Heat exchanger in an extracorporeal blood circuit

Abstract: The invention relates to a heat exchanger in an extracorporeal blood circuit, including a disposable oxygenation/heat exchanger module (1) connected to a reusable manifold (2). Corrugated surfaces create adjacent chambers (5,19) through which blood and water flow for efficient heat transfer.

Description: The present invention relates to a heat exchanger for an extracorporeal blood circuit. It is known that extracorporeal blood circuits are created during surgery. The circuits typically include a heat exchanger in which the blood exchanges heat with a fluid (usually water) to regulate blood temperature, and a mass transfer device such as an oxygenation apparatus which supplies oxygen to the blood. Frequently, the oxygenation apparatus and the heat exchanger are combined in a single device. A common embodiment of known heat exchangers provides for the flow of blood and water in respective contiguous interspaces or chambers. Also, exchangers are known in which one wall of the chamber or interspace is corrugated, whereas the other one is smooth. An example of such a heat exchanger is one in which the blood circuit is provided in a single-use module which is removably associated with a water distributor or manifold designed for continued use. The above-described configuration leads to disadvantageous performance, since the blood undergoes heavy load losses, i.e., a pressure differential between the blood entering and exiting the device, with the danger of damaging the blood. In order to reduce these load losses it is necessary to resort to configurations which increase priming, i.e., the amount of blood contained in the device. Increased priming adds further negative attributes to the heat exchanger including a reduced circulation rate of the blood through the device causing stagnation and clotting of the blood. For these reasons, known heat exchangers are not fully satisfactory and are not suited to be reduced in size so that they can be coupled to so-called infant or neonatal oxygenation apparatuses to be used with patients having an extremely low weight, with the necessary miniaturization. In these situations the patients have a small blood supply that cannot be used to prime the heat exchanger. Therefore, a solution or donor blood must be used to prime the heat exchanger which is generally recognized as an undesirable situation. Also, prior art combinations of a heat exchanger and an oxygenation apparatus in a single device provides a bulky and often unwieldy structure. Known from EP-A-0 114 732 is a blood oxygenator including a heat exchanger, the heat exchanger being of a coiled bellow configuration including a plurality of individual smooth rounded surface ribs spaced apart by smaller diameter sections, inner and outer scalloped members engaging opposed portions of the bellows ribs and providing a spiral blood flow path along adjacent windings of the heat exchanger coil. An object of the present invention is to provide a heat exchanger for an extracorporeal blood circuit which exploits fluid-dynamic characteristics for improved heat exchange, in conjunction with a low priming requirement, so that the heat exchanger can be coupled advantageously to infant and neonatal oxygenation apparatuses. A further object of the present invention is to provide a heat exchanger for an extracorporeal blood circuit which can be associated with an oxygenation apparatus in a compact system, minimizing bulk and facilitating the handling of the system. The above objects are achieved by a heat exchanger in an extracorporeal blood circuit, according to the invention, as defined in the appended claims. The invention relates to an improved heat exchanger which may be associated with a hollow-fiber oxygenation apparatus or other mass transfer means. The oxygenation apparatus includes a coaxial external body monolithically associated with the substantially cylindrical shell, by means of two end heads, with the interposition of an annular portion of space containing hollow fibers. The hollow fibers are embedded at the ends of the external body in rings of polyurethane resin, termed potting. The annular portion of space is connected, at one hand, to openings for the exit of the blood from the first annular chamber and, at the other end, with a blood exit connector. The first head comprises an oxygen inlet section and the second head comprises at least an oxygen outlet section. Further characteristics and advantages will become apparent from the description of a preferred, but not exclusive, embodiment of the invention, illustrated only by way of example in the accompanying drawings, wherein: figure 1 is a longitudinal sectional view of the heat exchanger according to the invention wherein the module comprising the oxygenation apparatus and the blood circuit of the heat exchanger and the module comprising the manifold are associated; figure 2 is a longitudinal sectional view of the module comprising the oxygenation apparatus and blood circuit of the heat exchanger; figure 3 is a longitudinal sectional view of the module comprising the manifold; figure 4 is a schematic exploded view of the shell, the core, and the manifold with discordant helical corrugations which can be seen in figures 1 through 3; figure 5 is a schematic view of the shell, the core, and the manifold according to an alternative embodiment of the present invention with concordant helical corrugations. With reference to the above figures 1 to 4, the reference numerals 1 and 2, respectively, designate a first disposable module comprising the mass transfer means, typically an oxygenation apparatus, and the blood circuit of the heat exchanger and a second module comprising the water distributor or manifold of the heat exchanger. These modules, 1 and 2, when assembled together, produce the blood oxygenation apparatus with heat exchanger shown in figure 1. In the preferred embodiment of the invention, oxygenation/heat exchanger 1 is a single-use module, whereas manifold 2 can be used repeatedly. Therefore, manifold 2 is normally connected to a fixed support, and removable oxygenation/heat exchanger modules 1 are coupled with it. Typically, an oxygenation/heat exchanger 1 is locked in a removable manner at the beginning of an operation and is removed and discarded at the end of the operation. The blood circuit of integrally constructed module 1 includes a hollow and substantially cylindrical shell 3, having an interior surface with left-handed, multiple-start, helical corrugations 3a. Figure 4 shows the helical corrugations 3a having four starts. A tube or core 4 is coaxially aligned within shell 3 and its wall is shaped so as to form right-handed, helical corrugations 4a with four starts, and is made of a material which is a good heat conductor, for example, steel. A first annular chamber 5 is thus formed between the interior surface of shell 3 and corrugated outer surface of core 4. Chamber 5 is closed by a first sealing means at its upper and lower ends. The upper end is closed by an O-ring sealing gasket 6, interposed between core 4 and shell 5. Chamber 5 is closed at its lower end by a double seal formed by O-ring gasket 7, interposed between core 4 and the internal wall of a head 8a (which will be described in detail hereinafter), and by a potted polyurethane resin ring 7a. Ring 7a is located in a channel at the lower end of head 8a and the end of core 4 is embedded therein. Ring 7a also provides stability to core 4. As shown in figures 1 and 2, core 4 and the internal surface of shell 3 both have slight tapers from top to bottom. During assembly, the crests or outer periphery of the corrugations of the outer surface of core 4 contact at one or more points the corrugations of the internal surface of shell 3 due to the discordant orientation of the core 4 and shell 3 corrugations. These points of contact correctly position the core 4 within the shell 3. Also, the outer periphery of the corrugations on the exterior surface of the manifold 2 may contact at one or more points the corrugations of the corrugated inner surface of core 4 due to the discordant orientation of manifold 2 and core 4. Blood enters chamber 5 through a connector 9 located within head 8a in the direction indicated by the arrow F1 of figure 1 forming a first fluid inlet means, and leaves blood chamber 5 through openings 10, forming a first fluid outlet means. As blood travels through chamber 5, the discordant helical corrugations create an intense turbulence of the blood, preventing the formation of boundary layers, which limit heat transfer, of the blood volume passing through chamber 5. External body 11 is monolithically associated with shell 3 by means of heads 8a and 8b. External body 11 is coaxial to shell 3. The annular portion of space between body 11 and shell 3 contains hollow fibers 12 having an inner and outer surface, which are embedded at each end of body 11 in polyurethane resin rings 13 and 14, by a process known as potting. Blood exits chamber 5 and enters the annular portion of space of the mass transfer means through openings 10, flowing over fibers 12 and absorbing oxygen or an oxygen-containing gas. As oxygen flows through fibers 12, some of the oxygen passes through the microporous membrane which constitutes the wall of fibers 12 and is absorbed into the blood flowing over fibers 12. The blood leaves the annular portion of space through connector 15 which is monolithically formed in body 11, along the direction of the arrow F2 of figure 1. Oxygen is supplied to hollow fibers 12 through hole 16 formed within head 8b. The part of the oxygen which does not pass into the blood through the walls of fibers 12 reaches section 17, which is provided with output connector 18. The manifold 2 of the device is now described with particular reference to figure 3. Manifold 2 is inserted in the internal cavity of module 1 , i.e., coaxially aligned within core 4, as shown in figure 1. The external surface of manifold 2 is provided with left-handed, two-start, helical corrugations 2a. A second annular chamber 19 is defined by the helical corrugated exterior surface of manifold 2 and the corrugated inner surface of core 4. As water flows through chamber 19, the discordant helical corrugations 2a (left-handed) and 4a (right-handed) create an intense turbulence in the water flow, preventing the formation of boundary layers, which limit heat transfer, for the water volume passing through water chamber 19. At the lower end of manifold 2, base 20 includes connector 21 for water entry along the direction indicated by the arrow F3. Connector 21 is connected to inlet duct 22 which extends axially inside manifold 2 and reaches the upper end, where openings 23 connect duct 22 with water chamber 19, all forming a second fluid inlet means. Base 20 also includes connector 24 for water discharge along the direction indicated by the arrow F4. Connector 24 is connected to duct 25, which is coaxial to duct 22. Openings 26 connect duct 25 with water chamber 19, forming a second fluid outlet means. Therefore, water entering from connector 21 passes through duct 22 in an upward direction, then passes, by means of openings 23, into water chamber 19 and flows downward through chamber 19, passing along the inner surface of tube 4 in the opposite direction of the blood which flows through chamber 5 in an upward direction and passing along the outer surface of tube 4, effectively exchanging heat. Finally, the water enters duct 25 by means of openings 26, and flows into the outlet connector 24. Water chamber 19 is closed at each end by a second sealing means including gaskets which must be able to expand to provide watertightness during the operation of the device and must contract when a module 1 is inserted or removed. For this purpose, manifold 2 includes, adjacent to base 20, section 27 on which washer 28 is superimposed. Washer 28 is shaped complementarily to stem 29 which is threaded at its end and extends from knob 30. Section 27 includes the external surface with helical corrugations 2a, openings 23 and openings 26. O-ring gaskets 31a, 32a are provided in seats 31 and 32, respectively, which are formed between section 27 and washer 28 and between section 27 and base 20, respectively. Knob 30 can be activated to compress gasket 31a, 32a to cause expansion in contact with the circumferential bands, respectively, 4b and 4c, of core 4 when the device is to be used and watertightness is essential, or can be released in order to remove module 1. It should be noted that the provision of independent gaskets for blood chamber 5 and water chamber 19 ensures that any leakage of one of the gaskets does not cause the mixing of the blood and water, and fluid (blood or water) simply leaks outward. As shown in figure 1, a removable locking means allows for the selective removal or attachment of disposable module 1 to manifold 2. Base 20 includes a plurality of pivoting claws 33 which are manually activated to release from or lock into groove 34 in head 8a. Alternatively, a spring mechanism could be used to activate claws 33. The present invention incorporates the fluid-dynamic advantages of the helically corrugated chamber walls, effectuating an improved heat transfer characteristic. Further, the present invention reduces the need for priming which allows for a compact, easy-to-handle device that is desirable in the operating room environment. The present invention is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept. Thus, for example, figure 5 is a view of a shell 35, core 36, and manifold 37 which have helical corrugations, respectively 35a, 36a, 37a, which have concordant left-handed orientations. In other embodiments, for example, the water distributor 2 and core corrugations 4a are left-handed whereas the shell corrugations 3a are right-handed. It is furthermore obvious that the number of starts of the helical corrugations may vary. The same is true for the method of providing the seals at the ends of the blood and water chambers. In the preferred embodiment, core 4 and interior surface of the shell 3 have a slight taper. According to another embodiment, both core 4 and shell surface may be perfectly cylindrical, and in this case appropriate references for correct mutual assembly are provided. Further, other fluids with good heat exchange characteristics can be used to replace water. Finally, it should be noted that the heat exchanger according to the invention might be inserted in oxygenation apparatuses or other mass transfer devices whose general structure is different from the one described, and that the heat exchanger may also be used as an independent unit. In the practical embodiment of the invention, all the details may be replaced with other technically equivalent elements. Also, the materials employed, as well as the shapes and dimensions, may vary. Where technical features mentioned in any claim are followed by reference signs, such reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: A device for heat exchange comprising: -- a cylindrical shell (3) having a corrugated interior surface; -- a core (4) having a corrugated inner and corrugated outer surface, the core being coaxially aligned within the cylindrical shell (3), wherein the interior surface of the cylindrical shell (3) is opposed to the outer surface of the core to form a first annular chamber (5); -- a manifold having a corrugated exterior surface, the manifold being coaxially aligned within the core (4), wherein the exterior surface of the manifold (2) is opposed to the inner surface of the core to form a second annular chamber (19); -- a first fluid inlet means (9) for introducing a first fluid into the first annular chamber (5)and a first fluid outlet means (10) for discharging the first fluid from the first annular chamber (5), wherein the first fluid inlet means (9) and first fluid outlet means (10) are opposed axially at opposite ends of the first annular chamber for passing the first fluid axially through the first annular chamber (5); -- a second fluid inlet means (21, 22, 23) for introducing a second fluid for heat exchange into the second annular chamber (19) and a second fluid outlet means (24, 25, 26)for discharging the second fluid from the second annular chamber (19), wherein the second fluid inlet means and second fluid outlet means (24, 25, 26) are opposed axially at opposite ends of the second annular chamber (19) for passing the second fluid axially through the second annular chamber (19), wherein heat exchange occurs across the core (4) between the first and second fluid. The device of claim 1, characterized in that the corrugated interior surface of the cylindrical shell(3), the inner and outer surfaces of the core (4), and the corrugated exterior surface of the manifold (2) each have helical corrugations (2a, 4a). The device of claim 2, characterized in that the corrugated outer surface of the core (4)is discordant with the corrugated interior surface of the cylindrical shell (3). The device of claim 2, characterized in that the corrugated inner surface of the core (4)is discordant with the corrugated exterior surface of the manifold (2). The device of claim 2, characterized in that the corrugated outer surface of the core (4)is concordant with the corrugated interior surface of the cylindrical shell (3). The device of claim 2, characterized in that the corrugated inner surface of the core (4) is concordant with the corrugated exterior surface of the manifold (2). The device of claim 1, characterized in that the first fluid inlet means (9)and second fluid inlet means (21, 22, 23) are axially opposed at opposite ends of the core. The device of claim 1, characterized in that the first fluid outlet means (10) and second fluid outlet means (24, 25, 26) are axially opposed at opposite ends of the core. The device of claim 1, characterized in that the cylindrical shell (3) and corrugated core are integrally constructed to form a disposable module. The device of claim 9, characterized in that the disposable module is removably coupled to the manifold (2). The device of claim 1, characterized in that the outer periphery of at least one corrugation of the corrugated interior surface of the cylindrical shell (3) is in contact with the corrugated outer surface of the core (4), and the outer periphery of at least one corrugation of the corrugated exterior surface of the manifold (2) is in contact with the corrugated inner surface of the core (4). The device of claim 1, characterized in that it further comprises a first and a second sealing gasket 6,7 for sealing a first and a second end, respectively, of the first annular chamber 5, and a third and a fourth sealing gasket 31a, 32a for sealing a first and a second end, respectively, of the second annular chamber (19). The device of claim 1, characterized in that it further comprises a mass transfer means having an inner surface and an outer surface, the first fluid outlet means (24, 25, 25) being in fluid communication with the outer surface of the mass transfer means, and a third fluid inlet (16) and a third fluid outlet (18) in fluid communication with the inner surface of the mass transfer means; mass transfer occurs between the first fluid and a third fluid passing within the inner surface of the mass transfer means. The device of claim 13, characterized in that the mass transfer means comprises a blood oxygenator, the first fluid inlet (9) is a blood inlet, the first fluid outlet (10) is a blood outlet, the second fluid inlet (21, 22, 23) is a water inlet, the second fluid outlet (24, 25, 26) is a water outlet, the third fluid inlet (16) is an oxygen inlet, and the third fluid outlet (18) is an oxygen outlet. Use of a device according to claim 1 for heat exchange between a first fluid which is blood and a second fluid which is water.

Inventors: GHELLI NICOLA, GRANDI GIUSEPPE, PANZANI IVO, GHELLI, NICOLA, GRANDI, GIUSEPPE, PANZANI, IVO
Applicants: DIDECO SPA, DIDECO S.P.A.
Application year: 1993
Main classification: A61M1
IPC codes: A61M1