Patent No. 4019518 Electrical stimulation system

 

Patent No. 4019518  Electrical stimulation system (Maurer, et al., Apr 26, 1977)

Abstract

An electrical stimulation system for selectively stimulating portions of the body. The system includes an external device for alternately transmitting stimulus signals and control signals to an implantable receiver. The receiver includes a plurality of output devies adapted to apply the stimulus signals to the body and circuitry for routing the stimulus signal to the output devices under the control of the control signals. In a preferred embodiment, the control signals are formed of an alterably preselected number of pulse signals with the routing circuitry routing each of the stimulus signals to the output devices in predetermined correspondance with the number of pulse signals within a different one of the control signals. The system of the present invention may be employed to sequentially stimulate several stimulation sites, with the stimulation sites being selected to combat the same or different body disfunctions. Alternatively, the system of the present invention may be employed to repetitively stimulate the same stimulation sites while allowing an alteration in the stimulation sites to combat nerve fatigue or to provide a more effective electrode configuration, for example.

 

Notes:

BACKGROUND OF THE INVENTION

The electrical stimulation of various biological systems is known to the prior art. For example, pain suppression by electrical nerve stimulation is an accepted technique. Motor control through selective nerve and/or muscle stimulation has also been usefully employed. More recent developments include electrical treatment of spinal curvature and brain stimulation for various purposes including thalamic stimulation for pain suppression and cerebellum stimulation for the treatment of epilepsy and for motor control.

In each of the above mentioned electrical stimulation applications, the value of alternative electrode configurations is readily apparent. For example, in many direct nerve stimulation applications the nerves to be stimulated are sheathed with other nerve bundles, or bundle branches. Thus, to optimize the desired stimulation of a specific nerve bundle it is necessary to provide a specific orientation of the electrode or electrodes relative to the several nerve bundles. It has also been established that an electrode may migrate, either longitudinally or by rotating around the nerve bundles, thus requiring a reorientation of the electrodes relative to the nerve.

Within other environments, the optimization of the electrode configuration may be impossible, or nearly so, for some time after placement of the electrodes. For example, the effects of cerebellum stimulation are often delayed for several weeks after the implant. In this situation, it is impossible, at the time of implant, to accomplish anything more than the positioning of a plurality of electrodes with the optimization of the electrodes through which the stimulation is to occur being delayed. Thus, a system by which electrodes can be positioned, and later selected, is desirable for these and many other stimulation applications. In other instances, it may be desirable to stimulate various biological systems with a single implanted receiver by sequentially selecting differing electrode configurations. For example, a spinal curvature having two treatable curves may be treated through the implantation of a single stimulator with the output of that stimulator being sequentially alternated between the electrodes to treat each of the curves. Other multiple treatment situations may similarly be accomplished with a stimulator having the ability to sequentially select differing electrode configurations.

In addition to the above, it is also known that changing the location of the sites at which the stimulation energy is applied can reduce the fatigue, nerve fatigue, for example, commonly attending a repetitive stimulation at the same site or sites.

Electrodes having multiple leads and electrode contacts have been developed for altering the electrode configuration, an example being illustrated in U.S. Pat. No. 3,738,368, issued June 12, 1973. With this electrode, selective nerve bundle stimulation is accomplished by coupling less than all of the leads to a source of stimulation energy. The lead selection may be altered until the optimal combination is found. Within the system disclosed in the referenced patent, it is contemplated that the electrode will be positioned on the nerve and the leads brought out through the skin for temporary connection to a suitable source of stimulation energy. After several days of stimulation utilizing different combinations of leads, the most effective electrode configuration is determined and the unnecessary leads are severed.

Other systems have been proposed in which alternate output paths may be selected through the application of an external signal. For example, in U.S. Pat. No. 3,311,111 the use of bistable magnetic reed switches is proposed for the control of several stimulator functions including, pulse rate, voltage, current or duration as well as the selection of alternative output paths or leads. Within this system, a magnetic field is applied to effect the desired alteration with that alteration remaining effective until the reapplication of the magnet field. Of course, the system is susceptible to a "switching" by an extraneous magnetic field.

Although system in which the output path is selected in accordance with an external signal is disclosed in application Ser. No. 422,896, filed Dec. 7, 1973, now U.S. Pat. No. 3,888,261 which is commonly owned with the present application and which is hereby incorporated by reference. Within this system, alternating stimulus and control signals are transmitted to an implanted receiver with the receiver switching the stimulus signals between the outputs under the control of the control signals. The outputs each include independent channels with the receiver switching from channel to channel on the occurrence of a control signal.

SUMMARY OF THE PRESENT INVENTION

The present invention provides an electrical stimulation system capable of selectively stimulating portions of the body. An external transmitter alternately transmits stimulus signals and control signals to an implantable receiver. The receiver includes a plurality of output devices adapted to apply the stimulus signals to the body and includes circuitry responsive to the control signals for selectively routing stimulus signals to the output devices. In a preferred embodiment, the control signals include at least one pulse signal with the number of pulse signals occurring between stimulus signals being alterable. The routing circuitry includes components responsive to the number of pulse signals in each control signal for selectively routing each stimulus signal to a predetermined output device configuration in predetermined correspondence with the number of pulse signals within a different one of the control signals.

The system of the present invention selects an output device configuration for each stimulus signal which allows a sequential application of the stimulus signals to varying output configurations or, alternatively, a periodic alteration in output configurations. Thus, the stimulator of the present invention allows an initial optimization of the electrode configuration, a later alteration or reoptimization of that configuration or a periodic alteration in the output device configuration in a manner which may be used in any of the biological system stimulation environments discussed above. Other biological systems to which the stimulator of the present invention can be usefully applied will be immediately apparent to those familiar with the art. Also, inasmuch as the routing of each stimulus signal is independently established, any effects of extraneous noise will be automatically corrected on the next succeeding control pulse.

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Many modifications and variations of the present invention are possible in light of the above teaching, for example, the illustrated logic circuitry may be altered to provide differing electrode combinations for each state of the counter 92, without departing from the scope of the present invention. Also, the number of electrodes may be altered without departing from the scope of the present invention. It is therefore to be understood that the invention may be practiced otherwise than as specifically described.