Abstract:
A method of manufacturing a microdialysis catheter, comprises the steps of extruding a flexible material to form an elongate catheter body having a substantially cylindrical outer surface and a plurality of continuous internal channels extending in the longitudinal direction of said catheter body; sealing a free end of said catheter body; providing in said surface at a distance from said free end an opening extending into said catheter body to communicate with a portion of a first of said channels; providing communication between said first channel and a second of said channels at a distance from said free end shorter that said distance; and covering said opening by a microdialysis membrane.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a method of manufacturing a microdialysis catheter to be inserted into and guided by a blood vessel of a living being.  
         BACKGROUND OF THE INVENTION  
         [0002]    Microdialysis is used to monitor the interstitial fluid in various body organs with respect to local metabolic changes. To perform Microdialysis, a catheter is used including an elongate flexible body having at least two internal channels therealong, and, at its distal end, a dialysis chamber. U.S. Pat. No. 4,694,832 to Ungerstedt discloses a dialysis probe provided in a distal end of an elongate, flexible hose. The probe consists of several elements that have to be carefully assembled and mounted at a free end of the hose during manufacture of the microdialysis catheter. This involves a substantial risk that the various elements come loose when the catheter is in use. Furthermore, the brittle microdialysis membrane is not internally supported well enough to make this known microdialysis probe suitable for insertion into and guidance by a blood vessel, mounted in the end of the flexible hose.  
         SUMMARY OF THE INVENTION  
         [0003]    It is an object of the invention to set aside these drawbacks by proposing a method of manufacturing a microdialysis catheter that is robust, simple to insert in a vessel, and has a simple construction.  
           [0004]    According to the present invention there is provided a method of manufacturing a microdialysis catheter, comprising the steps of extruding a flexible material to form an elongate catheter body having a substantially cylindrical outer surface and a plurality of continuous internal channels extending in the longitudinal direction of said catheter body; sealing a free end of said catheter body; providing in said surface at a distance from said free end an opening extending into said catheter body to communicate with a portion of a first of said channels; providing communication between said first channel and a second of said channels at a distance from said free end shorter that said distance; and covering said opening by a microdialysis membrane.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    Two embodiments of the present invention will be described hereinafter, reference being made to the accompanying drawings, wherein:  
         [0006]    [0006]FIG. 1 is a partly broken diagrammatic view of a first embodiment of a catheter according to the invention,  
         [0007]    [0007]FIG. 2 is a cross sectional view taken at II-II in FIG. 1,  
         [0008]    [0008]FIG. 3 is a cross sectional view taken at III-III in FIG. 1,  
         [0009]    [0009]FIG. 4 is a longitudinal section taken at IV-IV in FIG. 2,  
         [0010]    [0010]FIG. 5 is a partly broken diagrammatic view of a second embodiment of a catheter according to the invention,  
         [0011]    [0011]FIG. 6 is a cross sectional view taken at VI-VI in FIG. 5, and  
         [0012]    [0012]FIG. 7 is a longitudinal section taken at VII-VII in FIG. 5.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    It is to be noted that like or corresponding parts are designated by like reference numerals throughout the drawings.  
         [0014]    [0014]FIG. 1 is a partly broken diagrammatic view of a first embodiment of a catheter  1  according to the invention. The catheter comprises an elongate catheter body  2  having an essentially cylindrical outer surface, a distal end  21 , and a proximal end  22 , between which it preferably is continuous, except for the openings, which will be explained below. The catheter body  2  is preferably made of radio opaque PVC or other suitable material, and its outer diameter is preferably in the range of 5-7, 5 Fr (≈1, 5-2, 5 mm).  
         [0015]    As seen in FIG. 3, which is a cross section taken at III-III in FIG. 1, the catheter body  2  includes a number of longitudinal channels. Two of the channels  23 ,  24  are designed for circulating dialysis solution, and at their proximal ends they are connectable to means  10  for circulating, monitoring or analyzing, and preferably collecting the dialysis solution. In the figure, the channels  23 ,  24  are shown to have the same inner diameters. However, the channels can have different inner diameters, and their cross sections can have different shapes than the shown. In the case of different inner diameters, channel  24  preferably has the smaller, and dialysis solution flows from the means  10  through channel  24  and back through channel  23 .  
         [0016]    At a distance from its distal end, the catheter body has an opening  25 , which is best seen in FIGS. 1 and 2. The form of the opening  25  in the outer surface of the catheter body  2  can for example be circular, oval or essentially rectangular. The length of the opening  25 , in the longitudinal direction is preferably 10-30 mm. The opening in the catheter body  2  can be formed by removing a part of its wall by cutting away a portion of the catheter body  2  in a wall region of channel  23 , whereby a section of channel  23  is opened, and thus a space or chamber  26  is formed. As will be explained further below, the chamber  26  is provided with a wall formed by a microdialysis membrane  30 , in order to provide a microdialysis chamber  26 . Preferably the chamber  26  is enlarged in this section by the removal of the wall part, as shown in the figures. A part of or the whole circumference of said region can be cut away to further enlarge the chamber  26  and thus enlarge the dialysis surface.  
         [0017]    In FIG. 4, which is a longitudinal section taken at IV-IV in FIG. 2, it is shown that channels  23  and  24  are connected by a channel or opening  27  between the chamber  26  and channel  24 , so that dialysis solution can flow between the channels. The channel or opening  27  is preferably arranged so as to connect a distal portion of the chamber  26  and the channel  24 , but other placements could also be possible. Preferably the channels  23  and  24  are plugged or sealed between channel  27  and the distal end of the catheter body  2 , by means of a plug or a seal  28 ,  29 , in order to prevent dialysis solution from entering channels  23 ,  24  beyond channel  27 . Further, channels  23  and  24  are plugged or sealed at the distal end  21  of the catheter body  2 .  
         [0018]    In a region around the opening  25  the catheter body  2  is provided with microdialysis membrane  30  having a socket-like shape, and surrounding a portion of the catheter body  2 . In FIG. 1 the microdialysis membrane  30  is partly broken up, so that the opening  25  and the chamber  26  can be seen. The microdialysis membrane  30  can be slid on to the catheter body  2  over the distal end  21 . At regions of its edges  301 ,  302  the microdialysis membrane  30  is further bonded or fastened with a glue or adhesive, or by other suitable means to the catheter body  2 , in order to prevent any liquid to enter or exit between the microdialysis membrane  30  and the catheter body  2  from or to the outside.  
         [0019]    Possibly, the catheter body  2  can be provided with an annular recess, for receiving the microdialysis membrane  30 , in said region surrounding the opening  25 .  
         [0020]    Depending on the substances to be detected at the microdialysis, a microdialysis membrane  30  of cuprophane, polycarbonate or PES (molecular cut-off between 1-200 kD) can be used. In order to prevent trigging of coagulation when in contact with blood, the microdialysis membrane  30  may be surface heparinized.  
         [0021]    To facilitate the insertion of the catheter  1  into a certain blood vessel, a guide wire channel  50 , for receiving a guide wire  51 , can be arranged in the catheter body  2 . The distal end of the catheter body  2  is closed or sealed except for an opening  52 . This opening  52  forms a continuation of the inner surface of the guide wire channel  50 . The guide wire  51  is used during insertion of the catheter, to increase the stiffness of the catheter  1 , and to make it possible to bend the catheter  1  into a desired curve, in order to facilitate its insertion. After insertion of the catheter  1  the guide wire  51  is removed, and a blood sample can be taken out at the proximal end of the catheter  1  through the opening  52  and the guide wire channel  50 . To prevent the guide wire  51  from passing through the opening  52  the guide wire  51  is provided with a stop  53 .  
         [0022]    The catheter body  2  can advantageously be manufactured from an extruded continuous profile body. The profile body is cut to a desired length, and the channels, except the guide wire channel, are sealed or plugged at their distal ends. Further the microdialysis chamber is formed by cutting, the channel between the channels (microdialysis chamber and channel) is formed, and the blind ends of the channels are sealed or plugged. Thereafter the catheter body  2  is provided with a microdialysis membrane, and connections or connection tubes at the proximal end.  
         [0023]    The distal portion of the catheter may be preformed into a desired curvature so that by torquing the catheter about its longitudinal axis, the catheter can be manipulated to the desired location.  
         [0024]    The preform is also advantageous in that, it helps the catheter to remain in the right position when once correctly located.  
         [0025]    In FIG. 5 a second embodiment of a catheter according to the invention is shown. This catheter includes a first microdialysis chamber  26 , with associated channels  23 ,  24 , a first opening  25  and a first microdialysis membrane  30 , as described in connection to the first embodiment according to FIG. 1. At a center distance of about 100-120 mm from the first opening  25  in the catheter body  2 , in the direction towards the proximal end  22 , a second opening  45  is provided in the catheter body  2 , located on the opposite side to the first opening  25 . As seen in FIGS. 5 and 7, a second microdialysis chamber  46  with associated second microdialysis membrane  31 , and channels  43 ,  44 , is arranged in connection with the second opening  45 , in the same manner as in the first embodiment. Channels  43 ,  44  are connected by means of a channel  47 , preferably at the distal portion of the second microdialysis chamber, and the channels  43 ,  44  are preferably sealed or plugged  48 ,  49  to prevent dialysis solution to enter the portions of the channels between channel  47  and the distal end of the catheter body  2 , in the same manner as in the first embodiment. The two channels  43 ,  44  are connected at their proximal ends to the same means  10 , for circulating, monitoring or analyzing, and preferably collecting the dialysis solution, as the two channels  23 ,  24 , or to separate means.  
         [0026]    [0026]FIG. 6 is a cross sectional view taken at VI-VI in FIG. 5, showing a possible placement of the two channels  23 ,  24 , the two channels  43 , 44 , the guide wire  51 , and the guide wire channel  50  inside the catheter body  2 .  
         [0027]    Although the invention has been described in conjunction with two preferred embodiments, it is to be understood that various modifications may still be made without departing from the spirit and scope of the invention, as defined by the appended claims. For example the dimensions can vary, depending on the specific use.