Cannula

Abstract

The present invention provides a cannula capable of transporting a sufficiently large amount of material. [Solution] The cannula 1, when placed inside a blood vessel, moves a substance between the blood inside the blood vessel and an external fluid introduced from outside the blood vessel. The cannula 1 comprises an outer cylinder 10, an inner cylinder 20, and a hollow fiber 30. The outer cylinder 10 is a cylindrical shape with bottoms at both ends. The inner cylinder 20 is a cylindrical shape with one end open and its outer surface facing the inner surface of the outer cylinder 10, with one end facing one bottom surface of the outer cylinder 10 in the internal space of the outer cylinder 10 and the other end protruding from the bottom surface so as to penetrate the other bottom surface of the outer cylinder 10. The hollow fiber 30 has an internal space through which an external fluid passes, and is folded back in the space SP3 between one end of the inner cylinder 20 and one bottom surface of the outer cylinder 10, thereby extending across both the space SP1 between the outer circumferential surface of the inner cylinder 20 and the inner circumferential surface of the outer cylinder 10, and the internal space SP2 of the inner cylinder 20.

Description

Technical Field

[0001] The present invention relates to a cannula.

Background Art

[0002] A cannula that moves substances between blood in a blood vessel and an external fluid introduced from outside the blood vessel while being indwelling in the blood vessel is known. As one such cannula, the cannula described in Patent Document 1 includes a cylindrical body with both ends being bottomless cylinders and hollow fibers located in the internal space of the cylindrical body. The blood flowing into the cannula flows through the internal space of the cylindrical body. Thereby, substances are moved between the blood in the internal space of the cylindrical body and the external fluid in the internal space of the hollow fibers.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, since the above-mentioned cannula is indwelling in a blood vessel, it cannot be made very long. Therefore, the blood flow path in the cannula cannot be made sufficiently long. Accordingly, in the above-mentioned cannula, there was a concern that the amount of substances to be moved could not be made sufficiently large.

[0005] One object of the present invention is to make the amount of substances to be moved sufficiently large.

Means for Solving the Problems

[0006] On one side, the cannula moves substances between blood in a blood vessel and an external fluid introduced from outside the blood vessel while being indwelling in the blood vessel. A cannula comprises an outer tube, an inner tube, and a hollow fiber.

[0007] The outer cylinder is cylindrical with bottoms at both ends. The inner cylinder is cylindrical with one end being bottomless and its outer surface facing the inner surface of the outer cylinder. One end faces one bottom surface of the outer cylinder within the internal space of the outer cylinder, and the other end protrudes from the bottom surface so as to penetrate the other bottom surface of the outer cylinder.

[0008] The hollow fiber has an internal space through which an external fluid passes, and is folded back in the space between one end of the inner cylinder and one bottom surface of the outer cylinder, thereby extending across both the space between the outer circumferential surface of the inner cylinder and the inner circumferential surface of the outer cylinder, as well as the internal space of the inner cylinder. [Effects of the Invention]

[0009] The amount of material being moved can be made sufficiently large. [Brief explanation of the drawing]

[0010] [Figure 1] This is a perspective view of the cannula of the first embodiment. [Figure 2] This is a plan view of the cannula of the first embodiment. [Figure 3] This is a cross-sectional view of the cannula of the first embodiment. [Figure 4] This is an end view of the cannula of the first embodiment. [Figure 5] This is a cross-sectional view of the cannula of the second embodiment. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments of the cannula of the present invention will be described with reference to Figures 1 to 5.

[0012] <First Embodiment> (overview) The cannula of the first embodiment transfers substances between the blood in the blood vessel and the external fluid introduced from outside the blood vessel when it is placed in the blood vessel. The cannula includes an outer cylinder, an inner cylinder, and hollow fibers.

[0013] The outer cylinder is a cylindrical shape with both ends having bottoms. The inner cylinder is a cylindrical shape with one end being bottomless and its outer peripheral surface facing the inner peripheral surface of the outer cylinder. One end faces one bottom surface of the outer cylinder in the internal space of the outer cylinder, and the other end protrudes from the bottom surface so as to penetrate the other bottom surface of the outer cylinder.

[0014] The hollow fibers have an internal space through which the external fluid passes and are folded back in the space between one end of the inner cylinder and one bottom surface of the outer cylinder, extending across both the space between the outer peripheral surface of the inner cylinder and the inner peripheral surface of the outer cylinder and the internal space of the inner cylinder.

[0015] According to this, the blood flowing into the cannula flows through the internal space of the inner cylinder, the space between one end of the inner cylinder and one bottom surface of the outer cylinder, and the space between the outer peripheral surface of the inner cylinder and the inner peripheral surface of the outer cylinder. In other words, the blood flow path is folded back. Therefore, the blood flow path can be made sufficiently long. Furthermore, the hollow fibers extend along the blood flow path. Thereby, the amount of substances moving between the blood and the external fluid can be made sufficiently large.

[0016] Furthermore, since the blood flow path is folded back, the opening through which blood flows into the cannula and the opening through which blood flows out of the cannula can be made sufficiently close to each other. Thereby, it is possible to promote the blood flowing out of the cannula from flowing back into the cannula again (in other words, reperfusion). Thereby, the amount of substances moving between the blood and the external fluid can be made sufficiently large. Next, the cannula of the first embodiment will be described in more detail.

[0017] (Configuration) As shown in FIGS. 1 to 4, the cannula 1 of the first embodiment will be described using a right-handed orthogonal coordinate system having an x-axis, a y-axis, and a z-axis. In this specification, the same coordinate system is also used in FIG. 5 described later. Further, the cannula 1 may be referred to as a cannula or a catheter.

[0018] In this example, the x-axis direction, the y-axis direction, and the z-axis direction may be respectively represented as the left-right direction, the front-back direction, and the up-down direction of the cannula 1. Also, in this example, the positive direction of the x-axis, the negative direction of the x-axis, the positive direction of the y-axis, the negative direction of the y-axis, the positive direction of the z-axis, and the negative direction of the z-axis may be respectively represented as the right direction, the left direction, the front direction, the back direction, the up direction, and the down direction of the cannula 1.

[0019] As shown in FIGS. 1 to 4, the cannula 1 includes an outer cylinder 10, an inner cylinder 20, a plurality of hollow fibers 30, and an axial flow pump 40. In this example, the cannula 1 is introduced into a blood vessel of a living body and, in a state of being ind留置ed in the blood vessel, moves substances between the blood in the blood vessel and an external fluid introduced from outside the blood vessel.

[0020] In this example, the cannula 1 moves oxygen from the external fluid to the blood in the blood vessel and moves carbon dioxide from the blood in the blood vessel to the external fluid. In this example, the external fluid is a gas containing oxygen. Note that the external fluid may be a liquid instead of a gas. Also, the cannula 1 may be used only for either the movement of substances from the external fluid to the blood in the blood vessel or the movement of substances from the blood in the blood vessel to the external fluid. For example, the substances that can be moved between the blood in the blood vessel and the external fluid may be substances other than oxygen and carbon dioxide (for example, heavy metals, alcohol, glucagon, insulin, urea, glucose, or creatinine, etc.).

[0021] Figure 1 is a view of cannula 1 from a position to the right of cannula 1, behind cannula 1, and above cannula 1 (in other words, a right rear-upper perspective view). Figure 2 is a view of cannula 1 from above cannula 1 (in other words, a plan view). Figure 3 is a view of both ends of the cross-section of cannula 1 in the y-axis direction, cut by the plane represented by line III-III in Figure 2, viewed in the negative x-axis direction. Figure 4 is a view of the end face of cannula 1 in the positive y-axis direction, cut by the plane represented by line IV-IV in Figure 2. Note that in Figure 3, of the multiple hollow fibers 30, all but two hollow fibers 30 are omitted from the illustration.

[0022] The outer cylinder 10 is cylindrical and extends in the y-axis direction. Therefore, the outer cylinder 10 has an internal space. This internal space of the outer cylinder 10 may also be referred to as a cavity or lumen. For example, the length of the outer cylinder 10 in the y-axis direction is 100 mm to 200 mm.

[0023] In this example, the end face of the outer cylinder 10, cut by a plane perpendicular to the longitudinal direction of the outer cylinder 10, is circular in shape. For example, the outer diameter of the outer cylinder 10 is 8 mm to 12 mm in length. Also, for example, the inner diameter of the outer cylinder 10 is 0.5 mm to 2 mm shorter than the outer diameter of the outer cylinder 10. Furthermore, the end face of the outer cylinder 10, which is cut by a plane perpendicular to the longitudinal direction of the outer cylinder 10, may have a shape other than a circle (for example, an elliptical shape or a polygonal shape).

[0024] The outer cylinder 10 has a first bottom surface 11 at one end in the positive direction of the y-axis and a second bottom surface 12 at the other end in the negative direction of the y-axis. In other words, the outer cylinder 10 has bottoms at both ends in the y-axis direction. In this example, the first bottom surface 11 corresponds to one bottom surface of the outer cylinder 10, and the second bottom surface 12 corresponds to the other bottom surface of the outer cylinder 10.

[0025] The outer cylinder 10 has a plurality of (six in this example) first openings 13 on its outer circumferential surface near the second bottom surface 12. The internal space of the outer cylinder 10 communicates with the outside of the outer cylinder 10 through each of the first openings 13. In this example, the plurality of first openings 13 are positioned at equal intervals in the circumferential direction of the outer circumferential surface of the outer cylinder 10. The number of first openings 13 on the outer cylinder 10 may be one to five, or seven or more.

[0026] The inner cylinder 20 is cylindrical and extends in the y-axis direction. Therefore, the inner cylinder 20 has an internal space. This internal space may also be referred to as a bore or lumen. For example, the length of the inner cylinder 20 in the y-axis direction is between 50 mm and 200 mm.

[0027] In this example, the end face of the inner cylinder 20, when cut by a plane perpendicular to the longitudinal direction of the inner cylinder 20, is circular. For example, the outer diameter of the inner cylinder 20 is 0.4 to 0.6 times the outer diameter of the outer cylinder 10. Also, for example, the inner diameter of the inner cylinder 20 is 0.5 mm to 2 mm shorter than the outer diameter of the inner cylinder 20. Furthermore, the end face of the inner cylinder 20, which is cut by a plane perpendicular to the longitudinal direction of the inner cylinder 20, may have a shape other than a circle (for example, an elliptical shape or a polygonal shape).

[0028] As shown in Figure 3, the inner cylinder 20 is housed in the internal space of the outer cylinder 10, with the portion of the inner cylinder 20 excluding the end in the negative direction of the y-axis. In this example, the portion of the inner cylinder 20 excluding the end in the negative direction of the y-axis may be referred to as the housing portion. The outer circumferential surface of the housing portion of the inner cylinder 20 faces (in other words, is separated from) the inner circumferential surface of the outer cylinder 10.

[0029] The end of the inner cylinder 20 in the positive y-axis direction faces (or is separated from) the first bottom surface 11 of the outer cylinder 10 within the internal space of the outer cylinder 10. In other words, the end of the inner cylinder 20 in the positive y-axis direction is located in the negative y-axis direction relative to the first bottom surface 11 of the outer cylinder 10. In this example, the end of the inner cylinder 20 in the positive y-axis direction corresponds to one end of the inner cylinder 20.

[0030] The end of the inner cylinder 20 in the negative y-axis direction protrudes from the second bottom surface 12 of the outer cylinder 10 in the negative y-axis direction, penetrating the second bottom surface 12. In this example, the end of the inner cylinder 20 in the negative y-axis direction may be referred to as the protruding portion. In this example, the protruding portion corresponds to the other end of the inner cylinder 20.

[0031] The inner cylinder 20 has no bottom at both ends in the y-axis direction. In other words, the inner cylinder 20 does not have a bottom at either end in the y-axis direction. However, the inner cylinder 20 may have a bottom at the end in the negative direction of the y-axis.

[0032] The inner cylinder 20 has a plurality of (two in this example) second openings 21 on the outer circumferential surface of the protruding portion. In this example, the plurality of second openings 21 are located near the second bottom surface 12. The internal space of the inner cylinder 20 communicates with the outside of the inner cylinder 20 through each second opening 21. In this example, the plurality of second openings 21 are located at equal intervals in the circumferential direction of the outer circumferential surface of the inner cylinder 20. The number of second openings 21 in the inner cylinder 20 may be one or three or more.

[0033] With this configuration, an inner cylinder outer circumferential space SP1 is formed between the outer circumferential surface of the housing portion of the inner cylinder 20 and the inner circumferential surface of the outer cylinder 10. In this example, the internal space of the inner cylinder 20 may be represented as the inner cylinder inner circumferential space SP2. Furthermore, an end space SP3 is formed between the end of the inner cylinder 20 in the positive direction of the y-axis and the first bottom surface 11 of the outer cylinder 10.

[0034] The hollow fiber 30 has an internal space through which an external fluid passes. This internal space of the hollow fiber 30 may also be referred to as a lumen or cavity. In this example, the end face of the hollow fiber 30, when cut by a plane perpendicular to the longitudinal direction of the hollow fiber 30, is circular in shape. For example, the outer diameter of the hollow fiber 30 is 0.2 mm to 1.0 mm in length. Also, for example, the inner diameter of the hollow fiber 30 is 0.05 mm to 0.3 mm shorter than the outer diameter of the hollow fiber 30.

[0035] The hollow fiber 30 is folded back at the end space SP3, thereby extending across both the outer circumferential space SP1 and the inner circumferential space SP2 of the inner cylinder.

[0036] In this example, the hollow fiber 30 extends across both ends in the y-axis direction within the outer circumferential space SP1 of the inner cylinder, and also extends across both ends in the y-axis direction within the inner circumferential space SP2 of the inner cylinder. In other words, one end of the hollow fiber 30 is located at the negative y-axis end of the outer circumferential space SP1 of the inner cylinder, and the other end of the hollow fiber 30 is located at the negative y-axis end of the inner circumferential space SP2 of the inner cylinder.

[0037] The introduction pipe 51 has an internal space through which the external fluid passes. The introduction pipe 51 is connected to a pump (not shown) that pumps the external fluid. The introduction pipe 51 introduces the external fluid into the multiple hollow fibers 30 by allowing the pumped external fluid to pass through its internal space.

[0038] In this example, the inlet pipe 51 is connected to the ends of multiple hollow fibers 30 by being sealed with resin PD in the outer peripheral space SP1 of the inner cylinder, so that the internal space of the inlet pipe 51 and the internal space of each hollow fiber 30 are in communication. The resin PD may also be referred to as potting resin. Furthermore, the sealing with resin PD may be referred to as potting. The introduction pipe 51 and the multiple hollow fibers 30 may be connected outside the outer cylinder 10.

[0039] The outlet pipe 52 has an internal space through which the external fluid passes. The outlet pipe 52 discharges the external fluid from the multiple hollow fibers 30 by allowing the external fluid to pass through its internal space.

[0040] In this example, the outlet tube 52 is connected to the ends of multiple hollow fibers 30 by being sealed with resin PD in the inner circumferential space SP2 of the inner cylinder, so that the internal space of the outlet tube 52 and the internal space of each hollow fiber 30 are in communication. The outlet pipe 52 and the multiple hollow fibers 30 may be connected outside the outer cylinder 10.

[0041] As shown in Figure 4, when the cannula 1 is viewed in the positive direction of the y-axis, the multiple hollow fibers 30 are arranged in a circular pattern along the outer surface of the inner cylinder 20 in the outer peripheral space SP1 of the inner cylinder. In this example, the multiple hollow fibers 30 do not overlap each other radially in the outer peripheral space SP1 of the inner cylinder. In other words, the multiple hollow fibers 30 form one layer in the outer peripheral space SP1 of the inner cylinder. However, the multiple hollow fibers 30 may overlap each other radially in the outer peripheral space SP1 of the inner cylinder. In other words, the multiple hollow fibers 30 may form multiple layers in the outer peripheral space SP1 of the inner cylinder. Furthermore, at least a portion of the multiple hollow fibers 30 may be separated from the outer peripheral surface of the inner cylinder 20 in the outer peripheral space SP1 of the inner cylinder. Furthermore, the multiple hollow fibers 30 are arranged to overlap each other radially in the circumferential space SP2 inside the inner cylinder.

[0042] As shown in Figure 3, the axial flow pump 40 is housed in the negative y-axis end of the inner circumferential space SP2 within the inner cylinder. The axial flow pump 40 comprises a drive unit 41, a shaft 42, and an impeller 43.

[0043] In this example, the drive unit 41 is positioned in the negative y-axis direction relative to the second opening 21. The drive unit 41 closes the end of the inner cylinder circumferential space SP2 in the negative y-axis direction. At least a portion of the impeller 43 is positioned in the positive y-axis direction relative to the second opening 21. The drive unit 41 is connected to the impeller 43 via a shaft 42 and rotates the impeller 43 via the shaft 42 using power supplied from a power source (not shown).

[0044] With this configuration, the axial flow pump 40 pumps blood in the inner circumferential space SP2 of the inner cylinder from the end of the inner cylinder 20 in the negative direction of the y-axis toward the end of the inner cylinder 20 in the positive direction of the y-axis.

[0045] (operation) Next, we will explain the operation of Cannula 1. Cannula 1 is inserted into a blood vessel in the body such that the end of the outer tube 10 in the positive y-axis direction is the leading end. In this example, when cannula 1 is introduced into the blood vessel, the end of cannula 1 in the negative y-axis direction is located upstream of the blood flow in the blood vessel compared to the end of cannula 1 in the positive y-axis direction. For example, when cannula 1 is introduced into the blood vessel, the positive y-axis direction approximately coincides with the direction of blood flow in the blood vessel.

[0046] The cannula 1 is then placed inside the blood vessel. Next, the axial flow pump 40 rotates the impeller 43 of the cannula 1. As a result, as shown by the dashed arrow FL1 in Figure 3, blood in the blood vessel flows from the second opening 21 of the inner cylinder 20 into the inner circumferential space SP2 of the inner cylinder. The blood that has flowed into the inner circumferential space SP2 flows from the end of the inner cylinder 20 in the negative direction of the y-axis to the end of the inner cylinder 20 in the positive direction of the y-axis.

[0047] Next, in the end space SP3, the blood flows back into the outer space SP1 of the inner cylinder. Then, the blood that has flowed into the outer space SP1 of the inner cylinder flows from the end of the outer cylinder 10 in the positive direction of the y-axis to the end of the outer cylinder 10 in the negative direction of the y-axis. Finally, the blood flows out of the cannula 1 through the first opening 13 of the outer cylinder 10. In other words, the blood returns to the blood vessel.

[0048] Furthermore, the pumping of the external fluid into the introduction pipe 51 is initiated. As a result, as shown by the dotted arrow FL2 in Figure 3, the external fluid flows through the introduction pipe 51 into the internal space of each hollow fiber 30 at the end of the outer peripheral space SP1 of the inner cylinder in the negative direction of the y-axis. Subsequently, in the portion of each hollow fiber 30 that extends into the outer peripheral space SP1 of the inner cylinder, the external fluid flows from the end of the outer peripheral space SP1 in the negative direction of the y-axis toward the end space SP3.

[0049] Next, in the portion of each hollow fiber 30 that extends through the end space SP3, the external fluid flows back into the portion of each hollow fiber 30 that extends through the inner circumferential space SP2 of the inner cylinder. Then, in the portion of each hollow fiber 30 that extends through the inner circumferential space SP2 of the inner cylinder, the external fluid flows from the end in the positive y-axis direction of the inner circumferential space SP2 of the inner cylinder to the end in the negative y-axis direction of the inner circumferential space SP2 of the inner cylinder. Finally, the external fluid flows out of the cannula 1 through the outlet pipe 52.

[0050] In other words, the external fluid flows in the portion of each hollow fiber 30 that extends in the outer peripheral space SP1 of the inner cylinder, from the end of the inner cylinder 20 in the negative direction of the y-axis to the end of the inner cylinder 20 in the positive direction of the y-axis. Furthermore, the external fluid flows in the portion of each hollow fiber 30 that extends in the inner peripheral space SP2 of the inner cylinder, from the end of the inner cylinder 20 in the positive direction of the y-axis to the end of the inner cylinder 20 in the negative direction of the y-axis.

[0051] In this way, while cannula 1 is placed inside a blood vessel, it moves oxygen from the external fluid to the blood and carbon dioxide from the blood to the external fluid.

[0052] As described above, the cannula 1 of the first embodiment, when placed inside a blood vessel, facilitates the movement of substances between the blood inside the blood vessel and an external fluid introduced from outside the blood vessel. The cannula 1 comprises an outer cylinder 10, an inner cylinder 20, and a hollow fiber 30. The outer cylinder 10 is cylindrical with bottoms at both ends. The inner cylinder 20 is cylindrical with one end being bottomless and its outer surface facing the inner surface of the outer cylinder 10. One end (in this example, the end in the positive direction of the y-axis) faces one bottom surface of the outer cylinder 10 (in this example, the first bottom surface 11) within the internal space of the outer cylinder 10, and the other end (in this example, the end in the negative direction of the y-axis) protrudes from the other bottom surface of the outer cylinder 10 (in this example, the second bottom surface 12) so as to penetrate it.

[0053] The hollow fiber 30 has an internal space through which an external fluid passes, and is folded back in the space between one end of the inner cylinder 20 and one bottom surface of the outer cylinder 10 (in this example, the end space SP3), thereby extending across both the space between the outer surface of the inner cylinder 20 and the inner surface of the outer cylinder 10 (in this example, the outer space SP1 of the inner cylinder) and the internal space of the inner cylinder 20 (in this example, the inner space SP2 of the inner cylinder).

[0054] According to this, the blood flowing into the cannula 1 flows through the internal space of the inner cylinder 20, the space between one end of the inner cylinder 20 and one bottom surface of the outer cylinder 10, and the space between the outer surface of the inner cylinder 20 and the inner surface of the outer cylinder. In other words, the blood flow path is folded back. Therefore, the blood flow path can be made sufficiently long. Furthermore, the hollow fiber 30 extends along the blood flow path. This allows for a sufficiently large amount of material to be transferred between the blood and the external fluid.

[0055] Furthermore, because the blood flow path is folded back, the opening through which blood flows into cannula 1 and the opening through which blood flows out of cannula 1 can be brought close together. This promotes the flow of blood that has flowed out of cannula 1 back into cannula 1 (in other words, reperfusion). This allows for a sufficiently large amount of material to be transferred between the blood and the external fluid.

[0056] Furthermore, in the cannula 1 of the first embodiment, the inner cylinder 20 has an opening on the outer circumferential surface of the other end (in this example, a second opening 21). The outer cylinder 10 has an opening on the outer circumferential surface near the other bottom surface (in this example, a first opening 13).

[0057] According to this, the opening through which blood flows into cannula 1 (the second opening 21 in this example) and the opening through which blood flows out of cannula 1 (the first opening 13 in this example) can be brought close together. This promotes the flow of blood that has flowed out of cannula 1 back into cannula 1. This allows for a sufficiently large amount of material to be transferred between the blood and the external fluid.

[0058] Furthermore, the cannula 1 of the first embodiment includes an axial flow pump 40 that delivers blood from one end of the inner cylinder 20 to the other end of the inner cylinder 20 within the internal space of the inner cylinder 20.

[0059] According to this, blood is discharged from one end of the inner cylinder 20 towards the other end within the internal space of the inner cylinder 20. As a result, the blood flows into the internal space of the inner cylinder 20 through an opening on the outer circumferential surface of the other end of the inner cylinder 20. At this time, the blood is guided by the bottom surface of the outer cylinder 10 (the second bottom surface 12 in this example). This increases the amount of blood flowing into the internal space of the inner cylinder 20. As a result, the amount of substance moving between the blood and the external fluid can be sufficiently increased.

[0060] Furthermore, in the cannula 1 of the first embodiment, the external fluid flows from one end of the inner cylinder 20 to one end of the inner cylinder 20 in the portion of the hollow fiber 30 that extends in the space between the outer surface of the inner cylinder 20 and the inner surface of the outer cylinder 10, and also flows from one end of the inner cylinder 20 to the other end of the inner cylinder 20 in the portion of the hollow fiber 30 that extends in the internal space of the inner cylinder 20.

[0061] Incidentally, when a substance moves from an external fluid to the blood, the concentration of the substance downstream of the blood becomes higher than the concentration of the substance upstream of the blood, while the concentration of the substance downstream of the external fluid becomes lower than the concentration of the substance upstream of the external fluid. Therefore, the difference between the concentration of the substance in the blood and the concentration of the substance in the external fluid tends to become smaller downstream of both the external fluid and the blood.

[0062] Furthermore, unless the difference between the concentration of a substance in the blood and the concentration of a substance in the external fluid is sufficiently large, the movement of substances through the hollow fibers is unlikely to occur. For this reason, if the direction of blood flow and the direction of external fluid flow are the same, the movement of substances through the hollow fibers is unlikely to occur downstream of the external fluid.

[0063] In contrast, with Cannula 1, the direction of blood flow and the direction of external fluid flow are opposite to each other. Therefore, even downstream of the external fluid, the difference between the concentration of a substance in the blood and the concentration of a substance in the external fluid can be made sufficiently large. As a result, the amount of substance that moves between the blood and the external fluid can be made sufficiently large.

[0064] <Second Embodiment> Next, the cannula of the second embodiment will be described. The cannula of the second embodiment differs from the cannula of the first embodiment in that the outer cylinder has an opening on the outer circumferential surface of the end in the positive direction of the y-axis. The following description will focus on the differences. In the description of the second embodiment, parts that are given the same reference numerals as those used in the first embodiment are the same or substantially the same.

[0065] As shown in Figure 5, in the cannula 1 of the second embodiment, the outer cylinder 10 has a plurality of (six in this example) third openings 14 on its outer circumferential surface near the first bottom surface 11. The internal space of the outer cylinder 10 communicates with the outside of the outer cylinder 10 through each first opening 13 and each third opening 14. In this example, the plurality of third openings 14 are positioned at equal intervals in the circumferential direction on the outer circumferential surface of the outer cylinder 10. The number of third openings 14 on the outer cylinder 10 may be one to five, or seven or more.

[0066] With this configuration, a portion of the blood flowing through the end space SP3 flows out of the cannula 1 through the third opening 14 of the outer cylinder 10. As a result, it is possible to prevent the blood flow rate within the blood vessel from becoming excessively low.

[0067] The outer cylinder 10 may have a third opening 14 on its first bottom surface 11. Furthermore, the outer cylinder 10 may have a third opening 14 at multiple positions in the y-axis direction that are distinct from each other at the end of the outer cylinder 10 in the positive y-axis direction.

[0068] As described above, the cannula 1 of the second embodiment can also produce the same actions and effects as the cannula 1 of the first embodiment. Furthermore, in the cannula 1 of the second embodiment, the outer cylinder 10 has an opening on one of its bottom surfaces (in this example, the first bottom surface 11), or on the outer circumferential surface near one of its bottom surfaces.

[0069] According to this, it is possible to prevent the blood flow rate within the blood vessels from becoming excessively low.

[0070] It should be noted that the present invention is not limited to the embodiments described above. For example, various modifications can be made to the embodiments described above that are understandable to those skilled in the art, without departing from the spirit of the present invention. [Explanation of Symbols]

[0071] 1 Cannula 10 Outer cylinder 11 1st bottom 12 Second bottom surface 13. First opening 14. Third opening 20 Inner cylinder 21. Second opening 30 hollow fibers 40 Axial flow pump 41 Drive unit 42 shafts 43 Impeller 51 Introductory tube 52 Outlet pipe PD resin SP1 Outer circumference space of the inner cylinder SP2 Inner cylinder circumferential space SP3 End space

Claims

1. A cannula, while placed inside a blood vessel, for moving a substance between the blood inside the blood vessel and an external fluid introduced from outside the blood vessel, An outer cylinder that is cylindrical with bottoms at both ends, An inner cylinder having a bottomless end at one end and a cylindrical shape with its outer surface facing the inner surface of the outer cylinder, the one end facing one bottom surface of the outer cylinder in the internal space of the outer cylinder, and the other end protruding from the bottom surface so as to penetrate the other bottom surface of the outer cylinder, The hollow fiber has an internal space through which the external fluid passes, and is folded back in the space between one end of the inner cylinder and one bottom surface of the outer cylinder, thereby extending across both the space between the outer circumferential surface of the inner cylinder and the inner circumferential surface of the outer cylinder, and the internal space of the inner cylinder. A cannula equipped with this feature.

2. A cannula according to claim 1, The inner cylinder has an opening on the outer circumferential surface of the other end, The outer cylinder has an opening on its outer circumferential surface near the bottom surface of the other body, forming a cannula.

3. A cannula according to claim 2, A cannula comprising an axial flow pump that delivers the blood from one end of the inner cylinder toward one end of the inner cylinder within the internal space of the inner cylinder.

4. A cannula according to claim 3, A cannula in which the external fluid flows from one end of the inner cylinder to one end of the inner cylinder in the portion of the hollow fiber that extends in the space between the outer surface of the inner cylinder and the inner surface of the outer cylinder, and flows from one end of the inner cylinder to the other end of the inner cylinder in the portion of the hollow fiber that extends in the internal space of the inner cylinder.

5. A cannula according to claim 1 or claim 2, The outer cylinder has an opening on one of its bottom surfaces or on its outer circumferential surface near the one bottom surface, thus forming a cannula.

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