Surgery – Specula – Laryngoscope
Reexamination Certificate
1999-07-26
2001-07-10
Recla, Henry J. (Department: 3731)
Surgery
Specula
Laryngoscope
60
Reexamination Certificate
active
06258026
ABSTRACT:
BACKGROUND OF THE INVENTION
In recent years, a number of medical devices have been designed which are adapted for compression into a small size to facilitate introduction into a vascular passageway and which are subsequently expandable into contact with the walls of the passageway. These devices, among others, include blood clot filters which expand and are held in position by engagement with the inner wall of a vein. It has been found to be advantageous to form such devices of a shape memory material having a first, relatively pliable low temperature condition and a second, relatively rigid high-temperature condition. By forming such devices of temperature responsive material, the device in a flexible and reduced stress state may be compressed and fit within the bore of a delivery catheter when exposed to a temperature below a predetermined transition temperature, but at temperatures at or above the transition temperature, the device expands and becomes relatively rigid.
Known self expanding medical devices have been formed of Nitinol, an alloy of titanium and nickel which provides the device with a thermal memory. The unique characteristic of this alloy is its thermally triggered shape memory, which allows a device constructed of the alloy to be cooled below a temperature transformation level to a martensitic state and thereby softened for loading into a catheter in a relatively compressed and elongated state, and to regain the memorized shape in an austenitic state when warmed to a selected temperature above the temperature transformation level, such as human body temperature. The two interchangeable shapes are possible because of the two distinct microcrystalline structures that are interchangeable with a small variation in temperature. The temperature at which the device assumes its first configuration may be varied within wide limits by changing the composition of the alloy. Thus, while for human use the alloy may be focused on a transition temperature range close to 98.6° F., the alloy readily may be modified for use in animals with different body temperatures.
U.S. Pat. No. 4,425,908 to Simon discloses a very effective blood clot filter formed of thermal shape memory material. This filter, like most previously developed vena cava filters such as those also shown by U.S. Pat. Nos. 5,108,418 to Lefebvre, 5,133,733 to Rasmussen et al., 5,242,462 to El-Nounou et al., 5,800,457 to Gelbfish and 5,853,420 to Chevillon et al. is a permanent filter which, when once implanted, is designed to remain in place. Such filters include structure to anchor the filter in place within the vena cava, such as elongate diverging legs with hooked ends that penetrate the vessel wall and positively prevent migration in either direction longitudinally of the vessel. The hooks on filters of this type are rigid and will not bend, and within two to six weeks after a filter of this type has been implanted, the endothelium layer grows over the diverging legs and positively locks the hooks in place. Now any attempt to remove the filter results in a risk of injury to or rupture of the vena cava.
A number of medical procedures subject the patient to a short term risk of pulmonary embolism which can be alleviated by a filter implant. In such cases, patients are often adverse to receiving a permanent implant, for the risk of pulmonary embolism may disappear after a period of several weeks or months. However, most existing filters are not easily or safely removable after they have remained in place for more than two weeks, and consequently longer term temporary filters which do not result in the likelihood of injury to the vessel wall upon removal are not available.
In an attempt to provide a removable filter, two filter baskets have been formed along a central shaft which are conical in configuration, with each basket being formed by spaced struts radiating outwardly from a central hub for the basket. The central hubs are held apart by a compression unit, and the arms of the two baskets overlap so that the baskets face one another. Devices of this type require the use of two removal devices inserted at each end of the filter to draw the baskets apart and fracture the compression unit. The end sections of the arms are formed to lie in substantially parallel relationship to the vessel wall and the tips are inclined inwardly to preclude vessel wall penetration. If a device of this type is withdrawn before the endothelium layer grows over the arms, vessel wall damage is minimized. However, after growth of the endothelium layer the combined inward and longitudinal movement of the filter sections as they are drawn apart can tear this layer. U.S. Pat. No. 5,370,657 to Irie is illustrative of a prior art removable filter of this type which requires two removal devices.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a vessel implantable filter of shape memory material having temperature induced austenitic and martensite states which maybe easily removed by a single removal device after an extended period of time without significantly injuring the vessel wall.
Another object of the present invention is to provide a blood clot filter of shape memory material which operates in a temperature induced austenitic state to exert a force on the wall of a vessel by means of oppositely disposed legs to maintain the filter in place, but which may easily be removed after the endothelium layer has covered the ends of the filter legs without significant damage to the vessel wall.
A further object of the present invention is to provide a novel and improved vessel implantable filter having a group of arms and a group of legs which incline from a central axis. The ends of the arms in the group of arms are oriented to engage a vessel wall to orient and center the filter in the vessel, and the ends of the legs of the group of legs are oriented to engage the vessel wall to prevent longitudinal movement of the filter along the vessel. The ends of at least some of the legs are provided with hooks configured to be more elastic than the legs to permit the hooks to straighten in response to a withdrawal force to facilitate withdrawal from the endothelium layer without risk of significant injury to the vessel wall. In some cases, similar hooks can be formed on the ends of at least some of the arms.
Yet another object of the present invention is to provide a novel and improved vessel implantable filter having one or more expandable appendages which engage the wall of the vessel. An elastic hook is formed on the free end of an appendage to pierce the vessel wall and insure that the filter does not migrate in response to normal respiratory functions or in the event of a massive pulmonary embolism. The hook is formed to have a maximum migration force, and when subjected to forces below the maximum migration force, the hook retains its shape. When subjected to forces above the maximum migration force, the hook straightens and can be withdrawn without significant damage to the vessel wall.
A further object of the present invention is to provide a novel and improved vessel implantable filter having a plurality of expandable appendages which engage the wall of a vessel. Three to twelve of such appendages are provided which have an elastic hook formed on the free end of the appendage to pierce the vessel wall and insure that the filter does not migrate when subjected to a pressure gradient falling within a range of from 10 mmHg to 120 mmHg in a 28 mm vessel (filter migration resistance). Each hook is formed to have a maximum migration force, and when subjected to forces below the maximum migration force, the hook retains its shape. When subjected to forces above the maximum migration force, the hook straightens and can be withdrawn without significant damage to the vessel wall. The maximum migration force for each hook is dependent upon the desired total filter migration resistance and the number of hooks formed on the filter.
A still further object of the present invention is to provide a novel and improved rem
Kleshinski Stephen J.
Ravenscroft Adrian C.
Ngo Lien
Nitinol Medical Technologies Inc.
Nixon & Peabody LLP
Recla Henry J.
Sixbey Daniel W.
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