sa and 5b show plan and side eleva~ional vlews, respectively, o~ a coll constructed in accordance with the present invention.
Fiyures 5c and 5d show the magnitudes of magnetlc fields developed within a treatment volume along the depth axis Z of Figures 5a and 5b, respectively.
Figures 6a and 6b show plan and elevational views, respectively, of another embodiment of a coil constructed in accordance wlth the present invention.
Figures 5c and 6d show the magnitudes of magnetic fields generated along the depth axis Z of Figures 6a and 6b, respectively.
In Figures 1 to 3, the invention is shown in application to a slngle coil 10 of multiple turns of a single length of bunched multiple strands of flexible insulated conductors of equal but rela~ively fine gauge wire. The;turns are in radially spiralling adjacency, forming a thin annular dlsc havlng relatively great axial flexibility whereby, although initlally producible flat ~as suqgested in Fiqure 2~, the coil 10 may readily adapt itself to locally applicable body contours (as suggested by the contour-conforming drape of coll 10 around an afflicted shoulder region 11 of a human body 1~). As shown in Figure 1, 4a ~ 3 1 ~

an upper suspension strap 13 wraps over the opposite shoulaer, and a lower such strap l~ wraps the body beneath said opposite shoulder. Corresponding first ends of these straps may be secured to coil 10 at location A in Fig. 2, and corresponding opposite ends of these straps may be secured to coil 10 at location B in Fig. 2. The ends of coil 10 are shown to terminate at a receptacle 15 at one of the locations A, B, for removable connection via a plug 16 and flexible cabling 17 to a pulse-signal generator 18. For present illustrative purposes, it may be assumed that a fracture or other condition to be treated exists within the included volume defined by and between the front and back wraps of coil 10 over and around the involved shoulder.
The relatively great axial flexibility of coil lO results from using bunched multiple strands of fine-gauge conductors as the single length from which the multiple turns of the coil are developed. The multiple turns may be developed to a circular, elliptical, rectangular or other general outline, but in Fig. 2 the outline is generally elliptical, to an outer major-axis dimension ~, an outer rninor-axis dimension Y, and to annular (radial) width W. Generally, tne X:Y relation will be in the range l:l to 2:1, and will be of size and proportions which depend upon the in-depth volume to be targeted ~or therapy within the body; the radial width w is generally in a range 5 defined by the expression w = k P, where P is the outer 2~
perimeter of the coil, and the value is in the range 0.15 to 0.75.
The bunched multiple s-trands are preferably of so-called "Litz wire", which is a commercially available product designed to reduce a-c losses in high-frequency apparatus; in the present case, however, Litz wire is preferred for its mechanical properties of extreme flexibility and durability under flexion. For present purposes, copper wire is preferred because it is readily available and because it offers lowest resistance for smalle~t cross-sectional area. This is important because both low resistance and compactiveness are separately important characteristics of coil 10.

131~9~1 Each gauge of Litz wire is available in many forms, whlch are stated for their AWG-equivalent gauge. For example, for 24-AWG equivalence, these can range from 3 strands of 28-AWG
wire to 300 strands of 48-AWG ~Jire. For present purposes, it is desirable to use a-relatively large number of strands to ensure good flexibility and durability, but not to use excessively fine strands, since cost is thereby significantly increased, and sectional area and weight also increase significantly for a given overall resistance value. The appropriate range for strand size is 24 AWG to 38 AWG.
Increased flexibility for a given size can be realized by use of softer copper alloys, but at increased expense.
Wha-tever the selected AWG-equivalent size and the AWG size of strands to make up the AWG-equivalent size, all individual strands are conductively connected at one end to a first -terminal 21 and at the opposite end to a second terminal 22, it being understood that these are the terminals within receptacle 15. In Fig. 2, the showings of coil 10 at 24, 25 are expansive, for the sole purpose of suggesting the multiple strands of the single length 23 of Litz wire, and it will be further understood that no such expansion is needed in the construction of coil 10.
Fig. 3 is a fragmentary showing of -the section of coil lO, wherein the Litz wire is of bunched circular section. And Fig.
4 is a simi]ar showing, for the situation in which the Litz wire is of bunched rectangular section, wherein the rectangular section has a relatively long dimension and a relatively short dimension, and the radially spiralling adjacency of successive coil turns is with respect to the long-dimension sides of the rectangular section. In both cases, the radially spiralling integrity of coil 10 is illustratively retained by a thin-gauge flexible annular envelope 26, as of vinyl, suitably of 1 to 3-mil thickness and in vacuum-sealed wrap of the coil.
Two illustrative éxamples of use of the invention will be given.

~3~9~

Example 1, a coil 10' for clinical evaluation of treatrnent for failed spinal fusion by pulsed electromagnetic fields.
In this case, the coil 10 is circular and consists of a single layer of 34 turns of 20-AWG-equivalent wire, wherein the wire consists of 66 filaments (strands) of 38-AWG wire. Each filament is individually insulated and the 66-strand bundle is wrapped in nylon, the same being type NEL B66/3~SPSN, a product of New England Electric Wire Corporation. The annular form of this single layer has an inner radius o 8.5 inches and an outer radius of 11.5 inches, all encased in an annular envelope of flexible ~inyl.
The coil 10' is worn in place against the lumbar region of the bac~ and, because of its flexibility, the coil conforms to the involved body contours, generally as shown in plan in Fig. 5a (looking at orthogonal axes X-Z) and in side elevation in Fig.
5b (looking at orthogonal axes Y-~); for an erect body, the axis ~-X is horizontal and the axis '~-~ is vertical. The lumbar region of the baclc is taken as tangent to the plane ~-Y, and the normal Z to the plane ~-Y is indicative of penetration depth into the body, dimensional numbers being shown in centimeters, with the central a~is of the coil determining the Z axis, through the center of the afflicted lumbar region. As seen in plan (Fig. 5a), the coil 10' appears as a stretched-out letter "w", with a depth dimension Hl of approximately one inch.
For the treatment of a failed spinal fusion, pulsed mag-netic-field therapy with the coil 10' of~E~ample 1 is in thè
form of bursts of pulses. Each burst has a duration of 50 milliseconds, and there are two bursts per second. Each burst contains 190 pulses. T,lithin each individual pulse, the magnetic field of the coil linearly increases from zero for 250 microseconds, then linearly decreases back to zero for eight microseconds, followed by a four-microsecond quiescent period ~before the next pulse.
The field is obtained by driving the coil with a current which has the above time characteristics and ~aries from zero to a ma~imum of 2.1 arnps. The magnitudes of the magnetic ~ield ~31~9~L

at points within the treatment volume can be mapped as il~u-strated in Figs. sa and 5b, to obtain values tabulated in Figs.
5c and 5d, for two specific planes of offset from the X-Y plane of body tangency, namely, at depths of 6 cm and 10 cm, respectively; the points for which values have been measured appear as dots in Figs. 5a and 5b, namely in parallel planes at 2-cm increments along the depth axis Z, but the mapped data are presented in Figs. 5c and 5d only for outer planes which are spaced to define between them the zone of relevant therapeutic 10 concern. Since the therapeutic effect is related to the electric field induced in the tissue by the time-varying magnetic field, the mapped values are characterized in Tesla/sec, measured during the rising portion of the pulse.
Field values deemed realistic for treatment of the indicated affliction are in the range 0.7 to 1.4 Tesla per second; this is a 2:1 range for which therapeutic benefit is deemed to be substantially uniform. Reference to Figs. 5c and 5d reveals such substantially uniform distribution, at least to the extent ~8 cm, on either side of central intercepts with the Z-axis.
In the indicated application to failed spinal fusion, pulsed-magnetic-field treatment is applied for ten hours each day, for up to twelve months.
In Example 1, the characteristics of the desired pulse of 25 the current into coil 10 allow an acceptable LR time-constant to be achieved using a relatively fine gauge of wire. In certain other circumstances, it is necessary to have a lower wire resistance and thus to use strands of heavier gauge.
_ample 2, a coil 10" for evaluating treatment of avascular 30 necrosis in the head of the femur by pulsed electromagnetic fields.
In this case, the coil 10" is placed around the involved lower hip region. To obtain the desired signal in the target zone, the coil is necessarily of relatively large area and is 35 curved in its adaptation around the hip. This is achieved by making coil 10" of elliptical annular shape, namely, to a major-axis outer dimension (X) of 16 inches, to a minor-axis outer ~ 31~9~

dimension (Y) of 13 inches, and to an annular width W of 3.5 inches. The coil consists of a single-thickness radial-spiral development of 45 turns. And when its major axis is bent into a U-shape for wear around the hip, the span Sx between bent ends is 8.75 inches (see Fig. 6a). The coil 10"
conforms to involved body contours and is generally as shown in plan (Fig. 6a) and ln elevation ~Fig. 6b).
In Example 2, field requirements were such that much lower wire resistance was needed than in Example 1. Hence, a Litz wire of flat rectangular section was used, wi-th ll-AWG equiva-lence. This wire consisted of 98 strands of 30-AWG wire in a compacted rectangular section of 0.256-in width and 0.063-in thickness. Each filament is separately insulated and the entire bundle wrapped in fine nylon; and the bunched wire is type N~L B98/30HN, Erom said New England Electric Wire Corporation. Adiacent winding turns lie with contacting wide faces of the rectangular section. The resulting coil 10" has a well-defined elliptical annular shape, but it can readily flex about its minor axis into a curved saddle-like form, allowing close fit around the patient's hip.
The pulsing field used in the avascular-necrosis appli-cation of Example 2 is in the form of single pulses repeated at a constant rate of 72 Hz. During each pulse, the field is increased virtually linearly from zero to a maximum value over a 380 microsecond period, then decreased back to zero in an approximately exponential way, over a period of about 6.5 milliseconds. The field is produced by driving the coil with a current which has the above time characteristics and varies from zero to a maximum of 14 amps. The magnitudes of the magnetic field at points within the treatment volume have been mapped for each of the offset planes at Z=1, 3, 5 ...15, but the zone of therapeutic interest is between the planes at Z=9 cm and Z=15 cm, for which field mapping measurements are tabulated in Figs. 6c and 6d, respectively, with values stated in Tesla per second.
Field values deemed realistic for treatment of the indicated affliction are in the range 3.5 to 7.0 Tesla per 131~9~1 second, in which range therapeutic benefit is deemed to be substantially uniform. Reference to Figs. 6c and 6d reveals such substantial uniformity, at least to the e~tent + 8 cm in the X direction (Fig. 6a), and to the extent +2 cm in the Y
direction (Fig. 6b) at the plane (Z=9 cm) of Fig. 6c, and ~8 cm in both the X and Y directions at the plane (Z=15 cm) of Fig. 6d.
In the indicated application to avascular necrosis, the indicated pulsed-magnetic-field treatment is also applied for ten hours each day, for up to twelve months.
Coils of the invention will be seen to meet all the stated objects, being wound to a basic circular, oval or other form to suit the body feature and in-depth volumetric region of therapy required for particular cases. The thin flexible wrapper or envelope substantially retains the wound shape in two dimensions while permitting easy flexing in the third dimension. By using wire of many fine-gauge strands, a very durable conductor results, even when under constant flexing.
The coil is able to conform to the individual patient's shape and to changes in that shape under movement. This conformability assures a lesser tendency for the coil to migrate from its desired location on the body.
For greatest wearing comfort, the coil 10 is wound with all turns initially in a plane, forming a thin flat annulus. In some circumstances, there may be more than one layer of winding turns, but these should be as few as possible to keep the coil as thin as possible.
To have wound the coil in a ~lat annular form, with radially adjacent turns, results in a further advantage, when compared to the conventional multi-turn windings of a single conductor, as in the above-noted pri.or art. This further advantage arises from the fact that field strength close to the windings remains locally smaller in magnitude when the winding turns are dispersed in flat side-by-side relation, as distinguished from their being bunched. The range of field strength variation is thus reduced by the invention, within the :~ 3 ~

included volume defined by and between wrapped limits of the contour-conformed coil.
A still further advantage for coils of the invention is that a specific size and type coil can be used to serve any one of a greater range of anatomical sites and to suit a greater anthropometric range at each site, all as compared to the limited ranges of electrically equivalent conventional rigid coils. This is possible within limitations set by the overall size and shape of the target treatment zone, relative to the body surface against which the coil is adapted. As long as the field pattern of the particular coil can be matched to the target requirement in the body, and as long as the coil can be consistently replaced into its correct position and shape, the flexibility feature is a significant asset. And the reduced tendency to migrate with body movement contributes to assurance that the field pattern in space will not materially change.
While the invention has been shown and described for specific embodiments and examples, it will be understood that modifications may be made without departing from the scope of the invention. It will for exampLe be understood that variations in coil dimensions can be as extreme as are necessary to apply the invention to the particular body zone needed for any particular case, involving for example, coils as small as 5-cm diameter or as large as 60-cm diameter or more.
Also, reference herein to generally circular, in respect of the initial winding, will be understood to be for convenience of description, in tha-t initial winding shapes in use of the invention may just as well be other then circular, e.g.
29 pear-shaped, elliptical or otherwise.

Claims (10)

1. In an electromagnetic body-treatment device for surgically non-invasive modification of the growth, repair and maintenance behavior of living tissues and cells by a specific and selective change in electrical environment, comprising a single multi-turn electrical coil of initially generally circular configuration, wherein a central axis of symmetry extends normal to the plane of said coil, said coil having an external lead-cable connection, the improvement wherein plural turns of said coil are in radially spiralling adjacency and are formed from a single length of bunched multiple strands of flexible insulated conductors of equal gauge, said lead-cable connection comprising first and second terminal means in permanent conductive relation with all strands at the respective ends of said coil, and axially flexible means retaining the radial adjacency of the turns of said coil.

2. The improvement of claim 1, in which said coil comprises multiple turns of Litz wire.

3. The improvement of claim 1, in which said coil in flattened condition is characterized by an elliptical major/minor axis ratio in the range 1:1 to 2:1.

4. The improvement of claim 2, in which the Litz wire is of bunched circular section.

5. The improvement of claim 2, in which the Litz wire is of bunched rectangular section.

6. The improvement of claim 5, in which the rectangular section has a relatively long dimension and a relatively short dimension, and said radially spiralling adjacency is with respect to the long-dimension sides of said rectangular section.

7. The improvement of claim 2, in which the Litz wire is in the range from 10 AWG-equivalent to 26 AWG-equivalent.

8. The improvement of claim 1, in which said coil is an annulus of radial width W and perimeter P, wherein W = , and the value k is in the range 0.15 to 0.75.

9. The improvement of claim 7, in which the gauge of strands in the Litz wire is in the range 30 AWG to 38 AWG.

10. The improvement of claim 7, in which the number of strands in the Litz wire is in the range 50 to 100.