Patent Publication Number: US-2020276411-A1

Title: Catheter systems for applying effective suction in remote vessels and thrombectomy procedures facilitated by catheter systems

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of copending U.S. patent application Ser. No. 14/949,574 filed on Nov. 23, 2015 to Ogle et al., entitled “Catheter Systems For Applying Effective Suction In Remote Vessels And Thrombectomy Procedures Facilitated By Catheter Systems,” incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to catheters designed for use in bodily vessels with tortuous paths, such as cerebral arteries. The invention further relates to methods of using such catheters. 
     BACKGROUND OF THE INVENTION 
     Procedures in blood vessels of the brain are gaining interest as an approach for ameliorating acute stroke events or other interventions in blood vessels in the brain. Blood vessels in the brain follow particularly tortuous paths which can increase the difficulty of reaching target locations in these vessels. Other vessels in a patient can also follow winding paths that increase the difficulty of reaching target locations. 
     Aspiration catheters have found use with respect to removal of clots from vessels. Furthermore, a significant reason for ischemic injury during percutaneous procedures can be generation of emboli that block smaller distal vessels. Aspiration catheters used alone or with embolic protection device can be effective to capture emboli generated during procedures. The delivery of effective devices to the small blood vessels of the brain to remove clots and/or to capture emboli remains challenging. 
     Ischemic strokes can be caused by clots within a cerebral artery. The clots block blood flow, and the blocked blood flow can deprive brain tissue of its blood supply. The clots can be thrombus that forms locally or an embolus that migrated from another location to the place of vessel obstruction. To reduce the effects of the cut off in blood supply to the tissue, time is an important factor. In particular, it is desirable to restore blood flow in as short of a period of time as possible. The cerebral artery system is a highly branched system of blood vessels connected to the interior carotid arteries. The cerebral arteries are also very circuitous. Medical treatment devices should be able to navigate along the circuitous route posed by the cerebral arteries for placement into the cerebral arteries. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the invention pertains to a suction catheter system comprising a guide catheter and a suction extension. The guide catheter can comprise a tubular shaft with a central lumen having an inner diameter, a proximal end and a distal opening, and a proximal section operably connected with the proximal end of the tubular shaft and having fittings that connect to a suction device. The suction extension can comprise a proximal portion, a suction tip comprising a distal opening and extending from the proximal portion in a distal direction, and a control structure connecting the proximal portion with the proximal section of the guide catheter. In some embodiments, the suction tip can have a distal inner diameter that is from about 20 percent to about 90 percent of the central lumen inner diameter. Generally, the proximal portion can be configured to slide within the central lumen of the tubular shaft to change the relative position of the proximal portion within the central lumen and provide for at least a portion of the narrow diameter suction extension to extend outward from the distal opening of the tubular shaft at appropriate configurations of the proximal portion. A suction lumen is formed extending from the fitting configured to connect to the suction device through a portion of the central lumen, the proximal portion and the suction tip to a distal opening. 
     In a further aspect, the invention pertains to a method for using the suction catheter system described above for performing a thrombectomy procedure. In general, the method can comprise applying suction through the suction lumen of the suction catheter system positioned with the guide catheter extending into a vessel of a patient in a percutaneous configuration, to draw fluid into the distal opening of the suction tip to remove thrombus from the vessel. The suction catheter system can be particularly suitable for performing procedures in the cerebral arteries. 
     In another aspect, the invention pertains to a method for performing a medical procedure in a bodily vessel using a suction catheter system comprising a guide catheter and a suction extension slidably engaged with the guide catheter, the suction extension comprising a proximal portion configured to remain in a central lumen of the guide catheter and a suction tip extending in a distal direction from the proximal portion. The method can comprise tracking the suction tip to a desired location within a vessel by sliding the suction extension relative to the guide catheter. 
     In additional aspects, the invention pertains to a delivery catheter comprising a proximal tubular element having an outer diameter from about 1 mm to about 3 mm and a distal tubular element comprising a distal opening and extending from the distal end of the proximal tubular element wherein the distal tubular element has an initial inner diameter no more than about 1.5 mm and at least a factor of two smaller than the proximal tubular element inner diameter. The distal tubular element generally is formed from an elastic material that can stretch to at least about 1.5 times greater than the initial inner diameter. 
     Moreover, the invention pertains to a method based on the delivery catheter described above for placement of a first medical device into a narrow tortuous vessel of the body. In appropriate embodiments, the method can comprise: advancing the first medical device over a guidewire through the delivery catheter out through the distal opening of the distal tubular element, and the first medical device has a radial profile relative to the guidewire axis greater than the initial inner diameter of the distal tubular element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a suction system comprising a guide catheter with a suction extension with the guide catheter shown as transparent in this and most subsequent figures, as would be clear from the figure, to allow visualization of structure within the guide catheter. 
         FIG. 2  is a fragmentary side view of an expanded portion of the catheter system of  FIG. 1  showing the interface of the suction extension with the guide catheter. 
         FIG. 3  is a sectional view taken along line  3 - 3  of  FIG. 2  with two inserts showing expanded views of two embodiments with coatings. 
         FIG. 4  is a fragmentary side view of an embodiment of a seal between the suction expansion and the guide catheter comprising o-rings. 
         FIG. 5  is a fragmentary side view of an embodiment of a seal between the suction expansion and the guide catheter comprising an elastic seal. 
         FIG. 6  is a sectional view taken along line  6 - 6  of  FIG. 5 . 
         FIG. 7A  is a fragmentary side view of an interface between a suction extension and guide catheter comprising a seal involving elastic deformation based on movement of a slidable loop, shown in the unsealed configuration. 
         FIG. 7B  is a fragmentary side view of the sealing structure of  FIG. 7A  shown in the sealed configuration. 
         FIG. 8A  is a fragmentary side view of an interface between a suction extension and a guide catheter with an elastic deformation based seal incorporating a pivot ring to selectively activate the seal, shown in an unsealed configuration. 
         FIG. 8B  is a fragmentary side view of the sealing structure of  FIG. 8A  shown in the sealed configuration. 
         FIG. 9A  is a fragmentary side view of an interface between a suction extension and a guide catheter with an elastic deformation based seal incorporating a deformable element of the suction extension activated with a pullable actuation element, shown in an unsealed configuration. 
         FIG. 9B  is a fragmentary side view of the sealing structure of  FIG. 9A  shown in the sealed configuration. 
         FIG. 10A  is a fragmentary side view of an interface between a suction extension and a guide catheter with an elastic deformation based seal incorporating a deformable element of the guide catheter activated with a pullable actuation element, shown in an unsealed configuration. 
         FIG. 10B  is a fragmentary side view of the sealing structure of  FIG. 10A  shown in the sealed configuration. 
         FIG. 11  is a fragmentary side view of an interface between a suction extension and a guide catheter with an elastic deformation based seal with an electromagnetic actuatable seal. 
         FIG. 12  is a side view of a suction system comprising an interface between a suction extension and a guide catheter with a balloon based seal. 
         FIG. 13  is a section view of the balloon based seal taken along line  13 - 13  of  FIG. 12 . 
         FIG. 14  is a fragmentary side view of a structure providing simultaneous stop and seal functions. 
         FIG. 15  is an end view from the distal end of the suction system of  FIG. 14  with dashed lines showing the outer diameter of the proximal portion of the suction extension. 
         FIG. 16  is a fragmentary side view of a stop design for the engagement of a ridge along the inner diameter of a guide catheter with a widening section along the outer surface of a proximal portion of s suction extension. 
         FIG. 17  is a fragmentary side view of a suction system having a stop mounted at the distal end of a guide catheter. 
         FIG. 18  is a sectional view taken along line  18 - 18  of  FIG. 17  showing a stop at the distal opening of the guide catheter. 
         FIG. 19  is a fragmentary, exploded side view of showing the suction extension separated from the guide catheter, in which a projection along the proximal portion of the suction extension rides within a track within guide catheter. 
         FIG. 20  is a sectional view depicting the guide catheter having a channel with the section taken along lines  20 - 20  of  FIG. 19 . 
         FIG. 21  is a sectional view depicting the proximal portion of the suction extension along a portion having ridges with the section taken along line  21 - 21  of  FIG. 19 . 
         FIG. 22  is a side view of the suction extension with the expanded insert showing the attachment of a control wire to the proximal portion. 
         FIG. 23  is a side view of a suction extension embodiment having low or no extent transition portion with reinforcement. 
         FIG. 24  is a side view of a suction extension embodiment with a gradual tapered transition portion. 
         FIG. 25  is a side view of a suction extension embodiment having a suction tip with two successively narrowed sections. 
         FIG. 26  is a fragmentary side view of a suction tip with a bend. 
         FIG. 27  is a fragmentary side view of a suction tip with a bend and an angled opening. 
         FIG. 28  is a cut-away portion of a catheter wall showing some features of its construction. 
         FIG. 29  is a series of side views depicting the construction of a catheter structure on a mandrel in which one or more steps are performed including application of a wire braiding, placement of a metal coil, application of a polymer over sheet and heating the polymer to embed the metal structures within the polymer. 
         FIG. 30  is a side view of a delivery catheter having a narrow diameter elastic tip. 
         FIG. 31  depicts a series a fragmentary side views with a medical device progressively delivered with assistance of a delivery catheter of  FIG. 30  in which the medical device for delivery a) is initially depicted in the proximal section of the catheter, b) is expanding the elastic tip for delivery past the elastic tip, and c) is located on the distal side of the elastic tip. 
         FIG. 32  is a schematic depiction of a collection of medical devices that can be used together or in selected sub-combinations for selected percutaneous procedures in bodily vessels including a suction system as described herein and a delivery catheter as described herein. 
         FIG. 33  is a schematic depiction of a human patient with alternative access approaches for directing catheters into the blood vessels of the brain. 
         FIG. 34  is a view within a branched blood vessel section showing the delivery of medical devices along a guidewire from a guide catheter to a clot. Inserts show expanded views of two internal sections of the guide catheter. 
         FIG. 35  is a schematic view in a section of blood vessel of a suction system being used to remove a clot. 
         FIG. 36  is a schematic view in a section of blood vessel with a suction system positioned upstream from a clot and a fiber based filter deployed downstream from the clot. 
         FIG. 37  is a schematic view of the section of blood vessel of  FIG. 36  with the fiber based filter being drawn toward the suction tip to draw the clot to the tip for facilitating removal of the clot. 
         FIG. 38  is a schematic view of a section of blood vessel with a suction system positioned upstream from a clot, a fiber based filter deployed downstream from the clot and another medical device positioned at the clot. 
         FIG. 39  is a schematic view of the section of blood vessel of  FIG. 38  with the various medical devices being used in concert for the removal of the clot. 
         FIG. 40  is a side view of a prototype suction system with a fixed suction tip. 
         FIG. 41  is a fragmentary sectional view of the guide catheter of the suction system of  FIG. 40  with the section taken along line A-A of  FIG. 40 . 
         FIG. 42  is a fragmentary sectional view of the suction tip of the suction system of  FIG. 40  with the section taken along line B-B of  FIG. 40 . 
         FIG. 43  is a side view of a MI-AXUS commercial catheter used for comparative measurements of suction performance. 
         FIG. 44  is a schematic view of a catheter suction test set up used to test the suction system prototype and comparative catheters. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A catheter system can include a guide catheter adapted with a suction extension with a narrower distal tube that can provide suction with a high flow rate and a low pressure drop. Suction catheters can be used advantageously for the removal of thrombus and emboli from bodily vessels, such as arteries. Some vessels can have a narrow diameter, and treatment locations can be downstream along a circuitous path, and for such vessels there are constraints on the catheter structures able to reach the treatment locations in the vessel. The designs described herein comprise a slidable extended suction tip that can be adapted for use in conjunction with a guide catheter, which forms a significant portion of the overall suction lumen. The slidable suction tip comprises a slide that engages the inner wall of the guide catheter to make a suitably tight fit and a control wire or other suitable control element can be attached to the suction extension to position the slidable suction tip. The extendable suction tip, which may have an optional curved tip, can be tracked well over a guidewire to reach difficult to reach locations in the vessel. While the suction catheter system can be used in any suitable vessels of the body, the system can be particularly desirable in cerebral blood vessels, such as for the treatment of acute stroke. The catheter system can be effectively used as an effective standalone suction catheter. Furthermore, the catheter system can be effective as a component of a thrombectomy treatment system or other medical system to provide suction with the use of other medical devices, such as an atherectomy device, to disrupt thrombus and/or a filter structure that can catch emboli generated in the procedure as well as to be used to pull toward the suction catheter system. The treatment system can be effectively designed for stroke treatment. 
     Also herein, a delivery catheter is described with an elastic narrow diameter distal tip. The narrow diameter tip can have an inner diameter just larger than a guidewire, so that the narrow tip can be effectively tracked over the guidewire to difficult to reach locations within the vasculature or other tortuous vessel. Due to the elastic nature of the tip structure, other percutaneous devices can be delivered through the delivery catheter and past the tip, which can expand significantly to accommodate passage of the device through the tip. Once other devices as desired are delivered though the delivery catheter, the delivery catheter can be removed or drawn back to a more proximal position to avoid interfering with subsequent procedures. 
     Less invasive procedures, which are commonly referred to in the art as minimally invasive procedures, are desirable in the medical context to reduce patient recovery times and hopefully to improve outcomes when appropriate. In particular, less invasive procedures are commonly performed in the vasculature using catheter based system for reaching remote locations in a selected blood vessel for the performance of various treatment processes. These procedures can also be referred to as percutaneous procedures or transluminal procedures, in contrast with open surgical procedures, to emphasize the delivery through a vessel lumen. The discussion herein focuses on treatment of ischemic stroke since the devices can be particularly effective to treat these clinically important conditions, although the devices can be used in other procedures both in the vasculature and other bodily vessels. Patients include humans and can include other mammals, such as pet animals and farm animals. The terms proximal and distal are used in their conventional sense in the art, i.e., proximal refers to closer to the point of entry into the patient along the path in the vasculature or other vessel and distal refers to farther from the point of entry along the path in the vasculature. 
     For the treatment of strokes, the treatment devices are advanced through arteries to blood vessels of the brain. Blood vessels generally relevant for acute stroke treatment are downstream in the blood flow from the internal carotid arteries, and arteries generally branch and decrease in average diameter as the vessel proceeds in a downstream direction in the arterial vasculature. The body has a right internal carotid artery and a left internal carotid artery. For convenience, the blood vessels downstream from the internal carotid arteries are referred to herein as cerebral arteries. The cerebral arteries can be accessed with catheter based systems from, for example, a femoral artery in the groin, an artery in the arm, or the carotid artery in the neck using hemostatic procedures and appropriate fittings, such as those known in the art. The cerebral arteries are known to follow circuitous paths, and complications in tracking devices along the vessels also follows due to shrinkage in diameter and branching of the vessels in a distal direction from the carotid artery as well as potentially dangerous conditions from damage to the blood vessel. It can be desirable to access tortuous narrow arteries for stroke treatment. The devices described herein are designed for advantageous use in these tortuous narrow cerebral vessels, but a person of ordinary skill in the art will recognize utility of these devices in other medical procedures. 
     The present suction catheter systems incorporate guide catheters adapted with a slideable suction extension suitable for cerebral procedures. In vascular procedures generally, a guide catheter can be used to facilitate the delivery of therapeutic devices while allowing for more rapid, accurate delivery with less risk to vessel walls through providing a protected channel leading most of the way to the treatment site. In the cerebral procedures, a guide catheter can be placed from exterior of the patient at the point of entry into the vasculature with the distal end of the guide catheter in the carotid artery or interior carotid artery. Thus, a guide catheter provides a lumen to a location relatively near to a treatment site. The size of the guide catheter sets limits on the diameter of treatment structures delivered to the treatment site, but this is generally not a significant issue since extendable devices can be delivered in a lower profile configuration with subsequent deployments to the extended and configuration and since the vessel sizes generally decrease in a distal direction from the guide catheter limiting the need for larger treatment devices. The suction devices described herein provide a suction extension that can protrude from the distal end of the guide catheter an adjustable amount through the positioning of a proximal portion of the suction extension interfacing the suction extension with the walls of the guide catheter. The proximal portion can make a sufficiently tight seal with the guide catheter walls such that suction in the guide catheter lumen is transmitted along the lumen of the suction extension. Desirable degrees of suction can be obtained through the suction extension using suction applied at the proximal end of the guide catheter. 
     The suction extension generally comprises a proximal portion and a suction tip extending in a distal direction from the proximal portion. The suction extension generally interfaces with the guide catheter and can be designed to be positioned with its tip at a selected position distal to the guide catheter for the performance of a procedure at a selected location, such as near the location of thrombus occluding a vessel. Since the relative position of the treatment location and the distal end of the guide catheter generally vary for a specific medical situation, the degree in which the suction extension extends from the guide catheter can be adjusted through relative movement of the suction extension. A control element, e.g., wire, can be secured to the suction extension to provide for the positioning of the suction extension. The suction extension should move within the guide catheter lumen without the need for excessive force, such as through the use of low friction polymers on one or both adjacent surfaces. Also, the proximal portion of the suction extension should provide for a relatively tight fit with the guide catheter inner wall so that significant amounts of fluid do not flow between the suction extension and the guide catheter wall when negative pressure is applied in the guide catheter lumen. The tight fit can be provided, for example, through a low clearance between the proximal portion of the suction extension and the catheter wall, through the use of a mechanical seal, such as an o-ring, wiper seal, expandable balloon, other suitable elastic seal or the like. Also, since it is desirable to prevent the proximal portion of the suction extension from exiting from the distal end of the catheter, the suction extension and/or catheter can be provided with a stop that limits the distal movement of the suction extension. 
     By replacing most of the length of the suction element with a control element, the device may have less friction when advanced relative to a suction catheter with a tube extending the whole length of the device since a control wire or other control element can offers less resistance for its movement. The tip of the suction extension can be given a curved tip to facilitate tracking of the device over a guidewire. Suction catheters with a curved tip have been found to improve tracking for a rapid exchange style catheter, as described in U.S. Pat. No. 8,021,351 to Boldenow et al., entitled “Tracking Aspiration Catheter,” incorporated herein by reference. Thus, a suction extension for aspiration with a curved tip for tracking the tip over a guidewire can be effectively guided to difficult to reach locations with the use of a control wire or other control element moving the slide portion at or near the distal end of the suction extension, and the design provides for good suction ability without sacrificing the ability to reach difficult to reach vessels, such as within cerebral vessels. While the suction extension is moved, the guide catheter portion of the suction lumen can remain in place 
     When suction is applied at or near the proximal end of the guide catheter with a suitable negative pressure device, fluid is sucked into a distal opening at the end of the suction extension. It has been found that surprisingly strong suction can be transmitted through to the suction extension. A suction lumen extends from a negative pressure device, generally attached at a fitting associated with a proximal section, at or near the proximal end of the suction system through the guide catheter lumen to the suction extension and through the proximal portion of the suction extension and the suction tip of the suction extension to the distal opening. Suitable negative pressure devices include, for example, syringes, pumps or the like. The guide catheter can provide a large lumen proximal section of the overall suction lumen. The effective suction lumen then can appear to have a large proximal section contributed by the guide catheter and a tapered distal section contributed by the suction extension, which can have one or more tapered segments. 
     The suction tip of the suction extension has a lumen with a reduced diameter relative to the guide catheter lumen and good flexibility to provide for placement of its distal end into smaller vessels. The lumen of the suction tip though is maintained at a sufficiently large diameter that provides for delivery of additional therapeutic devices through the lumen to the treatment location. Thus, the outer diameter of the suction tip generally is (diameter in mm=(Fr value)/3, Fr represents the French catheter scale) at least about 1.5 Fr less than the outer diameter of the distal section of the guide catheter. Based on bench testing and calculations presented below, the pressure drop from the proximal connection of the guide catheter with the negative pressure device and the distal tip of the suction extension can be surprisingly small. However, the decrease in diameter provides access to desirable vessels, such as cerebral vessels. 
     It was previously discovered that good suction properties could be obtained with a suction catheter with a stepped down diameter in a distal section. Thus, for example, the majority of the length of the suction catheter can be 6 Fr outer diameter while a distal section may be 5 Fr outer diameter, which roughly corresponding decreases in the inner diameters. Such a catheter can provide access into vessels suitable for a 5 Fr catheter, but can provide significantly better suction than a suction catheter with a 5 Fr catheter body along its entire length. Commercial stepped down suction catheters, such as Mi-Axus™ catheters (MIVI Neuroscience, Inc.) and ACE™ 64 catheters (Penumbra, Inc.) are finding good clinical results. The step down suction catheters and their use for thrombectomy procedures in cerebral arteries are described in published U.S. patent application 2012/0253313 A1 to Galdonik et al. (hereinafter the &#39;313 application), entitled “Aspiration Catheters for Thrombus Removal,” incorporated herein by reference. Comparisons of suction results from testing of these catheters are also presented below. While these catheters achieve better suction than catheters with constant diameters corresponding with the distal diameters, the present suction catheters with a sliding suction extension are found to provide surprisingly good suction suggesting that the diameter over the majority of the suction lumen length contributes to a large extent to the suction provided at the distal opening of the suction lumen. In particular, while the suction extension may have a longer length of the distal reduced diameter section, these features are more than compensated for by the longer length of the larger diameter guide catheter lumen that extends for a majority of the suction lumen. 
     Also described herein, a delivery catheter can provide a desirable very flexible distal tip with a narrow diameter that can track along a guidewire into particularly challenging positions in a vessel. For example, in regions of the cerebral vasculature, the arteries can twist and turn very significant amounts. To the extent that a guidewire can be placed at the target location, it still may be difficult to track a catheter or the like over the wire to the desired location. The delivery catheter described herein has an elastic distal section that can have an inner diameter comparable to the guidewire outer diameter so that it tracks closely over the wire which when combined with the desired flexibility provides for tracking. Once the delivery catheter is in place, desired additional medical devices can be tracked over the wire and through the delivery catheter for improved guidance of the device to the treatment location. To actually provide a delivered medical device for use at the treatment location, the medical device should be placed outside of the interior of the delivery catheter. The elasticity of the distal tip of the delivery catheter provides for the pushing of the delivered medical device past the elastic distal tip through the appropriate expansion of the elastic tip, which may or may not resume its narrow diameter following delivery of the medical device through the tip. Suitable medical devices for delivery include, for example, a suction tip associated with a suction system described herein, a microcatheter optionally associated with additional treatment structures, filters, angioplasty balloons, stent delivery devices, atherectomy devices or the like. 
     The proximal portion of the delivery catheter has a diameter selected to fit within a guide catheter, if relevant, and large enough to allow for delivery through its inner lumen of other percutaneous devices appropriate for delivery through to the treatment site. The elastic distal tip can have a suitable length to reach to appropriate treatment sights accounting for placement of its proximal end in an appropriate location based on its dimensions and flexibility. Since the distal tip may extend many times its original diameter to allow for delivery of medical devices through its lumen, the material forming the distal tip can be selected to stretch many times it diameter without tearing. It may or may not be desired for the elastic polymer to remain within its elastic limit such that it would resume its approximate original shape if the strain is withdrawn. For example, if the polymer is stretched beyond its elastic limit, the polymer remains distorted if the strain is removed. However, the polymers generally should be selected to be stretched to values below their elongation limit to prevent significant failure of the polymers and tearing to avoid any generation of debris within the vessel, although a sufficiently cohesive polymer may tear without creating a significant risk of fragmenting to leave debris in the vessel. Various biocompatible elastomers are suitable for the formation of the proximal portion of the delivery catheter as described further below. 
     An initial part of the procedure using the devices described herein generally involves accessing the treatment location within the vasculature. Guidewires have been designed to facilitate access to difficult to reach locations. The term guidewire is used herein to refer broadly to wire structures that may or may not have internal structure are referred to as guidewires whether or not they are formed from a solid or woven metal, such as corewire-overtube integrated structures, coils or the like which do not have a closed inner lumen over at least a portion of the devices length. 
     In particular, with the devices described herein procedures can be performed to provide re-profusion in vessels that are blocked completely or partially with clots. Clots in cerebral arteries can cause strokes with corresponding serious consequences, and time generally is of the essence of treating these conditions. The suction extension with the guide catheter can be used to provide aspiration that can be useful to remove clots or fragments thereof. Thus, the suction extension combined with the guide catheter and negative pressure device can be used as stand alone devices for thrombectomy procedures. However, the suction extension with aspiration can be effectively used as part of a treatment system comprising, for example, also a fiber based filter and/or other components to facilitate removal of a clot or portions thereof. The delivery catheter with the expandable tip is designed to facilitate access, so it is useful as a tool for the practice of various other procedures. 
     As demonstrated below, the aspiration system formed with a guide catheter and a suction extension provides enhanced suction ability within relatively narrow vessels downstream from the positioning of the guide catheter, such as cerebral vessels. The enhanced suction power can be valuable for the removal of clots from the vessel and thus can improve clinical results, whether used alone or used with additional components of a treatment system. As described below, the guide catheter based suction catheter can be used to generate good flow under aspiration through the tip of the suction extension and with a low pressure drop from the proximal connection of the negative pressure device to the distal opening of the catheter. With the combination of features, the catheter provides good access to smaller vessels, relative ease of placement and desirable degrees of suction power. 
     In some embodiments of the procedure, a guidewire can be placed at or near an occlusion and a guide catheter with a positionable suction extender can be placed in the vasculature upstream from the occlusion with the guidewire extending through the interior of the suction extender. If the suction catheter is to be used alone, then the suction extender can be advanced using a control wire over the guidewire to a suitable position near the clot. Then, with or without removing the guidewire, suction can be initiated to suck the clot or a portion thereof into the distal opening or against the tip of the suction extender. Suction may or may not be continued as the suction extender and/or guide catheter are removed from the patient. 
     While suction with the suction extension can be effective as the only device for clot removal, particularly effective systems can combine other devices for use with the suction catheter. In particular, a filter device can be used to provide both embolic protection as well as a tool to facilitate removal of the clot or portions thereof, which may involve direct engagement of the clot with the filter device. Fiber based filters/embolic protection systems have been developed that can be effectively used in the narrow vessels of interest. In particular, fiber-based filter systems with an appropriate actuation system can be used for delivery in a low profile configuration past an occlusion and deployed to provide protection from any clot fragments that may be released during the removal process. 
     The devices described herein provide improved functionality for performing procedures for the removal of clots from vessels. As noted herein, the devices can be used in various combinations within medical systems for percutaneous procedures. 
     Suction System with Extendable Suction Tip 
     Suction Systems are described that take advantage of good suction available with a suction catheter having a larger proximal suction lumen and a narrower diameter suction tip that uses the guide catheter lumen as a proximal suction lumen. A laterally slidable suction tip extends from a proximal section located within the guide lumen, and the suction tip can have a reduced diameter to provide access to narrow vessels while providing for delivery of other treatment structures and/or embolic protection structures as well as for a desirable level of suction for the removal of debris from the vessel. A control wire or other structure can be attached to the slidable suction tip to provide for selective lateral placement of the suction tip relative to a fixed guide catheter and a target treatment location. The catheter generally comprises structure, such as a seal, to limit flow through the guide catheter circumventing the suction tip and/or, such as a stop, to retain the proximal portion of the suction tip within the guide lumen at the distal end of the guide catheter. Some particular embodiments are shown in the figures as discussed in the following. 
     Referring to  FIG. 1 , suction system  100  comprises a suction adapted guide catheter  102  and a suction extension  104 . The suction adapted guide catheter  102  comprises proximal section  106  and tubular shaft  108 . Proximal section  106  generally is suitable for use also as a handle and generally can comprise a proximal fitting  120 , a suction port  122  and an optional control wire port  124 , as well as possibly other additional ports and/or fittings to provide desired functionality and access, in which all such ports and fittings can be arranged in a branch configuration or other suitable configuration. Proximal fitting  120  can comprise a suitable hemostatic valve, Luer fitting or the like to provide for entry of a guidewire and/or structures delivered over the guidewire into the guide catheter lumen, such as alternative treatment structures and/or embolic protection devices. Suitable embolic protection devices can be mounted on a guidewire. Suitable treatment structures are described further below and can include, for example, stents, stent retrievers, atherectomy devices or the like. As shown in  FIG. 1 , a negative pressure device  126  is shown connected with suction port  122 , and suitable negative pressure devices include, for example, syringes, pumps, such as peristaltic pumps, piston pumps or other suitable pumps, aspirator/venturi, or the like. 
     Tubular shaft  108  can have an approximately constant diameter along its length, or the guide catheter can have sections with different diameters, generally with a smaller diameter section distal to a larger diameter section. Tubular shaft  108  can have one or more radiopaque marker bands to facilitate positioning of the tubular shaft within the patient, and  FIG. 1  shows a marker band  128  near the distal end of tubular shaft  108 , although alternative positions can be used as desired. At or near the distal end of the shaft, a stop  130  is positioned to retain a portion of suction extension  104  within the lumen of tubular shaft  108 . Suitable designs of stop  130  are presented below. Tubular shaft  108  can further comprise a seal  132  to provide for reducing or eliminating any flow within tubular shaft  108  that avoids suction extension  104 . In some embodiments, seal  132  can be combined with stop  130 , or seal  132  as a distinct element can be avoided through a design with a sufficiently tight fit between suction extension  104  and the lumen wall of tubular shaft  108 . As described below, tubular shaft  108  can have coatings on the inner surface and/or the outer surface or portions thereof. 
     Suction extension  104  comprises a proximal portion  140 , suction tip  142 , connection portion  144 , optional engagement element  146  and control structure  148 , such as a control wire. All or a part of proximal portion  140  can be configured to remain within the lumen of guide catheter  102 . As shown in  FIG. 1 , proximal portion  140  comprises a radiopaque marker band  152 , although proximal portion may not have a marker band in some embodiments and in other embodiments can comprise a plurality of marker bands, and suction tip  142  is shown with radiopaque marker band  154  near the distal tip of suction tip  142 , although again suction tip  142  can comprise a plurality of radiopaque marker bands if desired. Connection portion  144  connects proximal portion  140  and suction tip  142 , which can be a transition portion that gradually changes diameter or a connector that forms a seal between the proximal portion and suction tip. Optional engagement element  146  can engage stop  130  to establish the distal placement limit of suction extension  104  relative to guide catheter  102 . In some embodiments, stop  130  is configured to engage an edge or other limiting structure of proximal portion  140  so that engagement element  146  is effectively integrated with the proximal portion  140  or connection portion  144 . Control structure  148  can be a control wire or the like that connects with proximal portion  140  and extends exterior to the catheter, such as exiting through control wire port  124 . Control structure  148  can be used to control positioning of proximal portion  140  within the lumen of tubular_shaft  108 . Control structure  148  can comprise a control tool  156 , such as a handle, slide or other the like that can anchor a control wire or other connecting element to facilitate movement of the control wire. In some embodiments, alternative structures such as a plurality of wires or wire cylindrical assembly can connect the proximal portion to the proximal end of the suction catheter system to provide a desired level of control with respect to positioning the proximal section. 
     Referring to  FIG. 2 , an expanded view is presented of the interface between tubular shaft  108  and proximal portion  140  of suction extension  104 . A cross sectional view is shown in  FIG. 3 . Several seals are described in the subsequent figures to reduce or eliminate flow between the inner surface of tubular shaft  108  and the outer surface of proximal portion  140 . Flow arrows indicate desired flow directions when suction is applied. However, in some embodiments, the clearance can be made sufficiently small between the outer surface of proximal portion  140  and the inner surface of tubular shaft  108 . For example, the tolerance measured as a difference between the adjacent inner surface and outer surface can be, for example, no more than about 5 mils (1 mil=1/1000 of an inch; 5 mil˜127 microns), and in further embodiments, no more than about 4 mils (101.6 microns) or in additional embodiments no more than about 3 mils (76.2 microns), and can be approximately zero within the measurement uncertainty. A person of ordinary skill in the art will recognize that additional ranges within the explicit ranges of tolerances above are contemplated and are within the present disclosure. A lubricious coating  160  (see left insert of  FIG. 3 ), which may or may not be a hydrophilic coating, can be placed on the outer surface of the proximal portion  140 , and/or a lubricious coating  162  (see right insert of  FIG. 3 ) can be placed on the inner surface of tubular shaft  108  to facilitate longitudinal movement of the suction extension  104  with a low tolerance friction fit. Suitable coatings include, for example, hydrophobic coatings such as polytetrafluoroethyelene, or other fluoropolymers, or hydrophilic coatings, such as polyvinyl alcohol. Suitable coatings can include, for example, a gel or fluid, such as polyfluoropolyether fluid or triglycerides that can be applied at the time of use. 
     It can be desirable to include specific structural elements to effectuate the seal rather than relying only on friction/coatings. Various embodiments of seal  132  are shown in  FIGS. 4-15 . Referring to  FIG. 4 , a portion of a catheter is shown indicating the use of o-rings to form the seal. Specifically, o-rings  200 ,  202  are positioned within grooves  204 ,  206  along the surface of proximal portion  208  or suction extension  210 . O-rings  200 ,  202  engage inner surface of tubular shaft  212  to form the seal such that flow is confined to suction lumen  214 . While  FIG. 4  shows two adjacent o-rings, a seal can comprise a single o-ring, such as either  200  or  202  alone, or three or more o-rings. O-rings can be formed from suitable materials, such as biocompatible elastic polymers, examples of which are provided in the materials summary below. 
     Referring to  FIGS. 5 and 6 , an elastic seal  230  is provided around proximal portion  232  of suction extension  234  in which suction tip  236  extends in a distal direction. Elastic seal  230  can be secured to proximal portion  232  with adhesive, heat bonding, or other suitable technique. Elastic seal  230  can provide for relative movement of suction extension  234  and shaft  238  due to the elasticity. Elastic seal  230  can be angled, arched or other suitable configuration. Elastic seal  230  can be formed form elastic polymers presented below. 
       FIGS. 7A-11  display embodiments in which sealing is based on minor distortion of the catheter elements to releasably engage the shaft with the proximal element of the suction extender to block potential flow between the elements. The different figures involve distinct mechanism to provide corresponding forces to engage the elements. For these embodiments, the sealing engagement is generally performed once the suction extension is laterally placed at a desired position. 
     Referring to  FIGS. 7A and 7B , suction extension  250  engages guide catheter  252  with an engageable sealing element  254 . Sealing element  254  comprises a slidable loop  260  controllable with a loop control wire  262  that engages a circular ramp  264 . Loop control wire  262  extends in a proximal direction and edits the catheter through a proximal port so that the medical professional using the catheter can control the engagement of the seal through positioning of the loop. When slidable loop  260  in a proximal position, as shown in  FIG. 7A , the seal is unengaged and suction extension  250  can more longitudinally within the lumen of guide catheter  252 . Referring to  FIG. 7B , when slidable loop is positioned in a distal direction, slidable loop  260  engages circular ramp  264  and forms a bulge  266  that engages the inner wall of guide catheter  252  to form a seal. Bulge  266  does not need to physically extend very far since the clearance between suction extension  250  and guide catheter  252  can be small. 
     A similar structure is shown in  FIGS. 8A and 8B  based on a pivoting loop. In this embodiment, suction extension  280  engages guide catheter  282  with deforming sealing element  284 . Deforming sealing element  284  comprises ring  290 , secured at pivot  292  and control wire  294 . Ring  290  has an outer diameter somewhat larger than inner diameter of proximal portion  296  of suction extension  280  and an inner diameter in some embodiments can be at least as large as the inner diameter of proximal portion  296 . Control wire  294  can be used to pivot ring  290  to an engaged configuration shown in  FIG. 8B  where suction extension  280  deforms slightly at the position of the ring to form a seal with guide catheter  282 . Control wire  294  extends in a proximal direction to exit the catheter at a proximal fitting. In alternative embodiments, the unengaged position of ring  290  can be in a distal orientation relative to pivot  292  so that the control wire can be pulled to engage the seal. 
     Referring to  FIGS. 9A and 9B , a seal is shown based on a deformable section of the proximal portion of the aspiration extension.  FIG. 9A  depicts the relevant portion of the device in the un-deformed configuration, and  FIG. 9B  depicts the relevant portion of the device in the deformed and sealed configuration. Suction extension  300  is positioned within guide catheter  302 . Suction extension  300  comprises proximal section  310  having a deformable element  312 , and an actuation element  314 . Deformable element  312  can have a bridge shaped cross section and can be formed from a distinct material and/or have a distinct structure providing for deformation upon application of suitable forces. The bridge shaped cross section can be rectangular, square, elliptical, round, or more complex shapes, such as an “M” shape, and can be of a suitable catheter material, which can be the same or different relative to the remaining portion of the catheter. As shown in  FIGS. 9A and 9B , actuation element  314  comprises inner sleeve  316  secured to proximal section  310  at anchor point  318 . Inner sleeve  316  extends proximally to the exterior of the catheter through a fitting such that relative movement of inner sleeve  316  and a control wire (not shown for this embodiment) controlling the position of proximal section  310  applies force that can deform deformable element  312 . Inner sleeve is used to transmit force and may be generally cylindrical or other shape that provides for appropriate force transfer. Deformable element  312  may or may not provide for substantial restoration of the deformable element to its original configuration upon the reversal of forces used to deform the deformable element. 
     Referring to  FIGS. 10A and 10B , a complementary embodiment is shown in this a deformable element is formed as a portion of the guide catheter rather than the suction extension. Suction extension  330  extends within guide catheter  332 . Suction extension comprises suction tip  334  and proximal section  336 . Guide catheter  332  comprises catheter body  340 , deformable element  342  and actuation element  344 . As shown in  FIGS. 10A and 10B , actuation element  344  comprises an outer sleeve  346  secured to catheter body  340  at anchor point  348 . As with deformable element  312  of  FIGS. 9A and 9B , deformable element  342  may or may not provide for substantial restoration of the deformable element to its original configuration upon the reversal of forces used to deform the deformable element. As with inner sleeve  316 , outer sleeve  346  is used to transmit force and may be generally cylindrical or other shape that provides for appropriate force transfer. 
       FIG. 11  shows a catheter and suction extension with a magnetic based seal. Guide catheter  370  comprises a metal coil  372  embedded in the polymer wall of the catheter. Metal coil is connected to electrical wires  374 ,  376  that are electrically insulated from each other and extends down the length of the catheter to a proximal section (not shown). Electrical wires  374 ,  376  are connected to metal coil  372  such that current can flow between electrical wires  374 ,  376  along all or a majority of the metal coil such that the current generates an electrical field. At the proximal end of electrical wires  374 ,  376 , electrical wires  374 ,  376  are connected to a power source  378 , such as a battery, through a switch  380 . Suction extension  390  comprises a permanent magnet  392  embedded in a polymer wall of proximal section  394  and suction tip  396  extends in a distal direction from proximal section  394 . When switch  380  is turned to the on position by a medical professional, current flows through metal coil  372  to generate a magnetic field that attracts permanent magnet  392  to distort the wall of proximal section  394  and form the seal. Turning switch  380  to off can relax the seal such that suction extension  390  can move longitudinally within guide catheter  370 . 
     A balloon based seal is shown in the embodiment of  FIG. 12 . The suction system comprises guide catheter  400  and suction extension  402 . Guide catheter  400  comprises proximal section  404  and tubular shaft  406  connected at or near the distal end of proximal section  404 . Proximal section  404  comprises a proximal fitting  410 , a branched connector  412  for connection to a suction device  414  and a branched connector  416  for passage of tube  418  through a diaphragm seal or the like  420  in which tube  418  is connected to a fluid source  422  for inflating and deflating a balloon seal. Diaphragm seal  420  or a suitable hemostatic fitting can be made of rubber or other suitable material or construction so that tube  418  can be moved in and out from the interior of guide catheter  400  with little or no blood loss. Suction extension  402  comprises a proximal section  430  and suction tip  432 . 
     Referring to the expanded insert of  FIG. 12 , balloon  434  is located around the circumference of proximal section  430 . Tube  418  can connect directly to balloon  434  or as shown in  FIGS. 12 and 13  to a channel  436  that extends within proximal section  430  in which the channel is in fluid connection to the interior of balloon  434  through one or more openings  438 . Thus, when fluid is injected from fluid source  422 , balloon  434  inflates and subsequent removal of fluid back into fluid source  422  or an alternative fluid reservoir, then balloon  434  deflates. Inflation of balloon  434  forms a controllable seal at the contact point of balloon  434  and tubular shaft  406 . 
     As noted above, the guide catheter generally comprises a stop that retains at least a significant portion of the proximal section of suction extension within the lumen of the shaft of the guide catheter. In some embodiments, the seal and the stop elements are combined in a single structure, such as shown in  FIGS. 14 and 15 . Referring to  FIG. 14 , guide catheter  450  comprises tubular shaft  452  with, at its distal end, an elastic seal  454  having sufficient mechanical rigidity to also function as a stop. Suction extension  456  has a proximal portion  458  and suction tip  460  extending outward from guide catheter  450  through elastic seal  454 . For example, as shown in  FIG. 14 , elastic seal  454  can have elastic polymer contacting suction tip  460  and optionally a more rigid material, such as thermoplastic polymer, metal or other appropriate material, connecting to tubular shaft  452 . 
     Another embodiment of a stop is shown in  FIG. 16 . In this embodiment, tubular shaft  480  of the guide catheter comprises a ridge  482  that narrows the inner diameter of tubular shaft  480  at a location at or near the distal end of tubular shaft  480 . Ridge  482  may or may not go around the circumference of the inner wall of tubular shaft  480 , and in some embodiments may be only at 1, 2, 3, 4 or other number of specific locations around the circumference. As shown in  FIG. 16 , the narrowed inner diameter at ridge  482  (evaluated at diameter through the center of the shaft connecting isolated points providing the narrowing in appropriate embodiments) is wider than the outer diameter of proximal section  484  of suction extension  486 . Widening structure  488  along the exterior of proximal section  484  provides a diameter that exceeds the narrowed inner diameter at ridge  482  so that widening structure  488  cannot pass ridge  482  so that ridge  482  functions as a stop. Widening structure  488  can be, but may not be, portions of a balloon seal or other seal components, or widening structure  488  can be provided just to provide the stop function. Widening structure  488  may or may not go around the entire circumference of proximal section  484 , but widening structure  488  and ridge  482  can be designed to provide sufficient circumferential coverage so that they cannot circumvent the stop function of the elements. 
     A similar stop design is shown in  FIGS. 17 and 18 . In this embodiment, tubular shaft  500  has a lip  502  at the distal opening, although in alternative embodiments, the lip can be moved inside the inner lumen of tubular shaft  500  reasonably near the distal opening. Lip  502  reduces the diameter at the lip to a value less than the outer diameter of proximal section  504  of suction extension  506  with suction tip  508  extending in a distal direction. Due to the reduced diameter at lip  502 , it functions as a stop. 
     Referring to  FIGS. 19-21 , the stop function is provided by a track that interfaces tubular shaft  520  and suction extension  522 .  FIG. 19  is a sectional exploded view that cuts the elements through the central axis to render the track elements visible. Referring to tubular shaft  520  in  FIGS. 19 and 20 , the inner surface of the wall is contoured to have two channels  524 ,  526  that end prior to the distal end of tubular shaft  520 . Referring to  FIGS. 19 and 21 , suction extension  522  comprises proximal section  530  and suction tip  532 , and proximal section  530  has two ridges  534 ,  536 . Ridges  534 ,  536  fit within channels  524 ,  526  so that channels limit the movement of ridges  534 ,  536  and correspondingly the relative movement of suction extension  522  so that the distal termination of channels  524 ,  526  function as a stop. 
     Referring to  FIG. 1 , in some embodiments a control structure, such as a control wire, interfaces with the proximal portion of the suction extension. Referring to  FIG. 22 , an embodiment is shown in which suction extension  550  has a control wire  552  with its distal end embedded within the polymer wall of proximal portion  554 . Suction tip  556  extends in a distal orientation relative to proximal portion  554 . As described further below, the polymer walls of components of a suction extension can comprise braided and/or coiled wires embedded within the polymer walls. Referring to the expanded view in the balloon insert, the embedded end of control wire  552  is shown under the embedded braiding/coil reinforcement  558 , which can further secure control wire  552  to proximal portion  554 . In alternative embodiments such as shown in  FIG. 12 , a tube or other structure can be used in addition to or as an alternative to a control wire, and such a tube can be securely attached to a proximal portion with suitable reinforcements and can also be under a portion of braiding or coil if desired. 
     As noted above, the suction extension has a connection portion connecting the proximal portion and the suction tip, and the design may generally depend on manufacturing selections. Referring to  FIG. 23 , an embodiment of suction extension  570  has a connection portion essentially no transition region connecting proximal portion  572  and suction tip  574 . Basically, wall  576  connects suction tip  574  to proximal portion  572 . An optional reinforcement  578 , such as a polymer or metal element at the connection, can be used to help secure the elements. Referring to  FIG. 24 , an embodiment of suction extension  584  has a transition portion  586  connecting proximal portion  588  with suction tip  590 . As shown in  FIG. 24 , transition portion provides an approximately linear transition of diameters from the wider diameter of proximal portion to the narrower diameter of suction tip  590 . In alternative embodiments, a transition portion can have nonlinear changes in diameter if desired, but the change is generally monotonic. The transition regions can be formed through an extrusion process or through confirming of a thermoplastic polymer to a mandrel shape or other suitable process approach known in the art. 
     A significant aspect of the suction extension is the narrower diameter suction tip. The effective suction lumen then extends through the guide catheter into the proximal portion of the suction extension and then into the suction tip. The narrow diameter of the suction tip provides for reach into small circuitous blood vessels and the use of the larger diameter proximal suction lumen improves the suction performance significantly without detracting from the ability to reach appropriate locations. To further provide for suction strength, the suction tip itself can have different sections with stepped down diameters. In general, the arteries progressively decrease in diameter so a section with a somewhat larger diameter may be desirable consistent with the reach of the suction tip into a selected narrow vessel. 
     Referring to an embodiment shown in  FIG. 25 , suction extension  600  comprises proximal portion  602 , first tip section  604 , distal tip section  606 , first optional transition section  608  and second optional transition section  610 . Proximal portion  602  can be any of the various embodiments described above with corresponding seal structures. Similarly, optional transition section  608  and  610  can have transition structures as described above or independently replaced with a connection structure such as shown in  FIG. 23 . Dimensions overall of the proximal portion and suction tip are described further below. With respect to first tip section, this section generally has an approximately constant diameter that is generally from about [d+0.9(D−d)] to about [d+0.1(D−d)], in further embodiments from about [d+0.75(D−d)] to about [d+0.25(D−d)], and in some embodiments from about [d+0.65(D−d)] to about [d+0.35(D−d)], where d is the diameter of distal tip section  606  and D is the average diameter of proximal portion_ 602 . The length of first tip section can be from about 10% to about 90%, in further embodiments from about 20% to about 80% and in additional embodiments form about 30% to about 70% of the total length of suction tip, i.e., the total length of first tip section  604 , distal tip section  606 , first optional transition section  608  and second optional transition section  610 . A person of ordinary skill in the art will recognize that additional ranges of relative dimensions within the explicit ranges above are contemplated and are within the present disclosure. This embodiment is shown with 3 radiopaque marker bands, marker band  611  near the distal tip, marker band  612  near the second (distal) transition position and marker band  614  near the first (proximal) transition region. While  FIG. 25  shows one intermediate tip section between proximal portion and the distal tip section, in other embodiments there can be multiple constant diameter intermediate sections which divide the length available for the intermediate sections specified above and on average have the diameters for the intermediate section specified above, for example, there can be two intermediate sections, three intermediate sections or more than three intermediate sections. 
     Regardless of whether or not the suction tip includes intermediate sections, the distal tip of the catheter can be bent or curved in its natural unstressed configuration. It has been found that a bent tip catheter can facilitate tracking of the catheter over a guidewire without adversely altering the suction abilities. See U.S. Pat. No. 8,021,351 to Boldenow et al., entitled “Tracking Aspiration Catheter,” incorporated herein by reference. Two version of a bent tip suction tip are shown in  FIGS. 26 and 27 . Referring to  FIG. 26 , suction tip  620  comprises a straight section  622 , bend  624  and bent tip section  626  with a flat distal opening  628  approximately perpendicular to the axis of bent tip section  626 . Referring to  FIG. 27 , suction tip  634  comprises a straight section  636 , bend  638  and bent tip section  640  with an angled distal opening  642  at a non-perpendicular angle to the axis of bent tip section  640 . Bent tip sections  626 ,  640  are generally cylindrical and can have approximately the same diameters as corresponding straight sections  622 ,  636 . While two shapes of openings are shown in  FIGS. 26 and 27 , any reasonable shape of the opening generally can be used. 
     The angle of the curved tip relative to a straight tip generally is less than 90 degrees and can be, for example, from about 10 degrees to about 60 degrees and in further embodiments from about 25 degrees to about 50 degrees. The selected angle corresponds with a radius of curvature, and the radius of curvature can be, for example, from about 3 mm to 20 mm and in further embodiments from about 4 mm to about 16 mm. In some embodiments, a straight portion of the tip after the curve can have a length no more than about 1 cm, and in other embodiments from about 0.1 mm to about 6 mm and in further embodiments from about 0.5 mm to about 4 mm. In alternative embodiments, the curve consists of a gradual arc with no significant straight section distal to it, such that the curve or bend is specified by the angle and radius of curvature. A person of ordinary skill in the art will recognize that additional ranges of angles, radii and lengths within the explicit ranges above are contemplated and are within the present disclosure. 
     Proximal portion of suction extension provides a transition of the suction lumen from the guide catheter to the suction tip. As noted above, the proximal portion generally is associated with a seal and may be designed to be constrained within the lumen of the guide catheter with a stop. The lateral extent of the proximal portion should be sufficient to provide mechanical stability within the guide catheter lumen, but otherwise does not need to be particularly long. In general, the proximal portion can have a lateral extent from about 5 millimeters (mm) to about 25 centimeters (cm), in further embodiments from about 8 mm to about 20 cm and in other embodiments from about 1 cm to about 18 cm. The outer diameter of the proximal section can be close to the inner diameter of the guide catheter, and with respect to the average inner diameter of the proximal section, it can be from about 80% to about 97% of the inner diameter of the guide catheter, in further embodiments from about 82% to about 95% and in additional embodiments from about 84% to about 93% of the inner diameter of the guide catheter. The diameter of the proximal portion may or may not be approximately constant, and structure, such as a small gradual taper or sections with step down diameters generally may be acceptable. The division of the proximal portion and a transition zone may be somewhat arbitrary, although the proximal portion is generally associated with the seal. A person of ordinary skill in the art will recognize that additional ranges of proximal portion dimensions within the explicit ranges above are contemplated and are within the present disclosure. 
     The suction tip or distal suction tip for appropriate embodiments can have an inner diameter from about 20 percent to about 90 percent of the inner diameter of the tubular shaft of the guide catheter, and in further embodiments from about 30 percent to about 85 percent and in additional embodiments from about 35 percent to about 80 percent of the average diameter of the tube. For example, the distal tip can have an inner outer diameter range from about 0.667 mm to about 2 mm, in further embodiments from about 0.85 mm to about 1.9 mm, and in other embodiments from about 0.9 mm to about 1.75 mm. The distal tip can have a length from about 3 cm to about 50 cm, in some embodiments from about 5 cm to about 40 cm and in further embodiments from about 8 cm to about 35 cm. The guide catheter can have an outer diameter from about 5.5 Fr (1.667 mm diameter) to about 10 Fr (3.333 mm_diameter), in further embodiments from about 6 Fr (1.833 mm diameter) to about 9 Fr (3 mm diameter), and in some embodiments from about 6.25 Fr (2 mm diameter) to about 8.5 Fr (2.833 mm diameter). The guide catheter measurement are generally referenced to the outer diameter, and the inner diameter is less than the outer diameter by twice the wall thickness. The length of the guide catheter can be from about 30 cm to about 150 cm, in further embodiments from about 35 cm to about 130 cm and in additional embodiments from about 40 cm to about 120 cm. The length of tubular shaft can be from about 30 cm to about 150 cm, in further embodiments from about 35 cm to about 130 cm and in additional embodiments from about 40 cm to about 120 cm. A person of ordinary skill in the art will recognize that additional ranges of dimensions within the explicit ranges above are contemplated and are within the present disclosure. 
     Catheter components can be formed from one or more biocompatible materials, including, for example, metals, such as stainless steel or alloys, e.g., Nitinol®, or polymers such as polyether-amide block co-polymer (PEBAX®), nylon (polyamides), polyolefins, polytetrafluoroethylene, polyesters, polyurethanes, polycarbonates, polysiloxanes (silicones), polycarbonate urethanes (e.g., ChronoFlex AR®), mixtures thereof, or other suitable biocompatible polymers. Radio-opacity can be achieved with the addition of metal markers, such as platinum-iridium alloy, tantalum, tungsten, gold, platinum-tungsten alloy or mixtures thereof, such as wire or bands, or through radio-pacifiers, such as barium sulfate, bismuth trioxide, bismuth subcarbonate, powdered tungsten, powdered tantalum or the like, added to the polymer resin. Generally, different sections of aspiration catheter can be formed from different materials from other sections, and sections of aspiration catheter can comprise a plurality of materials at different locations and/or at a particular location. In particular, it may be desirable to form seal components from an elastomeric polymer, such as suitable polyurethanes, polydimethyl siloxane and polytetrafluoroethylene. In addition, selected sections of the catheter can be formed with materials to introduce desired stiffness/flexibility for the particular section of the catheter. Similarly, fitting can be formed from a suitable material, such as one or more metals and/or one or more polymers. 
     In some embodiments, the guide catheter, suction extension or appropriate portions thereof comprises a thermoplastic polymer with embedded metal elements, which reinforces the polymer. Suitable polymers include, for example, polyamides, i.e., nylons, polyolefins, or the like. The wire can be braided, coiled or otherwise placed over a polymer tubing liner with some tension to keep the wire in place over the tubing liner. A cutoff portion of a reinforced catheter section is shown in  FIG. 28 , in which catheter section  650  has metal reinforcement  652  embedded in the polymer wall  654 . In some embodiments, suction tip can comprise both braided wire and a metal coil, which provide desirable flexibility and resilience to the element as well as mechanical strength with a thin wall. A polymer jacket, such as a heat shrink polymer, can then be placed over the top or the polymer softened to allow incorporation of the metal reinforcements. Upon heating to a temperature over the softening temperature or heat shrink temperature of the polymer and subsequent cooling, the wire becomes embedded within the polymer. In appropriate embodiments, the liner and jacket can be the same or different materials. Suitable wire includes, for example, flat stainless steel wire or the like. Wire diameters can range from about 0.00025 inch (0.00635 mm) to about 0.004 inch (0.1 mm) and in further embodiments from about 0.0005 inch (0.013 mm) to about 0.003 inch (0.075 mm). Braid picks per inch can be from about 20 to about 250 picks per inch and in further embodiments from about 50 to about 150 picks per inch. Coils can be single or multiple filament coils having, for example, pitches from about 0.005 inch (0.13 mm) to about 0.1 inch (2.54 mm) and in further embodiments from about 0.01 inch (0.26 mm) to about 0.050 inch (1.27 mm). A person of ordinary skill in the art will recognize that additional ranges within the explicit ranges below are conceived and are within the present disclosure. The wire adds additional mechanical strength while maintaining appropriate amounts of flexibility. The wire can provide some radio-opacity although radiopaque bands generally would provide a darker and distinguishable image relative to the wire. However, the image of the wire can provide further visualization of the catheter during the procedure. 
     To decrease the chance of accidental removal of the radiopaque band from the catheter and to decrease the chance of the radiopaque band catching onto other objects within the vessel, a metal reinforcing wire can be used to cover or enclose the radiopaque band with the metal wire subsequently being embedded within the polymer. As described in the previous paragraph, the metal wire can comprise interwoven wires, coil, combinations thereof, or the like. A polymer jacket can be placed over the metal wire, which is correspondingly covering the radiopaque band(s), and the heat bonding embeds the radiopaque marked band also. Placement of the marker band under metal wire can prevent the band from being separated from the catheter in the event that the wall is kinked or collapsed. If collapse or kinking of the catheter wall occurs, the braid-wire over the surface of the band collapses down over the marker band to prevent it from separating from the structure. 
     Referring to  FIG. 29 , an example of a procedure for forming a section of reinforced catheter is shown. Polymer liner  660  is placed over mandrel  662 . In the second sequential figure, braided wire  664  has been placed over the polymer liner, and commercial braiding equipment can be used for this step. As shown in the third figure of the series, a metal coil  666  is placed over braided wire  664  and a polymer cover  668  is placed over the metal coil  666 . A heat source  670  can be used to heat shrink polymer cover  668  to complete the reinforced catheter section  672 , as shown in the fourth sequential figure of  FIG. 29 . 
     Catheter Structures—Delivery Catheter with Elastic Guide Tip 
     In some embodiments, to facilitate delivery of medical devices to vessels along a circuitous route, a delivery catheter can be used with an expandable elastic tip. The delivery catheter comprises an elastic tip having an initial un-stretched diameters relatively small relative to a guidewire diameter. Due to the elasticity and small diameter guiding close tracking, the elastic tip can be guided along the guidewire following a circuitous route. Once the delivery catheter is in place, the lumen of the delivery catheter can provide a relatively low friction pathway for delivery of medical devices that would be more difficult to track solely over the guidewire. Because of the elasticity of the delivery catheter tip, the delivered medical device can be pushed out from the tip, which can expand to accommodate the device, to a treatment location in the vessel. The delivery catheter may or may not be removed following the delivery of the desired devices. 
     Referring to  FIG. 30 , delivery catheter  700  comprises a proximal fitting  702 , tubular shaft  704  and narrow diameter elastic distal tip  706 . Elastic distal tip  706  can be specified to include portions of the catheter connecting or transitioning from tubular shaft  704  to the distal tip, as shown with the dashed line in  FIG. 30  since most or all of a connection/transition portion can be designed to expand to provide for the delivery of medical devices through the delivery catheter. Proximal fittings can be any suitable design, such as a conventional design, e.g., Tuohy-Borst adapter or the like, to allow for the placement of appropriate hemostatic valves or the like. Tubular shaft  704  can be designed similarly to tubular shaft  108  of  FIG. 1  and can comprise metal reinforcement, such as braiding, coils or the like. Thus, the discussion of catheter materials and construction above can apply equally to tubular shaft  704  and is included here by reference without expressly repeating the language. With respect to dimensions of tubular shaft  704 , the diameter can be selected to allow for passage of the largest medical device planned for delivery through the delivery catheter. Generally, tubular shaft  704  can have an outer diameter from about 1 mm to about 3.5 mm, in further embodiments from about 1.2 mm to about 3 mm, and in other embodiments from about 1.333 mm to about 2.666 mm. The length of tubular shaft  704  can be from about 30 cm to about 150 cm, in further embodiments from about 35 cm to about 130 cm and in additional embodiments from about 40 cm to about 120 cm. A person of ordinary skill in the art will recognize that additional ranges of dimensions of the tubular shaft within the explicit ranges above are contemplated and are within the present disclosure. 
     The elastic distal tip generally is long enough to provide its tracking function. In some embodiments, elastic distal tip  706  has a length of an approximately constant diameter section from about 5 mm to about 10 cm, in further embodiments from about 7.5 mm to about 8 cm and in other embodiments from about 1 cm to about 7 cm. The inner diameter of the distal end of elastic distal tip  706  generally can be approximately equal to the diameter of a corresponding guidewire or larger by a millimeter or less, in further embodiments, 0.75 mm or less and in some embodiments 0.5 mm or less. With respect to absolute dimensions of the inner diameter of the distal end of elastic distal tip  706 , the inner diameter can be at least a factor of two smaller than the inner diameter of tubular shaft  704  and can be no more than about 2.0 mm, in further embodiments from about 0.2 mm to about 1.5 mm and in other embodiments from about 0.25 mm to about 1.25 mm. A person of ordinary skill in the art will recognize that additional ranges of elastic distal tip dimensions within the explicit ranges above are contemplated and are within the present disclosure. The elastic distal tip may have various shapes including the transition region, and as long as the tip appropriately tracks over the guidewire, the shapes are not otherwise limited. For example, the narrowest diameter portion of the elastic distal tip may be a small fraction of the total length of the elastic distal tip or a large fraction of the length of the elastic distal tip. 
     The materials and dimensions of the delivery catheter tip can be selected to provide for placement of a treatment structure past the delivery catheter through the expansion of the deliver catheter expandable tip. The expansion of the tip may or may not expand the polymer of tip beyond its elastic limit. If stretched beyond the polymer&#39;s elastic limit, the tip does not relax back to its original shape once the stresses are removed, but once in position, the tip&#39;s original narrow configuration is no longer used to guide the tip. Generally, the elastic tip can stretch to at least 1.5 times the initial inner diameter, in further embodiments at least about 2 times, and in other embodiments at least about 2.5 times the initial inner diameter at the distal end of the distal tip. A plurality of therapeutic devices can be sequentially delivered through the delivery catheter, and previously delivered devices may or may not be removed prior to delivery of additional devices depending on their intended use. At an appropriate time on the procedure, the delivery catheter can be removed, which may be prior to the completion of therapeutic treatments. Various elastomeric polymers can be used to form elastic distal tip  706 . Suitable elastomers include, for example, rubber, synthetic rubbers (polyisoprene), polybutadiene, styrene-butadiene copolymer, nitrile rubber, silicone rubber, polyether block amides, vinylidene fluoride, polyurethane elastomers (such as Estane®, Pellethane®, Tecothane®, Tecoflex® and Carbothene™ all from Lubrizol), polychronoprene (such as Neoprene™ from PuPont) and the like. 
     Delivery of a therapeutic device with the delivery catheter is shown schematically in  FIG. 31 . In the first view, first medical device  720  is delivered over guidewire  722  through delivery catheter  724 , push structure  726 , such as a catheter can be used to advance first medical device  720 . Downward arrows indicate later stages of the procedure. In the second view, first medical device  720  is being pushed through elastic distal tip  728 , which is shown in an extended state to provide for the passage of first medical device  720 . Referring to the last view in  FIG. 31 , first medical device  720  and a second medical device  730  are shown advanced past elastic distal tip  728  of delivery catheter  724 . Delivery catheter  724  may or may not be removed prior to performing additional steps of the procedure. 
     Treatment Systems 
     The suction system described herein can be used effectively to remove blood clots from the vasculature, including the vasculature of the brain to treat acute stroke conditions. In particular, the narrow tip catheter of the &#39;313 application have performed well in human clinical trials to restore blood flow in persons with an acute embolic stroke with good patient performance. The device described herein may be expected to provide even better suction while maintaining access capability into vessels challenging to navigate. Nevertheless, for some acute stoke conditions or other embolic events, it can be desirable to use the suction catheter systems described herein with other medical tools for performing the therapy. 
     Referring to  FIG. 32 , a treatment system  750  is shown comprising a guidewire  752 , embolic protection system  754 , suction system  756 , shown with guide catheter  758  and suction extension  760  separated, a percutaneous medical device  762 , microcatheter  764  and delivery catheter  766 . Not all embodiments of medical systems may have all of these components, and some medical system embodiments may have multiple components of each type, such as multiple distinct percutaneous medical devices. Guidewires suitable for use in tortuous bodily vessels are described in copending published U.S. patent application 2016/0199620 A1_to Pokorney et al., entitled “Medical Guidewires for Tortuous Vessels,” incorporated herein by reference. In some embodiments, embolic protection system  754  can comprise a guide structure to provide for delivery of the device as a guide wire, and for these systems a separate guidewire may or may not be used. Suction system  756  embodiments are described in detail herein, and the various embodiments described herein can be adapted for use with the medical systems as well as standalone devices. If desired for particularly challenging device delivery, the medical system can include a delivery catheter  766 , as described herein. 
     Embolic protection devices with small filter lateral extent and designed for suitable manipulations to facilitate delivery in vessels have been developed that are suitable for use in the medical systems described herein. See, for example, U.S. Pat. No. 7,879,062B2 to Galdonik et al., entitled “Fiber Based Embolism Protection Device,” and U.S. Pat. No. 8,092,483B2 to Galdonik et al., entitled “Steerable Device Having a Corewire Within a Tube and Combination with a Functional Medical Component,” both of which are incorporated herein by reference. FiberNet® embolic protection devices based on the technology in these patents are commercially available from Medtronic Inc. Additional fiber-based filter devices particularly designed for delivery into tortuous vessels are described in U.S. Pat. No. 8,814,892B2 to Galdonik et al. (hereinafter the &#39;892 patent), entitled “Embolectomy Devices and Methods of Treatment for Acute Ischemic Stroke Condition,” incorporated herein by reference. The &#39;892 patent describes the use of the filter device as a clot engagement tool for use with an aspiration catheter. The &#39;892 patent also envisions the use of supplementary structures to facilitate engagement of the clot. The use of supplementary structures are also contemplated in procedures described herein. 
     Microcatheters have been designed to allow for access to small blood vessels, such as cerebral blood vessels, and cerebral microcatheters are available commercially, e.g., Prowler Select™ (Cordis Neurovascular Inc.) and Spinnaker Elite™ (Boston Scientific Co.). Of course the term microcatheter can cover a range of devices, and the present discussion can focus on catheters useful for the procedures described herein. In some embodiments, microcatheters can comprise a distal section that is narrower than a proximal section. However, in further embodiments, a microcatheter can have an approximately constant diameter along its length to facilitate delivery of other devices over the microcatheter. A narrow distal diameter allows for the catheter to navigate the tortuous vessels of the brain. The distal section can be highly flexible enough to navigate the vessels, but resilient enough to resist kinking. A microcatheter comprises at least one lumen. The microcatheter can then be used to deliver other treatment devices, aspiration, therapeutic agents, or other means of treating a condition. While microcatheters can have a selected size, in some embodiments, the microcatheters can have a distal outer diameter from about 1.0 Fr to about 3.5 Fr and in further embodiments from about 1.5 Fr to about 3 Fr, and a length from about 30 cm to about 200 cm and in further embodiments from about 45 cm to about 150 cm. A person of ordinary skill in the art will recognize that additional size ranges within the explicit ranges above are contemplated and are within the present disclosure. 
     With respect to percutaneous medical devices  762 , suitable devices include, for example, angioplasty balloons, stent delivery devices, atherectomy devices, such as stent retrievers, and the like. Stents may be, for example, balloon extendable, self-extendable or extendable using any other reasonable mechanism. Balloon extendable stents can be crimped to the balloon for delivery. Some balloon-stent structures are described further, for example, in U.S. Pat. No. 6,106,530, entitled “Stent Delivery Device:” U.S. Pat. No. 6,364,894, entitled “Method of Making an Angioplasty Balloon Catheter:” and U.S. Pat. No. 6,156,005, entitled “Ballon [sic] Catheter For Stent Implantation,” each of which are incorporated herein by reference. Self-expanding stents are described further in U.S. Pat. No. 8,764,813 to Jantzen et al., entitled “Gradually Self-Expanding Stent” and U.S. Pat. No. 8,419,786 to Cottone, Jr. et al., entitled “Self-Expanding Stent,” both of which are incorporated herein by reference. Stent retrievers are described, for example, in U.S. Pat. No. 8,795,305 to Martin et al., entitled “Retrieval Systems and Methods for Use Thereof,” incorporated herein by reference. 
     Procedures Making Use of Treatment Systems 
     As indicated above, the medical systems comprising a suction system described herein can be used with the suction system as stand alone treatment device, perhaps with a guidewire and/or other delivery support devices, or used with supplemental medical devices for treatment of ischemic vessel blockage. In particular, in some embodiments, the suction system is used with an embolic protection device, and in additional embodiments, some form of stent, balloon, athetectomy device or the like may also be used. In any case, a guidewire is generally used to provide access to the treatment site. The guide catheter portion of the suction device may or may not be positioned prior to the introduction of the suction extension. The structures of the particular components are described in detail above, and are not repeated so that this section can focus on the use of the devices. 
     For the treatment of an acute aschemic stroke condition, referring to  FIG. 33 , a patient  780  is shown with three alternative access points into the vasculature, femoral artery  782 , artery in the arm  784  or carotid artery in the neck  786 . Regardless of the access point, the catheter and associated devices are guided to the left or right carotid artery to reach a clot  788  in a cerebral artery  790  of the brain. Referring to the schematic view in  FIG. 34 , clot  788  is shown in cerebral artery  790  with a guidewire  792  positioned with its distal tip past the clot. Guide catheter  794  is positioned over the guidewire within the carotid artery  786 . Suction extension  796  with proximal portion  798  within guide catheter  794  and suction tip  800  extending from guide catheter  794  over guidewire  792 . Referring to  FIG. 35 , the suction tip can be advanced over the guidewire to a position near clot  788 . Suction can be applied as shown with the flow arrows in the figure. Guidewire  792  may or may not be removed before suction is applied. Suction catheters have successfully removed clots responsible for ischemic stroke without further medical devices in the intervention. However, for more difficult clots, additional medical devices can be used as described in the following. 
     Referring to  FIGS. 36 and 37 , the use of a fiber-based filter device is shown in use along with the aspiration system. As shown in  FIG. 36 , clot  810  is shown in cerebral artery  812  with a deployed fiber-based filter  814  supported on a suction tip  816  positioned with the filter deployed past the clot. Fiber-based filter  814  can have fiber elements extending to the wall of the vessel, cerebral artery  812 . Suction tip  816  can be positioned just proximal to the clot, and the remaining portions of the suction system are not shown in this view. Referring to  FIG. 37 , fiber-based filter  814  can be pulled toward suction tip  816  with suction being applied to facilitate removal of clot  810 . Clot  810  can be broken up and removed by suction, and/or all or a portion of clot  810  can be pulled into suction tip  816  optionally along with all or part of the fiber-based filter, and/or all or a portion of clot  810  can be held to the opening of suction tip  816  with the fiber-based filter holding the clot. In any case, once the clot is appropriately stabilized, the devices and any clot still within the vessel or catheter can be removed from the patient. 
     The further use of an additional medical device to facilitate clot removal is shown in  FIGS. 38 and 39 . As shown in  FIG. 38 , clot  830  is shown in cerebral artery  832  with a medical device  834  positioned at the clot and deployed fiber-based filter  836  supported on a guidewire  838  positioned with the filter deployed past the clot. Suitable medical devices include, for example, angioplasty balloons, stents delivery systems, stent retrievers, other atherectomy devices and the like, and these are described further above. The selected medical device is deployed generally with protection from the deployed fiber-based filter and optionally with suction. Once the clot is treated with the medical device, the recovery of the remaining portions of the clot and the medical devices can be removed as shown in  FIG. 39 , similarly to the process shown in  FIG. 37 . In particular, the medical device can be removed, although portions such as a stent may be left behind, and the removal can precede or be done in conjunction with removal of the filter and/or remaining fragments of clot. All or a portion of clot  830 , if not already broken up and removed with suction can be pulled into suction tip  840  optionally along with all or part of the fiber-based filter, and/or all or a portion of clot  810  can be held to the opening of suction tip  840  with the fiber-based filter holding the clot. Again, once the clot is appropriately stabilized, the devices and any clot still within the vessel or catheter can be removed from the patient. The use of a plurality of additional medical devices can be performed through extension of the procedure outlined above to repeat steps involving the additional medical device. 
     The suction system is generally appropriately sterilized, such as with e-beam or gas sterilization. The suction system can be packaged together or separately in a sealed package, such as plastic packages known in the art. The package will be appropriately labeled, generally according to FDA or other regulatory agency regulations. The aspiration system can be packages with other components, such as a guidewire, filter device, and/or other medical device. The packaged system generally is sold with detailed instructions for use according to regulatory requirements. 
     Bench Testing and Calculations 
     To evaluate the performance of the suction tip with a substantial portion of the aspiration lumen provided by the guide catheter both bench testing and calculations were performed. Both the bench testing and calculation confirm the excellent performance of the suction systems described herein with surprising strong suction obtained with the suction tip. With respect to calculation, both fluid dynamic calculations and modeling were performed with consistent results. 
     Bench testing was performed with seven suction catheters: two prototype nozzle/suction system along with two MIVI Neuroscience, Inc. commercial suction catheters with a reduced diameter distal portion, and three Penumbra, Inc. suction catheters with reduced diameter distal portions. The prototype suction systems was formed without the ability to slide the suction tip position to simplify the construction, but they were based on a guide catheter used for the corresponding component of the system.  FIG. 40  shows one of the prototypes, and cross sections are shown in  FIGS. 41 and 42 . The prototype has a standard catheter fitting (Luer Lock)  850  attached at its proximal end, a catheter shaft  852 , suction tip  854  and a sealed connection  856  with a 2 mm overlap. Catheter shaft  852  including a section of the shaft extending into a designated portion of the catheter fitting  850  has a length of 31.777 inches. Catheter shaft  852  has a constant diameter ( FIG. 41 ) with an inner diameter (ID 1 ) of 0.90 inches and an outer diameter of 0.108 inches (2.74 mm or 8.2 Fr). Suction tip ( FIG. 42 ) had a length of 7.8 inches, an inner diameter (ID 2 ) of 0.054 inch and an outer diameter (OD 2 ) of 0.065 inch (1.65 mm or 5.0 Fr). The suction tip overlapped 2 mm with catheter shaft  852 , and the total length was about 1 m (39.4 inches). A second prototype was the same except for having a longer guide catheter (1 m) and a longer suction extension (0.3 m). 
     For comparison, bench testing was also performed with two sizes of MI-AXUS™ 6 suction catheter (MIVI Neuroscience, Inc.), and 5MAX, 5MAX ACE™ and 3MAX commercial catheters (Penumbra, Inc.). The Mi-Axus™ 6 catheter is shown in  FIG. 43  and comprises a proximal fitting  870 , proximal shaft  872 , distal shaft  874  and transition region  876 . Proximal shaft  872  (including a section of proximal shaft extending into the proximal fitting as marked), distal shaft  874 , transition region  876  has a total length L MA of 50.906 inches (1.28 m). Transition region  876  has a length L TR of 0.39 inches, and distal shaft  874  has a length L DS of 9.96 inches. Proximal shaft  872  has an inner diameter (ID MA 1 ) of 0.064 inch and an outer diameter (OD MA 1 ) of 0.075 inch, and distal shaft  874  has an inner diameter (ID MA 2 ) of 0.054 inch and an outer diameter (OD MA 2 ) of 0.065 inch except for an outer diameter taper (OD MA 3 ) to 0.058 inch over the last 0.12 inches of length of the catheter. A second MI-AXUS 6 catheter had a shorter total length of about 1.10 m. The properties of the seven catheters that were bench tested is summarized in Table 1. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Proximal  
                 Distal  
                   
                   
               
               
                   
                 Inner 
                 Inner 
                 Total  
                 Distal Tip 
               
               
                   
                 Diameter  
                 Diameter  
                 Length 
                 Length  
               
               
                 Catheter 
                 (Fr) 
                 (Fr) 
                 (m) 
                 (m) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Prototype 1 
                 6.705 
                 4.11 
                 0.98 
                 0.18 
               
               
                 Prototype 2 
                 6.705 
                 4.11 
                 1.32 
                 0.30 
               
               
                 MI-AXUS  
                 4.80 
                 4.30 
                 1.28 
                 0.27 (1 cm 
               
               
                 6 (1) 
                   
                   
                   
                 transition) 
               
               
                 MI-AXUS  
                 4.80 
                 3.90 
                 1.10 
                 0.27 (1 cm 
               
               
                 6 (2) 
                   
                   
                   
                 transition) 
               
               
                 5MAX 
                 4.89 
                 4.11 
                 1.32 
                   
               
               
                 5MAX ACE 
                 5.19 
                 4.56 
                 1.32 
                   
               
               
                 3MAX 
                 3.27 
                 2.67 
                 1.53 
               
               
                   
               
            
           
         
       
     
     To conduct the bench testing, two 30 cc syringes were used in parallel with a closed stopcock. A schematic diagram of the test set up is shown in  FIG. 44 . A shown, two 300 cc syringes  900  are connected to a Y-adapter  902 , which connects to a 2-way stopcock  904 . Stopcock  904  is connected to a short length of tubing  906  that has a luer lock fitting element that then is connected to the corresponding Luer lock fitting element on the catheter  908  to form connected fitting  910 . The distal end of the catheter is in a water reservoir  912 . The syringes were fully retracted and locked in place. A timer was set and the valve was opened for a selected amount of time. The extracted water was then weighed to obtain an accurate reading of the amount of water. This configuration was measured to produce a maximum gauge pressure of 89 kPa and an average of roughly 78 kPa. The fluid transmission results are presented in Table 2. 
                                         TABLE 2                           Flow Rate    Flow Rate    Flow Rate               Measured   ANSYS   (Pipeflow)           Catheter   (mL/s)   (mL/s)   (mL/s)                          Prototype 1   5.569   5.801   10.65           Prototype 2   5.280   4.155   7.319           MI-AXUS   4.550   2.872   2.648           6 (1)                       MI-AXUS   3.680   2.392   2.927           6 (2)                       5MAX   4.036   2.880   2.701           5MAX ACE   4.877   3.180   3.529           3MAX   1.342   0.406   0.463                        
The prototype catheters had significantly improved suction performance relative to all of the other catheters. Thus, based on the flow rate measurements, a flow rate of at least 5 mL/s and in some embodiments at least about 5.25 mL/s can be established with the catheter systems based on a suction pressure of −78 kPa. A person of ordinary skill in the art will recognize that additional ranges of flow rate within the explicit ranges above are contemplated and are within the present disclosure. For comparison, simulations were performed and fluid dynamics calculations were also performed. In general, the calculated values were not quantitative, but reasonably indicated trends. The ANSYS simulations were somewhat more predictive of the trends than the Pipeflow calculations, such as the correct ordering of the two Mi-AXUS flow rates.
 
     Analytical fluid dynamic calculations were performed using a web based “Pipe Flow Calculator.” The analytical calculations were available on http://www.pipeflowcalculations.net/pressuredrop.xhtmp. The following settings were used for calculations: 1060 kg/m 3 , dynamic viscosity 3.3 centipoise, p1 1 atmosphere, and delta p −75 kPa. To perform these calculations, an average inner diameter had to be input. Calculated flow rates for the catheters used in the bench testing can be found in Table 2. 
     The simulation results were performed with ANSYS CFX R16.1 software (ANSYS Inc.). To perform the simulations, some assumptions were tested and determined to yield appropriate results with negligible effect on the results. A Steady State solution was determined, neglecting the impact of unsteady and turbulent effects on the flow as in the “flow regime” internal to the catheter is also well within the theoretical limit for “laminar” or steady flow. The fluid directly outside the walls of the catheter was neglected, and it was sufficient to simulate a fluid region of 5 cm forward of the distal tip. The tip was modeled as being of constant diameter, which greatly increases the regularity with which the simulation determined fluid properties at each point while reducing computational time, and while also introducing negligible, conservative inaccuracy. For both cases, the simulation assumed to have “converged” when the “residuals”, i.e. the unsolved leftovers from the thousands of approximated differential equations, drop below a certain, specified threshold. This threshold, in standard practice, is 1.0×10 −4 . For these simulations, the threshold was set to be 1.0×10 −6 , which required more computational time, and produced more accurate results. A maximum number of iterations, i.e., the number of times the simulation refines its calculations, is in standard practice  100 . 
     The fluid region is set to be a homogenous fluid, of density 1060 kg/m 3 , dynamic viscosity of 3.3 centipoise, and temperature equal 20 degrees C. with no heat transfer. Two simulations were done for each geometric configuration. To determine volumetric flow rate in cc/s, a 75 kPa pressure difference was then applied as a boundary condition between the proximal and distal ends of the fluid region. For determining the pressure loss, a mass flow rate was specified across the proximal and distal ends of the fluid region. Simulated flow rates for the catheters used in the bench testing are found in Table 2. 
     In the spirit of evaluating additional prototype performance using simulation and calculations, additional evaluations were performed with a range of catheter dimensions using both ANSYS and the pipe flow calculator. The catheter parameters are found in Table 3 and the results are presented in Table 4. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Proximal  
                 Distal  
                   
                 Distal  
               
               
                   
                 Inner 
                 Inner 
                 Total  
                 Tip 
               
               
                   
                 Diameter  
                 Diameter  
                 Length 
                 Length  
               
               
                 Model Catheter 
                 (Fr) 
                 (Fr) 
                 (m) 
                 (m) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Straight 1 
                 6.00 
                 6.00 
                 1.20 
                 — 
               
               
                 Straight 2 
                 5.00 
                 5.00 
                 1.20 
                 — 
               
               
                 Straight 3 
                 2.10 
                 2.10 
                 1.20 
                 — 
               
               
                 Straight 4 
                 4.88 
                 4.88 
                 1.32 
                 — 
               
               
                 Straight 5 
                 5.18 
                 5.18 
                 1.32 
                 — 
               
               
                 Extended Tip 1 
                 8.00 
                 6.00 
                 1.20 
                 0.20 
               
               
                 Extended Tip 2 
                 4.00 
                 2.10 
                 1.20 
                 0.20 
               
               
                 Extended Tip 3 
                 6.81 
                 3.90 
                 1.20 
                 0.60 
               
               
                 Extended Tip 4 
                 6.81 
                 3.90 
                 1.20 
                 1.00 
               
               
                 Extended Tip 5 
                 6.705 
                 4.70 
                 1.32 
                 0.30 
               
               
                 Extended Tip 6 
                 6.705 
                 4.60 
                 1.32 
                 0.30 
               
               
                 Extended Tip 7 
                 6.705 
                 4.50 
                 1.32 
                 0.30 
               
               
                 Extended Tip 8 
                 6.705 
                 4.25 
                 1.32 
                 0.30 
               
               
                 Extended Tip 9 
                 6.705 
                 4.11 
                 1.20 
                 0.30 
               
               
                 Extended Tip 10 
                 6.705 
                 4.88 
                 1.32 
                 0.30 
               
               
                 Extended Tip 11 
                 6.705 
                 2.10 
                 1.50 
                 0.60 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                 Pressure Drop  
                 Flow Rate  
                 Flow Rate 
               
               
                   
                   
                 ANSYS 
                 ANSYS 
                 (Pipeflow) 
               
               
                   
                 Catheter 
                 (kPa) 
                 (mL/s) 
                 (mL/s) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Straight 1 
                 — 
                 3.360 
                 7.437 
               
               
                   
                 Straight 2 
                 — 
                 — 
                 3.590 
               
               
                   
                 Straight 3 
                 — 
                 0.008 
                 0.112 
               
               
                   
                 Straight 4 
                 88.05 
                 — 
                 2.959 
               
               
                   
                 Straight 5 
                 69.31 
                 — 
                 3.756 
               
               
                   
                 Extended Tip 1 
                 — 
                 8.030 
                 13.26 
               
               
                   
                 Extended Tip 2 
                 — 
                 0.044 
                 1.060 
               
               
                   
                 Extended Tip 3 
                 — 
                 4.084 
                 4.772 
               
               
                   
                 Extended Tip 4 
                 — 
                 3.162 
                 2.112 
               
               
                   
                 Extended Tip 5 
                 41.77 
                 5.682 
                 7.960 
               
               
                   
                 Extended Tip 6 
                 43.83 
                 5.460 
                 7.858 
               
               
                   
                 Extended Tip 7 
                 46.14 
                 5.212 
                 7.714 
               
               
                   
                 Extended Tip 8 
                 53.24 
                 4.533 
                 7.463 
               
               
                   
                 Extended Tip 9 
                 — 
                 5.387 
                 7.739 
               
               
                   
                 Extended Tip 10 
                 38.53 
                 6.147 
                 8.218 
               
               
                   
                 Extended Tip 11 
                 — 
                 0.311 
                 2.561 
               
               
                   
                   
               
            
           
         
       
     
     As demonstrated by these experiments and calculations, the suction catheter systems described herein can achieve improve suction through a narrow tip that can be used to access remote blood vessels. 
     The embodiments above are intended to be illustrative and not limiting. Additional embodiments are within the claims. In addition, although the present invention has been described with reference to particular embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention. Any incorporation by reference of documents above is limited such that no subject matter is incorporated that is contrary to the explicit disclosure herein.