Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
1999-04-30
2001-05-08
Seidel, Richard K. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S288030
Reexamination Certificate
active
06228050
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates generally to implantable drug delivery devices. More particularly, the invention relates to overfill protection systems for preventing the overfilling and over pressurization of a reservoir of an implantable drug delivery device.
Description of Related Art
Implantable drug delivery systems are in widespread use to provide site-specific and/or sustained delivery of beneficial agents to address adverse patient conditions. Such delivery systems may include implantable infusion pumps, which typically include a pressurized drug reservoir and some form of fluid flow control. One example of an implantable infusion pump is the SYNCHROMED™ pump manufactured by Medtronic, Inc. of Minneapolis, Minn.
Typically, implantable drug delivery devices are periodically refilled in situ and percutaneously using a refill device, such as a hypodermic syringe inserted into a refill chamber of the device. A common problem related to refilling is the potential for overfilling or over pressurization of the device. Typically, the clinician who refills the device must rely on tactile pressure to sense that the drug reservoir has been filled to capacity. Any additional fluid injected into the device beyond capacity of the reservoir may cause severe damage to the drug administration device and may cause other adverse consequences.
Prior art overfill prevention devices, such as those described in U.S. Pat. No. 5,158,547, the entire writing of which is incorporated herein by reference, are exemplified by
FIG. 1
, which is a cross-section of a drug delivery device in the form of an implantable infusion pump
10
. Generally, a valve
12
having a rigid valve stem
14
is fastened, usually by welding, to an inner surface
16
of the pump diaphragm or bellows
18
. As new drug supply is injected through the septum
20
using a refill device (not shown), the reservoir chamber
22
fills with drug and the surface
16
moves towards a full position (downward in FIG.
1
). As the reservoir chamber
22
reaches capacity, the valve
12
is pulled into sealing engagement with a valve seat
26
, resulting in a detectable increase in pressure in the refill device and preventing overfilling and/or over pressurization of the drug delivery device
10
. Notably, in prior art devices, as the reservoir collapses, the valve
12
and valve stem
14
must travel within the pump housing
30
a distance approximately equal to the distance traveled by the surface
16
of the reservoir
18
.
Large reservoir sizes are desirable because they permit more quantity of a given therapeutic agent to be stored in the device and reduce the amount of refills necessary for a given period of time. On the other hand, it is desirable to reduce or maintain the size of the “footprint” of the overall drug delivery device so as to increase the ease of implantation and reduce associated trauma to the living body. As the size of the power and flow control features of drug delivery devices becomes reduced, due to advances in the related arts, there is potential for larger size reservoirs without associated increases in the size of the overall delivery device. However, prior art overfill protection systems are characterized by valve displacement that is equal to the displacement of the reservoir surface and therefore require that the pump housing depth be increased to accommodate the increased valve displacement that would occur with reservoirs of increased depth. Thus, prior art devices present an obstacle to further reduction in delivery device size and increase in reservoir size.
What is needed is an overfill protection system for implantable drug delivery devices which addresses the aforementioned problems. Specifically, what is needed is an overfill protection system for an implantable drug delivery device that does not require an increase in housing depth when the reservoir depth is increased.
SUMMARY OF THE INVENTION
The present invention solves the aforementioned problems by providing an overfill protection system for an implantable drug delivery device that incorporates a link for moving a refill valve in response to movement of the reservoir surface, wherein the link provides for reduced travel or displacement of the valve compared to prior art devices.
In a preferred embodiment, the collapsible link is provided as a telescoping member, which may be formed as a coil spring that is situated partially around the valve stem, which is separate from the reservoir surface but positioned to contact the reservoir surface as the reservoir collapses. The dimensions of the coil spring are such that positive contact between the reservoir surface occurs before the coil spring is fully compressed. In operation, when the drug delivery device is refilled, the reservoir expands and the reservoir surface moves towards a full position. Since the coil spring is affixed to the reservoir surface, it eventually extends beyond its natural length and exerts a force on the valve. As the valve is pulled into contact with its seat, a detectable pressure increase is sensed in the refill device. In accordance with the invention, as the drug supply contained in the reservoir depletes, the reservoir surface moves towards a collapsed position, compressing the coil spring and eventually contacting the valve stem, thereby lifting the valve from its seat. By virtue of telescoping link, the valve displacement is less than the reservoir surface displacement, thus eliminating the need for increased housing depth when larger reservoirs are used.
In another preferred embodiment, the collapsible link includes a second spring combined with a telescoping link. The second spring is situated on a side of the valve opposite the telescoping link, thereby providing a downward force on the valve and valve stem. This embodiment eliminates the need for fastening the first spring of the telescoping member to the reservoir surface and provides for reduced construction costs and increased dependability.
Still another aspect of the invention provides a lever arm for actuating the refill valve. A pivot for the lever arm is situated near the refill valve and a distal end of the lever arm maintained in contact with the reservoir surface using a spring bias. An intermediate portion of the lever arm engages the valve stem. Thus, as the reservoir surface moves towards the collapsed position, the displacement of the valve is a fraction of the displacement of the distal end of the lever arm.
The unique advantages provided by the invention reduce the displacement of refill valves in an implantable drug delivery device. Thus, housings of drug delivery device according to the invention need not be configured to accommodate valve displacement in an amount that is equal to the reservoir surface travel. Accordingly, reservoirs of increased depth may be utilized without a corresponding increase in the housing size.
REFERENCES:
patent: 4832054 (1989-05-01), Bark
patent: 4978338 (1990-12-01), Melsky et al.
patent: 5158547 (1992-10-01), Doan et al.
patent: 5242406 (1993-09-01), Gross et al.
patent: 5665070 (1997-09-01), McPhee
Christiansen Chris
Kratoska Paul
Olsen James M.
Robinson Reginald D.
Banner & Witcoff , Ltd.
Medtronic Inc.
Seidel Richard K.
Thanh Loan H.
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