GB2136297A - Electronic Stimulation of Muscles - Google Patents

Abstract

An electrode harness for stimulating bodily movements in a human patient comprises two locating members 22, 23, extending longitudinally of a limb, for example a leg, electrode support bands 30 to 33 carrying electrodes 40 to 47, and securing them to the body of the patient. A locating member 24 passes under the instep to secure the harness against movement. A train of electrical pulses is supplied to the harness, and the voltage and spacing of pulses in the pulse train may be varied. By application of pulses to stimulate at least two separate muscles in the lower part of the body of a patient using means operated by the upper part of the body, complex movement of the lower part of the body e.g. walking, sitting or standing movement can be produced. <IMAGE>

Description

SPECIFICATION Method and Apparatus for the Electronic Stimulation of Muscles This invention relates in one aspect to apparatus for the electrical stimulation of muscles, for example paralysed muscles of an at least partially paralysed patient, to cause movement, for example walking, standing, sitting or the like.

It has been well known for many years that muscles stimulated with electricity can be caused to contract. A great deal has been written on the subject, and apparatus is available to stimulate a single muscle. I have now found that by applying to muscles of the body a pulse train of a particular form, and having a controlled voltage, smooth contraction of muscles can be caused, without spasm or so-called "tetanus" contractions of the muscle. I have also found that, by applying electrical stimulation simultaneously to two separate muscles in the lower part of the body of the patient, simultaneous contraction of two muscles of the lower part of the body can be caused to generate complex movement of the lower part of the body. Such movement can be generated in a partially paralysed patient by a functioning upper part of the body, for example a hand or arm.

Furthermore, I have discovered that the electrical voltage required for stimulating various muscles of the body to movement varies, making desirable means for controlling independently the voltage applied to different muscles of the body to cause contraction.

Previous attempts to stimulate muscles electrically have generally been carried out by affixing electrodes to the skin, for example by means of adhesive tape or the like. This method is adequate for experimental purposes under hospital conditions, but it has the disadvantage that, if it is desired to attach a large number of electrodes, for example sufficient to stimulate the legs to a walking-type movement, a substantial length of time is required. Furthermore, the placing of the electrodes in the correct position on the body requires substantial experience, and is prone to error. With a view to minimising these substantial difficulties, I have devised an electrode harness for maintaining a plurality of electrodes in electrical contact with a human limb.

In accordance with a first aspect of the invention, there is provided an electrode harness for maintaining a plurality of electrodes in electrical contact with a human limb, which could be an arm or a leg, which harness comprises a flexible support adapted to be secured to a human limb, a plurality of electrodes on the support adapted in use to contact the limb surface to permit the application of an electrical voltage thereto, and means on the harness for locating the harness with respect of the limb to maintain the electrodes in substantially fixed positions which respect to the limb.

In order to ensure good electrical contact between the electrodes and the limb of the patient, it is in general necessary to provide a conductive gel, between the electrode and the skin of the patient. In order to minimise smearing of such gel when the harness is applied, it is generally preferable that the harness should include means for enabling attachment to the limb by wrapping the harness around the limb, without the need to slide the harness longitudinally of the limb. Thus, for example, a plurality of lateral bands adapted to extend around the limb may be provided, and the electrodes may be affixed to the lateral bands.

Alternatively, but less preferably, the harness may simply take the form of a sleeve, sock, or the like, having electrodes affixed thereto at suitable points, and including some appropriate means, such as those discussed below, for ensuring correct location of the harness.

In a particular preferred embodiment of the invention, there is provided an electrode harness for fixing a plurality of electrodes to a human limb, comprising at least two locating members adapted to extend longitudinally of the limb, a plurality of electrode support bands affixed to the locating members and adapted to extend around the limb, and a plurality of electrodes affixed to the electrode support bands, adapted to effect electrical contact with the skin of the user when the harness is in use.

The locating means may simply take the form of means for enabling lateral bands, such as those discussed above, for example at the ankle or knee in respect of a leg harness, or at the wrist and elbow, in respect of an arm harness, to be tightened sufficiently to hold the harness in place.

However in a particularly preferred embodiment, the locating means may include means, for example a band, adapted to pass around the extremity of the limb, for example under the instep, or between the thumb and fingers of the hand, to restrain the harness against movement proximally of the limb. In a leg harness the band passing under the instep may be a continuous band which passes up both the inside and outside of the leg of the patient, both ends then being secured to a belt around the patient's waist. Such attachment to the clothing prevents movement of the harness distally of the limb.

The electrode support band are preferably spaced along the locating members at intervals so as to provide secure location of the electrodes in the region of the ankle, immediately above and below the knee, and on the upper thigh.

Adjustable means may be provided for fastening the locating members around the limb, for example by means of self-adhesive velvet like material such as that sold under the Trade Mark VELCRO or the like material. Electrode pads may also be provided for stimulating the psoas and adjacent muscles. Such pads may be likewise secured to the longitudinal locating members.

Connections to the various electrodes may pass along the locating members for connection to muscle stimulating electrical apparatus.

I have also found that the nature of the electrical voltages applied to the electrodes is of importance in obtaining the optimum muscle stimulation.

Electrical pulses of approximately 3 millisecond duration have been found to cause pain, whereas pulses of approximately 1 millisecond duration have the desired effect of causing the motor function of the muscles to operate.

According to-a further aspect of the invention, there is therefore provided apparatus for stimulating movement in a human patient, comprising a harness as described above, means for generating and applying to the electrodes a train of electrical pulses having a length of not more than 3 milliseconds, means for varying the spacing of pulses in the pulse train, and means for varying the voltage of the electrical pulses applied to the electrodes.

The means for varying the voltage is preferably such as to enable the voltage to be varied over a range of from 20 to 150 volts, and the means for varying the spacing of the pulses in the pulse train preferably permits variation over a range of from 5 to 100 pulses per second. It has been found that, at such voltage levels, a capacity to pass a current of up to 250 milliamperes is required.

The apparatus preferably includes means for simultaneously applying an electrical pulse train to two or more muscles, for example to the psoas ahd dorsiflexor muscles in the leg, to enable the leg to be lifted on electrical stimulation. It is particularly desirable that means should be provided to enable the voltage applied to separate muscles to be varied independently, since if excessive voltage is applied to a particular muscle, for example to the dorsiflexor in the front of the shin, leakage can occur to an adjacent muscle, for example the plantiflexor in the rear part of the leg, to cause simultaneous contraction of that muscle. Since, in general, the plantiflexor is a stronger muscle than the dorsiflexor, and works in the opposite direction, an opposite result of that required can be produced if the optimum voltage is exceeded.

In a particularly preferred embodiment, means may be provided for simultaneously activating the psoas and dorsiflexor muscles, to lift the leg, followed after a short time by actuation of the quadriceps, to straighten the leg, to enable walking. The pulses in the pulse train are preferably DC pulses having a generally squarewave form, although the detail of the shape of the wave form is not of particular impotance.

It has however been found advantageous to provide means for rounding slightly the leading edge of the square-wave pulses, since this has been found to minimise pain in patients.

According to a further aspect of the invention; there is provided apparatus for causing movement in at least partially paralysed patient, which apparatus comprises means for attaching at least two pairs of electrodes to the legs of the patient in positions so as to permit by application of a voltage to the electrodes the stimulation of at least two separate muscles in the lower part of the body of the patient, means for applying an electrical voltage to the pairs of electrodes to cause contraction of the respective muscles, and means operable by the upper part of the body of the patient to cause simultaneous contraction of at least two of the said muscles to generate a complex movement of the lower part of the body of the patient, for example a walking, sitting, or standing movement.Means operable by the upper part of the body of the patient may be brought into operation by the hands or arms, or any other function of the upper part of the body over which the patient has control.

We have also discovered that a particularly convenient aid for assisting a partially paralysed patient to walk can be provided by mounting apparatus as described above, on a walking frame, and providing on the walking frame appropriate switch means.

A number of preferred embodiments of the various aspects of the invention will now be described with reference to the accompanying drawings, in which:~ Fig. 1 is a schematic circuit diagram of apparatus according to the invention for causing movement in a patient, Fig. 2 is a schematic circuit diagram of a distribution box for use with the circuit of Fig. 1, Fig. 3 shows an electrode harness for a leg, Fig. 4 shows an optional part of the harness of Figure 3, Fig. 5 is an enlarged sectional view of one of the electrodes of Fig. 3, and Fig. 6 is a prospective view of an alternative electrode.

Figure 1 shows illustrates in schematic forms means for producing a pulse train, in a form of a pulse generator 2, of conventional form, and preferably taking the form of a known integrated circuit, with associated circuitry, for producing substantially square-wave pulses of one millisecond duration. The pulse generator 2 is powered by a battery 1, which may preferably be rechargeable. A variable resistance 5 permits the pulse rate to be varied. The output from the pulse generator 2 is connected to the input of a pulse shaping circuit 3, again of conventional form, for stabilising the shape of the wave-form produced.

Pulse shaping circuit 3 also causes the leading edge of the pulses to be somewhat rounded. The output from circuit 3 is passed to the input of means 4 for increasing the voltage. This may take the form of a simple transformer, adapted to produce the desired increase in voltage level. A variable resistor 6 permits the output to terminals 7 to be controlled as desired. The variable resistance 5 permits the rate of pulse generation to be varied over a range of from 5 to 100 pulses per second; and the variable resistance 6 permits the total output voltage to be varied over a range of from 20 to 150 volts. The pulse length is maintained constant at approximately 1 millisecond, since this has been found to give the greatest stimulation to the muscles with the minimum pain effect.

The output from terminal 7 is passed to the input of a distribution box, a schematic diagram of which is shown in Fig. 2. The distribution box simply comprises five outputs A, B, C, D and E connected in parallel to the input terminals 7, each provided with a respective variable resistance 8,9,10,11, and 12 and switch 13, 14, 1 5, 16, and 17. The switches 13 to 17 enable the pulse train produced at terminal 7 to be optionally connected to each of five sets of output terminals, and the voltage applied to each set of terminals can be varied at will in accordance with the setting of the variable resistances 8 to 12.In the arrangement shown, switches 14 and 16 are connected to electrodes for stimulating the psoas and dorsiflexors respectively, and are mechanically coupled together by a link 19, such that simultaneous operation of switches 14 and 17 is facilitated, to cause lifting of the leg.

Similarly, switches 13 and 16 are connected together by mechanical means shown as 18.

Switch 13 is connected to electrodes for stimulating the quadriceps muscle, and switch 16 to electrodes for stimulating the plantarflexors.

The output terminals from the distribution box are connected to electrodes mounted on a harness, as shown in Fig. 3. The harness of Fig. 3 comprises a pair of elongate locating members 22 and 23, made of a soft cloth material, and adapted to pass respectively along the outer and inner side of the leg of a patient. The elongate locating members 22 and 23 are continuous, in that they are joined by a loop part 24, adapted to pass under the instep of the patient. The upper ends 25 and 26 of the members 22 and 23 have loops 22a, 23a to enable the harness to be supported by the belt of a patient. Sewn into the elongate members 22 and 23 are connecting wires 27, to enable connection of electrodes on the harness to the output terminals of the connecting box shown in Figure 2.

Sewn to the longitudinal supporting members 22 and 23 are four lateral electrode support bands, 30, 31,32, and 33. Each band carries on the inside of one of its ends and on the outside of the opposite end (not shown) a strip of selfadhesive velvet-like material, such as that sold under the Trade Mark VELCRO. The bands 30 to 33 are adapted to extend around the leg, and be secured in an adjustable fashion by means of the VELCRO strips 34.

The electrode support bands 30 to 33 carry a plurality of electrodes, arranged in groups as follows. 40 and 41 are, respectively, the upper and lower sets of electrodes adapted to stimulate the quadriceps muscles, 42 and 43 are the upper and lower electrodes respectively for stimulation of the hamstring muscles, 44 and 45 are, respectively, the upper and lower electrodes position for activating the dorsiflexors, and 46 and 47, are respectively, electrodes positioned for activating the plantarflexors. All the electrodes within each set (i.e. sets 40, 41, 42, 43, 44 and 46) are connected together, and the sets are utilised in pairs, each pair being connected to one of the outputs A to E of Figure 2. For example, electrodes 40 and 41 are corrected respectively to the positive and negative sides of output A.The bands 30 to 33 are so positioned along the locating members 22 and 23 as to position the respective electrodes accurately at or close to the end of the respective muscle. Thus, the band 30 is located around the upper part of the thigh, band 31 just above the knee, band 32 just below the knee, and band 33 around the ankle.

Stimulation of the psoas and adjacent muscles may be caused using an electrode harness somewhat as shown in Figure 4, in conjunction with that shown in Figure 3. The apparatus of Figure 4 shows two sets of electrode pairs 50, 51 and 52, 53. These pairs of electrodes are mounted on supporting pads 54 and adapted to lie generally in the region of the groin, with the upper electrode 50 and 53 lying adjacent the end of the hip bone, and the lower electrode 51, 52 in the region of the upper part of the leg. The pads 54 are connected together by straps 55 of such a length as to allow the correct positioning of the pads, and securing tabs 56 are provided to enable the pads 54 to be secured to the outer elongate member 22 of electrode harnesses provided on each of the legs of the patient.

The electrodes are connected to the distribution box of Figure 2 such that electrodes 41,43,44,46, 50 and 53 have negative polarity, and electrodes 40, 42, 45, 47, 51 and 52 have positive polarity. In an alternative and a preferred embodiment, electrodes 51 and 52 are omitted, and electrodes 50 and 53 are used in conjunction with electrodes 40 and 42, electrodes 50 and 53 both having negative polarity, and electrodes 40 and 42 having positive polarity.

Figure 5 shows a cross section through an electrode assembly as used on the harness. The assembly comprises a brass disc 60 embedded in a silicone rubber pad 61. A connecting wire 27 is soldered to the rear of the brass disc 60, and a graphite electrode is secured to the front face of the disc 60. The whole assembly is embedded and a foam rubber pad 64, having a cloth backing 65, constituting the respective electrode support band 30 to 33.

An alternative, and presently preferred construction of electrode is shown in Figure 6.

The electrode of Figure 6 takes the form of a strip of graphite-loaded silicone rubber material 80 approximately 1 mm thick and 4.5 mm wide.

Raised portions 81 are provided at each end of the strip, and are provided with through holes 82 adapted to receive terminals for the connection of electrical wires to the electrodes. The strip illustrated in Figure 6 is approximately 20cm long, and can thus be cut to length to provide the various configurations of electrode provided on the harness. Thus, the set of electrodes 40 may be replaced by a single strip of the silicone rubber material of an appropriate length, and the single electrodes 44, 45, and 47 may be replaced by an approximately square-shaped piece of the silicone rubber material. The silicone rubber material may be stitched, glued, or otherwise affixed to the bands 30, 31, 32, and 33.

In order to ensure good contact between the electrode and the skin, an conductive gel is interposed between the electrodes and the skin surface. Any suitable conductive gel may be utilised, but it has been found that a particularly suitable gel may be formed by dissolving 60 grams of sodium chloride, 60 grams of cellulose wallpaper adhesive, 100 cl. of glycerine, and 2 cl.

of disinfectant in 1 litre of water.

In operation of the device, a harness is affixed to each leg of the patient, and the wires 27 connected to the respective terminals of the distribution box. Each of the variable resistances 8 to 12 are adjusted so as to produce the minimum output voltage, and the pulse generator 2 is brought into operation, initially using a nominal pulse rate of approximately 40 pulses per second, and a pulse width of 1 millisecond. The variable resistance 6 is adjusted so as to produce the maximum voltage likely to be desired, at output terminal 7. The variable resistances 8 to 12 are then each adjusted in turn with their respective switches 13 to 17 closed, so as to produce the minimum voltage pulse on each respective pair of electrodes capable of producing a smooth response from the respective muscle.When a response has been obtained, the pulse rate may be adjusted by means of the variable resistance 5, in order to ascertain the pulse rate at which the minimum voltage can be used for the patient in question.

In the preferred embodiment, the electrical apparatus is mounted on a walking frame, which the patient grasps. Switches 14 and 17 are simultaneously closed by means of the link 19, and this activates the psoas and neighbouring muscles, and the dorsiflexors respectively, which lifts the leg. It is an advantageous feature of the appdratus as described that some leakage of the electrical current occurs between electrodes of different pairs, since this has the effect of generally increasing the muscle "tone". When the leg has been lifted, switches 13 and 16 are closed simultaneously by means of link 18, to straighten the leg. Thus, walking can be achieved.

The first action lifts the leg, and the second straightens it. At the same time, the trunk must turn and the balance be moved from one leg to the other.

Standing can be accomplished simply by activating the quadriceps alone.

When a patient has been paralysed for a long period, strengthening exercises with and without stimulation should be carried out, together with practice in balancing, before successful walking can be achieved.

Claims (14)

1. An electrode harness for monitoring a plurality of electrodes in electrical contact with a human limb which harness comprises a flexible support adapted to be secured to a human limb, a plurality of electrodes on the support adapted in use to contact the limb surface to permit the application of an electrical voltage thereto, and means on the harness for locating the harness with respect to the limb to maintain the electrodes in substantially fixed positions with respect to the limb.

2. A harness as claimed in claim 1, including means for enabling attachment of the harness to the limb by wrapping the harness around the limb.

3. A harness as claimed in claim 2, wherein the means enabling attachment of the harness by wrapping the harness around the limb comprises a plurality of lateral bands adapted to extend around the limb, and wherein the said electrodes are affixed to the lateral bands.

4. A harness as claimed in Claim 3, wherein the lateral bands are spaced along the locating members at intervals so as to provide secure location of the electrodes in the region of the ankle, immediately above and below the knee, and on the upper thigh.

5. A harness as claimed in any one of the preceding claims, comprising a plurality of elongate location members adapted to extend longitudinally of the limb.

6. A harness as claimed in any one of the preceding claims, wherein the locating means includes means adapted to pass around the extremity of the limb to restrain the harness against movement proximally of the limb.

7. A harness as claimed in claim 6, adapted for use on a leg, wherein the location means includes a band adapted to pass down the outside of the leg, under the instep and up the inside of the leg.

8. A harness as claimed in claim 1, wherein the locating means includes means for attaching the proximal end of the harness to clothing worn by the user to prevent movement of the harness distally of the limb.

9. An electrode harness for fixing a plurality of electrodes to a human limb, comprising at least two locating members adapted to extend longitudinally of the limb, a plurality of electrode support bands affixed to the locating members and adapted to extend around the limb, and a plurality of electrodes affixed to the electrode support bands, adapted to effect electrical contact with the skin of the user when the harness is in use.

10. An electrode harness substantially as hereinbefore described with reference to, and as illustrated by Figures 3,4 and 5, or 3,4 and 6 of the accompanying drawings.

11. Apparatus for stimulating movement in a human patient, comprising a harness as claimed in any one of claims 1 to 10, means for generating and applying to the electrodes a train of electrical pulses having a length of not more than 3 milliseconds, means for varying the spacing of pulses in the pulse train, and means for varying the voltage of the electrical pulses applied to the electrodes.

12. Apparatus as claimed in claim 11, including means for simultaneously applying an electrical pulse train to two or more pairs of electrodes on the harness.

13. Apparatus as claimed in claim 11 or claim 12, wherein the pulse generating means is mounted on a walking frame, the frame including switch means mounted on the frame for operation by the hands of a patient for controlling the application of the electrical pulses to the electrodes of the harness.

14. Apparatus as claimed in claim 11 for stimulating movement in a human patient, substantially as hereinbefore described with reference to, and as illustrated by Figures 1 and 2 of the accompanying drawings.