HK1201899B - Fluid pump with a rotor - Google Patents

Abstract

The invention relates to a fluid pump, in particular to a liquid pump having a rotor (18) with at least one rotor blade (20, 21) for conveying the fluid, the rotor being variable with respect to its diameter between a first, compressed state and a second expanded state. In order to produce simple compressibility and expandibility of the rotor of the pump, it is provided according to the invention that at least one rotor blade is deformable between a first state which it assumes in the compressed state of the rotor and a second state which it assumes in the expanded state of the rotor by means of a fluid counterpressure (23) during a rotation of the rotor during pump operation.

Description

Fluid pump with rotor

The present invention is in the field of fluid pumps and relates to a pump whose rotor has a variable diameter in order to be able to be guided through, for example, a narrow opening, such as a tube, in particular a blood vessel, and to be able to be operated in an expanded state after being guided through.

The invention can thus on the one hand provide support for the heart in a minimally invasive manner in the medical field, for example as a blood pump, however, on the other hand the use in stirrers or as a propulsion element for a ship is also conceivable.

The invention can show particular advantages in the medical field due to the possible miniaturization.

After the introduction of the fluid pump into the ventricle through the great vessels and the subsequent setting of the rotor operation after the rotor expansion, the pumping power of the heart can be assisted considerably, for example in the human body, or can be partially replaced. The therapeutic advantage of this application is that at least a partial reduction of the heart muscle occurs.

Such expandable fluid pumps are known from the prior art. For example, DE 10059714C 1 discloses a pump which can be pushed through a blood vessel together with a pump driver. Where blood flows through the cannula, the diameter of the cannula may be expanded and compressed to change the flow ratio.

A blood pump whose rotor can be compressed and expanded radially is known from WO03/103745a2, in which patent application different configurations are proposed to achieve expandability. The compression and radial widening of the pump housing associated therewith can be achieved, for example, by means of different parts of the catheter which are movable relative to one another after introduction. On the other hand, by rotating the drive shaft relative to the wire located within the conduit, the possibility is disclosed of producing a helical structure of the wire, which in addition carries a film which forms the rotor blades after assuming the helical structure.

Furthermore, rotor structures are known from this document which have a plurality of blades which are rigid in themselves and are pivotably hinged to the central part, said blades unfolding in operation and thus generating a fluid pressure.

From EP 0768900B 1a pump is known in which the rotor blades are hinged to a shaft in the pump housing in such a way that they can be folded up against the shaft in the inactive state and can be unfolded perpendicular to the shaft for conveying fluid during operation.

From US2006/0062672a 1a rotor of a fluid pump is known, which rotor has vanes with flexible fixation to a hub and deployment by means of fluid back pressure generated by initial rotation of the rotor.

Common to the known prior art is that the rotor blades of the pump are expanded by means of a pivoting mechanism or by pivoting by the fluid back pressure during rotation, or by mechanical means in the manner of bowden cables or the like for pump expansion only.

On the background of the prior art, the object of the present invention is to produce a fluid pump with a rotor whose diameter can be compressed, which is constructed as simply as possible in terms of construction, which preferably comprises a biocompatible material similar to the pump housing surrounding the rotor, whose expansion and compression of the housing can be achieved as simply as possible and with the necessary reliability during operation.

According to the invention, this object is achieved by the features of claim 1.

Furthermore, the invention relates to a method for operating a fluid pump according to the invention as claimed in claim 16, 17 or 18.

The knowledge according to the invention is to make possible a construction of the fluid pump which is as simple as possible by deforming the rotor blades themselves. To this end, the rotor of the fluid pump has at least one rotor blade, which is in a first state as long as the rotor assumes a first compressed state, the rotor blade assuming a second state during the transition of the rotor to an expanded state by deformation.

The rotor blades are thereby transferred from the first state to the second state by fluid back pressure occurring during rotation of the rotor during operation of the pump.

The invention has the following special advantages: the fact that no other actuating elements need to be provided for rotor expansion apart from the actual drive of the pump, and due to the deformability of the rotor blades themselves, there is no need to provide a pivotal coupling of the rotor blades or other components of the pump.

By providing a working side and a trailing side of the blade in the direction of movement during the conveying operation, deformation of the blade is facilitated and at the same time also limited, wherein the sides have different configurations in the form of different material properties and/or a configuration component at least along a part of the distance between the radially outer extremity of the blade and the radially inner extremity of the blade.

This definition should therefore advantageously be such that a rotor shape is adopted which, due to the deformation, allows optimum power delivery. In other words, the deformability of at least one rotor blade is advantageously defined in such a way that it does not exceed the shape of the rotor at which the maximum possible fluid back pressure is generated.

When the fluid pump is guided through a tube, such as a blood vessel, the rotor does not attempt to expand without external influence. Such attempts are not desirable in medical use, as the vessel wall through which the pump is guided should not be damaged. Said restoring forces present particularly great difficulties when applied through a tubular artificial channel (valve), since large frictional forces will be generated on the wall of the artificial tube and significant forces will be required to pump the fluid into the interior of the body.

The rotor remains in compression and can be fed through the blood vessel as long as the pump is not operating, i.e. not rotating on the pump shaft.

If the pump is put into operation on site, the rotor is actuated in the conveying direction and the rotor blades are deformed by the fluid pressure and are thus unfolded, with the result that a substantial amount of the conveying is set into operation. It is advantageous if the deformation of the rotor blades is elastic, since in many application situations the fluid pump must be compressed again after application in order to be removed.

In this case, after stopping the pump operation and stopping the rotor, the rotor blades again assume their first state in which the rotor is compressed.

Typically, the leading, working side (high pressure side) of the rotor during operation is subjected primarily to tension, while the trailing side (suction side) is subjected to compressive stress. The interface between the leading side and the trailing side can thus be imagined as where neutral loads are present in the pump operation. The interface must absorb the corresponding transverse shear stress.

It may be provided, for example, that the leading side and the trailing side of the rotor blade are bonded to one another at an interface region or are connected to one another by means of other joining techniques.

The properties of the rotor blade that are advantageous for the invention can be realized, for example, in that the leading side of at least one rotor blade comprises a first material and the trailing side comprises a second material that is different from the first material. Both materials may be different plastics, e.g. polymers with different properties, e.g. different plastics with different additives or one of them reinforced by fibres. It is also possible that one of the layers, preferably on the trailing side, comprises an elastomer and the other layer comprises a polymer. The rotor blade may also be made of several thin layers of plastic material, where each layer has different properties, e.g. a first layer having a low parameter, a second layer having a higher parameter than the first layer, a third layer having a higher parameter than the second layer, etc. (which may be any mechanical property, etc.). If the layers are sufficiently thin, the parameter variation with respect to the blade thickness is (at least macroscopically) continuous. Such multiple layers may be made by spraying and/or splashing, etc. a different material for each layer.

It has proved advantageous if the first material is more stretchable than the second material.

The first material should thus have a fixed elongation limit, so that during deformation of the rotor blade, a limit which is as precisely defined as possible is achieved during operation of the pump, and the defined shape of the rotor blade is set during operation. Such a fixed elongation limit is for example provided by a non-linear range of the elastic coefficient of the material, such that the force required for elongation increases over a certain fixed elongation limit (hyperproliferationly) and the shape is thus stable. This property may be inherent to the first material, but it may be assisted or substantially brought about in that stretch-resistant fibres are embedded in the first material, which fibres are much more stretch-resistant than the first material itself and assume an unstretched form in the first state of the rotor blade and a stretched form in the second state of the first material. Such fibres may for example be formed from a high strength plastics material or glass or carbon fibres.

The second material on the trailing side of the rotor blade may be incompressible or only deformable to a certain compression limit. The deformability is advantageously elastic. The compression limit may be formed, for example, by means of non-linearity of the compression factor, since the force required for compression increases over-proportionally from a certain degree of compression.

It may also be advantageous if a first material layer on the working side and a second material layer on the trailing side are provided, wherein the second material layer comprises grooves which allow compression of said second layer to such an extent that said grooves are closed.

The slots may be circumferentially tangential to the rotor to allow the rotor blades to bend along their radial length.

It can also be provided with advantage that at least one rotor blade has profiled elements on the trailing side, which profiled elements are spaced apart from one another in the first state and abut one another in the second state.

The profiled elements can be separated from each other by the slot in the first state or also embedded in the compressible material. They define a further deformability of the rotor blade in any ratio, since they abut each other in the second state.

A further advantageous embodiment of the invention provides that at least one stop element is mounted on one side of at least one rotor blade, which stop element passes through the interface between the leading side and the trailing side and is movable in a limited manner in a groove located on the other side of the rotor blade.

The stop element is advantageously made of a material which is virtually as incompressible or exactly as incompressible as the material of which the trailing side of the rotor blade consists, in order to achieve a limited stop position. The stop element may for example comprise a metal or a hard plastic material.

The invention also relates to a method for operating a fluid pump of the above-described type, which pump is started by rotating a rotor in an operating direction, and the rotor is expanded by a fluid back pressure.

It may also be provided that, in order to reduce the rotor diameter, the rotor is actuated in the opposite direction to the operating direction.

It is thus made possible by the invention that the rotor is actuated in the opposite direction to the operating direction and is thus compressed when the pump is guided through an opening, in particular a blood vessel.

The present invention may also include: the at least one rotor blade includes at least one sail for optimizing fluid conditions (see fig. 13/14, where "W" indicates sail and "B" indicates blade). Fig. 15 shows an alternative embodiment with a flap "W '" only on the working side of the blade B'.

It may be advantageous for at least one winglet to project from the working side of the blade and/or from the trailing side of the blade.

By locating at least one wing at the blade tip, the fluid conditions between the rotor and the inner wall of the pump housing are optimised. Such a vane may also provide a bearing for the rotor as long as it is in the range where it slides at the inner wall of the pump housing. However, the vanes may also be disposed between the tips of the blades and the radially inner ends where they may affect the fluid flow.

The vanes may be pivotally fixed relative to the blades and may be easily pivoted into their operative position by fluid back pressure created as the rotor rotates (see fig. 14 and 15).

The invention also relates to a method for manufacturing a fluid pump as described above.

The invention is subsequently illustrated in the drawings with reference to an embodiment and is subsequently explained.

In the drawings:

figure 1 schematically illustrates the use of a fluid pump for delivering blood in the heart,

figure 2 shows schematically in longitudinal section a pump head with radial inflow,

figure 2a shows schematically in longitudinal section a pump head with axial inflow,

figure 3 shows schematically in a plan view a rotor with two rotor blades,

figure 4 shows the rotor in a side view,

figure 5 shows a cross-sectional view through a part of a rotor blade,

figure 6 shows a cross-section through a part of a rotor blade in a different embodiment,

figure 7 shows a cross-sectional view through a part of a rotor blade,

figure 8 shows an enlarged cross-sectional view of the detail indicated by VIII in figure 7,

figure 9 shows a cross-sectional view through a rotor blade in another embodiment,

figure 10 shows an embodiment of a rotor with helical rotor blades supported by profiled elements,

fig. 11 shows a rotor, the helical blades of which are supported by helical windings,

fig. 12 shows a rotor, the helical rotor blades of which are supported by the connecting member guides,

figure 13 shows a perspective view of a blade with a flap,

figure 14 shows a cross-sectional view of the device of figure 13 taken along line 14-14 of figure 13,

fig. 15 shows a cross-sectional view of an alternative design of the blade/vane, taken along 14-14 in fig. 13.

Fig. 1 schematically shows a heart 1 in a sectional view, wherein a head 3 of a fluid pump protrudes into a heart chamber 2. The pump head 3 is arranged at the end of the cannula 4 and has a pump housing 5 rounded at the front.

The driving of the pump is effected by means of a drive shaft 6, which drive shaft 6 extends longitudinally through the cannula 4 and is connected externally to a motor 7.

The motor 7 can be actuated in both directions 8, 9, while the fluid transport is actually performed in only one direction of rotation.

Fig. 2 shows schematically a longitudinal section of the pump head 3 with the pump housing 5 and the drive shaft 6. The drive shaft 6 is rotatably mounted in a bearing housing 10 at the front end of the pump head 3 by means of a bearing 11.

Fig. 2 shows the pump head in an expanded form, i.e. with an increased radius relative to the view of fig. 1.

In order to introduce the pump head 3 into the heart through the blood vessel 12, the pump head 3 is compressed radially by relaxing the shaft (slack) or by axial pressure exerted on the shaft, even if the pump head 3 is in its least possible radially extended state.

If the pump head has reached the desired position, the pump housings can be pulled together in the axial direction by applying a tensioning force in the direction of arrow 13, so that the pump housings can expand in the radial direction, as indicated by arrows 14, 15.

The compression and expansion of the shell due to the deformation of the shell is conceivable by using a shape memory material. The shape memory material's ability to recover at a particular temperature is thus exploited. Through the slots 16, 17 extending in the axial direction of the shaft 6, the fluid, i.e. blood in the present example, can flow through the pump housing 5 towards the rotor 18 of the pump and can be further conveyed through the rotor 18, for example axially through the cannula 4. In fig. 2, the inflow of the rotor has a radial configuration. In fig. 2a, an embodiment with axial inflow and outflow is schematically presented.

The rotor has a rotor blade carrier 19 and rotor blades 20, 21, the rotor blades 20, 21 being foldable during operation of the pump, i.e. in the expanded state of the rotor.

In the rotor expanded state, the rotor radius is adjusted to fit the inner diameter of the pump housing during operation.

If the pump head is intended to be moved away from the heart 1, the pump operation is stopped and the rotor blades 20, 21 abut the rotor blade carrier 19 to reduce the radius of the rotor 18. This is advantageously assisted by the rotor 18 rotating in a rotational direction opposite to the pump operation.

If the shaft 16 is moved towards the pump head 3 in the manner of a Bowden wire, the pump head again assumes its compressed form and can be moved through the blood vessel 12.

Fig. 3 shows in a plan view the rotor 18 with the rotor blade carrier 19 and the rotor blades 20, 21 thereon in detail, which components in their first state, i.e. the compressed state of the rotor, are present in a continuous shape. In the first state, the rotor blade can also abut against the rotor blade carrier 19 in a much tighter manner.

Importantly, when the pump operation and the rotation of the rotor 18 are started in the direction of rotation 22 required for the delivery operation, a fluid counter pressure is generated in the direction of arrow 23 towards the rotor blades, and these rotor blades are bent by enlarging the radius of the rotor 18. If the pump is designed as a radial pump, the fluid is displaced and thus conveyed radially outward in the direction of arrow 24.

If the rotor blades 20, 21 are configured in the axial direction, the fluid can also be conveyed in the axial direction, as indicated by the arrows 25, 26 in fig. 4.

If the rotor is operated in a rotational direction opposite to the rotational direction 22 required for the transport, a fluid back pressure is generated on the rotor blades 20, 21, which back pressure is opposite to the direction 23 and causes the rotor blades to fold against the rotor blade carrier 19 and a corresponding reduction in the rotor diameter. In this state, the rotor can be moved out of the heart with the correspondingly compressed pump housing 5 through the blood vessel.

By selecting the direction of rotation and the speed of rotation, on the one hand, the rotor diameter can thus be varied specifically, and on the other hand, the delivery power of the pump can be adjusted as desired.

Fig. 5 shows by way of example a rotor blade 21 with a leading working side 27 and a trailing side 28 during pump operation, which rotor blade has different properties on its two sides along an interface 29. During operation, a fluid back pressure acts on the rotor blades in the direction of arrow 23 and deforms the rotor blades in the second state of rotor expansion. For this purpose, the working side 27 must be able to elongate to a certain extent, and the respective first material layer 30 has film properties for this reason. The first material layer may for example comprise a rubber or elastic plastic material which is elastically deformable to a fixed elongation limit and thereafter resists further elongation as much as possible.

On the trailing side 21, the second material layer 31 comprises a pressure-resistant material configured, for example, to be so hard that only a minimal deformation occurs when a force is applied, so that only a bending of the rotor blade can be brought about by means of an elongation of the first material layer 30.

However, the second material layer 31 may be made to have a certain degree of compressibility.

Fig. 6 shows another example of a suitable rotor blade construction, in which indentations 32 are provided in the second material layer 31, which indentations 32 allow the trailing side to be compressed and bent until the indentations 32 are closed and the individual lamellae formed between these indentations 32 abut against one another in a form-fitting (fit) manner. In this state, further bending of the rotor blade will be prevented.

The material of the second material layer 31 in this case may similarly be a hard plastic material, from which parts are cut or recessed in a casting or stamping process.

Also in this case, the material of the first material layer 30 comprises a material that is extensible to a limited extent.

In fig. 7, the rotor blade is presented in a cross-sectional view, the detail VIII being shown in more detail in fig. 8. The detail VIII thus shows the pressure-resistant second material layer 31a, the pressure-resistant second material layer 31a having a multilayer structure in the manner of a sandwich structure, which comprises the outer layers 33, 34, 35, 36 which are resistant to stretching and/or compression, and the volume layer 37. The outer layers 33, 34, 35, 36 may be reinforced, for example, with a textile material.

A very pressure-resistant layer is thus formed on the trailing side, so that the deformability of the rotor blade is essentially determined by the elongation capability of the working side 27.

In fig. 9, a variant is represented in which the stop element 38 is mounted in the first layer of material 30, for example by means of a countersunk screw 39, the stop element 38 projecting into an opening 40 of the second layer 31.

If the rotor blade 21 is deformed, the opening 40 in the second material layer 31 will tend to decrease and move until the edge of the opening 40 abuts the stop element 38. The stop element comprises a similar hard material as the second material layer 31, so that after abutment no further compression is possible on the trailing side and the paddle blade (paddle blade) is reinforced against further deformation.

Fig. 10 shows a helical rotor blade in which a series of profiled elements 41, 42 on the trailing side of the blade are connected to one another, for example glued, or applied in different joining methods. In the compressed state of the rotor, a space is present between the profiled elements. During operation of the pump and after unfolding of the blades, these profiled elements abut against each other and reinforce into a continuous sheet supporting the flat part of the blades acting as a membrane and preventing further deformation. A plurality of such forming elements arranged in rows may be arranged axially along the drive shaft 6 and angularly offset.

A similar configuration is shown in fig. 11, wherein for reinforcing the rotor blade the strips are formed by windings comprising e.g. coils, spring wires or hoses comprising a plastic material. The coils form a profiled element and are connected to the film-like surface of the rotor blade by adhesive bonding. The notches between the windings and openings close the windings and openings during blade deployment during rotor compression. In order to stabilize the winding, a continuous core is provided within the winding, which core is able to bend.

Fig. 12 shows that the support of the rotor blade is provided by a solid rail/connecting member 45, wherein the stop element is movable in a limited manner. The stop element is connected to the rotor blade.

The rail/connecting member 45 may be constructed as a component that is resistant to bending and compression with respect to forces and moments acting as desired. In this embodiment, a small additional restoring force is generated due to the bending. Due to this low material thickness, in absolute terms, a small restoring force is generated.

In fig. 12, the stop element is in the lower position. Bending up to the bent position would require a large force to be applied at this location due to the small length between the connecting member take-up device located on the shaft 6 and the location of the guide pin located in the track/connecting member 45.

The above described configurations of the rotor blade are only examples, and by means of the different configurations of the respective sides of the rotor blade, a limited deformability during operation can be achieved by utilizing the fluid back pressure.

During the counter-rotation of the rotor in the operating direction, the deformation of the rotor blades becomes opposite and these rotor blades abut against the rotor, assuming a first state and thus defining a compressed state of the rotor in which the rotor can easily pass through a narrow opening, such as a blood vessel or a tubular artificial passage (valve).

The invention thus allows the manufacture of rotors in a constructionally particularly simple manner, the diameter of which can be varied for use in a variety of applications, but which are particularly advantageously used in the medical field.

Claims (46)

1. Fluid pump for conveying a fluid, having a rotor (18) with at least one rotor blade (20.21), which rotor is variable in its diameter between a first compressed state in which the at least one rotor blade (20.21) assumes a compressed state in the rotor and a second expanded state in which the at least one rotor blade (20.21) assumes an expanded state in the rotor by means of a fluid back pressure (23) during rotation of the rotor during operation of the pump, wherein the at least one rotor blade (20.21) has a leading side (27) and a trailing side (28) in the direction of movement during the conveying operation,

characterized in that the rotor is designed such that when the pump operation and the rotation of the rotor (18) are started in the direction of rotation (22) required for the conveying operation, a fluid back pressure (23) is generated in the direction towards the rotor blades and the at least one rotor blade is curved by enlarging the radius of the rotor (18).

2. Fluid pump according to claim 1, characterised in that the at least one rotor blade (20.21) is elastically deformable by means of the fluid back pressure (23).

3. Fluid pump according to claim 1 or 2, characterised in that the deformability of the at least one rotor blade (20.21) is defined by the material properties and/or additional support elements on one side of the rotor blade.

4. A fluid pump according to claim 3, characterised in that the deformability of the at least one rotor blade (20.21) is defined in such a way that the deformation does not exceed the shape of the rotor at which the maximum possible fluid back pressure is generated.

5. Fluid pump according to claim 4, characterised in that the working side (27) of the at least one rotor blade (20.21) comprises a first material and the trailing side (28) comprises a second material different from the first material.

6. The fluid pump of claim 5, wherein the first material is more stretchable than the second material.

7. The fluid pump of claim 6, wherein the first material has a fixed elongation limit.

8. The fluid pump of claim 6, wherein fibers are embedded in the first material and are therefore more resistant to stretching than the first material.

9. The fluid pump of claim 5, wherein the second material is incompressible.

10. The fluid pump of claim 5, wherein the second material is resiliently compressible to a compression limit.

11. The fluid pump of claim 5 wherein rotor blades include a first layer of material on the working side and a second layer of material on the trailing side, and wherein the second layer of material includes slots that permit the second layer of material to compress to the extent that the slots close.

12. Fluid pump according to claim 1, characterised in that the at least one rotor blade (20.21) comprises in its constructional assembly a profiled element (31.41.42.43.44) on the trailing side (28) or the at least one rotor blade (20.21) is connected to a profiled element, which profiled elements are spaced apart from one another in the first compressed state and abut against one another in the second expanded state.

13. The fluid pump of claim 12, wherein the shaped elements (31.41.42.43.44) are separated from each other by slots (32) in the first compressed state.

14. Fluid pump according to claim 12, characterised in that the profiled element (41.42) is glued on the trailing side of the rotor blade.

15. Fluid pump according to claim 12.13 or 14, characterised in that the profiled element (43.33) is formed by individual coils of a winding.

16. The fluid pump of claim 12, wherein the molded element (31.41.42.43.44) is embedded in a compressed material.

17. Fluid pump according to claim 1, characterised in that at least one stop element (38.39) is mounted on one side of the at least one rotor blade, the at least one stop element (38.39) passing through the interface (29) between the working side and the trailing side, wherein the opening (40) tends to decrease and move until the edge of the opening (40) abuts against the stop element (38).

18. The fluid pump of claim 1, wherein the at least one rotor blade comprises at least one vane.

19. The fluid pump of claim 18 wherein said at least one wing projects from a working side of said blade.

20. The fluid pump of claim 18 wherein said at least one vane projects from a trailing side of said blade.

21. The fluid pump of claim 18.19 or 20, wherein said at least one vane is positioned at a tip of said blade.

22. Fluid pump according to claim 18, 19 or 20, characterised in that the at least one wing is pivotable relative to the blade.

23. The fluid pump of claim 22 wherein the at least one pivotable vane is pivoted to its operating position by fluid back pressure generated as the rotor rotates.

24. The fluid pump according to claim 1, characterized in that the pump is designed as a radial pump, wherein the fluid is displaced and thus conveyed radially outwards.

25. Fluid pump according to claim 1, characterised in that the working side (27) and the trailing side (28) of the rotor have different configurations in the form of different material properties and/or the assembly is configured at least along a part of the distance between the radially outer tip of the blade and the radially inner end of the blade.

26. Method for manufacturing a fluid pump according to claim 11, characterized in that for manufacturing the blade, the first material layer and the second material layer are fixed to each other.

27. The method of manufacturing a fluid pump of claim 26, wherein the first material layer and the second material layer are bonded or welded to each other.

28. Method for manufacturing a fluid pump according to claim 12, characterised in that for manufacturing the blade, a profiled element is fixed to the working side (27).

29. Method for operating a fluid pump according to claim 1, characterised in that the pump is started by the rotor (18) rotating in the direction of rotation 22 required for the delivery operation and the rotor is expanded by the fluid back pressure (23).

30. Method for operating a fluid pump according to claim 1, characterized in that for reducing the rotor radius, the rotor is actuated in the direction opposite to the operating direction.

31. Method of operating a fluid pump according to claim 1, characterized in that the rotor (18) is actuated when the pump is guided through the opening in a direction opposite to the operating direction.

32. A method of operating a fluid pump according to claim 31, wherein the opening is a blood vessel or a tubular artificial passage.

33. Method of operating a fluid pump according to claim 1, characterised in that, in operation, the diameter of the rotor widens until it reaches a maximum.

34. A method of operating a fluid pump according to claim 1, wherein the leading edge of the rotor is substantially straight when the rotor reaches a maximum diameter.

35. A fluid pump comprising a rotor for conveying a fluid having at least one rotor blade, the rotor being variable in diameter between a compressed state and an expanded state, wherein the at least one rotor blade is deformable when transitioning between the compressed state and the expanded state of the pump, wherein the at least one rotor blade has a working side and a trailing side in a direction of rotation during pump conveying operation, and wherein the rotor is configured such that when the rotor rotates during pump conveying operation a fluid back pressure is created against the working side of the at least one rotor blade in a direction opposite to the direction of rotation, and wherein the rotor comprises a first material, wherein fibers reinforce the first material.

36. The fluid pump of claim 35, wherein the fibers are selected from the group consisting of: high strength plastic fibers, glass fibers or carbon fibers.

37. The fluid pump of claim 35, wherein the first material has a range of non-linear spring coefficients.

38. The fluid pump of claim 37, wherein the range of non-linear spring rates is provided to the first material by embedding a stretch resistant fiber in the first material.

39. The fluid pump of claim 38, wherein said stretch-resistant fiber is more stretch-resistant than said first material.

40. The fluid pump of claim 38, wherein the stretch resistant fiber comprises a high strength plastic fiber.

41. The fluid pump of claim 38, wherein the stretch resistant fiber comprises a glass fiber.

42. The fluid pump of claim 38, wherein the stretch resistant fiber comprises carbon fiber.

43. The fluid pump of claim 38 wherein said stretch resistant fiber is unstretched in said compressed state of said rotor.

44. The fluid pump of claim 38, wherein said stretch resistant fiber is stretched in said expanded state of said rotor.

45. The fluid pump of claim 1, wherein the working side is made of a first material, and wherein the first material is fiber reinforced.

46. The fluid pump of claim 45, wherein the fibers are selected from the group consisting of: high strength plastic fibers, glass fibers or carbon fibers.