Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-04-30
2001-05-29
Kamm, William E. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06240317
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the implantable medical devices and more specifically to telemetry systems for allowing communication between implanted medical devices and external programmers or monitors.
In the context of implantable medical devices, it has become common to provide a communication link between the implanted device and an external programmer or monitor in order to allow for transmission of commands from the external device to the implanted device and to allow for transmission of stored information and/or sensed physiological parameters from the implanted device to the external programmer. Conventionally, communication between an implanted device and an external programmer has been accomplished by means of a telemetry system which includes a transceiver located within the implanted medical device and an external programmer or monitor, each having a radio transmitter/receiver and one or more antennas.
The implanted device typically includes an antenna located either within the hermetic device housing containing the circuitry, as disclosed in U.S. Pat. No. 4,542,532 issued to McQuilkin, in a plastic header or connector block used to interconnect the device to electrical leads as disclosed in U.S. Pat. No. 5,697,958 issued to Patrick et al. or mounted to the device housing as in U.S. Pat. No. 5,861,019 issued to Sun et al. and U.S. Pat. No. 5,720,770 issued to Nappholz et al., all incorporated herein in their entireties. The programmer or monitor typically includes or consists of a programming head containing an antenna, intended to be placed on the patient's body in close proximity to the implanted device. The programming head may be coupled to the external programmer or monitor by means of a cord, as disclosed in U.S. Pat. No. 5,766,232 issued to Grevious et al.
More recently it has been proposed to provide communication systems for implantable devices in which the programming head is done away with, and communication occurs directly between the programmer or monitor, which may be located some distance from the patient, and the implanted medical device. Such systems are disclosed in U.S. Pat. No. 5,404,877 issued to Nolan et al, and U.S. Pat. No. 5,113,869 issued to Nappholz. In the Nappholz patent, in particular, the use of an electrical lead as the antenna for broadcasting RF signals to the programmer or monitor which may be located some feet away from the patient is suggested.
SUMMARY OF THE INVENTION
The present invention is directed toward a telemetry system for an implantable device which, like the devices in the above cited Nolan and Nappholz patents allows for communication between an implanted device and an associated external programmer or monitor without the necessity of a programming head placed on the patient's body in close proximity to the implanted device. In conjunction with this invention, an improved antenna configuration for the implanted device is provided, optimized to allow for reliable communication between an implanted device and the antenna of an external programmer or monitor which may be spaced at least several feet from one another.
In preferred embodiments of the invention, the antenna of the implanted device takes the form of a monopole antenna located external to the hermetic enclosure of the implanted device, having a length tuned to function optimally at the radio frequencies chosen for use in the telemetry system. In a first embodiment of the invention, the antenna takes the form of a tab-loaded monopole, comprising a wire encased in an insulative material, extending from the connector block assembly of the device and coupled to the RF transceiver located within the device by means of a folded metal strip or tab located in the connector block, extending between the proximal end of the insulated wire and a feed-through coupled to the RF transceiver circuitry within the housing of the device. In particular, the folded metal strip may be fabricated of metal foil or a metallized plastic film and may take the general form of an isosceles triangle provided with laterally extending tabs at its base. In this embodiment, the base of the triangle is coupled to the antenna while the opposite apex of the triangle is coupled to the feed-through and in turn to transceiver circuitry within the device housing. The length of the insulated wire is chosen to be optimized for the intended operational frequency range of the transceiver. In one preferred embodiment, the transceiver takes the form of a RF transceiver operating at about 400 megaHertz and the length of the insulated wire is approximately 12 centimeters. In particular, the insulated wire in this embodiment may be a stranded wire, insulated in a silicone rubber sleeve.
In a second embodiment, the antenna of the implanted device takes the form of a length of coaxial cable having a central or core wire coupled to a feedthrough, in turn coupled to transceiver circuitry within the device housing and having a coaxial shield extending over only a portion of the length of the cable. For example, in the context of an implanted device having a transceiver intended to operate in the vicinity of 400 megaHertz, the coaxial cable may extend for a length of approximately 12 centimeters from the point at which it is coupled to the feedthrough, of which length only the four centimeters closest to the feedthrough are provided with a coaxial shield. In particular, the antenna may be a length of coaxial type cable, having a metallic center conductor, a 3.1 dielectric and a braided wire coaxial shield, stripped of its outer insulation and stripped of its coaxial shield over the eight centimeters most distant from the feedthrough. The four centimeters over which the shield extends may conveniently be located in the connector block of the device, with the remaining eight centimeters either extending freely outward from the connector block or mounted to the device housing and encased in an insulating material.
In either of the two embodiments described above, the antenna may be manufactured as an integral part of implanted device or, that portion of the antenna extending external to the connector block may be manufactured as a separate piece part, coupled to the portion of the antenna within the connector block by means of a standard electrical connector. In this context, the portion of the antenna extending from the connector block may be included as a portion of an implantable stimulation lead, also inserted into the connector block. In a preferred embodiment, the portion of the antenna located external to the connector block is mechanically coupled at its distal end to the stimulation lead.
An implantable device according to the invention is preferably employed with a programmer or monitor having a spatial diversity antenna array in order to facilitate reception of signals from the implanted device and transmission of signals to the implanted device, within a wide area surrounding the monitor or programmer. One appropriate embodiment of an antenna for the programmer or monitor takes the form two antennas, each comprising two conductive plates mounted orthogonally to one another on exterior or interior surfaces of a housing which may be the programmer or monitor housing. In this embodiment, the portion of the housing to which the antennas are mounted is fabricated of a non-conductive material such as plastic. The two metallic plates of each antenna may be mounted adjacent opposing comers edges of the housing. For example, in the context of programmers or monitors provided with an LCD or CRT display, the antennas may be mounted adjacent opposite upper comers of the housing enclosing the display. In such an embodiment, each of the two antennas would include a plate mounted to the upper surface of the display housing and a plate mounted to an adjacent side surface of the display housing.
In each of the two antennas, the two plates are coupled to an RF feed cable by means of a 180° splitter and tuned circuit. Selection of which of the two antennas is employed to transm
Dublin Garry L.
Villaseca Eduardo H.
Duthler Reed A.
Kamm William E.
Medtronic Inc.
Patton Harold R.
Wolde-Michael Girma
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