US3344792A - Method of muscular stimulation in human beings to aid in walking - Google Patents

Description

Oct. 3, 1967 OFFNER ET AL 3,344,792

METHOD OF MUSCULAR STIMULATION IN HUMAN BEINGS TO AID IN WALKING Filed Jan. 13,- 1965 INVENTORS I Fran/(Lin F OfF/ver 10 v h LacLcmirneodoreLLberson A5 Hm I: rQfi/SQD ATTORNEYS United States Patent 3,344,792 METHOD OF MUSCULAR STIMULATION IN HUMAN BEINGS TO All) 1N WALKING Franklin F. Oifner, 1890 Telegraph Road, Deerfield, Ill.

60015, and Wladimir T. Liberson, VA. Hospital, Box

28, Hines, Ill. 60141 Filed Jan. 13, 1965, Ser. No. 426,476 1 Claim. (Cl. 128-419) This application, which is a continuation-in-part of application Ser. No. 110,433, filed May 16, 1961, now abandoned, relates to electrical therapy in humans having mus cle disfunction, and in particular to means by which individuals having such disfunction may regain at least par tial utilization of their muscular function.

In the past, therapy of muscles subject to various sets of illness has been conducted by application of electrical currents for stimulating the muscles. Such electrical currents, while having possible therapeutic benefits, have not been capable of themselves providing useful muscle function. In particular, in individuals who have lost their neurological control of muscular function, it has been impossible to secure useful muscle functioning, even though the muscular electrical therapy was such as to maintain the muscle in healthy physiologic condition.

A particular object of the present invention is to provide an improved method for usefully stimulating muscles into operational functioning, apart from the normal neurological stimulation of the muscle or muscles involved. In particular, this objective is obtained by controlling the application of a pulse-type stimulating current to the muscle involved in a periodic manner coordinated to periodic movement of a member of the human being having a normal mode of motion physiologically correlated with the normal functioning mode of the muscle or muscles to be stimulated.

A more specific object of the invention is to provide an improved method for stimulating into action in a periodic manner the toe raising tibialis anticus and peroneus longus muscles of the leg of the human being not otherwise under proper neurological control in order to obtain a quasi-normal use of these muscles to assist in walking. According to the improved method, application of a pulse-type stimulating current to these muscles in a periodic manner is controlled by the periodic up and down movement of the heel part of the foot on the leg involved, periodic raising of the heel during walking serving to turn on the stimulating current and lowering of the heel serving to turn off the stimulating current. In this manner, the person involved receives the necessary muscular assistance for raising the toe during walking in a manner essentially normal.

Other objects and advantages of the invention will become more apparent from the following detailed description of an exemplary embodiment of the invention in conjunction with the accompanying drawings wherein:

FIG. 1 is a View of the lower portion of the leg and foot showing the electrode pads in place over the tibialis anticus and peroneus longus muscles and the heel-controlled switch for actuating the electrical stimulator; and

FIG. 2 is an electrical schematic view showing the circuit details of the electrical stimulator.

Due to a number of pathological conditions in patients, they may lose neurological control of muscular function. A very common cause of such loss of neurological control is disease in the central nervous system. Certain diseases in the region of the brain controlling motor function may cause the loss of neurological control of muscular function on one side of the body, or a portion thereof. Such a condition is termed, hemiplegia. The effect of the disability on a patient may be such as to prevent normal activities, due to the lack of ability of control of critical muscles.

Patented Oct. 3, 1967 As a concrete example, a common disability is the inability of the patient to control the tibialis anticus and the peroneus longus muscles in one foot, muscles which control the raising of the toe from the ground, as during walking. While these muscles may be relatively healthy, with no control of the muscle through nerve fibers, the subject is unable to make use of the muscles. This is a type of subject which we have been able to help substantially with our invention.

What the invention does in this case is to stimulate the tibialis anticus and peroneus longus directly or through the nerve which activates them into quasi-normal use each time the heel of the subject leaves the ground. This stimulation is accomplished by electrodes placed over the muscle and the nerve. The stimulator, which generates the particularly effective currents later to be described, is activated by a switch under the heel of the same foot, so that when the heel is raised from the ground, the stimulator is turned on. The current then stimulates the muscle, causing the toe to be raised at the same time.

With reference now to the drawings and to FIGS. 1 and 2 in particular, the tibialis anticus muscle 1 to be stimulated is shown in dotted outline in its approximate location in the leg of the subject. An electrode 2 is placed on the skin over this muscle. The peroneus longus muscle 3 is also indicated in dotted outline and an electrode 4 is placed on the skin over this muscle and on the peroneal nerve 5. Electrodes 2 and 4- will be made in various sizes, so that for each individual to be aided, a proper balance between their respective actions will be achieved. In some cases, one or both of these electrodes may be implanted in the muscle itself.

As shown in FIG. 1, the two electrodes are connected 'by suitable conductors to the output terminals 11 and 12 of a stimulator unit 6 which will be carried by the individual in some suitable and comfortable manner, not shown. The stimulator 6 itself is controlled by a pressure responsive foot-actuated electrical switch 7 which is connected to the input terminals 8 and 9 on the stimulator unit. The contacts of switch 7 are closed in the absence of pressure but are opened when pressure is applied to a pad 10 within which the contacts are enclosed, the pad 10 being located beneath the heel of the individual, and the switch contacts being opened as the individual rests his heel upon the ground. As will be later explained, opening of the switch contacts serves to interrupt the pulse output from stimulator unit 6. When, however, the individual raises his heel off the ground, which is the initial action involved in taking a step, pressure is released from pad 10 and the contacts of switch 7 close thus starting stimulator unit 6 into operation, and causing the stimulating current to flow from output terminals 11 and 12 to the two electrodes 2 and 4. The current flowing through electrode 2 which is directly over the tibialis anticus muscle 1 causes it to be artificially stimulated into action in the same manner as would be caused normally by a signal carried thereto from the brain over the related nervous system, whereupon the muscle contracts thus raising the toe and permitting essentially normal walking. The same action takes place as regards artificial stimulation of the toe raising peroneus muscle 3 from electrode 4.

In order to obtain stimulation of muscle through the skin, without causing discomfort to the individual, we have found it desirable to carefully control the type of current employed. Preferably the current should be in the form of brief pulses having a duration of fifty microseconds or less, and should be applied from fifty to one hundred times per second. The amplitude of the current required will depend upon the muscle to be stimulated, but may be in a range of the order of from fifty milliamperes to several hundred milliamperes.

While these current parameters are the range which we have found most desirable, it is to be understood that widely varying parameters may be used. For example, we have, on occasion used currents as long as one millisecond in duration but with somewhat more discomfort to the individual, however.

Stimulation of the muscle as has been described is not merely a therapeutic method, in order to keep the muscle healthy, but actually becomes a substitute for the individuals own nervous system, providing effective utilization of the individuals muscles. As such, it may be used routinely and continuously by the individual, for the normal functioning of his limbs, for example. It is thus quite desirable and practically essential that the stimulator employed be suitable, and particularly that it be very light in weight and be able to be powered by small batteries which the individual may readily carry, and which will last for a reasonable length of time. It is, of course essential also that the stimulator unit develop the proper waveform of current.

The stimulator unit, in accordance with our invention is particularly well suited to this use. It develops a stimulating current of the proper waveform, uses a minimum of electric power from small dry cell batteries and is very small and light in weight. The electrical circuit of the stimulator unit 6 is illustrated in FIG. 2. There it will be seen that the circuit comprises a transistor 13 capable of delivering large current impulses. These current impulses are furnished from a dry cell battery 14. Since small dry cell batteries will usually develop an appreciable internal resistance as they discharge; and since large, but brief, current pulses must be delivered to the transistor, the battery circuit is preferably by-passed by a large capacitor 15, i.e., connected in parallel therewith. This then makes it necessary for the battery to supply only the average current to the transistor, and eliminates the high peak currents from flowing through the battery.

The collector current from transistor 13 flows through one half 16a of the primary winding of pulse transformer 16. The large surge of current through this portion of the primary winding induces a large voltage of opposite phase in the second half 16b of the transformer primary, which serves as a positive feedback and applies a signal to the base circuit of transistor 13. The feedback signal introduced into the base of transistor 13 in this manner is such as to increase the current through the collector circuit and thus through the primary winding 16a, 16b. This current increases until such time as the current flowing through the base charges capacitor 17, connected between the base and the lower end of transformer primary winding half 16b, to such a point that the voltage developed across capacitor 17 is equal to the voltage applied from the transformer primary 16a, 16b. At this point, no further current will flow through the base of transistor 13, and the current through the collector circuit thereupon also stops. This process occurs very rapidly, the whole current pulse being completed in approximately twenty microseconds with the components employed in our stimulator unit.

No further current will flow through transistor :13 until capacitor 17 has discharged to the point where transistor 13 is no longer cut off by this bias. Capacitor 17 is discharged by the aid of resistor 18 connected in parallel therewith. The ohmic value of resistor 18 is chosen so as to give the desired pulse stimulation frequency.

The repetitive pulses will continue for as long as the heel is raised from the ground and the contacts of switch 7 remain closed. In this connection it will be noted from the circuit of FIG. 2 that a connection extends from a center tap at the junction between the transformer windings 16a, 1611 through battery 14 and switch 7 in series to the emitter circuit of transistor 13. As soon as the heel is re-lowered to the ground the contacts of switch 7 re-,

open thus opening the circuit between the emitter of transistor 13 and battery 14.

The secondary winding of transformer '16 which is connected to the output terminals 11 and 12 has a large number of turns as compared with the primary, in order to permit a sufficiently high voltage to be applied between the electrodes 2 and 4 to produce the desired stimulating current. The voltage required will generally be of the order of fifty to one hundred fifty volts, depending upon how well the electrodes make contact with the skin .of

the individual, the resistance of the skin, and the amount of the stimulating current desired, etc.

The merits of the circuit shown in FIG. 2 are, among others, the fact that it is highly efficient, negligible power being lost in transistor 13; it operates from a dry battery source which may have a relatively low voltage, of the order of six to nine volts, and is thus economical as compared with miniature high voltage batteris. Also, all of the components of the stimulator unit can be made very small so that it is not cumbersome or inconvenient for the individual to wear.

The embodiment which has been illustrated is repre sentative of but one particular application of the broader inventive principle which may be used in conjunction with other muscles of the body, the essential feature being that the control member is activated by the normal physiological functioning of the individual. Moreover, the various specific details of the control and circuit may be modified in various aspects without, however, departing from the spirit and scope of the invention as defined in the appended claims.

We claim:

In the method of stimulating into action in a periodic manner the toe raising tibialis anticus and peroneus longus muscles of the leg on a human body not otherwise under proper neurological control in order to obtain a quasinormal use of said muscles to assist in walking which includes the steps of attaching electrode means to the muscles to be stimulated, connecting a source of pulse type electrical stimulating current to the electrode means, and interposing a switch in the circuit of the source to alternately energize and de-energize the source and thereby stimulate the muscles, the improvement which resides in the step of locating said switch under the heel part of the foot on said leg for automatic periodic operation coordinated to the periodic up and down movements of said heel during walking.

References Cited UNITED STATES PATENTS 3,083,712 4/1963 Keegan 128-423 3/1956 Giaimo 128-424

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