Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-10-26
2002-04-02
Evanisko, George R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C623S003270
Reexamination Certificate
active
06366817
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to energy transfer devices and methods and, more particularly, to devices and processes for transcutaneous energy transfer (TET) to a secondary coil implanted in a subject.
2. Related Art
Many medical devices are now designed to be implanted in humans or animals, including pacemakers, defibrillators, circulatory assist devices, cardiac replacement devices such as artificial hearts, cochler implants, neuromuscular simulators, biosensors, and the like. Since many of these devices require a source of power, inductively coupled transcutaneous energy transfer (TET) systems are coming into increasing use. A TET system may be employed to supplement, replace, or charge an implanted power source, such as a rechargeable battery. Unlike other types of power transfer systems, TET systems have an advantage of being able to provide power to the implanted electrical and/or mechanical device, or recharge the internal power source, without puncturing the skin. Thus, possibilities of infection are reduced and comfort and convenience are increased.
TET devices include an external primary coil and an implanted secondary coil, separated by intervening layers of tissue. The two coils constitute a transcutaneous transformer. The transformer is designed to induce alternating current in the subcutaneous secondary coil, typically for transformation to direct current to power the implanted device. TET devices therefore also typically include an oscillator and other electrical circuits for periodically providing appropriate alternating current to the primary coil. These circuits, referred to for convenience herein as “TET primary circuits,” receive their power from an external power source.
Generally, the non-implanted portions of conventional TET systems are attached externally to the patient, typically by a belt or other fastener or garment, such that the primary coil of the TET is operationally aligned with the implanted secondary coil. The TET primary circuits and external power supply are also generally attached to the patient's body at or near the site of the attachment of the primary coil. Such a configuration typically is disadvantageous, however, particularly when the patient is sleeping or resting. For example, if a patient is sleeping on a mattress, the patient would likely be uncomfortable, or restricted in movement, if all or some of the TET primary circuits and external power supply were attached to the patient. In addition to discomfort or restriction of movement, additional disadvantages of such body attachments include possibilities of injury to the patient or the devices. Movements of the patient may alter the position of the primary coil so that it is not properly positioned over the implanted secondary coil to achieve a desired or required transfer of power.
To overcome these drawbacks, other conventional approaches require only the primary coil be attached to the patient. Wires connect the primary coil to the TET primary circuits, which, with the power supply, may be located at a distance from the patient outside of the sleeping or resting surface. However, such an alternative configuration also has significant disadvantages. First, the primary coil is still attached to the patient and therefore subject to the above drawbacks may cause discomfort or restriction of movement. Also, as the patient moves, the wires connecting the externally attached primary coil to the TET primary circuits may become tangled or entangled with bedding or the patient. In addition to being uncomfortable, such tangling may result in dislodging the primary coil from its required alignment; it may injure the patient, such as by restricting blood or oxygen supply; or it may interfere with tubes or other devices attached to the patient.
SUMMARY
To overcome the above and other drawbacks to conventional systems, the present invention provides an electromagnetic field source (EFS) for providing electromagnetic energy to a secondary coil. In one embodiment, the EFS includes two or more primary coils that each carry a time-varying current to produce an electromagnetic field. The EFS also includes a controller that selectively provides current to one or more of the primary coils based on their position relative to the secondary coil. The controller may be implemented in electrical circuits, software, firmware, or any combination thereof.
In another embodiment, the invention provides a transcutaneous energy transmission (TET) device including a secondary coil implanted in a human being. In this embodiment, the secondary coil is used to provide power for the operation of an implanted medical device, such as an artificial heart or ventricular assist device. In some implementations, the primary coils are housed in furniture, such as a bed mattress. Also, the primary coils may be housed in bed covering, such as a blanket or mattress pad.
In certain embodiments the controller includes a proximity detector that identifies a quantity of primary coils that are closest to the secondary coil, referred herein to as the “closest” primary coils. A current director that is responsive to the proximity detector is also included in the controller. The current director selectively directs time-varying currents through the closest primary coils.
One advantage of a TET in accordance with certain aspects of the present invention is that there are no wires connecting the subject of the implanted device to external components, such as a power supply or other electrical circuits. Rather, a recipient of the implanted device may rest on furniture that houses the primary coils, and those primary coils that are closest to the implanted secondary coil may be energized. Thus, the recipient is uninhibited with respect to movement on or in the furniture, such as a bed, couch, or chair, and is provided with a more comfortable resting environment. Also, serious disadvantages of known systems, such as becoming entangled with a wire, or of dislodging a primary coil, are avoided by the present invention.
Another advantage is the portability of implementations such as those in which the primary coils are housed in a bed covering or a mattress pad. Thus, a recipient may pack such housing, together with the controller and power supply, in suitcases or similar containers for traveling. Similarly, a hospital mattress may readily be converted to include portions of a TET by covering it with a blanket or mattress pad containing primary coils in accordance with embodiments of the present invention.
Advantageously, the primary coils may be disposed over substantially all of the top surface of the mattress, or throughout the bed covering or mattress pad. Thus, in such embodiments, if the recipient shifts position on the mattress, there will be one or more primary coils located close to the implanted secondary coil. In some implementations, the primary coils may be positioned in generally even rows and columns with respect to the top surface of the mattress. In other implementations, they may be positioned generally in hexagonal arrangements. It will be understood to those of ordinary skill that there are many possible configurations that provide primary coils over the entire surface upon which the recipient is resting or reclining.
Also advantageously the controller of the EFS or TET may determine the approximate distance between the primary coils and the secondary coil, and adjust the amount of current to the closest primary coils accordingly. In particular, a proximity detector may be included to determine an approximate distance between one or more of the closest primary coils and the secondary coil. In embodiments that include such a proximity detector, if that distance is greater than a nominal threshold value, current director may increase the currents through selected ones of the closest primary coils. For example, if the recipient is sleeping on a pillow or is otherwise raised above the mattress, the distance from the implanted secondary coil to the primary coils in
Abiomed, Inc.
Evanisko George R.
Nutter & McClennen & Fish LLP
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