Abstract:
The present invention is directed to an insertion device, such as a catheter, including a tip having a hollow, substantially radial cross sectional configuration and a substantially parabolic longitudinal configuration with a circular tip curvature. The outer wall of the novel tip of the invention is completely curved, and contains no straight or angled outer walls within the length of the tip. The inner wall of the tip defines a substantially straight passageway through which a piercing device such as a needle may be inserted.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/162,322, filed Oct. 28, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a tip for an insertion device. More specifically, the invention is directed to a curved tip for an insertion device such as a catheter. The surface profile of the novel tip of the invention is completely curved and includes a generally parabolic tubular surface profile with an insertion end that assumes a generally circular surface profile. 
     BACKGROUND OF THE INVENTION 
     A catheter is usually inserted through the skin of a patient by use of a sharp instrument, such as a needle. In many applications, the needle extends through the catheter wherein the point of the needle is adjacent to and extending slightly beyond the tip of the catheter. The needle pierces the skin of the patient to form an opening and the tip of the catheter follows the needle into the opening. 
     Traditional catheter tips generally have straight edges and blunt insertion ends. The bluntness of traditional tips impedes the forward progress of the catheter into the opening in the skin. The force required to insert a blunt ended, straight edged catheter tip into the skin, which is also known as “transition force,” is generally sufficiently high to cause pain to the patient upon insertion. 
     Attempts have been made to reduce the transition force required to insert a catheter into the skin of a patient. An example of such a catheter is shown in U.S. Pat. No. 4,588,398. In this patent, the tip of the catheter is angular, although still with straight edges and a blunt insertion end. 
     It has been found that there is a need for a catheter tip that provides for the smooth and easy transition from a needle to a catheter as the device moves through the skin, to reduce the transition force during insertion of a catheter into a patient. The present invention satisfies this need. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an insertion device, such as a catheter, including a tip having a hollow, substantially radial cross sectional configuration and a substantially parabolic longitudinal configuration with a longitudinally circular tip curvature. The outer wall of the novel tip of the invention is completely curved, and contains no straight or angled outer walls within the length of the tip. The inner wall of the tip defines a substantially straight passageway through which a piercing device such as a needle may be inserted. 
     An embodiment of the present invention provides an insertion device that reduces the transition force required to insert the device into the skin of a patient. 
     An embodiment of the present invention also provides a tip for an insertion device having an entirely curved outer wall in the longitudinal dimension. 
     An embodiment of the invention further provides a catheter tip configuration which is thin enough to reduce the above-referenced transition force yet tough enough to eliminate splitting, tearing, or bunching of the catheter tubing material during insertion. 
     An embodiment of the present invention provides a catheter tip with a smoothly convex outer wall. 
     Other embodiments and advantages of the present invention shall become apparent to those skilled in the art upon a review of the following detailed description of the preferred embodiments and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of the insertion device according to the present invention positioned on a handle assembly with a needle extending through the insertion device; 
     FIG. 2 is a side view cutaway of the generally parabolic tip of the invention, illustrating the completely curved outer wall of the tip and the longitudinally circularly curved insertion end of the tip. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiment and best mode of the present invention will now be described in detail with reference being made to the drawings. The insertion device such as a catheter is indicated generally in the drawings by the reference number  10 . 
     Referring to FIGS. 1 and 2, the catheter  10  includes a longitudinally extending tube  12  having a tip  14 , located at the first end  18 , and a second end  16 . The second end  16  includes an attachment device  20  attaching the catheter  10  to, for example, a safety needle retraction assembly  22  or a luer-fitted coupling device (not shown). The tube  12  includes an interior surface  24  and an exterior surface  26 . The interior surface  24  is adapted to receive a needle  28  having a pointed end  30 . 
     The catheter  10  is typically comprised of a plastic material. In a preferred embodiment, the plastic material is polyurethane, but it can also be TEFLON or any commonly known catheter material. It has been found that polyurethane has a relatively low coefficient of drag or friction, but the invention contemplates that other suitable materials may also be used. A low coefficient of friction aids the insertion of the catheter  10  into the skin of a patient in a smooth and efficient manner. The catheter  10  and/or the needle  28  can be treated with a lubricant. In the preferred embodiment, the lubricant is a conventional silicone-based compound. The lubricant reduces friction between the catheter  10  and the skin of a patient during insertion. 
     Referring now to FIG. 2, in one preferred embodiment of a catheter having a tip formed according to the present invention, the tip  14  is substantially generally parabolic in profile having a length “L”  36 , over which length the catheter tube  12  is smoothly and gradually reduced from its original wall thickness “t”  38  to intersect the surface of the needle  28  at catheter insertion end  40 . The insertion end  40  is the end that is inserted, along with a needle  28 , through a patient&#39;s skin. Over the length “L”, the surface profile of the catheter tip  14  generally follows a smooth, substantially parabolic curve  32  except at the point of insertion into a patient&#39;s skin,  40 . At this point, the surface profile of the insertion end becomes substantially circular, and is described by an arc on a circle having a radius “r”,  42 , as shown in FIG.  2 . Length “L” may vary, and the generally parabolic surface profile  32  of tip  14  substantially flattens at or near point  34  where it assumes the generally cylindrical profile of the catheter tube with substantially parallel walls, with thickness “t” being relatively constant over the remaining length of tube  12  from point  34  to the second end  16  (as shown in FIG.  1 ). Thus, it will be seen that the substantially parabolic surface profile of tip  14  includes a narrowing of the profile to intersect the surface of needle  28  and includes a muting of the tip of the insertion end  40 , which insertion end  40  assumes the shape of a an arc on a circle of radius “r”  42 , at some point before the parabola intersects the surface of needle  28 . The insertion end  40  then follows this circular profile until it intersects the needle surface  28 , as illustrated in FIG.  2 . It is this unique combination of the smoothly convex, generally parabolic narrowing-down of the catheter tube  14 , terminating in a slight muting of the parabolic curve by means of the circular surface contour at the insertion end  40 , that reduces the transition force while maintaining the physical integrity of the catheter material at the insertion end  40 . 
     It should be noted that the parabolic profile is not configured such that its apex would intersect the circumference of the circle; if it did, it could create a dimple in the smoothly convex overall outer wall configuration. Rather, the apex of the parabola lies on the surface of the needle just beyond the point at which the circle of radius “r” intersects the surface of needle ( 28 ). Point “p” ( 46 ) defines a smooth, dimple-free transition between the parabolic and circular profiles of the tip  14  of the invention. Thus, the convex, parabolic shape is analogous to a comet tail, rolling over and out from the ball of the comet. 
     It is to be emphasized that the geometric characteristics described above are key in providing physical and operational integrity of the tip (i.e., prevent splitting and bunching and other side effects), and to minimize the transition force. The radius “r” is determined as an optimization between material strength and catheter penetration force. If “r” is too large the bulk profile of the tip makes penetration into the skin and vein high and not acceptable. If “r” is too small the material integrity is such that the tip can buckle going into the skin and vein and thus requires a high entry force. If “r” is too small the tip may also split or tear. Radius “r” is generally independent of catheter gauge. 
     We have found that “r” may vary between 0.0001 inch and 0.0030 inches, preferably between 0.0001 inch and 0.0020 inches, and most preferably between 0.0005 inches and 0.0010 inches, for most common catheter materials. It should be understood that other values for “r” may be readily achieved using different materials. 
     In addition, it is important that the tip  14  be of overall convex configuration and that a convex, smoothly curving shape be maintained from the tip over the entire length “L”. Length “L” will vary depending upon the gauge of the catheter, and various lengths are considered within the scope of the invention. 
     By way of example and not by way of limitation, various dimensions for tips of the invention are provided in Table 1, wherein the radius and length are referenced in FIG.  2 . Of course, different gauge catheters will have differently dimensioned tips, and the examples provided here are not intended to be exhaustive of all possible dimensions. For instance, for a very large catheter, “r” may be larger than the dimensions shown below. The lengths provided in table 1 are nominal lengths. 
     
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Sample 
                 Gage 
                 Radius, r (inch) 
                 Length, L (inch) 
               
               
                   
                   
               
             
             
               
                   
                 1 
                 18 
                 0.00040 
                 0.075 
               
               
                   
                 2 
                 18 
                 0.00015 
                 0.075 
               
               
                   
                 3 
                 18 
                 0.00010 
                 0.075 
               
               
                   
                 4 
                 18 
                 0.00011 
                 0.075 
               
               
                   
                 5 
                 22 
                 0.00010 
                 0.063 
               
               
                   
                 6 
                 22 
                 0.00020 
                 0.063 
               
               
                   
                   
               
             
          
         
       
     
     The above detailed description of the present invention is given for explanatory purposes. It will be apparent to those skilled in the art that numerous changes and modifications can be made without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be construed in an illustrative and not a limitative sense, the scope of the invention being defined solely by the appended claims.