Abstract:
The present invention relates to a double lumen catheter tube having a substantially circular cross-section and comprising a catheter tube body having a longitudinal axis, and further comprising an outer tubular and an inner divider wall inside the catheter tube body dividing said catheter tube body into a first and a second lumen. The first and the second lumen each comprise a cross section having the shape of an isosceles triangle with three rounded vertices. The tubular wall comprises wall sections that have a smaller wall thickness.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of international patent application PCT/EP2010/001529, filed on Mar. 11, 2010 designating the U.S., which international patent application has been published in English language and claims priority from European patent application 09155029.3, filed on Mar. 12, 2009. The entire contents of these priority applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a double lumen catheter tube having a substantially circular cross section and comprising a tubular wall having an outer surface and an inner surface, each extending about a longitudinal central axis of the catheter tube. 
         [0003]    Such double lumen catheter tubes are, e.g., used in medical devices which are used to provide access to vessels of a patient during, e.g. infusion and/or removal of body fluids. Catheters, which represent such catheter tubes, have tapered distal tips to be percutaneously inserted into the patient. Double lumen catheters include a tubular wall that forms a fluid conduit which typically has a circular cross-section. Inside the catheter tube there is provided a divider wall which divides the lumen into two lumens. In many circumstances it is desirable to have two lumens with substantially equal cross-sectional areas; this is of particular importance where maximum fluid delivery rates through both lumens have to be guaranteed. 
         [0004]    The catheter is inserted by means of guide wire that is first inserted to the later position of the catheter. Subsequently, the distal end of the catheter is moved over the guide wire and inserted into the position by means of the guide wire. As soon as the catheter is in its position, the guide wire is withdrawn. In the catheters, there may be provided a separate guide wire lumen for the guide wire in addition to the two lumens of the catheter, or one of the lumens is being temporarily used as the lumen for the guide wire and afterwards as lumen for withdrawing/delivering fluids to the body. 
         [0005]    One of the most important features of such catheters is their kinking resistance, since upon kinking the catheter gets blocked and the withdrawal and/or the return of the fluid, e.g. blood, is obstructed. Thus, kinking may lead to complications and malfunctions during the operation of the medical devices which use a catheter of this kind. 
         [0006]    In general, kinking might be avoided by means of increased wall thicknesses but, as an adverse effect, the lumen of a catheter tube designed in this way is impaired, i.e. a potential fluid flow through that catheter tube is adversely effected. Thus the ratio of the outer diameter i.e. the overall cross-section area of a catheter tube and the usable clearance, i.e. the lumen area is most important. 
         [0007]    Many different approaches are known in the state of the art, which try to overcome the problem of the kinking resistance. 
         [0008]    Many multilumen catheters of the prior art address the problem of kinking by including in the tube at least one lumen reinforced with a support member which may include a polymeric or metallic braid, coil or knit material, see, e.g., EP 1 144 039 A2. 
         [0009]    Other approaches, like the one disclosed in US 2005/0277910 A1, try to overcome the problem of kinking by designing the catheter tube as a layered composite tube, whereby the interior that faces the lumen consists of a polyamide layer and the exterior consists of a polyurethane layer. These tubes are supposed to have improved characteristics in terms of resistance to kinking, a higher degree of rigidity during application and a reduced rigidity after application. 
         [0010]    On the other hand, U.S. Pat. No. 5,968,009 discloses a double lumen catheter having a supposedly increased kinking resistance. The lumen&#39;s central wall dividing the catheter tube&#39;s lumen into two lumens comprises an arcuate portion and has two surfaces, one bordering a first lumen, the other bordering the second lumen. Further, the first surface has a central convex arcuate portion, the second surface has a central concave arcuate portion, both portions having adjacent wing portions extending in the opposite directions to the tubular wall. 
         [0011]    However, the catheters of the state of the art represent catheter tubes which are not only complicated but also high in costs in view of their manufacturing. 
       SUMMARY OF THE INVENTION 
       [0012]    Thus, and despite the different catheters addressing the improvement of the kinking resistance of its catheter tube, there still is a need for alternative catheter tubes, with which an improved kinking resistance can be achieved whilst at the same time being easy to manufacture. 
         [0013]    According to one aspect of the invention, there is provided a double lumen catheter tube having a substantially circular cross section and comprising a catheter tube body, an outer tubular wall having an outer surface and an inner surface, each extending about a longitudinal central axis of the catheter tube. The catheter tube has a wall thickness which is defined between the outer surface and the inner surface, and the catheter tube comprises an inner wall inside the catheter tube for dividing it into a first and second lumen, each lumen being defined by the inner surface of the tubular wall and the inner wall, and each lumen comprising a cross section with an arcuated portion and a substantially plane portion opposite of the arcuated portion, the plane portions of the lumens lying adjacent to one another. 
         [0014]    Further, the wall thickness of the catheter tube according to the invention is modulated as a function of the circumferential angle. This means that the catheter tube according to the invention is modulated such, that a region of the arcuated portion of the cross section of at least one of the first or second lumen, and the regions where the tubular wall meets the inner wall, has a wall thickness that is smaller than the wall thickness of two tubular wall regions located left and right of said centre region. 
         [0015]    With the catheter tubes&#39;s design according to the invention, the catheter tube overall gains a higher kinking resistance while at the same time achieve a favorable ratio of outer diameter to lumen area and, even more, being easy and cost-effective in its manufacturing. The catheter tube according to the invention has proven to have an improved kinking resistance values compared to other catheter tube solutions having different wall thicknesses. These improved characteristics are due to the fact that the arcuated portion of the tubular wall of the first and/or the second lumen, an its highest point of the arch, and lying perpendicular to the longitudinal axis of the catheter tube, and the regions where the tubular wall meets the inner wall, have a wall thickness that is smaller than the wall thickness of portions left and right to the highest point of the arch. 
         [0016]    With the expression “located left and right” from the centre region, regions of the tubular wall are meant that are located on the tubular between the centre region and the regions where the tubular wall meets the inner wall. 
         [0017]    Double lumen catheter tubes as known in the art have—in general—a circular cross-section with a divider wall separating the catheter tube in two lumens each having a substantially semi-circular cross-section. With the catheter tube according to the invention, the cross-section of each of the lumens rather has—due to the different wall thicknesses in portions of the walls forming the lumens—the form of an isosceles triangle having “chopped-off”, i.e. rounded vertices/edges, with the vertex formed by the meeting point of the two equal sides being more chopped-off than the other vertices. The isosceles triangle has three rounded vertices, with two of the vertices having the same angle, and the other vertex—having a different angle from the other two vertices—representing the centre region of the arcuated portion. 
         [0018]    In other words, the wall of each of the two lumens has, respectively at portions that are located from about 20° to about 80°, preferably about 45°, with respect to a virtual line perpendicularly cutting through the divider wall and the highest point of the arcuated portion, a wall thickness that is thicker compared to the wall portions forming the highest point of the of the arcuated portion and the divider wall. 
         [0019]    In a preferred embodiment, the angle of the two equal angles of the isosceles triangle is about 45°. 
         [0020]    According to another aspect of the invention, the centre region of the tubular wall as defined above has a wall thickness of about 40% to 80%, preferably of about 50%, of the tubular wall regions located left and right of said centre region. 
         [0021]    With this measure, it is intended that, if the wall thickness of the tubular wall regions located left and right of the centre region is about 0.4 mm, the wall thickness of the centre region is about 0.2 mm, which would represent 50% of the wall thickness of the regions located left and right of the centre region. 
         [0022]    According to other preferred embodiments of the invention, the two tubular wall regions located left and right of said centre region have a wall thickness of about 0.55 mm to about 0.80 mm. 
         [0023]    According to a particular preferred embodiment, the centre region of the tubular wall has a wall thickness of about 0.50 mm, and the two tubular wall regions located left and right of said centre region have a wall thickness of about 0.64 mm. 
         [0024]    In yet another preferred embodiment, the two tubular wall regions are each from about 10° to about 80° offset to the centre region, more preferably from about 30° to about 60° offset to said centre region, and most preferably about 45° offset to said centre region. 
         [0025]    With these embodiments of the invention, double lumen catheter tubes are provided that show a maximum kinking resistance, which is one of the most important features of catheter tubes employed in medical applications. 
         [0026]    In yet another embodiment, the cross-sectional areas of the first and the second lumens are substantially equal. 
         [0027]    This measure has the advantage that the amount of blood flowing though the lumens and the blood flow characteristics in the lumens will be about the same. 
         [0028]    The expression “substantially equal” as it is used herein, means that the cross-sections of the two lumens have the same shape and dimension with minor tolerances being possible which stem either from the manufacturing process or from an intended deviation. The cross-sectional areas are considered to be substantially equal in accordance with the invention if the larger of the two areas is no more than approximately 15% larger than the smaller one. 
         [0029]    According to another embodiment of the invention, the cross-sectional areas of the first and the second lumen are different. 
         [0030]    This measure has the advantage that a different flow amount and different flow characteristics in the lumens can be achieved which may be desirable in certain medical approaches. 
         [0031]    According to a preferred embodiment, the catheter tube comprises flexible material, wherein it is preferred that the tubular wall and/or the inner wall comprises a flexible material. 
         [0032]    A flexible material that may be used in this connection is any flexible homo- or co-polymer, or polymer mixtures, which are commercially available and used in medical appliances. Thus, materials that can be used in the present invention comprise polyurethane, polyamide, silicone, polyethylene, polyamide or mixture thereof, or other materials with the same or similar characteristics as those just mentioned. 
         [0033]    Of course, also non-flexible materials may be used with the present invention, e.g. metallic materials or alloys, such as stainless steel, cobalt-chromium alloys or others, in which case the catheter represents a rigid catheter, or comprises portions that are rigid in case flexible and non-flexible materials are used for the manufacture of the catheters. 
         [0034]    Many different materials for use with a catheter are known in the state of the art, and it lies within the proficiency of a person skilled in the art to choose a material or a mixture of different materials for a certain application. 
         [0035]    According to another embodiment of the invention, at least one of the first and the second lumen comprise a cross-sectional area of about 4 to about 6 mm 2 , and more preferably if at least one of the first and the second lumen comprises a cross-sectional area of about 5.5 mm 2 . 
         [0036]    It is within the proficiency of a person skilled in the art to choose different or the same cross-sectional area of the lumens, depending of the respective application and vessel characteristics of the patient to be treated. 
         [0037]    The double lumen catheter tube according to the invention may be preferably used as a catheter, and is, thus, insertable/implantable into a vessel of a patient. 
         [0038]    Thus, the invention also concerns the use of the catheter according to the invention in the withdrawing and delivery of fluids to a patient. The catheter according to the invention is particularly suited for use in hemodialysis. 
         [0039]    It is to be understood, that the term “vessel” includes blood vessels, in particular veins of a patient. The patient is a mammal, preferably human. 
         [0040]    It will be appreciated that the aforementioned features and those still to be explained below can be used not only in the respectively cited combination but also in other combinations or on their own, without departing from the scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]    Further advantages and features will become evident from the following description and from the attached drawing, in which 
           [0042]      FIG. 1  shows a cross-sectional view of a first preferred double lumen catheter tube in accordance with the present invention; and 
           [0043]      FIG. 2  shows views of longitudinal cuts (left hand, respectively) and a cross sections (right hand, respectively) through a portion of a double lumen catheter in accordance with the present invention (B) in comparison with double lumen catheter tubes (A, C and D) not having the characteristics/dimensions of the catheter tube according to the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0044]    The double lumen catheter tube according to the invention is designed for use as a catheter, and it may be used with any catheter device in any application where a double lumen catheter is needed. 
         [0045]    A first preferred embodiment according to the invention is shown in general with number  10  in  FIG. 1 . The double lumen catheter tube body  10  includes a tubular wall  12 , which has an outer surface  14  and an inner surface  16 . The catheter tube body  10  also comprises an inner or divider wall  18 , dividing the lumen of the catheter tube body  10  in two lumens, a first lumen  20  and a second lumen  22 . Thus, each of the lumens  20  and  22  is defined by the inner surface  16  of the tubular wall body  12  and the inner (or divider) wall  18 . 
         [0046]    The cross-sectional area of each of the lumens  20 ,  22  comprises an arcuated portion  24 ,  24 ′ and a substantially plane portion  26 ,  26 ′ opposite to the respective arcuated portion  24 ,  24 ′, the plane portion  26 ,  26 ′ being defined by the surface  27 ,  27 ′ of inner wall  18 , the arcuated portion  24 ,  24 ′ being defined by the inner surface  16  of the tubular wall  12 . 
         [0047]    A centre region, indicated at arrow  30 ,  30 ′ in  FIG. 1 , of the arcuated portion in the tubular wall  12  of the lumens  20 ,  22 , perpendicular to the longitudinal axis of the catheter tube body  10  and opposite to the plane portion  26 ,  26 ′, has a wall thickness that is smaller than the wall thickness of two tubular wall regions located left and right of the centre region  30 ,  30 ′, which are indicated with arrows  32  and  34  in  FIG. 1 . The thickness of the tubular wall  12  in the regions  39  where the inner wall  18  meets the tubular wall  12  is then, again, smaller than the thickness of the tubular wall regions  32  and  34 , and can have about the thickness of the centre region  30 ,  30 ′. 
         [0048]    In the embodiment as shown in  FIG. 1 , the centre region  30 ,  30 ′ represents the highest point of the arcuated portion  24 ,  24 ′ of the cross-sectional areas of the lumens  20 ,  22 . Further, in the embodiment shown in  FIG. 1 , the wall regions  32 ;  34  left and right of the centre region  30 ,  30 ′ of the arcuated portion, which have a larger thickness than the centre region  30 ,  30 ′, are located about 45° with respect to a virtual line perpendicularly cutting through the inner wall  18  and the highest point of the arcuated portion, i.e. the centre region  30 ,  30 ′. 
         [0049]    Further, and this can also be seen in the embodiment as shown in  FIG. 1 , the cross-sections of the lumens  20 ,  22  are about equal and have the shape of an isosceles triangle having chopped-off vertices  36 ,  36 ′,  38 ,  38 ′, with the vertex  36 ,  36 ′ formed by the meeting point of the two equal sides being more chopped-off, and therefore being more rounded, than the other two vertices  38 ,  38 ′. In the embodiment shown in  FIG. 1 , the angle a of the two equal angles of the isosceles triangle is about 45°. 
         [0050]    Thus, in a preferred embodiment, with the diameter of the catheter tube  12  being 5 mm—which represent 15 French—and with a wall thickness in the regions  32 ,  32 ′,  34 ,  34 ′ being about 0.64 mm and a wall thickness in the centre region  30 ,  30 ′ of the tubular wall  12  being about 0.5 mm, a cross-sectional area of the lumens  20 ,  22  of about 5.5 mm 2  each may be reached. 
         [0051]    Further, the wall thickness in the area where the inner wall  18  and the tubular wall meet each other, which is indicated by bracket  40  in  FIG. 1 , is about 0.45 mm. Also, in the embodiment shown in  FIG. 1 , the wall thickness of inner wall  18  is about 0.25 mm. 
         [0052]    It lies within the proficiency of a person skilled in the art to transfer the dimensions exemplary given for a 15 French catheter tube to catheter tubes having a smaller or a larger diameter. 
         [0053]      FIG. 2  represents schematic views of a catheter tube according to the invention (B) and other catheter tubes (A, C, D) the kinking of which is being virtually simulated by means of a respective computer program. 
         [0054]    The views presented in  FIG. 2  show tubular cross-sections each of the same outer diameter and the same lumen areas but with different circumferential wall thickness distributions. As can be seen from  FIG. 2 , the catheter tube according to the invention (B) is much more resistant to kinking (see the simulated kinking view on the left hand side, respectively). The catheter tube according to the invention (B) has in the centre region of the tubular wall a smaller wall thickness than in regions left and right to that centre region, as indicated by the arrows  50 ,  51  (see cross-sectional view on the right hands, respectively). The tubular wall of the catheter tube as shown in A of  FIG. 2  has an equal thickness; the tubular wall of the catheter tube as shown in C, although having a smaller thickness in the centre portion, it does not have also a smaller wall thickness in the region where the tubular wall meets the inner wall compared to the thickness of the tubular wall located left and right to the centre region. The tubular wall of the catheter tube as shown in D has a larger thickness in the centre region than in the regions left and right of the centre region.