GB1604956A - Heat exchangers for regulating the temperature of blood in an extracorporeal circuit - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO HEAT EXCHANGERS FOR REGULATING THE TEMPERATURE OF BLOOD IN AN EXTRACORPOREAL CIRCUIT (71) We, SHILEY INCORPORATED, a corporation organized and existing under the laws of the State of California, United States of America, of 17600 Gillette Avenue, Irvine, State of California 92705, United States of America. (Assignee of JOHN EDWARD LEWIN), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to heat exchangers for regulating the temperature of blood in an extracorporeal circuit.

Extracorporeal circulation is and has been a routine procedure in the operating room for several years. An important component in the extracorporeal blood circuit is a heat exchanger used to lower the temperature of the blood prior to and during a surgical procedure and subsequently rewarm the blood to normal body temperature. The cooled blood induces a hypothermia which substantially reduces the oxygen consumption of the patient. The published literature indicates that the oxygen demand of the patient is decreased to about one-half at 30"C, one-third at 250C and one-fifth at 200C. Light (33 to 35"C), moderate (26 to 32"C), and deep (20"C and below) hypothermia are commonly used in clinical practice. Hypothermia is used to protect the vital organs including the kidneys, heart, brain and liver during operative procedures which require interrupting or decreasing the perfusion.

A number of different structural configurations for heat exchangers have been used in the extracorporeal blood circuit including hollow metal coils, cylinders and plates through which a heat transfer fluid (typically water) is circulated. A survey of a number of different types of heat exchangers used in extracorporeal circulation is included in the book entitled "Heart-Lung Bypass" by Pierre M. Galletti, M.D. et al, pages 165 to 170.

Notwithstanding the plurality of different types of heat exchanger configurations which have been used in the past there remains a need for a safe highly efficient heat exchanger design which is simple to use and yet inexpensive enough to be manufactured as a disposable item. Thus, it is important that there not be any leakage of the heat transfer fluid into the blood. This fluid is typically circulating water flowing from plumbing fixtures located in the operating room. Certain of the heat exchangers commonly used today for clinical bypass operations have an upper pressure limit which is sometimes lower than the water pressures obtainable in the hospital operating room. The person who connects up the heat exchanger must therefore be very careful to never apply the full force of the water pressure through such a heat exchanger. Failing to take this precaution, or an unexpected increase in water pressure, could cause a rupture within the heat exchanger resulting in contamination of the blood flowing through the blood oxygenator.

It is also important that the heat exchanger must have a high performance factor in order to reduce to a minimum the time required to lower the temperature to induce hypothermia and subsequently raise the blood temperature to normal. Some physiological degradation of the blood occurs after a patient is connected only a few hours to any of the bubble oxygenators presently in use. Therefore, time saved in cooling and rewarming the blood is of direct benefit to the patient and also gives the surgeon additional time to conduct the surgical procedure if necessary.

In the complete specification of our United Kingdom Patent No. 1,536,625 we have claimed inter alia a heat exchanger apparatus for an extracorporeal blood circuit, said heat exchanger comprising a chamber through which the blood is circulated, and tubular heat transfer means positioned in said chamber for regulating the temperature of said blood, said heat transfer means having at least one substantially continuous rib extending helically along its length providing at least a portion of a wall for at least one continuous flute passage along the exterior surface of said heat transfer means, said flute passage being considerably longer than the length of said heat transfer means, the interior of said rib being hollow and in communication with the interior of said heat transfer means, the periphery of said rib being located in contact with or closely proximate to surfaces defining a flow space within said chamber so that substantially all of said blood flows in contact with the external surface of said heat transfer means through a plurality of restricted area, extended length flow paths around the exterior of said heat transfer means provided by said flute passage in combination with said surfaces, with a resulting relatively long residence time of the blood in contact with the exterior of said heat transfer means, said heat transfer means having heat transfer fluid inlet and outlet means.

According to the present invention there is provided a heat exchanger for an extracorporeal blood circuit, comprising a chamber through which blood is circulated and tubular heat transfer means positioned in said chamber for regulating the temperature of said blood, said heat transfer means having heat transfer fluid inlet and outlet means and hollow rib means other than continuously helical along its length, the periphery of said rib means being located in contact with or closely proximate to surfaces defining a flow space within said chamber so that substantially all of said blood flows in contact with the external surface of said tubular heat transfer means through a plurality of restricted area, extended length flute passages around the exterior of the heat transfer means provided by said hollow rib means in combination with said surfaces with a resulting relatively long residence time of the blood in contact with the exterior of said heat transfer means.

The hollow rib means can take the form of a plurality of discrete hollow annular ribs disposed along the length of the heat transfer means which is a fluid conduit or tube. This tube in turn is formed in an overall helical configuration and mounted between an inner cylindrical column extending within the helically configured tube and an outer cylindrical shell. Both the column and the shell are sized such that peripheral portions of the ribbing are in contact with or are closely proximate to the exterior wall of the column and the interior wall of the cylindrical shell. In use a heat transfer fluid is flowed through the tube and blood is flowed in a counterflow direction over the exterior surface of the ribbed tube.

The combination of the hollow rib means and the contacting surfaces of the cylinder and chamber confine the flow of blood substantially within paths of restricted area and extended length provided by the ribbing.

A heat exchanger embodying the present invention enjoys several significant advantages.

Thus, its performance factor is very high due to the long residence time of the blood the high conductivity of the heat exchange tube, the counterflow operation, and high flow rate of the heat transfer fluid through the ribbed tube.

Heat exchangers embodying the present invention can have the reliability necessary for routine use in open heat surgery and other procedures utilizing extracorporeal circulation.

The metal heat transfer fluid tube is an integral member which may be completely tested, both before and after assembly into the blood chamber, for leaks under substantially higher fluid pressures than are ever encountered in an operating room environment. The integral nature of the heat exchange tube also provides an important advantage in that only the ends of the tube pass through the wall of the blood carrying chamber, thus minimizing the number of openings in the chamber which must be hermetically sealed. Moreover, no connections need to be made to the tube within the blood chamber since a heat transfer fluid inlet and heat transfer fluid outlet are provided by the ends of the tube extending out from the chamber. Any leakage at the connection of the heat exchanger tube and the fluid supply conduit will merely leak water or other heat transfer fluid external of the blood chamber.

The ribbed heat exchanger tube may be mounted within a blood chamber separate from a blood oxygenator or may be incorporated integral with a blood oxygenator, e.g., in the venous side within the blood-oxygen mixing chamber or in the outlet side within the defoaming chamber. In the embodiment described below in which the heat exchanger is incorporated within the mixing chamber of a bubble oxygenator the flow of the blood and blood foam through the lengthy paths of restricted cross-sectional area contributes to the blood-gas transfer process. Moreover, this flow of blood and blood foam can effect substantially all of the blood-gas transfer process.

The heat exchangers of this invention are sufficiently economical in terms of material and manufacturing costs so that it is disposed of after use, thus avoiding the problems and cost of sterlization in the hospital. In addition, the heat exchangers constructed in accordance with this invention may be made biologically inactive and compatible with human blood.

The present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a vertical elevational sectional view along the line 1-1 of Figure 2 of a blood oxygenator having an internal heat exchanger in accordance with the present invention; Figure 2 is a front elevational view of the embodiment of Figure 1; Figure 3 is a fragmentary rear elevational view of the defoamer section of the embodiment of Figure 1.

Figure 4 is a horizontal partially sectional view taken along line 4-4 of Figure 1; Figure 5 is a bottom plan view taken along line 5-5 of Figure 1, of the preferred embodiment of a blood oxygenator and Figure 6 is a vertical elevational partial sectional view of the oxygenating chamber of the embodiment of Figure 1 incorporating a modified form of the heat transfer fluid tube.

A blood oxygenator incorporating an integral heat exchanger is shown in Figures 1 to 5.

A paediatric blood oxygenator comprises a bubble oxygenating chamber 240 formed by a pair of mating plastic shells, front shell 242 and rear shell 244, each including a flat peripheral flange 246 and 248 which are joined together to form a complete cylindrical shell 250. Shell halves 242 and 244 are advantageously formed by vacuum forming polycarbonate plastic, and may be advantageously bonded together with ethylene dichloride.

Rear shell half 244 includes a blood outlet opening 252 having an integral rearwardly extending, tapered neck 254, which is generally elliptical in cross section. Front shell half 242 includes an upper side opening 256 and a lower side opening 258, each having an integral forwardly extending cylindrical boss 260 through which extend the respective ends of a single helically ribbed heat transfer fluid tube 262. The inside wall of these extending cylindrical bosses 260 and the proximate exterior surface of the heat exchanger tube 262 are bonded together to effect a hermetic seal.

Assembly is effected by inserting an extruded cylindrical interior column 264 within the helically formed ribbed tube 262. Both ends of the column 264 are hermetically sealed by end caps 265. The column 264 and the tube 262 are placed in the front shell half 242 such that the two ends of the heat exchange tube 262 extend through the openings 256 and 258.

The mating shell half 244 is placed over the heat exchanger tube 262 and the mating flanges 246 and 248 are bonded together to provide a completely sealed, cylindrical shell unit 250.

The peripheral portions of the ribs 266 of the tube 262 are closely proximate to and advantageously in contact with both the interior wall of the chamber 240 and the exterior wall of the column 264.

The mating shells 242 and 244 are necked in at the bottom to form a passage 268 defined by a hollow cylindrical neck 270. The neck 270 snugly mates with the exterior wall of a hollow, injection moulded cylindrical member 272. As shown, a small, annular groove 274 may be formed in the neck 270 to accommodate additional bonding material to provide a hermetic seal between the cylindrical shell unit 250 and the member 272.

The cylindrical member 272 includes one or more blood inlet ports 276, one such port 276 being connected to the extracorporeal blood circuit by a flexible venous blood conduit (not shown).

An end cap 278 is secured to and closes off the bottom of the cylindrical member 272. In the centre of the cap 278 and extending from the bottom thereof is an oxygen inlet port 280 which is attached to a flexible oxygen line (not shown). The oxygen entering the inlet port 280 is caused to form a plurality of oxygen bubbles by means of a sparger 282. These bubbles flow through the venous blood entering the cylindrical member 272. The sparger 282 fills the entire cross-section of the cylindrical member 272, and rests on an annular support 283. The sparger 282 is sealed around its periphery to the inner wall of the cylindrical member 272. Advantageously, the sparger 282 will be selected to produce small sized oxygen bubbles, e.g., of the order of 0.3 cm or smaller, for most efficient oxygenation in this embodiment.

The venous blood and oxygen bubbles then rise into the oxygenating chamber 240, where they contact the exterior of the tube 262. The combination of the tube ribbing 266 and the contacting surfaces of the cylinder 264 and the chamber 240 confines the flow of blood and oxygen bubbles substantially within paths of restricted area and extended length provided by the ribbing, thus providing a tortuous path for the blood and oxygen bubbles which effect a medically adequate transfer of oxygen into the blood and removal of carbon dioxide from the blood, without additional mixing means in the oxygenator fluid path, either upstream or downstream of the ribbed tubing.

The arterialized blood, in the form of blood and blood foam, then flows out of the oxygenating chamber through the outlet opening 252 and the tapered, elliptical cross-section neck 254 into a defoamer chamber 284.

The neck 254 communicates with an opening 286 in a flat vertical plate 288 forming a side portion defoamer chamber top cap 290, which may advantageously be formed by injection moulded plastic polycarbonate. The opening 286 in turn communicates with a fluid channel member 292, located within the top cap 290, which empties the arterialized blood into an annular defoamer inlet chamber 294.

Sealingly fixed to the underside of the top cap 290 is an extruded hollow cylindrical cascade column 296 which runs through a central axial void 298 in a tubular defoamer 300.

The defoamer 300 is contaned within a cylindrical injection moulded, polycarbonate plastic defoamer shell 302 which is bonded hermetically around its upper periphery to a downwardly extending peripheral flange 304 depending from the top cap 290. The bottom of the defoamer shell 302 is sealed by a vacuum-formed, polycarbonate plastic bottom cap 306, which includes an inner upwardly concave portion forming an annular seat 308 for a defoamer lower support member 309.- At the inner periphery of the annular seat 308, the bottom cap extends still further upwardly to form a circular, centrally raised portion 310.

The support member 309 bends appropriately so as to contact the inner surface of the raised portion 310, forming a circular centrally raised platform 311, the inner surface of which closes the bottom portion of the axial void 298 and seals the bottom of the cascade column 296.

The defoamer 300 shown is essentially as described in United States Patent Application Serial No. 655,039 filed on February 3, 1976 (United States Patent Specification No.

4067696) (to which our United Kingdom Patent Specification No 1570517 substantially corresponds) consists of an annular tube of reticulated porous sponge material, such as polyurethane foam, and is enclosed in a filter cloth 312 of nylon tricot or dacron mesh. The filter cloth 312 is secured by nylon cable ties 314 to an annular upper flange 315 which extends upwardly from an annular defoamer upper support member 316, which, in turn, is bonded to a downwardly extending cylindrical boss 317 in the top cap 290; and to a lower cylindrical flange 318 extending downwardly from the defoamer lower upport member 309.

Both the cloth 312 and the defoamer 300 are advantageously treated with a suitable antifoam compound.

The arterialized blood and blood foam flow from the inlet chamber 294 into the annular axial void 298 through an annular inlet 320. The majority of liquid blood entering the void 298 is guided by the column 296 to fill up the bottom of the void 298. This liquid blood flows through the defoamer 300, as generally shown by arrows 322. The blood and blood foam enter at the upper end of the defoamer 300 so that a substantial portion of the interior wall surface of the defoamer 300 is contacted by the blood foam. As a result, a substantial portion of the defoamer 300 is used to separate the blood foam from the entrapped gas such that the foam collapses and fluid blood flows into an annular reservoir 324 between the defoamer 300 and the interior wall of the defoamer chamber 284 and settles at the bottom of the chamber 284 and in the bottom cap 306. The entrapped gas, primarily oxygen and CO2, which the defoamer separates out pass out of the chamber 284 through a vent 326 located in the upper end of the chamber at the juncture of the top cap 290 and the cylindrical shell 302. As a result, only whole liquid blood collects in the reservoir 324, after having been cleansed of any particulate matter, such as blood fragments and microemboli, by the filter cloth 312. The oxygenated, filtered whole blood then passes through one or more outlet ports 328 located in the lower-most portion of the bottom cap 306 and is returned to the patient by a flexible arterial conduit (not shown).

The defoamer chamber 284 advantageously includes externally applied indicia 330 of the volume of blood contained therein. The oxygenator may also include one or more externally threaded venous blood sampling ports 332 proximate the venous blood inlet 276, and one or more arterial blood sampling ports 334 in the lower portion of the defoamer chamber 284. One or more priming ports 336 may also be provided in the top cap 290. Each of the ports 332, 334, and 336 is conveniently sealed by screw caps 338.

Figure 6 shows a modification of the embodiment of Figures 1 to 5 wherein the helically ribbed heat transfer fluid tube is replaced by a tube 340 having discrete spaced annular hollow ribs 342 formed in the wall of the tube along its length. As with the helically ribbed tube 262 shown in Figures 1 to 5, the peripheral portions of the annular ribs 342 are closely proximate to and advantageously in contact with both the interior wall of the chamber 240 and the exterior wall of the column 264. These discrete spaced annular ribs provide a plurality of discontinuous flute passages around the tube which, when their individual lengths are added, total a distance considerably longer than the length of the fluid conduit.

The combination of the ribs 342 and the contacting surfaces of the column 264 and the chamber 240 confine the flow of blood and oxygen bubbles substantially within extended length, restricted area paths and provide a thorough mixing of the blood and oxygen bubbles, thereby effecting a medically adequate transfer of oxygen into the blood and CO2 from the blood without additional mixing means. Except for the configuration of the ribbing on the tube, the embodiment illustrated in Figure 6 is in all other respects identical to that illustrated in Figures 1 to 5.

The helically-ribbed heat transfer fluid tube 262, shown in Figures 1 to 5, is advantageously formed of a continouus length of aluminium tubing with the exterior coated with a polyurethane coating as described in our United Kingdom Patent Specification No.

1536625 or, alternatively, the exterior surfaces are electrolytically oxidized, or anodized, to form a "hard anodized" coating, as disclosed in the complete specification of our copending Patent Application No. 22715/78 (Serial No. 1604955).

The annular-ribbed heat transfer fluid tube 340, shown in Figure 6 may likewise be formed of anodized or polyurethane coated aluminium. Alternatively, it may be formed of brass or bronze tubing having a blood compatible coating.

The preferred embodiment of Figures 1 to 6 is suited for use in both adult and paediatric applications. It is advantageous to construct the oxygenating chamber with as small a volume as possible, consistent with the requirements for heat and gas transfer so as to minimize the amount of blood contained in the oxygenating chamber during use.

By way of specific example, a paediatric oxygenator with an integral heat exchanger constructed in accordance with the preferred embodiment comprises an oxygenating chamber 240 having an inside diameter of approximately two inches, and contains a central cylindrical column 264 having an outside diameter of approximately one inch. The heat exchanger tube 262 is formed of half-inch outside diameter aluminum tubing, which, when twisted to form the helical ribbing, has an outside diameter of 0.490 inches from ridge to ridge of the ribs and 0.340 inches from groove to groove between the ribs. The wall thickness of the tube 262 is approximately 0.014 inches. The tubing is anodized, as hereinabove described, and the anodized coating adds approximately 0.001 inches to the wall thickness and approximately 0.002 inches to the respective outside diameter measurements. When completely assembled, and incorporating the heat exchanger tube 262 and the central column 264, the oxygenating chamber has a capacity of approximately 100 millilitres. The adult sized unit is larger in scale with a capacity of approximately 450 millilitres.

In constructing the oxygenating chamber, it is necessary to coil the tube 262 tightly so as to have the peripheral portions of the ribbing come into contact with, or at least be closely proximate to, the exterior surface of the central column 264. The hollow ribbing on the tube enables the tube to be so coiled without kinking. Any kinking would be quite deleterious since it would result in obstructed fluid flow and also a weakened wall structure, which would make the tube prone to leaks. This ability to be tightly coiled displayed by the ribbed tubing makes it possible an oxygenating chamber having the relatively small capacity of 100 millilitres, and such a capacity has been found to be particularly advantageous in pediatric applications.

Tests conducted on both adult and paediatric units constructed in accordance with this embodiment show a medically adequate transfer of oxygen into the blood and removal of carbon dioxide therefrom. In general. tests conducted on identical units with and without the mixing material of the prior embodiments show that to achieve a given level of oxygenation compared to these previous described embodiments, a higher level of oxygen flow rate is required for a given blood flow rate. In addition these tests show that the level of oxygenation increases with an increase of the blood flow rate, e.g., at a blood flow of 6 litres per minute. the oxygen gas content of the arterialized blood output from the embodiment of Figures 1 to 5 with a 1:1 oxygen to blood ratio closely approaches the oxygen gas content achieved with the prior embodiments, whereas at a blood flow rate of 2 litres per minute, a ratio of greater than 1:1 is required to achieve oxygen gas content levels which are comparable to those achieved with the prior embodiments as disclosed in Figures 1, 2, 3, 4, 8 and 9 of our Patent Specification No. 1,536625.

By way of specific example, the gas transfer data obtained during a specific test are listed in Table 1. This test was conducted on the Ist of November 1977, on a female Suffolk lamb weighing 26 kg which underwent a six-hour, partial veno-arterial cardiopulmonary bypass using the oxygenator of the preferred embodiment. The data indicate efficient oxygenation with CO2 removal in an oxygenator having an integral heat exchanger constructed in accordance with the present invention, and lacking any additional mixing structure in the oxygenating chamber. The oxygenator used in these tests used a heat exchanger of anodized aluminum as previous described.

TABLE I Venous Parameters Q2 Transfer CO2 Transfer O2 Hemoglobin Q Volume Volume

Satur- (gmHb/ V:Q (blood) #O2 Content #CO2 Content ation P-CO2 100 ml Oxygen Flow flow (mlO2/ (mlCO2/ #P-O2 (%) pH (torr) blood) Blood Flow (1/min) 100 ml blood) 100 ml blood) (torr) 71.6 7.58 32 9.8 .37 1.5 3.41 1.85 90 67.6 7.50 38 10.3 .37 1.5 3.96 2.34 64 62.1 7.46 48 10.3 .37 1.5 4.55 NRV 52 56.5 7.46 43 8.8 .50 1.5 5.10 NRV 86 52.1 7.43 43 9.1 .50 1.5 5.21 2.38 45 48.1 7.49 41 8.7 1.0 1.5 5.89 4.76 171 40.7 7.47 43 8.8 1.0 0.5 6.82 4.91 178 66.6 7.49 41 9.1 .68 2.2 4.05 3.72 280 65.5 7.48 43 9.5 .30 2.2 4.03 1.35 93 No recorded vent gas (recording equipment failure).

A number of factors contribute to the excellent heat transfer efficiency of the present invention and include the following: 1. The combination of the flutes of the heat transfer fluid tube and proximate inner and outer surface walls of the blood chamber provides a plurality of continuous, restricted area flow paths offering substantially uniform flow impedance to the blood and blood foam. As a result, the blood and blood foam have a long residence time in the heat exchanger.

Moreover, this structure avoids areas of stagnation which otherwise hinder heat transfer from the blood and are also undesirable from a physiological standpoint. In the tests conducted to date on the embodiments of Figures 1 to 5, the blood and blood foam was observed to be in constant circulation through these restricted flow paths and having extensive contact with and long residence time with the heat exchanger tube. Only minimal areas of stagnation were evident.

2. The extensive hollow ribs of the heat transfer fluid tube provide a substantial surface area for transferring heat from the heat transfer fluid to the blood and blood foam. The tubes used in the above-described embodiments typically have an external surface area of the order of 2()() to 300 square inches. The surface area of the tubes used in the paediatric units is of the order of 100 square inches.

3. Although the direction of fluid flow through the heat exchanger tube may be in either direction, the heat transfer performance is optimized by operating as a counterflow exchanger, i.e., in the manner described above wherein the blood and heat transfer fluid flow in generally opposite directions.

4. The wall thickness of the ribbed tube may be relatively thin, e.g. O.I)14 to 0.016 inch, so as to further improve its heat transfer properties. As disclosed in the complete specification of our copending patent application No. 22715/78 (Serial No. 16()4955), very high thermal conductivity can be achieved using an anodized aluminum tube. The polyurethane coated aluminum tubes referred to above also have a high thermal conductivity, notwithstanding that the polyurethane coating reduces the overall thermal conductivity of the aluminum tube by some 15 percent.

5. The ribbed heat exchanger tube has a sufficiently large average internal diameter, e.g., approximately 0.5 inch, for providing a high rate of flow of the heat transfer fluid, e.g.

21 litres/minute of water. The average inside diameter of the tubes used in paediatric units is approximately 0.34 inch and accommodates a proportionately lower flow rate.

Although the integral heat exchanger embodiments described above have incorporated the heat exchanger within the oxygenation chamber, it will be apparent to those knowledgeable in the art that the significant features of the heat exchanger tube which contribute to its high heat transfer efficiency will be beneficial in other locations within the blood oxygenator. Thus, by way of specific example, the ribbed heat transfer fluid tube may be located within the defoamer column such that the blood flowing within or through the defoamer member is caused to circulate through the flutes of the heat exchanger tube.

The integral nature of the heat exchanger tube also provides an important advantage in providing an effective seal for preventing any possible contamination of the blood by the heat transfer fluid. Thus, in the present invention, the heat exchanger tube is advantageously constructed as a continuous member with no connection being made to the tube within the blood chamber. Any leak at the connection of the heat exchanger tube and the flexible water or other heat transfer fluid conduit will merely leak water or other fluid external of the blood chamber.

In

Claims (16)

WHAT WE CLAIM IS:

1. A heat exchanger for an extracorporeal blood circuit, comprising a chamber through which blood is circulated and tubular heat transfer means positioned in said chamber for regulating the temperature of said blood, said heat transfer means having heat transfer fluid inlet and outlet means and hollow rib means other than continuously helical along its length, the periphery of said rib means being located in contact with or closely proximate to surfaces defining a flow space within said chamber so that substantially all of said blood flows in contact with the external surface of said tubular heat transfer means through a plurality of restricted area extended length flute passages around the exterior of the heat transfer means provided by said hollow rib means in combination with said surfaces with a resulting relatively long residence time of the blood in contact with the exterior of said heat transfer means.

2. A heat exchanger as claimed in claim 1, wherein said hollow rib means is a plurality of discrete hollow annular ribs disposed along the length of said tubular heat transfer means.

3. A heat exchanger as claimed in claim 2, wherein said annular ribs provide a plurality of annular flute passages around the tube which total a distance longer than the length of the tubular heat transfer means.

4. A heat exchanger as claimed in claims 2 or 3, wherein said chamber has first and second sealed openings through which extend the opposite ends of said heat transfer means whereby connections to said heat exchange fluid inlet and outlet means are made outside said chamber.

5. A heat exchanger as claimed in any one of claims 1 to 4, wherein said heat transfer means is a continuous length of metal tubing having said hollow rib means formed integrally therein.

6. A heat exchanger as claimed in claim 5, wherein said heat transfer tubing has an overall helical configuration.

7. A heat exchanger as claimed in claim 6, wherein a centrally located cylindrical column is located within said chamber and said helically configured heat transfer tubing is located between said column and the interior wall of said chamber so that said exterior wall of said column is located in contact with or closely proximate to peripheral portions of said rib means.

8. A heat exchanger as claimed in any of claims 1 to 7, wherein said chamber comprises two halves mated along a seam, said halves being located over and surrounding said tubular heat transfer means and bonded together to form a hermetic seal along said seam.

9. A heat exchanger as claimed in claim 8, wherein one of said chamber halves includes first and second openings through which extend the opposite ends of said tubular heat transfer means.

10. A heat exchanger as claimed in any preceding claim when dependent on claim 2 or 3, in which the tubular heat transfer means is of brass or bronze with a blood compatible exterior coating.

11. A heat exchanger as claimed in any preceding claim, embodied in a blood oxygenator.

12. A heat exchanger as claimed in claim 11, in which the chamber is the oxygenator chamber of the blood oxygenator and includes means for introducing blood and bubbles of oxygen into said chamber for forming blood foam within said chamber for oxygenating the blood by transferring oxygen into the blood and removing carbon dioxide from the blood.

13. A heat exchanger as claimed in claim 12, in which combination of said hollow rib means and the surfaces defining the flow space within said chamber whereby the blood and oxygen bubbles flow through said plurality of restricted area, extended length flute passages effects substantially all of the transfer of oxygen into the blood and the removal of carbon dioxide from the blood without additional mixing means in said oxygenating chamber either upstream or downstream of said flute passages.

14. A heat exchanger as claimed in claim 12, in which the combination of said hollow rib means and the surfaces defining the flow space within said chamber and forming the plurality of restricted area, entended length flute passages effects substantially all of the transfer of oxygen into the blood and the removal of carbon dioxide from the blood while the blood and blood foam are in contact with said hollow rib means and said surfaces.

15. A heat exchanger for an extracorporeal blood circuit, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Figure 6 of the accompanying drawings.

16. A heat exchanger as claimed in claim 15, embodied in a blood oxygenator.