Patent Publication Number: US-2015079580-A1

Title: Systems and Methods for Ex Vivo Organ Care

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims, under 35 U.S.C. §121, the benefit of the filing date of U.S. patent application Ser. No. 12/892,451, filed on Sep. 28, 2010, which claims the benefit of the filing date, under 35 U.S.C. §121, of U.S. patent application Ser. No. 11/788,865, filed on Apr. 19, 2007, now U.S. Pat. No. 8,535,934, which claims the benefit of the filing date of U.S. Patent Application No. 60/793,472, filed on Apr. 19, 2006, contents of which are incorporated by reference herein in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The invention generally relates to systems, methods, and devices for ex vivo organ care. More particularly, in various embodiments, the invention relates to caring for an organ ex vivo at physiologic or near-physiologic conditions. 
     BACKGROUND OF THE INVENTION 
     Current organ preservation techniques typically involve hypothermic storage of the organ in a chemical preservation solution on ice. These techniques utilize a variety of solutions, none of which sufficiently protect the organ from damage resulting from ischemia. Such injuries are particularly undesirable when an organ is intended to be transplanted from a donor into a recipient. 
     Using conventional approaches, such injuries increase as a function of the length of time an organ is maintained ex vivo. For example, in the case of a lung, typically it may be preserved ex vivo for only about 6 to about 8 hours before it becomes unusable for transplantation. A heart typically may be preserved ex vivo for only about 4 to about 6 hours before it becomes unusable for transplantation. These relatively brief time periods limit the number of recipients who can be reached from a given donor site, thereby restricting the recipient pool for a harvested organ. Even within the time limits, the organs may nevertheless be significantly damaged. A significant issue is that there may not be any observable indication of the damage. Because of this, less-than-optimal organs may be transplanted, resulting in post-transplant organ dysfunction or other injuries. Thus, it would be desirable to develop techniques that can extend the time during which an organ can be preserved in a healthy state ex vivo. Such techniques would reduce the risk of post-transplant organ failure and enlarge potential donor and recipient pools. 
     Effective preservation of an ex vivo organ would also provide numerous other benefits. For instance, prolonged ex vivo preservation would permit more careful monitoring and functional testing of the harvested organ. This would in turn allow earlier detection and potential repair of defects in the harvested organ, further reducing the likelihood of post-transplant organ failure. The ability to perform simple repairs on the organ would also allow many organs with minor defects to be saved, whereas current transplantation techniques require them to be discarded. 
     In addition, more effective matching between the organ and a particular recipient may be achieved, further reducing the likelihood of eventual organ rejection. Current transplantation techniques rely mainly on matching donor and recipient blood types, which by itself is a relatively unreliable indicator of whether or not the organ will be rejected by the recipient. A more preferred test for organ compatibility is a Human Leukocyte Antigen (HLA) matching test, but current cold ischemic organ preservation approaches preclude the use of this test, which can often require 12 hours or more to complete. 
     Prolonged and reliable ex vivo organ care would also provide benefits outside the context of organ transplantation. For example, a patient&#39;s body, as a whole, can typically tolerate much lower levels of chemo-, bio- and radiation therapy than many particular organs. An ex vivo organ care system would permit an organ to be removed from the body and treated in isolation, reducing the risk of damage to other parts of the body. 
     In view of the foregoing, improved systems, methods, and devices for caring for an organ ex vivo are needed. 
     SUMMARY OF THE INVENTION 
     The invention addresses the deficiencies in the state of the art by, in various embodiments, providing improved systems, methods, solutions and devices relating to portable ex vivo organ care. 
     In one aspect of the invention, the invention includes a method for perfusing one or more lungs ex vivo for an extended period of time in a “steady” or “equilibrium” state maintenance mode. The method generally includes the step of connecting the lungs within a fluid perfusion circuit, which includes a pump, a fluid source, and a fluid flow interface that allows the fluid to flow in and out of the lungs. The method also includes the steps of flowing a perfusion fluid into the lungs through a pulmonary artery interface and flowing the perfusion fluid away from the lungs through a pulmonary vein interface, ventilating the lungs through a tracheal interface, which provides periodic breaths that include alternating inspiration and expiration of gas in and out of the lungs, similar to inspiration and expiration by lungs in-vivo, and providing a respiratory gas, having a pre-determined composition of gas components, to the lungs for use in metabolism by the lungs. In this method, the perfusion system is brought to a steady state, wherein the perfusion fluid flowing into the lungs includes gas components in a first composition that is substantially constant over time, and the perfusion fluid flowing away from the lungs includes gas components in a second composition that is substantially constant over time. Because the lungs are separated from the rest of the donor&#39;s body, they do not need to supply metabolic requirements for the rest of the body, such that during perfusion in the systems described herein less gas exchange is used than lungs in-vivo, and the oxygen and carbon dioxide exchange requirement is reduced. The composition of gas components in the respiratory gas is thus selected so as to provide adequate oxygen and carbon dioxide to the lungs for metabolism and control of perfusion fluid pH in an amount that approximates physiologic levels. 
     In one embodiment, a tracheal oxygen delivery approach is used to implement the maintenance mode. According to this approach, one or more explanted lungs are instrumented within the perfusion circuit and are perfused by a perfusion fluid that is oxygenated to a desired level prior to initiating the perfusion of the lungs. During perfusion, the oxygenated perfusion fluid flows into the explanted lungs via the pulmonary artery interface and flows away from the lungs via the pulmonary vein interface. In addition, the respiratory gas is delivered to the lungs by the first gas source through the tracheal interface, such that the explanted lungs are ventilated by a respiratory gas in periodic breaths through the tracheal interface with alternating inspiration and expiration periods. In particular, the ventilating/respiratory gas delivers a pre-determined composition of gas components through the tracheal interface. In certain implementations, the gas flowing through the tracheal interface is a combination having at least oxygen, carbon dioxide and nitrogen. In certain embodiments, oxygen is about 10% to about 20% and carbon dioxide is about 2% to about 8% of the combination. In one embodiment, the ventilating/respiratory gas combination is about 14% oxygen and about 5% carbon dioxide, and the balance is nitrogen. In this mode, gas leaving the lungs is removed from the lungs via the tracheal interface, for example, through an outlet valve located along a conduit extending from the tracheal interface. After perfusing the lungs for a period of time in this mode, steady state occurs when the first and second gas compositions are substantially the same. Upon reaching the steady-state, the oxygen and carbon dioxide components in the perfusion fluid flowing into the lungs and in the perfusion fluid flowing away from the lungs reach a substantially constant composition. Moreover, the lungs are perfused with the perfusion fluid and ventilated through the tracheal conduit, while the oxygen, carbon dioxide and other gases are maintained in the perfusion fluid at a substantially constant gas component composition, and the gas delivered to the lungs through the tracheal interface differs from the second gas composition in an amount sufficient to supply the lungs&#39; metabolic requirement, and, in certain embodiments, the two gas compositions differ by an amount approximate to support the metabolic requirement. 
     In another embodiment, an isolated tracheal volume re-breathing approach is used to implement the maintenance mode. In this embodiment, one or more explanted lungs are first instrumented within the perfusion circuit and are perfused with a perfusion fluid that flows into the lungs via the pulmonary artery interface and flows away from the lungs via the pulmonary vein interface. A ventilating gas source is provided to the lungs through the tracheal interface, and one or more respiratory gas mixtures, each containing a pre-determined composition of gas components, are supplied to the perfusion fluid via a gas exchange device (e.g., an oxygenator) in the perfusion circuit. In one exemplary embodiment, a gas supplied to the gas exchange device is pre-mixed to include a desired gas composition for infusion into the perfusion fluid. In another embodiment, gases having different compositions are controllably released from the appropriate gas sources to the oxygenator  1042  at rates and volumes that allow the desired gas mixture composition to be obtained. 
     In certain embodiments, a respiratory gas source may be supplied to the gas exchange device that includes a gas composition of about 3% to about 7% carbon dioxide, about 11% to about 14% oxygen, and the balance being nitrogen. In this mode, the ventilating gas source is provided in an isolated volume that interfaces with other fluids and exchanges with other gases only through the alveoli of the lungs. In certain embodiments, the isolated gas volume is provided by a flexible bag. In certain embodiments, the isolated gas volume is provided by a hose. The gas components in the isolated gas volume are able to reach a constant composition by exchanging with the gas components in the perfusion fluid. Exhaled carbon dioxide is carried away from the lungs by the circulating perfusion fluid and substantially removed from the perfusion fluid by mixing with the one or more oxygen-containing gas mixtures supplied through the gas exchange device. In operation, the lungs are ventilated during perfusion in this mode by applying a compression force to the isolated volume. As the isolated volume compresses, its components flow through the tracheal interface and into the lungs, where the lungs inflate and the gas components exchange with gas components in the perfusion fluid through the alveoli in the inflated lungs. As the compression force is withdrawn from the hose or flexible bag, the lungs exhale. The application and withdrawal of the compression force is repeated until the gas components flowing into the tracheal interface reach equilibrium with the components in the perfusion fluid. 
     Upon reaching a steady state in the isolated tracheal volume re-breathing approach, the oxygen and carbon dioxide components in the perfusion fluid flowing into the lungs includes a substantially constant composition and the gas components in the perfusion fluid flowing away from the lungs also include a substantially constant composition. In certain embodiments, a constant composition of a component is achieved when the composition of the component varies over time by an amount less than about 3%, less than about 2%, less than about 1% over time in a given sampling location within the system. Although at a steady state, in the isolated tracheal volume technique, the composition of oxygen and carbon dioxide in the perfusion fluid flowing into the lungs may differ from the composition of such components in the perfusion fluid flowing away from the lungs. In certain embodiments, the compositions of such components in the in-bound fluid differ from the compositions in the out-bound fluid by amounts substantially equivalent to the quantity resulting from lung metabolism. In certain embodiments, the oxygen component is maintained during perfusion at a steady-state partial pressure that is greater in the perfusion fluid flowing into the lungs than in the perfusion fluid flowing away from the lungs. In certain embodiments, the carbon dioxide component is maintained during perfusion at a steady state partial pressure that is lower in the perfusion fluid flowing into the lungs than in the perfusion fluid flowing out of the lungs. 
     In certain embodiments of the maintenance mode, the composition of gas components in the perfusion fluid is chosen to provide steady-state partial pressures of the gas components within the circulating fluid in a range between a pre-determined arterial gas composition and pre-determined venous gas composition. In certain embodiments, the pre-determined arterial gas composition is physiologic arterial blood gas composition, and the pre-determined venous gas composition is physiologic venous blood gas composition. For example, the composition of the oxygen component in the perfusion fluid may be at a partial pressure that is greater than a composition of the oxygen component in physiologic venous blood and less than a composition of the oxygen component in physiologic arterial blood. More specifically, this partial pressure of the oxygen component in the perfusion fluid may be between about 60 mmHg to about 100 mmHg, between about 80 mmHg to about 90 mmHg, or between about 83 mmHg to about 85 mmHg. In addition, the composition of the carbon dioxide component in the perfusion fluid is at a partial pressure that is less than a composition of the carbon dioxide component in physiologic venous blood and greater than a composition of the carbon dioxide component in physiologic arterial blood. More specifically, this partial pressure of the carbon dioxide component in the perfusion fluid may be between about 40 mmHg to about 50 mmHg or between about 42 mmHg to about 50 mmHg. 
     In certain embodiments of the maintenance mode, one or more therapeutics is delivered to the lungs during perfusion. The one or more therapeutics may be selected from antimicrobials, vasodilators, and anti-inflammatory drugs. The one or more therapeutics may also be selected from isuprel, flolan, prostacycline and nitric oxide donors. In addition, the one or more therapeutics may be delivered to the lungs through the tracheal interface via a nebulizer, or to the perfusion fluid through a maintenance solution bag, or by injection directly into the perfusion fluid reservoir at the point of use. 
     In certain embodiments of the maintenance mode, the perfusion fluid is maintained and provided to the lungs at a near physiologic temperature. According to one implementation, the perfusion fluid employs a blood product-based perfusion fluid to more accurately mimic normal physiologic conditions. In alternative embodiments, a synthetic blood substitute solution is used, while in other embodiments, the solution may contain a blood product in combination with a blood substitute product. The perfusion fluid may include a blood product, such as whole blood, and it may be partially or completely depleted of leukocytes and/or platelets. 
     In certain embodiments, one or more tests can be performed on the lungs while they are maintained in the perfusion circuit for ex vivo care. For example, levels of an arterial-venous (AV) oxygen gradient between the perfusion fluid flowing into the lungs and flowing away from the lungs can be measured. Levels of oxygen saturation of blood hemoglobin in the perfusion fluid flowing into the lungs and flowing away from the lungs can also be measured, as can pulmonary vascular resistance ventilation rate, tidal volume, peak respiratory pressure and positive end-expiratory pressure (PEEP). 
     According to another aspect of the invention, the invention includes a lung care system for perfusing one or more lungs ex vivo. The exemplary system includes a portable multiple use module and a single use disposable structure that is sized and shaped for interlocking with the multiple use module. The single use module also includes a lung chamber assembly mounted to the disposable structure. The exemplary system also includes a pump adapted to deliver a perfusion fluid to the lung chamber assembly. The lung chamber assembly includes a pulmonary artery interface for allowing a flow of the perfusion fluid into the lungs, a tracheal interface for allowing ventilation of the lungs, and a pulmonary vein interface for allowing the perfusion fluid to flow away from the lungs. In addition, the single use module may include a respiratory gas source having a predetermined gas component composition. In certain embodiments, the respiratory gas source is included in the multiple-use module. 
     In certain embodiments, the pulmonary vein interface of the lung care system includes a portion of the donor&#39;s left atrium, which is severed from the donor upon explanting the lungs. A portion of the left atrium, known as the left atrial cuff, is left to hang freely from the lungs and is exposed to the lung chamber assembly for allowing the perfusion fluid to flow from the lungs to the lung chamber assembly. In certain embodiments, the pulmonary vein interface includes a cannulation to the left atrial cuff. In one example of cannulation to the left atrial cuff, a semi-sealable connection between the left atrial cuff and a cannula is formed that directs the perfusion fluid to a reservoir. The semi-sealable connection may be formed by a connector device that mates the cannula with the left atrial cuff, and the connection may be releasable. In one instance, the connector device includes a first surface for engaging the left atrial cuff and a second surface for engaging the cannula. In one instance, the first surface of the connector device includes a plurality of perforations for engaging a plurality portions of the left atrial cuff. The left atrial cuff may also extend vertically above the lungs and fit semi-sealably within a vertically extending cannula, wherein the cannula has a cross-section with a diameter that is larger than a diameter of the left atrial cuff. The cannula can be loosely fitted around the left atrial cuff. In other practices, cannulation to the left atrial cuff can be formed by sealing a tip portion of the cannula substantially within a pocket formed by the left atrial cuff. In yet another embodiment, the pulmonary vein interface includes the left atrial cuff disposed in a cup-shaped interface inside of the lung camber assembly for allowing the perfusion fluid to flow from the lungs and away from the lung chamber assembly via an outlet conduit coupled to the cup-shaped interface. The cup-shaped interface may additionally include multiple openings at respective heights along a sidewall of the interface, and the openings are in fluid communication with a selector valve. The selector value is used to controllably draw the perfusion fluid in the cup-shaped interface away from the lung chamber assembly through a selected one of the multiple openings and through the outlet conduit. Hence, the perfusion fluid is able to fill the cup-shaped interface to a height where the select opening is located in order to create a desired level of back pressure on the pulmonary veins. 
     In certain embodiments of the lung chamber assembly, a housing is mounted inside of the lung chamber assembly for supporting the lungs. The housing substantially prevents the lungs from contacting at least one wall of the lung chamber assembly. The housing may be stiff or flexible, and is configured to distribute the weight of the lungs as evenly as possible about the surface of the lungs. In this manner it is believed that pressure upon the alveoli of the lungs can be reduced. In one practice, the housing includes a flexible membrane, such as a cloth, a netting or other fabric, that suspends the lungs within the lung chamber assembly. In another practice, the housing has a shape of a stiff or flexible ribcage having, optionally, a diaphragm structure and/or padding. 
     The system may also include a heater for maintaining the perfusion fluid provided to the lung chamber assembly at a near physiologic temperature. The system may additionally include a gas exchange device in fluid communication with at least one gas supply and the perfusion fluid, the gas exchange device being adapted to controllably modulate the composition of a gas component in the perfusion fluid. In certain embodiments, the gas exchange device (e.g., an oxygenator) includes a gas select switch for selecting from a plurality of gas supplies to modulate the composition of a gas component in the perfusion fluid. The system may further include a respiration device for providing a gas supply through the tracheal interface. To operate the system in the isolated tracheal mode, a volume compartment may be cannulated to a tracheal conduit of the lungs and adapted to ventilate the lungs during perfusion. 
     In another aspect of the invention, the invention includes a method for operating a perfusion circuit in an evaluation mode. One or more lungs may be evaluated for transplant suitability during the evaluation mode. The method includes positioning the lungs in an ex vivo perfusion circuit, flowing a perfusion fluid into the lungs through a pulmonary artery interface, and flowing the perfusion fluid away from the lungs through a pulmonary vein interface, the perfusion fluid being at a physiologic temperature. In addition, the method includes providing gas containing oxygen to the lungs through a tracheal interface. The oxygen level in the gas can be adjusted to allow for evaluation at various oxygen composition levels. The gas may comprise about 100% oxygen, less than 100% oxygen, less than about 75% oxygen, less than about 50% oxygen, less than about 25% oxygen, or no oxygen. In certain embodiments, this gas may be the same composition as ambient air. 
     The evaluation mode is useful, for example, for performing tests to evaluate the gas-transfer capacity of the lungs by determining the oxygen or carbon dioxide saturation or partial pressure of oxygen in the perfusion fluid both before and after it flows through the lungs. To perform this test in the evaluation mode, a low-oxygen content gas source is used to adjust the gas content of the perfusion fluid such that the fluid resembles that of physiologic venous blood. The blood gas composition of the perfusion fluid is then monitored by taking sample measurements of oxygen saturation or partial pressure of gas components in the perfusion fluid flowing into the lungs via the pulmonary artery interface and flowing away from the lungs via the pulmonary vein interface. The resulting pulmonary artery and pulmonary vein oxygen saturation or partial pressure measurements, collected over a period of time after ventilation begins, are then compared with each other to identify a maximum difference that is representative of the gas-transfer capacity of the lungs. 
     Other evaluations can be performed on the instrumented lungs. These evaluations include measuring a fractional inspired oxygen concentration, measuring an arterial-venous (AV) oxygen gradient between the perfusion fluid flowing into the lungs and the perfusion fluid flowing away from the lungs, measuring an alveolar arterial (AA) oxygen gradient, measuring a tidal volume, measuring oxygen saturation of blood hemoglobin or partial pressure of oxygen in the perfusion fluid flowing into and away from the lungs, and measuring the PEEP. 
     In certain embodiments of the evaluation mode, a suction force is applied through the tracheal interface to clear lungs alveoli of debris. The lung alveoli debris may also be cleared by causing the lungs to inhale breaths that are of variable volume. For example, in sigh breathing, the breaths include a first breath having a volume that is larger than the volume of at least two next breaths. 
     In another aspect of the invention, the invention includes compositions and solutions for infusion into a perfusion fluid that is used to perfuse the lungs prior to transplantation. The solutions include a substantially cell-free composition, where the compositions comprise one or more carbohydrates that include dextran, and a plurality of amino acids that do not include asparagine, glutamine, or cysteine. 
     According to various aspects, the systems and/or devices of the invention include, and/or the methods of the invention employ, one or more of: an lung chamber assembly sized and configured for containing one or more lungs during ex vivo care; a reservoir for containing and optionally, defoaming and/or filtering a volume of perfusion fluid; a perfusion fluid pump for pumping/circulating perfusion fluid to and from the harvested lungs; a heater assembly for maintaining the temperature of the perfusion fluid at or near to physiologic temperatures; a gas exchange device for exchanging gases with the perfusion fluid in the system; a nutritional subsystem for replenishing nutrients in the perfusion fluid as they are metabolized by the lungs and for providing preservatives to the perfusion fluid to reduce, for example, ischemia, edema and/or other reperfusion related injuries to the lungs; a sensor subsystem for monitoring, for example, temperature, pressure, flow rate and/or oxygenation of the perfusion fluid, and/or the various components employed to maintain suitable flow conditions to and from the lungs; an operator interface for assisting an operator in monitoring system operation and/or the condition of the lungs, and/or for enabling the operator to set various operating parameters; a power subsystem for providing fault tolerant power to the organ care system; and a control subsystem for controlling operation of the organ care system. 
     Operationally, in one practice, the lungs are harvested from a donor and is instrumented to the lung chamber assembly by processes described above. The perfusion fluid pump pumps perfusion fluid from a reservoir to the heater assembly. The heater assembly heats the perfusion fluid to or near a normal physiologic temperature. According to one embodiment, the heater assembly heats the perfusion fluid to between about 30° C. and about 37° C., or in between about 34° C. and 37° C. From the heater assembly, the perfusion fluid flows to a first interface on the lung chamber assembly. Also referred to as a pulmonary artery interface, the first interface is cannulated to vascular tissue of the pulmonary artery via a conduit located within the lung chamber assembly. The perfusion fluid then flows out of the lungs through the pulmonary vein via a second interface on the lung chamber assembly. The second interface, also referred to as a pulmonary vein interface, connects to the remainder of the perfusion circuit as described above. Optionally, the pulmonary vein is allowed to drain directly into the lung chamber assembly without cannulation. From the pulmonary vein interface, the perfusion fluid flows back to a fluid reservoir, where it may be infused with nutrients prior to recirculation through the perfusion circuit. 
     When applicable (e.g., during the isolated tracheal volume mode), a gas exchange device is positioned within the perfusion circuit between the fluid reservoir and the lung chamber assembly. The gas exchange device receives a gas from an external or onboard gas source and applies gas (e.g., oxygen, a mixture of oxygen and carbon dioxide, or a mixture of oxygen, carbon dioxide and nitrogen) to the perfusion fluid prior to flowing the fluid into the lungs. Alternatively, oxygen and other blood gas levels may be determined by drawing fluid samples from the perfusion fluid and analyzing the samples in a commercially available blood gas analyzer or using partial pressure sensors onboard the system. The system may include one or more oxygen saturation sensors to measure the oxygen saturation level of the perfusion fluid to ensure that the perfusion fluid is maintained at physiologic or other user-defined oxygen levels. In the embodiments where the perfusion fluid is blood-product based, it contains red blood cells (i.e., oxygen carrying cells). Optionally, the oxygen sensors also provide a hematocrit measurement of the concentration of red blood cells in the perfusion fluid. 
     The nutritional subsystem infuses the perfusion fluid with a supply of maintenance solutions as the perfusion fluid flows through the system, and in some embodiments, while it is in the reservoir. According to one feature, the maintenance solutions include nutrients, such as glucose. According to another feature, the maintenance solutions include a supply of therapeutics, vasodilators, endothelial stabilizers, and/or preservatives for reducing edema and providing endothelial support to the lungs. 
     According to another practice, the perfusion fluid includes blood removed from the donor through a process of exsanguination during harvesting of the lungs. Initially, the blood from the donor is loaded into the reservoir and the cannulation locations in the lung chamber assembly are bypassed with a bypass conduit to enable normal mode flow of perfusion fluid through the system without a lung being present. Prior to cannulating the harvested lungs, the system may be primed by circulating the exsanguinated donor blood through the system to heat and/or filter it, and, if desired, oxygenate it. 
     In one embodiment, the portable multiple use module includes a portable housing constructed on a portable chassis, and the single use disposable module includes a disposable structure, such as a housing or a frame. To reduce weight, in one configuration, the disposable structure along with various components of the single use module are formed from molded plastic such as polycarbonate, and the multiple use module chassis is formed from molded materials such as polycarbonate or carbon fiber composites. According to one feature, the unloaded single use disposable structure weighs less than about 12 pounds and the loaded single use module weighs less than about 18 pounds. According to another feature, the multiple use housing and chassis unloaded with components weighs less than about 50 pounds, and when loaded with a multiple use module, batteries, gas, maintenance solutions, perfusion fluid and an organ, weighs about 85 pounds or less. According to another advantage, the system of the invention including both single and multiple use modules, exclusive of any perfusion, nutrient, preservative or other fluids, batteries and gas supply, weighs less than about 65 pounds. 
     The single use disposable structure (e.g., frame or housing) is sized and shaped for interlocking with the portable chassis of the multiple use module for electrical, mechanical, gas and fluid interoperation with the multiple use module. According to one feature, the multiple and single use modules communicate with each other via an optical interface, which comes into optical alignment automatically upon the single use disposable module being installed into the portable multiple use module. According to another feature, the portable multiple use module provides power to the single use disposable module via spring loaded connections, which also automatically connect upon the single use disposable module being installed into the portable multiple use module. According to one feature, the optical interface and spring loaded connections ensure that power and data connection between the single and multiple modules is not lost due to jostling, for example, during transport over rough terrain. 
     In various embodiments, the lung chamber assembly mounts to the disposable structure. 
     In one configuration, the various sensors associated with the heater assembly, the gas exchange device and/or the perfusion fluid pump are included on the disposable single use module. However, this need not be the case, for example, with regard to non-perfusion fluid contacting sensors. According to one embodiment, the single use disposable module employs an oxygen sensor including in-line cuvette through which the perfusion fluid passes, an optical source for directing light at the perfusion fluid passing through the cuvette, and an optical sensor for measuring an optical quality of the perfusion fluid passing through the cuvette. Preferably, the in-line cuvette seamlessly or substantially seamlessly attaches to a perfusion fluid flow conduit to reduce turbulence in the perfusion fluid and provide one or more accurate measurements. The seamless or substantially seamless configuration also reduces damage to any blood based components of the perfusion fluid. 
     According to a further configuration, the disposable single-use module includes the above-mentioned plurality of inline compliance chambers located, for example, at an outlet of the perfusion fluid pump, an outlet of the gas exchange device or an outlet of the heater assembly. In a further embodiment, the disposable single-use module includes a plurality of ports for sampling fluids from the lung chamber assembly. 
     In a further aspect, the invention is directed to a method of transporting one or more lungs ex vivo, including the steps of placing the lungs for transplantation in a protective chamber of a portable organ care system, pumping a perfusion fluid into the lungs via a pulmonary artery of the lungs, providing a flow of the perfusion fluid away from the lungs via a pulmonary vein of the lungs, and transporting the lungs in the portable organ care system from a donor site to a recipient site while pumping the perfusion fluid into an artery of the lungs. 
     These and other features and advantages of the invention are described in further detail below with regard to illustrative embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following figures depict illustrative embodiments of the invention in which like reference numerals refer to like elements. These depicted embodiments may not be drawn to scale and are to be understood as illustrative of the invention and not as limiting, the scope of the invention instead being defined by the appended claims. 
         FIG. 1  is a schematic diagram of a portable organ care system according to an illustrative embodiment of the invention. 
         FIG. 2  is a diagram depicting a harvested heart. 
         FIG. 3  is a conceptual diagram depicting the harvested heart of  FIG. 2  interconnected with the organ care system of  FIG. 1  in a normal flow mode configuration according to an illustrative embodiment of the invention. 
         FIG. 4  is a conceptual diagram depicting the harvested heart of  FIG. 2  interconnected with the organ care system of  FIG. 1  in a retrograde flow mode configuration according to an illustrative embodiment of the invention. 
         FIGS. 5A-5F  show various views of an organ chamber assembly of the type employed in the organ care system of  FIG. 1  according to an illustrative embodiment of the invention. 
         FIGS. 6A-6F  show various views of a perfusion heater assembly of the type employed in the organ care system of  FIG. 1  according to an illustrative embodiment of the invention. 
         FIG. 7  shows a more detailed view of an exemplary resistive heater element of the type employed in the heater assembly of  FIGS. 6A-6F . 
         FIGS. 8A-8C  show various views of a perfusion fluid pump interface assembly according to an illustrative embodiment of the invention. 
         FIG. 9  shows a perspective view of a pump driver side of a perfusion fluid pump assembly of the type depicted in  FIG. 1 , along with a bracket for mounting with the perfusion pump interface assembly. 
         FIG. 10  shows a side view of the perfusion fluid pump interface assembly of  FIGS. 8A-8C  mated with the pump driver side of the perfusion fluid pump assembly of  FIG. 9 . 
         FIG. 11  depicts a block diagram of an illustrative control scheme for controlling operation of the organ care system of  FIG. 1 . 
         FIG. 12  is a block diagram of an exemplary data acquisition subsystem of the type that may be employed with an the illustrative organ care system of  FIG. 1 . 
         FIG. 13  is a block diagram of an exemplary heating control subsystem of the type that may be employed for maintaining perfusion fluid temperature in the illustrative organ care system of  FIG. 1 . 
         FIG. 14  is a block diagram of an exemplary power management subsystem of the type that may be employed in the illustrative organ care system of  FIG. 1 . 
         FIG. 15  is a block diagram of an exemplary pumping control subsystem of the type that may be employed for controlling operation of a perfusion fluid pump assembly in the illustrative organ care system of  FIG. 1 . 
         FIG. 16  is a graph depicting an r-wave with which the pumping control subsystem of  FIG. 15  synchronizes according to an illustrative embodiment of the invention. 
         FIG. 17A-17J  depict exemplary display screens of the type that may be employed with an operator interface according to an illustrative embodiment of the invention. 
         FIGS. 18A and 18B  show an exemplary implementation of the system of  FIG. 1  according to an illustrative embodiment of the invention. 
         FIGS. 19A-19C  show various views of the system of  FIGS. 18A and 18B  with its top off and front panel open according to an illustrative embodiment of the invention. 
         FIG. 20A  is a front perspective view of the system of  FIGS. 18A and 18B  with the top removed, the front panel open and the single use disposable module removed according to an illustrative embodiment of the invention. 
         FIG. 20B  is a side view of a slot formed in a basin of the multiple use module of  FIG. 20A  for engaging with a corresponding projection in the single use disposable module. 
         FIG. 21A  shows a mounting bracket for receiving and locking into place the single use disposable module within the multiple use module of  FIG. 20A . 
         FIGS. 21B and 21C  show installation of the single use disposable module into the multiple use module using the mounting bracket of  FIG. 21A  according to an illustrative embodiment of the invention. 
         FIGS. 22A-22C  show exemplary mechanisms for automatically making electro-optical interconnections between the single use disposable module and the multiple use module during the installation of  FIGS. 21B and 21C . 
         FIGS. 23A-23C  show various views of the system of  FIGS. 18A and 18B  with all of the external walls removed according to an illustrative embodiment of the invention. 
         FIG. 23D  is a conceptual diagram showing interconnections between the circuit boards of  FIGS. 23A-23C  according to an illustrative embodiment of the invention. 
         FIGS. 24A-24E  show various top perspective views of a single use disposable module according to an illustrative embodiment of the invention. 
         FIGS. 25A-25C  show various bottom perspective views of the illustrative single use disposable module of  FIGS. 24A-24D . 
         FIGS. 26A and 26B  depict the operation of a flow mode selector valve according to an illustrative embodiment of the invention. 
         FIGS. 27A and 27B  show various top views of the single use disposable module of  FIGS. 19A-19C  with the top off of illustrative organ chamber. 
         FIGS. 28A-28C  show various views of an exemplary hematocrit and oxygen saturation sensor of the type employed in the illustrative single use disposable module of  FIGS. 19A-19C . 
         FIG. 29A  is a flow diagram depicting a donor-side process for removing an organ from a donor and placing it into the organ care system of  FIG. 1  according to an illustrative embodiment of the invention. 
         FIG. 29B  is a diagram depicting a harvested heart with suture and cannulation sites according to an illustrative embodiment of the invention. 
         FIG. 30  is a flow diagram depicting a recipient-side process for removing an organ from the organ care system of  FIG. 1  and transplanting it into a recipient according to an illustrative embodiment of the invention. 
         FIG. 31  depicts a chart demonstrating electrolyte stability for an organ under going perfusion in forward mode according to an embodiment of the invention. 
         FIG. 32  depicts a chart demonstrating electrolyte stability for an organ under going perfusion in retrograde mode according to another an embodiment of the invention. 
         FIG. 33  depicts a chart demonstrating the arterial blood gas profile for an organ under going perfusion according to an embodiment of the invention. 
         FIG. 34  is a schematic diagram of a portable lung care system with a disposable module configured according to an illustrative embodiment of the invention. 
         FIG. 35A  is a diagram depicting a pair of harvested lungs. 
         FIG. 35B  is a diagram depicting a single harvested lung. 
         FIG. 36  is a diagram depicting a portion of a body&#39;s pulmonary circuit from which at least one lung may be harvested. 
         FIG. 37  is a flow diagram depicting an exemplary process for implementing a maintenance mode of operation within the lung care system of  FIG. 34 . 
         FIG. 38  is a flow diagram depicting another exemplary process for implementing a maintenance mode of operation within the lung care system of  FIG. 34 . 
         FIG. 39  shows exemplary measurement data collected during a maintenance mode operation of the lung care system. 
         FIG. 40  is a flow diagram depicting an exemplary process for implementing an evaluation mode of operation within the lung care system of  FIG. 34 . 
         FIG. 41  shows an embodiment of the disposable module configured to preserve the harvested lungs of  FIG. 35A . 
         FIG. 42  shows another embodiment of the disposable module configured to preserve the harvested lungs of  FIG. 35A . 
         FIG. 43  shows yet another embodiment of the disposable module configured to preserve the harvested lungs of  FIG. 35A . 
         FIG. 44  depicts a top view and a profile view of an exemplary lung chamber assembly employed in the illustrative single use disposable module of  FIGS. 41-43 . 
         FIG. 45  depicts a top view and a profile view of another exemplary lung chamber assembly employed in the illustrative single use disposable module of  FIGS. 41-43 . 
         FIG. 46  depicts a top view and a profile view of another exemplary lung chamber assembly employed in the illustrative single use disposable module of  FIGS. 41-43 . 
         FIG. 47  depicts a top view and a profile view of yet another exemplary lung chamber assembly employed in the illustrative single use disposable module of  FIGS. 41-43 . 
         FIG. 48A  and  FIG. 48B  show various views of an exemplary connector device used for cannulating the pair of harvested lungs of  FIG. 35A . 
         FIG. 49A  and  FIG. 49B  show various views of another exemplary connector device used for cannulating the pair of harvested lungs of  FIG. 35A . 
         FIG. 50A  and  FIG. 50B  show various views of yet another exemplary connector device used for cannulating the pair of harvested lungs of  FIG. 35A . 
         FIG. 51A  depicts an illustrative arrangement for cannulating the pair of harvested lungs of  FIG. 35A . 
         FIG. 51B  depicts an exemplary cup-shaped interface according to an embodiment of the invention. 
         FIG. 52  depicts an illustrative screen for real-time displaying and plotting of data collected from the lung care system of  FIG. 34 . 
         FIG. 53  is a flow diagram depicting a donor-side process for removing lungs from a donor and placing them into the lung care system of  FIG. 34  according to an illustrative embodiment of the invention. 
         FIG. 54  is a flow diagram depicting a recipient-side process for removing lungs from the lung care system of  FIG. 34  and transplanting them into a recipient according to an illustrative embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     As described above in summary, the invention generally provides improved approaches to ex vivo organ care. More particularly, in various embodiments, the invention is directed to improved systems, methods and devices relating to maintaining an organ in an ex vivo portable environment. According to one improvement, the organ maintenance system of the invention maintains a heart beating at or near normal physiologic conditions. To this end, the system circulates an oxygenated, nutrient enriched perfusion fluid to the heart at near physiologic temperature, pressure and flow rate. In other embodiments the system maintains other organs, such as one or more lungs, at or near normal physiologic conditions. According to one implementation, the system employs a perfusion fluid solution that more accurately mimics normal physiologic conditions. In one embodiment, the perfusion fluid is blood-product based. In alternative embodiments, the solution is synthetic blood substitute based. In other embodiments the solution may contain a blood product in combination with a blood substitute product. The blood product may be derived from donor blood or blood from a blood bank. 
     According to various illustrative embodiments, the improvements of the invention enable an organ to be maintained ex vivo for extended periods of time, for example, exceeding 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 or more hours. Such extended ex vivo maintenance times expand the pool of potential recipients for donor organs, making geographic distance between donors and recipients less important. Extended ex vivo maintenance times of the invention also provide the time needed for better genetic and HLA matching between donor organs and organ recipients, increasing the likelihood of a favorable outcome. The ability to maintain the organ in a near physiologic functioning condition also enables a clinician to evaluate the organ&#39;s function ex vivo, further increasing the likelihood of transplantation success. In some instances, the extended maintenance time enables medical operators to perform repairs on donor organs with minor defects. According to another advantage, the increased ex vivo organ maintenance times of the invention enable an organ to be removed from a patient, treated in isolation ex vivo, and then put back into the body of a patient. Such treatment may include, without limitation, pharmaceutical treatments, gas therapies, surgical treatments, chemo-, bio-, gene and/or radiation therapies. 
     The illustrative systems, methods and devices of the invention are described below in the following order. First, the components of an illustrative organ care system  100  for use with a heart are described. Second, illustrative operation of the system  100  is discussed. Third, a subset of the components of the system  100  are described in further detail. Fourth, illustrative control systems and methods for the system  100  are discussed. Fifth, an illustrative user interface is described. Sixth, mechanical features of the system  100  are discussed in further detail with regard to an exemplary implementation. Seventh, exemplary methods for employing the system  100  during an organ harvest, transport, and transplantation procedure are described. Eighth, illustrative implementations of a system  1000  adapting the system  100  for preserving lungs are described, and ninth illustrative perfusion, nutritional and preservative solutions suitable for use with the system  1000  are presented. 
     Turning to the illustrative embodiments,  FIG. 1  depicts a schematic diagram of a portable organ care system  100  according to an illustrative embodiment of the invention.  FIG. 2  shows a conceptual drawing of a heart  102 , which may be preserved/maintained ex vivo by the organ care system  100  of the invention. Referring to  FIGS. 1 and 2 , the illustrative system  100  includes an organ chamber assembly  104  for containing the heart  102  during ex vivo maintenance, a reservoir  160  for holding, defoaming and filtering the perfusion fluid  108 , portal  774  for loading perfusion fluid  108  into the reservoir  160  and a portal  762  for applying therapeutics to the fluid  108  contained in the reservoir  160 , a perfusion fluid pump  106  for pumping/circulating perfusion fluid  108  to and from the harvested heart  102 ; a heater assembly  110  for maintaining the temperature of the perfusion fluid  108  at or near physiological temperatures; a flow mode selector valve  112  for switching between normal and retrograde aortic flow modes (also referred to as “normal flow mode” and “retrograde flow mode,” respectively); an oxygenator  114  for re-oxygenating the perfusion fluid  108  subsequent to it being expelled by the heart  102 ; a nutritional subsystem  115  for replenishing nutrients  116  in the perfusion fluid  108  as they are metabolized by the heart  102  and for providing additional preservatives  118  to the perfusion fluid to reduce, for example, ischemia and/or other re-perfusion related injuries to the heart  102 . The illustrative system  100  also includes a plurality of sensors, including without limitation: temperature sensors  120 ,  122  and  124 ; pressure sensors  126 ,  128 ,  130  and  132 ; perfusion flow rate sensors  134 ,  136  and  138 ; a perfusion fluid oxygenation sensor  140 ; and sensor electrodes  142  and  144 , and defibrillation source  143 . The system  100  further includes: various components employed for maintaining suitable flow conditions to and from the heart  102 ; an operator interface  146  for assisting an operator in monitoring operation of the system  100 , and the condition of the heart  102 , and for enabling the operator to select various operating parameters; a power subsystem  148  for providing fault tolerant power to the system  100 ; and a controller  150  for controlling operation of the organ care system  100 . 
     Referring also to  FIGS. 3 and 4 , according to the illustrative embodiment, the system  100  can maintain the heart  102  in two modes of operation—a normal flow mode, shown in  FIG. 3 , and a retrograde flow mode shown in  FIG. 4 . Generally, in the normal flow mode of  FIG. 3 , the system  100  circulates the perfusion fluid  108  to the heart  102  in the same manner as blood would circulate in the human body. More particularly, referring to  FIGS. 1-3 , the perfusion fluid enters the left atrium  152  of the heart  102  via the pulmonary vein  168 . The perfusion fluid  108  is flowed away from the right ventricle  154  via the pulmonary artery  164  and away from the left  156  ventricle via the aorta  158 . In normal flow mode, the system  100  pumps the perfusion fluid to the heart  102  at a near physiological rate of between about 1 liter/min and about 5 liters/minute. This mode is useful, for example, for performing functional testing to verify that the heart  102  is defect free, both prior and subsequent to transportation to a donor location. 
     Alternatively, in retrograde flow mode, shown in  FIG. 4 , the system  100  flows the perfusion fluid  108  into the heart  102  via the aorta  158 , through the coronary sinus  155  and other coronary vasculature of the heart, and out of the right ventricle  154  of the heart  102  via the pulmonary artery  164 . As discussed in further detail below with regard to  FIGS. 24A and 24B , the system  100  also provides a trickle flow  769  to the left atrium  152  through trickle valve  768 . The trickle flow is provided in an amount sufficient to moisten the left atrium  152  and left ventricle  156 . In certain applications the trickle flow is less than about 5 ml/min, less than about 1 ml/min, or less than about 0.1 ml/min. In this mode of operation, the system  100  reduces the flow rate of the perfusion fluid  108  to between about 300 milliliters/minute and about 1 liter/minute. The inventors have found that the retrograde flow path of  FIG. 4 , along with the reduced flow rate, reduces damage to the heart  102  during extended periods of ex vivo maintenance. Thus, according to one feature of the invention, the heart  102  is transported to a donor site in retrograde flow mode. 
     Having briefly described the normal and retrograde flow modes, the system  100  will next be described in further detail operationally. Referring once again to  FIGS. 1-4 , in one practice, the heart  102  is harvested from a donor and cannulated into the organ chamber assembly  104 . The perfusion fluid  108  is prepared for use within system  100  by being loaded into the reservoir  160  via portal  774  and, optionally, being treated with therapeutics via portal  762 . The pump  106  pumps the loaded perfusion fluid  108  from a reservoir  160  to the heater assembly  110 . The heater assembly  110  heats the perfusion fluid  108  to or near a normal physiological temperature. According to one embodiment, the heater assembly  110  heats the perfusion fluid to between about 32° C. and about 37° C. The heater assembly  110  has an internal flow channel with a cross-sectional flow area that is approximately equal to the inside cross-sectional area of fluid conduits that carry the perfusion fluid  108  into and/or away from the heater assembly  110 , so as to minimize disturbance of fluid flow. From the heater assembly  110 , the perfusion fluid  108  flows to the flow mode selector valve  112 . 
     Initially, the flow mode selector valve  112  is positioned in retrograde mode to direct the perfusion fluid  108  from the heater assembly  110  into the organ chamber assembly  104  via a first interface  162 . Also referred to as an aorta interface or left ventricle interface, the interface  162  includes cannulation to vascular tissue of the left ventricle via an aperture  228   b  located on the organ chamber assembly  104  (as shown in  FIGS. 5A-5B ). As the heart  102  warms, it begins to beat which causes the heart  102  to pump the perfusion fluid  108  through the coronary vasculature  155  and out of the heart  102  through the right ventricle  154  via a second interface  166 . The second interface  166 , also referred to as a pulmonary artery interface or a right ventricle interface, includes cannulation to vascular tissue of the right ventricle via an aperture  228   c  located on the organ chamber assembly  104  (as shown in  FIGS. 5A-5B ). As mentioned above, in retrograde flow mode, fluid is not actively pumped into or out of the left side of the heart, except for a relatively small trickle  769  of perfusion fluid, which is delivered to moisten the left atrium  152  and left ventricle  156 , as described below in reference to  FIGS. 24A-24E . 
     In response to the flow mode selector valve  112  being placed in the normal mode position, it directs the perfusion fluid  108  into the left atrium  152  of the heart  102  via a third interface  170 . The third interface  170 , also referred to as a pulmonary vein interface or left atrium interface, includes cannulation to vascular tissue of the left atrium  152  via an aperture  228   a  located on the organ chamber assembly  104  (as shown in  FIGS. 5A-5B ). The heart  102  then expels the perfusion fluid  108  through the left ventricle  156  via the aorta interface  162  and through the right ventricle  154  via the pulmonary artery interface  166 . 
     Each of the interfaces  162 ,  166  and  170  may be cannulated to the heart  102  by pulling vascular tissue (e.g., an aorta stub) over the end of the interface, then tying or otherwise securing the tissue to the interface. The vascular tissue is preferably a short segment of a blood vessel (e.g., an aorta stub  158 ) that remains connected to the heart  102  after the heart  102  is severed and explanted from the donor. For example, the aorta interface  162  is cannulated to a small segment of the severed aorta  158  which has been formed by severing the aorta  158  in a location down-stream from the coronary sinus  155 . In certain applications, the short vessel segments may be about 5 to about 10 inches in length or longer. The segments may also be shorter than about 5 inches. The segments may be about 2 to about 4 inches in length, or about 1 to about 2 inches in length; in other applications the segments may be less than about ½ inch, or less than about ¼ inch. 
     Alternatively, the cannulation may occur by affixing the interface directly to the applicable atrium or ventricle, as may be preferred in applications where the heart  102  is prepared for explantation by severing an entire blood vessel without leaving any stub portion of the vessel connected to the heart  102 . For example, a left atrium  152  cannulation can be formed by inserting the interface  170  directly into the left atrium  152  and clamping the interface  170  in place, without the need to tie to any pulmonary vein  168  tissue. 
     With continued reference to  FIG. 1 , in both flow modes the perfusion fluid  108  flows from the pulmonary artery interface  166  into the oxygenator  114 . The oxygenator  114  receives gas from an external or onboard source  172  through a gas regulator  174  and a gas flow chamber  176 , which can be a pulse-width modulated solenoid valve that controls gas flow, or any other gas control device that allows for precise control of gas flow rate. A gas pressure gauge  178  provides a visual indication of how full the gas supply  172  is. The transducer  132  provides similar information to the controller  150 . The controller  150  can regulate automatically the gas flow into the oxygenator  114  in dependence, for example, on the perfusion fluid oxygen content measured at the sensor  140 . According to various illustrative embodiments, the oxygenator  114  is a standard membrane oxygenator, such as the Liliput 2 manufactured by Dideco, a division of Sorin Biomedical, or the MINIMAX PLUS manufactured by Medtronic, Inc. In the illustrative embodiment, the gas includes an oxygen and carbon dioxide mixture. An exemplary composition of such a mixture contains about 85% O 2 , about 1% CO 2 , with the balance being N 2 . Subsequent to re-oxygenation, the oxygenator  114  returns the perfusion fluid  108  to the reservoir  160 . According to the illustrative embodiment, the sensor  140  measures the amount of light absorbed or reflected by the perfusion fluid  108  when applied at a multi-wavelength to provide an optical-based measurement of oxygen saturation. Since the perfusion fluid  108  is blood product based in certain embodiments, it may contain red blood cells (i.e., oxygen carrying cells). Accordingly, the sensor  140  also provides a signal  145  indicative of a hematocrit measurement of the perfusion fluid  108 . In alternative embodiments the solution  108  is formed of a synthetic blood substitute, while in other embodiments, the solution  108  may contain a blood product in combination with a blood substitute product. 
     Also, in both flow modes, the nutritional subsystem  115 , including a supply of maintenance solutions  116 / 118  and an infusion pump  182 , infuses the perfusion fluid  108  with nutrients  116 , such as glucose, as the perfusion  108  solution flows through the system  100 , and in some embodiments, while it is in the reservoir  160 . The maintenance solutions  116 / 118  also include a supply of therapeutics and preservatives  118  for reducing ischemia and other re-perfusion related injuries to the heart  102 . 
     Both normal and retrograde flow modes are described in further detail below with reference to  FIGS. 24A-26B . 
     According to the illustrative embodiment, the system  100  is primed prior to introducing an organ into the organ chamber assembly  104 . During priming, a priming solution (described below) is inserted into the organ chamber  160  and pumped through the system  100 . In one exemplar application, the priming occurs for a period of between about 5 and about 20 minutes. The cannulation interfaces  162 ,  166  and  170  in the organ chamber assembly  104  are bypassed to enable normal mode flow of perfusion fluid  108  through the system  100 , without the donor heart  102  being present. Blood (or a synthetic blood substitute) is then loaded into the reservoir  160 . 
     The blood may be the blood exsanguinated from the donor during harvesting of the heart  102  or obtained from typed and cross-matched banked blood. The system  100  then circulates the blood (or blood substitute) through the system  100  to heat, oxygenate, and filter it. Nutrients, preservatives and/or other therapeutics are provided via the infusion pump  182  of the nutritional subsystem  115 . Various parameters may also be initialized and calibrated via the operator interface  146  during priming. Once the system  100  is running appropriately, the pump rate can be decreased or brought to zero, and the heart  102  can be cannulated into the organ chamber assembly  104 . The pump rate can then be increased. Priming of the system  100  is described in further detail below with reference to the flow diagram of  FIG. 29A . 
     As shown in  FIG. 1 , the system  100  also includes a plurality of compliance chambers  184 ,  186  and  188 . The compliance chambers  184 ,  186  and  188  are essentially small inline fluid accumulators with flexible, resilient walls designed to simulate the human body&#39;s vascular compliance by aiding the system in more accurately mimicking blood flow in the human body, for example, by providing flow back-pressure and/or by filtering/reducing fluid pressure spikes due, for example, to flow rate changes and/or the pumping of the pump  106 . According to the illustrative embodiment, the compliance chamber  184  is located between an output  112   a  of the mode valve  112  and the reservoir  160  and operates in combination with an adjustable clamp  190  during normal flow mode to provide back pressure to the aorta  158  to cause perfusion fluid to flow into the coronary sinus  155  to feed the heart  102 . In the illustrative embodiment, the fluid back-pressure provided to the aorta  158  is between about 55 mmHg and about 85 mmHg, which is within an acceptable near-physiologic range of mean aortic blood pressure (which is typically between about 80 mmHg and about 100 mmHg). The back pressure to the aorta  158  aids the system  100  in simulating normal physiologic conditions. The compliance chamber  186  is located between an output  112   b  of the mode valve  112  and the pulmonary vein cannulation interface  170  of the organ chamber assembly  104 . The primary function of the compliance chamber  186  is to provide back-pressure to the left atrium  152  and to smooth pressure/flow spikes caused from the pumping action of the perfusion fluid pump  106 , which delivers blood to the heart without causing substantial fluid pressure spikes. In the illustrative embodiment, the fluid back-pressure provided to the left atrium  152  is between about 0 mmHg to about 14 mmHg, which is approximately the same as the left atrial pressure under normal physiologic conditions. The compliance chamber  188  is located between an output of a one way valve  310  and an inlet  110   a  of the heater  110 . The primary function of the compliance chamber  188  is also to smooth pressure/flow spikes caused by the pumping action of the perfusion fluid pump  106  and to provide fluid back-pressure to the pulmonary artery  164 . In the illustrative embodiment, the fluid back-pressure provided to the pulmonary artery  164  is between about 0 mmHg and about 25 mmHg, which is within an acceptable near-physiologic range of mean arterial blood pressure (between about 0 mmHg and about 12 mmHg). 
     The compliance chambers  184 ,  186  and  188  provide the benefits described above through their size and shape and the materials used in their design. The chambers  184 , 186  and  188  are sized to contain about 20 ml to about 100 ml of fluid  108 , and they are shaped in an oval configuration to allow them to receive fluid  108  and expand to dampen pressure spikes and to provide back-pressure to the heart  102 . In certain applications, the material used for the chambers  184 ,  186  and  188  includes at least one flexible membrane, selected so that the chambers have a Shore A durametric hardness (ASTM D2240 00) of about 10 (more flexible) to about 60 (less flexible), with certain preferred embodiments having a hardness of between about 30 (+/− about 8) and about 50 (+/− about 8). In the illustrative embodiment, the compliance chamber  184  has a Shore A hardness of about 50 (+/− about 8) and the compliance chamber  186  has a Shore A hardness of about 30 (+/− about 8). In the illustrative embodiment, the compliance chamber  188  has a dual-layered configuration, with an inner chamber having a Shore A hardness of about 50 (+/− about 8) and an outer sleeve having a Shore A hardness of about 30 (+/− about 8). Alternatively, the inner chamber can have a lower hardness (e.g., about 30, +/− about 8) and outer sleeve can have a higher hardness (e.g., about 50, +/− about 8)). 
     Having provided an operational overview of the system  100 , the organ chamber assembly  104 , the perfusion heater assembly  110 , and a pump head interface assembly  192  for interfacing with the pump  106  are next described in further detail.  FIGS. 5A-5F  depict various views of the illustrative organ chamber assembly  104  of  FIG. 1 . As shown most clearly in  FIGS. 5A-5D , the organ chamber assembly  104  includes a housing  194 , a outer lid  196  and an intermediate lid  198 . The housing includes a bottom  194   e  and one or more walls  194   a - 194   d  for containing the heart  102 . The intermediate lid  198  covers an opening  200  to the housing  194  for substantially enclosing the heart  102  within the housing  194 . As most clearly shown in  FIGS. 5E and 5F , the intermediate lid  198  includes a frame  198   a  and a flexible membrane  198   b  suspended within the frame  198   a . The flexible membrane  198   b , preferably, is transparent but may be opaque, translucent, or substantially transparent. According to one feature, the flexible membrane includes sufficient excess membrane material to contact the heart  102  when contained within the housing  195 . This feature enables a medical operator to touch/examine the heart  102  indirectly through the membrane  198   b , or apply an ultrasound probe to the heart  102  through the membrane  198   b , while maintaining sterility of the housing  195 . The membrane  198   b  may be made, for example, from any suitable flexible polymer plastic, for example polyurethane. The membrane  198   b  may also have integrated electrically conductive pads/contacts  199   a  and  199   b  through which electrical activity of the heart may be sensed via electrodes such as the electrodes  142  and  144 , and/or for through which defibrillation or pacing signals may be delivered, as described more fully below. Alternatively, the contacts  199   a  and  199   b  may be electrodes including all or a portion of the functionality of the electrodes  142  and  144 . As shown in  FIG. 5C , the outer lid  196  opens and closes over the intermediate lid  198  independently from the intermediate lid  198 . Preferably, the outer lid  196  is rigid enough to protect the heart  102  from physical contact, indirect or indirect. The outer lid  196  and the chamber  194  may also be made from any suitable polymer plastic, for example polycarbonate. 
     According to one implementation, the housing  194  includes two hinge sections  202   a  and  202   b , and the intermediate  11   d  frame  198   a  includes two corresponding mating hinge sections  204   a  and  204   b , respectively. The hinge sections  202   a  and  202   b  on the housing  194  interfit with the hinge sections  204   a  and  204   b  on the intermediate  11   d  frame  198   a  to enable the intermediate lid  198  to open and close relative to the opening  200  of the housing  194 . As shown most clearly in  FIGS. 5D and 5F , the organ chamber assembly  104  also includes two latches  206   a  and  206   b  for securing the intermediate lid  198  closed over the opening  200 . As shown in  FIGS. 5E and 5F , the latches  206   a  and  206   b  rotatably snap fit onto latch hinge section  208   a  and  208   b , respectively, on the wall  194   c  of the housing  194 . As shown most clearly in  FIGS. 5A and 5E , the intermediate  11   d  frame  198   a  also includes a hinge section  210 . The hinge section  210  rotatably snap fits with a mating hinge section  212  on the outer lid  196  to enable the outer lid  196  to open without opening the intermediate lid  198 . As shown best in  FIGS. 5B ,  5 D and  5 F, the outer lid  196  also includes two cutouts  214   a  and  214   b  for enabling the latches  206   a  and  206   b  to clamp down on the edge  216  of the intermediate  11   d  frame  198   a . As shown in  FIGS. 5B ,  5 D and  5 F, the organ chamber assembly  104  also includes a latch  218 , which rotatably snap fits onto a hinge part  220  on the wall  194   c  of the housing  194 . In operation, the latch  218  engages a tab  221  on the edge  225  of the outer lid  196  to secure the outer lid  196  closed over the intermediate lid  198 . 
     As shown most clearly in  FIGS. 5E and 5F , the intermediate  11   d  also includes two gaskets  198   c  and  198   d . The gasket  198   d  interfits between a periphery of the intermediate  11   d  frame  198   a  and a periphery of the outer lid  196  to form a fluid seal between the intermediate lid  198  and the outer lid  196  when the outer lid  196  is closed. The gasket  198   c  interfits between an outer rim  194   f  of the housing  194  and the intermediate  11   d  frame  198   a  to form a fluid seal between the intermediate lid  198  and the periphery  194   f  of the housing  194  when the intermediate lid  198  is closed. 
     Optionally, the organ chamber assembly  104  includes a pad  222  or a sac assembly sized and shaped for interfitting over an inner bottom surface  194   g  of the housing  194 . Preferably, the pad  222  is formed from a material resilient enough to cushion the heart  102  from mechanical vibrations and shocks during transport, for example a closed-cell foam. According to one feature, the pad  222  includes a mechanism for adjustably positioning a pair of electrodes, such as the electrodes  142  and  144  of  FIG. 1 . According to the illustrative embodiment, the mechanism includes two through-apertures  224   a  and  224   b  for passing electrical leads from the under side of the pad  222  to corresponding electrodes  142  and  144  on the heart-contacting surface of the pad. Passing the electrical leads through the pad  222  to the electrodes  142  and  144  enables the electrodes  142  and  144  to be adjustably positioned within the pad  222  to accommodate variously sized hearts. In other embodiments, the mechanism may include, without limitation, one or more differently oriented slots, indentations, protrusions, through apertures, partially through apertures, hooks, eyelets, adhesive patches, or the like. In certain embodiments, the pad  222  may be configured with one or more sleeve-like structures that allow an electrode to be inserted within the pad  222 , thus providing a membrane-like surface of the pad  222  positioned between the electrode and the heart  102 . 
     In some illustrative embodiments, the pad  222  is configured as a pad assembly, with the assembly including one or more electrodes, such as the electrodes  142  and  144 , adjustably located in or on the pad  222 . According to one advantage, the pad/electrode configuration of the invention facilitates contact between the electrodes and the heart  102  placed on the pad  222 , without temporarily or permanently suturing or otherwise mechanically connecting the electrodes to the heart  102 . The weight of the heart  102  itself can also help stabilize the electrodes during transport. According to the illustrative embodiment, the electrodes  142  and  144  include one or more sensors for monitoring one or more electrical signals from the heart and/or defibrillators for providing an electrical signal to the heart. As shown in  FIGS. 1 and 5C , the organ chamber assembly  104  includes electrical interface connections  235   a - 235   b , which mount into the apertures  234   a - 234   b , respectively, in the wall  194   b  of the housing  194 . A cover  226  is provided for protecting the electrical interface connections  235   a - 235   b  when not being used. 
     As described below in further detail with reference to  FIG. 15 , the interface connections  235   a  and  235   b  couple electrical signals, such as ECG signals, from the electrodes  142  and  144  out of the housing  194 , for example, to the controller  194   
     and/or the operator interface  146 . As described in further detail below with reference to  FIG. 22A , the interface connections  235   a  and  235   b  may also couple to a defibrillation source, which may be either provided by external instrumentation or through circuitry within the system  100 , and which can send a defibrillation or pacing signal  143  through electrodes  142  and  144  to the heart  102 . 
     As shown most clearly in  FIGS. 5E and 5F , the organ chamber assembly  104  includes a resealable membrane interface  230 , which mounts in an interface aperture  232 . The interface  230  includes a frame  230   a  and a resealable polymer membrane  230   b  mounted in the frame  230   a . The membrane  230   b  may be made of silicone or any other suitable polymer. In operation, the interface  230  is used to provide pacing leads, when necessary, to the heart  102 , without having to open the chamber lids  196  and  198 . The membrane  230   b  seals around the pacing leads to maintain a closed environment around the heart  102 . The membrane  230   b  also reseals in response to removing the pacing leads. 
     As shown in  FIGS. 5A and 5B , the organ chamber assembly  104  includes apertures  228   a - 228   c  for receiving the aorta interface  162 , the pulmonary artery interface  166  and the pulmonary vein interface  170 , described above with reference to  FIGS. 1-4 , and below with reference to  FIGS. 24A-28C . As shown in  FIG. 5D , the organ chamber assembly  104  also includes a drain  201  for draining perfusion fluid  108  out of the housing  194  back into the reservoir  160 , and mounting receptacles  203 A- 203   d  for mounting the organ chamber assembly  104  onto the single use module (shown at  634  in  FIG. 19A ). 
       FIGS. 6A-6F  depict various views of the perfusion fluid heater assembly  110  of  FIG. 1 . As shown in  FIGS. 6A and 6B , the heater assembly  110  includes a housing  234  having an inlet  110   a  and an outlet  110   b . As shown in both the longitudinal cross-sectional view of  FIG. 6D  and the lateral cross-sectional view of  FIG. 6E , the heater assembly  110  includes a flow channel  240  extending between the inlet  110   a  and the outlet  110   b . The heater assembly  110  may be conceptualized as having upper  236  and lower  238  symmetrical halves. Accordingly, only the upper half is shown in an exploded view in  FIG. 6F . 
     Referring now to  FIGS. 6D-6F , the flow channel  240  is formed between first  242  and second  244  flow channel plates. The inlet  110   a  flows the perfusion fluid into the flow channel  240  and the outlet  110   b  flows the perfusion fluid out of the heater  110 . The first  242  and second  244  flow channel plates have substantially bioinert perfusion fluid  108  contacting surfaces (which may contain a blood-product in certain embodiments) for providing direct contact with the perfusion fluid flowing through the channel  240 . The fluid contacting surfaces may be formed from a treatment or coating on the plate or may be the plate surface itself. The heater assembly  110  includes first and second electric heaters  246  and  248 , respectively. The first heater  246  is located adjacent to and couples heat to a first heater plate  250 . The first heater plate  250 , in turn, couples the heat to the first flow channel plate  242 . Similarly, the second heater  248  is located adjacent to and couples heat to a second heater plate  252 . The second heater plate  252  couples the heat to the second flow channel plate  244 . According to the illustrative embodiment, the first  250  and second  252  heater plates are formed from a material, such as aluminum, that conducts and distributes heat from the first  246  and second  248  electric heaters, respectively, relatively uniformly. The uniform heat distribution of the heater plates  250  and  252  enables the flow channel plates to be formed from a bioinert material, such as titanium, reducing concern regarding its heat distribution characteristic. 
     Referring particularly to  FIGS. 6E and 6F , the heater assembly  110  also includes O-rings  254  and  256  for fluid sealing respective flow channel plates  242  and  244  to the housing  234  to form the flow channel  240 . 
     The heater assembly  110  further includes first assembly brackets  258  and  260 . The assembly bracket  258  mounts on the top side  236  of the heater assembly  110  over a periphery of the electric heater  246  to sandwich the heater  246 , the heater plate  250  and the flow channel plate  242  between the assembly bracket  258  and the housing  234 . The bolts  262   a - 262   j  fit through corresponding through holes in the bracket  258 , electric heater  246 , heater plate  250  and flow channel plate  242 , and thread into corresponding nuts  264   a - 264   j  to affix all of those components to the housing  234 . The assembly bracket  260  mounts on the bottom side  238  of the heater assembly  110  in a similar fashion to affix the heater  248 , the heater plate  252  and the flow channel plate  244  to the housing  234 . A resilient pad  268  interfits within a periphery of the bracket  258 . Similarly, a resilient pad  270  interfits within a periphery of the bracket  260 . A bracket  272  fits over the pad  268 . The bolts  278   a - 278   f  interfit through the holes  276   a - 276   f , respectively, in the bracket  272  and thread into the nuts  280   a - 280   f  to compress the resilient pad  268  against the heater  246  to provide a more efficient heat transfer to the heater plate  250 . The resilient pad  270  is compressed against the heater  248  in a similar fashion by the bracket  274 . 
     As mentioned with respect to  FIG. 1 , and as also shown in  FIG. 6A , the illustrative heater assembly  110  includes temperature sensors  120  and  122  and dual-sensor  124 . The dual sensor  124  in practice includes a dual thermistor sensor for providing fault tolerance, measures the temperature of the perfusion fluid  108  exiting the heater assembly  110 , and provides these temperatures to the controller  150 . As described in further detail below with respect to the heating subsystem  149  of  FIG. 13 , the signals from the sensors  120 ,  122  and  124  may be employed in a feedback loop to control drive signals to the first  246  and/or second  248  heaters to control the temperature of the heaters  256  and  248 . Additionally, to ensure that heater plates  250  and  252  and, therefore, the blood contacting surfaces  242  and  244  of the heater plates  250  and  252  do not reach a temperature that might damage the perfusion fluid, the illustrative heater assembly  110  also includes temperature sensors/lead wires  120  and  122  for monitoring the temperature of the heaters  246  and  248 , respectively, and providing these temperatures to the controller  150 . In practice, the sensors attached to sensors/lead wires  120  and  122  are RTD (resistance temperature device) based. As also discussed in further detail with respect to  FIG. 13 , the signals from the sensors attached to sensors/lead wires  120  and  122  may be employed in a feedback loop to further control the drive signals to the first  246  and/or second  248  heaters to limit the maximum temperature of the heater plates  250  and  252 . As a fault protection, there are sensors for each of the heaters  246  and  248 , so that if one should fail, the system can continue to operate with the temperature at the other sensor. 
     As described in further detail below with respect to  FIG. 13 , the heater  246  of the heater assembly  110  receives from the controller  150  drive signals  281   a  and  281   b  (collectively  281 ) onto corresponding drive lead  282   a . Similarly, the heater  248  receives from the controller  150  drive signals  283   a  and  283   b  (collectively  283 ) onto drive lead  282   b . The drive signals  281  and  283  control the current to, and thus the heat generated by, the respective heaters  246  and  248 . More particularly, as shown in  FIG. 7 , the drive leads  282   a  includes a high and a low pair, which connect across a resistive element  286  of the heater  246 . The greater the current provided through the resistive element  286 , the hotter the resistive element  286  gets. The heater  248  operates in the same fashion with regard to the drive lead  282   b . According to the illustrative embodiments, the element  286  has a resistance of about 5 ohms. However, in other illustrative embodiments, the element may have a resistance of between about 3 ohms and about 10 ohms. As discussed in more detail below with regard to  FIGS. 11 and 13 , the heaters  246  and  248  may be controlled independently by the processor  150 . 
     According to the illustrative embodiment, the heater assembly  110  housing components are formed from a molded plastic, for example, polycarbonate, and weighs less than about one pound. More particularly, the housing  234  and the brackets  258 ,  260 ,  272  and  274  are all formed from a molded plastic, for example, polycarbonate. According to another feature, the heater assembly is a single use disposable assembly. 
     In operation, the illustrative heater assembly  110  uses between about 1 Watt and about 200 Watts of power, and is sized and shaped to transition perfusion fluid  108  flowing through the channel  240  at a rate of between about 300 ml/min and about 5 L/min from a temperature of less than about 30° C. to a temperature of at least about 37° C. in less than about 30 minutes, less than about 25 minutes, less than about 20 minutes, less than about 15 minutes or even less than about 10 minutes, without substantially causing hemolysis of cells, or denaturing proteins or otherwise damaging any blood product portions of the perfusion fluid. 
     According to one feature, the heater assembly  110  includes housing components, such as the housing  234  and the brackets  258 ,  260 ,  272  and  274 , that are formed from a polycarbonate and weighs less than about 5 lb. In other embodiments, the heater assembly may weigh less than about 4 lb, less than about 3 lb, less than about 2 lb, or even less than about 1 lb. In the illustrative embodiment, the heater assembly  110  has a length  288  of about 6.6 inches, not including the inlet  110   a  and outlet  110   b  ports, and a width  290  of about 2.7 inches. The heater assembly  110  has a height  292  of about 2.6 inches. The flow channel  240  of the heater assembly  110  has a nominal width  296  of about 1.5 inches, a nominal length  294  of about 3.5 inches, and a nominal height  298  of about 0.070 inches. The height  298  and width  296  are selected to provide for uniform heating of the perfusion fluid  108  as it passes through the channel  240 . The height  298  and width  296  are also selected to provide a cross-sectional area within the channel  240  that is approximately equal to the inside cross-sectional area of fluid conduits that carry the perfusion fluid  108  into and/or away from the heater assembly  110 . In one configuration, the height  298  and width  296  are selected to provide a cross-sectional area within the channel  240  that is approximately equal to the inside cross-sectional area of the inlet fluid conduit  792  (shown below with reference to  FIG. 25C ) and/or substantially equal to the inside cross-sectional area of the outlet fluid conduit  794  (shown below with reference to  FIG. 24E ). 
     Projections  257   a - 257   d  and  259   a - 259   d  are included in the heater assembly  110  and are used to receive a heat-activated adhesive for binding the heating assembly to the multiple-use unit  650  (referenced in  FIG. 20A ). 
       FIGS. 8A-8C  show various views of a pump interface assembly  300  according to an illustrative embodiment of the invention.  FIG. 9  shows a perspective view of a pump-driver end of the perfusion fluid pump assembly  106  of  FIG. 1 , and  FIG. 10  shows the pump interface assembly  300  mated with the pump-driver end of the perfusion fluid pump assembly  106 , according to an illustrative embodiment of the invention. Referring to  FIGS. 8  A- 10 , the pump interface assembly  300  includes a housing  302  having an outer side  304  and an inner side  306 . The interface assembly  300  includes an inlet  308  and an outlet  310 . As shown most clearly in the bottom view of  FIG. 8B  and the exploded view of  FIG. 8C , the pump interface assembly  300  also includes inner  312  and outer  314  O-ring seals, two deformable membranes  316  and  318 , a doughnut-shaped bracket  320 , and half-rings  319   a  and  319   b  that fit between the o-ring  314  and the bracket  320 . The half-rings  319   a  and  319   b  may be made of foam, plastic, or other suitable material. 
     The inner O-ring  312  fits into an annular track along a periphery of the inner side  306 . The first deformable membrane  316  mounts over the inner O-ring  312  in fluid tight interconnection with the inner side  306  of the housing  302  to form a chamber between an interior side of the first deformable membrane  316  and the inner side  306  of the housing  302 . A second deformable membrane  318  fits on top of the first deformable membrane  316  to provide fault tolerance in the event that the first deformable membrane  316  rips or tears. Illustratively, the deformable membranes  316  and  318  are formed from a thin polyurethane film (about 0.002 inches thick). However, any suitable material of any suitable thickness may be employed. Referring to  FIGS. 8A and 8B , the bracket  320  mounts over the second deformable membrane  318  and the rings  319   a  and  319   b  and affixes to the housing  302  along a periphery of the inner side  306 . Threaded fasteners  322   a - 322   i  attach the bracket  320  to the housing  302  by way of respective threaded apertures  324   a - 324   i  in the bracket  320 . As shown in  FIG. 8B , the outer O-ring  314  interfits into an annular groove in the bracket  320  for providing fluid tight seal with the pump assembly  106 . Prior to inserting O-ring  314  into the annular groove in bracket  320 , the half-rings  319   a  and  319   b  are placed in the groove. The O-ring  314  is then compressed and positioned within the annular groove in bracket  320 . After being positioned within the annular groove, the O-ring  314  expands within the groove to secure itself and the half-rings  319   a  and  319   b  in place. 
     The pump interface assembly  300  also includes heat stake points  321   a - 321   c , which project from its outer side  304 . As described in further detail below with reference to  FIGS. 21A-21C  and  24 A- 24 C, the points  321   a - 321   c  receive a hot glue to heat-stake the pump interface assembly  300  to a C-shaped bracket  656  of the single use disposable module chassis  635 . 
     As shown in  FIG. 8C , the fluid outlet  310  includes an outlet housing  310   a , an outlet fitting  310   b , a flow regulator ball  310   c  and an outlet port  310   d . The ball  310   c  is sized to fit within the outlet port  310   d  but not to pass through an inner aperture  326  of the outlet  310 . The fitting  310   b  is bonded to the outlet port  310   d  (e.g., via epoxy or another adhesive) to capture the ball  310   c  between the inner aperture  326  and the fitting  310   b . The outlet housing  310   a  is similarly bonded onto the fitting  310   b.    
     In operation, the pump interface assembly  300  is aligned to receive a pumping force from a pump driver  334  of the perfusion fluid pump assembly  106  and translate the pumping force to the perfusion fluid  108 , thereby circulating the perfusion fluid  108  to the organ chamber assembly  104 . According to the illustrative embodiment, the perfusion fluid pump assembly  106  includes a pulsatile pump having a driver  334  (described in further detail below with regard to  FIG. 9 ), which contacts the membrane  318 . The fluid inlet  308  draws perfusion fluid  108 , for example, from the reservoir  160 , and provides the fluid into the chamber formed between the inner membrane  316  and the inner side  306  of the housing  302  in response to the pump driver moving in a direction away from the deformable membranes  316  and  318 , thus deforming the membranes  316  and  318  in the same direction. As the pump driver moves away from the deformable membranes  316  and  318 , the pressure head of the fluid  108  inside the reservoir  160  causes the perfusion fluid  108  to flow from the reservoir  160  into the pump assembly  106 . In this respect, the pump assembly  106 , the inlet valve  191  and the reservoir  160  are oriented to provide a gravity feed of perfusion fluid  108  into the pump assembly  106 . At the same time, the flow regulator ball  310   c  is drawn into the aperture  326  to prevent perfusion fluid  108  from also being drawn into the chamber through the outlet  310 . It should be noted that the outlet valve  310  and the inlet valve  191  are one way valves in the illustrated embodiment, but in alternative embodiments the valves  310  and/or  191  are two-way valves. In response to the pump driver  334  moving in a direction toward the deformable membranes  316  and  318 , the flow regulator ball  310   c  moves toward the fitting  310   b  to open the inner aperture  326 , which enables the outlet  310  to expel perfusion fluid  108  out of the chamber formed between the inner side  306  of the housing  302  and the inner side of the deformable membrane  316 . A separate one-way inlet valve  191 , shown between the reservoir  160  and the inlet  308  in  FIG. 1 , stops any perfusion fluid from being expelled out of the inlet  308  and flowing back into the reservoir  160 . 
     As discussed in further detail below with respect to  FIGS. 18A-27B , in certain embodiments the organ care system  100  mechanically divides into a disposable single-use unit (shown at  634  in  FIGS. 19A-19C  and  24 A- 25 C) and a non-disposable multi-use unit (shown at  650  in  FIG. 20A ). In such embodiments, the pump assembly  106  rigidly mounts to the multiple use module  650 , and the pump interface assembly  300  rigidly mounts to the disposable single use module  634 . The pump assembly  106  and the pump interface assembly  300  have corresponding interlocking connections, which mate together to form a fluid tight seal between the two assemblies  106  and  300 . 
     More particularly, as shown in the perspective view of  FIG. 9 , the perfusion fluid pump assembly  106  includes a pump driver housing  338  having a top surface  340 , and a pump driver  334  housed within a cylinder  336  of the housing  338 . The pump driver housing  338  also includes a docking port  342 , which includes a slot  332  sized and shaped for mating with a flange  328  projecting from the pump interface assembly  300 . As shown in  FIG. 10 , the top surface  340  of the pump driver housing  338  mounts to a bracket  346  on the non-disposable multiple use module unit  650 . The bracket  346  includes features  344   a  and  344   b  for abutting the tapered projections  323   a  and  323   b , respectively, of the pump interface assembly  300 . The bracket  346  also includes a cutout  330  sized and shaped for aligning with the docking port  342  and the slot  332  on the pump driver housing  338 . 
     Operationally, the seal between the pump interface assembly  300  and the fluid pump assembly  106  is formed in two steps, illustrated with reference to  FIGS. 9 and 10 . In a first step, the flange  328  is positioned within the docking port  342 , while the tapered projections  323   a  and  323   b  are positioned on the clockwise side next to corresponding features  344   a  and  344   b  on the bracket  346 . In a second step, as shown by the arrows  345 ,  347  and  349  in  FIG. 9 , the pump interface assembly  300  and the fluid pump assembly  106  are rotated in opposite directions (e.g., rotating the pump interface assembly  300  in a counter clockwise direction while holding the pump assembly  106  fixed) to slide the flange  328  into the slot  332  of the docking port  342 . At the same time, the tapered projections  323   a  and  323   b  slide under the bracket features  344   a  and  344   b , respectively, engaging inner surfaces of the bracket features  344   a  and  344   b  with tapered outer surfaces of the tapered projections  323   a  and  323   b  to draw the inner side  306  of the pump interface assembly  300  toward the pump driver  334  and to interlock the flange  328  with the docking ports  342 , and the tapered projections  323   a  and  323   b  with the bracket features  344   a  and  344   b  to form the fluid tight seal between the two assemblies  300  and  106 . 
     Having described the illustrative organ care system  100  from a system, operational and component point of view, illustrative control systems and methods for achieving operation of the system  100  are next discussed. More particularly,  FIG. 11  depicts a block diagram of an illustrative control scheme for the system  100 . As described above with reference to  FIG. 1 , the system  100  includes a controller  150  for controlling operation of the system  100 . As shown, the controller  150  connects interoperationally with the following six subsystems: an operator interface  146  for assisting an operator in monitoring and controlling the system  100  and in monitoring the condition of the heart  102 ; a data acquisition subsystem  147  having various sensors for obtaining data relating to the heart  102  and to the system  100 , and for conveying the data to the controller  150 ; a power management subsystem  148  for providing fault tolerant power to the system  100 ; a heating subsystem  149  for providing controlled energy to the heater  110  for warming the perfusion fluid  108 ; a data management subsystem  151  for storing and maintaining data relating to operation of the system  100  and with respect to the heart  102 ; and a pumping subsystem  153  for controlling the pumping of the perfusion fluid  108  through the system  100 . It should be noted that although the system  100  is described conceptually with reference to a single controller  150 , the control of the system  100  may be distributed in a plurality of controllers or processors. For example, any or all of the described subsystems may include a dedicated processor/controller. Optionally, the dedicated processors/controllers of the various subsystems may communicate with and via a central controller/processor. 
       FIGS. 12-17J  illustrate the interoperation of the various subsystems of  FIG. 11 . Referring first to the block diagram of  FIG. 12 , the data acquisition subsystem  147  includes sensors for obtaining information pertaining to how the system  100  and the heart  102  is functioning, and for communicating that information to the controller  150  for processing and use by the system  100 . As described with respect to  FIG. 1 , the sensors of subsystem  147  include, without limitation: temperature sensors  120 ,  122  and  124 ; pressure sensors  126 ,  128 , and  130 ; flow rate sensors  134 ,  136  and  138 ; the oxygenation/hematocrit sensor  140 ; and electrodes  142  and  144 . The data acquisition subsystem  147  also includes: a set of Hall sensors  388  and a shaft encoder  390  from the perfusion pump assembly  106 ; battery sensors  362   a - 362   c  for sensing whether the batteries  352   a - 352   c , respectively, are sufficiently charged; an external power available sensor  354  for sensing whether external AC power is available; an operator interface module battery sensor  370  for sensing a state of charge of the operator interface module battery; and a gas pressure sensor  132  for sensing gas flow from the gas flow chamber  176 . How the system  100  uses the information from the data acquisition subsystem  147  will now be described with regard to the heating  149 , power management  148 , pumping  153 , data management  151 , and operator interface  146  subsystems, shown in further detail in  FIGS. 13-17J , respectively. 
     The heating subsystem  149  is depicted in the block diagram of  FIG. 13 . With continued reference also to  FIG. 1 , the heating subsystem  149  controls the temperature of the perfusion fluid  108  within the system  100  through a dual feedback loop approach. In the first loop  251  (the perfusion fluid temperature loop), the perfusion fluid temperature thermistor sensor  124  provides two (fault tolerant) signals  125  and  127  to the controller  150 . The signals  125  and  127  are indicative of the temperature of the perfusion fluid  108  as it exits the heater assembly  110 . The controller  150  regulates the drive signals  285  and  287  to the drivers  247  and  249 , respectively. The drivers  247  and  249  convert corresponding digital level signals  285  and  287  from the controller  150  to heater drive signals  281  and  283 , respectively, having sufficient current levels to drive the first  246  and second  248  heaters to heat the perfusion fluid  108  to within an operator selected temperature range. In response to the controller  150  detecting that the perfusion fluid temperatures  125  and  127  are below the operator-selected temperature range, it sets the drive signals  281  and  283  to the first  246  and second  248  heaters, respectively, to a sufficient level to continue to heat the perfusion fluid  108 . Conversely, in response to the controller  150  detecting that the perfusion fluid temperatures  125  and  127  are above the operator-selected temperature range, it decreases the drive signals  281  and  283  to the first  246  and second  248  heaters, respectively. In response to detecting that the temperature of the perfusion fluid  108  is within the operator-selected temperature range, the controller  150  maintains the drive signals  281  and  283  at constant or substantially constant levels. 
     Preferably, the controller  150  varies the drive signals  281  and  283  in substantially the same manner. However, this need not be the case. For example, each heater  246  and  248  may respond differently to a particular current or voltage level drive signal. In such a case, the controller  150  may drive each heater  246  and  248  at a slightly different level to obtain the same temperature from each. According to one feature, the heaters  246  and  248  each have an associated calibration factor, which the controller  150  stores and employs when determining the level of a particular drive signal to provide to a particular heater to achieve a particular temperature result. In certain configurations, the controller  150  sets one of the thermistors in dual sensor  124  as the default thermistor, and will use the temperature reading from the default thermistor in instances where the thermistors give two different temperature readings. In certain configurations, where the temperature readings are within a pre-defined range, the controller  150  uses the higher of the two readings. The drivers  247  and  249  apply the heater drive signals  281  and  283  to corresponding drive leads  282   a  and  282   b  on the heater assembly  110 . 
     In the second loop  253  (the heater temperature loop), the heater temperature sensors  120  and  122  provide signals  121  and  123 , indicative of the temperatures of the heaters  246  and  248 , respectively, to the controller  150 . According to the illustrated embodiment, a temperature ceiling is established for the heaters  246  and  248  (e.g., by default or by operator selection), above which the temperatures of the heaters  246  and  248  are not allowed to rise. As the temperatures of the heaters  246  and  248  rise and approach the temperature ceiling, the sensors  121  and  123  indicate the same to the controller  150 , which then lowers the drive signals  281  and  283  to the heaters  246  and  248  to reduce or stop the supply of power to the heaters  246  and  248 . Thus, while a low temperature signal  125  or  127  from the perfusion fluid temperature sensor  124  can cause the controller  150  to increase power to the heaters  246  and  248 , the heater temperature sensors  120  and  122  ensure that the heaters  246  and  248  are not driven to a degree that would cause their respective heater plates  250  and  252  to become hot enough to damage the perfusion fluid  108 . According to various illustrative embodiments, the controller  150  is set to maintain the perfusion fluid temperature at between about 32° C. and about 37° C., or between about 34° C. and about 36° C. According to a further illustrative embodiment, the controller  150  is set to limit the maximum temperature of the heater plates  250  and  252  to less than about 38° C., 39° C., 40° C., 41° C., or 42° C. 
     As can be seen, the second loop  253  is configured to override the first loop  251 , if necessary, such that temperature readings from temperature sensors  120  and  122  indicating that the heaters  246  and  248  are approaching the maximum allowable temperature override the effect of any low temperature signal from the perfusion fluid temperature sensor  124 . In this respect, the subsystem  149  ensures that the temperature of the heater plates  250  and  252  do not rise above the maximum allowable temperature, even if the temperature of the perfusion fluid  108  has not reached the operator-selected temperature value. This override feature is particularly important during failure situations. For example, if the perfusion fluid temperature sensors  124  both fail, the second loop  253  stops the heater assembly  110  from overheating and damaging the perfusion fluid  108  by switching control exclusively to the heater temperature sensors  120  and  122  and dropping the temperature set point to a lower value. According to one feature, the controller  150  takes into account two time constants assigned to the delays associated with the temperature measurements from the heaters  246  and  248  and perfusion fluid  108  to optimize the dynamic response of the temperature controls. 
       FIG. 14  depicts a block diagram of the power management system  148  for providing fault tolerant power to the system  100 . As shown, the system  100  may be powered by one of four sources—by an external AC source  351  (e.g., 60 Hz, 120 VAC in North America or 50 Hz, 230 VAC in Europe) or by any of three independent batteries  352   a - 352   c . The controller  150  receives data from an AC line voltage availability sensor  354 , which indicates whether the AC voltage  351  is available for use by the system  100 . In response to the controller  150  detecting that the AC voltage  351  is not available, the controller  150  signals the power switching circuitry  356  to provide system power high 358 from one of the batteries  352   a - 352   c . The controller  150  determines from the battery charge sensors  362   a - 362   c  which of the available batteries  352   a - 352   c  is most fully charged, and then switches that battery into operation by way of the switching network  356 . 
     Alternatively, in response to the controller  150  detecting that the external AC voltage  351  is available, it determines whether to use the available AC voltage  351  (e.g., subsequent to rectification) for providing system power  358  and for providing power to the user interface module  146 , for charging one or more of the batteries  352   a - 352   c , and/or for charging the internal battery  368  of user interface module  146 , which also has its own internal charger and charging controller. To use the available AC voltage  351 , the controller  150  draws the AC voltage  351  into the power supply  350  by signaling through the switching system  364 . The power supply  350  receives the AC voltage  351  and converts it to a DC current for providing power to the system  100 . The power supply  350  is universal and can handle any line frequencies or line voltages commonly used throughout the world. According to the illustrative embodiment, in response to a low battery indication from one or more of the battery sensors  362   a - 362   c , the controller  150  also directs power via the switching network  364  and the charging circuit  366  to the appropriate battery. In response to the controller  150  receiving a low battery signal from the sensor  370 , it also or alternatively directs a charging voltage  367  to the user interface battery  368 . According to another feature, the power management subsystem  148  selects batteries to power the system  100  in order of least-charged first, preserving the most charged batteries. If the battery that is currently being used to power the system  100  is removed by the user, the power management subsystem  148  automatically switches over to the next least-charged battery to continue powering the system  100 . 
     According to another feature, the power management subsystem  148  also employs a lock-out mechanism to prevent more than one of the batteries  352   a - 352   c  from being removed from the system  100  at a given time. If one battery is removed, the other two are mechanically locked into position within the system  100 . In this respect, the system  148  provides a level of fault tolerance to help ensure that a source of power  358  is always available to the system  100 . 
     The pumping subsystem  153  of  FIG. 11  will now be described in further detail with reference to  FIGS. 15 and 16 . More particularly,  FIG. 15  is a conceptual block diagram depicting the illustrative pumping subsystem  153 , and  FIG. 16  shows an exemplary ECG  414  of a heart  102  synchronized with an exemplary wave  385  depicting pumping output by the subsystem  153 . The ECG  414  shown in  FIG. 16  has P, Q, R, S, T, and U peaks. The pumping subsystem  153  includes the perfusion fluid pump  106  interoperationally connected to the pump interface assembly  300 , as described in more detail above with reference to  FIGS. 8A-10 . As shown in  FIG. 15 , the controller  150  operates the pumping subsystem  153  by sending a drive signal  339  to a brushless three-phase pump motor  360  using Hall Sensor feedback. The drive signal  339  causes the pump motor shaft  337  to rotate, thereby causing the pump screw  341  to move the pump driver  334  up and/or down. According to the illustrative embodiment, the drive signal  339  is controlled to change a rotational direction and rotational velocity of the motor shaft  337  to cause the pump driver  334  to move up and down cyclically. This cyclical motion pumps the perfusion fluid  108  through the system  100 . 
     In operation, the controller  150  receives a first signal  387  from the Hall sensors  388  positioned integrally within the pump motor shaft  337  to indicate the position of the pump motor shaft  337  for purposes of commutating the motor winding currents. The controller  150  receives a second higher resolution signal  389  from a shaft encoder sensor  390  indicating a precise rotational position of the pump screw  341 . From the current motor commutation phase position  387  and the current rotational position  389 , the controller  150  calculates the appropriate drive signal  339  (both magnitude and polarity) to cause the necessary rotational change in the motor shaft  337  to cause the appropriate vertical position change in the pump screw  341  to achieve the desired pumping action. By varying the magnitude of the drive signal  339 , the controller  150  can vary the pumping rate (i.e., how often the pumping cycle repeats) and by varying the rotational direction changes, the controller  150  can vary the pumping stroke volume (e.g., by varying how far the pump driver  334  moves during a cycle). Generally speaking, the cyclical pumping rate regulates the pulsatile rate at which the perfusion fluid  108  is provided to the heart  102 , while (for a given rate) the pumping stroke regulates the volume of perfusion fluid  108  provided to the heart  102 . 
     Both the rate and stroke volume affect the flow rate, and indirectly the pressure, of the perfusion fluid  108  to and from the heart  102 . As mentioned with regard to  FIG. 1 , the system includes three flow rate sensors  134 ,  136  and  138 , and three pressure sensors  126 ,  128  and  130 . As shown in  FIG. 15 , the sensors  134 ,  136 , and  138  provide corresponding flow rate signals  135 ,  137  and  139  to the controller  150 . Similarly, the sensors  126 ,  128  and  130  provide corresponding pressure signals  129 ,  131  and  133  to the controller  150 . The controller  150  employs all of these signals in feedback to ensure that the commands that it is providing to the perfusion pump  106  have the desired effect on the system  100 . In some instances, and as discussed below in further detail with reference to  FIGS. 17A-17J , the controller  150  may generate various alarms in response to a signal indicating that a particular flow rate or fluid pressure is outside an acceptable range. Additionally, employing multiple sensors enables the controller  150  to distinguish between a mechanical issue (e.g., a conduit blockage) with the system  100  and a biological issue with the heart  102 . 
     According to one feature of the invention, the pumping system  153  may be configured to control the position of the pump driver  334  during each moment of the pumping cycle to allow for finely tuned pumping rate and volumetric profiles. This in turn enables the pumping system  153  to supply perfusion fluid  108  to the heart with any desired pulsatile pattern. According to one illustrative embodiment, the rotational position of the shaft  337  is sensed by the shaft encoder  390  and adjusted by the controller  150  at least about 100 increments per revolution. In another illustrative embodiment, the rotational position of the shaft  337  is sensed by the shaft encoder  390  and adjusted by the controller  150  at least about 1000 increments per revolution. According to a further illustrative embodiment, the rotational position of the shaft  337  is sensed by the shaft encoder  390  and adjusted by the controller  150  at least about 2000 increments per revolution. The vertical position of the pump screw  341  and thus the pump driver  334  is calibrated initially to a zero or a ground position, corresponding to a reference position of the pump screw  341 . 
     According to the illustrative embodiment, the positional precision of the pumping subsystem  153  enables the controller  150  to precisely regulate the pumping of the perfusion fluid  108  through the heart  102 . This process of synchronizing the pulsatile flow of the perfusion fluid to the heart&#39;s natural rate is referred to herein as “r-wave synchronization,” which is described with continued reference to  FIGS. 2 ,  15 , and  16 . A normally functioning heart has a two-phase pumping cycle-diastole and systole. During the diastolic phase, also known as the “resting phase,” the heart&#39;s atria  157  and  152  contract, causing valves to open between the atria  157  and  152  and the ventricles  154  and  156  to allow blood to flow into and load the ventricles  154  and  156 . During the systolic phase, the loaded ventricles eject the blood, and the atria  157  and  152  are opened and fill with blood. The cyclical expansion and contraction of the heart  102  during this process can be represented by graphing the heart&#39;s ventricular ECG wave form, shown at  414  in  FIG. 16 .  FIG. 16  depicts the ECG waveform  414  synchronized with an exemplary wave  385  representative of a pumping output by the subsystem  153 . 
     The pumping subsystem  153  is configured to provide the maximum output at a time that will result in delivery of fluid  108  to the heart  102  at the most beneficial time. In the illustrated embodiment, in retrograde mode, the pumping subsystem  153  is configured to pump fluid  108  toward the heart  102  so that the maximum pump output  382  occurs during the diastolic phase of the heart, which begins after the S peak shown in  FIG. 16  and is when the left ventricle  156  has finished ejecting perfusion fluid  108  through the aorta  158 . Timing the pump output in this manner allows the user to maximize the injection of perfusion fluid  108  through the aorta  158  and into the coronary sinus  155 . The timed pumping is accomplished by starting the pumping at point  377  on wave  385 , which is a point prior to point  382  and corresponds to the peak of the heart&#39;s r-wave pulse  380  and the middle of ventricular systole. The point  377  is selected to account for time-delay between the time a signal is provided from the controller  150  to start pumping the fluid and the time of actual delivery of the pumped fluid  108  to the heart  102 . In another example, during normal flow mode where the left side of the heart fills and ejects perfusion fluid (as described in more detail with reference to  FIG. 24A ), the controller  150  synchronizes the pumping subsystem  153  to start pumping at a fixed period of time after the r-wave  380 , so as to match the natural filling cycle of the left atrium  152 . The synchronization may be adjusted and fine-tuned by the operator through a pre-programmed routine in the operating software on the system  100  and/or by manually operating the controls of the user interface display area  410 , as described in more detail below in reference to  FIGS. 17A-17J . 
     To achieve the synchronized pump output, the controller  150  predicts when the heart&#39;s r-wave pulses  380  will occur and causes the pump to pump at the appropriate time during the ECG  414 . To make this prediction, the controller  150  measures the length various r-wave pulses  380  from the electrical signals  379  and  381  provided from the electrodes  142  and  144 , respectively. From these pulses, the controller  150  tracks the time that elapses from one pulse  380  to the next, and uses this information to calculate a running average of the length of time separating two sequential r-wave pulses. From this information, the controller  150  projects the time of the next r-wave (and from the projection determines the time prior to or after that projected r-wave when the pumping should start to achieve optimal output delivery) by adding the average time separating two sequential r-wave pulses to the time of the previous r-wave  380 . Based on this running average of separation time between r-waves, the controller  150  has the option to adjust the time of pump output in relation to subsequent r-waves, as reflected in the movement of wave  385  to the left or the right along the ECG  414  as signified by the arrow  383  in  FIG. 16 . Adjusting the wave  385  thus allows the user to adjust and customize the timing of output by the pump  106  so as to optimize the filling of the heart. In addition, the pump  106  may also be adjusted to increase or decrease the pump stroke volume to customize the volume of fluid  108  provided by the pump  106 , and this may be done either in concert with or independent of the r-wave synchronization. 
     It should be noted that although the subsystem  153  particularly synchronizes with the r-wave cycle  385 , this need not be the case. In alternative illustrative embodiments, the subsystem  153  may pump in synchronicity with any available characteristic of the heart, including fluid pressures into or out of a particular chamber or vessel. Also, the subsystem  153  may be programmed to pump in any arbitrary pattern, whether periodic or not. 
     Referring back to  FIG. 11 , the data management subsystem  151  receives and stores data and system information from the various other subsystems. The data and other information may be downloaded to a portable memory device and organized within a database, as desired by an operator. The stored data and information can be accessed by an operator and displayed through the operator interface subsystem  146 . 
     Turning now to the operator interface subsystem  146 ,  FIGS. 17A-17J  show various illustrative display screens of the operator interface subsystem  146 . The display screens of  FIGS. 17A-17J  enable the operator to receive information from and provide commands to the system  100 .  FIG. 17A  depicts a top level “home page” display screen  400  according to an illustrative embodiment of the invention. From the display screen  400  an operator can access all of the data available from the data acquisition subsystem  147 , and can provide any desired commands to the controller  150 . As described in more detail in reference to  FIGS. 17B-17J , the display screen  400  of  FIG. 17A  also allows the operator to access more detailed display screens for obtaining information, providing commands and setting operator selectable parameters. 
     With continued reference to  FIG. 1 , the display screen  400  includes a display area  402 , which shows a number of numerical and graphical indications pertaining to the operation of the system  100 . In particular, the display area  402  includes a numerical reading of the aorta output pressure (AOP)  404  of the perfusion fluid  108  exiting the aorta interface  162  on the organ chamber assembly  104 , a wave form depiction  406  of the aortic fluid pressure (AOP)  404 , and an AOP alarm image  408  indicating whether the fluid pressure  404  is too high or too low (the alarm  408  is shown as “off in  FIG. 17A ). The display screen  400  also includes a display area  410  having a numerical indication  412  of the rate at which the heart  102  is beating, an ECG  414  of the heart  102 , a heart rate (HR) alarm image  416  indicating whether the HR  412  exceeds or falls below operator set thresholds, and a time log  418  indicating how long the system  100  has been running, including priming time (discussed in further detail below with reference to  FIG. 29A ). A numerical display  419  shows the amount of time for which the system  100  has been supporting the heart  102 . The indicator alarm  413  indicates when an operator preset time limit is exceeded. 
     The display screen  400  includes a number of additional display areas  420 ,  424 ,  432 ,  438 ,  444 ,  450 ,  456 ,  460 ,  462 ,  466 ,  472 ,  480 , and  482 . The display area  420  shows a numerical reading of the pulmonary artery pressure (PAP)  422 . The PAP  422  is an indication of the pressure of the perfusion fluid  108  flowing from the heart&#39;s pulmonary artery  164 , as measured by the pressure sensor  130 . The display area  420  also provides a PAP alarm indicator  424 , which signals when the PAP  422  is outside an operator preset range. The display area  426  indicates the temperature (Temp)  428  of the perfusion fluid  108  as it exits the heater  110 . The display area  426  also includes a Temp alarm indicator  430 , which signals in response to the Temp  428  being outside of an operator preset range. The upper limit of the operator preset range is shown at  427 . The display area  432  shows a numerical reading of the hematocrit (HCT)  434  of the perfusion fluid  108 , and an HCT alarm indicator  436  for signaling the operator if the HCT  434  falls below an operator preset threshold. The display area  438  shows the oxygen saturation (SvO 2 )  440  of the perfusion fluid  108 . The display area  438  also includes a SvO 2  alarm  442  for indicating if the SvO 2    440  of the perfusion fluid  108  falls below an operator preset threshold. The display area  444  indicates the aorta output flow rate (AOF)  446  of the perfusion fluid  108  as it flows out of the aorta  158 . The AOF  446  is measured by the flow rate sensor  134 . The AOF alarm  448  indicates whether the flow rate  446  falls outside of an operator preset range. The display area  450  shows the organ chamber flow rate (CF)  452 . The CF  452  is an indication of the flow rate of the perfusion fluid  108  as it exits the organ chamber  104 , as measured by the flow rate sensor  136 . The display area  450  also includes a CF alarm  454 , which signals in response to the CF  454  falling outside of an operator preset range. The display area  456  includes a graphic  458  for indicating when a file transfer to the memory card is occurring. 
     The display area  460  shows a graphical representation  459  of the degree to which each of the batteries  352   a - 352   c  (described above with reference to  FIG. 14 ) is charged. The display area  460  also provides a numerical indication  461  of the amount of time remaining for which the batteries  352   a - 352   c  can continue to run the system  100  in a current mode of operation. The display area  462  identifies whether the operator interface module  146  is operating in a wireless  464  fashion, along with a graphical representation  463  of the strength of the wireless connection between the operator interface module  146  and the remainder of the system  100 . The display area  462  also provides graphical indication  467  of the charge remaining in the operator interface module battery  368  (described above with reference to  FIG. 14 ) and a numerical indication  465  of the amount of time remaining for which the operator interface module battery  368  can support it in a wireless mode of operation. The display area  466  indicates the flow rate  468  of oxygen from the gas flow chamber  176 . It also provides a graphical indication  469  of how full an onboard oxygen tank is, and a numerical indication  470  of the amount of time remaining before the onboard oxygen tank runs out. The display area  472  shows the heart rate of the heart  102 , and the amount of time  476  for which the heart  102  has been cannulated onto the system  100 . This field is duplicative of the field  419  mentioned above. The display areas  480  and  482  show the current time and date, respectively, of operation of the system  100 . 
     Actuating a dial (or mouse, or other control device), such as the dial  626  shown in  FIG. 18  A, on the operator interface  146  opens a configuration menu  484 , such as shown in the display screen  401  of  FIG. 17B . As shown, accessing the configuration menu  484  covers the display areas  402  and  410  so they no longer show the graphical depictions of the pressure  406  and the heart rate  414 , but continue to display critical alpha/numeric information. As also shown, all other display areas remain unchanged. This enables an operator to adjust operation of the system  100  while continuing to monitor critical information. According to one feature, the configuration menu  484  allows the operator to pre-program desired operational parameters for the system  100 . Using the display screen  401 , the operator can view/edit working and diastolic (or retrograde) mode alarms by selecting the fields  488  and  490 , respectively. The operator can set particular ECG and LAP graphical options by selecting the fields  492  and  494 . Additionally, the operator can set oxygen flow rate and perfusion fluid temperature by selecting the fields  496  and  498 , respectively. Selecting the field  500  enables the operator to set the time and date, while selecting the field  502  enables the operator to select the language in which information is displayed. At the bottom of the display field  484 , the operator has the option to return  504  to the display screen  400 , cancel  506  any changes made to operational settings, save  508  the changes as new defaults, or reset  510  the operational settings to factory defaults. 
     Referring to  FIGS. 17C-17D , selecting the view/edit working mode alarms field  488  causes the working mode alarm dialog  512  of  FIG. 17D  to open within the display field  484  of  FIG. 17C . The working mode dialog  512  displays the parameters associated with normal flow mode (described above with reference to  FIGS. 1 and 3 ) and includes a field for setting numerical thresholds for each of the normal flow mode alarms. More specifically, the dialog  512  includes: CF alarm field  514 ; PAP alarm field  516 ; AOP alarm field  518 ; LAP alarm field  520 ; perfusion fluid Temp alarm field  524 ; SvO 2  alarm field  526 ; HCT alarm field  528 ; and HR alarm field  530 . By selecting a particular alarm field and actuating the up  532  and/or down  534  arrows, a operator can adjust the acceptable upper and/or lower thresholds for each of the parameters associated with each of the alarms. The dialog  512  also includes alarm graphics  536   a - 536   i , each of which being associated with a particular normal flow mode alarm. The operator can enable/disable any of the above normal flow mode alarms by selecting the associated alarm graphic  536   a - 536   i . Any changes made using the dialog  512  are reflected in corresponding fields in the display screen  400  of  FIG. 17A . 
     Referring to  FIGS. 17A ,  17 B and  17 E, selecting the view/edit non-working mode alarms field  490  causes the resting mode alarm dialog  538  of  FIG. 17E  to open within the display field  484  of  FIG. 17C . The resting mode dialog  538  displays the parameters associated with retrograde flow mode (described above with reference to  FIGS. 1 and 4 ) and includes a field for setting numerical thresholds for each of the retrograde flow mode alarms. According to the illustrative embodiment, the available alarms for the normal and retrograde flow modes are similar, but not necessarily the same. Additionally, even for those that are the same, the thresholds may differ. Accordingly, the invention enables the operator to select different alarms and/or different thresholds for each flow mode of operation. More specifically, the dialog  538  includes: CF alarm field  540 ; PAP alarm field  542 ; AOF alarm field  544 ; AOP alarm field  546 ; LAP alarm field  548 ; perfusion fluid Temp alarm field  550 ; SvO 2  alarm field  552 ; HCT alarm field  556 ; and HR alarm field  558 . By selecting a particular alarm field and actuating the up  560  and/or down  562  arrows, an operator can adjust the acceptable numerical upper and/or lower thresholds for each of the parameters associated with each of the alarms. The dialog  538  also includes alarm graphics  564   a - 564   i , each of which being associated with a particular normal flow mode alarm. The operator can enable/disable any of the above normal flow mode alarms by selecting the associated alarm graphic  564   a - 564   i . As is the case of the dialog  512 , any changes made using the dialog  538  are reflected in corresponding fields in the display screen  400  of  FIG. 17A . In one implementation, the system  100  may be configured to automatically switch between sets of alarm limits for a given flow mode upon changing the flow mode. 
     Referring to  FIGS. 17A ,  17 B,  17 F and  17 G, the operator interface  146  also provides graphical mechanisms for adjusting various parameters. For example, as noted above in reference to  FIG. 16 , one advantage of the user display area  402  is that it allows the operator to monitor (and adjust) the pumping of the subsystem  153 . Display area  410  identifies the ECG waveform  414  of the heart  102 , and display  402  shows in wave form  406  the pressure of fluid flowing through the aorta. In these two displays the operator can monitor the effect of the pumping profile on the heart&#39;s EGC  414 , which allows the user to adjust the stroke volume of the pumping subsystem  153 , to adjust the rate of the pumping subsystem  153  (and thus the flow-rate of the fluid  108  being pumped through the system  100 ), to manually impose, or adjust a time of, firing of the subsystem (e.g., by imposing a fixed delay between the r-wave  380  and the beginning of the pumping cycle), or to automatically program the pumping subsystem  153  to pump at a pre-determined time along the heart&#39;s ECG waveform  414 , as needed to properly fill the heart according to whether the heart is being perfused in retrograde or normal mode. These pumping adjustments may be made by use of the various graphical frames of the operator interface  146 . By way of example, in response to a operator selecting the ECG graphic frame option  492  located in the display field  484  of the display screen  401 , the operator interface  146  displays the dialog  568  of  FIG. 17F . The dialog  568  shows a graphical representation  572  of the ECG  414  along with a cursor  570 . The position of the cursor  570  indicates the point at which the pumping subsystem  153  will initiate an output pumping stroke (i.e., the portion of the pumping cycle at which the pump motor  106  will push perfusion fluid  108  to the heart  102 ) relative to the ECG  414  of the heart  102 . By rotating a mechanical knob  626  (shown in  FIGS. 18A and 18B ) on the operator interface  146 , the operator moves the position of the cursor  570  to adjust when the pumping subsystem  153  will initiate the output pumping stroke relative to the r-wave pulse  380 . As described above with regard to  FIGS. 15 and 16 , the pumping subsystem  153  receives an r-wave signal  380  from the ECG sensors  142  and  144 . The pumping subsystem  153  uses the r-wave signal  380  along with the pumping adjustment information from the cursor  570  to synchronize perfusion fluid pumping with the beating of the heart  102 . In another example, in response to the operator pressing the pump adjust button  625 , the operator interface  146  displays the dialog  574  of  FIG. 17G . From the dialog  574 , the operator can select the pointer  576  and rotate the knob  626  to turn the pump motor  106  on and off. Additionally, the operator can select the bar graphic  578  and rotate the knob  626  to adjust the volume of fluid being pumped, which is displayed in liters/minute. 
     The operator interface  146  also provides a plurality of warning/reminder messages. By way of example, in  FIG. 17H , the operator interface  146  displays a message to remind the operator to connect to AC power to recharge the batteries. This message appears, for example, in response to the controller  150  detecting an impending low battery condition. The operator interface  146  displays the message of  FIG. 17I  to confirm that the user wishes to enter standby mode and to remind the operator to insert a portable memory device, such as magnetic or optical disk, a portable disk drive, a flash memory card or other suitable memory device, to download and store information regarding a particular use of the system  100 . The operator interface  146  displays the error messages, such as the error message of  FIG. 17J , in response to an identifiable fault occurring. The error messages of  FIG. 17J  include, for example, error information  580  to aid a service technician in diagnosing and/or repairing the fault. 
     Having described an illustrative control systems and methods for achieving operation of the system  100 , illustrative mechanical features of the system  100  will now be discussed, along with an illustrative division of components between the single use disposable module  634  and multiple use module  650  units. More particularly,  FIGS. 18A-18B  show a mechanical implementation  600  of the system of  FIG. 1 , according to an illustrative embodiment of the invention. As shown, the illustrative implementation  600  includes a housing  602  and a cart  604 . The housing  602  conceptually divides into upper  602   a  and lower  602   b  housing sections, and includes front  606   a , rear  606   b , left  606   c , and right  606   d  sides. The cart  604  includes a platform  608  and wheels  610   a - 610   d  for transporting the system  600  from place to place. A latch  603  secures the housing  602  to the cart  604 . To further aid in portability, the system  600  also includes a handle  610  hinge mounted to the upper section  602   a  of the left side  606   c  of the housing  602 , along with two rigidly mounted handles  612   a  and  612   b  mounted on the lower section  602   b  of the left  606   c  and right  606   d  sides of the housing  602 . 
     The housing  602  further includes a removable top  614 , and a front panel  615  having an upper panel  613 , and a mid panel  616  hinged to a lower panel  617  by hinges  616   a  and  616   b . The top  614  includes handles  614   a  and  614   b  for aiding with removal. In the illustrated embodiment, the upper panel  613  is screwed, bolted or otherwise adjoined to the top  614 , such that removal of the top  614  also removes panel  613 . 
     As shown in  FIG. 18A , the system  600  includes an AC power cable  618 , along with a frame  620  for securing the power cable  618 , both located on the lower section  602   b  of the left side  606   c  of the housing  602 . A software reset switch  622 , also located on the lower section  602   b  of the left side  602   c , enables an operator to restart the system software and electronics. 
     As shown in  FIGS. 18A and 18B , the implementation  600  also includes the operator interface module  146 , along with a cradle  623  for holding the operator interface module  146 . The operator interface module  146  includes a display  624  for displaying information to an operator, for example, by way of the display screens of  FIGS. 17A-17J . As mentioned above, the operator interface module  146  also includes a rotatable and depressible knob  626  for selecting between the various parameters and display screens of  FIGS. 17A-17J . The knob  626  may also be used to set parameters for automatic control of the system  100 , as well as to provide manual control over the operation of the system  100 . For example, the knob  626  may be used to provide instructions to the controller  150  to increase perfusion fluid flow rates, gas flow rates, etc. As also discussed above with regard to  FIGS. 1 ,  14  and  17 A- 17 J, the operator interface module  146  includes its own battery  368  and may be removed from the cradle  623  and used in a wireless mode. While in the cradle  623 , power connections enable the operator interface module  146  to be charged. As shown, the operator interface module also includes control buttons  625  for controlling the pump, silencing or disabling alarms, entering or exiting standby mode, entering or adjusting ECG synchronization mode, and starting the perfusion clock, which initiates the display of data obtained during organ care. 
     As shown in  FIG. 18B , the illustrative implementation  600  also includes a battery compartment  628  and an oxygen tank bay  630 , both located on the lower section  602   b  of the right side  606   d  of the housing  602 . As shown, the battery compartment  628  houses the three system batteries  352   a - 352   c , described above with regard to  FIG. 14 . According to one feature, the battery compartment  626  includes three battery locks  632   a - 632   c . As described above with respect to  FIG. 14 , the battery locks  632   a - 632   c  interoperate mechanically so that only one of the three batteries  352   a - 352   c  may be removed at any given time. 
     The disposable module  634  and the multiple use unit  650  are constructed of material that is durable yet light-weight. In some illustrative embodiments, polycarbonate plastic is used to form one or more of the components of the units  634  and  650 . To further reduce the weight, the chassis  635  and the multiple use module chassis  602  are formed from low weight materials such as, for example, carbon fiber epoxy composites, polycarbonate ABS-plastic blend, glass reinforced nylon, acetal, straight ABS, aluminum or magnesium. According to one illustrative embodiment, the weight of the entire system  600  is less than about 85 pounds, including the multiple use module, heart, batteries, gas tank, and priming, nutritional, preservative and perfusion fluids, and less than about 50 pounds, excluding such items. According to another illustrative embodiment, the weight of the disposable module  634  is less than about 12 pounds, excluding any solutions. According to a further illustrative embodiment, the multiple use module  650 , excluding all fluids, batteries  352   a - 352   c  and oxygen supply  172 , weighs less than about 50 pounds. 
     With continued reference to  FIGS. 19A-19C , various views are shown of the implementation  600  of  FIGS. 18A and 18B  with the top  614  and upper front panel  613  removed and the front mid panel  616  open, according to an illustrative embodiment of the invention. With reference to  FIGS. 19A-19C , the system  100  is structured as a single use disposable module  634  (shown and described in detail below with reference to  FIGS. 24A-25C ) and a multiple use module  650  (shown without the single use module in  FIG. 20 ). As discussed in further detail below, according to one feature of the illustrative embodiment, all of the blood contacting components of the system  100  are included in the single use disposable module  634  so that after a use, the entire single use module  634  may be discarded, a new module  634  installed, and the system  100  available for use again within a very brief amount of time. 
     According to the illustrative embodiment, the single use module  634  includes a chassis  635  for supporting all of the components of the single use module  634 . As described in more detail with regard to  FIGS. 24A-25C , the components of the single use module  634  include the organ chamber assembly  104 , described above in detail with respect to  FIGS. 5A-5F , the perfusion fluid reservoir  160 , the oxygenator  114 , the perfusion fluid pump interface  300 , and all of the various fluid flow conduits and peripheral monitoring components  633 . 
     As shown in  FIGS. 19A-20A , with the top  614  removed and the front panel  616  open, an operator has easy access to many of the components of the disposable  634  and multiple use  650  modules. For example, the operator may install, remove and view the levels of the nutrient  116  and preservative  118  supplies of the nutritional subsystem  115 . The operator may also control operation of the nutrient  116  and preservative  118  infusion pump  182 . The operator may also cannulate an organ, such as the heart  102 , into the organ chamber assembly  104 . As described in detail below with reference to  FIGS. 21A-21C , this configuration also provides the operator with sufficient access to install and/or remove the single use module  634  to/from the multiple use module  650 . 
       FIG. 20A  shows a front perspective view of the multiple use module  650  with the single use module  634  removed. As shown, the multiple use module  650  includes: the cart  604 ; the lower section  602   b  of the housing  602 , along with all of the components externally mounted to it, along with those contained therein (described in further detail below, with reference to  FIGS. 21A-21C  and  23 A- 23 C); the upper section  602   a  of the housing  602  and all of the components externally mounted to it, including the top cover  614 , the handles  610 ,  612   a , and  612   b , and the front panel  616 ; the operator interface module  146 ; and the perfusion fluid pump motor assembly  106 . As described in detail below with reference to  FIGS. 21A-21C , the multiple use module  650  also includes a bracket assembly  638  for receiving and locking into place the single use module  534 . 
     As shown in  FIG. 20A  and described in further detail below with reference to  FIGS. 22A-22C , the multiple use module  650  also includes a front-end interface circuit board  636  for interfacing with a front-end circuit board (shown in  FIG. 24D  at  637 ) of the disposable module  634 . As also described in detail with reference to  FIGS. 22A-22C , power and drive signal connections between the multiple use module  650  and the disposable module  634  are made by way of corresponding electromechanical connectors  640  and  647  on the front end interface circuit board  636  and the front end circuit board  637 , respectively. By way of example, the front-end circuit board  637  receives power for the disposable module  634  from the front-end interface circuit board  636  via the electromechanical connectors  640  and  647 . The front end circuit board  637  also receives drive signals for various components (e.g., the heater assembly  110 , and the oxygenator  114 ) from the controller  150  via the front-end interface circuit board  636  and the electromechanical connectors  640  and  647 . The front-end circuit board  637  and the front-end interface circuit board  636  exchange control and data signals (e.g., between the controller  150  and the disposable module  134 ) by way of optical connectors (shown in  FIG. 22B  at  648 ). As described in more detail with reference to  FIGS. 22A-22F , the connector configuration employed between the front-end  637  and front-end interface  636  circuit boards ensures that critical power and data interconnections between the single and multiple use modules  634  and  650 , respectively, continue to operate even during transport over rough terrain, such as may be experienced during organ transport. 
     As shown in  FIG. 20A , according to another feature, the upper section  602   a  of the housing  602  includes a fluid tight basin  652 , which is configured to capture any perfusion fluid  108  and/or nutritional  116  and/or preservative  118  solution that may inadvertently leak. The basin  652  also prevents any leaked fluid  108  or solution  116 / 118  from passing into the lower section  602   b  of the housing  602 . In this way, the basin  652  shields the electronic components of the system  100  from any such leaked fluid  108  or solution  116 / 118 . Shielded components include, for example, the power board  720  shown in and discussed in further detail below with reference to  FIGS. 23C and 23D . The basin  652  includes a section  658 , which extends over and shields the perfusion fluid pump  106  from any inadvertently leaked fluid. According to another feature, the basin  652  is sized to accommodate the entire volume of perfusion fluid  108  (including the maintenance solutions  116 / 118 ) contained within the system  100  at any particular time. 
     Referring also to  FIG. 20B , according to a further feature of the illustrative embodiment, an outer side  659  of the pump covering portion  658  of the basin  652  includes a slot  660 . As described in further detail below with reference to  FIGS. 21A-21C  and  24 A, the slot  660  engages with a projection  662  on the single use module  634  during installation of the single use module  634  into the multiple use module  650 . 
     Turning now to the installation of the single use module  634  into the multiple use module  650 ,  FIG. 21A  shows a detailed view of the above-mentioned bracket assembly  638  located on the multiple use module  650  for receiving and locking into place the single use module  634 .  FIG. 21B  shows a side perspective view of the single use module  634  being installed onto the bracket assembly  638  and into the multiple use module  650 , and  FIG. 21C  shows a side view of the single use module  634  installed within the multiple use module  650 . With reference to  FIGS. 21A and 21B , the bracket assembly  638  includes two mounting brackets  642   a  and  642   b , which mount to an internal side of a back panel  654  of the upper housing section  602   a  via mounting holes  644   a - 644   d  and  646   a - 646   d , respectively. A cross bar  641  extends between and rotatably attaches to the mounting brackets  642   a  and  642   b . Locking arms  643  and  645  are spaced apart along and radially extend from the cross bar  641 . Each locking arm  643  and  645  includes a respective downward extending locking projection  643   a  and  645   b . A lever  639  attaches to and extends radially upward from the cross bar  641 . Actuating the lever  639  in the direction of the arrow  651  rotates the locking arms  643  and  645  toward the back  606   b  of the housing  602 . Actuating the lever  639  in the direction of the arrow  653  rotates the locking arms  643  and  645  toward the front  606   a  of the housing  602 . 
     As described above with respect to  FIG. 10 , the perfusion pump interface assembly  300  includes four projecting heat staking points  321   a - 321   d . As shown in  FIG. 24A , during assembly, the projections  321   a - 321   d  are aligned with corresponding apertures  657   a - 657   d  and heat staked through the apertures  657   a - 657   d  into the projections  321   a - 321   d  to rigidly mount the outer side  304  of the pump interface assembly  300  onto the C-shaped bracket  656  of the single use module chassis  635 . 
     With reference to  FIGS. 10 ,  20 B,  21 A,  21 B and  24 A, during installation, in a first step, the single use module  634  is lowered into the multiple use module  650  while tilting the single use module  634  forward (shown in  FIG. 21B ). This process slides the projection  662  of  FIG. 24A  into the slot  660  of  FIG. 20B . As shown in  FIG. 10 , it also positions the flange  328  of the pump interface assembly  300  within the docking port  342  of the perfusion pump assembly  106 , and the tapered projections  323   a  and  323   b  of the pump interface assembly  300  on the clockwise side of corresponding ones of the features  344   a  and  344   b  of the pump assembly bracket  346 . In a second step, the single use module  634  is rotated backwards until locking arm cradles  672  and  674  of the single use module chassis  635  engage projections  643  and  645  of spring-loaded locking arm  638 , forcing the projections  643  and  645  to rotate upward (direction  651 ), until locking projections  643   a  and  645   a  clear the height of the locking arm cradles  672  and  674 , at which point the springs cause the locking arm  638  to rotate downward (direction  653 ), allowing locking projections  643   a  and  645   a  to releasably lock with locking arm cradles  672  and  674  of the disposable module chassis  635 . This motion causes the curved surface of  668  of the disposable module chassis projection  662  of  FIG. 24A  to rotate and engage with a flat side  670  of the basin slot  660  of  FIG. 20B . Lever  639  can be used to rotate the locking arm  638  upwards (direction  651 ) to release the single use module  635 . 
     As shown in  FIG. 10 , this motion also causes the pump interface assembly  300  to rotate in a counterclockwise direction relative to the pump assembly  106  to slide the flange  328  into the slot  332  of the docking port  342 , and at the same time, to slide the tapered projections  323   a  and  323   b  under the respective bracket features  344   a  and  344   b . As the tapered projections  323   a  and  323   b  slide under the respective bracket features  344   a  and  344   b , the inner surfaces of the bracket features  344   a  and  344   b  engage with the tapered outer surfaces of the tapered projections  323   a  and  323   b  to draw the inner side  306  of the pump interface assembly  300  toward the pump driver  334  to form the fluid tight seal between the pump interface assembly  300  and the pump assembly  106 . The lever  639  may lock in place to hold the disposable module  634  securely within the multiple use module  650 . 
     As mentioned briefly above with reference to  FIG. 20A , interlocking the single use module  374  into the multiple use module  650  forms both electrical and optical interconnections between the front end interface circuit board  636  on the multiple use module  650  and the front end circuit board  637  on the single use module  634 . The electrical and optical connections enable the multiple use module  650  to power, control and collect information from the single module  634 .  FIG. 22A  is a conceptual drawing showing various optical couplers and electromechanical connectors on the front end circuit board  637  of the single-use disposable module  634  used to communicate with corresponding optical couplers and electromechanical connectors on the front end interface circuit board  636  of the multiple use module  650 . Since this correspondence is one for one, the various optical couplers and electromechanical connectors are described only with reference to the front end circuit board  637 , rather than also depicting the front end circuit board  650 . 
     According to the illustrative embodiment, the front end circuit board  637  receives signals from the front end interface circuit board  636  via both optical couplers and electromechanical connectors. For example, the front end circuit board  637  receives power  358  (also shown in  FIG. 14 ) from the front end interface circuit board  636  via the electromechanical connectors  712  and  714 . The front end circuit board  637  the power to the components of the single use module  634 , such as the various sensors and transducers of the single use module  634 . Optionally, the front end circuit board  637  converts the power to suitable levels prior to distribution. The front end interface circuit board  636  also provides the heater drive signals  281   a  and  281   b  of  FIG. 13  to the applicable connections  282   a  on the heater  246  of  FIG. 6E  via the electromechanical connectors  704  and  706 . Similarly, the electromechanical connectors  708  and  710  couple the heater drive signals  283   a  and  283   b  of  FIG. 13  to the applicable connections in  282   b  of the heater  248 . The front-end circuit board  637  may receive a defibrillation command from the front end interface circuit board  636  via the electromechanical connector  687 . In response, the front end circuit board  637  generates the defibrillation signal  143  having suitable current and voltage levels, and as shown in  FIG. 5E , couples the signal  143  to the organ chamber assembly  104  via the electrical interface connections  235   a - 235   b.    
     In another illustrative embodiment, the defibrillation command can be provided from an external source (not shown), rather than through the circuit board  636 . As an example, and with reference to  FIG. 5E  and  FIG. 1 , an external defibrillation device can be plugged into the electrical coupler  613  shown in  FIG. 24E , which is connected to the electrical interface connections  235   a - 235   b . The external defibrillation device sends a defibrillation signal  143  through the coupler  613  and the interface connections  235   a  and  235   b  to electrodes  142  and  144 . The electrodes  142  and  144  then deliver the signal  143  to the heart  102 . This alternative embodiment allows the user to provide defibrillation (and pacing) without passing the signal  143  through the circuit boards  618 ,  636 , and  637 . An exemplary external defibrillation device may include the Zoll M-Series Portable Defibrillator. 
     According to the illustrative embodiment, the front end circuit board  637  receives signals from temperature, pressure, fluid flow-rate, oxygentation/hematocrit and ECG sensors, amplifies the signals, converts the signals to a digital format and provides them to the front-end interface circuit board  636  by way of optical couplers. For example, the front end circuit board  637  provides the temperature signal  121  from the sensor  120  on the heater plate  250  (shown in  FIGS. 6A and 13 ) to the front end interface circuit board  636  by way of the optical coupler  676 . Similarly, the front end circuit board  637  provides the temperature signal  123  from the sensor  122  on the heater plate  252  (shown in  FIGS. 6A and 13 ) to the front end interface circuit board  636  by way of the optical coupler  678 . The front end circuit board  637  also provides the perfusion fluid temperature signals  125  and  127  from the thermistor sensor  124  (shown in  FIGS. 6A and 13 ) to the front end interface circuit board  636  via respective optical couplers  680  and  682 . Perfusion fluid pressure signals  129 ,  131  and  133  are provided from respective pressure transducers  126 ,  128  and  130  to the front end interface circuit board  636  via respective optical couplers  688 ,  690  and  692 . The front end circuit board  637  also provides perfusion fluid flow rate signals  135 ,  137  and  139  from respective flow rate sensors  134 ,  136  and  138  to the front end interface circuit board  636  by way of respective optical couplers  694 ,  696  and  698 . Additionally, the front end circuit board  637  provides the oxygen saturation  141  and hematocrit  145  signals from the oxygen saturation sensor  140  to the front end interface circuit board  636  by way of respective optical couplers  700  and  702 . 
     In other illustrative embodiments, one or more of the foregoing sensors are wired directly to the main system board  718  (described below with reference to  FIG. 23D ) for processing and analysis, thus by-passing the front-end interface board  636  and front-end board  637  altogether. Such embodiments may be desirable where the user prefers to re-use one or more of the sensors prior to disposal. In one such example, the flow rate sensors  134 ,  136  and  138  and the oxygen and hematocrit sensor  140  are electrically coupled directly to the system main board  718  through electrical coupler  611  shown in  FIG. 23  C, thus by-passing any connection with the circuit boards  636  and  637 . 
     As described above with respect to  FIGS. 11-16 , the controller  150  employs the signals provided to the front end interface circuit board  636 , along with other signals, to transmit data and otherwise control operation of the system  100 . As described with respect to  FIGS. 17A-17J , the controller  150  also displays sensor information, and may display to the operator various alarms relating to the sensor information by way of the operator interface module  146 . 
       FIG. 22B  illustrates the operation of an exemplary electromechanical connector pair of the type employed for the electrical interconnections between the circuit boards  636  and  637 . Similarly,  FIG. 22C  illustrates the operation of an optical coupler pair of the type employed for the optically coupled interconnections between the circuit boards  636  and  637 . One advantage of both the electrical connectors and optical couplers employed is that they ensure connection integrity, even when the system  100  is being transported over rough terrain, for example, such as being wheeled along a tarmac at an airport, being transported in an aircraft during bad weather conditions, or being transported in an ambulance over rough roadways. Additionally, the optical couplers electrically isolate the temperature, pressure and ECG sensors from the rest of the system  100 , which prevents a defibrillation signal from damaging the system  100 . The power for the front end board  637  is isolated in a DC power supply located on the front end interface board  636 . 
     As shown in  FIG. 22B , the electromechanical connectors, such as the connector  704 , include a portion, such as the portion  703 , located on the front end interface circuit board  636  and a portion, such as the portion  705 , located on the front end circuit board  637 . The portion  703  includes an enlarged head  703   a  mounted on a substantially straight and rigid stem  703   b . The head  703  includes an outwardly facing substantially flat surface  708 . The portion  705  includes a substantially straight and rigid pin  705  including an end  705   a  for contacting the surface  708  and a spring-loaded end  705   b . Pin  705  can move axially in and out as shown by the directional arrow  721  while still maintaining electrical contact with the surface  708  of the enlarged head  703   a . This feature enables the single use module  634  to maintain electrical contact with the multiple use module  650  even when experiencing mechanical disturbances associated with transport over rough terrain. An advantage of the flat surface  708  is that it allows for easy cleaning of the interior surface of the multiple use module  650 . According to the illustrative embodiment, the system  100  employs a connector for the electrical interconnection between the single use disposable  634  and multiple use  650  modules. An exemplary connector is part No. 101342 made by Interconnect Devices. However, any suitable connector may be used. 
     Optical couplers, such as the optical couplers  684  and  687  of the front end circuit board  637 , are used and include corresponding counterparts, such as the optical couplers  683  and  685  of the front end interface circuit board  636 . The optical transmitters and optical receiver portions of the optical couplers may be located on either circuit board  636  or  637 . For example, in the case of the ECG signal  379 , the optical transmitter  684  is located on the circuit board  637  for receiving the electrical signal  379  and optically coupling it to the optical receiver  683  on the circuit board  636 . In the case where the defibrillator signal is transmitted through the circuit boards  636  and  637  (rather than directly to the main board  718 ), the optical transmitter  685  on the circuit board  636  optically couples the signal to the optical receiver  687  on the circuit board  637 . 
     As in the case of the electromechanical connectors employed, allowable tolerance in the optical alignment between the optical transmitters and corresponding optical receivers enables the circuit boards  636  and  637  to remain in optical communication even during transport over rough terrain. According to the illustrative embodiment, the system  100  uses optical couplers made under part nos. SFH485P and/or SFH203PFA by Osram. However, any suitable coupler may be used. 
     The couplers and connectors facilitate the transmission of data within the system  100 . The front-end interface circuit board  636  and the front-end board  637  transmit data pertaining to the system  100  in a paced fashion. As shown in  FIG. 22C , circuit board  636  transmits to the front-end board  637  a clock signal that is synchronized to the clock on the controller  150 . The front-end circuit board  637  receives this clock signal and uses it to synchronize its transmission of system data (such as temperatures, pressures, ECG, r-wave detection, or other desired information) with the clock cycle of the controller  150 . This data is digitized by a processor on the front-end circuit board  637  according to the clock signal and a pre-set sequence of data type and source address (i.e. type and location of the sensor providing the data). The front-end interface circuit board  636  receives the data from the front-end board  637  and transmits the data set to the main board  618  for use by the controller  150  in evaluation, display, and system control, as described above with reference to  FIGS. 11 ,  12  and  14 . Additional optical couplers can be added between the multiple use module and single use module for transmission of control data from the multiple use module to the single use module, such data including heater control signals or pump control signals. 
     Having described the mechanical, electrical and optical interconnections between the single use module  634  and the multiple use module  650 , additional components of the multiple use module  650  will now be discussed with respect to  FIGS. 23A-23D , followed by a description of the mechanical arrangement of the components of the single use module  634  with respect to  FIGS. 24A-28C . As shown in  FIGS. 23A-23D , with the walls of the housing  602  removed, in addition to those components previously discussed, the multiple use module  650  includes an on-board gas supply  172 , located in the lower section  602   b  of the housing  602 . The gas supply  172  is depicted in  FIGS. 23A-23D  as a tank, positioned within the gas tank bay  630  by a support structure  712 , which abuts the tank  172 . Optionally, the gas supply  172  may be further secured within the gas tank bay  630  by a strap and buckle assembly  714  or other suitable mechanism. With particular reference to  FIG. 23B  and as described above with reference to  FIG. 1 , the gas supply  172  provides gas to the system  100  through the gas regulator  174  and the gas flow chamber  176 . The gas pressure sensor  132  measures the gas pressure in the gas supply  172 , and the gas pressure gauge  178  provides a visual indication of the fullness of the gas supply  172 . Additionally, an electrical connection between the controller  150  and the gas flow chamber  176  enables the controller  150  to regulate automatically the gas flow into the oxygenator  114 . 
     As shown most clearly in  FIG. 23  C, the battery bay  628  houses the batteries  352   a - 352   c . As noted above with reference to  FIG. 14 , a lock-out mechanism is used to prevent more than one of the batteries  352   a - 352   c  from being removed from the battery bay  628  at a given time while the system  100  is operating. 
     As discussed above, the system  100  includes a plurality of interconnected circuit boards for facilitating power distribution and data transmission to, from and within the system  100 . Particularly, as discussed above with reference to  FIGS. 22A-22E  and as shown in  FIG. 23C , the multiple use module  650  includes a front end interface circuit board  636 , which optically and electromechanically couples to the front end circuit board  637  of the single use module  650 . As also shown in  FIG. 23C , the system  100  further includes a main board  718 , a power circuit board  720 , and a battery interface board  711  located on the multiple use module  650 . The main board  718  is configured to allow the system  100  to be fault tolerant, in that if a fault arises in the operation of a given circuit board (as shown in  FIG. 23D ), the main board  718  saves pumping and heating parameters in non-volatile memory. When the system  100  reboots, it can re-capture and continue to perform according to such parameters. 
     Referring to the conceptual drawing of  FIG. 23D , cabling  731  brings power (such as AC power  351 ) from a power source  350  to the power circuit board  720  by way of connectors  744  and  730 . The power supply  350  converts the AC power to DC power and distributes the DC power as described above with reference to the power subsystem of  FIG. 14 . Referring also to  FIGS. 14 and 22A , the power circuit board  720  couples DC power and a data signal  358  via respective cables  727  and  729  from the connectors  726  and  728  to corresponding connectors  713  and  715  on the front end interface circuit board  636 . Cable  729  carries both power and a data signal to the front end interface board  636 . Cable  727  carries power to the heater  110  via the front-end interface board  636 . The connectors  713  and  715  interfit with corresponding connectors  712  and  714  (described above with respect to  FIG. 22A ) on the front end circuit board  637  on the single use module  634  to provide power to the single use module  634 . 
     As shown in  FIG. 23D , the power circuit board  720  also provides DC power  358  and a data signal from the connectors  732  and  734 , respectively, on the power circuit board  720  to corresponding connectors  736  and  738  on the main circuit board  718  by way of the cables  733  and  735 . Referring also to  FIGS. 14 and 19A , the cable  737  couples DC power  358  and a data signal from a connector  740  on the main circuit board  718  to the operator interface module  146  by way of a connector  742  on the operator interface module cradle  623 . The power circuit board  720  also provides DC power  358  and a data signal from connectors  745  and  747  via cables  741  and  743  to connectors  749  and  751  on a battery interface board  711 . Cable  741  carries the DC power signal and cable  743  carries the data signal. Battery interface board  711  distributes DC power and data to batteries  352   a ,  352   b  and  352   c . Batteries  352   a ,  352   b  and  352   c  contain electronic circuits that allow them to communicate with each other to monitor the respective charges, as described above in reference to  FIG. 14 , so that the controller  150  can monitor and control the charging and discharging of the batteries  352   a - 352   c.    
     According to some illustrative embodiments, the controller  150  is located on the main circuit board  718  and performs all control and processing required by the system  100 . However, in other illustrative embodiments, the controller  150  is distributed, locating some processing functionality on the front end interface circuit board  636 , some on the power circuit board  720 , and/or some in the operator interface module  146 . Suitable cabling is provided between the various circuit boards, depending on whether and the degree to which the controller  150  is distributed within the system  100 . 
     As described above with reference to  FIGS. 19A-19C  and  23 A- 23 C, the system  100  mechanically divides into the single use disposable module  634  and the multiple use module  650 . As also described above, according to the illustrative embodiment, the single use module  634  includes all or substantially all of the perfusion fluid  108  contacting elements/assemblies of the system  100 , along with various peripheral components, flow conduits, sensors and support electronics for operating the blood contacting components. As discussed above with reference to  FIGS. 22A and 23D , according to the illustrative embodiment, the module  634  does not include a processor, instead relying on the controller  150 , which may, for example, be distributed between the front end interface circuit board  636 , the power circuit board  720 , the operator interface module  146 , and the main circuit board  718 , for control. However, in other illustrative embodiments, the single use module  634  may include its own controller/processor, for example, on the front end circuit board  637 . 
     Referring to  FIGS. 24A-28C , the single use module  634  will next be described in terms of the components included therein. After that, exemplary forward and retrograde flow modes are traced through the described components. 
     Referring first to  FIG. 24A , the disposable module  634  includes a chassis  635  having upper  750   a  and lower  750   b  sections. The upper section  750   a  includes a platform  752  for supporting various components. The lower section  750   b  supports the platform  752  and includes structures for pivotably connecting with the multiple use module  650 . More particularly, the lower chassis section  750   b  includes the C-shaped mount  656  for rigidly mounting the perfusion fluid pump interface assembly  300 , and the projection  662  for sliding into and snap fitting with the slot  660  of  FIG. 20B . The lower chassis section  750   b  also provides structures for mounting the oxygenator  114 . As shown in  FIGS. 25A and 25C , the lower section  750   b  further includes structures for mounting the heater assembly  110 . Additionally, the reservoir  160  mounts to the underside of the platform  725  and extends into the lower chassis section  750   b . Various sensors, such as the O 2  saturation and hematocrit sensor  140  (shown in  FIG. 24A  and described in detail below with reference to  FIGS. 28A-28C ), the flow rate sensor  136  (shown in  FIG. 24A ), the flow rate sensor  138  (shown in  FIG. 25B ), are located within and/or mount to the lower chassis section  750   b . The flow pressure compliance chamber  188  (shown in  FIG. 25B ) is also located in the lower chassis section  750   b . As shown in  FIG. 24D , the lower chassis section  750   b  also mounts the front end circuit board  637 . Conduits located in the lower chassis section  750   b  are described in further detail below with reference to the normal and retrograde flow paths through the single use module  634 . 
     Referring to  FIGS. 24A-25C , and as mentioned above, the upper chassis section  750   a  includes the platform  752 . The platform  752  includes handles  752   a  and  752   b  formed therein to assist in installing and removing the single use module  634  from the multiple use module  650 . Alternatively, such handles can be located on the platform  757  to allow for easier accessibility during installation of the single use module into the multiple use module. As shown most clearly in  FIG. 24C , an angled platform  757  mounts onto the platform  752 . The organ chamber assembly  104  mounts to the angled platform  757 . According to the illustrative embodiment, with the single use module  634  installed within the multiple use module  650 , the platform  757  is angled at about 10° to about 80° relative to horizontal, to provide an optimal angle of operation for the heart  102  when placed within the organ chamber assembly  104 . In some illustrative embodiments, the platform  757  is angled at about 20° to about 60°, or about 30° to about 50° relative to horizontal. The flow mode selector valve  112 , the flow rate sensor  134 , and the perfusion fluid flow pressure compliance chambers  184  and  186  also mount onto the angled platform  757 . 
     Referring to  FIG. 24E , several fluid ports mount to the platform  752 . For example, a fluid sampling port  754  enables an operator to sample the flow into and/or out of the aorta  158  via the cannulation interface  162  on the organ chamber assembly  104 . A fluid sampling port  755  enables the operator to sample the flow into the left atrium  152  via the interface  170  on the organ chamber assembly  104 . Additionally, a fluid port  758  enables the operator to sample the coronary flow out of the pulmonary artery  164  via the pulmonary artery interface  166  on the organ chamber  104 . According to the illustrative embodiment, the operator turns the a respective valve  754   a ,  755   a  or  758   a  to obtain flow from the sampling ports  754 ,  755  and  758 . Flow from the particular port selected is provided at a single common outlet  764 . According to one feature, only flow from the left most port selected is provided at the outlet  764 . By way of example, if the operator opens both ports  755  and  758 , only flow from port  755  is provided at the outlet  764 . In this way, system  100  reduces the likelihood of an operator mixing samples from multiple ports. 
     The single use module  634  also includes a general injection port  762 , operable with the valve  762   a , for enabling the operator to inject medication into the perfusion fluid  108 , for example, via the reservoir  160 . Both the sampling  764  and injection  762  ports mount to the platform  752 . Also located on the upper chassis section  750   a  is an infusion port  766 , operable with the valve  766   a , for flowing the nutritional  116  and preservative  118  fluids into the perfusion fluid  108 . The upper chassis section  750   a  also includes a tube  774  for loading the exsanguinated blood from the donor into the reservoir  160 . As shown in  FIG. 24D , the single use module  634  also includes non-vented caps  776  for replacing vented caps on selected fluid ports that are used while running a sterilization gas through the single use module  634  during sterilization. Preferably, such sterilization takes place prior to packaging the single use module  634  for sale. 
     The upper chassis section  750   a  also includes the flow clamp  190  for regulating back pressure applied to the left atrium  152  when the heart  102  is cannulated and operating in normal flow mode in the organ chamber assembly  104 . The upper chassis section  750   a  further includes a trickle valve  768 . The trickle valve  768  may be opened and closed with the handle  768   a  to regulate a small fluid flow to the left atrium  152  to moisten the left atrium  152  during retrograde flow mode. The upper chassis section  750   a  also includes ports  770  for infusion of additional solutions and  772  for purging the oxygenator  114 , operable with respective valves  770   a  and  772   a.    
     As shown most clearly in  FIGS. 24A and 24D , the upper chassis section  750  further includes the flow pressure probes  126 ,  128  and  130 . As described above with reference to  FIG. 1 , the probe  126  measures the pressure of the perfusion fluid  108  flowing into/out of the aorta  158 . The probe  128  measures the pressure of the perfusion fluid  108  flowing into the left atrium  152  through the pulmonary vein  168 . The probe  130  measures the pressure of the perfusion fluid  108  flowing out of the pulmonary artery  164 . Each probe includes a respective connector  126   a ,  128   a  and  130   a  (shown shortened for clarity) for coupling a respective signal  129 ,  131 , and  133  to the front end circuit board  637 . 
     Referring particularly to the single use module  654  cross-sectional side view of  FIG. 24C , the reservoir  160  includes several components. More specifically, the reservoir  160  includes four inlets:  782 ,  784 ,  786  and  788 . The inlet  782  transfers perfusion fluid  108  from the drain  201  of the organ chamber  194  into the reservoir  160 . The inlet  784  receives exsanguinated blood from the tube  774 . The inlet  786  receives oxygenated perfusion fluid  108  from the oxygenator  114 , and the inlet  788  receives perfusion fluid  108  out of the aorta  158  via the back pressure clamp  190 . The reservoir  160  also has an outlet  790 , which provides the perfusion fluid to the one way inlet valve  191 . The reservoir  160  further includes a defoamer  778  and a filter  780 . The defoamer  778  removes bubbles out of the perfusion fluid  108  as it enters the reservoir  160 . According to the illustrative embodiment, the defoamer is made of porous polyurethane foam with an antifoam coating. The filter  780  is a polyester felt, which filters debris, blood particles, emboli, and air bubbles out of the perfusion fluid as it enters the reservoir  160 . 
     As mentioned above in the summary, the O 2  saturation and hematocrit sensor  140  employed in the single use module  634  includes important advantages over prior art approaches.  FIGS. 28A-28C  depict an illustrative embodiment of the O 2  saturation and hematocrit sensor  140  of the invention. As shown in  FIG. 28  A, the sensor  140  includes an in-line cuvette shaped section of tube  812  connected to the conduit  798 , which has at least one optically clear window through which an infrared sensor can provide infrared light. Exemplary sensors used in the in-line cuvette-shaped tube  812  are those made by Datamed, BL0P4. As shown in the cross-sectional view of  FIG. 28B , the cuvette  812  is a one-piece molded part having connectors  801   a  and  801   b . The connectors  801   a  and  801   b  are configured to adjoin to connecting receptacles  803   a  and  803   b , respectively, of conduit ends  798   a  and  798   b . This interconnection between cuvette  812  and conduit ends  798   a  and  798   b  is configured so as to provide a substantially constant cross-sectional flow area inside conduit  798  and cuvette  812 . The configuration thereby reduces, and in some embodiments substantially removes, discontinuities at the interfaces  814   a  and  814   b  between the cuvette  812  and the conduit  798 . Reduction/removal of the discontinuities enables the blood based perfusion fluid  108  to flow through the cuvette with reduced lysing of red blood cells and reduced turbulence, which enables a more accurate reading of perfusion fluid oxygen levels. This also reduces damage to the perfusion fluid  108  by the system  100 , which ultimately reduces damage done to the heart  102  while being perfused by the system  100 . 
     According to the illustrative embodiment, the cuvette  812  is formed from a light transmissive material, such as any suitable light transmissive glass or polymer. As shown in  FIG. 28A , the sensor  140  also includes an optical transceiver  816  for directing light waves at perfusion fluid  108  passing through the cuvette  812  and for measuring light transmission and/or light reflectance to determine the amount of oxygen in the perfusion fluid  108 . As illustrated in  FIG. 28C , in some embodiments a light transmitter is located on one side of the cuvette  812  and a detector for measuring light transmission through the perfusion fluid  108  is located on an opposite side of the cuvette  812 .  FIG. 28C  depicts a top cross-sectional view of the cuvette  812  and the transceiver  816 . The transceiver  816  fits around cuvette  812  such that transceiver interior flat surfaces  811  and  813  mate against cuvette flat surfaces  821  and  823 , respectively, while the interior convex surface  815  of transceiver  816  mates with the cuvette  812  convex surface  819 . In operation, when uv light is transmitted from the transceiver  816 , it travels from flat surface  811  through the fluid  108  inside cuvette  812 , and is received by flat surface  813 . The flat surface  813  may be configured with a detector for measuring the light transmission through the fluid  108 . 
     The fluid flow path through the single use module  634  in both normal and retrograde flow modes will now be described with reference to  FIGS. 24A-24D  and  FIG. 25A . As described above with reference to  FIGS. 1-4 , the system  100  can maintain the heart  102  in two modes of operation; a normal flow mode, shown in  FIG. 3 , and a retrograde flow mode shown in  FIG. 4 . As mentioned above with regard to  FIG. 1 , to change between normal and retrograde flow modes, the system  100  provides the flow mode selector valve  112 , shown in detail in  FIGS. 26A and 26B . To operate in normal flow mode, the operator sets the flow mode selector valve handle  112   e  to the position indicated in  FIG. 24A . This has the effect of aligning the flow paths through the selector valve  112  as shown in  FIG. 26A . Specifically, in normal flow mode, fluid can flow into port  112   b , through the flow channel  112   f  and out the port  112   c . Additionally, fluid can flow into port  112   d , through the flow channel  112   g  and out the port  112   a . To operate in retrograde flow mode, the operator sets the flow mode selector valve handle  112   e  to the position indicated in  FIG. 24B . This has the effect of aligning the flow paths through the selector valve  112  as shown in  FIG. 26B . Specifically, in retrograde flow mode, fluid can flow into port  112   b , through the flow channel  112   h  and out the port  112   d.    
     Referring to  FIG. 24A , in normal flow mode, the reservoir  160  provides the perfusion fluid  108  to the one way inlet valve  191  of the perfusion pump interface assembly  300 . Referring to  FIG. 25A , the perfusion pump  106  pumps the perfusion fluid  108  out the outlet valve  310 . Referring to  FIG. 25C , the perfusion fluid  108  then flows through the conduit  792  and the compliance chamber  188  and into the inlet  110   a  of the heater assembly  110 . The heater assembly  110  heats the perfusion fluid  108  and then flows it out the heater outlet  110   b . Referring to  FIG. 24A , the heated perfusion fluid  108  flows from the heater outlet  110   b  in the lower chassis section  750   b  through the chassis plate  752  and into the port  112   b  of the mode select valve  112  via the conduit  794 . Referring also to  FIG. 24D , the perfusion fluid  108  flows out the mode valve port  112   c , through the compliance chamber  186 , the conduit  796 , and the pressure sensor  128  into the pulmonary vein cannulation interface  170  on the organ chamber assembly  104 . 
     Referring to  FIG. 24A , in normal flow mode, the heart  102  pumps the perfusion fluid  108  out the pulmonary artery  164  through the pulmonary artery interface  166  and the pressure sensor  130 . The conduit  796  then flows the perfusion fluid  108  from the pulmonary artery interface  166  through the plate  752  and through the O 2  saturation and hematocrit sensor  140 . Referring also to  FIGS. 25A and 25C , the conduit  798  then flows the perfusion fluid  108  from the sensor  140  through the flow-rate sensor  136  into the oxygenator  114 . The conduit  800  flows the perfusion fluid  108  from the oxygenator  114  back into the reservoir  160  by way of the reservoir inlet  786 . 
     Referring to  FIGS. 24A ,  24 D and  24 E, in normal flow mode, the heart  102  also pumps the perfusion fluid  108  out of the aorta  158  through the aorta interface  162  and the pressure sensor  126 . The conduit  802  flows the perfusion fluid  108  from the pressure sensor  126  through the flow rate sensor  134  and back into the port  112   d  on the flow mode selector valve  112 . A clamp  804  holds the conduit  802  in place. A conduit  806  flows the perfusion fluid  108  out the port  112   a  from the flow mode selector valve  112  through the compliance chamber  184  and the back pressure adjustment clamp  190 . As mentioned above, the clamp  190  may be adjusted to restrict flow through the conduit  806  to adjust the back pressure seen by the aorta  158  during normal flow mode to more realistically simulate normal physiologic conditions. The compliance chamber  184 , which can expand and contract as perfusion fluid  108  is pumped into and out of it, interoperates with the clamp  190  to dampen flow pressure spikes to further improve simulation of near-normal physiologic conditions. The after-load clamp  190  is configured to closely emulate systemic vascular resistance of the human body which affects aortic pressure, left atrial pressure, and coronary flow. A conduit  808  returns the perfusion fluid  108  into the reservoir  160  by way of the reservoir inlet  788 . 
     In retrograde flow mode, the flow mode selector valve  112  is positioned as shown in  FIG. 24B . Referring to  FIG. 24B , the reservoir  160  provides the perfusion fluid  108  to the inlet valve  191 . As shown in  FIG. 25A , the perfusion pump  106  pumps the perfusion fluid  108  out the outlet valve  310 . As shown in  FIG. 25C , the perfusion fluid  108  then flows through the conduit  792  and the compliance chamber  188  and into the inlet  110   a  of the heater assembly  110 . The heater assembly  110  heats the perfusion fluid  108  and then flows it out the heater outlet  110   b . Referring to  FIG. 24B , the heated perfusion fluid  108  flows from the heater outlet  110   b  in the lower chassis section  750   b  through the chassis plate  752  and into the input  112   b  of the mode select valve  112  via the conduit  794 . Referring also to  FIG. 24D , the perfusion fluid  108  flows out the mode valve outlet  112   d , into the conduit  802 , through the flow rate sensor  134 , the pressure sensor  126  and into the aorta  158  via the aorta interface  162 . The perfusion fluid  108  then flows through the coronary sinus  155  and the rest of the coronary vasculature. 
     Referring to  FIG. 24B , in retrograde flow mode, the heart  102  pumps the perfusion fluid  108  out of the pulmonary artery  164  and through the pulmonary artery interface  166  and the pressure sensor  130 . The conduit  796  then flows the perfusion fluid from the pulmonary artery interface  166  through the plate  752  and into the O 2  saturation and hematocrit sensor  140 . Referring also to  FIGS. 25A and 25C , the conduit  798  then flows the perfusion fluid  108  from the sensor  140  through the flow rate sensor  136  into the oxygenator  114 . The conduit  800  flows the perfusion fluid  108  from the oxygenator  114  back into the reservoir  160  by way of the reservoir inlet  786 . In retrograde flow mode, substantially no perfusion fluid is pumped into or out of the left atrium  152  via the pulmonary vein  168  and the pulmonary vein interface  170 , with the exception of a small amount of perfusion fluid diverted by the trickle valve  768  from the conduit  794  around the flow mode selector valve  112  into the compliance chamber  186 . As mentioned above, the trickle flow provides sufficient perfusion fluid  108  to keep the left atrium  152  moistened during retrograde flow. 
     As described above, the illustrative embodiment of the system  100  has one or more sensors or probes for measuring fluid flow and pressure. The probes and/or sensors may be obtained from standard commercial sources. The flow rate sensors  134 ,  136  and  138  are conventional, ultrasonic flow sensors, such as those available from Transonic Systems Inc., Ithaca, N.Y. The fluid pressure probes  126 ,  128  and  130  may be conventional, strain gauge pressure sensors available from MSI or G.E. Thermometries. Alternatively, a pre-calibrated pressure transducer chip can be embedded into organ chamber connectors and wired to a data collection site such as the front end board  637 . 
     Having described the electrical and mechanical components and functionality of illustrative embodiments of the system  100  and certain modes of operation thereof, the system  100  will next be described with reference to the illustrative organ harvest and transplant procedures of  FIGS. 29A and 29B . More particularly,  FIG. 29A  is a flow diagram  900  depicting exemplary methodologies for harvesting the donor heart  102  and cannulating it into the system  100  at a donor location.  FIG. 29B  depicts particular points of care for handling the heart  102  in preparation for cannulation, and  FIG. 30  is a flow diagram  902  of exemplary methodologies for removing the donor organ  102  from the system  100  and transplanting it into a patient at a recipient site. 
     As shown in  FIG. 29A , the process of obtaining and preparing the heart  102  for cannulation and transport begins by providing a suitable organ donor  904 . The organ donor is brought to a donor location, whereupon the process of receiving and preparing the donor heart  102  for cannulation and transport proceeds down two intersecting pathways  906  and  908 . The pathway  906  principally involves preparing the donor heart  102  for transplant, while the pathway  908  principally involves preparing the system  100  to receive the donor heart  102  and then transporting the heart  102  via system  100  to the recipient site. 
     With particular reference to  FIG. 29A , the first pathway  906  includes exsanguinating the donor  910 , arresting the donor heart  914 , explanting the heart  916 , and preparing the heart  102  for cannulation  918  into the system  100 . In particular, in the exsanguination step  910 , the donor&#39;s blood is removed and set aside so it can be used to perfuse the heart  102  during preservation on the system  100 . This step is performed by inserting a catheter into either the arterial or venous vasculature of the donor to allow the donor&#39;s blood to flow out of the donor and be collected into a blood collection bag. The donor&#39;s blood is allowed to flow out until the necessary amount of blood is collected, typically 1.0-2.5 liters, whereupon the catheter is removed. The blood extracted through exsanguination is then filtered and added to a fluid reservoir  160  of the system  100  in preparation for use with the system  100 . Alternatively, the blood can be exsanguinated from the donor and filtered for leukocytes and platelets in a single step that uses an apparatus having a filter integrated with the cannula and blood collection bag. An example of such a filter is a Pall BC2B filter. After the donor&#39;s blood is exsanguinated, the donor heart  102  is injected in step  914  with a cardioplegic solution to temporarily halt beating in preparation for harvesting the heart  102 . 
     After the heart  102  is arrested, the heart  102  is explanted  916  from the donor and prepared  918  for loading onto the system  100 . In general, the steps of explanting the heart  916  and preparing for loading  918  involve severing the connections between the vasculature of the heart  102  and the interior chest cavity of the donor, suturing various of the severed connections, then lifting the heart  102  from the chest cavity. 
     More particularly, as shown in  FIG. 29B , the right and left pulmonary arteries  164   a  and  164   b  are severed, and the right pulmonary artery  164   a  is tied-off by a surgical thread  901   a  or other suitable mechanism. The tying prevents fluid from flowing through the severed end  903   a  of the left pulmonary artery  164   a . As described above with reference to  FIGS. 24A-24B , the left pulmonary artery  164   b  remains unsutured to allow it to be cannulated to the organ chamber assembly  104 , thereby allowing perfusion fluid  108  to flow through the left pulmonary artery  164   b , through the pulmonary artery cannulation interface  170 , and back to the reservoir  160 . The left pulmonary veins  168   b  and  169   b  and the right pulmonary veins  168   a  and  169   a  are also severed, and all except a single pulmonary vein  169   b  are tied off with surgical thread  901   b ,  901   c , and  901   d , respectively. This prevents fluid from flowing through the severed ends  903   b  and  903   c  of the right pulmonary veins  168   a  and  169   a , or through the severed end  903   d  of the left pulmonary vein  168   b , but allows the untied pulmonary vein to be cannulated to the organ chamber assembly  104  through the pulmonary vein interface  170 . As described above with reference to  FIGS. 24A-24B , this arrangement allows the perfusion fluid  108  to flow through the right pulmonary artery  164   b , through the pulmonary artery interface  166 , and back to the oxygenator  114 . Alternatively, blood can be expelled from the right ventricle via cannulating the pulmonary arterial trunk. The pulmonary arterial trunk is not shown but includes the segment of pulmonary artery  164  between the branches  164   a  and  164   b  of the pulmonary artery  164  and the right ventricle  159 . The superior vena cava  161  is also severed and, once the heart is connected to the system  100  and begins beating, is tied with thread  901   e  to prevent fluid from flowing through its end  903   e.    
     The inferior vena cava  163  is similarly severed and tied with thread  901   f  or oversewn to prevent fluid from flowing through its end  903   f . The aorta  158  is also severed (in the illustrated embodiment at a point downstream from the coronary sinus  155 ) but is not tied off, allowing it to be cannulated to the organ chamber assembly  104 . In one embodiment, the aorta  158  is cannulated to an aortic connector, which can be easily attached to the aorta interface  170 . 
     With continued reference to the flow chart of  FIG. 29A , after the heart vasculature is severed and appropriately tied, the heart  102  is then loaded onto the system  100  by inserting it into the organ chamber assembly  104  and cannulating the aorta  158 , left pulmonary artery  164   b , and a pulmonary vein  169   b  to the appropriate points in the organ chamber assembly  104 . 
     Often, hearts obtained from donors who have also donated their lungs are missing part or all of the left atrium  152 . In this situation, the heart  102  can still be instrumented and perfused in the retrograde mode by cannulating the aorta  158  and either the right pulmonary artery  164   a  or pulmonary artery trunk (not shown, but described above), and allowing any remaining left atrium  152  portion to remain open during the preservation period. 
     With continued reference to  FIG. 29A , during the preparation of the heart via path  906 , the system  100  is prepared through the steps of path  908  so it is primed and waiting to receive the heart  102  for cannulation and transport as soon as the heart  102  is prepared. By quickly transferring the heart  102  from the donor to the system  100 , and subsequently perfusing the heart  102  with the perfusion fluid  108 , a medical operator can minimize the amount of time the heart  102  is deprived of oxygen and other nutrients, and thus reduce ischemia and other ill effects that arise during current organ care techniques. In certain embodiments, the amount of time between infusing the heart  102  with cardioplegic solution and beginning flow of the perfusion fluid  108  through the heart  102  via the system  100  is less than about 15 minutes. In other illustrative embodiments, the between-time is less than about ½ hour, less than about 1 hour, less than about 2 hours, or even less than about 3 hours. Similarly, the time between transplanting the heart into an organ care system  100  and bringing the heart  102  to a near physiological temperature (e.g., between about 34° C. and about 37° C.) occurs within a brief period of time so as to reduce ischemia within the heart tissues. In some illustrative embodiments, the period of time is less than about 5 minutes, while in other applications it may be less than about ½ hour, less than about 1 hour, less than about 2 hours, or even less than about 3 hours. According to some illustrative embodiments, the heart can be transferred directly from the donor to the system  100 , without the use of cardioplegia, and in such applications the time to beginning the flow of warm perfusion fluid  108  and/or time to the heart reaching near physiologic temperature is similarly less than about 5 minutes, less than about ½ hour, less than about 1 hour, less than about 2 hours, or even less than about 3 hours. In one implementation, the donor heart is not arrested prior to removal from the donor, and is instrumented onto the system  100  while the heart  102  is still beating. 
     As shown in  FIG. 29A , the system  100  is prepared in pathway  908  through a series of steps, which include preparing the single use module  634  (step  922 ), priming the system  100  with priming solution (step  924 ), filtering the blood from the donor and adding it to the system  100  reservoir  160  (step  912 ), and connecting the heart  102  into the system  100  (step  904 ). In particular, the step  922  of preparing the single use module  634  includes assembling the disposable single use module  634 . Suitable assemblies are shown, for example, in  FIGS. 24A-24D ,  FIGS. 25A-25C , and  FIG. 26 . After the module  634  is assembled, or provided in the appropriate assembly, it is then inserted into multiple use module  650  through the process described above with reference to  FIGS. 21A-21C . 
     In step  924 , the loaded system  100  is primed with priming solution, as described in more particular detail below with reference to Table 1. According to one feature, to aid in priming, the system  100  provides an organ bypass conduit  810  shown installed into the organ chamber assembly  104  in  FIG. 27A . As depicted, the bypass conduit includes three segments  810   a - 810   c . Segment  810   a  attaches to the pulmonary artery cannulation interface  170 . The segment  810   b  attaches to the aorta cannulation interface  810   b , and the segment  810   c  attaches to the pulmonary vein cannulation interface  166 . Using the bypass conduit  810  so attached/cannulated into the organ chamber assembly  104 , an operator can cause the system  100  to circulate the perfusion fluid  108  through all of the paths used during actual operation. This enables the system  100  to be thoroughly tested and primed prior to cannulating the heart  102  into place. 
     In the next step  912 , blood from the donor is filtered and added to the reservoir  160 . The filtering process helps reduce the inflammatory process through the complete or partial removal of leukocytes and platelets. Additionally, the donor blood is mixed with one or more nutritional  116  and/or preservative  118  solutions to form the perfusion fluid  108 . In step  926 , the system  100  is primed with the perfusion fluid  108  by pumping it through the system  100  in the retrograde flow mode, as described above in reference to  FIG. 24B , and with the bypass conduit  810  in place. As the perfusion fluid  108  circulates through the system  100  in priming step  926 , it is warmed to the desired temperature as it passes through heater assembly  110 . The desired temperature range and heating applications are described above in reference to  FIGS. 6A through 6E , and in respect to  FIG. 13 . In step  920 , after the system  100  is primed with the perfusion fluid  108 , the bypass conduit  810  is removed, and the heart  102  is instrumented, as described above and shown in  FIG. 27B , onto the system  100 . 
     After the heart  102  is instrumented onto the system  100 , the pump  104  is activated and the flow mode valve  112  is positioned in retrograde flow mode (described above with reference to  FIGS. 1 and 4 ) to pump the perfusion fluid  108  in retrograde flow mode through the aorta into the vasculature of the heart  102 . The pumping of the warm, oxygen and nutrient enriched perfusion fluid  108  through the heart  102  allows the heart  102  to function ex vivo in a near normal physiologic state. In particular, the warm perfusion fluid  108  warms the heart  102  as it perfuses through it, which may cause the heart  102  to resume beating in its natural fashion. In some instances, it is desirable to assist the heart  102  in resuming its beating, which may be done by providing hand massage or a defibrillation signal  143  (shown in  FIG. 22E ) to the heart  102 . This may be done as described above with reference to the organ chamber assembly of  FIGS. 5A-5F  and operator interface  146  of  FIGS. 17A-17J . 
     After the heart is instrumented onto the system  100  at step  920 , subsequent steps  928  and  930  allow the operator to test the heart  102  and the system  100 , and to evaluate their respective conditions. Illustratively, step  928  involves evaluating ECG signals  379  and  381  from the sensors  142  and  144  (positioned as shown in  FIG. 27A ), respectively, as well as hematocrit  145  and oxygen saturation  141  levels of the perfusion fluid  108  from the sensor  140 . As further described in reference to  FIG. 12  and  FIGS. 17A-17I , the operator can also monitor the fluid flows, pressures, and temperatures of the system  100  while the heart  102  is cannulated. As described above with reference to  FIGS. 5E and 5F , the testing step  928  may also include having the operator touch/examine the heart  102  by lifting an outer lid  196  of the organ chamber  104  and touching/examining the heart  102  indirectly through the flexible membrane  198   b . During the evaluation step  930 , based on the data and other information obtained during testing  928 , the operator determines whether and how to adjust the system  100  properties (e.g., fluid flows, pressures, and temperatures), and whether to provide additional defibrillation, or other needed modes of treatment to the heart  102 . The operator makes any such adjustments in step  932 , then repeats steps  928  and  930  to re-test and re-evaluate the heart  102  and the system  100 . In certain embodiments, the operator may also opt to perform surgical, therapeutic or other procedures on the heart  102  during the adjustment step  932 . For example, the operator can conduct an evaluation of the physiological fitness of the heart, such as for example, performing an ultrasound or other imaging test, performing an echocardiogram or diagnostic test on the heart, measuring arterial blood gas levels and other evaluative tests. 
     In another application, during or after step  932 , the system  100  allows a medical operator to evaluate the organ for compatibility with an intended recipient after explantation but prior to implantation into the donor. For example, the operator can perform a Human Leukocyte Antigen (HLA) matching test on the organ while the organ is cannulated to the system  100 . Such tests may require 12 hours or longer and are performed to ensure compatibility of the organ with the intended recipient. The preservation of an organ using the system  100  described above may allow for preservation times in excess of the time needed to complete an HLA match, potentially resulting in improved post-transplant outcomes. In the HLA matching test example, the HLA test can be performed on the heart while a preservation solution is pumping into the heart. 
     According to a further illustrative embodiment, after the heart is functioning as determined by the step  932 , the operator can perform surgery on the heart or provide therapeutic or other treatment, such as immunosuppressive treatments, chemotherapy, genetic testing and therapies, or irradiation therapy. Because the system  100  allows the heart  102  to be perfused under near physiological temperature, fluid flow rate, and oxygen saturation levels, the heart  102  can be maintained after the adjustment step  932  for a long period of time (e.g., for a period of at least 3 days or more, greater than at least 1 week, at least 3 weeks, or a month or more) to allow for repeated evaluation and treatment. 
     According to the illustrative embodiment, the testing  928 , evaluation  930  and adjustment  932  steps may be conducted with the system  100  operating in retrograde flow mode, or may be conducted with the system  100  operating in normal flow mode. In normal flow mode, the operator can test the function of the heart  102  under normal or near normal physiologic blood flow conditions. Based on the evaluation  930 , the settings of the system  100  may be adjusted in step  932 , if necessary, to modify the flow, heating and/or other characteristics to stabilize the heart  102  in step  934  in preparation for transport to the recipient site in step  936 . After the heart  102  and the system  100  is tested and evaluated to ensure appropriate performance, the system  100  with the loaded heart  102  is transported to the recipient site at step  936 . 
     Referring now to  FIG. 30 , the first phase  942  of the transplant process involves repeating the testing  928  and evaluation  930  steps undertaken just prior to leaving the donor site  936 . If the function and characteristics of the heart  102  are not acceptable, the system  100  can be adjusted  942  as appropriate, for example, to provide appropriate fluid oxygenation or nutritional levels, or to increase or decrease the appropriate fluid temperature. As noted above, surgical and/or other therapeutic/remedial procedures may be performed on the heart  102 , along with the testing  928  and evaluation  930 . According to the illustrative embodiment, testing at the recipient site may be performed in retrograde flow mode, normal flow mode, or a combination of both. 
     At step  946 , after testing is complete, the system  100  is placed in normal/forward flow mode. In certain embodiments, this step  946  is not initiated until the left atrium  152  and pulmonary vein  164  are cannulated, there is adequate operating volume in the system, the heart exhibits stable electrical activity, the ABG and electrolytes are within acceptable ranges, SvO 2  is &gt;80%, and blood temperature is between about 34° C. and about 36° C. The step  946  is may be accomplished by slowing and/or stopping the retrograde pumping of the system  100 , then restarting the pumping in forward mode. In certain embodiments, prior to restarting in forward mode, the user opens the aortic sampling port  754   a , releases the pressure control clamp  190  by turning it counterclockwise, then increases the flow rate of pump  106  to about 1.0 L/min, sets the flow control valve  112  to normal/forward flow, and increases the flow rate of pump  106  to about 2.0 L/min to allow the blood  102  to displace air in the perfusate lines (e.g.,  802 ) of the system  100  and pass through the left side of the heart  102  and down the reservoir return line  808 . The user then closes the aortic sampling port  754   a.    
     The flow rate of the perfusion fluid  108  emitted from the pump  106  is then increased at step  950  to a level of the clinician&#39;s choosing (typically between about 1 L/min to about 5 L/min) to approximate the physiologic flow rate provided by the heart  102  while functioning in normal beating mode. The heart  102  and the system  100  are again tested at step  952  in a similar fashion to that described above with respect to steps  928  and  930 . The clinician may also choose to perform any other tests or evaluations on the heart, for example echocardiogram, electrolyte measurements, cardiac enzyme measurements, metabolyte measurements, intravascular ultrasound evaluation, pressure-volume loop evaluation, and Millar pressure evaluation. 
     In the third phase  946  at the recipient site, the heart  102  is prepared for implantation into the recipient. This phase includes the step  956  of powering down the pump  106  to stop the flow of perfusion fluid  108 . Next, in step  958 , the heart  102  is arrested, for example by injecting it with cardioplegic solution in a similar fashion to what is done in step  914  at the donor site. In step  960 , the heart  102  is de-cannulated and removed from the organ chamber assembly  106 . In step  962 , the heart  102  is transplanted into the recipient patient by first removing the sutures  901   a - 901   f , then inserting the heart  102  into the recipient&#39;s chest cavity, and suturing the various heart vesicles (e.g.,  158 ,  164   a ,  164   b ,  168   a ,  168   b ,  169   a ,  169   b , and  903   a - 903   f ) to their appropriate mating vesicles within the recipient. 
     While external devices and methods have been described to defibrillate the heart, deliver pacing signals to the heart, and perform blood chemistry analyses from samples taken from the perfusion fluid, it may also be beneficial to integrate these features into the portable system. Such features include defibrillation, pacing, diagnostic ECG sensing, and blood chemistry analyses. 
     As described above, the system  100  employs a priming solution, and also employs a perfusion fluid  108  that combines a nutritional supplement  116  solution and a preservative solution  118  with a blood product or synthetic blood product to form the perfusion fluid  108 . The priming, supplement  116 , and preservative  118  solutions are described next. 
     According to certain embodiments, solutions with particular solutes and concentrations are selected and proportioned to enable the organ to function at physiologic or near physiologic conditions. For example, such conditions include maintaining organ function at or near a physiological temperature and/or preserving an organ in a state that permits normal cellular metabolism, such as protein synthesis. Exemplary solutions for perfusing a heart are disclosed in U.S. Provisional Application Ser. No. 60/793,472 and are incorporated by reference herein. 
     Certain experimental data are available to describe certain embodiments of solutions described herein and their use in heart perfusion and are set forth in  FIGS. 31-33 .  FIG. 31  depicts a chart demonstrating electrolyte stability for a heart under going perfusion in forward mode according to an embodiment of the system  100 . In the embodiment associated with  FIG. 31 , the organ is a heart  102  wherein perfusion is conducted in forward mode (as described above) by pumping perfusion fluid  108  containing solution  116 / 118  to the let atria  152  and out of the aorta  158 . The rate of perfusion is approximately 30 mL/hr. As can be seen from  FIG. 31 , the levels of various electrolytes: sodium, potassium, calcium, and chloride ions, as well as dissolved glucose, remain at stable levels throughout the course of perfusion, from before the organ is cannulated to the perfusion system  100  to six hours after cannulation within the system  100 . 
       FIG. 32  depicts a chart demonstrating electrolyte stability for an organ under going retrograde perfusion according to another embodiment of the system  100 . In the embodiment associated with  FIG. 32 , the organ is a heart wherein perfusion occurs by pumping the perfusion fluid  108  containing the solution  116 / 118  into the aorta  158  and through the coronary sinus  155 . The rate of perfusion is approximately 30 mL/hr. As can be seen from  FIG. 32 , the levels of various electrolytes: sodium, potassium, calcium, and chloride ions, as well as dissolved glucose, remain at stable levels throughout the course of perfusion, from before the organ is cannulated to the perfusion system  100  to six hours after cannulation.  FIG. 32  also demonstrates that the levels of the electrolytes and glucose remain at levels similar to those for the base line (BL) normal physiological state for the organ. 
       FIG. 33  depicts a chart demonstrating the arterial blood gas profile for an organ under going perfusion according to another embodiment of the invention. As can be seen from  FIG. 33 , the levels of various blood gasses: carbon dioxide and oxygen, and pH remain at stable levels throughout the six hour course of perfusion.  FIG. 33  also demonstrates that the levels of carbon dioxide, oxygen, and pH remain at levels similar to those for two base line (BL) measurements for the normal physiological state for the organ.  FIGS. 31-33  demonstrate the ability of the present systems and methods to maintain an organ under stable physiological or near physiological conditions. 
     The systems and methods described above for use in perfusing a heart ex vivo may also be adapted for the maintenance of one or more lungs in an ex vivo environment. In general, an exemplary system adapted for ex vivo lung maintenance includes a perfusion circuit that can circulate warm blood or other perfusion fluid through the lungs, and one or more gas sources for ventilating and supplying necessary oxygen, carbon dioxide and nitrogen to the lungs. An exemplary perfusion circuit includes a pump to circulate the perfusion fluid and one or more cannulation or other interfaces for connecting the lungs within the perfusion circuit. Similar to the system  100 , the lung maintenance system may also include other features such as a gas exchange device (e.g., an oxygenator, or a ventilator), a fluid heater to allow the user to control the temperature of the perfusion fluid, and fluid pumping and heating process control systems. Nutritional sources may also be provided to replenish carbohydrates, electrolytes and other components of the perfusion fluid that are consumed during system operation. 
     An exemplary system for lung maintenance will next be described, along with a description of lung anatomical features that impact how the lungs are harvested and connected into the system. Exemplary techniques are then described for maintaining lungs ex vivo and for evaluating lungs to ascertain their functionality and suitability for transplantation. An exemplary embodiment of the system and components thereof are then described in further detail. 
     In certain embodiments, a lung maintenance system is configured in a portable module similar to the heart system described above, with both single-use and multiple use components that allow for optimal costs of production and system re-use.  FIG. 34  depicts a schematic diagram of an exemplary portable lung care system  1000 . The illustrated system  1000  includes a disposable single use module  1002 , similar to the single use module  634 , and designed to inter-fit within the system  1000  for containing at least one lung during ex vivo maintenance and for regulating gas composition and flow of the perfusion fluid  108  (not shown) to and from the harvested organ. More particularly, as shown in  FIGS. 41-43 , the disposable module  1002  includes a lung chamber assembly  1018 , wherein at least one lung  1004  is instrumented via a pulmonary artery interface  1022 , a pulmonary vein interface  1026 , and a tracheal interface  1024 . The disposable module  1002  also includes a fluid reservoir  160  for containing the circulating perfusion fluid  108 , a perfusion pump interface  300 , a heater assembly  110 , and a plurality of fluid flow conduits and peripheral monitoring components. The single use module  1002  is described in further operational detail below with reference to FIGS.  34  and  41 - 43 . The system  1000  also includes a perfusion fluid pump  106 , a nutritional subsystem  115 , a power subsystem  148 , an operator interface  146 , a ventilation source  1003  (e.g., a ventilator/respirator or a breathing circuit including a bag), a controller  150  and a multiple use module  650  (not shown), similar to those described above. In addition, the system  1000  includes one or more gas sources connected to the single use module  1002 , each having an ability to control pressure and flow rate of the gases. The exemplary system  1000  also includes a gas exchange device, which in certain embodiments is an oxygenator  114 , for receiving and mixing gases from the one or more gas sources. 
       FIG. 35A  depicts a pair of explanted lungs  1004  that can be connected into the system  1000  for extended ex vivo maintenance. The explanted lungs  1004  are excised from a donor along with a portion of the donor&#39;s pulmonary circuitry  1010 , as illustrated in  FIG. 36 . In particular, the harvested lungs  1004  are excised from the donor by cutting across the donor&#39;s left atrium  1009 , which allows for the explantation of a plurality of pulmonary veins  1007  that connect respective lungs  1004  to the piece of excised left atrial tissue, known as a left atrial cuff  1008 . The pulmonary veins  1007  are four in number, two from each lung, and include a right inferior vein  1007   a , a right superior vein  1007   b , a left inferior vein  1007   c  and a left superior vein  1007   d . In an alternative embodiment, multiple pieces of left atrial tissue are excised from a donor, each connecting one or more pulmonary veins  1007  to a single aggregation of the left atrial cuff. Excision is also made at the donor&#39;s main pulmonary artery  1012 , beginning at the base of the donor&#39;s right ventricle  1014 , to which both the donor&#39;s right pulmonary artery  1005   a  and left pulmonary artery  1005   b  are confluently attached. Optionally, the explanted lungs  1004  also include the donor&#39;s trachea  1006  through which air is transported into both of the lungs  1004 . 
       FIG. 35B  sets forth a close-up view of a single lung  1004  that is explanted for use in the system  1000 . The depicted left lung  1004   b  is excised from a donor by cutting across the donor&#39;s left atrium  1009 , as described above, which allows for the explantation of the left superior  1007   c  and inferior veins  1007   d  that are joined at the excised left atrial cuff  1008 . The explanted lung  1004   b  may also include the donor&#39;s left pulmonary artery  1005   b  and, optionally, the donor&#39;s trachea  1006 . 
     After explantation, lungs  1004  are placed in an ex vivo perfusion system in which they are perfused during transport to a donor site, and in which they can be evaluated to ascertain their functionality and suitability for transplantation. 
     More particularly, the system  1000  of  FIG. 34  is adapted to maintain the explanted lungs  1004  in two modes of operation—a maintenance mode and an evaluation mode. The maintenance mode is used by the system  1000  to preserve the lungs  1004  ex vivo for an extended period of time. In general, in the maintenance mode, the system  1000  circulates the perfusion fluid  108  into the lungs  1004  through the pulmonary artery interface  1022  and away from the lungs  1004  through the pulmonary vein interface  1026 . The system  1000  also ventilates the lungs  1004  through the tracheal interface  1024  during perfusion. Ventilation occurs mechanically by delivering a gas through the tracheal interface  1024  in breaths that include periodic inspiration and expiration, in a manner that approximates the normal mechanical function of a lung in-vivo. In an alternative embodiment, periodic inspiration and expiration is obtained in a protective ventilation fashion, whereby the breaths are triggered by a critical opening pressure and a critical closing pressure to achieve a PEEP of about 8 to about 10 cmH 2 O and a tidal volume of about 5 to about 7 ml/kg indicating the volume of gas flowing into the lungs with each breath. The breathing rate of the lung may be selected by the operator. In certain implementations, the system  1000  provides 12 or fewer breaths per minute; in certain implementations the system provides 6 breaths per minute. The number of breaths per minute is determined by the operator through the controller  150 , which sends one or more electrical signals to a valve in the tracheal conduit, which opens and allows gas from the gas mixture to flow through the tracheal interface  1024  and into the lung. Ventilation can be done by lung ventilators for example, VentiPAC Model 200D or PneuPac. 
     In addition, the system  1000  supplies a flow of a respiratory gas, having a predetermined composition of gas components, to the lungs  1004  for use in respiration by the lungs  1004  during perfusion. Upon reaching a steady state of the system  1000 , the perfusion fluid  108  flowing into the lungs  1004  includes a substantially constant composition of gas components, and the perfusion fluid  108  flowing away from the lungs  1004  also includes a substantially constant composition of gas components. As used herein, a substantially constant composition of a component in a fluid is achieved at equilibrium, which occurs when the quantity of the component in the fluid varies over time by an amount less than about 5%, less than about 3%, or less than about 1% at a given sampling location within the system. In this respect, the perfusion fluid  108  used to perfuse the lungs  1004  includes equilibrium compositions of gas components. This mode of operation provides the amount of gas that needs to be supplied to the lungs  1004  for sustaining their viability during extended periods of ex vivo maintenance and economizes the transportation of the explanted lungs  1004  to the donor location. As illustrated in  FIGS. 37 and 38 , the maintenance mode may be implemented using two different approaches, both of which yield the steady state condition in the perfusion fluid  108  as described above. In addition,  FIG. 39  provides exemplary steady-state measurements of gas components in the perfusion fluid  108  obtained during one of the two maintenance mode approaches. 
     The maintenance mode is implemented in two exemplary approaches—a tracheal oxygen delivery approach, and an isolated tracheal volume re-breathing approach.  FIG. 37  depicts a flow diagram  1300  of the steps involved in the tracheal oxygen delivery approach of the maintenance mode. At step  1302 , the explanted lungs  1004  are instrumented within a perfusion circuit of the system  1000 . At step  1304 , the explanted lungs  1004  are perfused by a perfusion fluid  108  that is oxygenated to a desired level prior to initiating the perfusion of the lungs  1004 . Optionally, the perfusion fluid  108  may be brought to a high level of oxygen prior to initiating the perfusion of the lungs  1004  so that an initial high level of oxygen is delivered to the explanted lungs  1004 . During perfusion of the lungs  1004 , the oxygenated perfusion fluid  108  flows into the explanted lungs  1004  via the pulmonary artery interface  1022  and flows away from the lungs  1004  via the pulmonary vein interface  1026  (step  1306 ). The explanted lungs  1004  are ventilated through the tracheal interface  1024  by a gas mixture that contains a pre-determined composition of gas components for organ respiration (step  1308 ). 
     Ventilation is performed in this approach by flowing the ventilation/respiratory gas into the tracheal interface  1024  in periodic breaths containing a pre-determined volume and pressure of gas. Each breath includes a compression stage where the gas is delivered into the lung in a desired volume, followed by decompressing or relaxing of the lungs  1004  (and allowing the lungs  1004  to expel gas in an unaided manner) so that the lungs  1004  exhale the gas through the tracheal interface  1024  in a volume approximately equal to the compression volume. An outlet valve on the tracheal interface  1024  may be used to ensure a minimum PEEP is maintained by preventing the pressure falling below a user-determined value. 
     In certain embodiments, the respiratory gas mixture includes about 10% to about 20% oxygen, about 2% to about 8% carbon dioxide, and the balance is nitrogen. In certain embodiments, the gas mixture includes about 14% oxygen, about 5% carbon dioxide, and the balance is nitrogen. The oxygen component in the ventilation/respiratory gas provided through the tracheal interface  1024  enters alveoli of the lungs  1004  and exchanges with carbon dioxide from the perfusion fluid  108  flowing into the lungs  1004 . The perfusion fluid  108  that enters the lungs  1004  is oxygenated as a result of this exchange and then flows into the vasculature of the lung, where oxygen is consumed and carbon dioxide produced. The lungs  1004  may consume oxygen in an amount less than the amount of oxygen provided in the tracheal breaths. The carbon dioxide produced by the lungs  1004  passes into the perfusion fluid  108 , then into the alveoli and is excreted from the lungs  1004  via exhaled breaths through an outlet valve in the tracheal interface  1024 . The outlet valve is provided across the tracheal interface  1024  to allow the exhaled breaths to be expelled from the system  1000  and is described below with reference to  FIG. 43 . 
     In the tracheal oxygen delivery approach, the composition of the ventilation/respiratory gas is pre-determined by the operator so as to establish gas component equilibrium in the system. In other words, oxygen supplied to the lungs  1004  through the tracheal interface  1024  is consumed in the lungs  1004  and resulting carbon dioxide is expelled through the tracheal interface  1024  without altering the gas composition in the perfusion fluid  108  entering or exiting the lung. In equilibrium by this delivery approach, the perfusion fluid  108  flowing into the lungs  1004  and flowing away from the lungs  1004  have substantially the same composition of oxygen and carbon dioxide, as indicated at step  1310 . Moreover, at step  1312 , the lungs  1004  are perfused over an extended period of time while maintaining fluid and gas equilibrium in the lung. 
       FIG. 38  depicts a flow diagram  1400  of the steps involved in the second implementation of the maintenance mode. Similar to the first mode, at step  1402 , the explanted lungs  1004  are instrumented within the lung care system  1000 . At step  1404 , the instrumented lungs  1004  are perfused with a perfusion fluid  108  that flows into the lungs  1004  via the pulmonary artery interface  1022  and flows away from the lungs  1004  via the pulmonary vein interface  1026 . In addition, one or more respiratory gas mixtures, each containing a pre-determined composition of gas components, are supplied to the perfusion fluid  108  via a gas exchange device (e.g., oxygenator)  1042  of the system  1000  (step  1406 ). More specifically, a first gas source supplied to the oxygenator  1042  includes a gas composition of about 11% to about 14% oxygen and about 3% to about 7% carbon dioxide, and the balance is nitrogen. In certain instances, the first gas source includes about 12% oxygen and about 5% carbon dioxide, and the balance is nitrogen. Other gases may be used, for example nitric oxide (for endothelial protection and vasodilation) and carbon monoxide (to provide anti-apoptototic effects). 
     At step  1408 , the lungs  1004  are also ventilated with an isolated gas volume delivered through the tracheal interface  1024 . The isolated gas volume is provided in a configuration that prevents it from communicating or otherwise interfacing with other fluids except in the lung alveoli. In this approach, the gas components in the isolated gas volume are able to reach a substantially constant composition by exchanging with the gas components from the perfusion fluid  108  pumped into the lungs  1004  via the pulmonary artery interface  1022  (step  1408 ). This gas exchange takes place across the alveolar membrane of the lungs  1004 . Exhaled carbon dioxide component produced from the exchange is then carried away from the lungs  1004  via the circulating perfusion fluid  108 . This carbon dioxide component is substantially removed from the perfusion fluid  108  by the gas exchange device  1042 . 
     Upon reaching equilibrium, as indicated in step  1410 , oxygen and carbon dioxide in the perfusion fluid  108  flowing into the lungs  1004  have a substantially constant first composition, and oxygen and carbon dioxide in the perfusion fluid  108  flowing away from the lungs  1004  have a substantially constant second composition. However, unlike in the tracheal oxygen delivery mode, in the isolated tracheal volume mode the first composition of oxygen and carbon dioxide components in the perfusion fluid  108  flowing into the lungs  1004  may differ from the second composition of the gas components in the perfusion fluid  108  flowing away from the lungs  1004 . In preferred embodiments of this approach, such first and second compositions differ by amounts substantially equivalent to the quantity of oxygen consumed by the lungs  1004  and the quantity of carbon dioxide produced by the lungs  1004  during metabolism. 
     In certain embodiments, the oxygen composition in the perfusion fluid  108  is maintained during perfusion at a steady-state partial pressure or oxygen saturation that is greater in the perfusion fluid  108  flowing into the lungs  1004  than in the perfusion fluid  108  flowing away from the lungs  1004 . In certain embodiments, the carbon dioxide component is maintained during perfusion at a steady state partial pressure that is lower in the perfusion fluid  108  flowing into the lungs  1004  than in the perfusion fluid  108  flowing out of the lungs  1004 . This approach of implementing the maintenance mode is also referred to as an isolated tracheal volume re-breathing approach, wherein oxygen supplied to the perfusion fluid  108  through the oxygenator  1042  is consumed in the lungs  1004  and resulting carbon dioxide is carried away from the lungs  1004  by the perfusion fluid  108  and removed through the oxygenator  1042 . 
     Ventilation is performed in the second mode with breaths that occur approximately as frequent as those provided in the first mode. However, ventilation in the second mode occurs by first compressing the isolated gas volume, thereby flowing the gas from the isolated volume and into the tracheal interface  1024 , and then allowing the lungs to relax and expirate gas, in an unaided manner, from the lung alveoli to fill the isolated volume. 
     In the maintenance mode, the system  1000  pumps the perfusion fluid  108  to the lungs  1004  at a rate of about 500 to about 5000 ml/min. This mode of operation may help reduce damage to the lungs  1004  during extended periods of ex vivo maintenance. Thus, according to one feature of the invention, the lungs  1004  are transported to a donor site in the maintenance mode. Additionally, the functional tests performed during the evaluation mode, described below, can also be conducted during the maintenance mode to evaluate various lung capabilities. In certain instances, recruitment of the lungs  1004  may be performed in the maintenance mode. For example, a suction force may be applied to the lungs  1004  via the tracheal interface  1024  to clear the lungs  1004  of fluid or alveoli debris. Collapsed alveoli in the lungs  1004  may be inflated by causing the lungs  1004  to inhale breaths that are of variable volume, such as sigh breathing which causes the lungs  1004  to inhale a first breath having a volume that is larger than the volumes of at least two next breaths using, for example, a ventilator or a breathing circuit including a bag. 
     Having described the two different approaches of implementing a maintenance mode of operation with respect to  FIGS. 37 and 38 , exemplary measurements of gas components in the perfusion fluid  108  flowing into and away from a pair of lungs  1004  equilibrium is described next for an isolated tracheal volume re-breathing approach. In particular, as shown in  FIG. 39 , data in column  4000  provides steady-state measurements of gas components in the perfusion fluid  108  flowing into the explanted lungs  1004  through the pulmonary artery interface  1022 . Data in column  4002  provides steady-state measurements of gas components in the perfusion fluid  108  flowing away from the explanted lungs  1004  through the pulmonary vein interface  1026 . The data in  FIG. 39  was obtained using a blood gas analyzer, such as Radiometer ABL800 FLEX, to analyze samples of perfusion fluid  108  taken during the isolated tracheal volume re-breathing approach. Briefly referring to the lung maintenance system  1000  of  FIGS. 41-43 , a first sample of the perfusion fluid  108  was taken at port  1080  on the artieral fluid flow. This fluid sample was analyzed by the blood gas analyzer to generate the data in column  4000 . For the sake of measurement accuracy, the radiometer was recalibrated after performing each analysis on a fluid sample. A second sample of the perfusion fluid  108  was taken at port  1082  and was analyzed by the blood gas analyzer to generate the data in column  4002 . The two sets of measurements were spaced apart in time because of the recalibration requirement. 
     In general, during the maintenance mode, the perfusion fluid  108  flowing into and away from the lungs  1004  are maintained at a relatively similar gas component composition. For instance, the partial pressure  4000   a  of carbon dioxide in the arterial fluid flow (43.8 mmHg) is only slightly lower than the partial pressure  4002   a  of carbon dioxide in the venous fluid flow (44.6 mmHg), and the partial pressure  4000   b  of oxygen in the arterial fluid flow (84.5 mmHg) is only slightly higher than the partial pressure  4002   b  of oxygen in the venous fluid flow (83.9 mmHg). These differences in the partial pressures can be attributable to imprecision in the measuring system, lung metabolism, or interactions with the oxygenator  1042 . 
     In certain embodiments, the composition of gas components in the perfusion fluid  108  is chosen to provide steady-state partial pressures of the gas components within the circulating fluid in a range between a body&#39;s physiologic arterial blood gas composition and physiologic venous blood gas composition. For example, as shown in  FIG. 39 , the composition of the oxygen component in the perfusion fluid  108  is at a partial pressure that is greater than a composition of the oxygen component in physiologic venous blood and less than a composition of the oxygen component in physiologic arterial blood. More specifically, this partial pressure of the oxygen component in the perfusion fluid  108  may be between about 75 mmHg to about 100 mmHg, between about 80 mmHg to about 90 mmHg, or between about 83 mmHg to about 85 mmHg. In addition, as shown in  FIG. 40 , the composition of the carbon dioxide component in the perfusion fluid  108  is at a partial pressure that is less than a composition of the carbon dioxide component in physiologic venous blood and greater than a composition of the carbon dioxide component in physiologic arterial blood. More specifically, this partial pressure of the carbon dioxide component in the perfusion fluid  108  may be between about 40 mmHg to about 50 mmHg or between about 42 mmHg to about 48 mmHg. 
     Having discussed the maintenance mode in detail with respect to  FIGS. 37-39 , the evaluation mode is explained next. Techniques for evaluating the lungs  1004  to ascertain their functionality and suitability for transplantation will also be described. 
     In particular,  FIG. 40  provides a flow diagram  1200  illustrating the steps involved in implementing the evaluation mode. As depicted, the system  1000  perfuses the explanted lungs  1004  with a perfusion fluid  108 . The perfusion fluid  108  is made to be similar in partial pressures of blood gases to a body&#39;s physiologic venous blood. This venous gas composition in the perfusion fluid  108  may be achieved by mixing one or more gases, having a combined composition of carbon dioxide and low or no oxygen, with the perfusion fluid  108  (step  1204 ), until a desired venous composition is reached ( 1206 ), at which point the gases may optionally be stopped from being supplied to the perfusion fluid  108  (step  1208 ). In one embodiment, the gases include about 5% carbon dioxide and about 95% nitrogen. The perfusion fluid  108  is adapted to flow into the lungs  1004  through the pulmonary artery interface  1022  and flow away from the lungs  1004  through the pulmonary vein interface  1026 . As indicated at step  1210 , the explanted lungs  1004  may be ventilated by an oxygen-containing gas that is flowed into the tracheal interface  1024  from a suitable ventilation source, such as from a ventilator/respirator. This gas may comprise about 100% oxygen, about less than 100% oxygen, less than about 75% oxygen, less than about 50% oxygen or less than about 25% oxygen. In certain embodiments, this gas may be the same composition as ambient air. 
     The evaluation mode is useful, for example, for performing tests to evaluate the gas-transfer capacity of the lungs  1004  by determining the partial pressure or oxygen saturation of the perfusion fluid  108  both before and after it flows through the lungs  1004 . To perform this test in the evaluation mode, as shown at steps  1212  and  1214 , the system  1000  monitors the blood gas composition of the perfusion fluid  108  after ventilation begins by taking sample measurements of oxygen saturation or partial pressure of oxygen in the perfusion fluid  108  flowing into the lungs  1004  via the pulmonary artery interface  1022  and flowing away from the lungs  1004  via the pulmonary vein interface  1026 . The resulting pulmonary artery and pulmonary vein oxygen saturation or partial pressure oxygen measurements are then compared with each other to identify a maximum difference that is representative of the gas-transfer capacity of the lungs  1004 . In a second approach to evaluating the gas-transfer capacity of the lungs, the oxygen saturation or partial pressure of oxygen in the perfusion fluid flowing into the lungs  1004  is taken before ventilation begins. At a pre-determined time period after ventilation begins, another measurement of oxygen saturation or partial pressure of oxygen in the perfusion fluid flowing away from the lungs  1004  is taken and is compared with the first measurement to evaluate the gas-transfer capacity of the lungs  1004 . The operator determines whether this capacity is sufficient and decides to carry out the transplant, or not. In addition, other functional tests on the lungs  1004  may be performed, such as diagnostic bronchoscopy, visual evaluation and biopsy, both prior and subsequent to transportation of the lungs  1004  to a donor location. 
     Exemplary functional tests performed on the lungs  1004  during the evaluation mode include tests that assess the gas exchange functionality of the lungs  1004 , which may be conducted using blood gas analysis of fluid samples taken from both the arterial-side (e.g., through port  1080 ) and venous-side (e.g., through port  1082 ) of fluid flow in the perfusion circuit. Tests can be conducted to assess pulmonary circulation of the perfusion fluid  108  through the lungs. This may involve the calculation of pulmonary vascular resistance (PVR) which is a measure of the ability of the lungs  1004  to resist fluid flow. Details regarding the PVR value calculation are provided below with respect to  FIG. 52 . In addition, alterations in the PVR value may be monitored in response to an infusion of nitric oxide into the perfusion fluid  108  to detect any reversibility of pulmonary hypertension. Pulmonary angiography on the lungs  1004  may also be performed. In certain implementations, assessment of the bronchial tree is conducted using bronchoscopy along with other analysis applications such as inspecting the airways, collecting bronchial washings for cytological or microbiological studies or obtaining multiple biopsies. In certain implementations, image studies are performed on the lungs  1004  using, for example, x-rays, CTs, or nuclear studies such as perfusion or ventilation scans. These imaging devices may be external to or onboard the organ care system  1000 . In certain instances, viability studies are conducted on parenchymal or bronchial tissue of the lungs  1004  using techniques such as biopsies or measurements of tissue levels of AMP, ADP and ATP. Additionally, assessments may be performed such as assessing the severity of ischemia reperfusion injury in the instrumented lungs  1004  by measuring levels of indicator agents, such as conjugated dienes or lactate, in the perfusion fluid  108 . Moreover, a lung permeability test may be perform on the explanted lungs to determine if the lungs are injured or otherwise comprised. This test includes injecting an agent, such as a dye, into the perfusion fluid and, after a time period of perfusion, visually inspecting the lungs. If the agent is visually detectable in the endo-bronchial tree of the lungs or in the alveoli, then the lungs are injured because they are permeable to the injected substance. Further assessments include using biomarkers based on proteomic or genomic approaches to predict organ graft rejection or development of bronchiolitis obliterans syndrome (BOS) in a potential organ recipient. In certain instances, one or more of the above-mentioned tests can be performed on the lungs  1004  during a maintenance mode of operation. 
     Having described the exemplary processes for implementing the maintenance mode and the evaluation mode, along with techniques for evaluating lungs  1004  to ascertain their functionality and suitability for transplantation, features of the lung care system  1000  will be described next in further detail with respect to these two modes of operation. In particular, instrumentation of the lungs  1004  within the system  1000  is described in further detail. Then a generalized approach for operating the system is described, followed by a discussion of specific system features that are tailored to each mode of operation. 
       FIGS. 41-43  illustrate a pair of explanted lungs  1004 , such as the explanted lungs  1004  of  FIG. 35  a, cannulated within an embodiment of the disposable single use module  1002 . In particular, the module  1002  includes a lung chamber assembly  1018  that contains the explanted lungs  1004  connected to the assembly  1018  from at least one of the pulmonary artery interface  1022 , the pulmonary vein interface  1026 , and the tracheal interface  1024 . The lungs  1004  may lay prone or supine in the lung chamber assembly  1018 . With brief reference to  FIG. 35  A, the pulmonary artery interface  1022  includes a cannulation of the lungs  1004  at or near the main pulmonary artery  1012 . The tracheal interface  1024  may include a cannulation of the lungs  1004  at or near the trachea  1006 . In optional embodiments, where the trachea  1006  is not excised with the lungs  1004 , the tracheal interface  1024  may include a conduit that is directly placed in a bronchial branch of each lung  1004 , and the lungs  1004  are vented by such conduit. The pulmonary vein interface  1026  may include cannulation to the lungs  1004  at the excised left atrial cuff  1008  where at least one of the pulmonary veins  1007  of the two lungs  1004  is attached. However, in certain embodiments, the excised left atrial cuff  1008  remains un-cannulated. Specific details regarding the pulmonary vein interface  1026  are discussed below in the context of exemplary operational processes and with reference to  FIGS. 48-51 . The module  1002  also includes the reservoir  160  for holding the perfusion fluid  108  and an oxygenator  1042  that provides at least one appropriate gas mixture to the perfusion fluid  108 . 
     Referring again to FIGS.  34  and  41 - 43 , in an illustrative embodiment of a general operational process, the perfusion fluid  108  is prepared for use within the module  1002  (and, ultimately, within the system  1000 ) by being loaded into the reservoir  160  via portal  774  and, optionally, is treated with therapeutics via portal  762 . The loaded perfusion fluid  108  is subsequently pumped from the reservoir  160  to the heater assembly  110  and warmed to a near physiologic temperature. In this illustrated embodiment, this pumping action is provided by an alignment of the pump interface assembly  300  with the pump driver  334  of the multiple use module  650  which is described above with reference to  FIG. 8C . The pump interface assembly  300  receives a pumping force from the pump driver  334  and translates the pumping force to the perfusion fluid  108 , thereby circulating the perfusion fluid  108  to the lung chamber assembly  1018 . However, any fluid pump may be used to flow the perfusion fluid  108  in the perfusion circuit. The heat assembly  110  includes temperature sensors  120  and  122  and dual-sensor  124  that provide temperature measurement of the perfusion fluid  108 . A plurality of compliance chambers, such as compliance chambers  1086   a - c , may be included in the system  1000 . They are essentially small inline fluid accumulators with flexible, resilient walls designed to simulate the human body&#39;s vascular compliance by aiding the system  1000  to more accurately mimic blood flow in the human body. In particular, compliance chamber  1086   a  is located at an outlet of the perfusion fluid pump  300 , compliance chamber  1086   b  is located at an outlet of the heater assembly  110 , and compliance chamber  1086   c  is located at an outlet of the oxygenator  1042 . Any one of these compliance chambers  1086   a - c  may be used individually or a plurality of compliance chambers may be used in any combination. 
     The perfusion fluid  108  from the heater assembly  110  is then pumped to the gas exchange device  1042 . Depending on the flow mode selected as well as the type of implementation chosen for executing the selected flow mode, one or more mixing gases, each having a pre-determined gas composition, may be automatically or manually supplied to the perfusion fluid  108  through the gas exchange device (e.g., an oxygenator)  1042 . In certain embodiments, the flow mode type selection is made using a mode selector switch  1020  located on the system  1000  between the gas supplies and the oxygenator  1042 . The mode selector switch  1020  may be operated manually as well as by the controller  150 . In certain embodiments, the order of the oxygenator  1042  and the heater assembly  110  along the illustrated perfusion circuit is switched. 
     Depending on the mode switch  1020  selected, the oxygenator  1042  receives one or more mixing gases, from respective gas sources through gas regulators  174 ,  1030   a  and  103   b  and gas flow chambers  172 ,  1028   a  and  1028   b . The gas sources may be external to or onboard the system  1000 . Gas pressure gauges, such as gauges  178 ,  1036   a  and  1036   b , provide visual indication of the level of gas in the respective gas supplies  172 ,  1028   a  and  1028   b . Transducers  132 ,  1032   a  and  1032   b  provide similar information to the controller  150 . The controller is able to regulate automatically the gas flow from each gas source into the oxygenator  1042  in dependence, for example, on the perfusion fluid oxygen content measured at oxygenation/hematocrit sensor  1064 , much like the sensor  140  described above. This sensor also provides a signal indicative of a hematocrit measurement of the perfusion fluid  108 . Subsequent to the mixing of the selected gases with the perfusion fluid  108 , the perfusion fluid  108  is pumped towards the lungs  1004  through the pulmonary artery interface  1022 . In one exemplary embodiment, a mixing gas supplied to the oxygenator  1042  from a gas flow chamber is pre-mixed to include a desired gas composition for infusion into the perfusion fluid  108 . One or more additional gas sources each containing, for example, a high level of oxygen, carbon dioxide or hydrogen, may be additionally supplied to the oxygenator  1042  from other gas flow chambers to modulate the composition of the mixing gas in the perfusion fluid  108 . In another embodiment, gases having different compositions are controllably released from the appropriate gas chambers to the oxygenator  1042  at rates and volumes that allow the desired gas mixture composition to be obtained in the perfusion fluid  108 . However, for certain perfusion modes, the oxygenator  1042  is not activated. 
     In certain practices, a flow rate sensor  1056 , much like the flow rate sensor  134 , is positioned along the arterial fluid flow from the oxygenator  1042  to the pulmonary artery interface  1022  to measure a flow rate of the fluid  108 . A pressure sensor  1050 , much like the pressure sensor  126  described above, is also positioned along the arterial fluid flow to measure the pressure of the perfusion fluid  108 . This pressure sensor  1050  may be on an edge of the lung chamber assembly  1018  or inside of the assembly  1018  and as close as possible to a site of pulmonary artery cannulation. In certain embodiments, a port  1080  is provided for allowing an operator to extract samples of the perfusion fluid  108  along the arterial flow for further offline analysis. 
     The perfusion fluid  108  is then pumped into the lung chamber assembly  1018  and the lungs  1004  cannulated therein via the pulmonary artery interface  1022 . The pulmonary artery interface  1022  includes cannulation to the main pulmonary artery  1005  through an aperture  1040   a  located on the lung chamber assembly  1018 . The lungs  1004  may be ventilated with a gas mixture via the trachea interface  1024  that includes cannulation to the trachea  1006  (or a substitute conduit not shown) via an aperture  1040   b  located on the lung chamber assembly  1018 . Alternatively, cannulation may be made to a portion of a trachea  1006  intact on the explanted lungs  1004 .  FIGS. 41-43  illustrate various approaches of ventilating the lungs  1004  through the tracheal interface  1024 . These approaches are mode-specific for the maintenance mode approaches described above and as described below in further operational detail. In certain embodiments, the controller  150  is able to regulate a composition of gas components supplied to the lungs  1004  via the tracheal interface  1024  based on fractional inspired O 2  (FiO 2 ) concentration measurements and fractional expired CO 2  concentration measurements obtained at FiCO 2  meter  1030  and FiCO 2  meter  1031 , respectively. A flow rate sensor  1067  may also be used to measure the rate at which the lungs  1004  are ventilated via the tracheal interface  1024 . A pressure sensor  1068  may be used to measure the pressure of the gas supplied to the lungs  1004  via the tracheal interface  1024 . In certain embodiments, electrode sensors  1060  and  1062  are coupled to the lung chamber assembly  1018  to measure the weight and elasticity, respectively, of the explanted lungs  1004 . 
     The perfusion fluid  108  is pumped out of the lung chamber assembly  1018  via the pulmonary vein interface  1026  that includes, in certain embodiments, a cannulation to the pulmonary veins  1007  through an aperture  1040   c  located on the lung chamber assembly  1018 . In other embodiments, the pulmonary veins  1007  remain un-cannulated. In general, the pulmonary vein interface  1026  establishes a return path of the perfusion fluid  108  from the pulmonary veins  1007  to the reservoir  160  for continued circulation through the perfusion circuit. In addition, a fluid passageway  1084  is provided that connects the lung chamber assembly to the reservoir  160 . Along a path of fluid flow from the pulmonary vein interface  1026  to the reservoir  160 , one or more sensors can be positioned to provide measurements such as fluid flow rate via flow rate sensor  1058 , fluid pressure via pressure sensor  1052 , and fluid oxygenation and hematocrit via sensor  1066 . The pressure sensor  1052  may be on an edge of the lung chamber assembly  1018  or inside of the assembly  1018  and as close as possible to the site of pulmonary vein cannulation. In certain embodiments, a port  1082  is provided for allowing the operator to extract samples of the perfusion fluid  108  along the venous flow. In certain embodiments, a flow clamp  1090 , much like flow clamp  190  described above, is positioned along the path of fluid flow from the pulmonary vein interface  1026  to the reservoir  160  for regulating a back pressure applied to the pulmonary veins  1007  when the lungs  1004  are instrumented in the lung chamber assembly  1018 . 
     Having described a generalized process for operating the system  1000 , the system  1000  is next described in further detail with reference to individual modes. These modes include the evaluation mode and the maintenance mode, the latter of which can be implemented using the tracheal oxygen delivery approach or the isolated tracheal volume re-breathing approach, as described above with reference to  FIGS. 37 and 38 . 
       FIGS. 41 and 42  illustrate various embodiments of the single-used module  1002  configured for use with the isolated tracheal re-breathing approach. In particular, the first gas source, including a gas composition of about 3% to about 7% carbon dioxide, about 11% to about 14% oxygen, and the balance being nitrogen, is supplied to the gas exchange device (i.e., an oxygenator)  1042  for circulation through the perfusion system  1000 . During perfusion, the perfusion fluid  108  is pumped into the lungs  1004  through the pulmonary artery interface  1022  and pumped away from the lungs  1004  through the pulmonary vein interface  1026 . In addition, an isolated gas volume is delivered to the lungs  1004  during perfusion via the tracheal interface  1024  to ventilate the lungs  1004 , as described above in  FIG. 38 . In one embodiment depicted in  FIG. 41 , the isolated gas volume is provided by a flexible bag  1069  that may contract and expand with each breath of the lungs  1004  during ex vivo care. In one embodiment depicted in  FIG. 42 , the constant gas volume is provided by a hose  1050  connected to a gas source  1052  such as a gas tank or a ventilator. The hose  1050  is appropriately configured to allow the lungs  1004  to inspire a constant gas volume during perfusion. In yet another embodiment, a specialized ventilator may be used to supply the constant gas volume to the lungs  1004 . 
       FIG. 43  illustrates an embodiment of the single-use module  1002  configured for use with the tracheal oxygen delivery approach described above with reference to  FIG. 37 . The perfusion fluid  108  is oxygenated to a desired gas component level prior to perfusing the lungs  1004 . This may be achieved by circulating the perfusion fluid  108  through the system  1000  before lung instrumentation and supplying the fluid  108  with an appropriate gas mixture through, for example, the oxygenator  1042 . After the perfusion fluid  108  reaches a desired gas component level, the oxygenator  1042  is deactivated to stop the delivery of respiratory gas to the perfusion fluid  108 . The oxygenated perfusion fluid  108  is subsequently stored in the reservoir  160  before organ perfusion begins. 
     During perfusion, the perfusion fluid  108  is pumped from the reservoir  160  to the heater assembly  110  and warmed to a near physiologic temperature before being supplied to the lungs  1004  in the lung chamber assembly via the pulmonary artery interface  1022 . In the embodiment of  FIG. 43 , the lungs  1004  are ventilated with a continuous supply of a gas mixture from an external gas source through an inlet valve  1060  of the tracheal interface  1024 . As described above, in one implementation the gas mixture includes a composition of about 14% oxygen, about 5% carbon dioxide, and the balance is nitrogen. The gas source may be a gas chamber  1062 , such as gas chambers  172 ,  1028   a  and  1028   b  of  FIG. 34 , housed external to or onboard the system  1000 . A gas pressure gauge  1064 , such as gauges  178 ,  1036   a  and  1036   b  of  FIG. 34 , provide visual indication of the pressure of gas in the chamber  1062 . During perfusion, the oxygen component in the gas mixture inhaled by the lungs  1004  through the inlet valve  1060  exchanges with the carbon dioxide component in the perfusion fluid  108  across the alveoli of the lungs  1004 , and the carbon dioxide component is subsequently expelled from the alveoli in an exhaled breath via an outlet valve  1066  of the tracheal interface  1024 . Both the inlet  1060  and the outlet  1066  valves are configured to prevent substantial mixing of gas components between the gas mixture flowing through each valve. The perfusion fluid  108  flows out of the lung chamber assembly  1018  via the pulmonary vein interface  1026 . 
     Having described the system  1000  in relation to the maintenance mode, the system  1000  is next discussed with respect to the evaluation mode. As mentioned above, the perfusion fluid  108  in the reservoir  160  is allowed to reach a predetermined gas composition before tests are performed on the lungs  1004  to evaluate, for example, their gas-transfer capability. The pre-determined gas composition may be, for example, a physiologic venous blood-gas composition. This venous blood-gas composition in the perfusion fluid  108  may be achieved by applying a low-oxygen or oxygen-free gas mixture to the perfusion fluid  108  through the oxygenator  1042  after the perfusion fluid  108  flows out of the reservoir  160 . Exemplary low-oxygen or oxygen-free gas mixtures include a mixture having about 4% to about 11% carbon dioxide, about 0% to about 8% oxygen, and the balance is nitrogen, a mixture having about 5% carbon dioxide, about 0% oxygen and the balance is nitrogen, and a mixture having about 5% carbon dioxide, about 5% oxygen, and the balance is nitrogen. The resulting perfusion fluid  108  is optionally passed through the heater assembly  110 , pumped into the lungs  1004  via the pulmonary artery interface  1022 , and flows away from the lungs  1004  via the pulmonary vein interface  1026 , thereafter returning to the reservoir  160  for subsequent return through the circuit. In this manner, the perfusion fluid  108  is circulated in the system  1000  until a venous blood gas composition is reached in the perfusion fluid  108  flowing into and flowing away from the lungs  1004 . After the perfusion fluid  108  reaches the desired venous gas composition, the oxygenator  1042  may be deactivated to stop the flow of low-oxygen or no-oxygen gas mixture to the perfusion fluid  108 . The lungs  1004  are then ventilated with an oxygen-containing gas from an external source via the tracheal interface  1024 . The gas-transfer capability of the lungs  1004  may thus be determined by monitoring the oxygen saturation or partial pressure of oxygen on the venous and arterial flows of the perfusion fluid  108  after ventilation begins. 
     Thus far, an exemplary system  1000  for lung maintenance has been described, along with a description of lung anatomical features that impact how the lungs  1004  are harvested and connected into the system  1000 . In addition, exemplary techniques have been described for maintaining lungs  1004  ex vivo during a maintenance mode of operation. Exemplary techniques have also been described for evaluating lungs  1004  to ascertain their functionality and suitability for transplantation during the evaluation mode. Moreover, exemplary features of the system  1000  have been described in detail in relation to the various modes. Next, additional exemplary features of the system  1000  are discussed, including the lung chamber assembly  1018 , the pulmonary vein interface  1026 , system controls, and data acquisition and display modules. An exemplary transplantation procedure is then described, along with a description of exemplary solutions that are used in the perfusion circuit to care for the lungs  1004 . 
     Various embodiments of the lung chamber assembly  1018  are described with reference to  FIGS. 44-47 . As depicted, the lung chamber assembly  1018  may be rectangular in shape to house a pair of explanted lungs  1004 . Alternatively, the lung chamber assembly  1018  may be triangular in shape to accommodate a single explanted lung  1004 . With brief reference to  FIGS. 41-43 , the lung chamber assembly  1018  includes apertures  1040   a - 1040   c  adapted to receive the pulmonary artery interface  1022 , the trachea interface  1024  and the pulmonary vein interface  1026 . Overall, the structure and material composition of the lung chamber assembly  1018  closely resembles the organ chamber assembly  104  for the containment of a heart described above and depicted in  FIGS. 5A-5F , but expanded to a size sufficient to house a pair of lungs  1004 . Particularly, the explanted lungs  1004  may be contained in either a soft or hard shell casing in the lung chamber assembly  1018 . In certain embodiments, the assembly  1018  lies flat. In other embodiments, the assembly  1018  is tilted at an adjustable angle such that the explanted lungs  1004  lie at the same angle therein. 
     The shell casing of the lung chamber assembly  1018  may include a suspension mechanism to provide support and stability to the lungs  1004 . Exemplary suspension mechanisms are depicted in  FIGS. 44-47 . In one illustrative embodiment of the lung chamber assembly  1018  shown in  FIG. 44 , a flexible membrane (e.g., a netting, fabric, cloth or other suitably flexible material) is used to suspend the explanted lungs  1004  in the lung chamber assembly  1018  so as to minimize contact between a surface of the lungs  1004  and one or more inner walls of the lung chamber assembly  1018 . The membrane contacts a large portion of the surface of the lung to support the lung&#39;s weight in a manner that distributes the weight across the membrane, thereby reducing the pressure on any particular region of the lungs  1004  and avoiding alveolar damage. The flexible membrane  1070  in the depicted embodiment is a netting structure. The netting structure  1070  may be meshed or porous and may substantially prevent alveoli in at least a portion of the lungs  1004  from collapsing while being held in the assembly  1018  for ex vivo maintenance. In an alternative embodiment of the lung chamber assembly  1018  as illustrated in  FIG. 45 , the lungs  1004  may be additionally or alternatively contained in a second netting  1072  that suspends the lungs  1004  from a top cover of or other structures within the assembly  1018 . This second netting  1072  simulates the effects a ribcage has on the lungs  1004  by preventing the lungs  1004  from over expanding during respiration while maintaining their physiologic shape. The second netting  1072  may be constructed from the same material as the first netting  1070  or may be constructed from a substantially different material. 
     In certain embodiments, there is a support structure for the lungs that simulates the interior of the chest cavity, supporting the lungs on anterior and posterior sides, and helping the lungs to maintain their physiologic shape. For example, in an illustrative embodiment of the lung chamber assembly  1018  as shown in  FIG. 46 , a ribcage-shaped housing  1074  is used to hold the explanted lungs  1004  in the lung chamber assembly  1018 . This ribcage-shaped housing  1074 , constructed from a flexible material, simulates the shape and movement of a real ribcage. In certain implementations as depicted in  FIG. 47 , a feature  1076  similar to a body&#39;s diaphragm is coupled to the ribcage-shaped housing  1074  (refer to the ribcage cut away in  FIG. 47  for better view) by extending across a bottom portion of the housing  1074 . This diaphragm  1076  may also be constructed from a flexible material so that it may contract and relax with each respiration of the lungs  1004 . 
     Having described specific features of the lung chamber assembly  1018 , exemplary features of the pulmonary vein interface  1026  are described next with reference to  FIGS. 48-51 . More specifically,  FIGS. 48-51  illustrate various embodiments of connecting the pulmonary veins  1007  in the system  1000  at the pulmonary vein interface  1026  as illustrated above with reference to  FIGS. 41-43 . In certain embodiments the veins  1007  are cannulated at the interface  1026 . However, the pulmonary veins  1007  may remain un-cannulated, such that fluid flowing away from the pulmonary veins  1007  freely drains into the lung chamber assembly  1018  and returns to the reservoir  160  through passageway  1084 , as depicted in the system of  FIGS. 41-43 . 
     FIGS.  48 Aa and  48 B depict an exemplary apparatus for cannulation at the pulmonary vein interface  1026  of  FIGS. 41-43 . As illustrated, the cannulation device  1001  includes a funnel-shaped cannula  1100  having proximal  1168   a  and distal  1168   b  ends and a connector device  1102  having legs  1102   a  and  1102   b . Using the connector device  1102 , an operator mates the cannula  1100  with the donor&#39;s excised left atrial cuff  1008  having all of the donor&#39;s pulmonary veins  1007  confluently attached. As the donor&#39;s pulmonary veins  1007  also attach to the donor&#39;s lungs  1004 , the mating of the cannula  1100  with the cuff  1008  secures such cuff  1008 , veins  1007  and lungs  1004  within the system  1000 . 
     As illustrated in  FIG. 48B , the connector device  1102  includes connection surfaces  1104  and  1112  that are used to form the mating interface between the cuff  1008  and the cannula  1100 . As shown, the surfaces  1104  and  1112  are each configured as a ring with a hollow center and attached to respective legs  1102   a  and  1102   b . The ring  1104  is larger than a cross-section  1164  of the distal end  1168   b  of the cannula  1100  but smaller than a cross-section  1162  of the proximal end  1168   a  of the cannula  1100  so that the ring  1104  can be secured behind the funneled portion  1160  of the cannula  1100 . In addition, the ring  1112  is configured to be small enough in comparison to the size of the left atrial cuff  1008  such that the cuff  1008  cannot easily be pulled out of the ring  1112  after the cuff  1008  has been pushed through the ring  1112 . 
     When operating the cannulation device  1001  according to the illustrative embodiment, the ring  1104  is inserted on the distal end  1168   b  of the cannula  1100  and slides through the length of the cannula  1100  until the ring  1104  abuts and optionally tightly encircles a section of the cannula  1100 . The excised left atrial cuff  1008  is then pushed through the ring  1112 , leaving a portion  1170  of the cuff  1008  extending beyond the perimeter of the ring  1112 . An operator then compresses the handles  1118  of the connector device  1102  until the left atrial cuff  1008  mates with the funneled opening at the proximal end  1168   a  of the cannula  1100  so that locking mechanism  1103   a  and  1103   b  engage each other to keep the connector device  1102  secured. The cannula  1100  is suitably configured such that the funnel portion  1160  of the cannula  1100  is able to receive and engage the left atrial cuff  1008 . In certain embodiments, the cannula  1100  is malleable to allow it to be bent as needed to secure the lungs  1004  and inter-fit with the system  1000 . A cannula  1100  is malleable, in general, if it is able to bend but maintain a generally consistent cross-sectional diameter regardless of how severely it is bent. In certain embodiments, appropriately sized cannulas and connector devices are provided to accommodate excised left atrial cuff of various sizes. 
     After engaging the cuff  1008 , the legs  1102   a  and  1102   b  are locked in place by the locking mechanism  1103   a  and  1103   b  or other suitable mechanisms to hold the connector device  1102  at the compressed position. 
       FIGS. 49A and 49B  depict another embodiment of the apparatus for cannulation at the pulmonary vein interface  1026 . This apparatus is also designed for use with a single piece of excised left atrial cuff having all four of the donor&#39;s pulmonary veins  1007  confluently attached. As shown in  FIG. 49A , the connector device  1102  includes a first connection surface  1130  configured as a ring with a first inner peripheral surface  1106  and a first outer O-ring seal  1108 . The first inner peripheral surface  1106  includes threads (not shown) that interlock with the outwardly extending grooves  1110  projecting from the funnel-shaped cannula&#39;s outer peripheral surface  1111 . Consequently, the cannula  1100  is coaxially coupled to the ring  1130 . The connector device  1102  also includes a second connection surface  1112  configured as a ring with a second inner peripheral surface  1114  and a second outer O-ring seal  1116 . In one embodiment as depicted in  FIG. 49B , projections  1120  are regularly spaced around the circumference of the inner peripheral surface  1114  to firmly engage a portion  1101  of the left atrial cuff  1008  to the ring  1112  when the cuff  1008  is pushed through the ring  1112 . Other suitable mechanisms may be used to provide the same tissue-securing function. It is noted that the size of the second O-ring seal  1116  may be small enough in comparison to the size of the left atrial cuff  1008  such that the portion  1101  of the cuff  1008  securely rests within the O-ring seal  1116 . In turn, the cannula  1100  and the first O-ring seal  1108  are accordingly configured such that when the first  1108  and second  1116  O-ring seals mate, a fluid tight seal is formed around the cannula  1100  and the portion  1101  of the left atrial cuff  1008 . In certain embodiments, appropriately sized cannulas and connector devices are provided to accommodate excised left atrial cuff of various sizes. 
     When operating the cannulation device  1001 , the ring  1130  is screwed to the outer peripheral surface  1111  of the cannula  1100  via the grooves  1110  until tight. A portion  1101  of the excised left atrial cuff  1008  is then pushed through the second inner peripheral surface  1114  of the second ring  1112  until the portion  1101  is securely fitted within the seal  1116 . An operator then pushes together the handles  1118  of the connector device  1102  until the first  1108  and second  1116  O-ring seals mate to provide a seal around the cannula  1100  and the left atrial cuff  1008 . The legs  1102   a  and  1102   b  are then locked in place by a locking pin (not shown) or other suitable mechanisms such as the locking mechanism  1103   a  and  1103   b  of  FIG. 48 . In certain embodiments, to break the seal around the cannula  1100  and the left atrial cuff  1008 , the operator releases the locking pin (not shown) followed by pulling apart the handles  1118  of the connector device  1102  until the first  1108  and second  116  O-ring seals separate. 
       FIGS. 50A and 50B  depict yet another embodiment of the apparatus for cannulation at the pulmonary vein interface  1026 . This apparatus is designed for use with the donor&#39;s left atrial cuff  1008  that is attached to the four pulmonary veins  1007  of the donor. As illustrated  50 B, the cannulation device  1001  includes a funnel-shaped cannula  1100  having a proximal end  1168   a , a connection surface  1800 , a stopper  1804 , and legs  1102   a  and  1102   b  attached to the cannula  1100  and the connection surface  1800 , respectively. 
     In certain embodiments, the proximal end  1168   a  of the cannula  1100  and the connection surface  1800  are configured to form a mating surface when the handles  1118  of the cannulation device  1001  are in a compressed position and the stopper  1804  inter-fits within a center perforation  1802  of the connection surface  1800 . More specifically, the connection surface  1800  is configured as a square structure having a square perforation  1802  etched through a center portion of the connection surface  1800 . The stopper  1804  is adapted to inter-fit within the square perforation  1802  such that the square perforation  1802  is divided into four smaller square perforations  1802   a - d . A cross-section of the proximal end  1168   a  of the cannula  1100  is also square in shape and is similarly sized as a cross-section of the connection surface  1800 . In addition, the size of each the smaller square perforations  1802   a - d  is small enough in comparison to the size of the left atrial cuff  1008  that the cuff  1008  cannot easily be pulled out of the perforations  1802   a - d  after the cuff  1008  has been pushed through the large perforation  1802  and secured into place by the stopper  1804 . 
     When operating the cannulation device  1001  according to the illustrative embodiment, the excised left atrial cuff  1008  is pushed through the large center perforation  1802  of the connection surface  1800 , leaving a portion of the cuff  1008  extending beyond a perimeter of the perforation  1802 . An operator then inter-fits the stopper  1804  into the center perforation  1802  to secure the cuff  1800  to the connection surface  1800 . The operator then compresses the handles  1118  of the cannulation device  1001  until the left atrial cuff  1008  mates with the funneled opening at the proximal end  1168   a  of the cannula  1100 . The cannula  1100  is suitably configured such that it is able to receive and engage all the left atrial cuff  1008  secured to the connection surface  1800 . In certain embodiments, the cannula  1100  is malleable to allow it to be bent as needed to further secure the lungs  1004  and inter-fit with the system  1000 . 
     After engaging all the left atrial cuff  1008  to the cannula  1100 , the legs  1102   a  and  1102   b  are locked in place by a locking pin (not shown) or other suitable mechanisms to hold the connector device  1102  at the compressed position. 
     Referring again to  FIGS. 48-50B , in certain instances, a cross-section of a proximal opening  1168   a  of a cannula  1100  may be larger in size than a cross-section of the left atrial cuff  1008  cannulated to the cannula  1100 . This configuration allows a portion of the perfusion fluid  108  flowing through the pulmonary veins  1007  to drain into the lung chamber assembly  1018  instead of flowing into the cannula  1100 . In certain instances, the mating interface between the cannula  1100  and the left atrial cuff  1008  is configured to be semi-sealable so that at least a portion of the perfusion fluid  108  flowing from the pulmonary veins  1007  to the cannula  1100  is able to leak into the lung chamber assembly  1018 . In certain instances, the cannula  1100  is situated in the lung chamber assembly  1018  in a relatively upright position in relation the left atrial cuff  1008  such that the perfusion fluid  108  flows in an upward direction from the left atrial cuff  1008  to the cannula  1100 . Due to the semi-sealable mating interface formed between the cannula  1100  and the left atrial cuff  1008 , a portion of the perfusion fluid  108  is adapted to seep out of the mating interface and drain into the lung chamber assembly  1018 . A back pressure is subsequently created by the perfusion fluid  108  in the cannula  1100 . In one example, this back pressure is created by a column of perfusion fluid  108  in the cannula  1100  that is between about 1 cm to about 3 cm high. 
       FIG. 51A  illustrates another embodiment of connection (e.g., by cannulation) at the pulmonary vein interface  1026 . An excised left atrial cuff  1008 , having one or more pulmonary veins  1007  attached thereto, is folded upon itself and sealed at a seam  1900  to form a pocket interface  1902 . In particular, the left atrial cuff  1008  is folded in a manner such that the pulmonary veins  1007  are fluidly connected to a void interior region defined by the pocket interface  1902 . In addition, a proximal end  1168   a  of a cannula  1100  is sealed within the pocket  1902  such that that the proximal opening  1168   a  of the cannula  1100  is also fluidly connected to the void region of the pocket interface  1902 . This two-way connection between the pulmonary veins  1007  and the cannula  1100  via the pocket interface  1902  is adapted to conduct the perfusion fluid  108  away from the lungs  1004  during perfusion. The pocket interface  1902  may be surgically sewn or stapled together. In certain embodiments, the pocket interface  1902  is relatively leak proof so that almost all of the fluid  108  flowing through the pulmonary veins  1007  are conducted to the proximal opening  1168   a  of the cannula  1100 . In certain embodiments, the pocket interface  1902  is designed to allow a certain amount of the fluid  108  to drain into the lung chamber assembly  1018  instead of flowing into the cannula  1100 . This leaked-through fluid  108  may be returned to the reservoir  160  via the passageway  1084  that connects the lung chamber assembly  1018  to the reservoir  160 . 
       FIG. 51B  illustrates yet another embodiment of connection (e.g., by cannulation) at the pulmonary vein interface  1026 . An excised left atrial cuff  1008  is lowered into a cup-shaped interface  4202  from a top opening  4210  (not shown) of the cup-shaped interface  4202  that is located inside of the lung chamber assembly  1018 . In an exemplary embodiment, a size of the top opening  4210  is less than the size of the explanted lungs  1004 , but is small enough to allow the left atrial cuff  1008  to be lowered comfortably into the interface  4202 . The cup-shaped interface  4202  also includes openings  4203   a - c  situated at varying heights along a sidewall of the interface  4202  and in fluid communication with a selector valve  4206  via conduits  4204   a - c , respectively. The selector valve  4206  is additionally coupled to an outlet conduit  4208  that is adapted to conduct perfusion fluid  108  away from the lung chamber assembly  1018  and into the reservoir  160 . In certain instances, the selector valve  4206  is manually or electromechanically controlled by controller  150  and/or user interface  146  to perform selective and controlled dispensing of the perfusion fluid  108  from the cup-shaped interface  4202  through a selected one of the openings  4203   a - c  and into the outlet conduit  4208 . Hence, the selector valve  4206  may be used to maintain a desired level of perfusion fluid  108  in the cup-shaped interface  4202 . In operation, as perfusion fluid  108  exits from the pulmonary veins  1007  via the left atrial cuff  1008 , it collects into the cup-shaped interface  4204  until the height of the perfusion fluid  108  within the interface  4202  reaches one of the openings  4203   a - c  as set by the selector valve  4206 . The fluid  108  then exists the cup-shaped interface  4202  via the selected opening, flows through the corresponding conduit, enters the selector valve  4206  and ported away from the lung chamber assembly  1018  via the outlet conduit  4208 . 
     Hence, the perfusion fluid  108  is able to fill the cup-shaped interface  4202  to a height where the selected one of the openings  4203   a - c  is located in order to create a desired level of back pressure on the pulmonary veins  1007 . 
     Having described specific features of the lung chamber assembly  1018  and exemplary processes for cannulation at the pulmonary vein interface  1026 , details regarding the data acquisition and display modules of the system  1000  are described next. 
     In one aspect, the illustrative control system scheme depicted in the block diagram of  FIG. 11  is used for operating the system  1000  to care for the explanted lungs  1004 . Each subsystem depicted in the functional blocks of  FIG. 11  is particularly configured to maintain the lungs  1004  in an optimally viable state at or near physiologic conditions. More specifically, the data acquisition subsystem  147 , as illustrated in the block diagram of  FIG. 12 , is modified to include sensors for obtaining information pertaining to the function of system  1000  and the lungs  1004 , and for communicating the information to the controller  150  for processing and use by the system  1000 . As described above with reference to  FIGS. 41-43 , the sensors used in the system  1000  include pressure sensors  1050 ,  1052  and  1068 , flow rate sensors  1056 ,  1058  and  1067 , oxygen/hematocrit sensors  1064  and  1066 , Fi02 and FiC02 concentration meters  1030  and  1031 , weight sensor  1060 , and elasticity sensor  1062 . Some of the sensors utilized by the system  100  may also be utilized by the system  1000 . These sensors include the temperature sensors  120 ,  122  and  124 , the set of Hall sensors  388  and shaft encoder sensor  390  from the perfusion pump assembly  106 , the battery sensors  352   a - 352   c , the external power available sensor  354  and the operator interface module battery sensor  370 . 
     The information obtained by the various sensors in the data acquisition subsystem  147  is transmitted to the controller  150  and displayed via the operator interface subsystem  146 . The operator interface subsystem  146  includes a display screen  3100 , as depicted in  FIG. 52 , that shows a number of numerical and graphical indications pertaining to the care of lungs  1004 . In particular, the display screen  3100  includes a display area  3140  showing a waveform depiction  3148  of the pulmonary arterial pressure (PAP). The display area  3140  also includes a numerical display  3152  of a PAP reading, as measured by the pressure sensor  1050 . Display area  3142  of the display screen  3100  shows a waveform depiction  3150  of the left atrial or pulmonary venous pressure (LAP) and a reading  3154  of the LAP, as measured by the pressure sensor  1052 . Display area  3144  includes a waveform depiction  3156  of the respiration-ventilation pressure through the tracheal interface  1024  (RESP) and a reading  3158  of the RESP, as measured by the pressure sensor  1068 . In certain embodiments, the displayed PAP, LAP and RESP values are instantaneous readings. In certain embodiments, the PAP and LAP values are displayed as an average, a mean or a minimum of instantaneous readings collected over a time period that is less than 30 seconds, less than 20 seconds, or less than 10 seconds. In certain embodiments, the RESP value is displayed as an average or a minimum of instantaneous readings collected over a time period that is less than 30 seconds, less than 20 seconds, or less than 10 seconds. In addition, the waveforms  3148 ,  3150 , and  3156  are displayed on a real-time basis or a periodic basis with each batch of data collected. 
     The display screen  3100  further includes a number of additional display areas  3102 ,  3104 ,  3106 ,  3108 ,  3110 ,  3112 ,  3114 , and  3116 . The display area  3102  shows a numerical reading  3160  of the pulmonary flow (PF) of the perfusion fluid  108  into the lungs  1004  via the pulmonary artery interface  1022 , as measured by the flow rate sensor  1056 . The display area  3104  shows a numerical value  3162  representative of pulmonary vascular resistance (PVR). The PVR value  3162  indicates the amount of resistance the lungs  1004  exert to a flow of the perfusion fluid  108  and is calculated by subtracting a LAP value, such as the LAP reading  3154 , from a PAP value, such as the PAP reading  3152 , divided by a PF value, such as the PF reading  3160  and applying a unit conversion factor. In general, a lower PVR value  3162  is preferable because it indicates a less restricted flow of the perfusion fluid  108  through the vasculature of the lungs  1004 . In certain embodiments, favorable values of the PVR is in a range between about 200 dynes to about 400 dynes. The display area  3106  shows the venous oxygen saturation (SvO 2 )  3164  of the perfusion fluid  108 , as measured from the oxygen/hemacorit sensor  1066 . Similarly, the display area  3108  shows the arterial oxygen saturation (SaO 2 )  3166  of the perfusion fluid  108 , as measured from the oxygen/hemacorit sensor  1064 . In certain embodiments, the display areas  3106  and  3108  additionally include a SvO 2  alarm and a SaO 2  alarm, respectively, for signaling the operator if each oxygen saturation value falls below an operator preset threshold. Such alarm may be implemented for any parameter measured, calculated or displayed. The display area  3110  includes a numerical reading  3168  of the hematocrit (HCT) of the perfusion fluid  108  and, optionally, an HCT alarm indicator for signaling the operator if the HCT  3168  falls below an operator preset threshold. The display area  3112  indicates the temperature (Temp)  3170  of the perfusion fluid  108  as it flows away from the heater assembly  110 . The display area  3112  may also include a Temp alarm indicator which signals in response to the Temp  3170  being outside of an operator preset range. A temperature set point  3172  selected by the operator is also shown in the display area  3112 . The display area  3114  shows a numerical reading  3174  of the ventilation rate measured as breaths per minute (BPM) of a gas delivered to the lungs  1004  via the tracheal interface  1024 . A BPM reading may be ascertained from a flow sensor, communicated from a respirator, or obtained from a pressure sensor, such as pressure sensor  1068 . The BPM value  3174  may be measured at the flow rate sensor  1067 . In addition, the display area  3114  includes a BPM alarm indicator  3176  signaling if the BPM value  3174  is outside of an operator preset range. The display area  3116  includes a numerical display  3178  of tidal volume (TDLV) of a gas flow into the lungs  1004  with each breath of the lungs  1004  and a TDLV alarm indicator  3180  signaling if the TDLV value  3178  is outside of an operator preset range. 
     The display screen  3100  further includes a circulatory pump indicator  3118  showing a status of the system&#39;s circulatory pump, a perfusion fluid warmer indicator  3120  showing a status of the perfusion fluid heater assembly  110 , and an SD card indicator  3124  showing whether an SD card is used to store data collected during organ perfusion. A display area  3126  is provided that includes a gas tank image  3182  graphically indicating a remaining gas volume in a gas supply connected to the system  1000 . The display area  3126  also includes one or more numerical displays  3184  indicating a flow rate of the gas in the gas supply along with the time remaining for which the gas is delivered to the lungs  1004  during perfusion. This remaining time may be calculated based on the remaining gas volume and the gas flow rate. Display area  3122  shows an organ type indicator  3186  that indicates which organ is being perfused and an organ mode indicator  3188  that indicates what mode of operation is being used to perfuse the organ. For example, an “R” is used to indicate a maintenance mode of operation. Display area  3190  shows a graphical representation  3128  of the degree to which each of the batteries  352   a - 352   c  of the multi-use module  650  is charged. Battery status symbol  3130  indicates that the batteries  352   a - 352   c , whose status are represented by graphical representation  3128 , are used to power the multi-use module  650 . The display area  3146  may also provide a numerical indication of the amount of time remaining for which the batteries  352   a - 352   c  can continue to run the system  1000  in the current mode of operation. Display area  3192  shows a graphical representation  3132  of the degree to which the user interface battery  368  is charged and a numerical indication  3194  of the amount of time remaining for which the user interface battery  368  can continue to run the user interface module  146 . A battery status symbol  3134  indicates that the user interface battery  368 , whose status is represented by the graphical representation  3132 , is used to power the user interface  146 . Display area  3136  identifies whether the operator interface module  146  is operating in a wireless fashion  3196 , along with a graphical representation  3198  of the quality of the wireless connection between the operator interface module  146  and the remainder of the system  1000 . The display screen  3100  also includes an alarm image  3101  indicating whether any parameter of the system  1000  is outside of a preset operator threshold for that parameter (the alarm  3101  is shown as “off in  FIG. 52 ) or communicating a system-related alarm message. The display screen  3100  further includes a display area  3146  showing a time and date of system operation and a display area  3138  showing the amount of time elapsed since perfusion begins. 
     In other embodiments, the display screen  3100  also shows FiO 2  and FiCO 2  concentrations, which are fractional concentrations of oxygen and carbon dioxide, respectively, measured via sensors  1030  and  1031  across the trachea interface  1024 . 
     Moreover, the display screen  3100  can additionally show readings of weight and elasticity of the lungs  1004 , PH of the perfusion fluid  108  circulating through the lungs  1004 , partial pressures of gas components in the perfusion fluid, and positive end expiratory pressures (PEEP) of the lungs  1004  which indicate the pressure in the lungs  1004  at the end of an exhaled breath. 
     Having described specific features of the lung chamber assembly  1018 , exemplary processes for cannulation at the pulmonary vein interface  1026 , and the data acquisition and display modules of the system  1000 , an exemplary lung transplantation procedure is described next with reference to  FIGS. 53 and 54 . 
     The process of obtaining and preparing the lungs  1004  for cannulation and transport as shown in  FIG. 53  is similar to the steps shown in  FIG. 29A  for the care of a heart. This process begins by providing a suitable organ donor at step  2000 . The organ donor is brought to a donor location, whereupon the process of receiving and preparing the donor lungs  1004  for cannulation and transport proceeds down two intersecting pathways. The pathways principally involve preparing the system  1000  to receive the donor lungs  1004  and then transport the lungs  1004  via system  1000  to a recipient site. In particular, pathway  2002  includes exsanguinating the donor, arresting the donor&#39;s heart, and preparing the lungs  1004  for cannulation into the system  1000 . In particular, in the exsanguination step  2006 , the donor&#39;s blood is removed and set aside so it can be used to perfuse the lungs  1004  during their maintenance on the system  1000 . Steps involved in removing blood from the exanguinated donor are described above with respect to  FIG. 29A . After the donor&#39;s blood is exanguinated, the donor heart is injected in step  2008  with a cardioplegic solution to temporarily halt its beating in preparation for harvesting the lungs  1004 . 
     After the donor&#39;s heart is arrested, a pneumoplegia solution is administered to the lungs at step  2009  before the lungs  1004  are explanted from the donor at step  2010  and prepared for loading onto the system  1000  at step  2012 . Processes involved in explanting a single lung or a pair of lungs  1004  are explained above with respect to  FIGS. 35 and 36 . 
     With continued reference to  FIG. 53 , after the lungs  1004  are explanted from the donor&#39;s body, they are instrumented onto the system  1000  at step  2021  by insertion into the lung chamber assembly  1018  and cannulation at the appropriate interfaces as described above with respect to FIGS.  34  and  48 - 51 . 
     According to other illustrative embodiments, the lungs  1004  can be transferred directly from the donor to the system  1000  without the use of cardioplegia. In one particular implementation, the donor&#39;s lungs  1004  are removed without the donor&#39;s heart being arrested and are subsequently instrumented into the system  1000  for maintenance. 
     During the preparation of the lungs  1004  via path  2002 , the system  1000  is prepared through the steps of path  2004  so it is primed and waiting to receive the lungs  1004  for cannulation and transport as soon as the lungs  1004  are prepared. In particular, the system  1000  is prepared in pathway  2004  through a series of steps including providing the single use module  1002  (step  2014 ), priming the system  1000  with a primary solution (step  2016 ), filtering the blood from the donor and adding it to the reservoir  160  (step  2018 ), and priming the system  1000  with a mixture of the blood and the perfusion fluid  108  (step  2020 ). In certain embodiments, the perfusion fluid  108  includes whole blood. In certain embodiments, the perfusion fluid  108  is partially or completely depleted of leukocytes. In certain embodiments, the perfusion fluid  108  is partially or completely depleted of platelets. The priming, supplemental, and preservative solutions utilized by the organ care system  100  for the maintenance of a heart may also be used in the system  1000 . In certain embodiments, the solutions used with the system  100  are used, but new additives including prostaglandin E, Prostacycline, dextran, isuprel, flolan and nitric oxide donors are added while epinephrine is removed. The additives may be generally selected from antimicrobials, vasodilators, and anti-inflammatory drugs. The additives may be delivered to the system  1000  via ports  762  and  774  coupled to the reservoir  160  or via the tracheal interface  1024  through a nebulizer or a bronchoscope. The various solutions utilized by the organ care system  1000  will be described below in further detail. 
     At step  2022 , the system  1000  is selected to operate in the maintenance mode. Different approaches of implementing the maintenance mode are described above with reference to  FIGS. 37 and 38 . In general, the explanted lungs  1004  are connected into the system  1000 . The perfusion fluid  108  is pumped into the lungs  1004  through the pulmonary artery interface  1022  and pumped away from the lungs  1004  through the pulmonary vein interface  1026 . A supply of gas, either as an isolated volume or a continuous flow, is provided to the lungs  1004  via the tracheal interface  1024 . A flow of a respiratory gas, having a pre-determined composition of gas components, is also provided to the lungs  1004  for use in respiration by the lungs  1004  during perfusion. In addition, at a steady-state of the system  1000 , a composition of gas components in the perfusion fluid  108  flowing into the lungs  1004  includes a substantially constant composition of components, and the perfusion fluid  108  flowing away from the lungs  1004  also includes a substantially constant composition of components. Moreover, at step  2024 , the instrumented lungs  1004  may be monitored and assessed using a plurality of monitoring components coupled to the system  1000 . 
     Based on the monitored parameters, in some instances, it is desirable to provide recruitment to the lungs  1004  during the maintenance mode (step  2026 ). For example, the lungs  1004  may be treated with antimicrobials or suctioned to remove fluid and alveoli debris in the trachea  1006 . Collapsed alveoli in the lungs  1004  may be inflated using sigh breathing by causing the lungs  1004  to inhale breaths that are of variable volume, such as causing the lungs  1004  to inhale a first breath having a volume that is larger than the volumes of at least two next breaths. In some instances, an operator may perform surgery on the lungs  1004  or provide therapeutic or other treatment, such as immunosuppressive treatments, chemotherapy, genetic testing or irradiation therapy. Additional assessments of the lungs  1004  are described above with respect to  FIGS. 37-40 . 
       FIG. 54  provides an exemplary process for conducting additional tests on the lungs  1004  while the system  1000  is at the recipient site (step  3000 ). In particular, at step  3002 , the system  1000  is set to operate in the evaluation mode in order to provide a perfusion condition that is suitable for the evaluation of the lungs  1004  to determine their gas-transfer capacity. Additional recruitment can be performed during the evaluation mode at step  3003  based on assessment of the lungs  1004  performed at step  3005 . Steps involved in implementing the evaluation mode are described above in detail with reference to  FIG. 39 . After testing is complete at the recipient site, the lungs  1004  are prepared for implantation into the recipient. This includes configuring the system  1000  for lung removal by powering down the pump  106  to stop the flow of perfusion fluid  108  (step  3004 ) and, optionally, administering a pneumoplegia solution to the lungs  1004 . Next, in step  3008 , the lungs  1004  are de-cannulated and removed from the lung chamber assembly  1018 . In step  3018 , the lungs  1004  are transplanted into the recipient patient by inserting them into the recipient&#39;s chest cavity and suturing the various pulmonary connections to their appropriate mating connections within the recipient. In certain embodiments, a portion of the recipient&#39;s left atrium may be excised and replaced with one or more of the donor&#39;s left atrial cuff  1008  to which the donor&#39;s pulmonary veins are attached. 
     As described above, the system  1000  employs a priming solution, and also a perfusion fluid  108  that combines a nutritional supplement  116  solution and a preservative solution  118  with a blood product or synthetic blood product to form the perfusion fluid  108 . The priming, supplement  116 , and preservative  118  solutions are described next. 
     According to certain embodiments, solutions with particular solutes and concentrations are selected and proportioned for the perfusion fluid  108  to enable the lungs  1004  to function at physiologic or near physiologic conditions. For example, such conditions include maintaining lung function at or near a physiologic temperature and/or preserving a lung in a state that permits normal cellular metabolism, such as protein synthesis. 
     In certain embodiments solutions are formed from compositions by combining components with a fluid, from more concentrated solutions by dilution, or from more dilute solutions by concentration. In exemplary embodiments, suitable solutions include an energy source and one or more amino acids selected and proportioned so that the organ continues its cellular metabolism during perfusion. Cellular metabolism includes, for example conducting protein synthesis while functioning during perfusion. Some illustrative solutions are aqueous based, while other illustrative solutions are non-aqueous, for example organic solvent-based, ionic-liquid-based, or fatty-acid-based. 
     The solutions may include one or more energy-rich components to assist the organ in conducting its normal physiologic function. These components may include energy rich materials that are metabolizable, and/or components of such materials that an organ can use to synthesize energy sources during perfusion. Exemplary sources of energy-rich molecules include, for example, one or more carbohydrates. Examples of carbohydrates include monosaccharides, disaccharides, oligosaccharides, polysaccharides, or combinations thereof, or precursors or metabolites thereof. While not meant to be limiting, examples of monosaccharides suitable for the solutions include octoses; heptoses; hexoses, such as fructose, allose, altrose, glucose, mannose, gulose, idose, galactose, and talose; pentoses such as ribose, arabinose, xylose, and lyxose; tetroses such as erythrose and threose; and trioses such as glyceraldehyde. While not meant to be limiting, examples of disaccharides suitable for the solutions include (+)-maltose (4-O-(□-D-glucopyranosyl)-□-D-glucopyranose), (+)-cellobiose (4-O-(□-D-glucopyranosyl)-D-glucopyranose), (+)-lactose (4-O-(□-D-galactopyranosyl)-□-D-glucopyranose), sucrose (2-O-(□-D-glucopyranosyl)-□-D-fractofuranoside). While not meant to be limiting, examples of polysaccharides suitable for the solutions include cellulose, starch, amylose, amylopectin, sulfomucopolysaccharides (such as dermatane sulfate, chondroitin sulfate, sulodexide, mesoglycans, heparan sulfates, idosanes, heparins and heparinoids), and glycogen. In some embodiments, monossacharides, disaccharides, and polysaccharides of both aldoses, ketoses, or a combination thereof are used. One or more isomers, including enantiomers, diastereomers, and/or tautomers of monossacharides, disaccharides, and/or polysaccharides, including those described and not described herein, may be employed in the solutions described herein. In some embodiments, one or more monossacharides, disaccharides, and/or polysaccharides may have been chemically modified, for example, by derivatization and/or protection (with protecting groups) of one or more functional groups. In certain embodiments, carbohydrates, such as dextrose or other forms of glucose are preferred. 
     Other possible energy sources include adenosine triphosphate (ATP), coenzyme A, pyruvate, flavin adenine dinucleotide (FAD), thiamine pyrophosphate chloride (co-carboxylase), β-nicotinamide adenine dinucleotide (NAD), β-nicotinamide adenine dinucleotide phosphate (NADPH), and phosphate derivatives of nucleosides, i.e. nucleotides, including mono-, di-, and tri-phosphates (e.g., UTP, GTP, GDF, and UDP), coenzymes, or other bio-molecules having similar cellular metabolic functions, and/or metabolites or precursors thereof. For example, phosphate derivatives of adenosine, guanosine, thymidine (5-Me-uridine), cytidine, and uridine, as well as other naturally and chemically modified nucleosides are contemplated. 
     In certain embodiments, one or more carbohydrates are provided along with a phosphate source, such as a nucleotide. One exemplary carbohydrate is dextran. The carbohydrate helps enable the organ to produce ATP or other energy sources during perfusion. The phosphate source may be provided directly through ATP, ADP, AMP or other sources. In other illustrative embodiments, a phosphate is provided through a phosphate salt, such as glycerophosphate, sodium phosphate or other phosphate ions. A phosphate may include any form thereof in any ionic state, including protonated forms and forms with one or more counter ions. 
     In some instances, additional components are provided to assist the lungs  1004  in conducting its metabolism during perfusion. These components include, for example, forms or derivatives of adenine and/or adenosine, which may be used for ATP synthesis, for maintaining endothelial function, and/or for attenuating ischemia and/or reperfusion injury. According to certain implementations, a magnesium ion source is provided with a phosphate, and in certain embodiments, with adenosine to further enhance ATP synthesis within the cells of the perfused lungs  1004 . 
     Solutions described herein may include one or more amino acids, preferably a plurality of amino acids, to support protein synthesis by the organ&#39;s cells. Suitable amino acids include, for example, any of the naturally-occurring amino acids. The amino acids may be, in various enantiomeric or diastereomeric forms. For example, solutions may employ either D- or L-amino acids, or a combination thereof, i.e. solutions enantioenriched in more of the D- or L-isomer or racemic solutions. Suitable amino acids may also be non-naturally occurring or modified amino acids, such as citrulline, orniithine, homocystein, homoserine, β-amino acids such as B-alanine, amino-caproic acid, or combinations thereof. 
     Certain exemplary solutions include some but not all naturally-occurring amino acids. In some embodiments, solutions include essential amino acids. For example, a solution may be prepared with one or more or all of the following amino-acids:
         Glycine   Alanine   Arginine   Aspartic Acid   Glutamic Acid   Histidine   Isoleucine   Leucine   Methionine   Phenylalanine   Proline   Serine   Thereonine   Tryptophan   Tyrosine   Valine   Lysine acetate       

     In certain embodiments, non-essential and/or semi-essential amino acids are not included in the solutions. For example, in some embodiments, asparagine, glutamine, and/or cysteine are not included. In other embodiments, the solution contains one or more non-essential and/or semi-essential amino acids. Accordingly, in other embodiments, asparagine, glutamine, and/or cysteine are included. 
     The solutions may also contain electrolytes, particularly calcium ions for facilitating enzymatic reactions, and/or coagulation within the organ. Other electrolytes may be used, such as sodium, potassium, chloride, sulfate, magnesium and other inorganic and organic charged species, or combinations thereof. It should be noted that any component provided hereunder may be provided, where valence and stability permit, in an ionic form, in a protonated or unprotonated form, in salt or free base form, or as ionic or covalent substituents in combination with other components that hydrolyze and make the component available in aqueous solutions, as suitable and appropriate. 
     In certain embodiments, the solutions contain buffering components. For example, suitable buffer systems include 2-morpholinoethanesulfonic acid monohydrate (MES), cacodylic acid, H 2 CO 3 /NaHCO 3  (pK a1 ), citric acid (pK a 3), bis(2-hydroxyethyl)-imino-tris-(hydroxymethyl)-methane (Bis-Tris), N-carbamoylmethylimidino acetic acid (ADA), 3-bis[tris(hydroxymethyl)methylamino]propane (Bis-Tris Propane) (pK a1 ), piperazine-1,4-bis(2-ethanesulfonic acid) (PIPES), N-(2-Acetamido)-2-aminoethanesulfonic acid (ACES), imidazole, N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES), 3-(N-morpholino)propanesulphonic acid (MOPS), NaH 2 PO 4 /Na 2 HPO 4  (pK a2 ), N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid (TES), N-(2-hydroxyethyl)-piperazine-N′-2-ethanesulfonic acid (HEPES), N-(2-hydroxyethyl)piperazine-N′-(2-hydroxypropanesulfonic acid) (HEPPSO), triethanolamine, N-[tris(hydroxymethyl)methyl]glycine (Tricine), tris hydroxymethylaminoethane (Tris), glycineamide, N,N-bis(2-hydroxyethyl)glycine (Bicine), glycylglycine (pK a2 ), N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (TAPS), or a combination thereof. In some embodiments, the solutions contain sodium bicarbonate, potassium phosphate, or TRIS buffer. 
     In another aspect, a blood product is provided with the solution to support the organ during metabolism. Exemplary suitable blood products may include whole blood, and/or one or more components thereof such as blood serum, plasma, albumin, and red blood cells. In embodiments where whole blood is used, the blood may be passed through a leukocyte and platelet depleting filter to reduce pyrogens, antibodies and/or other items that may cause inflammation in the organ. Thus, in some embodiments, the solution employs whole blood that has been at least partially depleted of leukocytes and/or whole blood that has been at least partially depleted of platelets. 
     The solutions are preferably provided at a physiologic temperature and maintained thereabout throughout perfusion and recirculation. As used herein, “physiologic temperature” is referred to as temperatures between about 25° C. and about 37° C., for example, between about 30° C. and about 37° C., such as between about 34° C. and about 37° C. 
     Table 1 sets forth components that are used in an exemplary aqueous priming solution. The component amounts in Table 1 are relative to each other and to the amount of aqueous solvent employed in the solution (about 500 mL in the exemplary embodiment) and may be scaled as appropriate. In certain embodiments, the quantity of aqueous solvent varies ±about 10%. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Composition of Exemplary Priming Solution 
               
               
                 (about 500 mL aqueous solution) 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Amount 
                 Specification 
               
               
                   
                   
               
               
                   
                 Dextran 
                  20 g 
                 ±about 50% 
               
               
                   
                 Sodium Chloride 
                  4.8 g 
                 ±about 10% 
               
               
                   
                 Potassium Chloride 
                 185 mg 
                 ±about 10% 
               
               
                   
                 Magnesium Sulfate heptahydrate 
                 185 mg 
                 ±about 10% 
               
               
                   
                 Sodium Glycerophosphate 
                 900 mg 
                 ±about 10% 
               
               
                   
                   
               
            
           
         
       
     
     With regard to the nutritional supplement solution  116 , in certain embodiments it includes one or more carbohydrates and may also include a phosphate source. The nutritional supplement solution  116  is typically maintained at a pH of about 5.0 to about 6.5, for example about 5.5 to about 6.0. 
     Table 2 sets forth components that are used in an exemplary nutritional supplement solution  116 . In some embodiments, the nutritional solution  116  further includes sodium glycerol phosphate. The amount of components in Table 2 is relative to the amount of aqueous solvent employed in the solution  116  (about 500 mL) and may be scaled as appropriate. In some embodiments, the quantity of aqueous solvent varies ±about 10%. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Components of Exemplary Nutritional Solution (about 500 mL 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Amount 
                 Specification 
               
               
                   
                   
               
               
                   
                 Dextrose 
                 40 g 
                 ±about 10% 
               
               
                   
                   
               
            
           
         
       
     
     In certain embodiments the nutritional solution  116  includes one or more carbohydrates and may also include a phosphate source. The nutritional solution  116  is typically maintained at a pH of about 5.0 to about 6.5, for example of about 5.5 to about 6.0. 
     Other components may be added to the preservation solution  118 , including, for example, adenosine, magnesium, phosphate, calcium, and/or sources thereof. In some instances, additional components are provided to assist the organ in conducting its metabolism during perfusion. These components include, for example, forms of adenosine, which may be used for ATP synthesis, for maintaining endothelial function, and/or for attenuating ischemia and/or reperfusion injury. Components may also include other nucleosides, such as guanosine, thymidine (5-Me-uridine), cytidine, and uridine, as well as other naturally and chemically modified nucleosides including nucleotides thereof. According to some implementations, a magnesium ion source is provided with a phosphate source, and in certain embodiments, with adenosine to further enhance ATP synthesis within the cells of the perfused organ. A plurality of amino acids may also be added to support protein synthesis by the heart&#39;s  102  cells. Applicable amino acids may include, for example, any of the naturally-occurring amino acids, as well as those mentioned above. 
     Table 3 sets components that may be used in a solution  118  for preserving an organ as described herein. The solution  118  may include one or more of the components described in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Component of Exemplary Composition or Preservative Solution 
               
            
           
           
               
               
            
               
                   
                 Exemplary Concentration Ranges in 
               
               
                 Component 
                 Preservative Solution 
               
               
                   
               
               
                 Alanine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Arginine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Asparagine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Aspartic Acid 
                 about 1 mg/L-about 10 g/L 
               
               
                 Cysteine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Cystine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Glutamic Acid 
                 about 1 mg/L-about 10 g/L 
               
               
                 Glutamine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Glycine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Histidine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Hydroxyproline 
                 about 1 mg/L-about 10 g/L 
               
               
                 Ioleucine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Leucine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Lysine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Methionine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Phenylalanine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Proline 
                 about 1 mg/L-about 10 g/L 
               
               
                 Serine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Threonine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Tryptophan 
                 about 1 mg/L-about 10 g/L 
               
               
                 Tyrosine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Valine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Adenine 
                 about 1 mg/L-about 10 g/L 
               
               
                 ATP 
                 about 10 ug/L-about 100 g/L 
               
               
                 Adenylic Acid 
                 about 10 ug/L-about 100 g/L 
               
               
                 ADP 
                 about 10 ug/L-about 100 g/L 
               
               
                 AMP 
                 about 10 ug/L-about 100 g/L 
               
               
                 Ascorbic Acid 
                 about 1 ug/L-about 10 g/L 
               
               
                 D-Biotin 
                 about 1 ug/L-about 10 g/L 
               
               
                 Vitamin D-12 
                 about 1 ug/L-about 10 g/L 
               
               
                 Cholesterol 
                 about 1 ug/L-about 10 g/L 
               
               
                 Dextrose (Glucose) 
                 about 1 g/L-about 150 g/L 
               
               
                 Multi-vitamin Adult 
                 about 1 mg/L-about 20 1 mg/L or 1 unit vial 
               
               
                 Folic Acid 
                 about 1 ug/L-about 10 g/L 
               
               
                 Glutathione 
                 about 1 ug/L-about 10 g/L 
               
               
                 Guanine 
                 about 1 ug/L-about 10 g/L 
               
               
                 Inositol 
                 about 1 g/L-about 100 g/L 
               
               
                 Riboflavin 
                 about 1 ug/L-about 10 g/L 
               
               
                 Ribose 
                 about 1 ug/L-about 10 g/L 
               
               
                 Thiamine 
                 about 1 mg/L-about 10 g/L 
               
               
                 Uracil 
                 about 1 mg/L-about 10 g/L 
               
               
                 Calcium Chloride 
                 about 1 mg/L-about 100 g/L 
               
               
                 NaHC0 3   
                 about 1 mg/L-about 100 g/L 
               
               
                 Magnesium sulfate 
                 about 1 mg/L-about 100 g/L 
               
               
                 Potassium chloride 
                 about 1 mg/L-about 100 g/L 
               
               
                 Sodium glycerophosphate 
                 about 1 mg/L-about 100 g/L 
               
               
                 Sodium Chloride 
                 about 1 mg/L-about 100 g/L 
               
               
                 Sodium Phosphate 
                 about 1 mg/L-about 100 g/L 
               
               
                 Insulin 
                 about 1 IU-about 150 IU 
               
               
                 Serum albumin 
                 about 1 g/L-about 100 g/L 
               
               
                 Pyruvate 
                 about 1 mg/L-about 100 g/L 
               
               
                 Coenzyme A 
                 about 1 ug/L-about 10 g/L 
               
               
                 Serum 
                 about 1 ml/L-about 100 ml/L 
               
               
                 Heparin 
                 about 500 U/L-about 1500U/L 
               
               
                 Solumedrol 
                 about 200 mg/L-about 500 mg/L 
               
               
                 Dexamethasone 
                 about 1 mg/L-about 1 g/L 
               
               
                 FAD 
                 about 1 ug/L-about 10 g/L 
               
               
                 NADP 
                 about 1 ug/L-about 10 g/L 
               
               
                 adenosine 
                 about 1 mg/L-about 10 g/L 
               
               
                 guanosine 
                 about 1 mg/L-about 10 g/L 
               
               
                 GTP 
                 about 10 ug/L-about 100 g/L 
               
               
                 GDP 
                 about 10 ug/L-about 100 g/L 
               
               
                 GMP 
                 about 10 ug/L-about 100 g/L 
               
               
                   
               
            
           
         
       
     
     Table 4 sets forth components that are used in an exemplary preservative solution  118 . The amounts provided in Table 4 describe preferred amounts relative to other components in the table and may be scaled to provide compositions of sufficient quantity. In some embodiments, the amounts listed in Table 4 can vary by ±about 10% and still be used in the solutions described herein. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Components of Exemplary Composition or Preservative Solution 
               
            
           
           
               
               
            
               
                   
                 Exemplary Concentration Ranges in 
               
               
                 Component 
                 Preservative Solution 
               
               
                   
               
               
                 Adenosin 
                 About 675 mg-About 825 mg 
               
               
                 Calcium Chloride dihydrate 
                 About 2100 mg-About 2600 mg 
               
               
                 Glycine 
                 About 315 mg-About 385 mg 
               
               
                 L-Alanine 
                 About 150 mg-About 200 mg 
               
               
                 L-Arginine 
                 About 600 mg-About 800 mg 
               
               
                 L-Aspartic Acid 
                 About 220 mg-About 270 mg 
               
               
                 L-Glutamic Acid 
                 About 230 mg-About 290 mg 
               
               
                 L-Histidine 
                 About 200 mg-About 250 mg 
               
               
                 L-Isoleucine 
                 About 100 mg about 130 mg 
               
               
                 L-Leucine 
                 About 300 mg-About 380 mg 
               
               
                 L-Methionine 
                 About 50 mg-About 65 mg 
               
               
                 L-Phenylalanine 
                 About 45 mg-About 60 mg 
               
               
                 L-Proline 
                 About 110 mg-About 140 mg 
               
               
                 L-Serine 
                 About 80 mg-About 105 mg 
               
               
                 L-Thereonine 
                 About 60 mg-About 80 mg 
               
               
                 L-Tryptophan 
                 About 30 mg-About 40 mg 
               
               
                 L-Tyrosine 
                 About 80 mg-About 110 mg 
               
               
                 L-Valine 
                 About 150 mg-About 190 mg 
               
               
                 Lysine Acetate 
                 About 200 mg-About 250 mg 
               
               
                 Magnesium Sulfate Heptahydrate 
                 About 350 mg-About 450 mg 
               
               
                 Potassium Chloride 
                 About 15 mg-About 25 mg 
               
               
                 Sodium Chloride 
                 About 1500 mg-About 2000 mg 
               
               
                 Dextrose 
                 About 25 gm-About 120 gm 
               
               
                 Insulin 
                 About 75 Units-About 150 Units 
               
               
                 MVI-Adult 
                 1 unit vial 
               
               
                 SoluMedrol 
                 About 200 mg-500 mg 
               
               
                 Sodium Bicarbonate 
                 About 10-25 mEq 
               
               
                   
               
            
           
         
       
     
     In the exemplary embodiment of a solution  118 , the components in Table 4 are combined in the relative amounts listed therein per about 1 L of aqueous fluid to form the solution  118 . In some embodiments, the components in Table 4 are combined in the relative amounts listed therein per about 500 mL of aqueous fluid and then combined with the solution  116 , also about 500 mL, to provide a maintenance solution  116 / 118  of about 1 L of aqueous fluid. In some embodiments the quantity of aqueous fluid in solutions  116 , 118 , and/or  116 / 118  can vary ±about 10%. The pH of the solution  118  may be adjusted to be between about 7.0 and about 8.0, for example about 7.3 and about 7.6. The solution  118  may be sterilized, for example by autoclaving, to provide for improved purity. 
     Table 5 sets forth another exemplary preservative solution  118 , comprising a tissue culture media having the components identified in Table 5 and combined with an aqueous fluid, which may be used in the perfusion fluid  108  as described herein. The amounts of components listed in Table 5 are relative to each other and to the quantity of aqueous solution used. In some embodiments, about 500 mL of aqueous fluid is used. In other embodiments about 1 L of aqueous fluid is used. For example, combination of about 500 mL of preservative solution  118  with 500 mL of nutritional solution  116  affords a maintenance solution  116 / 118  of about 1 L. In some embodiments, the quantity of aqueous solution can vary ±about 10%. The component amounts and the quantity of aqueous solution may be scaled as appropriate for use. The pH of the preservative solution  118 , in this embodiment, may be adjusted to be about 7.0 to about 8.0, for example about 7.3 to about 7.6. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Composition of Another Exemplary Preservative Solution 
               
               
                 (about 500 mL aqueous solution) 
               
            
           
           
               
               
               
               
            
               
                   
                 Tissue Culture Component 
                 Amount 
                 Specification 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Adenosine 
                 750 
                 mg 
                 ±about 10% 
               
               
                   
                 Calcium Chloride dihydrate 
                 2400 
                 mg 
                 ±about 10% 
               
               
                   
                 Glycine 
                 350 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Alanine 
                 174 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Arginine 
                 700 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Aspartic Acid 
                 245 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Glutamic Acid 
                 258 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Histidine 
                 225 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Isoleucine 
                 115.5 
                 mg 
                 +about 10% 
               
               
                   
                 L-Leucine 
                 343 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Methionine 
                 59 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Phenylalanine 
                 52 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Proline 
                 126 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Serine 
                 93 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Thereonine 
                 70 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Tryptophan 
                 35 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Tyrosine 
                 92 
                 mg 
                 ±about 10% 
               
               
                   
                 L-Valine 
                 171.5 
                 mg 
                 ±about 10% 
               
               
                   
                 Lysine Acetate 
                 225 
                 mg 
                 ±about 10% 
               
               
                   
                 Magnesium Sulfate Heptahydrate 
                 400 
                 mg 
                 ±about 10% 
               
               
                   
                 Potassium Chloride 
                 20 
                 mg 
                 ±about 10% 
               
               
                   
                 Sodium Chloride 
                 1750 
                 mg 
                 + about 10% 
               
               
                   
                   
               
            
           
         
       
     
     Since amino acids are the building blocks of proteins, the unique characteristics of each amino acid impart certain important properties on a protein such as the ability to provide structure and to catalyze biochemical reactions. The selection and concentrations of the amino acids provided in the preservative solutions provide support of normal physiologic functions such as metabolism of sugars to provide energy, regulation of protein metabolism, transport of minerals, synthesis of nucleic acids (DNA and RNA), regulation of blood sugar and support of electrical activity, in addition to providing protein structure. Additionally, the concentrations of specific amino acids found in the preservative solutions can be used to predictably stabilize the pH of the maintenance solution  116 / 118  and perfusion fluid  108 . 
     In one embodiment, a maintenance solution  116 / 118  is made from a combination of the preservative solution  118 , including one or more amino acids, and the nutritional solution  116 , including one or more carbohydrates, such as glucose or dextrose. The maintenance solution  116 / 118  may also have additives, such as those described herein, administered at the point of use just prior to infusion into the organ perfusion system. For example, additional additives that can be included with the solution or added at the point of use by the user include hormones and steroids, such as dexamethasone and insulin, prostacycline and other members of the prostoglandine family, beta-1-agonists (e.g., albuterol, isopreternaol), vitamins, such as an adult multi-vitamin, for example adult multivitamins for infusion, such as MVI-Adult. Additional small molecules and large bio-molecules may also be included with the solution or added at the point of use by the user at port  762 , for example, therapeutics and/or components typically associated with blood or blood plasma, such as albumin. 
     The solutions may include therapeutic components to help maintain the lungs  1004  and protect them against ischemia, reperfusion injury and other ill effects during perfusion, to help mitigate edema, or provide general endothelial tissue support for the lungs  1004 . In certain exemplary embodiments these components may include hormones (e.g., insulin), vitamins (e.g., an adult multi-vitamin, such as multi-vitamin MVI-Adult), and/or steroids (e.g., dexamethasone and SoluMedrol). In some embodiments, therapeutics that are included in the compositions and solutions for organ maintenance to help mitigate edema, provide endothelial support, and otherwise provide preventative or prophylactic treatment to the lungs  1004 . In certain embodiments, the systems described herein include hormones, such as thyroid hormones, for example T 3  and/or T 4  thyroid hormones added to the nutritional solution  116 , the preservative solution  118 , and/or the maintenance solutions  116 / 118  either before or during perfusion of the organ. Additional exemplary therapeutics include isuprel, flolan, prostacyclin or other prostaglandin, beta-1-agonists, beta-2-antagonists, brochodilators, isoproterenol, pentoxifylline, and nitric oxide donors (e.g., L-arginine, nitroglycerine, nitroprusside). The above therapeutics may also be added directly to the system, for example, to the perfusion fluid  108 , before or during perfusion of the organ. In certain embodiments, colloids are added, such as dextran, albumin, hydroxyethyl starches, or gelatins. Other components that may be added include antimicrobial agents, anti-fungal agents, anti-viral agents, vasodilators, surfactants adapted to resist collapsing of alveoli within the lung, and anti-inflammatory drugs. 
     In particular, the addition of dextran offers numerous benefits including improving erythrocyte deformability, preventing erythrocyte aggregation, inducing disbanding of already aggregated cells, improving pulmonary circulation and preserving endothelial-epithelial membrane. Dextran also has anti-thrombotic effects by being able to coat endothelial surfaces and platelets. The addition of prostaglandins into various solutions induce effects such as vasodilation of pulmonary vascular bed, inhibition of platelet aggregation, bronchilation, reducing endothelia permeability and reducing neutrophil adhesion. In addition, nitric oxide is used to treat ischemia-reperfusion injury of the lungs  1004  because it can improve ventilation-perfusion mismatch and decrease pulmonary artery pressures. Isoproterenol, as a therapeutic agent, acts a non-selective beta-adrenergic agonist. It is adapted to relax almost all varieties of smooth muscles, hence preventing or relieving broncho-constriction and producing pulmonary vasodilation. Moreover, therapeutics such as surfactants prevent the collapsing of alveoli within the lungs  1004  during the breathing cycle as well as protect the lungs  1004  from injuries and infections caused by foreign bodies and pathogens. Pentoxifylline, as a therapeutic agent, ameliorates ischemia-reperfusion injury by, for example, inhibiting leukocyte sequestration in the lungs  1004 , thus preventing the release of free radicals and cytokin. 
     The one or more therapeutics or other additives may be delivered to the lung through the tracheal interface  1024  via a nebulizer, or added to the perfusion fluid  108  through the maintenance solution, or added by injection directly into the perfusion fluid reservoir at the point of use. In certain embodiments, therapeutic agents such as nitric oxide are provided indirectly to the explanted lungs  1004  through the administration of an upstream precursor molecule such as L-arginine or through the infusion of a nitric oxide donor such as nitroglycerin or nitroprusside. In certain embodiments, therapeutics such as bronchodilators are provided to the lungs  1004  in an injectable form into the perfusion fluid  108  or through the tracheal interface  1024  in a nebulized form. In certain embodiments, exogenous surfactants are delivered to the lungs  1004  through the tracheal interface  1024  or provided to different sections of the lungs  1004  using bronchoscopy. In certain embodiments, pentoxifylline is added to the perfusion fluid  108  in an injectable form. 
     With further reference to Table 4, certain components used in the exemplary preservation solution  118  are molecules, such as small organic molecules or large bio-molecules, that would be inactivated, for example through decomposition or denaturing, if passed through sterilization. According to the system  100 , the inactivatable components of the solution  118  may be prepared separately from the remaining components of the solution  118 . The separate preparation involves separately purifying each component through known techniques. The remaining components of the solution  118  are sterilized, for example through an autoclave, then combined with the biological components. 
     Table 6 lists certain biological components that may be separately purified and added to the solutions described herein after sterilization, according to this two-step process. These additional or supplemental components may be added to solutions  118 ,  116 ,  116 / 118 , the priming solution or a combination thereof individually, in various combinations, all at once as a composition, or as a combined solution. For example, in certain embodiments, the epinephrine, insulin, and MVI-Adult, listed in Table 6, are added to the maintenance solution  116 / 118 . In another example, the SoluMedrol and the sodium bicarbonate, listed in Table 6, are added to the priming solution. The additional components may also be combined in one or more combinations or all together and placed in solution before being added to solutions  116 ,  118 ,  116 / 118 , and/or the priming solution. In some embodiments, the additional components are added directly to the perfusion fluid  108  through port  762 . The component amounts listed in Table 6 are relative to each other and/or to the amounts of components listed in one or more of Tables 1-5 as well as the amount of aqueous solution used in preparing solutions  116 , 118 , 116 / 118 , and/or the priming solution and may be scaled as appropriate for the amount of solution required. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Exemplary Biological Components Added Prior to Use 
               
            
           
           
               
               
               
               
            
               
                 Component 
                 Amount 
                 Type 
                 Specification 
               
               
                   
               
               
                 Insulin 
                 about 100 Units 
                 Hormone 
                 ±about 10% 
               
               
                 MVI-Adult 
                 1 mL unit vial 
                 Vitamin 
                 ±about 10% 
               
               
                 SoluMedrol 
                 About 250 mg 
                 Steroid 
                 ±about 10% 
               
               
                 Sodium Bicarbonate 
                 About 20 mEq 
                 Buffer 
                 ±about 10% 
               
               
                   
               
            
           
         
       
     
     In one embodiment, a composition for use in a maintenance solution  116 / 118  is provided comprising one or more carbohydrates, one or more organ stimulants, and a plurality of amino acids that do not include asparagine, glutamine, or cysteine. The composition may also include other substances, such as those used in solutions described herein. 
     In another embodiment, a system for perfusing an organ, such as a heart, is provided comprising an organ and a substantially cell-free composition, comprising one or more carbohydrates, one or more organ stimulants, and a plurality of amino acids that do not include asparagine, glutamine, or cysteine. Substantially cell-free includes systems that are substantially free from cellular matter; in particular, systems that are not derived from cells. For example, substantially cell-free includes compositions and solutions prepared from non-cellular sources. 
     In another aspect, the solutions  116  and  118  may be provided in the form of a kit that includes one or more organ maintenance solutions. An exemplary maintenance solution may include components identified above in one or more fluid solutions for use in an organ perfusion fluid  108 . In certain embodiments, the maintenance solution  116 / 118  may include multiple solutions, such as a preservation solution  118  and a nutritional solution  116  and/or a supplemental composition or solution, or may include dry components that may be regenerated in a fluid to form one or more solutions  116 / 118 . The kit may also comprise components from the solutions  116  and/or  118  in one or more concentrated solutions which, on dilution, provide a preservation, nutritional, and/or supplemental solution as described herein. The kit may also include a priming solution. In an exemplary embodiment, the maintenance solution includes a preservation solution  118  and a nutritional solution  116  such as those described above, and a priming solution such as that described above. 
     In certain embodiments, the kit is provided in a single package, wherein the kit includes one or more solutions (or components necessary to formulate the one or more solutions by mixing with an appropriate fluid), and instructions for sterilization, flow and temperature control during perfusion and use and other information necessary or appropriate to apply the kit to organ perfusion. In certain embodiments, a kit is provided with only a single solution  116 ,  118  and/or  116 / 118  (or set of dry components for use in a solution upon mixing with an appropriate fluid), and the single solution  116 ,  118  and/or  116 / 118  (or set of dry components) is provided along with a set of instructions and other information or materials necessary or useful to operate the solution  116 ,  118  and/or  116 / 118  in the system  100 . 
     In another aspect, the systems, solutions and methods may be used to deliver therapeutics to an organ during perfusion. For example, one or more of the solutions and/or systems described above may include one or more drugs, biologics, gene therapy vectors, or other therapeutics which are delivered to the organ during perfusion. Suitable exemplary therapeutics may include drugs, biologics, or both. Suitable drugs may include, for example, anti fungals, anti-microbials or anti-biotics, anti-infiamatories, anti-proliferatives, anti-virals, steroids, retinoids, NSAIDs, vitamin D3 and vitamin D3 analogs, calcium channel blockers, complement neutralizers, ACE inhibitors, immunosuppressants, and other drugs. Suitable biologics may include proteins; suitable biologics may also include vectors loaded with one or more genes for gene therapy application. 
     For example, suitable steroids include but are not limited to androgenic and estrogenic steroid hormones, androgen receptor antagonists and 5-α-reductase inhibitors, and corticosteroids. Specific examples include but are not limited to alclometasone, clobetasol, fluocinolone, fluocortolone, diflucortolone, fluticasone, halcinonide, mometasone, prednisone, prednisolone, methylprednisolone, triamcinolone, betamethasone, and dexamethasone, and various esters and acetonides thereof. 
     Suitable retinoids include but are not limited to retinol, retinal, isotretinoin, acitretin, adapalene, tazarotene, and bexarotene. 
     Suitable NSAIDs include but are not limited to naproxen, suprofen, ketoprofen, ibuprofen, flurbiprofen, diclofenac, indomethacin, celecoxib, and rofecoxib. 
     Suitable vitamin D3 analogues include but are not limited to doxercalciferol, seocalcitol, calcipotriene, tacalcitol, calcitriol, ergocalciferol, and calcifediol. 
     Suitable anti-viral agents include but are not limited to trifluridine, cidofovir, acyclovir, penciclovir, famciclovir, valcyclovir, gancyclovir, and docosanol. 
     Suitable human carbonic anhydrase inhibitors include but are not limited to methazoliamide, acetazolamide, and dorzolamide. 
     Suitable anti-proliferative agents include but are not limited to 5-FU, taxol, daunorubicin, and mitomycin. 
     Suitable antibiotic (antimicrobial) agents include but are not limited to bacitracin, chlorhexidine, chlorhexidine digluconate, ciprofloxacin, clindamycin, erythromycin, gentamicin, lomefloxacin, metronidazole, minocycline, moxifloxacin, mupirocin, neomycin, ofloxacin, polymyxin B, rifampicin, ruflozacin, tetracycline, tobramycin, triclosan, and vancomycin. The antiviral and antibacterial prodrugs described herein may be used to treat appropriately responsive systemic infections. 
     In certain embodiments, a solution system for use in a perfusion fluid  108 , comprising a first chamber containing a first solution, such as a preservation solution  118 , that includes one or more cardio stimulants and a plurality of amino acids that do not include asparagine, glutamine, or cysteine, and a second chamber, containing a second solution, such as a nutritional solution  116 , that includes one or more carbohydrates, such as dextrose. The system may also include a sterilization system for sterilizing the first solution and the second solution prior to using the solutions to perfuse a heart. In some embodiments, one or more of the solutions  118  and  116  includes one or more therapeutics. In some embodiments the solution system includes a third chamber comprising a priming solution, such as is described above, which may have one or more carbohydrates. In certain embodiments, the first solution  118  includes adenosine, insulin, one or more immuno-suppressants, a multi-vitamin, and/or one or more electrolytes. 
     It is to be understood that while the invention has been described in conjunction with the various illustrative embodiments, the forgoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. For example, a variety of systems and/or methods may be implemented based on the disclosure and still fall within the scope of the invention. Other aspects, advantages, and modifications are within the scope of the following claims. All references cited herein are incorporated by reference in their entirety and made part of this application.