This invention relates to urinary catheters.

Urinary catheters are used to assist or control the flow of urine from the bladder of a patient. When a patient needs to use a catheter for an extended period of time, they may use an indwelling urinary catheter. An indwelling urinary catheter has a tube which is introduced through the patient's urethra or directly via an abdominal incision (supra-pubic catheter). Once the distal tip of the catheter is in the bladder it is retained in position by means such as a balloon inflated within the bladder. A lumen extending through the catheter can then drain urine from the bladder.

A common design of indwelling urinary catheter is the Foley catheter. In the Foley catheter, the balloon is toroidal in shape and is located proximally of the catheter tip. A drainage opening which communicates with the lumen is located between the catheter tip and the balloon. Catheters of this design suffer from a number of problems. The tip of the catheter is exposed and can irritate the bladder wall. Material of the bladder wall can become drawn into the drainage opening, causing discomfort and mucosal damage. The drainage opening is spaced from the base of the bladder by the balloon, which prevents the bladder draining completely leading to a residual pool of urine that can become infected.

WO 2015/028786 discloses one approach to addressing at least some of these problems of the Foley catheter. It provides a urinary catheter having an inflatable balloon which extends over the tip of the catheter. The drainage ports are located close to the base of the bladder to prevent the pooling of stagnant urine.

Even when the drainage ports are located at the base of the bladder to prevent the pooling of urine beneath the ports, problems of encrustation can still arise. When large volumes of urine are required to flow through the small diameter drainage ports and drainage lumen disposed within the shaft of the catheter, flow can become insufficient, for example due to turbulent or non-streamlined flow.

A problem that may result from turbulent flow is encrustation. Encrustation by mineral salts in urine commonly leads to catheter blockage. Encrustations typically appear just below the drainage ports within the urine drainage lumen at a site of significant urine turbulence.

One way of addressing this problem is described in US 5,300,022. This document proposes providing an irrigation lumen within the main lumen of the catheter. The irrigation lumen terminates in a cavity distal of the drainage ports. US 5,300,022 proposes that washing fluid can be flushed through the irrigation lumen, which would then be deflected by the cavity and flow in a proximal direction over the interior ends of the drainage ports. This flow is intended to draw urine inwards through the drainage ports. To prevent the washing fluid from being exuded into the bladder the drainage ports are angled with respect to the axis of the main catheter lumen. Whilst this design might help to reduce encrustation, providing a separate irrigation lumen in the catheter makes it more difficult to manufacture.

There is a need for an improved design of urinary catheter.

According to a first aspect of the present invention there is provided an indwelling urinary catheter configured to be retained in the bladder of a patient, the catheter comprising: a shaft having a proximal end and a distal end, the distal end terminating in a tip; and a drainage opening located at the distal end of the shaft, the drainage opening extending through a sidewall of the shaft and communicating with a drainage lumen of the shaft; wherein: the proximal wall of the drainage opening extends through the sidewall at an oblique angle relative to the longitudinal axis of the shaft; and in the region of the shaft longitudinally coincident with the drainage opening the drainage lumen is unobstructed between its exterior walls. According to a second aspect of the present invention there is provided a catheter comprising: a shaft having a proximal end and a distal end, the distal end terminating in a tip; and a drainage opening located at the distal end of the shaft, the drainage opening extending through a sidewall of the shaft and communicating with a drainage lumen of the shaft; wherein: the proximal wall of the drainage opening extends through the sidewall at an oblique angle relative to the longitudinal axis of the shaft; and in the region of the shaft longitudinally coincident with the drainage opening the drainage lumen is unobstructed between its exterior walls.

The proximal wall of the drainage opening may meet the exterior wall of the shaft at an oblique angle.

The proximal wall of the drainage opening may meet the interior wall of the shaft at an oblique angle.

The proximal wall of the drainage opening may extend through the sidewall at an oblique angle relative to the longitudinal axis of the shaft such that the location where the proximal wall of the drainage opening meets the exterior wall of the shaft is distal of the location where the proximal wall of the drainage opening meets the interior wall of the shaft.

The distal wall of the drainage opening may extend through the sidewall at an oblique angle relative to the longitudinal axis of the shaft.

The distal wall of the drainage opening may meet the exterior wall of the shaft at an oblique angle.

The distal wall of the drainage opening may meet the interior wall of the shaft at an oblique angle.

The distal wall of the drainage opening may extend through the sidewall at an oblique angle relative to the longitudinal axis of the shaft such that the location where the distal wall of the drainage opening meets the exterior wall of the shaft is distal of the location where the distal wall of the drainage opening meets the interior wall of the shaft.

The catheter shaft may comprise a second drainage lumen.

The catheter may comprise a second drainage opening located at the distal end of the shaft, the second drainage opening extending through the sidewall of the shaft and communicating with a drainage lumen; wherein the proximal wall of the second drainage opening extends through the sidewall at an oblique angle relative to the longitudinal axis of the shaft.

Both drainage openings may communicate with the same drainage lumen. Alternatively, each drainage opening may communicate with a separate drainage lumen.

The second drainage opening may be longitudinally coincident with the first drainage opening.

The first drainage opening may be radially opposite the second drainage opening.

There may be a single fluid pathway in the region of the shaft longitudinally coincident with the or each drainage opening.

The shaft may have an absence of fluid pathways opening on to the or each drainage lumen distally of the junction of the or each drainage opening and the drainage lumen.

The catheter may be a urinary catheter.

The tip may be hollow distally of the/each drainage opening.

The catheter may further comprise a balloon located at the distal end of the shaft. The balloon may comprise a first region secured to the shaft, a second region secured to the shaft and an elastic-walled conduit extending between the first region and the second region, the elastic-walled conduit extending over the tip.

The drainage opening may be located on a side of the catheter shaft and the balloon is configured such that, when inflated, regions of the exterior of the balloon are located laterally outward of that side of the catheter shaft on either side of the drainage opening.

The balloon may be configured such that, when inflated, regions of the exterior of the balloon are located radially outward of the catheter shaft proximally of the most proximal part of the drainage opening.

The catheter may comprise two drainage openings and the balloon is secured to the shaft radially between the drainage openings.

The exterior of the or each drainage lumen may be at least partially defined by the sidewall of the shaft. The exterior of the drainage lumen may be defined by the sidewall of the shaft.

The drainage lumen may occupy the entirety of the internal volume of the shaft immediately proximally of the/each drainage opening.

The catheter may have an absence of internal means for washing the interior of the shaft.

The drainage opening may taper outward where it meets the sidewall of the shaft.

The drainage opening may comprise an outward portion of increasing width located adjacent the exterior wall of the shaft. The drainage opening may comprise an inward portion of substantially constant width located inward of the outward portion with respect to the shaft.

According to a third aspect of the invention there is provided an indwelling urinary catheter configured to be retained in the bladder of a patient, the catheter comprising: a shaft having a proximal end and a distal end, the distal end terminating in a tip; and a drainage opening located at the distal end of the shaft, the drainage opening extending through a sidewall of the shaft and communicating with a drainage lumen of the shaft, the drainage opening tapering outward where it meets the sidewall of the shaft.

According to a fourth aspect of the invention there is provided a catheter comprising: a shaft having a proximal end and a distal end, the distal end terminating in a tip; and a drainage opening located at the distal end of the shaft, the drainage opening extending through a sidewall of the shaft and communicating with a drainage lumen of the shaft, the drainage opening tapering outward where it meets the sidewall of the shaft.

The catheter may be a urinary catheter.

The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings:

Figure 1 is an isometric view of a urinary catheter without a balloon in place.

Figure 2 is a cross-section of the shaft of the catheter of figure 1 on line A-A.

Figure 3 is a cross-section of the distal part of catheter of figure 1 on line B-B, with a partially inflated balloon in place.

Figure 4 is a cross-section of the distal part of the catheter of figure 1 on the line C-C of figure 3, with a partially inflated balloon in place. Figure 5 is an isometric view of the distal part of the catheter of figure 1 , with a partially inflated balloon in place.

Figures 6A and 6B are cross-sections of the distal part of catheter of figure 3 on line D-D, with balloon omitted.

Figures 7 and 8 illustrate potential differences in flow observed for drainage openings with square and rounded edges respectively.

Figure 9 shows a catheter with a tapered drainage opening.

Figure 1 shows a urinary catheter having a shaft 1 . The catheter shaft has a proximal end 2. The proximal end is intended to sit outside the body when the catheter is in use. The catheter has a distal end 3. The distal end is intended to sit in the bladder of a user when the catheter is in use. The distal end of the catheter terminates in a tip 4. Two openings defined in the sidewall of the distal end of the catheter are shown in Figure 1. An inflation opening 5 is intended for inflating a balloon which can be attached to the catheter. The inflation lumen 6 communicates with an inflation port 5 which runs along the shaft. A drainage opening 7 in the sidewall of the distal end of the catheter is intended for draining urine from the bladder of a user. The drainage opening communicates with a drainage lumen 8 which runs along the shaft. There may be multiple drainage openings in the distal end of the catheter. Preferably each drainage opening communicates with the drainage lumen 8. The catheter shown in figure 1 has two such openings (one of which cannot be seen in figure 1 but is shown more clearly in figures 3 and 6).

Optionally, the catheter may have more than one drainage lumen which runs along the shaft. Each drainage lumen may communicate with a different drainage opening.

Figure 2 shows a cross-section of the shaft on line A-A of figure 1 , illustrating the lumens 6, 8. At the proximal end of the shaft, the inflation opening communicates with an inflation port 9 and the drainage opening communicates with a drainage port 10. Fluid can be introduced through the inflation port 9 to then pass through the inflation opening 5. Urine received through drainage opening 7 can be collected through drainage port 10. A collecting vessel can be attached to the drainage port.

In the examples shown in the figures, the inflation opening 5 and the drainage openings 7 overlap in the longitudinal axis of the catheter. There could be multiple inflation openings. The or each inflation opening could be distal of the drainage opening, or of a subset of the drainage openings or of all the drainage openings. The or each inflation opening could be proximal of the drainage opening, or of a subset of the drainage openings or of all the drainage openings. Configuring the catheter shaft so that the inflation opening(s) do/does not overlap the drainage opening(s) in a longitudinal direction may help to improve the strength of the shaft.

The entirety of the distal end may taper to the tip, or the distal part of the distal end may taper to the tip; or the distal end may be of constant diameter about the longitudinal axis of the catheter, in which case the tip may be generally hemispherical.

Figure 3 is a cross-section of the distal part 3 of the shaft on line B-B of figure 1 , with a partially inflated balloon of one possible configuration (not shown in figure 1 ) installed on the shaft. Figure 4 is a cross-section on line C-C of figure 3, and figure 5 is an isometric view showing the partially inflated balloon. The catheter of figure 3 has two drainage openings 7. The balloon may be generally in the form of a tube having an internal wall 1 1 abutting the catheter shaft and an external wall 12 free from the catheter shaft. The tube is generally elongate, extending between ends 13, 14. The balloon is made of an elastic sheet material. The tube constitutes a conduit part or all of whose walls are elastic and/or flexible. The balloon is sealed except for an aperture 15. The aperture may be near one of its ends (end 13). The interior of the balloon communicates with the inflation opening 5 by the aperture. The balloon is sealed to the shaft 1 of the catheter around the inflation opening. As a result, the balloon can be inflated by introducing fluid such as water or air into the balloon through the aperture 15. The tube-like form of the balloon extends over the tip 4 of the catheter. The balloon is bent around the tip 4. The end 14 of the balloon remote from the aperture 15 is also attached to the distal end of the catheter shaft. This holds the balloon bent over the tip.

Figure 4 is a cross-section of the distal part of the catheter on line C-C. Figure 4 shows the balloon configuration of figure 3 in its partially inflated state. Figure 4 shows in chain-dotted lines the urethra 16 and bladder wall 17 of a person into whom the catheter has been inserted; and dotted line 18 indicates the exterior form of the balloon in its fully inflated state. It should be noted that in its fully inflated state the balloon might be capable of further inflation (i.e. over-inflation). The fully inflated state is the state in which it would normally be left indwelling in a patient's bladder. In its fully inflated state, the size of the balloon, whose outer wall extends radially outward from the shaft of the catheter, resists withdrawal of the catheter through the urethra. This retains the distal end of the catheter in the bladder. The balloon can also form a seal at the base of the bladder to resist leakage of urine past the catheter.

In the examples shown in figures 3-5, the balloon comprises a tube extending over the tip of the catheter. Other balloon configurations are possible. For example, the balloon may fully enclose the tip, the tip being spaced from the internal surface of the balloon. The balloon may be sealed around the edges of the drainage opening(s) to create an airtight seal to allow the balloon to be inflated through the inflation port. In this case, the drainage opening(s) is/are located at the bottom of the balloon, such that the drainage opening(s) is/are located at the base of the bladder to prevent pooling of urine below the drainage opening(s).

Before the catheter is used, a reservoir containing a predetermined volume of fluid can be engaged with the inflation port. The reservoir could be a syringe or a bag. Once the tip of the catheter is in place in the bladder, the fluid can be squeezed from the reservoir into the balloon. The predetermined volume of fluid can be such as to cause the balloon to be fully inflated when the reservoir is fully evacuated. A valve may be provided in the inflation lumen to resist fluid flow in the inflation lumen towards the proximal end of the catheter. This can help the balloon to remain inflated. The shaft of the catheter may be formed of a material such as polyurethane, a silicone elastomer or latex. A polyurethane catheter shaft can be more rigid than comparable rubber catheter shafts. This can allow the shaft to have a larger urine carrying capacity without sacrificing rigidity for insertion. The exterior surface of the shaft may be coated with an inert hydromer.

The walls of the balloon may be formed of a material such as polyurethane, a silicone elastomer or latex. The walls of the balloon may be elastic or flexible or both. The walls of the balloon may include one or more regions of greater elasticity and/or flexibility than one or more other regions of the walls. The walls may be uniformly elastic across their area, or their Young's modulus may vary across their area. The walls may be uniformly biaxially elastic, or regions of the walls may have different Young's moduli in different directions. Varying the Young's modulus of the walls across their area can allow the shape of the balloon as it expands to be controlled. The walls of the balloon may be of uniform thickness or they may be provided with thickened regions such as ribs. Such thickened regions may influence the shape of the balloon as it expands.

It is desirable for there to be a relatively small spacing between the proximal end of the balloon, when inflated, and the proximal end(s) of the or each drainage opening. This promotes relatively complete draining of the bladder. To this end, it is preferred that the proximal free region of the outer skin of the balloon (i.e. the proximal part of the outer skin that is not directly adhered to the catheter shaft) is located between 0 and 10mm proximally of the most proximal part of the or each drainage opening, more preferably between 2 and 8mm proximally of the most proximal part of the or each drainage opening.

There may be one, two or more drainage openings. Preferably, where the balloon is a folded tube, there is a drainage opening between each leg of the balloon as it extends along the side of the catheter shaft. There may be one, two or more inflation openings. The balloon may be inflated from a single end or from more than one end.

Figures 6A and 6B are simplified cross-sections of the distal part of a catheter along a section analogous to D-D of figure 3. In this figure the catheter balloon is omitted for clarity. The catheter of figures 6A and 6B have two drainage openings 26 in the sidewall 27 of the distal end of the catheter. At the exterior of the shaft 1 of the catheter the drainage openings communicate with the bladder of a patient. At the interior of the catheter shaft 1 the drainage openings communicate with drainage lumen 8. The drainage openings each comprise an entrance 24 where the respective drainage opening intersects the exterior wall 28 of the catheter shaft 1 , an exit 25 where the respective drainage opening intersects the interior wall 29 of the catheter shaft 1 , and a channel 26 linking the entrance 24 of the drainage opening to the exit 25. In use, urine enters each drainage opening through the entrance 24 in the outer wall 28 of the sidewall, flows through the channel 26 between the outer wall and inner wall 29 of the sidewall and leaves the channel via the exit 25 in the inner wall of the sidewall. The urine then flows into the drainage lumen 8 to leave the catheter. The channels 26 may have substantially circular cross sections perpendicular to their length. Alternative cross-sections may also be used, for example, elliptical, square or rectangular.

As shown in the cross section of figure 6A, the channels 26 may be angled with respect to the central axis of the catheter shaft in a direction outwards towards the tip of the catheter. The channels extend through the sidewall of the catheter shaft at an oblique angle relative to the longitudinal axis of the catheter. The location at which a drainage opening intersects the inner wall 29 of the sidewall 27 is longitudinally proximal of where it intersects outer wall 28 of the sidewall. The most proximal location at which a drainage opening intersects the inner wall 29 of the sidewall 27 is longitudinally proximal of the most proximal location at which it intersects outer wall 28 of the sidewall. In the embodiment of figure 6A the most distal location at which a drainage opening intersects the inner wall 29 of the sidewall 27 is longitudinally proximal of the most distal location where it intersects outer wall 28 of the sidewall. Generally, the exit of a drainage opening is longitudinally proximal of the entrance of that drainage opening.

Each channel 26 is inclined with respect to the longitudinal axis of the catheter. The inclination is such that the interior part of the channel is proximal of the exterior part. The channel (e.g. as referenced by the axis of its mid-line) may be inclined at an angle of between 80 and 10 degrees to the longitudinal axis of the catheter where the channel meets the exterior of the catheter, or that angle may be between 70 and 20 degrees or between 60 and 30 degrees or between 50 and 40 degrees. Preferably the angle between the mid-line of the channel and the longitudinal axis of the catheter where the channel meets the exterior of the catheter is around 45 degrees. Preferably the channel extends proximally as it runs inwards from the exterior of the catheter. The proximal wall 31 of each channel is inclined with respect to the longitudinal axis of the catheter. The inclination is such that the interior part of the proximal wall is proximal of the exterior part. The proximal wall may be inclined at an angle of between 80 and 10 degrees to the distally-directed longitudinal axis of the catheter, or that angle may be between 70 and 20 degrees or between 60 and 30 degrees or between 50 and 40 degrees. In the embodiment of figure 6A the distal wall 31 of each channel is inclined with respect to the longitudinal axis of the catheter. The inclination is such that the interior part of the distal wall is proximal of the exterior part. The proximal wall may be inclined at an angle of between 80 and 10 degrees to the distally-directed longitudinal axis of the catheter, or that angle may be between 70 and 20 degrees or between 60 and 30 degrees or between 50 and 40 degrees. The proximal wall 31 of each channel is preferably straight. The distal wall 32 of each channel is preferably straight.

Figure 6B shows an embodiment in which the distal wall 32 of each channel is orthogonal to the longitudinal axis of the catheter shaft.

Studies have indicated that providing inclined drainage channels of the sort shown in figures 6A and 6B can help to reduce encrustation in urinary catheters. It is considered that this might be due to one or more of (i) more streamlined flow through the drainage channel and into the drainage lumen, with fewer eddies or standing fluid, leading to a reduced propensity for precipitation; and (ii) an absence of right-angled corners in the proximal profile of the drainage channel where it meets the drainage lumen resulting in a reduced likelihood of beads of fluid accumulating at the corners. This is illustrated in figures 7 and 8. Figure 7 shows potential flow lines 39 in a conventional catheter whose drainage port is orthogonal to the catheter shaft's longitudinal axis. It is believed that eddies or stagnant flow 40 may occur in the region of the exit of the drainage opening, and/or that beading of fluid may occur at 41 , near the sharp edge of the drainage opening. Figure 8 shows potential flow lines 39 in a catheter of the type illustrated in figure 6. It is believed that - as shown - the flow may pass more smoothly into the drainage lumen, with less propensity for turbulence. Regardless of the explanation, preliminary tests have suggested that the rate of flow for angled openings might be 35% better than for traditional right-angled openings.

Where there is continuous flow from the catheter, for example when a valve connecting the catheter shaft to a bag remains open to allow the continuous drainage of urine, the speeds of fluid flows in traditional catheters are low. For example, for 2 litres of urine emptying over 24 hours through a 4 mm internal diameter lumen this equates to an average velocity of approximately 2 mm/s. In this case, promoting improved flow by angling the ports may reduce turbulence and the resulting encrustation.

The patient may also periodically empty their bladder by using a valve at the exit of the catheter that they open when they are ready to empty their filled bladder. In this case, smoother flow will have a patient benefit of enabling them to empty their bladder more quickly for a given cross section of drainage lumen.

Thus, in addition to promoting a reduction in the occurrence of back eddies and slow spots that prompt crystallisation, this design may also promote faster throughput for a given lumen diameter. The diameter of each drainage opening may be greater than 50% of the mean diameter of the catheter shaft and/or of the mean diameter of that part of the catheter shaft distally of the most proximal point of attachment of the balloon to the catheter shaft. The diameter of each drainage opening may be less than 50% of the mean diameter of the catheter shaft and/or of the mean diameter of that part of the catheter shaft distally of the most proximal point of attachment of the balloon to the catheter shaft.

As can be seen from figures 6A and 6B, the drainage lumen is unobstructed internally in the region of the catheter longitudinally coincident with the drainage ports, and especially their exits into the drainage lumen. This can make the present catheter easier to manufacture than some prior designs. In cross-section perpendicular to the longitudinal axis of the catheter the drainage lumen is defined by its outermost periphery or exterior walls: that is by interior walls 29 of the catheter shaft. The area defined in that way is unobstructed by elements of the catheter, at least in the region of the catheter longitudinally coincident with the exits of the drainage ports. There is no lumen internally of the outer walls of the drainage lumen, at least in the region of the catheter longitudinally coincident with the exits of the drainage ports. There is an absence of means (such as a separate lumen terminating distally of the drainage ports) for conveying washing fluid distally of the drainage ports for generating a negative pressure internally of the drainage ports. There is a single longitudinal passageway in the catheter immediately proximally of the exits of the drainage openings in the inner wall of the sidewall of the catheter which communicates with the drainage openings. As shown in the cross-section of figure 3, the only passageway which communicates with the drainage openings is drainage lumen 8. There is no internal lumen opening into a cavity distally of the drainage opening within the catheter tip. There are no additional passageways located within the drainage lumen. Including additional lumens within the drainage lumen may make such a catheter more complicated to produce than a comparable catheter as shown in figure 6.

Outside the drainage lumen of the catheter of figure 6 there may be an inflation lumen of the type shown in figure 4. It may extend distally of the drainage openings, or terminate coincident with or proximally of the drainage openings. A balloon may be attached to the catheter in such a way that its interior communicates with the inflation lumen. The balloon may wrap over the tip of the catheter as illustrated in figure 4. Thus, the balloon may be anchored to the exterior of the shaft of the catheter in at least a first location between the drainage openings on one side of the catheter and a second location between the drainage openings on the other side of the catheter, and the portion of the balloon between those anchor points may extend over the tip of the catheter.

The inner wall of the sidewall of the shaft is approximately parallel to the outer wall of the sidewall of the shaft in the region between the drainage opening and the rounded tip of the catheter.

The edges of the entrance 24 of each drainage opening may also be rounded and/or countersunk within the outer wall of the catheter shaft to further promote the flow of urine from the bladder into the opening. The exit 25 of each drainage opening may also be rounded or countersunk within the inner wall of the catheter shaft. The entrance and/or exit may have a bevelled rim at the point where the channel intersects the outer and inner wall of the sidewall of the catheter shaft respectively.

A cross-section of the catheter with a countersunk drainage opening is shown in figure 9A. A view from the outside of the shaft 1 , where the drainage opening and channel have a circular cross section, is shown in figure 9B. At the entrance to the drainage opening, there may be a portion of decreasing opening width 42, being wider where the drainage opening meets the exterior wall of the catheter shaft. Following the portion of decreasing opening width 42, moving along the channel towards the exit 25, there may be a portion of the channel with substantially parallel walls 43.

The portion of decreasing width may help to prevent the fluid flow from undergoing sudden large changes in angle. The head loss (loss of energy of the fluid where the pipe changes dimension/direction) at the inlet of a pipe is a strong function of geometry and is lower for well-rounded inlets than for sharp-edged inlets. Fluid cannot make sharp turns easily, therefore the flow may separate at the corners when the edges are sharp. When the entrance to the drainage opening in the external wall of the catheter is smooth and rounded or countersunk, this may also assist in facilitating laminar flow and reducing encrustation.

The outer portion of the drainage opening or channel may be of frustoconical form, as illustrated in figure 9A. Alternatively, it may be rounded. It may join smoothly with one or both of the exterior surface of the catheter and the interior portion of the drainage channel. It may describe a continuous curve from the exterior surface of the catheter. The cross-sectional area of the channel where it meets the outer surface of the catheter is of greater cross-sectional area than the inboard portions of the channel.

Thus, the diameter or width or cross-sectional area of the or each drainage opening may increase towards the exterior of the catheter. Conveniently the or each drainage opening comprises a first, inner portion of substantially constant diameter or width or cross-sectional area and a second, outer portion located radially outward of the first portion with respect to the lumen of the catheter, the second portion having gradually increasing diameter or width or cross-sectional area towards the exterior wall of the catheter. The length of the second portion may be less than twice the width of the first portion. The length of the second portion may be greater than half the width of the first portion. The outer rim of the second portion may curve such that the surface of the second portion joins the exterior surface of the catheter smoothly and without an angular edge. This can help to promote smooth flow through the inlet constituted by the second portion.

Although the preferred embodiment of the indwelling urinary catheter described above uses an inflatable balloon to retain the catheter in the bladder of the patient, other means for retaining the catheter in the bladder may be employed. For example, the distal end of the catheter tip may have a bulbous shape or wing sections which are used to retain the catheter. Such examples are 'mushroom' catheters or winged (Malecot) catheters. The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.