External trial stimulator useable in an implantable neurostimulator system

An improved external trial stimulator provides neurostimulation functionality for implanted medical electrodes prior to implantation of an implantable neurostimulator. The external trial stimulator is housed in a four-part housing that provides mechanical and electrostatic discharge protection for the electronics mounted in a central frame of the housing. Connectors attached to leads from the electrodes connect to contacts that are recessed in the housing through ports that are centered for easy access. Multiple indicators provide information to users of the external trial stimulator.

FIELD OF THE INVENTION

The present invention relates to the field of implantable medical devices, and in particular to an improved architecture for an external trial stimulator for use with an implantable neurostimulator.

BACKGROUND

Implantable neurostimulator devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder subluxation, etc. The description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227. However, the present invention may find applicability in any implantable neurostimulator.

As shown inFIGS. 1A and 1B, an SCS system typically includes an implantable pulse generator (IPG)100, which includes a biocompatible device case130formed of a conductive material such as titanium. The case130typically holds the circuitry and battery necessary for the IPG100to function, although IPGs can also be powered via external RF energy and without a battery. The IPG100includes one or more electrode arrays (two such arrays102and104are shown), each containing several electrodes106. The electrodes106are carried on a flexible body108, which also houses the individual electrode lead wires112and114coupled to each electrode. In the illustrated embodiment, there are 16 electrodes on array102, labeled E1-E16, and 16 electrodes on array104, labeled E17-E32, although the number of arrays and electrodes is application specific and therefore can vary. The arrays102and104couple to the IPG100using lead connectors138A and138B, which are fixed in a non-conductive header material, such as an epoxy.

Prior to the implantation of the IPG100, external trial stimulators are commonly used to insure that the electrodes106are properly placed and to allow configuration of the program of stimulation to be performed by the IPG100. See, e.g., U.S. Patent Publication No. 2010/0228324 (the “'324 Publication”), discussing external trial stimulators in further detail, which is incorporated herein by reference in its entirety. The external trial stimulator connects to electrode lead wires112and114external to the body of the patient and provides the ability to stimulate the electrodes106similar to the way the IPG100stimulates once implanted. Current external trial stimulators however can be difficult to manufacture, or have lacked numerous features that would be useful or more comfortable for the patient, physician, or clinical staff.

DETAILED DESCRIPTION

An improved external trial stimulator is disclosed that provides neurostimulation functionality for implanted medical electrodes prior to implantation of an implantable neurostimulator. The external trial stimulator is housed in a four-part housing that provides mechanical and electrostatic discharge protection for the electronics mounted in a central frame of the housing. Connectors attached to leads from the electrodes connect to contacts that are recessed in the housing through ports that are centered for easy access. Multiple indicators provide information to users of the external trial stimulator.

FIG. 2is a perspective view illustrating an external trial stimulator (ETS)200according to one embodiment, with a connector250connected to one of the two ports of the ETS200. A switch205allows the patient to turn the ETS200on or off. The ETS200also provides indicator lights. Indicator light210provides information about the charge status of batteries (not shown inFIG. 2) that power the ETS200. Another indicator light225provides information about the status of the ETS200.

FIG. 3is an exploded perspective view illustrating various elements of the ETS200according to one embodiment. As illustrated in this view, the ETS200comprises a four-part housing: a battery cover310, a top cover320, a center frame330, and a bottom cover340. The top cover320, center frame330, and bottom cover340are assembled together, typically with screws threaded through screw holes322in the top cover320into posts345of bottom cover340. The battery cover310is removably attached to the top cover320using a catch of any type known in the art to allow a patient pressing on indentation315to slide the battery cover310outwards to remove the battery cover310from the top cover320, gaining access to battery compartment325formed in the center of top cover320. The center frame330forms a cavity335in which electronics (not shown inFIG. 3) can be attached, protecting the electronics from damage.

The center frame330also provides two ports332for connecting to two connectors250(only one of which is shown inFIG. 3). Although not shown, but as explained in the above-incorporated '324 Publication, connectors250are coupled to cables that terminate at cable boxes. The ends of the electrode lead wires112or114(FIG. 1A), or their extensions, can be placed into these cable boxes to ultimately electrically connect each of the electrodes106to a corresponding terminal in each of the ports332. As shown, two connectors250/ports332are used—one for each of the electrode arrays102and104(FIG. 1A), but other numbers of connectors250and ports332may be used.

The center frame330provides openings333for viewing indicators210and225, as well as for accessing switch205. As illustrated inFIG. 3, in one embodiment, the opening for switch205is located at a slightly recessed area339of center frame330, to reduce inadvertent actuation of the switch205. In one embodiment, the switch205is shaped like the recessed area339to reduce the likelihood of accidental actuation further. In a further embodiment, the switch205provides tactile feedback to let the patient know that the switch205has been actuated. The switch205is preferably large enough for easy actuation by the patient, and is positioned on the side of the ETS200to allow visibility and easy access to the switch205when the ETS200is worn by the patient (see, e.g.,FIG. 10). Other openings333in center frame330, top cover320, bottom cover340, or battery cover310may be included as desired for viewing or accessing other features of the ETS200.

The four component mechanical housing illustrated inFIG. 3provides mechanical robustness for the ETS200. The top and bottom covers320and340, together with battery cover310, provide the ability to deform slightly under shock, such as may occur should the patient drop the ETS200, while the rigid center frame330protects the electronics of the ETS200. The ETS200housing is easy to assemble, and in one embodiment can be (excluding the battery cover310) assembled using a Z-axis stacking of the pieces. In addition, by allowing access to the electronics from either side of the center frame330, the ETS200may be completely tested before enclosing the ETS200with the top and bottom covers320and340. In one embodiment, the ports332are centered on one end of the center frame330, allowing easy access regardless of whether the ETS200is worn on the right or left side of the patient's body.

In one embodiment, the body parts310,320,330, and340are manufactured from a high flow polycarbonate plastic, which provides good impact resistance and structural stability. The center frame330may be given a surface finish of a different color or finish than the covers310,320, and340, which may comprise a scratch resistant hard coating.

As illustrated inFIG. 3, the screw holes322for use in connecting the components of the ETS200may be recessed within the top cover320and covered by the battery cover310when it is mated with the top cover320. This ensures that the screws (not shown) are not exposed on the outside of the ETS200, which reduces the possibility that the screws can promote an electrostatic discharge (ESD) event that might damage the electronics within the ETS200. Additionally, not having exposed screws eliminates the screws as a possible source of contamination.

FIG. 4is a perspective view of a connector250according to one embodiment, illustrating electrical contacts410formed in a connector housing420. In one embodiment, an indentation440in the connector housing420provides an improved gripping area to allow gripping the connector250with sufficient force to allow the removal of the connector250from the ports332of the ETS200when desired. In one embodiment, there are 24 high-density electrical contacts410, and 17 of these contacts410are coupled to 17 electrodes—16 of which are electrodes106on one of the electrodes arrays102or104(FIG. 1A), and one of which comprises the IPG's conductive case130. Other of the remaining 24 contacts can be used to determine lead disconnection, lead addressing, or are simply not used.

As illustrated inFIG. 4, the contacts410on the connector250are recessed within the connector housing420to reduce the likelihood that the contacts410may be touched by fingers or other small objects. The contacts410in one embodiment employ leaf contacts that latch in place, yet can be easily removed without the need for pushbuttons or other unlatching mechanisms. Use of unlatching mechanisms that require manual disengagement of a latch is less preferred, as it is desired for patient safety that the connector250automatically disengages from the ports332on the ETS200upon exertion of a significant force. Allowing quick disconnection of the connector250from the ETS200also helps prevent damage to the connector250or the ETS200. At the same time, however, the connector250is preferably designed to prevent disconnection from the ETS200under normal usage. The indentation440allows easier gripping of the connector250with sufficient force to disengage it from the ETS200when desired. Preferably, the contacts410provide a stable mating force between the connector250and ports332on the ETS200that does not depend on pin interference.

In one embodiment, the connectors250and the ports332are configured to mate only in one orientation, preferably with connectors250and ports332having shapes that make the correct orientation easily detectable by the patient. This prevents inadvertent connection of the electrodes106, which could lead to incorrect stimulation by the ETS200and possibly danger to the patient.

FIG. 5is a top view of the top cover320, illustrating placement of batteries510in the battery compartment325. Although as illustrated inFIG. 5each battery510is oriented in the same direction, other embodiments may allow for batteries oriented in different directions. Although two batteries are illustrated inFIG. 5, any number of batteries may be used as desired. As is common in battery-operated devices, the correct orientation of the batteries510may be marked on the top cover320. Similarly, markings520may be made on the top cover to assist the connection of connectors250to the correct ports332.

In one embodiment, the batteries510are common AA-size batteries, although other types of batteries may be used. In one embodiment, a power converter820(FIG. 8) steps up the voltage produced by the AA batteries510to a voltage commonly output by Li-ion batteries (e.g., 4.1V). This occurs because the ETS200emulates stimulation circuitry residing within the IPG100, which circuitry is typically powered by a Li-ion battery. In fact, the circuitry internal to the ETS200may be the same as the circuitry within the IPG100, at least to some extent. Using the same circuitry for the ETS200and IPG100is efficient to design and manufacture.

The battery compartment325is configured in one embodiment so the placement of one or both of the batteries510in the wrong orientation will prevent the misoriented battery from making electrical contact with the battery terminals, avoiding electrically damaging the ETS200circuitry. In another embodiment, techniques for allowing insertion of the batteries510in any orientation may be used, although this adds to the manufacturing cost and weight of the ETS200. In one embodiment, battery misorientation protection involves both mechanical and electrical protection techniques.

FIG. 6is a top view illustrating a battery cover310according to one embodiment. As is common in implantable medical device systems, the ETS200(like the IPG100it emulates) uses telemetry to communicate with an external controller (not shown inFIG. 6), and therefore includes a telemetry antenna740(FIG. 7). In one embodiment, an orientation610is marked on the battery cover310to assist the patient in orienting the external controller relative to the ETS200for best communication reliability, which is described in further detail below. As shown inFIG. 6, the external controller is best positioned to the right or left of the ETS200, although this depends on the orientation of the antenna740inside the ETS200, which can be changed.

FIG. 7andFIG. 8are perspective views of a top and bottom side of a first circuit board700carrying the electronic components of the ETS200according to one embodiment.FIG. 7illustrates the side proximal to the batteries510, and includes positive and negative battery terminals750. Only one negative terminal750is illustrated inFIG. 7for clarity and to show pads for electrically connecting the terminals750to the first circuit board700. The battery terminals750in one embodiment may be fully self-supporting on the first circuit board700, without reliance on mechanical support by the top cover320or the central frame330. (Ports332are not shown inFIG. 7or8, but are shown inFIG. 9).

In addition to the battery terminals750,FIG. 7illustrates indicator lights210and225, switch205, telemetry antenna740, and one or more capacitors760. In one embodiment, indicator lights210and225are light emitting diodes (LEDs) with a green and yellow LED contained in a housing, allowing the indicator to appear green or yellow to convey information. The LED210in one embodiment illuminates green if the battery charge level is sufficient for proper operation of the ETS200, and yellow when the battery charge level is low.

In one embodiment, LEDs210and225are driven by an H-bridge and a charge pump to allow use of high-efficiency LEDs with a low current draw. Further power savings may be achieved by blinking the LEDs210and225at a predetermined rate instead of a constant load. In one embodiment, when power is supplied to the LEDs210and225, the power is gradually ramped up and down, rather than supplied at full power and turned off, to help patients see whether the LED210or225is turning on or off. This ramped on and off gives the LEDs210and225an appearance of “breathing,” rather than “blinking.” Markings (not shown) may be provided on the surface of the center frame330proximal to the LED indicators210and225to help the patient understand the meaning of the LED indicators210and225.

The ETS telemetry antenna740comprises a coil, as shown in dotted lines inFIG. 7. Communications between the ETS200and an external controller may occur using magnetic induction, and data may be transmitted using a communication protocol such as Frequency Shift Keying (FSK), as is well known in the implantable medical device system arts. Coupling to the external controller will be improved if the external controller is oriented along the axis745around which the coil740is wound. As discussed earlier with reference toFIG. 6, such optimal orientation610for the external controller can be indicated on the battery cover310, or elsewhere on the ETS's housing. Inductors used on the first circuit board700are positioned orthogonal to the axis745of the coil740to reduce interference with telemetry. The ETS200may perform telemetry with external controller to program the ASICs810and to report data to the external controller.

In one embodiment, one or more large capacitors760are provided on the first circuit board700to provide charge storage for temporarily powering the ETS200for an orderly shutdown of the ETS200when the batteries510are removed. These capacitors760in one embodiment may be 680 μF tantalum capacitors. The use of the capacitors760provides power to avoid corruption of data during a read from or write to the ETS200, should the batteries be removed during the process of reading or writing.

On the reverse side of the first circuit board700, as illustrated inFIG. 8, are a number of electronic circuit components that provide functionality for the ETS200. These components include two application specific integrated circuits (ASICs)810, each of which handles electrodes106coupled to a given one of the connectors250. The ASICs810include programmable neurostimulation logic to generate neurostimulation pulses to the electrodes106through lead wires112and114that are connected to ports332via the connectors250. Also illustrated inFIG. 8are a power converter820, a memory830, and a microcontroller840. The memory830provides storage for software or firmware for the microcontroller840and the ASICs810, as well as for data. The power converter820in one embodiment can operate in a high-efficiency power-saving mode that cycles power levels to reduce battery drain and a quiet mode that disables the power cycling. Because the power cycling of the high-efficiency mode may generate magnetic noise that could interfere with telemetry between the ETS200and an external device, in one embodiment the power converter820may be switched from the high-efficiency mode to the quiet mode for the duration of telemetry activities, then returned to the high-efficiency mode when telemetry is complete.

In one embodiment, before writing to the memory830, the ETS200checks the battery charge status to make sure sufficient charge exists in the batteries510to perform the write. If any of the batteries510are removed or lose charge during a write, the capacitor760provides sufficient backup power to make it more likely to complete the write, reducing the likelihood of data loss or corruption.

FIG. 9illustrates the first circuit board of700, with a connector250attached. The contacts410(FIG. 4) of each connector250mate with contacts in a shielded housing910positioned in one of the ports332. The housing910contains a second circuit board920which is relative rigid and is solderable to the housing contacts in the port332. The second circuit board920is then coupled to first circuit board700via a flexible member915, such as a flexible ribbon cable, to isolate mechanical forces exerted by the connector250from the first circuit board700. The housing910may be recessed in the ports332of the central frame330to provide additional mechanical robustness, such as protection from a drop of the ETS200.

In one embodiment, the second circuit board920is comprised of a laminate composite. Electrical contacts are formed on one end of the second circuit board920for mating with the contacts410of the connectors250. A mechanical retention tab and double-sided adhesive tape may be used to anchor the contacts end of second circuit board920in place within the port332of the ETS200.

In one embodiment, the ETS200may use some of the unused contacts for lead identification, as is discussed in the above-incorporated '324 Publication. As was already discussed with reference toFIG. 5, the ETS200may provide markings520on the cover320to show which of a pair of connectors250should be attached through which port332of the ETS200, but patients may still inadvertently insert leads in the wrong port332, leading to incorrect and possibly dangerous stimulation of electrodes. By providing lead identification, the ETS200may detect a connector250attached to the wrong port332and either automatically redirect signaling to the correct port332or indicate a lead misconnection and disable stimulation of electrodes until the misconnection is corrected. All signals output to the ports332may be AC coupled, to prevent any chance of delivering DC current to the patient.

In one embodiment, ESD protection may be provided in multiple ways. Each electrode106may have individual ESD protection provided by the ASICs810. In one embodiment, additional ESD protection may be provided by a guard ring around the first circuit board700. In a further embodiment, the guard ring is discontinuous, to reduce interference. The battery contacts750may also have ESD protection.

As illustrated inFIG. 10, ETS200is typically worn on a belt1010, although any other desired method of attaching the ETS200to a patient1000may be used. The ETS200is typically worn with the switch205and indicators210and225pointing upward, where the user can best see and access them.

It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments may be used in combination with each other. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention therefore should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.