Patent Application
20130310629
The various embodiments disclosed herein relate to methods and devices for transferring electrical power transcutaneously into a cavity of a patient to power electrical therapy devices, including, for example, heart assist devices in the patient's thoracic lung cavity.
Fully implanted electrical therapy devices have evolved from the battery powered pacemakers to new therapies that require higher levels of energy to be delivered to the body, including nerve stimulation, drug delivery, muscle stimulation (TENS), heart assist technologies, and heart replacement with an artificial heart. The evolution of battery technology has made it possible to implant low power medical devices for up to ten years of operation. However, most fully implanted high current devices are presently powered with percutaneous cables, because a safe high-power battery technology still does not exist. The cables deliver safe power to the implant, but can cause the patient significant discomfort and require maintenance to prevent infection, which occurs in approximately 40% of these implants.
The known use of transcutaneous energy transfer (TET) to power implanted medical devices can eliminate the cables and reduce the risk of infection. However, these prior art TET systems have not eliminated the risk of infection because the known systems are bulky and require a significant amount of surgery and implanted hardware. Also, the prior art technology requires close mechanical coupling for efficient energy transfer, which increases the power density and electromagnetic field exposure to the patient. This is undesirable, because high electromagnetic field exposure can cause the specific absorption rate to be exceeded for biologic tissue limits, and high power density can lead to localized heating of patient tissue, which can cause tissue necrosis.
There is a need in the art for an improved TET system.
Discussed herein are various embodiments relating to TET systems.
In Example 1, a transcutaneous energy transfer system comprises an internal coil sized to be positioned within a pleural cavity of a patient and an external coil configured to be positioned in proximity to the patient such that the external coil and the internal coil are inductively coupled. The internal coil is configured to be positioned in proximity with at least one lung within the pleural cavity.
Example 2 relates to the system according to Example 1, wherein the internal coil has a diameter of at least about 6 cm.
Example 3 relates to the system according to Example 1, wherein the internal coil is positioned substantially against an inner wall of the pleural cavity.
Example 4 relates to the system according to Example 1, further comprising a self-expanding structure operably coupled to the internal coil.
Example 5 relates to the system according to Example 4, wherein the self-expanding structure is made of a shape memory material.
Example 6 relates to the system according to Example 4, wherein the self-expanding structure is configured to expand such that the internal coil is in contact with an inner wall of the pleural cavity.
Example 7 relates to the system according to Example 4, wherein the self-expanding structure comprises at least one insulated connector configured to prevent formation of a competing electrical circuit.
Example 8 relates to the system according to Example 1, wherein the internal coil is configured to be positioned around the at least one lung.
Example 9 relates to the system according to Example 1, wherein the external coil comprises a shoulder strap cushion.
Example 10 relates to the system according to Example 1, wherein the external coil is integrated into a shoulder strap, backpack, bag, vest, shirt, jacket, bed, chair, or car seat.
In Example 11, a transcutaneous energy transfer system operably coupled to a heart assist system comprises an internal coil sized to be positioned within a pleural cavity of a patient, a compliance chamber associated with the internal coil, and an external coil configured to be positioned in proximity to the patient such that the external coil and the internal coil are inductively coupled.
Example 12 relates to the system according to Example 11, wherein the compliance chamber is coupled to the internal coil.
Example 13 relates to the system according to Example 11, wherein the internal coil is positioned within the compliance chamber.
Example 14 relates to the system according to Example 11, wherein the compliance chamber is an expandable compliance chamber having an inflated configuration and a deflated configuration.
In Example 15, a transcutaneous energy transfer system comprises an internal coil sized to be positioned within a pleural cavity of a patient, a repeater coil, and an external coil. The repeater coil is configured to be positioned in proximity to the patient such that the repeater coil and the internal coil are inductively coupled. The external coil is configured to be positioned such that the external coil and the repeater coil are inductively coupled, whereby the external coil is inductively coupled to the internal coil.
Example 16 relates to the system according to Example 15, wherein the repeater coil is positioned in proximity to skin of the patient.
Example 17 relates to the system according to Example 15, wherein the internal coil has a diameter of at least about 6 cm.
Example 18 relates to the system according to Example 15, further comprising a self-expanding structure operably coupled to the internal coil.
Example 19 relates to the system according to Example 15, wherein the external coil comprises a shoulder strap cushion.
Example 20 relates to the system according to Example 15, wherein the external coil is integrated into a shoulder strap, backpack, bag, vest, shirt, jacket, bed, chair, or car seat. While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.
Most prior art TET circuits have utilized some form of an electromagnetic transformer and many have incorporated resonant tuning to increase the efficiency of the power transfer. The use of resonant tuned circuits in power transfer was discovered by Nikola Tesla in the early 1900's, when wireless power circuits were first demonstrated. The best analogy to resonant energy transfer in nature is the transmission of acoustic energy through space, such as a vibrating string. That is, if parallel stretched wires tuned to the same frequency are excited, the mechanical vibration is transferred from one of the wires to the adjacent wire with near perfect absorption depending on the separation distance and coupling medium. Repeater wires can be added and the acoustic power transfer range can thereby be extended. This same phenomenon occurs in magnetic resonant power transfer, where the range can be extended by precise tuning and the use of passive resonant repeaters.
The transfer of power through inductive coupled coils is not new and can be described by Maxwell's laws and especially Faraday's law. Two inductive coils can operate in near field proximity as defined by Maxwell's criterion:
where d is distance between coils; and
λ is wavelength.
For example, at an excitation frequency of 5 MHz, the near field criterion is calculated (based on certain assumptions) at up to 9.54 meters. Typically, inductively coupled power systems will transfer power effectively from one coil to the other in the range of the diameter of the larger coil. The coupling of energy occurs by mutual inductance. That is, power from one coil is induced into the other and thereby the two coils essentially become a transformer with free space therebetween.
A transformer is an energy converter that takes an input power and converts it to an end use output power, usually with different current and voltage levels. A standard transformer converts the flow of electric current into a magnetic circuit that transfers the energy from the primary coil to the secondary coil. In transcutaneous energy transfer (TET), the primary coil is outside the body and the secondary coil is implanted inside the body. The TET transformer can be modeled as an air core transformer where the magnetic field is transferred from the primary coil to the secondary coil through free space. In the human body, the coupling actually occurs through body tissues—skin, bone, blood and interstitial fluid. The coupling circuit may include non-magnetic metal materials such as Nitinol, stainless steel and non-magnetic materials including fabric or plastic as well. As long as the coupling medium is not a ferrite or has a relative magnetic permeability less than 1, the effective primary to secondary core loss will predominately be a function of the operating frequency selected.
The various embodiments disclosed herein relate to systems having an internal resonant coil positioned inside the patient's body and an external resonant coil that is positioned outside the patient's body.
For example,
The external coil 24 in this embodiment is further coupled to a power source 26, which in this example is a battery 26. As shown in
According to one implementation, the internal coil 32 is a self-expanding coil that, upon insertion into the target cavity, expands to its maximum diameter. In one example, the self-expanding coil is made from shape memory nitinol. Alternatively, any shape memory or self-expanding polymer or material that can be utilized in a resonant coil can be used.
In a further alternative as shown in
The self-expanding nature of a self-expanding coil or self-expanding coil structure can result in a self-aligning, self-securing coil that expands within the target cavity—such as the lung cavity, for example—to provide an anatomical fit which anchors itself inside the cavity. That is, in some embodiments, the coil 32 is configured to expand until it comes into contact with the inner walls of the body cavity in which it is positioned, thereby providing some frictional adherence of the coil 32 to the inner walls of the cavity or internal organs or any other structures within the cavity (thereby resulting in the “anatomical fit”). In this manner, the internal coil 32 can “match the anatomy” in the cavity. For example, in the lung cavity, the coil 32 could anchor itself against the ribs and against the lung tissue. It is understood that the relatively large space within the lung cavity can allow the coil to have a very large effective diameter, which results in greater production of energy and reduces constraints associated with anatomical mating of the internal coil 32 and the external coil (such as the external coil 24 described above or any other external coil described or contemplated herein).
In accordance with one implementation, an internal coil can have an oval shape such as the internal coil 32 shown in
It is understood that the geometry of the internal coil impacts the strength of the resulting magnetic field (and other energy production parameters of the coil). Hence, each of the following structural characteristics of the coil can have a resulting impact on energy production: coil diameter (or “effective diameter” for those coils that are not round), number of turns, wire diameter, and resistivity.
As discussed above, in certain embodiments, an internal coil (such as the internal coils 24, 32, or any other internal coil described or contemplated herein, for example) should be constructed to minimize the heat production of the coil and absorption of the electromagnetic energy by the patient's tissue, both of which can be harmful to the patient. In further implementations, the coil should be made of materials that are biocompatible to minimize tissue encapsulation, infection, and electrical corrosion of the electrical connections and conductors. As such, the wires can be made of silver, stainless steel, copper, gold, or any other conductive material that can be used to create an electromagnetic field receiver coil. Alternatively, conductor structures other than wires could be used in the coil, such as, for example, semiconductors or other such structures. In addition, the coil can also have a coating that is made of silicone, urethane, polyimide, Teflon or any other material that can provide electrical insulation and isolation of the receiver coil from bodily fluids. In certain alternative embodiments, the coil can be made with polyimide flex circuits or similar materials that result in high density printed circuit capabilities. In a further alternative, the coil can be constructed by weaving wires into fabrics such as Dacron or polyester.
In one implementation, the internal coil (such as the internal coils 24, 32, or any other internal coil described or contemplated herein) has a minimum diameter of at least about 6 cm. That is, even for those implementations in which the coil has an oval shape, the shortest diameter at any point on the coil is at least about 6 cm. Alternatively, the internal coil has a minimum diameter of at least about 10 cm. In a further alternative, the internal coil has a diameter ranging from about 6 cm to about 30 cm. In further implementations, the coil is an oval-shaped coil as discussed elsewhere herein with height and width as shown in
According to one embodiment, the wire size in the coil is selected to carry the required current and not produce significant self heating. For example, in one implementation, the wire size ranges from about 0.005 inches to about 0.75 inches. Alternatively, the wire size ranges from about AWG 0000 to about AWG 40. In one example, the wire is a Litz wire (commercially available from Cooner Wire) that is used in resonant coils construction to reduce excessive heating in alternating fields. According to one specific exemplary implementation, the wire is Cooner Litz wire PN CW4114 that is constructed of 1050 individual 44 Ga. wires arranged in 5 bundles of 5 groups of 42 wires, which creates an effective 14 AWG (1.628 mm) coil conductor. The wire is copper and is coated with polyurethane insulation bound in a Dacron outer jacket.
As shown in
In a further alternative, the outer coil can be configured in any number of ways, such as, for example, sewn into a vest, shirt, jacket, or other article of clothing, attached to a belt, or incorporated into a bed, chair, or car seat. In yet another alternative, the outer coil can have any physical coil configuration that creates a desired effective area and electrical impedance. In a further implementation, the outer coil can be any coil that is not required to be adhered to the patient's skin. The outer coil can be made of any of the same materials as described with respect to the inner coil embodiments disclosed herein.
According to one embodiment, any internal coil embodiment described or contemplated herein—including the coil 52 depicted in FIG. 5B—can have two sides, each having a coating made of different materials. For example, the internal coil 52 has a first side (or “external side”) 58A of the coil can have a coating that is adherent, while the second side (or “internal side”) 58B of the coil has a coating that is lubricious or slippery. In one embodiment, the lubricious coating on the internal side 58B is intended to contact the lungs, while the adherent, flexible materials on the external side 58A are intended to contact the rib cage, thereby resulting in a coil 52 that is stable and comfortable. More specifically, the slipperiness of the lubricious coating on the internal side 58B is intended to not cause damage to the internal organs (such as the lungs) when the coating comes into contact with such organs, while the stickiness of the adherent coating on the external side 58A is intended to enhance the adherence of the coil 52 to the rib cage or other internal wall of the target cavity, thereby providing some stability or fixation of the coil 52.
Alternatively, the compliance chamber 74 need not be coupled to an outer edge of the coil 72. Instead, as shown in
The various embodiments disclosed herein generate energy that is sufficient to power any implantable medical device. That is, some combination of the large external and internal coils, the positioning of those coils with respect to each other (including the positioning of the internal coil in a patient cavity such as the lung cavity), and various other characteristics of the systems can result in energy generation that is more than sufficient for any known implantable medical device or device that is positioned on the patient's body. For example, the systems contemplated herein can power any drug delivery device, any CRM device, any heart assist device, or any other known implantable device. Alternatively, the various systems disclosed herein can also be used to power smaller devices, including, for example, devices intended for use in the eyes or ears of a patient.
In another implementation, resonant power can also incorporate passive resonant coils (also referred to as “repeater coils”) to increase effective coupling distance between the transmitter and ultimate receiver coil. For example, an external coil could be attached to the patient in the form of a vest, shoulder strap, or anatomical adhesive attachment, wherein the coil is not connected to a battery transmitter circuit. This offers a separation distance advantage from the heavy power generating transmitter coil without significant loss, since the repeater coils are tuned to the exact resonant frequency of the transmitter and receiver coils. Since the excitation energy is transferred to the passive coil causing it to create and collapse the energy field very efficiently, the repeater coils can be used both outside and inside the body.
One exemplary embodiment of a system having a repeater coil 36 is depicted in
A passive repeater coil is constructed via the same techniques as the receiver coils, but is self-contained electrically in that it is a closed loop circuit. A circuit description can be seen in
While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. Further, although the present invention has been described with reference to preferred embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
In one example, the system has an internal coil similar to the coil 20 depicted in
The effective diameter for this exemplary coil can be determined from the effective coil area. Based on certain simple assumptions, the effective coil diameter of the exemplary coil may be determined by calculating the area of the resulting anatomical coil geometry and resolving that into an equivalent circular radius. In the case of the internal coil having a width of 15 cm and a height of 25 cm, the effective coil area of 295 cm2 (π×r1×r2) can be equated to a circular coil (A=π×r2) where the effective radius would be 9.7 cm.
The inductance and resistance of the coil is:
L=2 μoDN2 and R=ρNπD/α;
Where μo=permittivity for free space, 4 π×10−7
D=effective diameter;
N=numbers of turns;
ρ=resistivity Ω−m;
α=wire cross sectional area m2;
and Q=4(/ρ)fN α; and
Where f=tuned frequency.
The selected operating frequency in human tissue must be above 125 kHz to prevent DC tissue stimulation and below 10 Mhz to minimize direct EM tissue heating described by the Specific Adsorption Rate (SAR) limits established by the ICNIRP. The current design example will be based on a 1 MHz design frequency.
The power requirements for heart assist devices is in the range 1 to 10 watt average. Assuming the voltage required to drive a motor or actuator is in the range 10 to 15 volts, a design voltage of 12 v will be used in this example. To keep heating below 40 mW/cm2, a Litz wire diameter is selected of a large enough diameter and high enough wire count to minimize Eddy currents and DC resistive heating. For this example 2 mm diameter Litz wire constructed with 5 bundles of 5/42/44 wire strands will utilized. The effective diameter will be 2 mm and the resistivity will be copper in this example but may also be silver or gold if desired for medical implant requirements.
The inner receiver coil 20 will be constructed from 6 turns of 2 mm wire coiled to give an effective diameter of r=97 mm. Solving for L and C is as follows:
F=ω/2π=1/2 π√LC
Leff=12.018 μH
Xeff=75.5Ω
Reff=0.159Ω
C=(1/2 πf)2/L
C=2107.7 pf
Q=1/R√LC
Qeff=473.3
The outer transmit receiver coil 24 will be constructed from 10 turns of 2 mm wire coiled to give an effective diameter of r=158 mm. Solving for L and C is as follows:
F=ω/2π=1/2 π√LC
Leff=49.009 μH
Xeff=307.9Ω
Reff=0.557Ω
C=(1/2 πf)2/L
C=516.8 pf
Q=1/R√LC
Qeff=552.3
The TET system in this example is configured to deliver power for a 3 W-6 W device powered at 12 volts, meaning that this system can power such devices as the heart assist device described in U.S. Pat. No. 6,808,484, which is hereby incorporated herein by reference in its entirety. It is understood that similar configurations can be created which deliver less power and can occur at greater separation distances. It is also understood that multiple receiver coils of identical design can be created to power multiple devices. One possible advantage of a cavity coil design or supported loop design is that looser coupling can occur between the primary and secondary coils. Patient comfort and safety and quality of life can be improved with the designs of this invention.
This application claims the benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/610,173, filed on Mar. 13, 2012, which is hereby incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61610173 | Mar 2012 | US |
