System and method for implantable stimulation lead employing optical fibers

An implantable lead, and method of manufacturing same, and a system and method for stimulation. The lead has proximal and distal ends having, respectively, a connector portion with a terminal and an electrode. An optically switched device is electrically connected to the electrode and to the terminal. An optical fiber is optically coupled to the connector portion at one end and to the optically switched device at another end. The optically switched device conducts a stimulus from the terminal to the electrode in response to an optical signal transmitted over the optical fiber.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to electrical leads, and in particular, an electrical lead for use in the medical field.

BACKGROUND

Implantable leads having electrodes are used in a variety of applications, including the delivery of electrical stimulation to surrounding tissue, neural or otherwise. Some leads include lumens (or channels) for the delivery of other elements, including chemicals and drugs. Whether in a stimulation or element delivery capacity, such leads are commonly implanted along nerves, within the epidural or intrathecal space of the spinal column, and around the heart, brain, or other organs or tissue of a patient.

Generally, several elements (conductors, electrodes and insulation) are combined to produce a lead body. A lead typically includes one or more conductors extending the length of the lead body from a distal end to a proximal end of the lead. The conductors electrically connect one or more electrodes at the distal end to one or more connectors at the proximal end of the lead. The electrodes are designed to form an electrical connection or stimulus point with tissue or organs. Lead connectors (sometimes referred to as terminals, contacts, or contact electrodes) are adapted to electrically and mechanically connect leads to implantable pulse generators or RF receivers (stimulation sources), or other medical devices. An insulating material typically forms the lead body and surrounds the conductors for electrical isolation between the conductors and for protection from the external contact and compatibility with a body.

Such leads are typically implanted into a body at an insertion site and extend from the implant site to the stimulation site (area of placement of the electrodes). The implant site is typically a subcutaneous pocket that receives and houses the pulse generator or receiver (providing a stimulation source). The implant site is usually positioned a distance away from the stimulation site, such as near the buttocks or other place in the torso area. In most cases, the implant site (and insertion site) is located in the lower back area, and the leads may extend through the epidural space (or other space) in the spine to the stimulation site (middle or upper back, or neck or brain areas).

Current lead designs have different shapes, such as those commonly known as percutaneous and paddle-shaped leads. Paddle leads, which are typically larger than percutaneous leads, are directional and often utilized due to desired stimulus effect on the tissues or areas. However, current paddle-shaped leads require insertion using surgical means, and hence, removal through surgical means.

Percutaneous leads are designed for easy introduction into the epidural space using a special needle. Therefore, such leads are typically smaller and more nearly circular in cross-section than paddle-shaped leads. This reduced size facilitates their implantation in the body, allows their implantation into more areas of the body, and minimizes the unwanted side effects of their implantation.

Larger cross-section leads are required, however, when greater numbers of electrodes are employed at the distal end of a lead. Several benefits can be gained from increasing the number of electrodes on a lead. More electrodes of smaller size allow a stimulation pattern to be more precisely localized, reducing unwanted stimulation of nearby areas and minimizing stimulation side effects. With more electrodes available, stimulation patterns can be moved from the electrodes selected during and immediately after implantation to other electrodes on the lead in order to adapt to post-implantation migration of the lead and changes in the body's responsiveness to stimulation. The presence of more electrodes permits adjacent electrodes to be employed in anode-cathode combinations for increased control of the directionality and penetration of stimulation patterns. However, an increase in the number of electrodes results in an increased number of conductors in the lead body and, thus, in leads of larger cross-section.

Smaller diameter conductors may be employed, in order to reduce the lead body diameter, but such conductors have a higher resistivity than larger diameter conductors. As will be understood by one skilled in the art, a higher resistivity conductor produces a greater voltage drop through the conductor, and thus delivers a lower stimulation voltage at the distal end electrode than would be delivered by a lower resistivity conductor. Greater resistivity in the conductor also results in less current being delivered at the stimulation site. More power is lost in the conduction of the stimulation signal through a higher resistivity conductor, and in some cases, requires more frequent recharging of the power source in the implantable medical device.

Rather than adding conductors to the lead body, an embedded controller may be employed at the distal end of the lead to control a greater number of electrodes with fewer conductors. Known techniques of signal multiplexing may be used to implement the embedded controller. Alternatively, microcontrollers may be used, and the desired stimulation pattern communicated from the connector at the proximal end of the lead to the microcontroller at the distal end using digital communication techniques. While such solutions permit a reduced cross-section in the lead body, they require an increased cross-section at the distal end of the lead to accommodate the circuitry required to implement the solution.

The presence of metallic conductors in stimulation leads can cause side effects when magnetic resonance imaging (MRI) is employed, as well. Currents and voltages induced in the conductors by the electromagnetic field of a MRI scanner may result in uncontrolled stimulation of nerves near the electrodes of a stimulation lead or, in extreme cases, in nerve damage. Such results have led the FDA and manufacturers of implantable medical devices to issue a contraindication for the use of MRI with patients with such devices implanted.

Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.

SUMMARY

The present invention provides an implantable stimulation lead of reduced cross-section with a reduced number of metallic conductors.

According to one embodiment of the present invention, there is provided a lead with proximal and distal ends having, respectively, a connector portion with a terminal and an electrode. An optically switched device is electrically connected to the electrode and to the terminal. An optical fiber is optically coupled to the connector portion at one end and to the optically switched device at another end.

In another embodiment of the present invention, there is provided a lead with proximal and distal ends having, respectively, a connector portion and an electrode. An optically switched device is electrically connected to the electrode. An optical fiber, optically coupled to the connector portion, illuminates an adjustable mirror device, and light reflected from the mirror device illuminates the optically switched device.

In yet another embodiment of the present invention, there is provided a method of administering a stimulus with a stimulation device. The method includes activating a light source in an illumination pattern that corresponds to a desired stimulation pattern. Light from the light source is conducted by an optical fiber to an optically switched device, which administers the stimulus in response to the light pattern.

In still another embodiment of the present invention, there is provided a method of administering a stimulus with a stimulation device. The method includes optically coupling a light source to one end of an optical fiber and an optically switched device to another end of the optical fiber. One terminal of the optically switched device is electrically connected to a power source and another terminal is electrically connected to a stimulation electrode. The stimulus is administered at the stimulation electrode in response to light emitted by the light source.

In another embodiment of the present invention, there is provided a method of manufacturing a lead. An implantable lead is provided with proximal and distal ends having, respectively, a connector portion with a terminal and an electrode. The method includes electrically connecting a first conductor to the first terminal and the optically switched device, and optically coupling a first optical fiber at a first end to the connector portion and at a second end to the optically switched device.

In another embodiment of the present invention, there is provided a system for stimulating a portion of the body. The system includes a stimulus source and an implantable lead. The lead has proximal and distal ends with, respectively, a connector portion with a terminal and an electrode. An optically switched device is electrically connected to the electrode and to the terminal. An optical fiber is optically coupled to the connector portion at one end and to the optically switched device at another end.

DETAILED DESCRIPTION OF THE INVENTION

An optical fiber is a thin strand of glass or plastic that conducts light by the principle of internal reflection. Light entering one end of the fiber exits the other end. If the light illuminating one end of the fiber is modulated, that modulation is preserved during transmission and is present in the light emitted from the other end of the fiber. An optical fiber is typically smaller than the typical metallic electrical conductor. Such conductors are typically around 0.25 millimeters in diameter, while an optical fiber is typically between about 250 micrometers and 125 micrometers and may be smaller.

FIG. 1shows a schematic view of one embodiment of the present invention, in which optical fibers are employed in an implantable lead to carry stimulation signals from an implantable medical device to the stimulation site. An implantable stimulation system100comprises a medical device102(in this embodiment an implantable pulse generator (IPG)) and a lead104. After surgical or percutaneous insertion of the lead104into the body, the lead104is connected to the medical device102, typically, by inserting a connector portion114of the lead104into the medical device102, wherein the connector portion114is secured by springs, set screws or other mechanism (not shown).

The medical device102includes a power source106and a stimulation control circuit108. The power source106is electrically connected to the stimulation control circuit108. Additionally, a terminal109of the power source106is electrically connected to the conductive case of the medical device102. A terminal105of the power source106is electrically connected to a contact112. The stimulation control circuit108stores one or more desired stimulation patterns and reproduces those patterns on light sources110(in this embodiment, light emitting diodes). When the administration of a stimulation voltage is desired, the stimulation control circuit108activates one or more light sources110. When the desired period of stimulation is ended, the circuit108deactivates the one or more light sources110. In the alternative, stimulation voltage may be administered when the light source(s) are deactivated and ended when the light source is activated.

Each of the light sources110individually illuminates a proximal end of a corresponding one of optical fibers120that extend substantially the length of the lead104. These proximal ends are mounted in the connector portion114of the lead104. Also mounted in the connector portion114of the lead104is a terminal116, which makes electrical contact with the contact112.

The distal portion122of the lead104includes one or more optically switched devices124. The optically switched devices124may be photodiodes, phototransistors, photodarlingtons or any other photosensitive device or photosensitive circuit whose electrical conductivity is controlled by the amount of received light. The distal ends of individual ones of optical fibers120illuminate each of optically switched devices124. A conductor118is electrically connected to each optically switched device124and provides electrical power from the terminal116to the optically switched devices124. The output of each optically switched device124is electrically connected to one of electrodes126at the distal end122of the lead104. The electrodes126produce electrical stimulation of the nerves, muscles, or other tissues at the stimulation site when the lead104is implanted within a body. In the embodiment shown inFIG. 1, the human body itself completes the electrical circuit back to the conductive case of the medical device102.

In operation, the stimulation control circuit108activates the light sources110in a desired stimulation pattern. The output (light) from the activated light sources110is input to the proximal ends of the associated ones of optical fibers120and is conducted (or transmitted) along the fibers to the distal ends, where the light signal illuminates the associated ones of optically switched devices124. The optically switched devices124coupled to the active light sources110are activated and conduct, thereby applying a voltage to the associated ones of electrodes126. As a result, the desired stimulation pattern is produced at the stimulation site.

In an alternative embodiment of the invention (not shown), the power source106is located outside the housing of the medical device102and electrically connected to the device by a cable. In another embodiment (not shown), such an externally located power source may deliver power to the medical device102through a wireless connection, such as RF or inductive conduction.

In another embodiment of the invention (not shown), the stimulation system100is fabricated as an integral unit, with the lead104forming a ‘pigtail’, permanently attached to the medical device102. In such an embodiment, the connector portion114would not be required, as the external body of the lead104would be permanently sealed to the housing of the medical device102, the conductor118permanently connected to the power supply106without the need for the terminal116and the contact112, and the proximal ends of the optical fibers120mechanically mounted within the housing of the medical device102so as to be optically coupled with the light sources110.

In yet another embodiment of the invention (not shown), a switch, controlled by the stimulation control circuit108, would be employed to connect the contact112in alternation to the terminals105and109of the power source106. The terminal105carries a first voltage and the terminal109carries a second voltage, each with reference to the other terminal. By illuminating the light sources110at appropriate, times, the stimulation control circuit108causes the optical switches124to switch either the first or second voltage onto the distal electrodes126, thereby causing them to operate in a tri-state stimulation mode.

Turning toFIG. 2, another embodiment of the present invention is presented in schematic form. An implantable stimulation system200includes a medical device202and a lead204. The lead204is connected to the medical device202, in this embodiment, by inserting a connector portion218of the lead204into the medical device202.

The medical device202includes a power source206, outputting two supply voltages. A power source terminal205provides a first voltage and a power source terminal209provides a second voltage. The power supply terminals205and209are electrically connected to contacts214and216, respectively. As described for the embodiment inFIG. 1, the power source206could alternatively be located outside the housing of the medical device202and electrically connected to the device with a cable or through wireless means.

A stimulation control circuit210is electrically connected to the power source terminals205and209. The stimulation control circuit210activates light sources212in a desired stimulation pattern, and the light sources212individually illuminate the proximal ends of optical fibers228.

The optical fibers228extend substantially the length of the lead204, and the proximal ends of optical fibers228are mounted in connector portion218of the lead. The connector portion218includes lead terminals220and222, which make electrical contact with the contacts214and216, respectively, when the lead204is connected to the medical device202. A distal end230of the lead204includes optically switched devices232,234,236and238. A distal end of each of the optical fibers228illuminates each of optically switched devices232,234,236and238.

A conductor224electrically connects a first terminal of each of the optically switched devices232and236to the lead terminal220. Similarly, a conductor226electrically connects a first terminal of each of the optically switched devices234and238to the lead terminal222. A stimulation electrode240in the distal end230of the lead204is electrically connected to a second terminal of the optically switched devices232and234. A stimulation electrode242is electrically connected to a second terminal of the optically switched devices236and238.

Individual ones of light sources212are optically coupled to individual ones of optical fibers228. Individual ones of optical fibers228are, in turn, coupled to individual ones of optically switched devices232,234,236and238. The light sources activated by the stimulation control circuit210illuminate their associated optical fibers, which in turn illuminate their associated optically switched devices. When the optically switched devices232and236are illuminated, they conduct the first voltage from the conductor224to the associated stimulation electrodes240and242, respectively. Similarly, illumination of the optically switched devices234and238applies the second voltage from the conductor226to the electrodes240and242, respectively. Thus, the stimulation electrodes240and242operate in a tri-state stimulation mode: depending on the illumination of the associated optically switched devices, the stimulation electrodes240and242provide either a first or second stimulation voltage, or no voltage at all, to the surrounding tissue.

In an alternative embodiment of the invention (not shown), a light source producing light of selectable wavelengths (colors, frequencies) or a plurality of light sources, each emitting different wavelengths, are employed. A single optical fiber optically couples the light source(s) to a plurality of optical switches sensitive to different wavelengths of light, thereby controlling a plurality of optical switches with a single optical fiber.

The power conducted by the optical switches232,234,236and238may be generated at the distal end230of the lead204in another embodiment of the invention (not shown). In this embodiment, the contacts214and216are replaced by a single light source, electrically connected to both the terminals,205and209, of the power source206, such that it is continuously illuminated. The conductors224and226are replaced with a single optical fiber, with a proximal end of the single optical fiber mounted in the connector portion218and optically coupled to the single light source. A distal end of the single optical fiber illuminates a photovoltaic device. Output terminals of the photovoltaic device are electrically connected to the optical switches232and236, and234and238. In this embodiment, the body of the lead204contains only optical fibers, and the elimination of all wire conductors further reduces the size of the lead204.

In yet another embodiment of the invention (not shown), the contacts214and216, the terminals220and222, and the conductors224and226are eliminated. Photovoltaic devices replace the optical switches232,234,236and238and are optically coupled to the optical fibers228. The electrodes in the distal end230of the lead204are electrically connected to the output terminals of the photovoltaic devices, such that a voltage produced when the photovoltaic devices are illuminated supplies the stimulus administered to the surrounding tissue. In this embodiment, too, the body of the lead204contains only optical fibers, which may reduce its size.

While the above descriptions are of neurostimulation systems, it will be appreciated by one skilled in the art that the techniques of the present invention may also be embodied in other stimulation systems—including pacemakers, cochlear implants, or deep-brain stimulation systems. It will be further understood that, whileFIGS. 1 and 2show stimulation leads having four and two electrodes, respectively, any number of electrodes may be employed, as desired, without departing from the spirit and scope of the invention.

Furthermore, whileFIGS. 1 and 2show a one-to-one relationship between light sources and optical fibers, and between optical fibers and optically switched devices, other embodiments of the invention may utilize a one-to-plural or plural-to-one relationship in either situation. It will be understood that a single medical device may provide stimulation power and stimulation control signals for a plurality of stimulation leads. It will also be appreciated by one skilled in the art that a photosensitive device may apply a stimulation voltage to an electrode in response to the absence of illumination, rather than in response to its presence.

FIG. 3shows a planar, multi-electrode stimulation paddle such as may be used in a stimulation system. In this embodiment of the invention, the paddle forms a distal end302of a lead300. A lead body306connects the paddle to a proximal end of the lead (not shown) having a connector portion including terminals (also not shown) similar to the connector portions of the leads ofFIGS. 1 and 2. Stimulation electrodes304are, in this embodiment, a rectangular array of electrically isolated electrodes, which can be individually energized to produce a desired stimulation pattern at a desired location on the array.

FIG. 4presents a schematic view of the interior of the stimulation paddle ofFIG. 3. In this view, the lead body306and the electrode array304can be seen, but the paddle body of the distal end302of the lead300has been eliminated to show the interior of the paddle. Conductors309electrically connect an array308of optically switched devices to the electrode array304. In this embodiment of the invention, individual photosensitive devices are connected to individual electrodes. The optically switched devices308are also electrically connected to a distal end of a conductor314, which conducts a stimulation voltage from a terminal in the connector portion (not shown) of the lead300. If tri-state operation is desired, as in the embodiment ofFIG. 2, two such conductors314may be provided, carrying positive and negative stimulation (relative to each other), respectively, and pairs of photosensitive devices may be electrically connected to each electrode in the array304.

An optical fiber316in the lead body306illuminates the entirety of a digital micromirror device (DMD)310, such as the 0.55SVGA DDR device, manufactured by Texas Instruments, as indicated by reference numeral318. A lens or lens system may be employed to produce the divergence pattern needed to illuminate the DMD310. The DMD310is shown with a rectangular array of hinge-mounted microscopic mirrors and control circuitry. The mirrors can be tilted to one of two positions: in one position, the mirrors reflect the illumination318from the optical fiber316away from the optically switched devices308; in the other position, the mirrors reflect the illumination318onto the optically switched devices308, as indicated by reference numeral320. Each photosensitive device in the array308is illuminated by light reflected from one or more mirrors in the DMD310. The control circuitry of the DMD310is electrically connected to distal ends of conductors312, which are electrically connected at their proximal ends to terminals (not shown) in a connector portion of the lead300. As will be appreciated, the control circuitry of the DMD310is shown at or near the lead300, however the circuitry may be located at the device202.

In operation, control signals on the conductors312cause selected ones of the mirrors of the DMD310to tilt into position to illuminate selected ones of the optically switched devices308, thereby causing the electrodes in array304that are associated with the illuminated devices to apply stimulation energy in a desired pattern to the surrounding tissue.

WhileFIG. 4illustrates an embodiment in which a digital micromirror device is used both to split the light from the optical fiber316into multiple beams and to direct those beams onto and away from the optical switches308, other techniques may be used to perform these two functions. For example, a diffraction grating may be used to split the light from the optical fiber316into multiple beams. Similarly, a bank of microelectromechanical system (MEMS) actuators may individually pass or block those beams in order to selectively illuminate optical switches or photovoltaic devices.

It will be appreciated that the conductors312may be wire conductors or may be optical fibers coupled by suitable conversion circuitry to the electrical control inputs of the DMD310. One skilled in the art will also appreciate that optical fibers may be employed in place of wire conductors to communicate with prior art embedded controllers in multi-electrode stimulation leads.

While the figures show leads containing only electrical conductors and optical fibers, it will be appreciated that implantable stimulation leads embodying the present invention may also incorporate one or more lumens for the delivery of drugs or other chemicals. A lead according to the invention may also include a stylet passage for receiving a stylet to provide better control over the lead during placement.

Aspects of the present invention can be used for any implantable devices, such as light actuated MEMS control devices, and control valves for drug delivery in implantable devices.

Although the present invention and its advantages have been described in the foregoing detailed description and illustrated in the accompanying drawings, it will be understood by those skilled in the art that the invention is not limited to the embodiment(s) disclosed but is capable of numerous rearrangements, substitutions and modifications without departing from the spirit and scope of the invention as defined by the appended claims.