Patent Publication Number: US-2021187255-A1

Title: Reinforced Balloon Catheter

Description:
RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. patent application Ser. No. 15/848,309 filed Dec. 20, 2017, entitled Reinforced Balloon Catheter, which is a continuation of and claims priority to U.S. patent application Ser. No. 13/405,113 filed Feb. 24, 2012, entitled Reinforced Balloon Catheter (now U.S. Pat. No. 9,884,172 issued Feb. 6, 2018), which claims benefit of and priority to U.S. Provisional Application Ser. No. 61/446,879 filed Feb. 25, 2011, entitled Reinforced Balloon Catheter, all of which are hereby incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to balloon catheters and, more particularly, to balloon catheters having a plurality of reinforced, co-axially oriented lumens. 
     BACKGROUND OF THE INVENTION 
     Balloon catheters are increasingly being employed to conduct neurological procedures in patients. However, the design parameters for balloon catheters intended for use in neurological procedures are significantly different than the design parameters for balloon catheters used in non-neurological procedures such as cardiological procedures. For example, the width of the circulatory system within the neuroanatomy is significantly smaller and more tortuous than the circulatory system in other parts of the body. In order to access the smaller and more tortuous regions of the neuroanatomy, it is necessary to minimize the outer diameter of the balloon catheter while simultaneously maintaining the pushability and trackability of the catheter. 
     In order to minimize the outer diameter, current balloon catheters intended for neurological procedures employ a non-reinforced, single lumen, over-the-wire design. Accordingly, these balloon catheters are prone to several problems. First, the non-reinforced lumen is susceptible to ovalizing and/or kinking which, in turn, hinders advancement of the catheter over the guidewire, as well as deflation of the balloon. Second, the single lumen is in communication with the arterial blood flow. As the guidewire and balloon catheter are manipulated through the circulatory system, blood is withdrawn into the single lumen of the balloon catheter. Blood may thereby enter the balloon during inflation and cause (1) poor imaging of the balloon, for example, poor fluoroscopic imaging; (2) poor passage of the balloon through the circulatory system due to the premature inflation of the balloon; and (3) poor deflation of the balloon due to blood coagulation in the balloon inflation/deflation port. An additional disadvantage of single lumen balloon catheters is that the interference fit of the guidewire and inflation seal of the balloon may result in removal or peeling of the hydrophilic coating of the guidewire. 
     In order to minimize the outer diameter, current balloon catheters intended for neurological procedures are also typically designed to work with only a narrow gauge guidewire that is supplied by a manufacturer along with the balloon catheter. The current balloon catheters employ guidewires having diameters in the range of 0.010 to 0.012 inches. These relatively narrow guidewires are soft and, therefore, are very difficult to maneuver through the small, tortuous neuroanatomy. 
     What is needed in the field is a balloon catheter that is operable to use with larger gauge guidewires; resists ovalizing and kinking of the inflation and guidewire lumen(s); and deploys with improved pushability and trackability. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is the objective of the present invention to provide a balloon catheter that is operable to use with large gauge guidewires; that resists ovalizing and kinking of the inflation and guidewire lumen(s); and that deploys with improved pushability and trackability. 
     One embodiment of the present invention achieves these objectives by providing a balloon catheter that employs a reinforced, co-axial, duel lumen design. In certain embodiments, the lumen are formed of a multilayer, tubular element in which one of the layers functions, in part, to provide radial reinforcement to the tubular element. 
     In another embodiment of the present invention the distal portion of an outer lumen is locked or fixed to a portion of an inner lumen. A proximal portion of a balloon is attached to a distal portion of the outer lumen and a distal portion of the balloon is attached to a distal portion of the inner lumen. In another embodiment a fluid flow passage is provided between the outer lumen and an interior volume of the balloon, and a passage exclusive to gas or air is formed from the interior volume of the balloon longitudinally through a distal portion of the balloon catheter. 
     In certain other embodiments de-airing channels or features are employed between an exterior surface of the inner lumen and an interior surface of the balloon in order to facilitate purging of gas from the inflation passageway of the balloon catheter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects, features and advantages of which embodiments of the invention are capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which: 
         FIG. 1  is an elevation view of a balloon catheter according to one embodiment of the present invention. 
         FIG. 2  is a partial elevation view of a balloon catheter according to one embodiment of the present invention. 
         FIG. 3  is a cross-sectional view taken along line A-A of  FIG. 1  of a balloon catheter according to one embodiment of the present invention. 
         FIG. 4A  is a partial elevation view of an outer assembly of a balloon catheter according to one embodiment of the present invention. 
         FIG. 4B  is a cross-sectional view taken along line C-C of  FIG. 4A  of an outer assembly of a balloon catheter according to one embodiment of the present invention. 
         FIG. 5A  is a partial elevation view of an inner assembly of a balloon catheter according to one embodiment of the present invention. 
         FIG. 5B  is a cross-sectional view taken along line D-D of  FIG. 5A  of an inner assembly of a balloon catheter according to one embodiment of the present invention. 
         FIG. 5C  is a cross-sectional view taken along line E-E of  FIG. 5A  of an inner assembly of a balloon catheter according to one embodiment of the present invention. 
         FIG. 6  is an expanded view of region  13  indicated in  FIG. 1  of a balloon catheter according to one embodiment of the present invention. 
         FIG. 7  is a cross-sectional view taken along line B-B of  FIG. 2  of an inner assembly of a balloon catheter according to one embodiment of the present invention. 
         FIG. 8  is a cross-sectional view taken along line D-D of  FIG. 5A  of an inner assembly of a balloon catheter according to one embodiment of the present invention. 
         FIG. 9  is a cross-sectional view taken along line B-B of  FIG. 2  of an inner assembly of a balloon catheter according to one embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Specific embodiments of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements. 
     The balloon catheter of the present invention addresses many of the shortcomings of the current balloon catheters intended for use in neurological procedures. Broadly speaking, the balloon catheter of the present invention employs a reinforced, co-axial, duel lumen design. The inner most lumen is operable to serve, among other functions, as a guidewire lumen for over-the-wire type procedures. The outer lumen is operable to serve as an inflation lumen for one or more balloons positioned along the length of the balloon catheter. Each lumen is formed by a multilayer, tubular element in which one of the layers, for example a middle layer in a three-layer embodiment, functions in part to provide radial reinforcement to the tubular element. Accordingly, the balloon catheter of the present invention is operable with larger gauge guidewires; resists ovalizing and kinking of the inflation and guidewire lumens; and deploys with improved pushability and trackability over current balloon catheters intended for use in neurological procedures. 
     With reference to  FIGS. 1-3 and 6 , a balloon catheter  10  according to one embodiment of the present invention comprises a hub  12 , a balloon  18 , and an outer assembly  14  having a lumen  20  through which an inner assembly  16  is co-axially positioned. As best shown in  FIG. 6 , an expanded view of region  13  indicated in  FIG. 1 , a proximal portion  36  of the outer assembly  14  is associated with an inflation port  32  of the hub  12 . A proximal portion  38  of the inner assembly  16  extends proximally from the lumen  20  of the outer assembly  14  and is associated with a guidewire port  34  of the hub  12 . At an opposite end of the catheter, a proximal portion  24  of the balloon  18  is associated with a distal portion  26  of the outer assembly  14 , and a distal portion  28  of the balloon  18  is associated with a distal portion  30  of the inner assembly  16 . Alternatively stated, the opposite ends of the balloon  18  span between the distal portion  26  of the outer assembly  14  and the distal portion  30  of the inner assembly  16 . 
     As shown in  FIGS. 4A and 4B , the outer assembly  14  is a tubular structure having a multilayer wall; an inner layer  40 , middle layer  42 , and outer layer  44 . The inner layer  40  of the outer assembly  14  is formed of a longitudinally continuous or segmented tubular element. In embodiments in which the inner layer  40  of the outer assembly  14  is formed of longitudinally segmented tubular elements the individual segments may be fabricated from the same or different materials and may be attached to one another by welding, fusing, adhering, melting, or other polymerizing or non-polymerizing methods. The inner layer  40  of the outer assembly  14  is fabricated from one or more different polymeric materials, or, alternatively, the inner layer  40  of the outer assembly  14  is formed of a single etched polytetrafluoroethylene, PTFE, tube. While a variety of materials are contemplated for use in fabricating the inner layer  40  of the outer assembly  14 , of particular importance is the feature that the material from which the inner layer  40  is formed has a higher melting temperature than the temperature employed to fuse or otherwise attach the outer layer  44  to the inner layer  40  and middle layer  42  of the outer assembly  14 . 
     In one embodiment of the present invention, the middle layer  42  of the outer assembly  14  comprises a wire  46  wound in a coil-like form around the outer surface  48  of the inner layer  40  of the outer assembly  14 . The wire  46  may be wound in a single layer from one end of the inner layer  40  to the other end to form a coil-like structure or, alternatively, may be wound repeatedly from one end of the inner layer  40  to the other end to form a multilayer coil-like form, as shown in  FIG. 4A . In embodiments employing the middle layer  42  having a multilayered coil-like form, the different windings may be formed from a single or multiple independent wires  46 . The wire  46  may have a circular, rectangular, triangular, or flattened ribbon-like cross-sectional shape, or combinations thereof. The wire  46  is fabricated from a variety of polymeric and/or metallic materials, for example stainless steel. The wire  72  has a diameter that is variable or consistent along the length of the wire  72 . For example, the wire  72  may have a diameter of approximately 0.001 inches. It is also contemplated that the middle layer  42  be formed of a mesh or interweaving of one of more wires  46 . 
     The pitch of the winding of the wire  46  may be either consistent or varied along the length of the inner layer  40 . For example, a first proximal segment of the winding may have a pitch of approximately 0.003 inches, a second more distal segment may have a pitch of approximately 0.0035 inches, a third more distal segment may have a pitch of approximately 0.004 inches, a fourth more distal segment may have a pitch of approximately 0.0045 inches, a fifth more distal segment may have a pitch of approximately 0.005 inches, and a sixth more distal segment may have a pitch of approximately 0.001 inches. In embodiments employing the middle layer  42  having a multilayered coil-like form the outer most winding may, for example, have a pitch of approximately 0.100 inches. 
     In one embodiment of the present invention, the outer layer  44  of the outer assembly  14  comprises a longitudinally continuous or segmented tubular element. The outer layer  44  of the outer assembly  14  is formed of longitudinally segmented, non-heat shrinkable, tubular elements. The individual segments may be fabricated from the same or different materials and may be attached to one another by welding, fusing, adhering, melting, or other polymerizing or non-polymerizing methods, or combinations thereof. 
     In one embodiment, the outer layer  44  of the outer assembly  14  is fabricated from multiple different polymeric tubular segments. For example, a proximal segment  50  of the outer layer  44  of the outer assembly  14  may be formed of a tubular polyamide such as Girlamid L25. The proximal segment  50  has a length  51 , of, for example, approximately 110 centimeters. A second more distal segment  52  may be formed of a tubular poly ether block amide such as Pebax 72D. The second more distal segment  52  has a length  53 , of, for example, approximately  10  centimeters. A third more distal segment  54  may be formed of a tubular poly ether block amide such as Pebax 63D. The third more distal segment  54  has a length  55 , of, for example, approximately 5 centimeters. A forth more distal segment  56  may be formed of a tubular poly ether block amide such as Pebax 55D. The forth more distal segment  56  has a length  57 , of, for example, approximately 20 centimeters. A fifth more distal segment  58  may be formed of a tubular poly ether block amide such as Pebax 45D. The fifth more distal segment  58  has a length  59 , of, for example, approximately 10 millimeters. A sixth more distal segment  60  may be formed of a polyolefin such a Plexar. The sixth more distal segment  60  has a length  61 , of, for example, approximately 2 millimeters. A distal most segment  62  may be formed of a polyolefin such an Engage 8003. The distal most segment  62  has a length  63  of, for example, approximately  13  centimeters. 
     The outer assembly  14  may be fabricated by first wrapping the wire  46  around the inner layer  40  thereby forming the middle layer  44 . The tubular segment or segments of the outer layer  44  are then slid over the middle layer  42 . A heat shrinkable tube of, for example, fluorinated ethylene propylene, FEP, is then slid over the outer layer  44 . The FEP is heated so as to deliver heat to the outer layer  44 , and the outer layer  44  then softens to encapsulate the wire  46 . The FEP tube is then removed from the outer layer  44 . 
     In one embodiment of the present invention, the outer diameter of the outer layer  44  of the outer assembly  14  is in the range of 0.03 to 0.040 inches. The lumen  20  of the outer assembly  14  may have an diameter of approximately 0.0285 inches. 
     As shown in  FIGS. 5A and 5B , the inner assembly  16  is a tubular structure having a multilayer wall formed of an inner layer  64 , middle layer  66 , and outer layer  68 . The inner layer  64  of the inner assembly  16  is formed of a longitudinally continuous or segmented tubular elements. In embodiments in which the inner layer  64  of the inner assembly  16  is formed of longitudinally segmented tubular elements, the individual segments may be fabricated from the same or different materials and may be attached to one another by welding, fusing, adhering, melting, or other polymerizing or non-polymerizing methods, or combinations thereof. The inner layer  64  of the inner assembly  16  is fabricated from one or more different polymeric materials, or, alternatively, the inner layer  64  of the outer assembly  14  is formed of a single, non-segmented, etched polytetrafluoroethylene, PTFE, tube. While a variety of materials are contemplated for use in fabricating the inner layer  64  of the inner assembly  16 , it is important to employ a material that has a higher melting temperature than the temperature employed to fuse or otherwise attach the outer layer  68  to the inner layer  64  and middle layer  66  of the inner assembly  16 . It is also desirable to employ a material that has a relatively low co-efficient of friction. 
     In one embodiment of the present invention, the middle layer  66  of the inner assembly  16  comprises a wire  70  wound in a coil-like form around the outer surface  72  of the inner layer  64  of the inner assembly  16 . The wire  72  may be wound in a single layer from one end of the inner layer  64  to the other or, alternatively, may be wound repeatedly from one end of the inner layer  64  to the other to form a multilayer coil-like form, as shown in  FIG. 4A  regarding wire  46  of the outer assembly  14 . In embodiments employing the middle layer  66  having a multilayered coil-like form, the different coils may be formed from a single or multiple independent wires  72 . The wire  72  may have a circular, rectangular, triangular, flattened, ribbon-like cross-sectional shape, or a combination thereof. The wire  72  may be fabricated from a variety of metallic and/or polymeric materials, for example stainless steel. The wire  72  may have a diameter that is variable or consistent along the length of the wire  72 . For example, the wire  72  may have a diameter of approximately 0.001 inches. It is also contemplated that the middle layer  42  may be formed of a mesh or interweaving of one of more wires  46 . 
     The pitch of the winding of the wire  72  may be either consistent or varied along the length of the inner layer  64  of the inner assembly  16 . For example, a first proximal segment of the wire  72  winding may have a pitch of approximately 0.003 inches, a second more distal segment may have a pitch of approximately 0.003 inches, and a third most distal segment may have a pitch of approximately 0.001 inches. 
     As shown in  FIGS. 2 and 5A , in one embodiment of the present invention, one or more marker bands  82 A,  82 B, and  82 C are placed, for example, over the wire  70  forming the middle layer  66  of the inner assembly  16 . The marker bands  82 A,  82 B, and  82 C comprise a radiopaque material such as gold, platinum, or silver, and are used for determining the location of the balloon catheter  10  within a patient. In certain embodiments of the present invention the maker band  82 A may be placed a distance L 3  proximate to a distal end  86  of the inner assembly  16 . For example, the distance L 3  may be 5 millimeters. 
     The marker bands  82 B and  82 C may be positioned further proximal of the marker band  82 A so as to indicate or mark the proximal portion  24  and the distal portion  28  of the balloon  18 . It will be understood that the exact placement of the marker bands  82 B and  82 C relative to the distal end  86  of the inner assembly  16  will depend on the dimensions of the balloon  18  employed in the balloon catheter  10 . 
     For example, in an embodiment employing a balloon  18  of 10 millimeters in length, a proximal end  84  of the marker band  82 C is a distance L 1  from the distal end  86  of the inner assembly  16 . For example, the distance L 1  may be approximately 19.5 millimeters. Opposite ends of the marker bands  82 B and  82 C are a distance L 2  from one another. For example, the distance L 2  may be 10 millimeters. In an embodiment employing a balloon  18  of 20 millimeters in length, the distance L 1  is, for example, approximately 29.5 millimeters, and the distance L 2  is, for example, 20 millimeters. 
     In one embodiment of the present invention, the outer layer  68  of the inner assembly  16  comprises a longitudinally continuous or segmented tubular element. Preferably the outer layer  68  of the inner assembly  16  is formed of series of longitudinally segmented, non-heat shrinkable, tubular elements. The individual segments are fabricated from the same or different materials and may be attached to one another by welding, fusing, adhering, melting, or other polymerizing or non-polymerizing methods. Preferably, the outer layer  68  of the inner assembly  16  is fabricated from multiple different polymeric tubular segments. For example, a proximal segment  74  of the outer layer  68  of the inner assembly  16  may be formed of a tubular poly ether block amide such as Pebax 63D. The proximal segment  74  has a length  75  of, for example, approximately 150 centimeters. A second more distal segment  76  may be formed of a tubular poly ether block amide such as Pebax 45D. The second more distal segment  76  has a length  77  of, for example, approximately 10 centimeters. A third more distal segment  78  may be formed of a polyolefin such as Plexar 3080. The third more distal segment  78  has a length  79  of, for example, approximately 2 millimeters. A distal most segment  80  may be formed of a polyolefin such as Engage 8003, and have a length  81  of, for example, approximately 5 centimeters. 
     The inner assembly  16  may be fabricated by first wrapping the wire  70  around the inner layer  64  thereby forming the middle layer  66 . Next, the marker bands  82 A,  82 B, and  82 C are placed over or within the middle layer  66 , and the tubular segment or segments of the outer layer  68  are then slid over the marker bands  82 A,  82 B, and  82 C and the middle layer  66 . A heat shrinkable tube of, for example, fluorinated ethylene propylene, FEP, is then slid over the outer layer  68 . The FEP is heated so as to deliver heat to the outer layer  68 , thereby softening the outer layer  68  so as to encapsulate the wire  70  forming the middle layer  66 . The FEP tube is then removed from the outer layer  68 . 
     In one embodiment of the present invention, the wire  70  forming the middle layer  66  of the inner assembly  16  may terminate proximal of the distal end  86  of the outer assembly  16 . A tubular element  100  may be employed in all or a portion of the length between the distal end  86  and the point at which the wire  70  terminates. The tubular element  100  may, for example, be formed of a crosslinked polyolefin tube having a length of approximately 5 millimeters. 
     In one embodiment of the present invention, the outer diameter of the outer layer  68  of the inner assembly  16  is in the range of 0.020 to 0.025 inches, and more preferably in the range of 0.020 to 0.0225 inches. 
     As shown in  FIGS. 2, 5A, and 5C , in one embodiment of the present invention, the inner assembly  16  may further comprise an inflation plug  88 . The inflation plug  88  is formed of a tubular segment of material having a wall of either uniform or asymmetric thickness. The inflation plug  88  may, for example be formed of a poly ether block amide such as Pebax 55D. The inflation plug may, for example, be approximately 5 millimeters in length and a distal end  90  of the inflation plug  88  may, for example, be positioned approximately 4 millimeters from the proximal end  84  of the marker band  82 C. An outer dimension or diameter of the inflation plug  88  is large enough so that the inflation plug  88  may not completely pass into the lumen  20  of the outer assembly without significant force. The inflation plug  88  may be formed on the inner assembly  16  as described above regarding the formation of the outer layer  68  of the inner assembly  16 . 
     As shown in  FIG. 5C , the inflation plug  88  may comprise one or more passages or channels  92  formed longitudinally along the length of the inflation plug. The channel  92  may be formed by placing a mandrel longitudinally along the outside surface of the inflation plug  88  prior to sliding the heat shrinkable tube of, for example, FEP over the inflation plug  88 . When the FEP is heated so as to deliver heat to the inflation plug  88 , the mandrel melts into the inflation tube thereby the channel  92  within the inflation plug  88 . The FEP tube is then removed from the inflation plug  88 . 
     The inflation plug  88  functions, in part, to longitudinally lock the inner assembly  16  to the outer assembly  14  so as to prevent changes in the length of the distal extension of the distal portion  30  of the inner assembly  16  relative to a distal end  98  of the outer assembly  14  due to the inflation and orientation of the balloon  18  during a procedure. The passage or channel  92  formed in the plug  88  allows for fluid communication between the lumen  20  of the outer assembly and an interior volume of the balloon  18 . 
     A shown in  FIG. 3, 5B, 5C, and 7 , the inner assembly  16  comprises an inner lumen  22 . The lumens functions as a guidewire lumen for over-the-wire procedures. The lumen  22  of the inner assembly  16  may have a diameter of at least approximately 0.0165 inches. Accordingly, the balloon catheter  10  of the present invention may be used with guidewires having a larger diameter than the guidewires supplied with current balloon catheters intended for use in neurological procedures. For example the present balloon catheter  10  may be used with a guidewire having a diameter of 0.014 inches. This feature allows a physician to more easily access a neuroanatomical target, such as an aneurysm, since the relatively larger guidewire provides more support for the balloon catheter  10  over which to track. 
     Additionally, the guidewire may be removed from the lumen  22  after placement of the balloon catheter within a patient and the lumen  22  may serve as a functional lumen for passage of additional medical devices or substances to the target location within the patient. 
     It will be understood that it is generally beneficial for the outer assembly  14  and the inner assembly  16  to be more flexible at their distal portions than their proximal portions. Furthermore, it is contemplated that the distal portions of the outer assembly  14  and/or the inner assembly  16  may be pre-shaped or operable to be shaped by a physician prior to initiating a procedure using, for example, steam shaping techniques. 
     As shown in  FIGS. 1 and 6 , the proximal portion  36  of the outer assembly  14  terminates distally of the proximal portion  38  of the inner assembly  16 . Accordingly, the lumen  20  of the outer assembly is in communication with the inflation port  32 .  FIGS. 1 and 6  also show that the proximal portion  38  of the inner assembly  16  extends proximally beyond the proximal portion  36  of the outer assembly  14  and is associated with the guidewire port  34  of the hub  12 . Accordingly, the lumen  22  of the inner assembly and the guidewire port  34  of the hub  12  together form a substantially continuous lumen through which a guidewire or other medical device may pass. The outer assembly  14  and the inner assembly  16  may be attached to the hub  12  by various methods, including welding, fusing, adhering, melting, or other polymerizing or non-polymerizing method, or combinations thereof. It is noted that this configuration of the hub  12  and association of the hub  12  with the outer assembly  14  and the inner assembly  16  advantageously provides for the isolation of the lumen  22  of the inner assembly  16  from the lumen  20  of the outer assembly  14 . The isolation of these lumens and their functionality serves, in part, to address many of the shortcomings described above regarding the current single lumen balloon catheters intended for neurological procedures. 
     As shown in  FIGS. 1 and 2 , the proximal portion  24  of the balloon  18  is associated with the distal portion  26  of the outer assembly  14 , and the distal portion  28  of the balloon  18  is associated with the distal portion  30  of the inner assembly  16 . The balloon  18  may be attached to the distal portion  26  of the outer assembly  14  and the distal portion  30  of the inner assembly  16  by various methods including welding, fusing, adhering, melting, or other polymerizing or non-polymerizing methods and combinations thereof. In certain embodiments, the distal portion of the balloon  18  covers and extends to the distal end  86  of the inner assembly  16 . The balloon  18  may, for example, be formed of Polyblend 45A or other polymeric elastomeric material. The balloon  18  may have an outer diameter of up to approximately 15 millimeters and a length in the range of 5 to 25 millimeter and, preferably a length in the range of 10 to 20 millimeters. 
     As shown in  FIG. 7 , in one embodiment of the present invention, one or more air purge ports  94  are employed at the interface of the distal portion  30  of the inner assembly  16  and the distal portion  28  of the balloon  18 . The air purge ports  94  are formed by placing one of more mandrels having diameters in the range of 0.001 to 0.030 inches on the outer surface of the outer layer  68  of the inner assembly  16 . An interior surface  96  of the balloon  18  is then attached over the mandrels to the outer layer  68  of the inner assembly  16 . After the balloon  18  is attached to the distal portion  30  of the inner assembly  16  the mandrels are removed. Accordingly, flow paths large enough for the passage of gas and small enough to seal against the passage of liquids are formed. 
     The air purge ports  94  function to facilitate removal of air from the lumen  20  and balloon  18  prior to initiating a medical procedure. With current co-axial balloon catheters, it is very difficult to remove all of the air from the inflation/deflation lumen prior to initiating a medical procedure. Physicians typically must remove the air from a balloon catheter through several minutes of aspiration or suction through the inflation/deflation lumen. Air that is not removed will show in images taken during the procedure and may obscure details that the physician may otherwise need to observe in order to perform the procedure. 
     In contrast, the air purge ports  94  of the present invention allow a user to more effectively and more efficiently remove air from the lumen  20 , the inflation/deflation lumen. In practice, prior to initiating the procedure, a physician would position the distal end of the balloon catheter  10  higher than the proximal end and then inject a balloon inflation medium, such as contrast medium or saline, through the inflation port  32  and associated lumen  20 . As the inflation medium fills the lumen  20 , air is forced out the air purge ports  94  until no air remains within the lumen  20  or balloon  18 . The physician may repeat the process as needed to ensure that all air is removed from the lumen  20  of the outer assembly  14  and balloon  18 . 
     In another embodiment of the present invention, as shown in  FIGS. 8 and 9 , the above described functionality of the inflation ports  32  is enhanced by employing one or more de-airing channels  102 . The de-airing channel  102  is formed in the outer layer  68  of the inner assembly  16 . At a minimum, the de-airing channel  102  initiates longitudinally approximate the distal end  90  of the inflation plug  88  and continues uninterruptedly to approximately a proximate end of the air purge port  94 . The length of the de-airing channel  102  may extend to or overlap with the distal end  90  of the inflation plug  88  and/or the proximate end of the air purge port  94 . The de-airing channel  102  may be either radially aligned or radially off set with the channel  92  of the inflation plug  88  and/or the air purge port  94  relative to an axis through the lumen  22  of the inner assembly  16 . 
     The de-airing channel  102  is formed by placing one of more mandrels having diameters in the range of 0.001 to 0.030 inches between the outer layer  68  of the inner assembly  16  and the heat shrinkable tube and then heating the heat shrinkable tube as described above. In certain embodiments, the de-airing channel  102  is radially aligned with the air purge port  94  and/or with the channel  92  formed in the inflation plug  88 . For example,  FIG. 9  shows an embodiment in which the de-airing channel  102  is radially aligned with the air purge port  94 . The de-airing channel  102  and the air purge port  94  each form a portion of a unified channel. In embodiments in which the de-airing channel  102  is radially aligned with the air purge port  94  and/or with the channel  92  formed in the inflation plug  88 , the de-airing channel  102  may extend longitudinally the length of the air purge port  94  and/or may extend longitudinally into or proximately beyond the channel  92  formed in the inflation plug  88 . 
     The de-airing channel  102  helps ensure that a fluid and air flow path is maintained unobstructed between the exterior surface of the inner assembly  16  and the interior surface  96  of the balloon  18 . Because the balloon  18  may be closely form fitted over the inner assembly  16  when the balloon is not inflated, absent a de-airing channel  102 , it may not always be possible to purge air from lumen  20  of the outer assembly  14  without inflating the balloon  18 . Hence, the de-airing channel  102  provides a recess or unobstructed channel on the exterior surface of the inner assembly  16  that allows the passage of air and fluid between the deflated balloon and the exterior surface of the inner assembly  16 . Hence, air may be purged from the balloon catheter  10  without inflating of the balloon  18 . 
     It is also contemplated that the de-airing channel  102  may take the form of one or more spiral channels or grooves, spiral ridges, and/or longitudinal ridges on the exterior surface of the inner assembly  16 . The de-airing channel  102  may also take the form of one or more small tubular elements bonded to the exterior surface of the inner assembly  16 . 
     It is noted that while the present invention has been described with respect to neurological procedures, it is contemplated that certain features of the present balloon catheter also address needs in non-neurological fields. 
     Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.