Surgery – Instruments – Internal pressure applicator
Reexamination Certificate
2000-12-14
2004-03-30
Milano, Michael J. (Department: 3731)
Surgery
Instruments
Internal pressure applicator
Reexamination Certificate
active
06712834
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of implantable blood filtering devices, and more specifically it is directed to filtering devices for implantation in arteries supplying blood to the brain. The invention is also concerned with a method for detecting and removing plaque debris from the filtering device.
BACKGROUND OF THE INVENTION
Blood to the brain hemispheres is supplied by two carotid arteries, each of which branches-off into a so-called internal carotid and an external carotid. Blood to the brain stem is supplied by two vertebral arteries.
Cerebralvascular diseases are considered among the leading causes of mortality and morbidity in the modern age. Strokes denote an abrupt impairment of brain function caused by pathologic changes occurring in blood vessels. The main causes of strokes is insufficient blood flow to the brain (referred to as “an ischemic stroke”) which are about 80% of stroke cases.
Ischemic strokes are caused by sudden occlusion of an artery supplying blood to the brain. Occlusion or partial occlusion (stenosis) are the result of diseases of the arterial wall. Arterial atherosclerosis is by far the most common arterial disorder, and when complicated by thrombosis or embolism it is the most frequent cause of cerebral ischemia and infarction, eventually causing the cerebral stroke.
Such disorders are treated in different ways such as by drug management, surgery (carotid endarterectomy) in case of occlusive disease, or carotid angioplasty and carotid stents as known in the art.
While endarterectomy, angioplasty and carotid stenting are procedures targeting at reopening the occluded artery, they do not prevent progression of new plaque (restenosis). Furthermore, embolisms from the new forming plaque in the internal carotid artery (with or without a stent implanted therein) can occlude smaller arteries in the brain and cause strokes. Even more so, the above treatment methods do not prevent proximal embolic sources, i.e. embolus formed at remote sites (heart and ascending aorta) to pass through the reopened stenosis in the carotid and occlude smaller arteries in the brain.
It will also be appreciated that endarterectomy is not suitable for intracarnial arteries or in the vertebrobasilar system since these arteries are positioned within unacceptable environment (brain tissue, bone issue) or are of a small diameter.
Introducing filtering means into blood vessels has been known for a while, in particular into veins. However, such filtering means are generally of a complex design which render such devices not suitable for implantation with carotid arteries and not suitable for handling fine plaque debris. However, when considering the possible cerebral effects of even fine plaque debris occluding an artery supplying blood to the brain, the consequences may be fatal or cause irreversible brain damage.
Occlusion of a vein is not a critical event and in most cases a time range of up to several hours is available before severe damage is caused to organisms. This applies also to arterial blood supply to the heart, which may survive a longer period of time before critical damage is caused.
However, in light of the short periods of time during which brain tissue can survive without blood supply (several minutes only, typically about 3 minutes), there is significant importance to provide filtering means suitable for entrapping even small plaque debris to prevent brain damage.
Whilst a large variety of patents in the field of inplantable filtering systems are known to Applicants, they are mostly intended for implantation in veins and in particular are intended for vena cava implantation. The following is a list of U.S. Pat. Nos., all being in the field of implantable blood filters: U.S. Pat. Nos. 5,391,196, 5,626,605, 5,827,324, 4,425,908, 3,996,938, 4,494,531, 4,619,246, 4,873,978, 4,817,600, 4,943,297, 4,957,501, 4,990,156, 5,059,205, 5,152,777, 5,324,304, 5,344,425, 5,370,657, 5,413,586, 5,549,626, 5,649,950, 5,695,519, 5,720,764, 5,800,525, 5,814,064, 5,800,525 and 5,709,704.
It is noted, however, that neither of the above patents refers to hemodynamic considerations which as appreciated by a skilled person are of critical importance. This is one of the reasons why, so far, filtering devices for implantation into carotid arteries are not available.
By using the term “hemodynamics” it is referred to blood flowing parameters which if not maintained may be fatal. Such parameters are, for example, wall shear stress, shear rates, pressure drop over the filter, platelet activation parameter (which is the dominant parameter governing blood coagulation). It is thus essential that such a filtering device does not change the hemodynamic parameters beyond some predetermined parameters.
It is the object of the present invention to provide an implantable filtering device for positioning in a blood vessel supplying blood to the brain so as to filter the blood and entrap embolic debris and thereby prevent extracranial embolus to occlude small intracranial arteries in the brain.
It is a second aspect of the present invention to provide a method for detecting plaque debris entrapped within the filtering device and a method for removal thereof.
SUMMARY OF THE INVENTION
According to the present invention there is provided an implantable filtering device for implanting within an artery supplying blood to the brain the device being made of bio-compatible material and comprising a filtering unit for entrapping plaque debris, and an anchoring member engageable with the walls of the carotid artery for anchoring said filtering unit at a fixed location within the artery;
the filtering device is characterized in that the filtering unit has a tapering shape extending between a wide inlet portion and a narrower outlet portion extending downstream, said outlet portion comprising a trap element for entrapping plaque debris.
The term “carotid artery” denotes any of the main arteries supplying blood to the brain. However, a preferred site for implanting such a filtering device would be the internal carotid artery, although not restricted thereto. Implanting a filtering device may also be possible within the carotid artery branches and in the vertebrobasilar system.
The device in accordance with the present invention is designed to retain some hemodynamic parameters and accordingly, the filtering unit is formed with a plurality of openings which are sized, shaped and disposed so as to ensure the following parameters:
i) 2<wall shear stress<10
2
[dynes/cm
2
]
ii) shear rate<5000 [sec
−1
]
however, preferably, the shear rate is smaller than 2000 [sec
−1
]. Furthermore, the pressure drop over the filtering device does not exceed about 20 mm Hg.
In a typical surgical procedure, the filtering device of the present invention is adapted for implanting within an internal carotid artery.
The trap element is adapted for trapping plaque debris which are filtered through the filtering unit. The trap element is a tubular body fixed to the filtering unit and comprises a plurality of deflectable trapping members radially extending within the body. The trapping members may also be arranged in a helical manner, extending inwardly from inner walls of the trap element. In accordance with one specific design, the trapping members constitute a maze and at a downstream end of the trapped member there are provided a plurality of deflectable end wires laterally extending across the end. In accordance with a most preferred embodiment, the trap element is cylindrical and coaxially extends at the outlet portion of the filtering unit. This particular design has significant importance in measuring flow parameters such as blood motion spectral signature and blood velocity profile. The trap element may also be formed with openings which may alternate in shape, depending on the desired flow pattern.
The arrangement is such that the end wires constitute a grid suitable for entrapping particles larger than about 100 &mgr;m. The trapping members and the end-wires of th
Grad Ygael
Levin Daniel
Rosenfeld Moshe
Yassour Yuval
Yodfat Ofer
Baxter Jessica R
G.E. Ehrlich (1995) Ltd.
Milano Michael J.
Mindguard Ltd.
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