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Devices for restoring blood flow within blocked vasculatureRelated Patent Categories: Surgery, Instruments, Means For Removing Tonsils, Adenoids Or Polyps, With Collecting Means For Removed MaterialDevices for restoring blood flow within blocked vasculature description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070185500, Devices for restoring blood flow within blocked vasculature. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a non-provisional of U.S. Provisional Application No. 60/765,496 filed Feb. 03, 2006 which is incorporated by reference in its entirety. FIELD OF THE INVENTION [0002] The devices and methods described herein relate to clearing of blockages within body lumens, such as the vasculature, by addressing the frictional resistance on the obstruction prior to attempting to translate the obstruction within the body lumen. In one variation, the devices and methods described below may treat conditions of ischemic stroke by remove blockages within arteries leading to the brain. Accordingly, variations of such methods and devices must navigate tortuous anatomy and vasculature without causing unacceptable damage to the anatomy. Also, the devices and methods first secure and surround the obstruction (such as a clot) prior to significantly moving the clot within the anatomy. BACKGROUND OF THE INVENTION [0003] Ischemic stroke occurs when a blockage in an artery leading to the brain causes a lack of supply of oxygen and nutrients to the brain tissue. The brain relies on its arteries to supply oxygenated blood from the heart and lungs. The blood returning from the brain carries carbon dioxide and cellular waste. Blockages that interfere with this supply eventually cause the brain tissue to stop functioning. If the disruption in supply occurs for a sufficient amount of time, the continued lack of nutrients and oxygen causes irreversible cell death (infarction). Accordingly, immediate medical treatment of an ischemic stroke is critical for the recovery of a patient. [0004] The infarction may not develop or may be greatly limited given a rapid clearing of the blockage to reestablish the flow of blood. However, if left untreated, ischemic stroke may lead to the permanent loss of brain tissue, and can be marked by full or partial paralysis, loss of motor control, memory loss, or death. [0005] Several different diseases may lead to an ischemic stroke. Typically, deposition of cholesterol (artherosclerosis), formation of blood clots, or other objects in the vessels may disrupt blood flow and lead to ischemic stroke. Furthermore, the substances that cause the blockages may break free from larger vessels outside the brain and become lodged within narrower arteries closer to the brain (embolism). [0006] Ischemic stroke may be divided into thrombotic strokes and embolic strokes. A thrombotic stroke occurs when the building and rupturing of atheromatous plaque within the brain blocks cerebral arteries. Clinically referred to as cerebral thrombosis or cerebral infarction, this condition represents approximately 10% of all strokes. An embolic stroke occurs when a clot or emboli forms somewhere other than in the brain, such as in the cervical carotid artery or in the heart, and travels in the bloodstream until the clot becomes lodged and can not travel any further. When such a condition occurs in the arteries supplying the brain, the condition results in almost immediate physical and neurological effects. [0007] While these are the most common causes of ischemic stroke, there are many other possible causes. Examples include use of drugs, trauma to the blood vessels of the neck, or blood clotting disorders. [0008] Apart from surgical techniques, medical practitioners could address such blockages with the use of Tissue Plasminogen Activator (t-PA). However, t-PA must be used within the first three hours of the onset of stroke symptoms and may take hours or even days to successfully restore flow. In addition, t-PA carries an increased risk of intracerebral hemorrhage. It is currently believed that the use of t-PA results in a 30% success rate as well as a 6% major complication rate. In view of these limitations, the majority of stroke patients in the U.S. do not receive t-PA treatment. [0009] In addition, there are a number of surgical techniques used to remove blockages. For example, an embolectomy, involves incising a blood vessel and introducing a balloon-tipped device (such as the Fogarty catheter) to the location of the occlusion. The balloon is then inflated at a point beyond the clot and used to translate the obstructing material back to the point of incision. The obstructing material is then removed by the surgeon. Concentric Medical, Inc. of Mountain View, Calif. supplies devices for an interventional approach to the removal of obstructions. Concentric supplies a Merci.RTM. Retriever system as a device based approach for the removal of clots. This system engages and ensnares a clot. Once captured, a balloon catheter inflates to temporarily halt forward blood flow while the clot is withdrawn. The clot is then pulled into the catheter and out of the body. [0010] Typically, the existing means to remove obstructions do not address the frictional forces that act on the obstruction during removal of the obstruction. For example, some conventional devices engage the clot from the distal (or downstream) side. As the device is pulled proximally (or upstream), the device attempts to either engulf or ensnare the clot. However, due to the consistency of the clot and because the clot is typically well lodged within the vessel, the act of pulling the clot in a proximal direction cause the clot to also compress in an axial direction. This axial compression (when viewed along the axis of the vessel) causes a contemporaneous radial expansion of the clot (when viewed relative to the vessel). As a result, the increase in diameter of the clot causes an increase in the frictional forces applied against the arterial wall. Thus, by not addressing the frictional forces acting on the obstruction, the process of removing the clot may actually increase the static force that would otherwise be required to remove or translate the clot within the vessel. Unfortunately, increasing the amount of force applied upon one side of the clot also increases the probability of complications during the procedure (e.g., fragmenting the clot, failing to remove the clot, failure to fully engulf/ensnare the clot, and/or device failure) and can cause potential damage to the surrounding vessel. [0011] While there are other drugs and suppliers of devices for removal of blockages, there remains a need for methods and devices that improve the success rate and/or reduce the complication rate in restoring flow and thereby limit the damage from an ischemic stroke. SUMMARY OF THE INVENTION [0012] It should be noted that the present methods and devices may be used to treat blockages leading to ischemic stroke as well as to treat blockages (caused by "obstructions") within other parts of the body (i.e., unless specifically noted, the devices and methods are not simply limited to the cerebral vasculature). The term obstructions may include blood clot, plaque, cholesterol, thrombus, naturally occurring foreign bodies (i.e., a part of the body that is lodged within the lumen), a non-naturally occurring foreign body (i.e., a portion of a medical device or other non-naturally occurring substance lodged within the lumen.) [0013] In one variation of the devices described herein, the device allows for surrounding the obstruction prior to aftempting to translate or move the obstruction within the vessel. It should be noted that although minimal axial movement of the obstruction may take place, the device surrounds the obstruction before such movement causes significant distortion to the geometry of the obstruction resulting in an increase in the static force required to remove the obstruction from the vessel. [0014] In another variation of the device, the device may include a low friction mode (such as a set of parallel wires, or wires extending axially along the lumen or vessel) that converts to an increased friction mode (such as a compressed set of wires acting on the obstruction or a twisted set of wires acting on the obstruction). The increase in friction is an increase in the friction between the obstruction and the device (as opposed to the vessel wall. In some cases, the low friction modes is a low surface area mode and the high friction mode is a high surface area mode. When configured in the low friction mode, the device is better suited to engage the obstruction without the undesirable effect of prematurely mobilizing the obstruction or compacting the obstruction (e.g., when wires are slid across the obstruction in a transverse motion). Upon engaging the obstruction, the device will conform to a high friction mode with respect to the obstruction (in some cases the device will have an increased surface area mode). This high friction mode permits the device to better grip the obstruction for ultimate removal of the obstruction. [0015] The operation of the devices and method described herein secure the obstruction, overcome the elastic forces of the obstruction, then remove the obstruction from the anatomy without losing or fractionating the obstruction. In one variation of the invention, this is accomplished by the obstruction removal device interacting with the obstruction in the following manner: (1) the traversing filaments traverse the obstruction by passing either through the obstruction or between the obstruction and the vascular wall; (2) the traversing portion is pulled proximally to engage the surrounding portion of the device around the obstruction, the surrounding portion engaging the obstruction without causing significant mobilization of the obstruction; (3) the obstruction removal device is pulled further proximally and the surrounding portion now mobilizes the obstruction. [0016] As shown below, variations of the devices have a configuration that provides a path for a portion of the device to surround the obstruction. The paths are made using traversing filaments that allow for low frictional translation of a surrounding portion of the device over the obstruction without causing axial translation of the obstruction. This mechanism is described in more detail below. [0017] Once in the proper position, a portion of the device (e.g., a surrounding portion) increases the frictional contact with the obstruction to disperse the pulling force more evenly across the obstruction. The increase points of contact allow for removal of the obstruction through tortuous anatomy while ensuring that the obstruction will not escape the encapsulation. [0018] The surrounding portion may be fabricated in a variety of ways. For example, the surrounding portion may comprise one or more filaments. The surrounding portion may comprise a filter/bag, a coil, helical filament, a mesh structure, corrugated sheet, braided filaments, single wound or crossing filaments, tubes, membranes, films, solid wires, filled tubes, castings. Furthermore, the surrounding portion may have one or more ports, openings, slits, and/or holes. The surrounding portion may be made by photochemical etching, mechanical drilling, weaving, braiding, laser cutting, or other means. [0019] It should be noted that reference to surrounding or securing the obstruction includes partially and/or fully surrounding, engulfing, encapsulating, and/or securing the obstruction. In any case, the surrounding portion engages the obstruction prior to translation of the obstruction within the lumen. As noted herein, a portion of the device may convert into a surrounding section (e.g., when traversing wires reorient to increase the friction acting on the obstruction). Accordingly, the traversing section converts into a surrounding section. [0020] The various devices described herein rely on a reduced profile for delivery and an expanded profile for ultimate removal of the clot. The devices, or components of the devices, may expand when released from a constraint, which allows the device, or component, to assume a predetermined shape. Alternatively, or in combination, the devices may be actuated to assume the expanded profiles. For example, the devices may be shape memory alloys that assume a profile when reaching a predetermined temperature (e.g.,.body temperature, or another temperature via delivery of energy to the shap e memory alloy to trigger a phase change). Actuation may also include use any expandable member (such as a coiled spring, balloon, wedge, etc.) that mechanically or fluidly forces expansion of the device. These modes are well known by those skilled in the art and are intended to be within the scope of the disclosure. When combined with the inventive concepts disclosed herein, such combinations fall within the inventive scope of this disclosure. Continue reading about Devices for restoring blood flow within blocked vasculature... 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