BALLOON-FREE URINARY CATHETER

Abstract: A balloon-free urinary catheter (15) comprising a tubular retention section (15A) shaped to locate in the neck of a patient's bladder and a tubular drainage section (15B) which, in use, is received in the patient's urethra. The retention section (15A) has a diameter which is normally greater than the neck of the bladder (2) but is stretchable on the application of an axial force thereto to reduce its diameter to less than that of the urethra (3). This allows the catheter to pass through the urethra until the retention section (15A) is positioned inside the bladder where it expands and returns to its original size on release of the axial force and locates in the neck of the bladder to form a seal therewith.

Description: Balloon-Free Urinary Catheter This invention relates to a balloon-free urinary catheter. Many people suffer from a variety of problems with their urinary system ranging from the inability or difficulty to pass urine to urinary incontinence which can be intermittent or chronic. The most common treatment for many of these disorders is to fit a FOLEY catheter to control drainage of urine from the bladder. A FOLEY catheter is a flexible tube, usually made from latex, which has a central lumen and an inflatable balloon incorporated into a wall of its distal end. With the balloon deflated, the catheter tube can be passed through the urethra into the bladder. Once the balloon at the distal end of the tube is located in the bladder, it is inflated and then rests in the neck of the bladder to provide a seal therewith and prevent the tube from being easily removed. A tubular extension extends a few centimetres beyond the top of the balloon and has holes in its wall to allow urine to pass from the bladder into the central lumen tube. It then flows to the proximal end of the device which is fitted with a connector to inflate the balloon and a second connector to close the central lumen. A collection bag is usually connected to the second connector. The FOLEY catheter was developed over 40 years ago and has many disadvantages. Firstly, about half of all catheterised patients block their catheters. The FOLEY catheter does not allow for easy removal and cleaning or back-flushing and drainage whilst inserted. Furthermore, it does not deal effectively with those patients whose catheters block and most catheterised patients develop infections of some sort when using a FOLEY catheter which in some cases can be problematic. The FOLEY catheter is very obtrusive, particularly for elderly patients requiring long term catheterisation (the largest group) so its use represents a significant degradation in their quality of life. The major advantage of the FOLEY design is that it is relatively cheap to manufacture, although it does require multiple-dip coatings of latex which can be time consuming. It is also widely available and accepted by the medical profession despite its shortcomings. It is an object of the present invention to provide a urinary catheter which overcomes or substantially reduces the aforementioned disadvantages. According to the present invention, there is provided a balloon-free urinary catheter comprising a tubular retention section which, in use, locates in the neck of a patient's bladder and a tubular drainage section which, in use, is received in the patient's urethra, the retention section having a diameter which is normally greater than the neck of the bladder but being stretchable on the application of an axial force thereto to reduce its diameter to less than that of the urethra to allow the catheter to travel therethrough until the retention section is positioned inside the bladder, the retention section being constructed so that it will expand and return to its original size on release of said axial force whereby it locates and engages with the neck of the bladder to form a seal. Preferably the retention section is made of braided material. The drainage section can also be made of a braided material but this is not essential. In the preferred embodiment, the retention section is of a greater diameter than the drainage section and incorporates locating means in the distal end thereof against which said axial force can be applied using a placement tool to axially stretch said section and thereby reduce its diameter. The locating means can be made of any suitable hard polymer material such as nylon, polypropylene, polyethylene, polycarbonate, PTFE or a shape memory metal such as NITINOL. Spring means can be incorporated into the retention section to assist in its recovery to its original diameter on release of the axial force. Preferably, the spring means are made of a polymer material such as polypropylene, nylon, polyurethane or polyethylene. In the preferred embodiment, the tubular retention section in its normal relaxed or rest condition has an internal diameter in the range of 12-30mm, the outer diameter of the tubular drainage section being in the range from 5-12mm. Preferably the retention section is made of a braided material including structural filaments that are arranged at an angle such that when the axial force is applied to the retention section, the tube decreases in diameter but returns to its original shape due to the hoop stress within the braid structure. Preferably, the retention section is made of a polymer such as polyurethane, neoprene, styrene ethylene butadiene styrene (SEBS), styrene butadiene styrene (SBS), plasticised PVC or thermoplastic valcanites. The structural filaments can be made of a ceramic material or metallic wires or polypropylene, nylon, polyurethane, polyethylene. The diameter of the retention section increases on the removal of said axial force until the angle of the braids in relation to the longitudinal axis of the catheter reaches a critical angle. The preferred critical angle is The tubular drainage section can also be made of a braided material including structural filaments that are arranged at an angle such that when the axial force is applied thereto, the tube decreases in diameter but returns to its original shape due to the hoop stress within the braid structure. In the preferred embodiment, the braid angle of the filaments in the tubular retention and drainage sections is different so that said tubular sections will expand differentially on release of the axial pressure applied to the retention section. Preferably the catheter is made of a thin walled elastomeric polymer tubing for example polyurethane, neoprene, styrene ethylene butadiene styrene (SEBS), styrene butadiene styrene (SBS), plasticised PVC or thermoplastic vulcanites. Conveniently a valve is located in the proximal end of the catheter which can be of any convenient type. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which Figure 1 is a cross section of the area surrounding the urinary tract showing a prior art FOLEY catheter fitted in the bladder; Figure 2 is a side view of a urinary catheter of the present invention in its normal relaxed state; Figure 3 is a view of the catheter shown in Figure 2 in its elongated reduced diameter state ready for insertion into the bladder; Figure 4 shows the urinary catheter of Figures 2 and 3 but in its relaxed normal state when in position in a patient's bladder; Figure 5 is an end view of the catheter shown in Figures 2-4; Figure 6 is a cross section through the catheter of Figures 2-5 but including the placement tool; Figure 7 is an end view of the catheter of Figures 2-6 but including a return spring in the retention section; and Figure 8 shows the catheter of Figure 4 in position in a patient's bladder. Referring to Figure 1 of the drawings, there is shown a bladder 1 having a neck 2 which tapers into prostatic part 4 of urethra 3 which is surrounded by prostate gland 5. The external sphincter 6 is also shown whose normal function is to keep the urethra closed until urination when it opens for emptying the bladder 1. A prior art FOLEY type catheter 7 having an elongate body section 8 and a balloon 11 at one end is seated in the tapered neck 2 of the bladder 1 to make a seal therewith. The balloon 11 has a tubular section 12 extending therefrom with holes 13 therein. To insert the catheter 7 into the bladder 1, the balloon 11 is collapsed and the catheter 7 is inserted through the urethra 3 until the balloon portion 11 has travelled beyond the tapered neck 2 of the bladder 1. The balloon 11 is then inflated to its condition illustrated in Figure 1 as a result of which it makes a seal with the tapered neck 2 of the bladder 1. The body portion 8 of the catheter 7 is located within the prostatic part 4 of the urethra 3 and its distal end 14 protrudes just beyond the end of the urethra 3. A valve incorporating a connector (not shown) would normally be attached to the distal end 14. Urine drains from the bladder 1 through the holes 13 in the extension 12 of the balloon 11 and passes out of the distal end 14 of the catheter to a bag (not shown) connected to the connector in said distal end. Referring now to the catheter 15 of the present invention shown in Figures 2-6, it can be seen that it comprises a tubular retention section 15A connected to a tubular drainage section 15B of reduced diameter. The retention section 15A has a normal outside diameter "X" in the range of 12-30mm and the drainage section 15B has a normal outside diameter "Y" of between 5-12mm. The length of the catheter is normally in the range of 10-50cms. These dimensions are preferred rather than essential. A flexible bead 16 is incorporated into the periphery of the proximal end of the retention section 15A for reasons to be explained hereafter. Fingers 16A (four are illustrated but any number could be used) extend radially inwardly to support locating means 20 having a central hole 21 therein. The catheter 15 is made from thin walled elastomeric polymer tubing which incorporates an expandable, braid- activated retainer. Preferred materials for the tubing are polyurethane, neoprene, styrene ethylene butadiene styrene (SEBS), styrene butadiene styrene (SBS), plasticised PVC or thermoplastic vulcanates. The structural filaments of the braiding are arranged at such an angle that when a longitudinal tensioning load is applied to the tube 15 in the direction of arrow A (for instance as shown in Figure 6), it elongates but also decreases in diameter as shown in Figure 3. However, when the tensioning load is released, the hoop stress within the braid structure dictates that the diameter of the tube 15 will increase until the angle of the braid, in relation to the axis of the tube, reaches a critical angle which can be defined as tan " 2 = 54.73°. As can be seen from Figure 2, the braid angle of the retention section 15A is different from that of the drainage section 15B. As a result, when the tube is released from tension as will be described shortly, sections 15A and 15B will expand differentially. This provides a tube that has different diameters relating to the diameter at which the braided component reaches its critical angle. As already explained, catheter 15 shown in Figure 2 is in its normal relaxed condition in which the outer diameter "X" of the retention section 15A is in the range from 12-30mm whereas the outer diameter "Y" of the drainage section 15B is in the range of 5-12mm. To insert the catheter 15 into a patient's bladder, a placement tool (known as a boogie) is used. The tool 22 is inserted into the distal end 17 of the catheter 15 and it is pushed along it until the nose 24 seats in the hole 21 in the locating means 20. Further axial force applied to the boogie in the direction of arrow A causes the retention section 15A and, if desired, the drainage section 15B, to reduce in diameter to approximately 5mm thereby facilitating easy placement of the catheter in the urinary duct 3. As can be seen from Figure 6, the end of the catheter 15 adopts the configuration shown in dotted line during insertion of the catheter. Once the catheter is in place with its retention section 15A in the tapered bladder neck 2, the longitudinal tensioning force applied by the insertion tool 22 can be released thereby allowing the retaining section 15A to expand back to its normal configuration shown in Figure 1 assisted by the resilient bead 16. Because full expansion is constricted by the shape and dimensions of the tapered bladder neck 2, it in fact assumes the configuration shown in Figure 4 when it is properly in position as shown in Figure 8. The catheter of the invention is made of a bio-compatible polymer material which reduces the rate of bio-film build up and reduce the levels of encrustation and infection normally associated with traditional devices. It also has a thin wall compared to prior art catheters which is achieved due to the high hoop strength of the braided tubing allowing a braided tube having a wall thickness of approximately 100 microns with an outer diameter x which performs with the same kink resistance as a latex tube with an outer diameter of x and a 2mm wall thickness. This enables the lumen size in the catheter of the invention to be significantly larger within the braided tube 15 compared to prior art latex catheters thereby facilitating higher flow rates within the catheter. Prototype devices have been evaluated using an in vitro artificial bladder model (Stickler D J, Morris N S and Winters C 'Simple physical model to study formation and physiology of biofilms on urethral catheters' Methods in Enzymology 310, p494-501, 1999; Stickler D J, Howe N S and Winters C, 'Bacterial film growth on ciprofloxacin treated urethral catheters' Cells Materials 4, p245-253, 1994) to determine the efficacy of catheter designs to provide functional drainage under adverse conditions in which artificial urine is inoculated with bacteria to induce urease production that initiates the cascade ( Bruce A.W. Sira S.S., Clark A.F. and Awad S.A. The problem of catheter encrustation. Can Med Ass J ill: p238-241, 1974; Stickler D J, Morris N S, Moreno M and Sabbuba N. Studies on the formation of crystalline bacterial biofilms on urethral catheters. Eur J Microbiol Infect Dis., 17: pl-4, 1998; Brocklehurst J C and Brocklehurst, S. The management of indwelling catheters. Br.J Urol 50: pl02-105, 1978; Warren J W, Platt R. Thomas R J, Rosner B, and Kass E H, 'Antibiotic Irrigation and Catheter-associated Urinary Tract Infections'. New England J Med 299: p570-573, 1978) resulting in precipitation of calcium and magnesium phosphate salts that subsequently block urethral catheters. Table 1 shows how the preferred catheter of the invention exceeded the performance of conventional urinary catheter designs (Morris N S, Stickler D B, and Winters C 'Which indwelling urethral catheters resist encrustation by Proteus mirabilis biofilms? Br J Urol 80, p58-63, 1997) thus providing an effective demonstration of the benefits of the design. TABLE 1 Catheter blockage times in the bladder model inoculated with Proteus mirabilis na: not applicable Polyurethane material which soften at body temperature can be used to give a more conformant and comfortable fit for the patient without the concern of latex allergy. Materials that soften significantly on placement can also be used to hold the retaining section in its low diameter configuration during handling so that when the material softens, the retention section 15A of the catheter can be deployed. It is envisaged within the scope of the invention that the catheter can incorporate a non-braided urethral tubular section 15B which normally lays flat in the urethra 3 but expands under pressure exerted by urine supplied from the bladder 1 to allow the urine to drain therefrom. It is also envisaged within the scope of the invention that a polymeric spring 25 such as that shown in Figure 7 could be incorporated into the retention section or funnel end 15A to facilitate funnel opening and ease of placement and to modify the retention force. This comprises fingers 26 (four are shown but any number could be used) connected to central locating means 20 having a central hole 21. The catheter of the present invention has the advantage that it provides control over the design parameters which allows for a range of performance criteria to be satisfied. The variables, which are easily changed, are the polymeric material, which affect the surface properties of the device and contribute to the physical properties of the tubing. The braid material can also be altered in shape and size to give a range of properties and also in configuration to allow modification of the three dimensional relaxed and stressed states of the tube. The manufacturing method of the present invention also allows the placement of inlaid wires or fibres within the drainage section 15B to transfer the longitudinal tension away from the braided section 15A thus preventing elongation and diameter changes within the drainage section 15B. A further advantage of the braided catheter of the present invention is it can be manufactured by a cost effective continuous co-extrusion process thereby avoiding the time consuming multiple-dip costing processes of prior art catheters.

Claims: Claims 1. A balloon-free urinary catheter comprising a tubular retention section which, in use, locates in the neck of a patient's bladder and a tubular drainage section which, in use, is received in the patient's urethra, the retention section having a diameter which is normally greater than the neck of the bladder but being stretchable on the application of an axial force thereto to reduce its diameter to less than that of the urethra to allow the catheter to travel therethrough until the retention section is positioned inside the bladder, the retention section being constructed so that it will expand and return to its original size on release of said axial force whereby it locates in the neck of the bladder and engages therewith to form a seal. 2. A urinary catheter as claimed in claim 1 wherein the retention section is made of a braided material. 3. A urinary catheter as claimed in claim 1 or claim 2 wherein the drainage section is made of a braided material. 4. A urinary catheter as claimed in any preceding claim wherein the retention section is of a greater diameter than the drainage section. 5. A urinary catheter as claimed in any preceding claim wherein locating means are incorporated into the distal end of the retention section against which said axial force can be applied to stretch said section and reduce its diameter. 6. A urinary catheter as claimed in claim 5 wherein said locating means is made of a shape memory metal. 7. A urinary catheter as claimed in claim 5 wherein the locating means is made of a polymeric material such as nylon, polypropylene, polyethylene, polycarbonate or PTFE.. 8. A urinary catheter as claimed in any preceding claim wherein spring means is incorporated into the retention section to assist in its recovery to its original diameter on release of the axial force. 9. A urinary catheter as claimed in claim 8 wherein the spring is radially expandable. 10. A urinary catheter as claimed in claim 9 wherein the spring is made of a polymer material. 11. A urinary catheter as claimed in claim 10 wherein the spring is made of polypropylene, nylon, polyurethane or polyethylene. 12. A urinary catheter as claimed in any preceding claim wherein a flexible bead is provided around the distal end of the retention section to restore said section to its original shape on release of said axial force. 13. A urinary catheter as claimed in claim 12 wherein the bead is made of an elastomeric polymer. 14. A urinary catheter as claimed in any preceding claim wherein the outer diameter of the tubular retention section in its relaxed condition in the range from 12-30mm. 15. A urinary catheter as claimed in any preceding claim wherein the outer diameter of the tubular drainage section is in the range from 5- 12mm. 16. A urinary catheter as claimed in any preceding claim wherein the retention section is made of a braided material including structural filaments that are arranged at an angle such that when the axial force is applied to the retention section, the tube decreases in diameter, but returns to its original shape due to the hoop stress within the braid structure. 17. A urinary catheter as claimed in claim 16 wherein the diameter of the retention tube will increase on the removal of the axial force thereto until the angle of the braid in relation to the longitudinal axis of the catheter reaches a critical angle. 18. A urinary catheter as claimed in claim 17 wherein the critical angle is tan " 2 = 54.73°. 19. A urinary catheter as claimed in any preceding claim wherein the tubular drainage section is made of a braided material including structural filaments that are arranged at an angle such that when the axial force is applied to the tubular drainage section, the tube decreases in diameter but returns to its original shape due to the hoop stress within the braid structure. 20. A urinary catheter as claimed in claim 19 wherein the braid angle of the filaments in the tubular retention and drainage section is different so that said tubular sections will expand differentially on release of the axial force applied to the retention section. 21. A urinary catheter as claimed in any preceding claim wherein the catheter is made of thin walled polyurethane tubing. 22. A urinary catheter as claimed in any preceding claim wherein a valve is located in the proximal end of the catheter. 23. A balloon-free urinary catheter substantially as herein described with reference to the accompanying drawings.

Inventors: SNELL ROBERT ADAM, SNELL, ROBERT, ADAM
Applicants: RANIER LTD, SNELL ROBERT ADAM, RANIER LIMITED, SNELL, ROBERT, ADAM
Application year: 2001
Main classification: A61M25
IPC codes: A61F5, A61M1, A61M25