BLOOD OXYGENATOR USING A HOLLOW-FIBER MEMBRANE

Abstract: The present invention provides a blood oxygenator of the outside perfusion type using hollow fibers (2) as the gas exchange membrane. In this blood oxygenater, a plurality of contact chambers (5) each containing a bundle or bundles of hollow fibers (2) for gas exchange use and communicating with a blood inlet (9) and a blood outlet (10) are disposed to make blood flow in multiple paths within a housing (1), and each bundle of hollow fibers (2) is arranged so as to be substantially perpendicular to the direction of blood flow. In spite of its compact construction, this blood oxygena­ tor has high oxygen and carbon dioxide exchange rates per unit of membrane even when used in the gas exchange of blood having high flow rate, exhibits only a small pressure loss, and causes little channeling of the blood gas. Moreover, it is easy to manufacture because of its relatively simple structure.

Description: 1. Field of the Invention This invention relates to a blood oxygenator of the outside perfusion type using a hollow-fiber membrane. 2. Description of the Prior Art A number of blood oxygenators using hollow fibers as the gas exchange membrane have already been proposed, for example, in U.S. Patent Nos. 2,972,349, 3,794,468, 4,239,729 and 4,374,802. In these blood oxygenators, hollow fibers made of a homogeneous membrane of gas-permeable material such as silicone or hollow fibers made of a microporous membrane of hydrophobic polymeric material such as polyolefins are used to bring blood into contact with gas through the medium of the hollow-fiber membrane and effect gas exchange therebetween. There are two types of blood oxygenators: the inside perfusion type in which blood is passed through the bores of the hollow fibers while gas is passed on the outside of the hollow fibers and the outside perfusion type in which, conversely, gas is passed through the bores of the hollow fibers while blood is passed on the outside of the hollow fibers. It is noted that blood channeling, a phenomenon in which blood flows unevenly, can occur when, for example, blood flow passes a point having low flow resistance such as when the space between the hollow fibers or the space between the hollow fibers and the inner walls of the housing is uneven. When blood channeling occurs, the efficiency of the hollow fibers drops. In addition, since the diffusion length of gas in the blood is increased due to the increase of the blood flow thickness, the gas exchange performance will decrease compared to cases in which blood flows uniformly. In blood oxygenators of the inside perfusion type, no channeling of the blood occurs if the blood is uniformly distributed and fed to the large number of hollow fibers. However, since the blood flowing through the bores of the hollow fibers moves in a perfect laminar flow, the internal diameter of the hollow fibers needs to be reduced in order to increase the oxygenation rate (i.e., the oxygen transfer rate per unit area of membrane). For this purpose, hollow fibers having an internal diameter of 150 to 300 µm have actually been developed for use in blood oxygenators. Nevertheless, even if the internal diameter is reduced, the laminar flow phenomenon of the blood passing through the hollow fibers is not mitigated and the oxygenation rate of a blood oxygenator of this type is not greatly enhanced. Moreover, as the internal diameter becomes smaller, clotting (i.e., blockade of the bore due to the coagulation of blood) may occur more frequently, thus posing a serious problem for a practical point of view. Furthermore, a blood oxygenator generally uses ten thousand to forty thousand hollow fibers made into a bundle or bundles and it is very difficult to distribute and feed the gas uniformly to the external surfaces of such a large number of hollow fibers, so that special consideration must be given to achieve the desired end. If the gas is not distributed uniformly, the carbon dioxide desorption rate (i.e., the carbon dioxide transfer rate per unit area of membrane) will be reduced. On the other hand, in blood oxygenators of the outside perfusion type, the gas can be distributed uniformly and the blood can be expected to move in a turbulent flow. However, they have the disadvantage of being subject to insufficient oxygenation due to channeling of the blood or blood coagulation at the sites of stagnation. Thus, no blood oxygenator having satisfactory performance has been realized as yet. In most of the conventionally known blood oxygenators, a cylindrical housing is simply packed with a large number of hollow fibers for gas exchange use in such a way that the hollow fibers are parallel to the longitudinal axis of the cylindrical housing. However, blood oxygenators of this construction have low gas exchange rate per unit area of the hollow-fiber membrane. As an improved form of the outside perfusion type, U.S. Patent No. 3,794,468 has proposed a blood oxygenator in which hollow tubular conduits of semipermeable membrane are wound about a hollow, cylindrical core having a large number of pores in the wall and then contained in a housing, and blood is allowed to flow out of the cavity of the core through its pores while gas is passed through the bores of the hollow tubular conduits. However, this blood oxygenator is disadvantageous in that the priming blood volume is unduly large and the manufacture thereof requires a complicated procedure because of its intricate structure. Thus, it has not yet been put to practical use. The conventionally known blood oxygenators in which the hollow fibers are disposed so as to be substantially perpendicular to the direction of blood flow can produce more marked turbulences of the blood flow and hence an improvement in oxygenation rate, as compared with those in which the hollow fibers are disposed so as to be parallel to the direction of blood flow. However, if the size of such a blood oxygenator is magnified or the flow rate of blood is increased in order to treat large volumes of blood, there arise such problems as an increase in pressure loss, channeling of the blood and blood coagulation at the sites of stagnation. The prior art has been unable to solve these problems. EP-A-0103899 discloses a hollow fiber-type artificial lung which is provided with a heat exchanger having slender tubes or a coil-shaped tubular body, and which employs hollow fibers as the gas exchange membranes. The blood flow and gas flow are parallel in the gas exchange portion of this artifical lung resulting in the gas exchange efficiency being relatively low. The gas exchange and heat exchange portions of the artificial lung are not integral although they are formed into a single body. Both portions are formed separately and then joined together only at a later stage. US-A-3998593 discloses a membrane blood oxygenator which contains a heat exchange section in which the gas and blood flow channels are generally perpendicular to each other. The blood oxygenator makes use of flat rectangular membranes. Blood and gas are caused to flow in a direction almost perpendicular to each other on different sides of the flat membrane but this causes very little turbulence. According to one aspect of the present invention, there is provided a blood oxygenator comprising a gas exchange section containing hollow fibers for gas exchange use and a heat exchange section, containing tubules for heat exchange use, characterized in that the blood oxygenator comprises: a cylindrical shape housing having a blood inlet and a blood outlet in its sidewall, having a gas inlet and a gas outlet in its opposite end surfaces, and having a heat exchange medium inlet and a heat exchange medium outlet in its opposite end surfaces, said housing having formed therein (a) two contact chambers through which blood flows, which are disposed in parallel so as to form two circular arcs along the sidewall of the housing, (b) gas passages, and (c) heat exchange medium passages, each of the contact chambers communicating with the blood inlet and the blood outlet and being divided into a plurality of compartments by blood flow channels narrowed in a direction substantially perpendicular to the direction of blood flow and hollow fibers, a bundle or bundles of hollow fibers for gas exchange use disposed in some of the compartments so as to be substantially parallel to the longitudinal axis of the housing, the opposite open ends of the hollow fibers communicating with the gas inlet and the gas outlet through the medium of the gas passages, and a bundle of tubules for heat exchange use disposed in the remaining compartments in the same manner as the bundle or bundles of hollow fibers for gas exchange use, the opposite open ends of the tubules for heat exchange use communicating with the heat exchange medium inlet and the heat exchange medium outlet through the medium of the heat exchange medium passages. According to a second aspect of the invention, there is provided a blood oxygenator comprising a gas exchange section containing hollow fibers for gas exchange use and a heat exchange section containing tubules for heat exchange use, characterized in that the blood oxygenator comprises: a cylindrical shape housing having a blood inlet and a blood outlet in its sidewall, having a gas inlet and a gas outlet in its opposite end surfaces, and having a heat exchange medium inlet and a heat exchange medium outlet in its opposite end surfaces, said housing having formed therein (a) a plurality of contact chambers through which blood flows, which are disposed in parallel so as to form two circular arcs along the sidewall of the housing , (b) a heat exchange chamber positioned centrally in the housing, (c) gas passages, and (d) heat exchange medium passages, each of said contact chambers communicating with the heat exchange chamber and the blood outlet and being divided into a plurality of compartments by blood flow channels narrowed in a direction substantially perpendicular to the direction of blood flow and hollow fibers, and the blood inlet communicating with each of the contact chambers through the medium of the heat exchange chamber; a bundle or bundles of hollow fibers for gas exchange use disposed in each of the contact chambers so as to be substantially parallel to the longitudinal axis of the housing, the opposite open ends of the hollow fibers communicating with the gas inlet and the gas outlet through the medium of the gas passages, and a bundle of tubules for heat exchange use disposed in the heat exchange chamber in the same manner as the bundle or bundles of hollow fibers for gas exchange use, the opposite open ends of the tubules for heat exchange use communicating with the heat exchange medium inlet and the heat exchange medium outlet through the medium of the heat exchange medium passages. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Fig. 1 is a longitudinal sectional view of one embodiment of the blood oxygenator of the present invention; Fig. 2 is a cross-sectional view taken along line X-X' of Fig. 1; Fig. 3 is a longitudinal sectional view of a further embodiment of the blood oxygenator of the present invention; and Fig. 4 and 5 are cross-sectional views taken along ling Y-Y' and line Z-Z', respectively, of Fig. 3. The blood oxygenator of the present invention will be more fully described with reference to the accompanying drawings. Figs. 1 and 2 show one embodiment of the blood oxygenator of the present invention. This blood oxygenator comprises a cylindrical housing 19 constituting its main body, bundles of hollow fibers 2 for gas exchange use, bundles of hollow fibers 20 for heat exchange use, and fastening members 3. As shown in Fig. 2, the cavity of the housing 19 is divided into two contact chambers 21 which are disposed so as to form two circular arcs along the sidewall of the cylindrical housing 19 and extend from a blood inlet 9 provided in the sidewall of the cylindrical housing 19 to a blood outlet 10 provided on the opposite side thereof. Also in this embodiment, each contact chamber 21 is divided into a plurality of compartments 23 to 26 by blood flow channels 22 narrowed in the direction of the thickness of the contact chamber. The blood flow channels 22 make it possible to prevent channeling of the blood flow. Although the embodiment shown in Fig. 2 includes two contact chambers each having four compartments connected in series (thus totaling eight compartments), the number of compartments provided in each contact chamber may be two or more. The housing 19 is also provided with a gas inlet 7 and a gas outlet 8. The hollow fibers 2 are disposed in each contact chamber 21 so as to be substantially rectilinear and fixed by two opposite fastening members 3 in such a way that their respective ends are in communication with the gas inlet 7 and outlet 8. In this blood oxygenator, an oxygen-containing gas is fed through the gas inlet 7 to a gas passage within the housing 19 and then passed through the bores of the hollow fibers 2 disposed in the contact chambers 21, where it undergoes gas exchange with the blood through the medium of the hollow-fiber membrane. The gas thus decreased in oxygen content and increased in carbon dioxide content is conducted to a gas passage and then discharged through the gas outlet 8. Of course, the oxygen-containing gas fed through the gas inlet 7 may comprise pure oxygen. On the other hand, blood withdrawn from a human body (i.e., venous blood) is introduced through the blood inlet 9 into a blood distribution chamber 28 within the housing 19 and then fed to the contact chambers 21. In the contact chambers 21, the venous blood flows in a direction substantially perpendicular to the hollow fibers 2, comes into contact therewith, and undergoes gas exchange, through the medium of the hollow-fiber membrane, with the oxygen-containing gas flowing through the bores of the hollow fibers 2. Thus the venous blood is converted into arterial blood, which is conducted through a blood collection chamber and discharged out of the blood oxygenator through the blood outlet 10. In the blood oxygenator of the present invention, the hollow fibres are disposed in the contact chambers so as to be substantially perpendicular to the direction of blood flow. The term "direction of blood flow" as used herein does not mean the direction of the blood flow actually produced by passing blood through the contact chambers, but the direction of the straight line connecting the blood inlet of each contact chamber with the blood outlet thereof. In order to prevent channeling of the blood, the hollow fibers need to form an angle of at least 45° with the direction of blood flow, and it is most preferable that the hollow fibers are substantially perpendicular to the direction of blood flow. Moreover, the hollow fibers contained in each contact chamber are preferably disposed in such a way that they are substantially rectilinear and parallel to one another. However, the hollow fibers may also be disposed in such a way that they are formed into bundles and each bundle of hollow fibers is twisted about its longitudinal axis at an angle of up to about 45°. In the blood oxygenator of the present invention, the degree of packing of the hollow fibers contained in each contact chamber preferably ranges from 10 to 55% and more preferably from 20 to 40%. The term "degree of packing" as used herein means the proportion of the total cross-sectional area of the hollow fibers to the cross-sectional area of the contact chamber, as viewed in a plane parallel to the direction of blood flow in the contact chamber. If the degree of packing is less than 10%, channeling of the blood will tend to occur, while if it is greater than 55%, the flow resistance of the blood may become unduly high and hemolysis may be induced. In order to improve the functionality (i.e., gas exchange capacity) of a blood oxygenator, it is important to reduce the thickness of its contact chamber. However, if the thickness is reduced, the cross-sectional area of the blood flow path will become smaller, resulting in an increase in blood flow velocity and hence an increase in pressure loss. In the blood oxygenator of the present invention, therefore, the blood introduced through the blood inlet is distributed to two or more flow paths. This makes it possible to reduce the velocity of the blood flowing through each contact chamber and thereby decrease the pressure loss. The hollow fibers contained in the blood oxygenator of the present invention may comprise any of various types of hollow fibers, and examples thereof include hollow fibers made of a homogeneous or porous membrane of such material as cellulosics, polyolefins, polysulfones, polyvinyl alcohol, silicone resins, PMMA and the like. However, hollow fibers made of a porous polyolefin membrane are preferred because of their excellent durability and gas permeability. Especially preferred are hollow fibers made of a membrane which comprises fibrils stacked in layers between both surfaces and nodes fixing the respective ends of the fibrils and, therefore, has micropores formed of the spaces between the fibrils and interconnected so as to extend from one surface to the other. As an example of such hollow fibers, there are polypropylene hollow fibers commercially available from Mitsubishi Rayon Co., Ltd. under the trade name of Polypropylene Hollow Fiber KPF. The fastening members may conveniently be formed in the same manner as in the manufacture of so-called hollow-fiber filter modules using hollow fibers. Specifically, this can be accomplished by using a potting material having good adhesion properties (such as a polyurethane resin) and molding it integrally with the hollow fibers and the partitioning members. Immediately after blood is introduced through the blood inlet into the first compartment of each contact chamber, the blood may flow slightly in oblique directions. Accordingly, as shown in Fig. 2, baffles 27 are preferably provided in order to prevent the blood introduced through the blood inlet 9 from flowing in radial directions. Where each contact chamber has three or more compartments, one or two compartments adjacent to the blood inlet 9 or the blood outlet 10 may be packed with a bundle of tubules or hollow fibers for heat exchange use, in place of the bundle of hollow fibers for gas exchange use, so as to function as a heat exchange chamber or chambers. In this blood oxygenator, the compartment 23 contains a bundle of hollow fibers 20 for heat exchange use while each of the compartments 24 to 26 contains a bundle of hollow fibers 2 for gas exchange use. In Fig. 2, the bundle of hollow fibers for heat exchange use and the bundles of hollow fibers for gas exchange use are disposed so as to be perpendicular to the plane of the drawing (or parallel to the longitudinal axis of the housing 19). The opposite open ends of the hollow fibers for heat exchange use communicate with a heat exchange medium inlet 29 and a heat exchange medium outlet 30, respectively. Although metallic tubules having good thermal conductivity may be used as the tubules for heat exchange use, it is preferable to use hollow fibers of plastic material having an internal diameter of 5 to 1,000 µm and a wall thickness of about 2 to 20 µm. For example, there may be used hollow fibers made of a non-porous membrane of polyethylene or polypropylene. Alternatively, hollow fibers made of a porous membrane may also be used, provided that the membrane has no pores extending from one surface to the other. In this blood oxygenator, the blood introduced through the blood inlet 9 is distributed to the two compartments 23 adjacent to the blood inlet 9. Then, in each contact chamber, the blood flows successively through the compartments 24, 25 and 26 in the circumferential direction of the cylindrical housing 19. On the other hand, the gas flows through the bores of the hollow fibers in the axial direction of the cylindrical housing. Thus, the blood and the gas flow in directions substantially perpendicular to each other and come into contact to effect gas exchange therebetween. The embodiment shown in Figs. 3 to 5 is a modification of the blood oxygenator shown in Figs. 1 and 2. In this embodiment, the blood inlet 9 and the blood outlet 10 are disposed on the same side of the sidewall of the cylindrical housing 31, and a heat exchange chamber 32 is provided in the center of the housing 31. Blood is introduced through the blood inlet 9 into the heat exchange chamber 32 containing a bundle of hollow fibers 20 for heat exchange use, where it undergoes heat exchange with the heat exchange medium flowing through the bores of the hollow fibers for heat exchange use. Then, the blood is distributed to two contact chambers 33 disposed in parallel, fed to the space on the outside of the hollow fibers for gas exchange use, and conducted toward the blood outlet 10, during which it undergoes oxygen-carbon dioxide exchange with the oxygen or oxygen-containing gas flowing through the bores of the hollow fibers for gas exchange use. The resulting oxygenated blood is withdrawn from the blood outlet 10. In order to prevent channeling of the blood, it is preferable that, similar to the blood oxygenator shown in Figs. 1 and 2, each of the contact chambers 33 disposed so as to form two circular arcs along the sidewall of the cylindrical housing be divided into a plurality of compartments 35, 36 by blood flow channels 34. Although the heat exchange chamber 32 contains a bundle of hollow fibers for heat exchange use in this embodiment, it is also feasible that the heat exchange chamber 32 contain a bundle of hollow fibers for gas exchange use and that the two compartments adjacent to the blood outlet 10 contain a bundle of hollow fibers for heat exchange use. If desired, this blood oxygenator may be provided with venting devices 37 which are positioned in the sidewall of the housing on substantially the opposite side of the blood inlet 9 and the blood outlet 10. These venting devices 37 communicate with the heat exchange chamber 32 and the contact chambers. Although it is preferable to provide two venting devices as shown in the embodiment of in Figs. 7 to 9, it is possible to provide only one venting device. The blood oxygenator should preferably be installed in such a way that the venting devices are positioned on the upper side thereof. Then, any gas entrapped in the blood accumulates at the top of the cavity owing to the difference in specific gravity between gas and blood and easily escapes from the housing through the venting devices 37. The venting devices 37 can include a venting member made of any material that is impermeable to blood, but permeable to gases. For example, there may be used porous or homogeneous membranes of such material as cellulosics, polyolefins, PMMA and silicone. Especially preferred are porous polyolefin membranes including hollow fibers commercially available from Mitsubishi Rayon Co., Ltd. under the trade names of Polypropylene Hollow Fiber KPF and Polyethylene Hollow Fiber EHF. In the blood oxygenators shown in Figs. 1 to 5, bundles of hollow fibers for gas exchange use and, if present, bundles of hollow fibers for heat exchange use can be disposed within a cylindrical housing in a well-balanced manner, which greatly facilitates potting of the hollow fibers and attachment of end caps to the housing. In addition, the improved strength of the housing itself makes it possible to make lightweight and compact blood oxygenators. Moreover, since the blood introduced through a single blood inlet is distributed to multiple channels constituting at least one half the length of the blood flow path from the blood inlet to the blood outlet, the average flow rate is reduced to about one-half, resulting decrease in flow resistance and hence a decrease in pressure loss. Furthermore, if venting devices are provided as shown in the blood oxygenator of Figs. 3 to 5, any gas entrapped in the blood accumulates at the top of the cavity of the housing and easily escapes to the outside through the venting devices, thus preventing blood coagulation or similar problems due to the retension of gas bubbles.

Claims: A blood oxygenator comprising a gas exchange section containing hollow fibers (2) for gas exchange use and a heat exchange section containing tubules (20) for heat exchange use, characterized in that the blood oxygenator comprises: a cylindrical shape housing (19) having a blood inlet (9) and a blood outlet (10) in its sidewall, having a gas inlet (7) and a gas outlet (8) in its opposite end surfaces, and having a heat exchange medium inlet (29) and a heat exchange medium outlet (30) in its opposite end surfaces, said housing having formed therein (a) two contact chambers (21) through which blood flows, which are disposed in parallel so as to form two circular arcs along the sidewall of the housing, (b) gas passages, and (c) heat exchange medium passages, each of the contact chambers communicating with the blood inlet (9) and the blood outlet (10) and being divided into a plurality of compartments (23, 24, 25 and 26) by blood flow channels (22) narrowed in a direction substantially perpendicular to the direction of blood flow and hollow fibers (2), a bundle or bundles of hollow fibers (2) for gas exchange use disposed in some of the compartments so as to be substantially parallel to the longitudinal axis of the housing (19), the opposite open ends of the hollow fibers communicating with the gas inlet (7) and the gas outlet (8) through the medium of the gas passages, and a bundle of tubules (20) for heat exchange use disposed in the remaining compartments in the same manner as the bundle or bundles or hollow fibers (2) for gas exchange use, the opposite open ends of the tubules for heat exchange use communicating with the heat exchange medium inlet (29) and the heat exchange medium outlet (30) through the medium of the heat exchange medium passages. A blood oxygenator according to claim 1, wherein said tubules (20) for heat exchange use comprise hollow fibers having an internal diameter of 5 to 1,000 um and a wall thickness of 2 to 20 um. A blood oxygenator comprising a gas exchange section containing hollow fibers (2) for gas exchange use and a heat exchange section containing tubules (20) for heat exchange use, characterized in that the blood oxygenator comprises: a cylindrical shape housing (31) having a blood inlet (9) and a blood outlet (10) in its sidewall, having a gas inlet (7) and a gas outlet (8) in its opposite end surfaces, and having a heat exchange medium inlet (29) and a heat exchange medium outlet (30) in its opposite end surfaces, said housing having formed therein (a) a plurality of contact chambers (33) through which blood flows, which are disposed in parallel so as to form two circular arcs along the sidewall of the housing, (b) a heat exchange chamber (32) positioned centrally in the housing, (c) gas passages, and (d) heat exchange medium passages, each of said contact chambers communicating with the heat exchange chamber and the blood outlet and being divided into a plurality of compartments (35 and 36) by blood flow channels (34) narrowed in a direction substantially perpendicular to the direction of blood flow and hollow fibers, and the blood inlet (9) communicating with each of the contact chambers (33) through the medium of the heat exchange chamber (32); a bundle or bundles of hollow fibers (2) for gas exchange use disposed in each of the contact chambers (33) so as to be substantially parallel to the longitudinal axis of the housing (31), the opposite open ends of the hollow fibers communicating with the gas inlet (7) and the gas outlet (8) through the medium of the gas passages, and a bundle of tubules (20) for heat exchange use disposed in the heat exchange chamber (32) in the same manner as the bundle or bundles of hollow fibers (2) for gas exchange use, the opposite open ends of the tubules for heat exchange use communicating with the heat exchange medium inlet (29) and the heat exchange medium outlet (30) through the medium of the heat exchange medium passages. A blood oxygenator according to claim 3, wherein said tubules (20) for heat exchange use comprise hollow fibers having an internal diameter of 5 to 1,000 um and a wall thickness of 2 to 20 um. A blood oxygenator according to claim 3 or claim 4 wherein said blood inlet (9) and said blood outlet (10) are positioned on substantially the same side of the circumference of said cylindrical housing (31) and at least one venting device (37) is provided on the opposite side thereof so as to communicate with said heat exchange chamber (32).

Inventors: HAMADA, EIICHI, KAMO, JUN, NAKASHIMA, ATUSHI, TAKEMURA, TOHRU, YOSHIDA, HARUHIKO
Applicants: MITSUBISHI RAYON CO., LTD.
Application year: 1985
Main classification: A61M1
IPC codes: B01D63, A61M1