HOLLOW FIBER-TYPE ARTIFICIAL LUNG

Abstract: An artificial lung (250) has an axially extending housing which accomodates a bundle of hollow fibers (146) retained within the housing (251) by a pair of walls (256, 257) provided at the ends of the housing. The housing has blood inlet (263) and outlet ports (268) defining a blood chamber (262) within the housing. Oxygen gas is passed through the hollow fibres (254) and blood is passed through the blood chamber so that the gas exchange take place through the hollow fiber walls. A heat exchanger (269) is disosed at a point preceding, follow­ ing or intermediate the blood chamber and blood reservior chamber, which constract a blood circuit.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: This invention relates to a hollow fiber-type artificial lung used in extracorporeal circulation to remove carbon dioxide from blood and add oxygen to the blood, according to the first part of claim 1. 2. Description of the Prior Art: Artificial lungs are broadly classified into those of porous and membrane type. The membrane artificial lung, such as of stacked membrane type, coil type or hollow fiber type, is widely recognised as being superior to the porous-type artificial lung in view of the fact that the blood conveyed through the lung undergoes less hemolysis, albumin degeneration, clotting and affixation, and as being extremely close to the human lung in terms of its operating mechanism. Nevertheless, because the membrane-type artificial lung possesses a number of disadvantages set forth hereinbelow, the artificial lung of porous type is that used most widely in open-heart surgery at the present time. In order to obtain sufficient oxygenation with the membrane-type artificial lung currently available, it is required that the blood flow layer be reduced in thickness. This means a narrow blood flow passage and, hence, a large flow passage resistance. In consequence, it is not possible to achieve perfusion of the blood within the artificial lung by utilizing the head developed between the patient and the lung. Accordingly, as shown in Fig. 1, a blood circuit using the membrane-type artificial lung requires that a pump 2 be disposed on the inlet or venous side of the artificial lung, indicated at numeral 1. Numeral 3 denotes a blood reservoir, and 4 a heat exchanger. With the blood circuit shown in Fig. 1, however, the magnitude of the pressure adjacent the outlet of the pump 2 is greater than the sum of the pressure loss at the blood feeding catheter and the pressure loss of the artificial lung. The problem that results is an increase in the internal pressure of the circuit on the blood feeding side. A proposed solution to this problem, disclosed in the specification of Japanese Patent Application Laid-Open No. 50-9299, is to pass the blood on the outer side of the hollow fibers. However, proposed arrangement has not put into practical use due to difficulties in removing air bubbles appeared in the blood in extracoporeal circuit. Further, there are difficulties in priming and the like to put the proposed artificial lung into practical use. The specification of the abovementioned publication discloses a theoretical arrangement for passing oxygen gas on the outer side of hollow fibers, but the arrangement does not maximize the gas exchange capability of the hollow fibers. To obtain a practical system, not only must the gas exchange capability be improved, but the following factors must be taken into consideration. Specifically, through use of the blood reservoir 3 shown in Fig. 1, the extracorporeally circulating blood is temporarily stored so that any air bubbles entrained within the blood may be removed. The reservoir 3 is also necessary for the purpose of maintaining a certain degree of blood flow in the event that the blood extracted from a vein is deficient because of a bend in the associated tubing, or if there is leakage of blood from the system. However, since the blood reservoir 3 is provided in the blood circuit independently of the artificial lung 1 in the conventional membrane-type artificial lung system, the circuit is structurally complex and much time and effort are involved in setting up the circuit and in extracting bubbles during priming. Furthermore, because of the extensive priming and the large amount of blood required to fill the conventional system, it is required that a preliminary transfusion of blood be made into the priming liquid, with which the artificial lung is filled in advance, in order to mitigate dilution of the blood within the patient's body. In particular, the allowable amount of blood available for filling an artificial lung for surgery involving infants and children is small because of low body weight. Therefore, when the membrane-type artificial lung, which requires a large quantity of blood to fill the entire circuit, is used in surgical operations on infants or children, a problem arises in that the total amount of blood available is small. The heat exchanger 4 in the blood circuit of Fig. 1 is needed for lowering blood temperature during a low body temperature process, and for heating the blood or for keeping the blood warm. However, since the heat exchanger 4, as well as the blood reservoir 3, is provided in the blood circuit independently of the artificial lung 1 in the conventional membrane-type artificial lung system, the circuit becomes even more complex structurally and greater time and effort are required for circuit set up and bubble extraction during priming. Also, as mentioned above, the extensive priming and the large amount of blood required to fill the conventional system require that a preliminary transfusion be made in the priming liquid, with which the artificial lung is filled in advance, to counter dilution of the blood within the patient's body. Because of the small amount of blood available for filling an artificial lung in surgery directed to infants and children, there is demand for an arrangement capable of greatly diminishing the amount of blood needed to fill the overall blood circuit. An artificial lung comprising the features of the first part of claim 1 except the features related to the heat exchanger is described in EP-A-0 048 943. However, since this known apparatus does not provide a heat exchanger, a separate heat exchanger is needed in use as shown in Fig. 1. Therefore, the disadvantages discussed above are valid also for an artificial lung described in said document. US-A- 3989 626 discloses an artificial lung comprising all the features of the first part of claim 1. This known apparatus provides no means to reduce the amount of air bubbles in the circulated blood. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a hollow fiber-type artificial lung which reduces the amount of blood needed to fill the associated blood circuit while providing heat exchange for the extra-corporeally circulating blood and wherein the air bubbles are removed from the blood. This object is achieved in accordance with the present invention in a fiber-type artificial lung as defined in the first part of claim 1, further comprising the features of the characterizing portion of claim 1. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram of a blood circuit to which a prior-art membrane-type artificial lung is applied; Fig. 2 is a perspective view illustrating an artificial lung according to an application of the present invention; and Fig. 3 is a perspective view illustrating an example of a slender tube having fins forming a heat exchanger. In the present invention, the hollow fiber-type artificial lung is equipped with a heat exchanger mechanism. Specifically, the artificial lung comprises an axially extended housing, a hollow fiber bundle having a multiplicity of hollow fibers accommodated within and along the axial direction of the housing, the hollow fibers forming blood channels between outer wall surfaces of neighboring ones thereof, and being arranged within the housing in such a manner that neighboring blood channels are brought into substantial communication, first and second walls liquid-tightly supporting the hollow fibers at both end portions thereof within the housing, the first and second walls, the inner wall of the housing and the outer wall surfaces of the hollow fibers defining a blood chamber, a blood inlet means provided in a side wall of the housing in the vicinity of the first wall and having an opening communicating with the blood chamber, a heat exchanger provided integral with a blood flow passage, which is formed by the blood chamber, at an upstream, portion of said blood flow passage, and gas inlet means provided on an outer side of at least one of the first and second walls. The housing has a blood outlet port, the blood reservoir being provided on the blood outlet means side. The housing has the heat exchanger which is provided in the blood chamber on the blood inlet means side. The heat exchanger is provided within the blood reservoir. The housing has a blood inlet means, the heat exchanger being provided on the side of the blood inlet means. The heat exchanger comprises a bundle of a multiplicity of slender tubes supported at both ends by a pair of walls. The ends of the tubes are open, so that the hollow interiors of the tubes define blood flow passages. The heat exchanger is so adapted that a heat transfer medium may be passed along the periphery of the tubes. Alternatively, the heat exchanger comprises a tubular body through the hollow interior of which a heat transfer medium may be passed. The blood reservoir has a gas vent communicating with the atmosphere, and an outer wall comprising a rigid material. The hollow fibers are made of microporous membrane. The housing comprises an inner cylinder accommodating the hollow fibers, and an outer cylinder surrounding a portion of the inner cylinder for defining the blood reservoir between itself and the inner cylinder. The first wall supporting the hollow fibers is retained in the inner cylinder, and the second wall supporting the hollow fibers is retained in the outer cylinder. Alternatively, both walls supporting the hollow fibers are retained in the inner cylinder. The inner surface of the housing at a portion communicating with the blood inlet means is flared outwardly relative to the intermediate portion of the housing, thereby forming an annular blood flow passage between the outer periphery of the hollow fiber bundle and the inner surface of the housing. The flared inner surface of the housing in the vicinity of the blood inlet means is off centered with respect to the hollow fiber bundle so as to increase the distance between the blood inlet port and the hollow fiber bundle, thereby enlarging the flow area of the blood flow passage facing the blood inlet means. Fig. 2 is a perspective view showing an example of an artificial lung according to the present invention. The artificial lung, designated at 320, has a housing 321 comprising an inner cylinder 322 and an outer cylinder 323. A bundle 325 of a multiplicity of hollow fibers 324 are accommodated within the inner cylinder 322. The ends of the hollow fibers 324 are retained liquid tightly within the inner cylinder 322 via walls 326, 327 retained in the upper and lower ends of the inner cylinder 322, respectively. A header 328 is attached to one end portion of the inner cylinder 322, and a header 329 to the other end portion thereof. The inner side of the header 328 and the wall 327 define a gas inlet chamber. The inner side of the header 329 and the wall 326 define a gas outlet chamber. The header 329 is formed to include a gas outlet port 331, and the header 328 is formed to include a gas inlet port 330. The inner wall of the housing 321, the outer wall of the hollow fibers 324, and the walls 326, 327 define a blood chamber 332. A blood inlet port 333 is connected to the lower end of the inner cylinder 322 through a communication portion 333A. Thus, a gas such as oxygen or air supplied from the gas inlet port 330 can be passed through the interior of the hollow fibers 324, while blood supplied from the blood inlet port 333 is passed in a turbulent state along the periphery of the hollow fibers 324 within the blood chamber 332, allowing a gas exchange to take place. Further, in the artificial lung 320, a blood reservoir 334, which communicates with the blood chamber 332, is formed between the inner cylinder 322 and outer cylinder 323, which form the housing 321. The side wall of that portion of the inner cylinder 322 inside the outer cylinder 323 is provided with a plurality of circumferentially spaced windows or communication passages 335 for communicating the blood chamber 332 inside the inner cylinder 322 with the interior of the blood reservoir 334. The outer cylinder 323 is provided at its upper portion with a gas vent 336 communicating with the interior of the reservoir 334. The lower portion of the outer cylinder 323 is formed to include a blood outlet port 334A communicating with the reservoir 334. Thus, the blood reservoir 334 is adapted to collect blood which has undergone a gas exchange. In the housing 321, there is defined between the blood inlet port 333 and the communication passage 333A a heat exchanger tank 336' constituting part of the blood chamber 332 and accommodating a heat exchanger 335. The heat exchanger 335 is supported at both ends by a pair of walls 337, 338 located within the heat exchanger tank 336', and comprises a bundle of slender tubes 339 opening at one end into the blood inlet port 333 and at the other end into the communication passage 333A. The hollow interior of each slender tube 339 serves as a blood flow passage, while the walls 337, 338 and the outer walls of the slender tubes 339 form a flow passage for a heat transfer medium. Inlet and outlet ports 340A, 340B for cooling and heating water are connected to the flow passage for the heat transfer medium. Thus, the artificial lung 320 improves the gas exchange performance per unit membrane area of the hollow fibers 324, makes it possible to achieve perfusion of the blood by virtue of the head developed between the patient and the artificial lung 320, and reduces the quantity of blood needed to fill the blood circuit in which the artificial lung is used, thanks to the blood reservoir 324 and heat exchanger tank 336, which form part of the the blood chamber 332. If a hollow heat exchanger is used as shown in Fig. 2, loss of momentum is minimal and satisfactory results can be obtained. There will be little influence from external temperature and, hence, a higher heat exchange efficiency if the heat exchanger is provided within the blood reservoir. A slender tube 342 having fins 341, as shown in Fig. 3, may be employed as the tubes forming the heat exchanger in the above embodiment. The actions and effects of the foregoing artificial lung will now be set forth. As described, the hollow fiber-type artificial lung, having the heat exchanger, comprises an axially extended housing, a hollow fiber bundle having of a multiplicity of hollow fibers accommodated within and along the axial direction of the housing, the hollow fibers forming blood channels between outer wall surfaces of neighboring ones thereof, and being arranged within the housing in such a manner that neighboring blood channels are brought into substantial communication, first and second walls liquid-tightly supporting the hollow fibers at both end portions thereof within the housing, the first and second walls, the inner wall of the housing and the outer wall surfaces of the hollow fibers defining a blood chamber, a blood reservoir provided integral with the blood chamber and having its interior communicated with the blood chamber, and a heat exchanger provided integral with a blood flow passage, which is formed by the blood chamber, at an upstream portion of the blood flow passage. Owing to such construction, gas exchange takes place while the blood is flowing in a turbulent state, making it possible to improve the gas exchange performance per unit membrane area. In addition, the blood flow resistance interiorly of the blood chamber is reduced to a small value, so that perfusion of the blood may achieved owing to the head developed between the patient and the artificial lung. Furthermore, the amount of blood needed to fill the blood circuit is small owing to provision of the heat exchanger interiorly of the blood chamber. Since the blood reservoir is provided integral with the blood chamber and communicates with the blood chamber, the blood circuit is reduced in length so that less blood is needed to fill the circuit. Further, the heat exchanger comprises a bundle of a multiplicity of slender tubes supported at both ends, which ends are open, the hollow interiors of the tubes define blood flow passages, and the heat exchanger is so adapted that a heat transfer medium may be passed along the periphery of the tubes. As a result, the blood flows through the tubes in the axial direction and meets little resistance, so there is but little loss in the blood momentum provided by the head. Operability is enhanced as well. Since the blood reservoir has a gas vent communicating with the atmosphere, the interior of the blood reservoir is held at atmospheric pressure at all times. The outer wall of the blood reservoir consists of a rigid material, and is provided with graduations so that a change in the amount of extracorporeally circulating blood can be verified with ease. The hollow fibers are made of microporous membrane. This diminishes membrane resistance to gas travel so that the gas exchange performance can be enhanced. The housing comprises an inner cylinder accommodating the hollow fibers, and an outer cylinder surrounding a portion of the inner cylinder for defining the blood reservoir between itself and the inner cylinder. The first wall supporting the hollow fibers is retained in the inner cylinder, and the second wall supporting the hollow fibers is retained in the outer cylinder. This results in a comparatively simple construction. Alternatively, both the first and second walls supporting the hollow fibers may be retained in the inner cylinder to further simplify construction and facilitate manufacture. The inner surface of the housing at a portion communicating with the blood inlet port is flared outwardly relative to the intermediate portion of the housing, thereby forming an annular blood flow passage between the outer periphery of the hollow fiber bundle and the inner surface of the housing. This makes it possible for the entrant blood to be distributed to each of the hollow fibers smoothly from the entire outer periphery of the bundle facing the blood flow passage. The flared inner surface of the housing in the vicinity of the blood inlet port is off centered with respect to the hollow fiber bundle so as to increase the distance between the blood inlet port and the hollow fiber bundle, thereby enlarging the flow area of the blood flow passage facing the blood inlet port. As a result, the blood from the blood flow passage is distributed in a uniform amount circumferentially of the hollow fiber bundle, making it possible for the flow rate of the blood traveling axially of the housing within the blood chamber to be uniformalized in relation to the circumferential direction of the hollow fiber bundle. As many apparently widely different embodiments of the present invention can be made without departing from the scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

Claims: A hollow fiber-type artificial lung comprising: an axially extended housing (321); a hollow fiber bundle (325) having a multiplicity of hollow fibers (324) accommodated within and along the axial direction of said housing, said hollow fibers forming blood channels between outer wall surfaces of neighbouring ones thereof, and being arranged within said housing (321) in such a manner that neighbouring blood channels are brought into substantial communication; first and second walls (326, 327) liquid-tightly supporting said hollow fibers (324) at both end portions thereof within said housing; said first and second walls (326, 327), the inner wall of said housing (321) and the outer wall surfaces of said hollow fibers defining a blood chamber (332); blood inlet means (333) provided in a side wall of said housing (321) in the vicinity of said first wall (326) and having an opening communicating with said blood chamber (332); blood outlet means (302A, 334A) provided in a side wall of said housing (321) in vicinity of said second wall (327) and having an opening communicating with said blood chamber; and gas inlet means (330) provided on an outer side of at least one of said first and second walls (326, 327); wherein said housing (321) is further vertically extended; said hollow fiber bundle (325) has a multiplicity of hollow fibers accommodated within and along the vertical direction of said housing (321); a heat exchanger (335) is provided integrally with the oxygenating means so as to integrate both in the blood flow passage; a blood reservoir (334) provided on a side of said blood outlet portion having a blood outlet port at a lower portion thereof; and said heat exchanger (333) being provided upstream of the oxygenation means and said blood reservoir (334) being provided downstream of said oxygenating means so that blood is directed to flow from the heat exchanger upward through the oxygenator and then to the blood reservoir, characterized in that the interior of said blood reservoir (334) being in communication with the atmosphere at a position higher than said blood outlet portion of said oxygenating means. The artificial lung according to claim 1, wherein said heat exchanger (335) is provided within said blood reservoir (334). The artificial lung according to claim 1, wherein said housing (321) has a blood inlet port (333), said heat exchanger (335) being provided on the side of said blood inlet port. The artificial lung according to claim 1, wherein said heat exchanger (335) comprises a bundle of a multiplicity of slender tubes (339) supported at both ends, which ends are open, the hollow interiors of said tubes defining blood flow passages, said heat exchanger (335) being so adapted that a heat transfer medium may be passed along the periphery of said tubes (339). The artificial lung according to claim 1, wherein said heat exchanger (311) comprises a tubular body (312) through the hollow interior of which a heat transfer medium may be passed. The artificial lung according to claim 2, wherein said blood reservoir (334) has a gas vent (341) communicating with the atmosphere. The artificial lung according to claim 2, wherein said blood reservoir (334) has an outer wall comprising a rigid material, said wall having graduations. The artificial lung according to claim 1, wherein said hollow fibers (324) are made of microporous membrane. The artificial lung according to claim 1, wherein said housing (251; 321) comprises an inner cylinder (322) accommodating said hollow fibers (324), and an outer cylinder (323) surrounding a portion of said inner cylinder for defining said blood reservoir (324) between itself and said inner cylinder, said first and second walls (326, 327) supporting said hollow fibers being retained in said inner cylinder.

Inventors: FUKASAWA, HIROMICHI, MONZEN, TAKASHI
Applicants: TERUMO KABUSHIKI KAISHA TRADING AS TERUMO CORPORATION
Application year: 1983
Main classification: A61M1
IPC codes: A61M1, B01D63