Abstract:
Apparatus for oxygenating and pumping blood includes a housing defining a blood flow path including, in series, a gas collection plenum, a pump space and a blood oxygenation element. A pump disposed in the pump space is configured to draw blood from the gas collection plenum and propel blood from the pump space through a heat exchanger and the blood oxygenation element. The heat exchanger includes a heat exchange plate and a coolant space.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of prior application Ser. No. 10/434,887, filed May 9, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to an extracorporeal blood handling system with an integrated heat exchanger.  
       BACKGROUND OF THE INVENTION  
       [0003]     For more than thirty years, vascular diseases have been treated using open surgical procedures. In 1999 alone, 753,000 open-heart procedures, including coronary artery bypass grafting (CABG), valve replacements, and heart transplants, were performed. During a typical CABG procedure, a sternotomy is performed to gain access to the pericardial sac, the patient is put on cardiopulmonary bypass (CPB), and the heart is stopped using a cardioplegia solution.  
         [0004]     Generally, previously-known CPB is accomplished by constructing an extracorporeal blood handling system including, inter alia, a venous line, a venous reservoir, a centrifugal or roller pump that perfuses blood through the extracorporeal circuit and the patient, an oxygenator for oxygenating the blood, an arterial line for returning oxygenated blood to the patient, and an arterial filter located in the arterial line.  
         [0005]     Many extracorporeal blood handling systems also include a heat exchanger. Heat exchangers are generally used to cool the blood and lower the patient&#39;s body temperature during surgery. Reducing body temperature significantly lowers the demand for oxygen by the patient&#39;s vital organs. The blood is heated near the end of surgery to raise the body temperature.  
         [0006]     Recently, the development of minimally invasive techniques for cardiac bypass grafting, for example, by Heartport, Inc., Redwood City, Calif., and CardioThoracic Systems, Inc., Cupertino, Calif., have placed a premium on reducing the size of equipment employed in the sterile field. Whereas open surgical techniques typically provide a relatively large surgical site that the surgeon views directly, minimally invasive techniques require the placement of endoscopes, video monitors, and various positioning systems for the instruments. These devices crowd the sterile field and can limit the surgeon&#39;s ability to maneuver.  
         [0007]     At the same time, however, the need to reduce priming volume of the oxygenator and pump, and the desire to reduce blood contact with non-native surfaces has increased interest in locating the oxygenator and pump as near as possible to the patient.  
         [0008]     In recognition of the foregoing issues, some previously known extracorporeal blood handling systems have attempted to miniaturize and integrate components including an oxygenator, heat exchanger and pump.  
         [0009]     One problem with previously known extracorporeal blood handling systems is the difficulty in designing an extracorporeal blood handling system including an integrated heat exchanger having improved heat transfer efficiency.  
         [0010]     Another problem with previously known extracorporeal blood handling systems is that the inclusion of an integrated heat exchanger necessitates additional priming volume.  
         [0011]     A further problem with previously known extracorporeal blood handling systems is the difficulty in designing an extracorporeal blood handling system having an integrated heat exchanger that is integrated in such a way as to minimize the overall size of the extracorporeal blood handling system.  
         [0012]     In view of the aforementioned limitations, it would be desirable to provide an extracorporeal blood handling system including an integrated heat exchanger having improved heat transfer efficiency.  
         [0013]     It also would be desirable to provide an extracorporeal blood handling system including an integrated heat exchanger that does not require additional priming volume.  
         [0014]     It would be also be desirable to provide an extracorporeal blood handling system including an integrated heat exchanger that is integrated in such a way as to minimize the overall size of the blood handling system.  
         [0015]     It further would be desirable to provide an extracorporeal blood handling systems wherein the integrated heat exchanger provides dual functionality as a blood filter and a heat exchanger.  
       SUMMARY OF THE INVENTION  
       [0016]     In view of the foregoing, it is an object of the present invention to provide an extracorporeal blood handling system including an integrated heat exchanger having improved heat transfer efficiency.  
         [0017]     It is another object of the present invention to provide an extracorporeal blood handling system having an integrated heat exchanger that is integrated in such a way as to minimize the overall size of the extracorporeal blood handling system.  
         [0018]     It is an additional object of the present invention to provide an extracorporeal blood handling system including an integrated heat exchanger that does not require additional priming volume.  
         [0019]     It is a further object of the present invention to provide an extracorporeal blood handling system including an integrated heat exchanger that provides dual functionality as a blood filter and a heat exchanger.  
         [0020]     These and other objects of the present invention are accomplished by providing an extracorporeal blood handling system having air removal, blood filtration, oxygenation, pumping and heat exchange capabilities in a low volume integrated housing. The apparatus comprises a housing defining a blood flow path including, in series, a gas collection plenum a pump space and a blood oxygenation element. A pump is disposed in the pump space, and is configured to draw blood from the gas collection plenum and to propel the blood from the pump space through the blood oxygenation element.  
         [0021]     In a first family of embodiments, housing is configured so that a heat exchanger disposed in the blood flow path between the gas collection plenum and the pump space. In a second family of embodiments, the heat exchanger is disposed within the housing in a compartment on the outlet side of the pump space.  
         [0022]     In a first embodiment, the heat exchanger comprises a heat exchange surface and a coolant space, wherein the heat exchange surface separates the coolant space from the pump space and provides a conductive medium through which coolant within coolant space can transfer heat to the blood in the pump space. Advantageously, since heat is transferred to blood within pump space, no additional priming volume is required to prime the apparatus. Preferably, the coolant space includes a plurality of coolant channels formed by baffles, wherein the coolant channels are configured to distribute coolant over the heat exchange plate and increase contact time between the coolant and heat exchange surface, thereby improving heat exchange efficiency.  
         [0023]     In a second embodiment, the heat exchanger preferably comprises a multiplicity of hollow tubes or fibers disposed within the gas collection plenum. The tubes serve as both a heat exchanger and the first stage of a progressive blood filter that filters air and particulate matter from the blood. Blood is drawn by the pump through the lumens of the tubes, while coolant is passed circumferentially about the exterior of the tubes.  
         [0024]     In an alternative family of embodiments, the apparatus comprises a housing defining a blood flow path including, in series, a gas collection plenum, a pump space, a heat exchanger and a blood oxygenation element. A pump disposed in the pump space draws blood from the gas collection plenum and propels it from the pump space through the heat exchanger and the blood oxygenation element. The heat exchanger preferably comprises a bellows including a corrugated wall having a blood-contacting surface and a coolant-contacting surface. The wall provides a conductive medium through which coolant adjacent to the coolant-contacting surface can transfer heat to blood adjacent to the blood contacting surface. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     The above and other objects and advantages of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:  
         [0026]      FIG. 1  is a schematic view of a preferred extracorporeal circuit suitable for use with the heat exchanger of the present invention;  
         [0027]      FIGS. 2A and 2B  are, respectively, perspective and exploded views of a preferred blood processing component suitable for use with the heat exchanger of the present invention;  
         [0028]      FIG. 3  is a side-sectional view of the blood processing component of  FIGS. 2 and 3 ;  
         [0029]      FIGS. 4A and 4B  are, respectively, perspective and cross-sectional views of a filter element of the blood processing component of  FIG. 3 ;  
         [0030]      FIG. 5  is a perspective view of a preferred blood handling system suitable for use with the heat exchanger of the present invention;  
         [0031]      FIGS. 6A and 6B  are, respectively, representative screens depicting the display of parameters monitored and/or controlled by the blood handling system of  FIG. 5 ;  
         [0032]      FIG. 7  is a side-sectional view of an embodiment of a first family of integrated blood processing components that include a heat exchanger disposed on the inlet-side of the pump;  
         [0033]      FIG. 8  is an enlarged side-sectional view showing the heat exchanger of  FIG. 7 ;  
         [0034]      FIG. 9  is a top perspective view of the heat exchanger of  FIG. 7 ;  
         [0035]      FIG. 10  is an exploded view of the heat exchanger of  FIG. 7 ;  
         [0036]      FIG. 11  is a perspective view of an alternative embodiment of the an integrated blood processing component of the present invention;  
         [0037]      FIG. 12  is an exploded view of the blood processing component of  FIG. 11 ;  
         [0038]      FIG. 13  is a side-sectional view of the blood processing component of  FIG. 11 ;  
         [0039]      FIG. 14  is a perspective view of a heat exchanger suitable for use with the blood processing component of  FIG. 11 ;  
         [0040]      FIG. 15  is a perspective view of an alternative heat exchanger suitable for use with the blood processing component of  FIG. 11 ;  
         [0041]      FIG. 16  is a side-sectional view of a second preferred embodiment of an integrated blood processing component including a heat exchanger according to the present invention;  
         [0042]      FIG. 17  is an exploded view of the heat exchanger of  FIG. 16 ;  
         [0043]      FIG. 18  is a magnified view of the wall of the heat exchanger of  FIG. 16 ;  
         [0044]      FIG. 19  is a perspective view of the heat exchanger core of the heat exchanger of  FIG. 16 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     Overview of a Preferred Blood Handling System  
       [0045]     Referring to  FIG. 1 , a preferred extracorporeal blood handling system  10  suitable for use with the heat exchanger of the present invention is described. Extracorporeal blood handling system  10  is designed to maintain a patient on full or partial bypass support, for example, during a coronary artery bypass graft procedure or mitral valve repair procedure, in either a full-bypass or beating heart mode of operation.  
         [0046]     Extracorporeal blood handling system  10  includes an extracorporeal blood circuit  11  having a perfusion circuit comprising venous line  12 , perfusion line segments  13   a,    13   b  and arterial line  14 , and a priming circuit comprising line  16 , priming line  17 , and segments  18   a  and  18   b.  The ends of perfusion line segments  13   a,    13   b  are shown extending into the sterile field as they would appear during use, where they are coupled to venous and arterial cannulae respectively.  
         [0047]     Extracorporeal blood circuit  11  illustratively includes pinch clamps  19  and sampling manifolds  20  disposed on various of the lines. Quick-disconnect couplings  21  are provided at the junctions of venous line  12  and venous segment of perfusion line  13   a  and arterial line  14  and arterial segment of perfusion line  13   b.  These couplings  21  permit venous line  12  to be directly coupled to arterial line  14  during priming. Quick-disconnect coupling  22 , provided in line  16 , permits the inclusion of additional optional elements when the priming circuit is used for recirculation.  
         [0048]     Extracorporeal blood handling system  10  further includes an integrated blood processing component  31  coupled to a drive unit  32  and controller  33 . In addition, the blood handling system  10  includes a gas removal system including sensors  25 - 27 , and valve  36  coupled to suction source  34  via line  35 . The sensors  25 - 27 , valve  36  and drive unit  32  preferably are electrically coupled to controller  33  so that controller  33  regulates operation of valve  36  and drive unit  32  in response to output of the sensors  25 - 27 . As explained in greater detail hereinafter, the gas removal system of the present invention removes air and other gases from extracorporeal blood circuit  11  and blood processing component  31  during priming and operation of the bypass system.  
         [0049]     Referring now to  FIGS. 2A, 2B  and  3 , integrated blood processing component  31  provides in a single disposable unit a blood oxygenator, blood pump, and blood filter, and optionally, a heat exchanger. Blood processing component  31  includes housing  40  having blood inlet  41 , blood outlet  42 , recirculation outlet  43 , gas inlet port  44 , gas outlet port  45  and gas removal port  46 . Blood outlet  42  and recirculation outlet  43  are disposed from blood outlet manifold  47 , which is located diametrically opposite blood inlet manifold  48  on housing  40 . Blood processing component  31  preferably includes tabs  49  or other means for coupling blood processing component  31  to reusable drive unit  32 .  
         [0050]     Referring to  FIG. 3 , housing  40  comprises a series of compartments, including: gas collection plenum  50 , central void  51 , upper gas plenum  52 , annular fiber bundle compartment  53 , lower gas plenum  54  and pump space  55 . In a preferred embodiment, central void  51  includes a larger diameter upper portion and a smaller diameter lower portion that couples to pump space  55 .  
         [0051]     Gas collection plenum  50  encloses a gas removal/blood filter  56  disposed within upper portion of central void  51 . Filter  56  comprises generally conical, fluid impermeable upper wall  57  having outlet  80 , baffled support structure  58  and filter material  59 . Filter  56  causes gas entrained in blood introduced into the gas collection plenum to separate and collect in the upper portions of gas collection plenum  50 . Blood inlet  41  is displaced tangentially relative to the centerline of housing  40 , so that blood passing through blood inlet  41  into gas collection plenum  50  swirls around upper wall  57 .  
         [0052]     Upper wall  57  also preferably has a portion defining an interior chamber that communicates with the upper portion of gas collection plenum  50  through outlet  80 . This configuration allows any gas that passes through filter material  59  to escape through outlet  80  in upper wall  57  and be evacuated from gas collection plenum  50 . Advantageously, this feature facilitates rapid and easy priming of the blood processing component  31 . In addition, low pressure caused by swirling of blood about upper wall  57  permits air-laden blood to recirculate through opening  80  into gas collection plenum  50 .  
         [0053]     Filter material  59  comprises one or multiple layers of a screen-like material, and is mounted to baffled support structure  58 . Filter material  59  serves to exclude bubbles from the blood flow by maintaining the swirling action of the blood in the central void for a sufficient time to allow the bubbles to rise to the gas collection plenum. Because the blood circulates around the outside of gas removal/blood filter  56  in central void  51 , bubbles impinge against filter material  59  tangentially, and thus “bounce off.” Filter material  59  preferably also forms a first stage of a progressive blood filter that is distributed throughout the blood processing component, and may also serve to filter out relatively large particulate matter.  
         [0054]     As illustrated in  FIGS. 4A and 4B , support structure  58  forms a fluid impermeable cruciform structure  63  having longitudinal struts  61  and support rings  62 . Struts  61  serve as baffles to reduce swirling of blood once the blood has passed through filter material  59 .  
         [0055]     Referring again to  FIG. 3 , blood oxygenation element  70  is disposed within annular fiber bundle compartment  53 , and comprises a multiplicity of gas permeable fibers arranged in an annular bundle. As is well known in the art, the gas permeable fibers are potted near the upper and lower ends of the bundle so gas may pass through the interior of the fibers, while allowing blood to pass along the exterior of the fibers. The bundle of fibers has an upper potting region  71  that separates the blood flow region within the annular bundle from upper gas plenum  52 , and lower potting region  72  that separates blood flow region from the lower gas plenum  54 .  
         [0056]     Blood passing into annular fiber bundle compartment  53  from blood inlet manifold  48  flows through blood oxygenation element  70  and to blood outlet manifold  47 . The annular fiber bundle also provides some filtration of blood passing through blood processing component  31 , by filtering out particulate matter that has passed through filter material  59  employed in gas removal/blood filter  56 .  
         [0057]     The lower portion of central void  51  communicates with pump space  55 , in which pump  55   a  is disposed. In a preferred embodiment, pump  55   a  is a centrifugal pump including an impeller  75  having a plurality of vanes  76  and is mounted on shaft  77  via bearings  78 . Impeller  75  preferably comprises an injection-molded part that encloses a ferromagnetic disk, so that the disk may be magnetically coupled to drive unit  32  (see  FIG. 1 ). Blood flows through central void  51 , through a pump inlet  82  and into pump space  55 , where it is accelerated by impeller  75  and ejected via a pump outlet  83 , which includes curved ramp  79 . Ramp  79  serves to redirect radially outward blood flow from impeller to a longitudinal flow within blood inlet manifold  48 .  
         [0058]     In a preferred embodiment, oxygen is introduced into upper gas plenum  52  through gas inlet port  44  and passes through the interiors of the multiplicity of hollow fibers in blood oxygenation element  70 . Carbon dioxide, any residual oxygen, and any other gases exchanged through blood oxygenation element  70  exits into lower gas plenum  54  and are exhausted through gas outlet port  45 .  
         [0059]     Referring again to  FIG. 1 , and in accordance with the present invention, the extracorporeal blood handling system  10  also includes sensors  25 ,  26  and  27  that monitor system parameters. Sensor  25  monitors the level of gas or blood in gas collection plenum  50 . Sensor  26  detects the presence of gas in venous line  12 ; sensor  27  monitors the pressure in the venous line.  
         [0060]     Sensor  25  is configured to sense a parameter indicative of a level or volume of air or other gas, or detect the absence of blood, and preferably operates by a non-contact method. Suitable sensor methods include electrical-charge based, optical and acoustic methods. A resistive contact method also could be employed, in which a low electrical current is passed between adjacent electrodes only in the presence of blood.  
         [0061]     Sensor  25  preferably is a capacitance-type sensor that detects a change in electrical capacitance between the bulk of a liquid (in this case, blood or saline) and gas. Alternatively, sensor  25  may be optical in nature, and use a light source that has a wavelength that is minimally attenuated by blood. In this case, the light source is directed, at an oblique angle, through the blood towards a photodetector, and sensor  25  is positioned to detect the change in the refractive index of the blood (or saline prime) caused by the presence of air or other gases. In another alternative embodiment, sensor  25  may use an ultrasonic energy source and receiver to detect the presence of gas or absence of blood by the change in acoustic transmission characteristics.  
         [0062]     The output of sensor  25  is supplied to controller  33  (see  FIG. 1 ), which in turn regulates valve  36 . When sensor  25  outputs a signal indicating that gas is present in the extracorporeal blood handling system  10 , controller  33  opens valve  36 , thereby coupling gas collection plenum  50  to suction source  34 . Suction source  34  may be any suitable suction source such as a vacuum bottle, pump or standard operating room suction port. Once the gas is evacuated, and sensor  25  detects blood at an appropriate level, and changes its output so that controller  33  closes valve  36 . In this manner, gas is continuously monitored and then automatically removed from the blood by the blood handling system  10 .  
         [0063]     Sensor  26  monitors for entrained air in the venous blood and comprises a sensor of the type described with respect to sensor  25 . Preferably, sensor  26  uses ultrasound to detect the presence of air entrained in venous blood, and is coupled to controller  33  so that an output of the sensor is used to evaluate one or more trigger conditions, as described hereinafter. Sensor  26  also may be used as a back-up to sensor  25  in the event sensor  25  fails. Sensor  27  may be any suitable pressure sensor such as a piezoelectric transducer or an electrostatic capacitance sensor, and is also coupled to controller  33  and provides an output corresponding to the pressure in venous line  13   a.    
         [0064]     In operation, deoxygenated blood from the sterile field is routed through venous line  12  to blood inlet  41  of integrated blood processing component  31 . Blood entering gas collection plenum  50  is induced to circulate around the exterior of filter  56  until air or other gases entrapped in the blood separate out of the blood and collect in the upper portion of the gas collection plenum  50 . Responsive to the detection of the presence of a predetermined level or volume of gas by sensor  25 , controller  33  controls operation of valve  36  to evacuate the gas.  
         [0065]     The gas removal system incorporated in the system of  FIGS. 1-3  is capable of removing large amounts of air from extracorporeal blood circuit  11  during initial startup, thereby reducing the time and manipulation required to prime the system. Advantageously, this feature facilitates rapid and easy set-up of blood handling system  10 .  
         [0066]     As blood circulates around filter  56  in central void  51 , it is drawn by the negative pressure head created by impeller  75  through filter material  59  and down through central void  51  into pump space  55 . Rotation of impeller  75  caused by drive unit  32 , under the control of controller  33 , propels blood up curved ramp  79  into blood inlet manifold  48 .  
         [0067]     From blood inlet manifold  48 , the blood traverses blood oxygenation element  70  where it exchanges carbon dioxide and other gases for oxygen. Oxygenated blood then passes into blood outlet manifold  47 . Oxygenated blood then is directed back to the sterile field through arterial line  14 .  
         [0068]      FIG. 5  depicts a preferred embodiment of a blood handling system suitable for implementing the features of the present invention. All blood, gas and electrical lines have been omitted for clarity from  FIG. 5 , and microprocessor-driven controller  33  (see  FIG. 1 ) and a back-up battery are enclosed in wheeled base  90 . Pole  91  is mounted in base  90 , and includes support arm  92  that supports blood processing component  31  on drive unit  32 . Support arm  92  also carries solenoid  93  that controls valve  36 , which is in turn coupled to suction source  34 . Pole  91  also carries support arm  93 , which carries display screen  95 . Screen  95  preferably is a touch-sensitive screen coupled to the controller, and serves as both an input device for the extracorporeal blood handling system  10  and a display of system function.  
         [0069]      FIGS. 6A and 6B  provide representative samples of the information displayed on the main windows of the blood handling system  10 . As will of course be understood by one of ordinary skill in the art of computer-controlled equipment, the software used to program operation of the controller may include a number of set-up screens to adjust particular system parameters.  FIGS. 6A and 6B  are therefore the windows that will most commonly be displayed by the clinician during a procedure.  
         [0070]     The display of  FIG. 6A  includes an indicator of battery status, a series of timers for pump operation, duration of cross-clamping, and an auxiliary timer, arterial and venous temperatures and pressures, the speed of centrifugal pump  55   a  and the corresponding blood flow rate. Preferably, controller  33  is programmed with a number of algorithms for determining an appropriate blood flow rate during the procedure, as determined based on body surface area (BSA). The window also may display the value of BSA determined by the selected algorithm based on the patient&#39;s dimensions, and the suggested blood flow rate.  
         [0071]     The display of  FIG. 6B  includes much of the same information provided in the window of  FIG. 6A , but further shows temperatures and pressures graphically as well as numerically, so that the clinician can quickly identify trends in the data and take appropriate corrective measures. In addition, a lower portion of the windows displayed in  FIGS. 6A and 6B  may present system status or help messages, and include touch sensitive buttons that permit to access the other available functions.  
       Description of the Integrated Heat Exchanger of the Present Invention  
       [0072]     In accordance with the principles of the present invention, an extracorporeal blood handling system includes an integrated heat exchanger for heating and/or cooling a patient&#39;s blood during a medical procedure. Two families of blood handling systems, each with illustrative embodiments, are described.  
         [0073]      FIGS. 7-10  show a first embodiment of an extracorporeal blood handling system with integrated heat exchanger constructed in accordance with the principles of the present invention. In  FIGS. 7-10 , like components of the system of  FIG. 3  have been numbered accordingly. In addition to the components described above with respect to blood handling component  31 , blood processing component  100  also incorporates heat exchanger  101 .  
         [0074]     Heat exchanger  101  comprises heat exchange surface  102  that separates pump space  55  from coolant space  103 . Preferably, heat exchanger  101  further comprises baffles  104  disposed within coolant space  103 . Baffles  104  form a maze having coolant channels  104   a  that define a tortuous path for the flow of coolant, such as water. Advantageously, coolant channels  104   a  help distribute coolant evenly over the heat exchange surface and increase the contact time between the coolant and heat exchange surface  102 , thus enhancing heat exchange. Heat exchange surface  102  thereby provides a conductive medium through which coolant flowing through baffles  104  may heat or cool the blood flowing within pump space  55 .  
         [0075]     Preferably, heat exchange surface  102  is a metal or metal alloy having high thermal conductivity and corrosion resistance, such as stainless steel. To enhance heat transfer, heat exchange surface  102  may have protrusions, e.g., dimples, fins, ridges, or the like, that increase the surface area available for heat exchange. The protrusions may extend into pump space  55 , coolant space  103 , or both. To further increase heat transfer, the heat exchanger preferably is arranged for counter-current flow, such that the blood and coolant flow in opposite directions on opposite sides of heat exchange surface  102 .  
         [0076]     Heat exchange surface  102  also includes cylinder  108  that defines pump inlet  82  and barrier  109  that encapsulates potting used to affix the heat exchange surface to blood processing component  100 . Barrier  109  prevents potting from overflowing onto heat exchange surface  102 , thereby ensuring that heat transfer efficiency is substantially maintained. Barrier  109  may be laser welded or brazed to heat exchange surface  102  along its contour. In addition, collar  111  is affixed by laser welding or brazing onto cylinder  108  to facilitate attachment of heat exchange surface  102  to blood processing component  100 . Collar  111  also supports the floor of lower gas plenum  54 . Baffles  104  optionally may be integrally molded with the floor of lower gas plenum  54 .  
         [0077]     In operation, coolant enters coolant space  103  via coolant inlet  115  and flows through channels  104   a  defined by baffles  104 . After transferring heat to or absorbing heat from the blood, the coolant exits coolant space  103  via coolant outlet  116 . Blood flows through gas removal/blood filter  56  and into pump space  55  via pump inlet  82 . As impeller  75  draws blood through pump space  55 , heat is transferred between the coolant and blood via heat exchange surface  102 .  
         [0078]     Convection between the blood and the heat exchange surface is enhanced by the action of impeller  75 , which propels the flow of blood across the heat exchange surface. Thereafter, blood is propelled out of pump space  55  via pump outlet  83  to blood inlet manifold  48  and blood oxygenation element  70 . Advantageously, since the blood is heated or cooled by heat exchanger  101  as the blood is driven through pump space  55 , heat exchanger  101  does not increase the priming volume of the extracorporeal blood handling system.  
         [0079]     Referring now to  FIGS. 11-15  an alternative embodiment of the extracorporeal blood handling system with integrated heat exchanger is described. In  FIGS. 15-19 , like components of the embodiment of  FIG. 3  have been numbered accordingly. In addition to the components described above with respect to blood handling component  31 , blood processing component  200  also incorporates an integrated heat exchanger  201 .  
         [0080]     Heat exchanger  201  includes filter  202  (see  FIGS. 14 and 15 ), preferably disposed entirely within gas collection plenum  50 . Compared to the system of  FIG. 3 , central void  51  may be narrowed as the need for baffled support structure  58  is obviated, thereby maintaining approximately the same the total priming volume of the blood processing component  200 . In accordance with the principles of the present invention, filter  202  serves substantially the same function as gas removal/blood filter  56 , which may be omitted from central void  51  (see  FIG. 13 ).  
         [0081]     Filter  202  comprises a multiplicity of vertically oriented hollow tubes or fibers  203 . In a preferred embodiment, tubes  203  are non-porous membranes. Alternatively, tubes  203  may be formed of a suitable metal or metal alloy Blood is drawn through the lumens of fibers  203  by the negative pressure head created by impeller  75 . As is well known in the art, the tubes are potted near the upper and lower ends of the filter so that blood may pass through the interior of the tubes, while allowing coolant to pass along the exterior of the tubes.  
         [0082]     Preferably, filter  202  forms the first stage of a progressive blood filter. The blood oxygenation element disposed within annular fiber bundle compartment  53  also provides some filtration of blood passing through blood processing component  200 , by filtering out air and particulate matter that has passed through filter  202 . In addition, filter  202  optionally may include screen  204  to filter out larger particulate matter including impurities and air bubbles.  
         [0083]     In operation, blood from blood inlet  41  enters gas collection plenum  50  tangentially and rotates about the top of the bundle of tubes  203  until it slows sufficiently for the blood to pass through the lumens of hollow tubes  203 , through central void  51 , and to pump  55   a.  As in the previous embodiment, rotation of blood entering gas collection plenum  50  causes air bubbles to “bounce off” the tops of the potted tube bundle and collect for subsequent evacuation. The blood flow through the system is indicated by arrows  207  in FIGS.  13 - 15 . Coolant enters heat exchanger  201  via coolant inlet  208  and exits via coolant outlet  209 . The path of coolant, as indicated by arrows  210 , is circumferential the outside of tubes  203 . The tubes provide a conductive medium through which the coolant may heat or cool the blood flowing within the tubes. Thus, heat exchanger  201  has dual functionality as both a mechanism for heat exchange and an air/blood filter.  
         [0084]     Referring to  FIG. 14 , coolant inlet  208  and coolant outlet  209  are optionally located adjacent to each other on the side of filter  202 . Filter  201  optionally may include an internal partition  211  so that coolant entering the heat exchanger must flow circumferentially around the perimeter of upper wall  57  before exiting via coolant outlet  209 . Alternatively, as depicted in  FIG. 15 , coolant inlet  208  and outlet  209  may be located on opposite sides of the filter  202 , so that partition  211  is not required to induce coolant to flow around the perimeter of upper wall  57 .  
         [0085]     Referring now to  FIGS. 16-19  an illustrative member of a second family of embodiments of an extracorporeal blood handling system with integrated heat exchanger is described. In  FIGS. 16-19 , like components of the embodiment of  FIG. 3  have been numbered accordingly. In addition to the components described above with respect to blood handling component  31 , blood processing component  300  also incorporates heat exchanger  301 , which comprises a metal bellows heat exchanger. Alternatively, heat exchanger  301  comprise a multiplicity of hollow tubes or fibers as described with respect to  FIGS. 13 and 14 , wherein the blood flows over the exterior of the tubes and the coolant passes through the lumens of the tubes.  
         [0086]     Heat exchanger  301  comprises a bellows  301  having corrugated wall  302  defining an outer, blood-contacting surface  303  having a plurality of blood flow channels and an inner, coolant-contacting surface  304  defining a plurality of coolant flow channels. Corrugated wall  302  permits the transfer of heat from or to the blood adjacent to blood-contacting surface  203  to a coolant, such as water, flowing adjacent to coolant-contacting surface  304 , depending upon the differential between blood and coolant temperatures.  
         [0087]     To improve heat transfer efficiency, heat exchanger  301  preferably is configured for counter-current flow, so that the blood and coolant flow in opposite directions on opposite sides of corrugated wall  302 . As will be appreciated by those familiar with heat exchanger designs, forming channels in wall  302  also improves heat transfer efficiency by increasing the overall area available for heat transfer. In addition, as depicted in  FIG. 18 , the surfaces of the corrugations of wall  302  may be dimpled to further increase the area available for heat transfer.  
         [0088]     As best seen in  FIG. 17 , wall  302  is preferably a cylindrical wall formed from a thin sheet of highly thermally conductive, corrosion resistant material, e.g. stainless steel, that has been formed into a plurality of substantially parallel channels. The channels are accessible on alternating sides of wall such that blood flows through the channels interdigitated with channels through which coolant flows. Over a large surface area, the blood and coolant are only separated by the thickness of the wall, thereby enabling efficient thermal energy transfer.  
         [0089]     Heat exchanger  301  is disposed between heat exchanger housing  307  and heat exchanger core  308 . An upper portion of housing  307  forms top wall  309  and collar  310 , which also defines lower gas plenum  54 . Collar  310  includes gas outlet port  45  for purging residual gases from blood oxygenation element  70 . Preferably, the outer diameter of the heat exchanger core has substantially the same shape (i.e., cylindrical) as heat exchanger  301  so that a coolant channel  313  is formed between core  308  and heat exchanger  301 . By confining the flow of coolant to channel  313 , the heat exchanger core forces the coolant to contact surface  304 , thus improving heat transfer efficiency.  
         [0090]     As shown in  FIGS. 16 and 17 , housing  307  is attached at its lower end to base portion  311 . Base portion  311  separates coolant space  312  from pump space  55  and includes coolant inlet  314  and coolant outlet  315  in fluid communication with coolant space  312 . Conduit  316  extends through central opening  317  in heat exchanger core  308  and aperture  318  on top wall  309  of housing  307  so that blood flows from central void  51 , through heat exchanger  301  via conduit  316 , and into pump space  55  via pump inlet  82 .  
         [0091]     Within pump space, impeller  75  accelerates and ejects the blood through pump outlet  83  and blood inlet manifold  320  into heat exchanger  301 . Blood flows circumferentially around heat exchanger  301  in contact with blood-contacting surface  303 . Depending upon the temperature of the fluid introduced into coolant space  312 , heat exchanger  301  may be used to either transfer heat to or absorb heat from the blood. From the heat exchanger  301 , blood flows up through blood outlet manifold  321  and into blood inlet manifold  48 .  
         [0092]     Preferably, blood outlet manifold  321  includes well  322  housing a temperature probe, so that the temperature of blood exiting the blood handling system may be monitored and the results displayed by the controller on the display screen. This feature advantageously may be employed with any of the above-described embodiments.  
         [0093]     Referring now to  FIG. 19 , heat exchanger core  308  includes inlet conduit  324  for coolant flow to the coolant-contacting surface of heat exchanger  301  and outlet conduit  325  for coolant flow back into coolant space  312 . Coolant flow within the heat exchanger core is indicated by arrows  326 . The heat exchanger core preferably includes a pair of partitions  327  for separating coolant entering through inlet  314  from coolant exiting coolant space  212  via outlet  315 .  
         [0094]     In operation, coolant enters coolant space  312  via coolant inlet  314 , and is guided by partitions  327  inlet conduit  325 . After transferring heat to or absorbing heat from the blood, the coolant flows through outlet conduit  325  into coolant space  312 . Partitions  327  then guide the coolant to coolant outlet  315 .  
         [0095]     Although preferred illustrative embodiments of the present invention are described above, it will be evident to one skilled in the art that various changes and modifications may be made without departing from the invention. It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention.