Abstract:
Venous reservoirs are interposed between the patient and the arterial pump and serve to remove air bubbles and provide compliance that accommodates variations in the volume of blood circulating in the extracorporeal circuit during cardiopulmonary bypass (CPB).  
     Venous drainage by gravity alone provides an inadequate rate of blood return during procedures such as minimally invasive cardiac surgery and bypass via femoral cannulation. In these cases the resistance of the venous cannula limits the maximum achievable flow. Vacuum assisted venous drainage (VAVD) is a technique that overcomes flow limitations by applying suction to venous blood thereby increasing the pressure difference between the venous site and venous reservoir. Prior art venous bags cannot be used with VAVD unless a more expensive and complicated two-pump system is used.  
     The present invention describes a soft-shell venous reservoir that allows VAVD using a single pump. The invention describes a soft shell reservoir that is sealed within a, preferably, clear rigid housing. A gas port connected to the space between the bag and rigid housing is used to adjust the pressure within that space: it allows the user to adjust the “atmospheric” pressure about the external walls of the soft-shell reservoir. Another aspect of the invention improves gas bubble removal. One form of the invention also incorporates means that improve gas bubble removal from blood transiting the collapsible reservoir. In another form of the invention the venous bag has all its ports extending from its top, an innovation that provides easy loading/unloading of the reservoir in/out of its holder and simplifies sealing the reservoir in a chamber thereby allowing the aforementioned VAVD.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation in part of pending U.S. application Ser. No. 09/141,960 filed Aug. 28, 1998, and pending application PCT/US99/19477 filed Aug. 30, 1999 (now published as WO012155A1: An Improved Soft Shell Venous Reservoir) the disclosures of these applications being incorporated herein by reference thereto.  
     
    
     GOVERNMENT INTERESTS  
       [0002] This invention was in part made with government support under an SBIR Grant # R44-HL55034 awarded by the National Institute Health, National Heart, Lung, and Blood Institute. As such the government may have certain rights in the invention.  
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    The invention is a blood reservoir with at least one pliable wall having at least three innovative features. First, the compliant reservoir is sealed within a rigid housing allowing control of the “atmospheric” pressure surrounding the bag, and therefore the pressure at which the bag would collapse. This first invention enables vacuum augmented venous drainage (VAVD) with a collapsible soft-shell reservoir (i.e. venous bag) and is particularly useful for cardiopulmonary bypass. Second, the invention incorporates means that improve gas bubble removal from blood transiting the collapsible reservoir. Third, a reservoir with all ports extending from its top is disclosed, an innovation that provides easy loading/unloading of the reservoir in/out of its holder and simplifies sealing the reservoir in a chamber thereby allowing the aforementioned VAVD.  
           [0005]    2. Description of the Prior Art  
           [0006]    Blood is routinely pumped outside the body during dialysis, cardiopulmonary bypass, and long-term cardiac and/or respiratory support (e.g. extracorporeal membrane oxygenation, ECMO). In general, blood flows from the venous side of the patient to a venous reservoir that is usually maintained at atmospheric pressure. Blood flow from the patient to the reservoir is a function of the resistance of the fluid conduit between patient and reservoir, and the pressure difference between patient and reservoir. When the reservoir is maintained at atmospheric pressure, that pressure difference is the height difference between patient and reservoir; the resulting flow is referred to as gravity drainage. Venous drainage by gravity alone provides inadequate return during procedures such as minimally invasive cardiac surgery and bypass via femoral cannulation. Usually it is the resistance of the venous cannula that limits the flow achievable. Vacuum augmented venous drainage (VAVD) is a technique that overcomes flow limitations by applying suction to the hard shell reservoir thereby increasing the pressure difference between the venous cannulation site and venous reservoir. VAVD allows for a decrease in the inner diameter of the venous line, thereby reducing prime volume and enabling the use of a smaller cannula, which translates to an easier insertion, a better surgical view and a smaller surgical incision. This method precludes the use of the safer soft-shell closed venous reservoir (venous bag) unless a more expensive and complicated two-pump system is used (see McKusker K, Hoffman D, Maldarelli W, Toplitz S, and Sisto D. High-flow femoro-femoral bypass utilizing small cannulae and a centrifugal pump on the venous side. Perfusion 1992; 7:295-300).  
           [0007]    Clinically, a venous bag is used because it provides significant safety features. If the bag empties, it collapses, thereby preventing gross air from being pumped to the patient. It usually has no air-blood interface, and it requires no antifoam agents that can embolize into the blood. A recent study by Schonberger et al (Schonberger JPAM, Everts PAM, and Hoffmann J J. “Systemic blood activation with open and closed venous reservoirs. Annals of Thoracic Surgery, 1995; Vol. 59, pages 1549-55) comparing the hard shell to the bag reservoir found significantly lower blood activation, shed blood loss, crystalloid infusion, and hemolysis, and less donor blood infusion with the bag reservoir. Schonberger&#39;s group recommended against routine use of an open (hard shell) venous reservoir system. Currently, a slight negative pressure applied to the venous line (to facilitate blood drainage) using a single pump is possible with less desirable hard shell venous reservoirs. It is impossible to apply negative pressure to current soft-shell reservoirs, but it is possible with the present invention.  
           [0008]    In an open, hard shell reservoir, air escapes by floating to the top of the reservoir. In a bag reservoir, air floats to the top but must be actively eliminated. This can be done manually with a syringe, or more frequently with a roller pump operating slowly so as to continuously pump fluid to the cardiotomy reservoir. With either method, a sudden large volume of air can overwhelm the air removal system and cause disastrous consequences, especially without a vigilant perfusionist. With one preferred embodiment of the present invention, air would be eliminated automatically without a roller pump or intervention by the perfusionist, and priming of the extracorporeal circuit would be facilitated through faster air removal utilizing either a floating ball valve or a hydrophobic membrane. Currently there are devices used in the CPB circuit that incorporate hydrophobic membranes that remove air yet do not allow blood to cross (e.g. Model # AutoVent-SV, Pall Corp Glen Cove N.Y.). Studies with filters used in these applications have shown that the membranes clear air from water almost indefinitely (many days), even if high suction is applied, without reducing gas transfer rate over time. However, when the membrane is exposed to blood, especially when high suction is applied, a film forms on the membrane over time, causing a significant increase in resistance to gas flow. The present invention incorporates designs and means to reduce this problem and extend the life of the membrane when used with blood. Likewise, U.S. Pat. No. 3,849,071 shows a floating ball within a blood filter that supposed to open a purge port when air enters and close when the blood level rises. However, as described, it is a physical impossibility for the ball to “fall” and open the purge port because, as shown, the weight of the floating ball is insufficient to overcome the force holding the ball against the purge port. With the present invention, the relative weight of the ball, the internal diameter of the purge port, and the suction applied to the purge port are designed to assure that the ball will drop to open the purge port in response to air level in the venous reservoir.  
           [0009]    With prior art soft-shell reservoirs (SSR) air may be trapped at the top of the liquid by the collapsed walls of the reservoir, see FIGS. 1 a  and  1   aa . U.S. Pat. No. 4,622,032 illustrates a soft shell reservoir having an inlet tube extending from the bottom half way into the reservoir. This arrangement helps bubbles move up to the top of the extended tubes but the bubbles can still be trapped above said tubes. U.S. Pat. No. 5,573,526 illustrate the prior art soft-shell reservoir having its gas removal tubes (i.e. 18 and 20 of FIG. 1) extending from the top less 40% of the height of its blood chamber into the reservoir. All other prior art SSR have air removal tubes that are shorter with many having vent tubes that do not extend into the SSR at all (e.g. U.S. Pat. No. 5,580,349). As FIGS. 1 b  and  1   bb  illustrates, a tube extending from the top and into the SSR prevents complete collapse of the pliable walls of the bag thereby forming a pathway for air to move upward. The prior SSR air removal tubes extend less than 40% of the height of the blood chamber and therefore air still may be trapped below said tubes.  
           [0010]    A soft shell venous reservoir sold by Johnson and Johnson (and now by Medtronic see reference 13) shows a soft shell reservoir with an inline tube extending, along one side of the bag, to the gas purge port at a 45° incline. This design has a rigid fluid path between blood inlet and gas purge port. However, this design is not as conducive to air removal as a vertical fluid path would be. In addition, the tube extending between inlet tube and purge port had an ID of ⅝″, or only 25% greater diameter than the inlet tube. Thus, the velocity of the liquid in the column slows to only 64% of the inlet velocity. In another aspect of the present invention, a vertical path is provided from the blood inlet at the bottom of the bag to the gas purge port at the top of the bag, such path limiting the aforementioned problem of trapped air. The vertical path also has a large enough diameter that slows the velocity of the liquid to 25% or less of the inlet velocity. A lower blood velocity is more conducive to bubble removal.  
           [0011]    State of the art soft shell venous reservoirs with a screen are designed such that a large portion of the screen contacts the internal walls of the bag, thereby increasing the resistance to blood flow across the screen, and rendering that portion of the screen ineffective, at least partially. This contact between the screen and the walls of the bag increases as the volume in the reservoir decreases. One aspect of the present invention reduces that problem by preventing the external walls of the venous reservoir from contacting the screen.  
           [0012]    The indication of blood level in present soft shell venous reservoir is very inaccurate and low level, or air-in-the-reservoir, alarms are not reliable because many are designed for hard shell reservoirs. The present invention provides effective means to alarm at low blood levels and in the soft shell venous reservoir.  
           [0013]    Currently, at the end of the bypass procedure, the patient is weaned off the heart lung machine by reducing the bypass flow. This is achieved by partially clamping the venous line and decreasing speed of the arterial pump. Once off bypass, the blood left in the venous reservoir is gradually pumped back to the venous side of the patient. Another aspect of the invention allows the user to adjust the positive pressure applied to the blood within the venous reservoir. By being able to increase the pressure of the venous reservoir, the user can effectively reduce venous drainage or perfuse the blood back to the patient. This is not possible with current venous reservoir bags and may be dangerous with hard shell reservoirs (i.e., air may be pushed to the patient).  
           [0014]    The inventor has also previously described an inline bladder (The Better-Bladder™, now U.S. Pat. No. 6,039,078), a device with a thin walled, sausage shaped bladder sealed inside a clear, rigid housing. Since the bladder is made from a single piece of tubing, the blood path is smooth with no flow discontinuities. The bladder portion is sealed within the housing that has an access port to the housing space outside the bladder. Because of its thin wall, the enlarged section can easily collapse. Thus, it can serve as an inline reservoir, providing compliance in the venous line to reduce the pressure pulsations at the pump inlet. The Better-Bladder also transmits the blood pressure flowing through it across its thin wall, allowing pump inlet pressure to be measured noninvasively by measuring the gas pressure of the housing via the gas port. The degree of “gravity drainage” is user-adjustable by setting the negative pressure in the Better-Bladder housing. If the suction generated by the venous pump becomes too great, the pump is slowed or stopped by a pump controller. The Better-Bladder does not have a gas purge port or a screen to inhibit gas bubbles. It is also much smaller, having nominal volume of 80 ml for adult perfusion as compared to over 1,000 ml for a venous reservoir.  
           [0015]    Despite users acknowledgement that SSR are safer, hard shell reservoirs are easier to use and therefore more widely used. For example, it is easier to connect the inlet tubing located at the top of the hard shell reservoir than to the inlet tube of the SSR located at the bottom. Though some SSRs are premounted by the manufacture to a supporting plate (e.g. Cobe see U.S. Pat. No. 5,693,039), most require multiple hanging hooks for proper support (e.g. Baxter&#39;s SSR model #BMR1900 has 3 holes at the top and 4 holes at the bottom), an inconvenience at best, a danger in an emergency. Present mounted SSR do not improve the tube connection by much. It would be a clinical advantage to provide a SSR that allows fast mounting and dismounting, and tube connection that are easy or even easier than that of hard shell reservoir. Another requirement for present SSR is the use of a supporting faceplate (e.g. see FIG. 3 of U.S. Pat. No. 5,573,526). These are used to improve the bubble path from the blood to the top of the reservoir. Such faceplates are again inconvenient, require additional assembly time by the user, and may obstruct the direct approach to the front wall of the bag. The latter is useful when bubbles “stuck” on the wall are to be dislodged. The elimination, or at least the reduced requirement, of a front plate is another desirable attribute.  
           [0016]    U.S. Pat. No. 5,823,045 “ Measuring Blood Volume in Soft-Shell Venous Resevoirs (sp.) by Displacement”  illustrates a SSR enclosed in a rigid housing. This invention suggests sealing a SSR within a rigid housing but does not suggest applying vacuum to the fluid surrounding the SSR. In fact, neither the figures nor the specifications mention a port for adjusting the fluid in sealed container  12 . Van Driel&#39;s patent has some major flaws. The tubes connected to the bag are to be “threaded through resilient seals 26 in the bottom of container 12 . . . ” also renders &#39;045 clinically irrelevant. If, though not described as such, container  12  is disposable, then the system as described is too expensive. If, as understood, container  12  is not disposable, then “threading” the tubes would break sterility, and would be very difficult, especially if a seal is required. Further, since the outside diameter of perfusion connectors are larger than the OD of the tubing they connect, it would be impossible to have any of the tubing of the SSR connected to anything until after they have been threaded. In addition, the housing needs to be sufficiently wide for the user to place their hands and thread the inlet and outlet tubes at the bottom of box  12 , a major disadvantage that hinders quick setup and increases the likelihood of contamination. This invention has not been reduced to clinical practice.  
           [0017]    Since the SSR is sealed in container  12 , external means are provided by &#39;045 to “massage” the SSR with “vibrator”  36 . In fact, since vibrator  36  is not connected to the wall of the SSR, it can only squeeze the wall rather than the pull and push motions required for vibration. This provides significantly less manipulation ability as compared to direct contact with the bag.  
           [0018]    PCT&#39;s International Publication Number WO 99/08734 entitled “ System and Method for Minimally Invasive Surgery Vacuum-Assisted Venous Drainage”  illustrates in FIG. 9 a standard SSR (“preferably BMR-800 or BMR-1900”) completely sealed in a rigid housing. It is also suggested that “ . . . a pressure differential between the interior and exterior of the reservoir . . . ” be maintained. This design is as impractical as that of U.S. Pat. No. &#39;045. If the bag and rigid housing are assembled and shipped to the end user as a single unit, the unit becomes very expensive and therefore would be used only for VADV cases. The expense arises from a housing required to support a large force. The force can be calculated as (Pressure)*(Area). Thus, to support a pressure of −250 mmHg with a safety factor of 2 for a box that holds a bag like the BMR-1900 (10″ high by 12″ wide), the force on each faceplate is 1200 lb! The inventors did not suggest, nor showed or described, a mechanism for the user to seal the bag in the box. Even if there was a mechanism, it would be very difficult, time consuming, and, as described with relation to &#39;045, most likely to break sterility. And, once sealed it would be impossible for the user to contact the bag.  
           [0019]    Both &#39;045 and &#39;08734 illustrate the rigid housing as a rectangular box. A better design to support the large external force due to the large area and vacuum used would be an ellipsoid cross section or at least rounded corners.  
           [0020]    Both &#39;045 and &#39;08734 illustrate the great need for designs that allow simple, inexpensive, and quick means to seal and remove the bag from its container even with long tubing or large connectors without affecting its sterility. Simple and quick means to reach the enclosed bag would also be welcomed. The present invention overcomes these clinically non-workable prior art designs.  
           [0021]    It is standard practice to place the venous reservoir above the oxygenator to assure that the microporous membrane is always under positive pressure. A negative pressure would result in air crossing the membrane and entering the arterial line, a very dangerous situation. When VAVD is used, suction can be applied to the venous reservoir only once the arterial pump is generating a positive pressure in the arterial line. Otherwise, the suction applied to the venous reservoir can draw air across the membrane. A one-way valve at the pump outlet prevents vacuum applied to the venous reservoir from reaching the membrane oxygenator, but a one-way valve incorporated into the outlet of the present venous reservoir is preferable. Means to assure that the gas side of the membrane oxygenator is always positive relative to the blood side would also be a major safety feature for all VAVD applications.  
         BRIEF SUMMARY OF THE INVENTION  
         [0022]    The present invention incorporates improved designs for venous reservoirs that provide the benefits of prior art devices (limiting pump suction using the safer, pliable blood reservoir) while avoiding their disadvantages (air entrapment, inability to utilize VAVD, required vigilance for air removal). Further, its advantages and uniqueness are also enhanced by providing the user with means to adjust the degree of suction applied for venous augmentation and assuring that a greater area of the screen is effective in liquid transport.  
           [0023]    Briefly, the present invention in its simplest form consists of a blood reservoir having at least one pliable wall, a blood inlet, a blood outlet, and a gas purge port. In one preferred embodiment, a first structure having tubular cross section and semirigid wall is placed above said inlet thereby providing a first path for undesirable bubbles entering the reservoir to move to the top where they are eliminated via said gas purge port. The first structure preferably has an effective cross section that is larger than the ID of said inlet tube thereby slowing any blood flow and allowing more favorable conditions (longer time, lower drag) for gas bubbles to float upward. The wall of the first structure is sufficiently rigid to prevent collapse of said pliable wall from blocking said first path. In another preferred embodiment, the pliable wall of the venous reservoir is sealed externally, forming a pressure chamber external to the venous reservoir. Controlled suction applied to said external chamber is transmitted across said pliable wall thereby controlling the negative pressure of the blood at which said pliable wall moves.  
           [0024]    Another preferred embodiment has all the tubes at the top of the SSR. These tubes pass through, sealed within, and physically supported by a rigid disposable supporting plate providing three major advantages. First, the bag is supported by hanging the supporting plate in a supporting fixture, much like the hard shell reservoir. This allows the user to “drop in” the SSR and just as easily remove the SSR from its holder. Second, the supporting plate provides simple sealing means along a single plane, an extremely important feature for simple and secure sealing of the SSR within housing for VAVD applications. Third, by having all the tubes for the bag entering from its top, the bottom of the bag is unhindered and can be placed lower to the floor allowing greater gravity drainage. In addition, because the bag hangs from the top, the weight of the SSR/blood contributes to the seal of the supporting plate against the housing. Designed properly, this gravitational force can eliminate or greatly simplify any clamping required by other designs.  
           [0025]    It is therefore the objective of the present invention to provide an improved venous blood reservoir with at least one pliable wall that provides a path for gas bubbles entering the inlet to move unhindered up to the gas purge port.  
           [0026]    A further objective of the present invention is an improved venous blood reservoir, having at least one pliable wall, allowing the user to adjust the negative pressure applied to said pliable wall thereby allowing for augmented venous drainage.  
           [0027]    A further objective of the present invention is an improved venous blood reservoir designed to maintain its external wall from contacting the screen material and thereby reducing the resistance to blood flow across the screen.  
           [0028]    Yet another objective of the present invention is to incorporate a one-way valve at the outlet of the venous reservoir, said valve preventing blood from being sucked into the venous reservoir when pressure at the outlet of the venous reservoir is positive relative to the liquid pressure in the venous reservoir.  
           [0029]    Another objective of the present invention is to provide an improved venous blood reservoir with at least one pliable wall that when placed at the pump inlet, provides compliance that reduces pressure fluctuations at said pump inlet.  
           [0030]    Another objective of the present invention is to provide an improved venous blood reservoir with at least one pliable wall that when placed at the pump inlet, provides automated means to eliminate air.  
           [0031]    Another objective of the present invention is to provide an improved venous blood reservoir with at least one pliable wall and with a relatively large gas purge port, said port providing a more volumetrically effective gas purge, and one that is less traumatic to the blood.  
           [0032]    Another objective of the present invention is to provide automated means to detect air in the venous reservoir and utilize said means to alarm the user or control the suction used to remove air from the venous reservoir.  
           [0033]    Another objective of the present invention is to provide the user with a SSR that is simple to use, and easy to load and unload from its holder or from its container.  
           [0034]    Another objective of the present invention is to provide the user with a SSR having all its connections above the bag facilitating said connections and allowing a lower placement of the reservoir thus providing greater gravity drainage.  
           [0035]    Another objective of the present invention is to utilize gravity to facilitate sealing of the SSR in its VAVD container.  
           [0036]    Another objective of the present invention is to utilize the applied suction to facilitate sealing the SSR within its VAVD container.  
           [0037]    Another objective of the present invention is to provide a single plane to seal SSR in VAVD container.  
           [0038]    Another objective of the present invention is to provide a non-disposable VAVD container that supports at least −100 mmHg.  
           [0039]    Another objective of the present invention is to provide a disposable cover/holder as part of the SSR for the VAVD container.  
           [0040]    Yet another objective of the present invention is to provide a single venous bag that can be used with either standard or with VAVD thus, reducing cost of inventory and simplifying the user&#39;s set up.  
           [0041]    Another objective of the present invention is to provide a disposable SSR incorporating a structure that facilitates sealing the bag within a non-disposable VAVD container, thus reducing cost.  
           [0042]    Another objective of the present invention is to provide a SSR incorporating means to prevent the SSR from pulling out of, or twisting within its holder.  
           [0043]    Another objective of the present invention is to provide a means to allow suction application to both SSR and cardiotomy independent of the height difference between the two.  
           [0044]    Another objective of the present invention is to provide a means to reduce the chance of gas pulled across the microporous membrane when suction is applied to the venous reservoir.  
           [0045]    Another objective of the present invention is to provide a VAVD housing having an ellipsoid cross section that can better support a large external force and streamlined to the shape of the SSR.  
           [0046]    Another objective of the present invention is to provide a VAVD housing for SSR that does not require the user&#39;s hands to be placed within said housing when mounting said SSR in said housing. Other objectives, features and advantages of the present invention will become apparent by reference to the following detailed description of the presently preferred, but nonetheless illustrative, embodiments thereof with reference to the accompanying drawings therein.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0047]    [0047]FIG. 1 is a line drawing of the pertinent components of a typical cardiopulmonary bypass (CPB) circuit showing the relative location of the venous reservoir of the present invention.  
         [0048]    [0048]FIG. 1 a  is a line drawing of a typical prior art venous reservoir illustrating how incoming air bubbles are prevented from reaching the gas exhaust port and are trapped midway in the bag.  
         [0049]    [0049]FIG. 1 aa  is a line drawing of a cross section taken of FIG. 1 a  along line  1   a - 1   a′.    
         [0050]    [0050]FIG. 1 b  is a line drawing of a typical venous reservoir according to the present invention, illustrating a pathway provided by channels formed along a tube extended into bag.  
         [0051]    [0051]FIG. 1 bb  is a line drawing of a cross section taken of FIG. 1 b  along line  1   b - 1   b′.    
         [0052]    [0052]FIG. 2 a  is a line drawing illustrating one preferred embodiment of the present invention where a perforated cylinder is used to keep the flexible walls of the venous reservoir bag away from its screen as well as provide an uninterrupted fluid path between blood inlet and gas exhaust port.  
         [0053]    [0053]FIG. 2 b  is a line drawing of a cross section taken of FIG. 2 a  along line  15 - 15 ′.  
         [0054]    [0054]FIG. 2 c  is a line drawing of a cross section taken of FIG. 2 a  along line  16 - 16 ′.  
         [0055]    [0055]FIG. 2 cc  is an enlarged view of the circled section taken from FIG. 2 c.    
         [0056]    [0056]FIG. 2 d  is a line drawing of a cross section taken of FIG. 2 a  along line  17 - 17 ′.  
         [0057]    [0057]FIG. 2 e  is a line drawing illustrating the flow of blood and air at the inlet of the venous reservoir shown in FIG. 2 a.    
         [0058]    [0058]FIG. 2 f  is a line drawing illustrating one preferred method to assemble the screen used with the venous reservoir shown in FIG. 2 a.    
         [0059]    [0059]FIG. 3 a  is a line drawing illustrating one preferred sealing scheme of an adult size venous reservoir that allows the use of a universal holder for it and the pediatric venous reservoir shown in FIG. 3 b.    
         [0060]    [0060]FIG. 3 b  is a line drawing illustrating one preferred sealing scheme of a pediatric size venous reservoir that allows the use a universal holder for it and the adult venous reservoir shown in FIG. 3 a.    
         [0061]    [0061]FIG. 4 is a line drawing illustrating one preferred embodiment of the present invention where the venous reservoir is topped with a microporous membrane that allows air, but not blood, to be removed.  
         [0062]    [0062]FIG. 5 a  is a line drawing illustrating another preferred embodiment of a microporous membrane placed at the top of the venous reservoir allowing air, but not blood, to be removed.  
         [0063]    [0063]FIG. 5 b  is a line drawing of a cross section taken of FIG. 5 a  along line b-b′.  
         [0064]    [0064]FIG. 6 a  is a line drawing illustrating one preferred embodiment of the present invention where air removal is automated by utilizing a floating ball valve.  
         [0065]    [0065]FIG. 6 b  is a line drawing illustrating another view of the bottom of the ball cage used in FIG. 6 a  taken along line  23 - 23 ′.  
         [0066]    [0066]FIG. 6 c  is a line drawing illustrating another view of the ball cage used in FIG. 6 a  taken along line  24 - 24 ′.  
         [0067]    [0067]FIG. 6 d  is a line drawing illustrating another embodiment of the present invention where air removal is automated by utilizing a floating ball valve incorporating two safety features.  
         [0068]    [0068]FIG. 7 a  is a line drawing illustrating another preferred embodiment of the present invention where a rigid cylinder, incorporated as one external wall of the venous reservoir, maintains the screen wall unhindered and provides an uninterrupted fluid path between blood inlet and gas exhaust port.  
         [0069]    [0069]FIG. 7 b  is a line drawing of a cross section taken of FIG. 7 a  along line  25 - 25 ′.  
         [0070]    [0070]FIG. 7 c  illustrates rigid cylinder  72 , shown in FIG. 7 a , isolated and rotated 90° clockwise.  
         [0071]    [0071]FIG. 7 d  is an enlarged view of the top, circled section of the venous reservoir shown in FIG. 7 a  illustrating the slot providing communication for removal of air external to the screen.  
         [0072]    [0072]FIG. 7 e  is a line drawing of a cross section taken of FIG. 7 d  taken along line  26 - 26 ′.  
         [0073]    [0073]FIG. 7 f  is a line drawing of a cross section taken of FIG. 7 e  taken along line  27 - 27 ′.  
         [0074]    [0074]FIG. 8 a  is a line drawing illustrating one preferred embodiment of the present invention where a venous reservoir can be sealed within a rigid housing where suction can be applied to the external flexible walls of said reservoir thereby providing venous augmentation.  
         [0075]    [0075]FIG. 8 b  is a line drawing of a cross section taken of FIG. 8 a  along line  28 - 28 ′.  
         [0076]    [0076]FIG. 8 c  is a line drawing of a cross section taken of FIG. 8 a  along line  29 - 29 ′ illustrating the rigid bottom cap used with the venous reservoir to seal the bottom of the housing shown in FIG. 8 a.    
         [0077]    [0077]FIG. 9 a  is a line drawing of another preferred embodiment of the present invention wherein the venous reservoir can be sealed within a rigid housing where suction can be applied to the external flexible walls of said reservoir thereby providing venous augmentation.  
         [0078]    [0078]FIG. 9 b  is a line drawing of a cross section taken of FIG. 9 a  along line  30 - 30 ′ showing the bottom seal of the venous reservoir within the housing and door shown in FIG. 9 a.    
         [0079]    [0079]FIG. 9 c  is a line drawing of a cross section taken of FIG. 9 a  along line  31 - 31 ′ showing the top seal of the venous reservoir within the housing and door shown in FIG. 9 a.    
         [0080]    [0080]FIG. 9 d  is a line drawing of a cross section taken of FIG. 9 a  along line  32 - 32 ′ showing another preferred sealing means incorporated into the inlet tube of the venous reservoir shown in FIG. 9 a.    
         [0081]    [0081]FIG. 9 e  is a line drawing of a cross section taken of FIG. 9 d  along line  33 - 33 ′ showing a top view of the means incorporated into the inlet tube of the venous reservoir shown in FIG. 9 a.    
         [0082]    [0082]FIG. 9 f  is a line drawing identical to that shown in FIG. 9 d  except that this embodiment incorporates a gasket having an indentation to seal about the inlet tube of the reservoir, and a deeper indentation in the housing to support said tube while the venous reservoir is loaded.  
         [0083]    [0083]FIG. 10 a  is a three dimensional rendering of another preferred embodiment illustratingun adaptation of the present invention to other venous reservoir having at least one flexible wall by sealing said flexible wall within a rigid housing such that suction can be applied externally to said flexible wall, thereby providing venous augmentation.  
         [0084]    [0084]FIG. 10 b  is a line drawing of a longitudinal cross sectional view of FIG. 10 a.    
         [0085]    [0085]FIG. 10 c  is a line drawing of a cross section taken of FIG. 10 b  along line  10   c - 10   c ′ showing another view of the venous reservoir within the housing shown in FIG. 10 a.    
         [0086]    [0086]FIG. 11 is a line drawing illustrating another embodiment of the present invention where air removal is automated by connecting the gas exhaust port of the venous reservoir to the inlet port of a cardiotomy reservoir, said cardiotomy having negative pressure applied to it.  
         [0087]    [0087]FIG. 12 a  is a line drawing illustrating another preferred embodiment of the present invention, similar to that shown in FIG. 8 a , except that all the tubes entering the bag enter from the bottom and incorporate a disposable cover plate.  
         [0088]    [0088]FIG. 12 b  is a line drawing of a cross section taken of FIG. 12 a  along line  112 - 112 ′.  
         [0089]    [0089]FIG. 12 c  is line drawing of a cross section taken of a bottom view of cover  89  of FIG. 12 a  along line  29 - 29 ′.  
         [0090]    [0090]FIG. 13 a  is a line drawing illustrating one preferred embodiment of the present invention where all the tubes entering the bag enter from the top and are supported by a disposable supporting plate.  
         [0091]    [0091]FIG. 13 b  is a line drawing of a cross section taken of FIG. 13 a  along line  131 - 131 ′.  
         [0092]    [0092]FIG. 13 c  is line drawing of a cross section taken of a top view of cover  1389  of FIG. 13 a  along line  132 - 132 ′.  
         [0093]    [0093]FIG. 13 d  is line drawing of a front view of a SSR shown in FIG. 13 a  having an outlet section with the outlet tube centered at the bottom and connected to the side wall of the bag.  
         [0094]    [0094]FIG. 13 dd  is a line drawing of a cross section taken of FIG. 13 d  along line  133 - 133 ′.  
         [0095]    [0095]FIG. 13 e  is line drawing of a front view of a SSR shown in FIG. 13 a  having a different outlet section with the outlet tube on the side and connected to the side wall of the bag.  
         [0096]    [0096]FIG. 13 ee  is a line drawing of a cross section taken of FIG. 13 e  along line  134 - 134 ′.  
         [0097]    [0097]FIG. 13 f  is line drawing of a preferred embodiment of top cover  1389  shown in FIG. 13 a  and a combination of components designed to reduce the chance of air crossing the into the arterial line by applying controlled suction to the gas side of the oxygenator.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0098]    Reference should now be made to the drawings wherein the same reference numerals are used throughout to designate the same or similar parts. It should be noted that the use of cardiopulmonary bypass, as shown in FIG. 1, is for descriptive purposes, and should not be taken as a limitation to the use of the devices described hereinafter. It should also be noted that the term soft shell reservoir, venous bag and bag are used interchangeably.  
         [0099]    [0099]FIG. 1 is a schematic representation of a system according to the present invention and showing the relative location of the venous reservoir in a typical cardiopulmonary bypass circuit. As shown, tubing  123  is inserted at one end by means of a cannula (not shown) in the vena cavae for obtaining venous blood from the heart (not shown) of patient  1102 . Tubing  123  is coupled, as an example, to venous reservoir  1103 . The blood is drawn from venous reservoir  1103  via tube  135  by roller pump  1104  and pumped through a membrane oxygenator  1105  wherein oxygen is supplied to the blood and carbon dioxide is removed. The blood from the oxygenator is then conducted by means of tubing  157  to arterial filter  1107  and then via tubing  172  and an arterial cannula (not shown) back to the patient. As described in the prior art, the venous blood, here shown coming from the patient&#39;s vena cavae, may contain air that must be eliminated before it is pumped back to the patient. This is one of the main functions of the venous reservoir. As shown, air entering venous reservoir  1103  rises to the top of said reservoir where it is removed by suction pump  1114  to cardiotomy reservoir  1115 . Roller pump  1104  is usually one of 3 to five pumps composing a heart-lung machine, which is part of a hardware required for cardiopulmonary bypass.  
         [0100]    [0100]FIGS. 2 a ,  2   b ,  2   c ,  2   d  and  2   e  illustrate line drawings of one preferred embodiment of the present invention. Here, venous blood enters the venous reservoir  1819  via inlet tube  1  and is directed into first inlet chamber  2 , shown as a cutaway. First inlet chamber  2  preferably has a circular cross section with its walls formed of fine screen  3  typically having a pore size of 40μ to 150μ and having an effective open area that is preferably greater than 40%. It is understood that though lower pore sizes result in higher resistance to blood flow, they prevent smaller bubbles from crossing the screen. It should also be understood that screen  3  is preferably heparin coated, to increase wettability and reduce clot formation. The top of chamber  2  is in fluid communication with gas purge port  4 . The bottom of chamber  2  is open and is in fluid communication with inlet tube  1  and, via expandable chamber  8 , with outlet tube  5 . Preferably outlet tube  5  is located on the opposite side of, and lower than, inlet tube  1 .(Bentley patent?)  
         [0101]    In one of the preferred embodiment, shown in FIG. 2 a , first inlet chamber  2  has a larger inside diameter than inlet tube  1  (e.g. 1.0″ v. 0.5″), said larger diameter serves to slow the velocity of the blood (e.g. ¼ the inlet velocity), and thus allow more time for any bubbles to rise to the top where they can be removed. Slowing the blood also reduces the tendency of the flowing blood to carry the bubbles, especially the smaller ones, by reducing the drag on the bubbles by the moving blood. Lower velocity also lowers the tendency of larger bubbles to break into smaller ones; larger bubbles have a higher buoyancy and less of a chance of crossing screen  3  into expandable chamber  8 , and flowing out of the bag through outlet tube  5  shown in FIG. 2 a . With sufficient pressure across screen  3 , the bubbles could cross into chamber  8  and travel to outlet  5  of the reservoir, a very undesirable outcome. To reduce that possibility, inlet chamber  2  is open at the bottom where debubbled blood can exit first inlet chamber  2  at  2   a . To improve flow conditions, the outlet of inlet tube  1 ,  1   a , is preferably centered with the centerline of chamber  2 , as also shown in FIG. 2 b  (cross-section  15 - 15 ′ in FIG. 2 a ). Also shown is one preferred embodiment of structure  28  that centers inlet tube  1  within chamber  2  formed by screen  3 . Connector  28 , shown in FIG. 2 a  and as a cross section taken of FIG. 2 a  along line  15 - 15 ′ shown in FIG. 2 b , lines up and connects inlet tube  1  to inlet chamber  2 . Thus, in one preferred embodiment, connector  28  has a wheel cross-section with an internal circular structure  28   a  connected via spokes  28   b  to an external circular structure  28   c . The inside diameter of inside structure  28   a  that allows interference fitting to the outside diameter of inlet tube  1  and the outside diameter of outside structure  28   c  supports cylinder  6 . The space between internal structure  28   a  and outside structure  28   c  maintained by spokes  28   b  forms a fluid communication between inlet chamber  2  and expandable chamber  8  as indicated by the downward facing arrow at the bottom of FIG. 2 e . It should also be obvious that since screen  3  may be flimsy, it may need radial support, as for example internal cage  26 , see FIG. 2 c  (cross section  16 - 16 ′ in FIG. 2 a ) and  2   f . Screen  3  can be attached to cage  26  by various means (e.g. insert molding) longitudinally and radially to  26   a  or  26   b  and longitudinally to ribs  26   c , for example, by adhesive. This would maximize the ID of first internal chamber  2  to provide a smooth and straight vertical flow path thereby facilitating the upward motion of the bubbles.  
         [0102]    With this design, as is the case for present venous reservoir bags (e.g. Bentley, Cobe, Sarns/3M, Minntech) most of the incoming blood would exit via screen  3  across which very few bubbles, if any, cross. However, present venous reservoir bags are made of four layers: the two outside layers being flexible PVC sheets and the two inside layers being a screen (e.g. U.S. Pat. No. 4,734,269). The screen is usually folded over with the fold being in the center of the venous reservoir bag and its edges sandwiched and sealed along at least two of edges of the two PVC outer layers. This design is simple but it provides no means to keep the internal surface of the external PVC walls from contacting the external wall of the screen. This contact reduces the effective screen area available for blood flow, especially at low blood volumes, causing further problems because more bubbles cross the screen at lower blood volumes. For example, tests conducted with the Cobe venous reservoir bag (Model # VRB, Cobe Lakewood, Colo.) showed that at a blood flow of 4.0 L/min and an air flow of 750 mL/min, the bubble count (size&gt; 50μ) with a blood volume of 750 ml in the bag was 35 bubbles/sec as compared to 94 bubbles/sec when the blood volume was 500 ml. The Baxter venous reservoir bag (Model #BMR-1900, Baxter/Bentley Irvine, Calif.) had similar results: the bubble count increased from 69 bubbles/sec to 160 bubbles/sec when the blood volume decreased from 750 to 500 ml.  
         [0103]    The present invention eliminates the problem of screen to wall contact by introducing means to maintain the wall of the venous reservoir bag away from the screen as well as to maintain a vertical column of blood within first inlet chamber  2 . This can be achieved by either incorporating the means into the disposable bag, or by interfacing a disposable bag with a nondisposable holder, the combination providing the aforementioned means. FIG. 2 a  illustrates one preferred embodiment of the disposable type. Here, a semi rigid cylinder  6  with perforated wall is placed over screen  3  forming second inlet chamber  7  in fluid communication with expandable chamber  8  via said perforations as well as its open bottom at  6   a . The perforations can be effectively formed by using a tubular net with, for example 0.030″ to 0.100″ diameter strands forming a diamond shaped opening, see  6 in FIG. 2 a , and can be obtained from Nalle Plastics Inc. Austin, Tex. The tubular net can be made of polypropylene, polyester, Nylon, or polyethylene. It must possess at least three properties: 1) sufficient stiffness (either by rigidity of the material or thickness of the yarn) and structure to keep walls  18  and  19  (FIGS. 2 b ,  2   c ,  2   d ) of venous reservoir bag  1819  (FIG. 2 a ) away from screen  3  thereby maintaining chamber  7 ; 2) an opening to allow unhindered fluid communication between chamber  7  and expandable chamber  8 ; and  3 ) cause no undesired interaction with biological fluids. Tubular net  6  preferably extends vertically from the bottom of venous reservoir  1819  at its inlet to the top of said reservoir and can be attached to the external wall of air-venting tube  4  for support. The inlet to cylinder  6 ,  6   a , may extend below screen  3  providing free fluid communication between inlet  1  and expandable chamber  8 . With this design, experiments similar to those described for the Cobe and Baxter bags result in a steady bubble count of 60 at bag volumes of 500 and 1000 ml.  
         [0104]    [0104]FIG. 2 e  illustrates the blood path of the present invention. Venous blood with some gas bubbles  23  enters the venous reservoir via inlet tube  1 . The inertial forces of the blood exiting outlet of tube  1  propel the blood and bubbles upward into first inlet chamber  2 . Chamber  2  is preferentially lined up within ± 15° of the vertical line. This essentially vertical position, unlike prior art devices, provides the least resistance for gas bubbles to rise up chamber  2  to air-venting tube  4  where they are evacuated by suction applied to the outlet of tube  4 , port  4   b.    
         [0105]    As shown in FIG. 2 a , screen  3  extends to the top of venous reservoir  1819  where it is sealed to gas venting tube  4 . This seal prevents blood from exiting at the top where it may drag bubbles out of inlet chamber  2  into expandable chamber  8 . Should gas volume increase at tube  4  and displace blood volume at the top of chamber  2 , the gas could cross screen  3  and enter chamber  7  and chamber  8 . Because screen wall  3  may get wet again before all the gas at the top of chamber  8  is removed, that gas can be trapped. Purge tube  9  (see FIGS. 2 a  and  2   e ) is provided to allow gas to be purged from chambers  7  and  8 . For that purpose, the topmost entry point of tube  9  into chamber  8  is the highest point in chamber  8  (e.g. point  8   a  is higher than point  8   b ). Tube  9  extends from air-venting tube  4  into chamber  8 , said extension preferably having holes  9   a  in its wall to provide better fluid communication with chamber  8  along the entire length of tube  9 . Holes  9   a  allows air to enter tube  9  and be evacuated as described before. Other holes may be punched into tube  9  to allow air to be evacuated at any blood level. The smaller diameter of tube  9  and the location of its outlet at the top of venting tube  4  reduces the chance of blood flowing (with bubbles) from chamber  2  to chamber  8  via tube  9 . The extension of tube  9  into chamber  8  also forms two channels, shown as  9   aa  in FIG. 2 cc , for air to travel along the tube upwards because the tube prohibits the opposite walls of the bag from making complete contact. Channels  9   aa  increase in size with increasing outside diameter of air removal tube  9  and thicker/stiffer walls  18  and  19  of bag  1819 . FIG. 1 b  and its associated view along  1   b - 1   b ′, FIG. 1 bb , illustrate how the present invention provides air channels. FIG. 1 a  and its associated view along  1   a - 1   a ′,  1   aa  illustrate how prior art shorter air removal tube (e.g. prior art U.S. Pat. No. 5,573,526 FIG. 1 tubes 18 and 20) lack such channels. Tube  9  extends downward into blood chamber  8  at least 40% but preferably over 50% of the height blood chamber  8 . As well known in the art, tube  9  can alternatively be sealed directly into chamber  8  and external to tube  4 . As shown, tube  9  is exposed to the same suction applied to air-venting tube  4 .  
         [0106]    With the present invention because, air moves freely to the top of bag  1819  where it can be purged easily. It therefore should be obvious that the degree of suction applied and the blood volume removed in order to purge the gas should be significantly lower than with present devices. The smaller blood volume removed, the lower flow required to remove the gas and the larger ID of the purge line all contribute to significantly lower blood damage. This is especially true when stopcocks, which have very small ID (e.g., 0.062″ and sometimes less) and are used with present devices, are eliminated.  
         [0107]    The user may not easily determine the presence of bubbles or the blood level in first inlet chamber  2  due to the opacity of the blood and/or screen  3 . Yet another innovation provides means to easily ascertain the presence of bubbles by increasing the ID of air-venting tube  4  to at least ¼″ but preferably ⅜″ or greater. Other venous reservoir bags have gas ports of ⅛″ ID or smaller, which presents a high resistance to gas and blood flow. The increased port diameter of the present invention increases the ease by which bubbles rise up tube  4  for two reasons. First, gas bubbles move up easier in a liquid filled tube having a diameter larger than the diameter of the bubbles. Second, a larger diameter tube accommodates larger bubbles with greater buoyancy, providing greater upward force on the bubbles relative to the capillary force within a liquid filled tube that inhibits their movement. Thus, by having an exhaust tube with a larger diameter, the user could pull blood up into tube  4 . Should air enter first inlet chamber  2 , it would travel up and replace the blood in tube  4  causing the visible blood level  4   d  (see FIG. 2 a ) in tube  4  to drop, an indication that air entered the venous reservoir and must be removed. It should be understood that the process can be automated by incorporating level detector  10  radial to tube  4 , said detector  10  connected to a suction controller and/or alarm monitor via transmitter line  10   a . Monitor/controller  12  alarms the user to air entering tube  4  and/or starts the required suction applied to the outlet of tube  4 ,  4   b , to remove said air and raise the liquid level. Once the level detector detects the rising liquid, it can stop the alarm and/or stop the suction used to remove the gas from the venous reservoir. Monitor/controller  12  can, for example, control the speed of the pump providing suction. Alternatively, it can open or close the tube providing suction (not shown) by a solenoid actuated tubing clamp. Also, as described in reference to one way valve  422  in reference to FIG. 4, preferably one-way valve  22 , placed just below outlet  4   b  of tube  4 , prevents air from entering the reservoir if the reservoir empties and is exposed to the suction generated by arterial pump  1104 . Further, defoamer sponge  24 , preferably incorporating anti-foam A and placed below valve  22 , may be used to break up blood in the form of foam that reaches the inlet of valve  22 . Placement of defoamer  24  at the top of tube  4  provides the desirable defoaming action while limiting contact between the defoamer and the blood that rises to that level.  
         [0108]    As shown in FIG. 2 a  the large diameter of chamber  2  allows more time for the bubbles to rise to the top and causes less turbulence that could hinder the upward motion of the bubbles. Most of the blood preferably flows from chamber  2  to chamber  7  across screen  3 , thereby assuring the upward motion of the bubbles. This preference is enhanced by cylinder  6  maintaining screen  3  free of contact with venous reservoir walls  18  and  19 , see FIG. 2 c . Typically, if wall screen  3  forms a cylinder with a 1″ diameter, then for an 8″ high structure, its surface area is 25in2. This large effective area is available for blood flowing from inlet chamber  2  to expandable chamber  8  and is virtually independent of the blood volume in expandable chamber  8 . Annular space  7  formed by cylinder  6  and screen  3  and better seen in FIG. 2 c , serves to separate gas from the blood; any bubbles that may have crossed wall  3  can still be buoyed upward to the top of chamber  7  where they can be removed by tube  9 . The blood then flows from expandable chamber  8  to outlet port  5 . Should air enter chamber  8 , it can still float to the top of said chamber and be eliminated via tube  9 . FIG. 2 cc , which is an enlargement of the circled section shown in FIG. 2 c , illustrates how tube  9  forms air channels  9   aa , described in reference to FIGS. 1 b  and  1   bb , thereby enhancing air removal by keeping walls  18  and  19  slightly apart along the length of tube  9 . Thus with this design, there are three chambers for air elimination: chambers  2 ,  7 , and  8 .  
         [0109]    A major reason a collapsible bag is used as a venous reservoir is to prevent air from being pumped out of the bag and into the patient should the venous reservoir empty. In present bags this is achieved by having the outlet port ( 5  in FIG. 2 a ) at the lowermost point of the bag. This can be incorporated into the present invention. Alternatively, the inlet of outlet tube  5 ,  5   a , can be cut on a diagonal (nominal 35° to 65°) with its pointed end protruding into expandable chamber  8  and its low point in line with the periphery of the bag at  8   c , as shown in FIG. 2 a . Tube  5  should be made of relatively soft material (e.g. 55 Shore A) and have a relatively large ID/wall ratio (e.g. 0.5″/0.062″=8). Since a larger ID/wall ratio, as well as softer durometer wall, requires a lower pressure difference across the wall of the tube to collapse the tube, then the combination of higher ratio and lower durometer can be used to quantify the ease of said collapse, (ID/wall)/durometer. Thus, for the above example, (0.5″/0.062″)/(55)= 0.147. This number is significantly higher than that obtained for the outlet tube typically used at the outlet of present venous reservoirs (0.5″/0.093″)/(65)= 0.082. Since the ease of tube collapse is related to (ID/wall) 3 , (see my U.S. Pat. No. 5,215,450: Innovative Pumping System for Peristaltic Pumps), even a small change in that ratio causes a large change in ease of collapse. Thus, the softer tubing and/or high ID/wall ratio allows collapsing walls  18  and  19  of venous reservoir bag  1819  to gradually, rather than suddenly, impede the flow out of outlet tube  5 . Once empty of liquids, the present aspect of the invention provides a looser seal about the outlet as compared to standard bags. Thus, when inlet flow resumes, less volume is needed to open the outlet tube, thereby providing resumption of flow sooner than present venous reservoir bags.  
         [0110]    An experiment was conducted to determine the negative pressure developed between the outlet of venous reservoir  1103  and the inlet of pump  1104  when pump  1104  (see FIG. 1) was pumping at 6.0 L/min out of venous reservoir  1103  and the venous flow into the venous reservoir was less than 6.0 L/min. The reservoir was emptied and its outlet collapsed. Also measured was the blood volume required in the venous reservoir to reopen the venous reservoir outlet. Once emptied, the outlet of the Cobe reservoir bag stayed closed until the volume in the bag increased to over 1,400 ml. During that time, the pump inlet pressure (measured in line  435  in FIG. 1) decreased to and remained at over −600 mmHg. Once the blood volume in the bag reached 1,400 ml, sufficient pressure was exerted to expand walls and release the collapsed outlet of the venous reservoir, thereby allowing resumption of blood flow from the venous reservoir to the pump inlet. A similar experiment with the Baxter bag required an increase in blood volume of 400 ml before the high negative pressure at the pump inlet (−580 mmHg) was relieved and the bag outlet opened up. With the present invention, only 350 ml were required to open the venous reservoir outlet and reestablish flow, and the maximum negative pressure was only −400 mmHg.  
         [0111]    As shown in FIGS. 2 a ,  2   b ,  2   c ,  2   d , layers  18  and  19  are heat sealed (e.g., by radio frequency welding) by a double margin along their upper and lower edges, by a relatively wide seal along their right edge and by a narrower seal along their left edge. Anchoring holes (eyelets)  27 , used to hang bag  1819 , can be formed by punching holes through, and along, the top and bottom of the heat sealed surface. The preferred configuration includes a hole on both sides of inlet tube  1 , outlet tube  5 , and air-venting tube  4 , and in the upper corner of the bag opposite tube  4  to facilitate secure attachment of the bag to the frame, see FIG. 2 a.    
         [0112]    It should be understood that various sizes of the venous reservoir can be made without necessarily affecting their performance; for example, three popular sizes having capacities of 400, 1200, and 2000 ml are some of the possibilities. To simplify manufacturing and reduce costs of the hardware, all reservoir sizes can have the same footprint so each size can utilize the same frame. Here, smaller capacity reservoirs have a smaller bag portion and larger peripheral area (FIG. 3). Anchoring holes  21   a ,  21   b ,  21   c ,  21   d ,  21   e ,  21   f , and  21   g  used to attach each bag to the frame can be accommodated by corresponding adjustable supporting pins in the frame, for example, as well known in the art.  
         [0113]    [0113]FIGS. 7 a ,  7   b , and  7   c  illustrate another preferred embodiment of the present invention. Here, rigid cylinder  72  replaces perforated cylinder  6 , shown in FIG. 2 a , to provide annular space  77  as well as to serve as part of the wall of venous reservoir  772 . Pliable venous reservoir walls  18  and  19  are sealed to rigid cylinder  72  on both sides of longitudinal slot  72   a , said slot better seen in FIG. 7 b —(a cross sectional view of cylinder  72  along lines  25  and  25 ′ in FIG. 7 a ) and  7   c  (a cross sectional view of cylinder  72  along lines  272  and  272 ′ in FIG. 7 a ), providing fluid communication between annular space  77  and expandable outlet chamber  8 . To reduce stasis and provide smooth blood flow, the incline at the bottom of the rigid cylinder  72 ,  72   d , matches the bottom incline of chamber  8 ,  8   d . Cylinder  72  (FIG. 7 b ) preferentially has longitudinal lips  72   b  and  72   c  along both sides of slot  72   a , said lips tapering and thinning as they extend outward. These lips serve to seal venous reservoir walls  18  and  19  about slot  72   a  (e.g., by radio frequency welding) as well as to form a smooth blood flow path from annular space  77  to expandable chamber  8 . It should be obvious that cylinder  72  preferentially is made of biocompatible, clear, rigid thermoplastic that can be easily sealed to venous reservoir walls  18  and  19 . A good choice would be rigid PVC. It should be obvious that screen  3 , air-venting tube  4 , outlet tube  5 , and expandable chamber  8  formed by walls  18  and  19  serve the same purpose described for the venous reservoir embodiment shown in FIG. 2 a.    
         [0114]    [0114]FIG. 7 d , which is an enlargement of the circled section shown in FIG. 7 a , illustrates another preferred embodiment providing a fluid path between chamber  8  and air-venting tube  74  that allows air removal present in annular space  77  and expandable chamber  8 . Here, cylindrical air-venting tube  74  has a notch  74   h , at its bottom, also seen in FIG. 7 e , which is a view of FIG. 7 d  taken along cross section  26 - 26 ′ and FIG. 7 f , which is a view of FIG. 7 e  taken along cross section  27 - 27 ′. As shown, the height of notch  74   h  extends beyond the top of screen cage  26 ,  26   b . The bottom of notch  74   h  extends onto the highest point of chamber  8 ,  8   a , which also preferentially corresponds to the highest point of screen  3 . Thus, notch  74   h  provides a fluid communication, see arrow  84  in FIG. 7 d , between air-venting tube  74  and chamber  8 . Notch  74   h  replaces the function of tube  9  shown in FIG. 2 a.    
         [0115]    As described so far, air removal is accomplished as it is by current techniques: suction pump  1114  (see FIG. 1) typically with ¼″ ID tubing is used to remove the gas from the top of the venous reservoir. This arrangement works but requires constant vigilance and intervention by the user to control air removal. Another innovative feature of the present invention is that air can be automatically eliminated from the reservoir with little or no user intervention required. Three preferable designs for the air purge port use a hydrophobic membrane, a floating ball, or controlled suction. All three methods allow air to be removed with very little, or no blood loss. The user would have the option to connect wall suction or one of the sucker pumps as the suction source for the air purge port, preferably having some regulating means to adjust/limit the degree of suction.  
         [0116]    [0116]FIG. 4 illustrates one preferred embodiment that achieves a large membrane area at the top of the venous reservoir. The design, with a cross section in the shape of an inverted “V” or “U”, achieves a large area and provides an inclined surface. Membrane  45  has an inclined surface that facilitates clearing of any blood film off the surface of the membrane. Gravity and wicking should encourage any such film to “peel” off the surface into the blood pool, thereby maintaining the membrane clearer and the gas transfer rate up. Membrane support  425  can be incorporated as the top of a semi-rigid PVC frame formed into a protective “roof”. The inside surface of the roof-contacting membrane incorporates ridges  425   a , which are in unimpeded fluid communication with air-venting tube  44 . Ridges  425   a  also support membrane  45  and prevent it from deforming due to pressure differences across its wall. The membrane should meet a high gas flow elimination requirement (at least 1 L/min at −100 mmHg). Membranes preferably are made of PTFE (e.g. Durapel™ from Millipore, Bedford, Mass.) or polypropylene (e.g. Zintex™ from W L Gore, Elkton, Md.), preferably having a pore size between 0.45μ and 1.0μ. The small pore provides a sterile barrier.  
         [0117]    The membrane is used to automatically remove air  423  that may accumulate at the top of the venous reservoir by applying suction (from the hospital supply) to air-venting tube  44 . Hydrophobic microporous membrane  45  prevents the loss of blood  46  from the venous reservoir. One-way valve  422  may be placed at the outlet of air-venting tube  44  to prevent air from entering the reservoir if the reservoir empties and is exposed to the suction generated by arterial pump  1104 . Membrane  45  has sufficient surface area to allow the removal of the expected volume of air entering the venous reservoir. Studies have shown that membranes that clear air from water can function almost indefinitely (many days) and high suction can be applied without reducing gas transfer rate over time. (However, over time, when the membrane is exposed to blood, especially when high suction is applied, a film overlays the membrane, resulting in a significant increase in resistance to gas flow. When applying lower suction (preferably between −50 and 200 mmHg), the transfer rate of gas across the membrane does not decrease as fast as with high suction (possibly due to less plasma penetration into the pores or lower holding force of the film). Therefore, removing air from blood requires a membrane with a larger area. The larger area compensates for the lower suction used to extend the life of the membrane and the lower transfer rates seen with blood as compared to water.  
         [0118]    Another preferred embodiment, shown in FIGS. 5 a  and  5   b , utilizes a tubular microporous membrane  55  in fluid communication with purge port  54 , said tubular membrane internally supported and sealed to perforated rigid housing  525 . Perforated rigid housing  525  allows gas to cross membrane  55  and enter chamber  59  unimpeded. Housing  525  is sealed at the bottom along  525   a . Chamber  59 , formed by housing  525 , is in fluid communication with purge port  54 . Annular space  57  is formed by circular membrane  55  and air-venting tube  4 . Air-venting tube  4  could be in fluid communication with first inlet chamber  2  shown in FIG. 2 a  and preferably located on top of chamber  2 . Normally annular space  57  is filled with blood. Should air  523  enter line  1  (see FIG. 2 a ), it would rise up chamber  2 , as shown in FIG. 2 f , enter annular space  57  (FIGS. 5 a  and  5   b ), across membrane  55  into chamber  59  (FIG. 5 a ), across port  522   a  of one-way valve  522 , and be purged via purge port  54 . Applying suction to purge port  54  facilitates air removal by increasing the pressure difference across membrane  55 . As with the “roof” design referenced in FIG. 4, vertical placement of the tubular membrane  55  facilitates “peeling” of the blood layer of the surface of the membrane, thereby improving long-term gas transfer.  
         [0119]    The second preferred method to remove air utilizes a floating ball, which allows air but not blood to be removed through the purge port. As shown in FIG. 6 a , housing  64   a  forms chamber  67  that allows air bubbles to rise unhindered as previously described for chamber  2  and tube  4  in reference to FIG. 2 a . Housing  64   a  incorporates ball cage  68 , floating ball  61  and unidirectional valve  622 . Port  622   a  of unidirectional valve  622  providing fluid communication between chamber  67  and gas exhaust port  64 , is open as long as air  623  is present in chamber  67 . When most of the air has been eliminated, the rising fluid level brings ball  61  to the top of chamber  67 , effectively closing port  622   a . In this position, any further withdrawal of fluid from the venous reservoir is prevented. When more air enters the reservoir, the blood level falls, ball  61  drops, and the applied suction removes air  623 . Suction may be provided by a wall source or a suction pump, but preferably is controlled for the purpose described below.  
         [0120]    There are two forces maintaining ball  61  up against port  622   a  keeping said port closed: the buoyancy of the ball and the suction force applied at the gas port (Fs). Fs= (πd2S/4, where d is the inside diameter of air port  622   a  in contact with ball  61 , and S is the negative pressure (suction) applied via air-venting tube  64  against said ball. The upward force, Fs, must be less than the weight of the ball so that when the blood level drops, the weight of the ball overcomes Fs and the ball falls. Cage  68 , in general has a larger ID than the OD of ball  61 , see  68   a  in FIG. 6 a  and  6   c , where FIG. 6 c  is a line drawing illustrating another view of the ball cage used in FIG. 6 a  taken along line  24 - 24 ′. Cage  68  aligns the ball with air port  622   a . The bottom of cage  68  narrows down to an ID smaller than the OD of ball  61 , see  68   b  FIGS. 6 a  and  6   b , where FIG. 6 b  is a line drawing illustrating another view of the bottom of the ball cage used in FIG. 6 a  taken along line  23 - 23 ′. The smaller ID  68   b  serves to retain ball  61  within its chamber  67  and prevents it from falling into the venous reservoir. For this design, for example, ball  61  may be a 1″ solid polypropylene ball (specific gravity sp= 0.90), or a hollow ball (where sp is adjustable). Air port seal  622   a  could, for example, be made of soft silicone and the ID of the air port may be {fraction (1/32)}″. To assure a good seal, the surface of the ball should have a fine finish, preferably with a tolerance of 0.001″ or better. The applied suction should be low to assure that ball  61  does not “stick” to gas port  622   a  in the closed position, and to minimize blood damage. For example, a pressure of −30 mmHg can be applied to remove the air. This degree of suction is sufficient to withdraw the air and maintain the liquid column within first and second inlet chambers  2  and  7  when flexible chamber  8  is less than full, see FIG. 2 a . To prevent excess suction (e.g. over −150 mmHg) from being applied, the line between air venting tube  64  and the suction source can include a t-connector  64   c  with a suction regulating valve  632  attached at the inlet of side port  64   c  (FIG. 6 d ). Such valves are commercially available at various cracking pressures and are currently used for IV infusion sets (e.g., NP Medical, Clinton, Mass., cost &lt; $0.25). As well known in the art, a blood trap (not shown) may be incorporated so any blood that may enter the line would not progress to the suction source, and, in fact, excess lost may be returned to the patient. Alternatively, the air-venting tube  64  may be connected at  64   b  to Cardiotomy reservoir  1115  (see FIG. 1), to which suction is applied. Thus, any blood that may pass the ball valve system would go back to the patient via cardiotomy  1115 . Safety is paramount. Therefore, side port  64   d , having for example a female Luer, in fluid communication with first inlet chamber (e.g., via chamber  67  in FIG. 6 d ), is placed prior to either the ball or the membrane. Port  64   d  provides the user means to eliminate incoming air in a fashion similar to that of present devices, in case the membrane or ball malfunctions.  
         [0121]    Another preferred method to remove air is a variation of the second method but without the floating ball valve combination. As shown in FIG. 11, the top of first inlet chamber  112  of venous reservoir  113  is extended into “chimney”  114  that serves to vent air and is connected to cardiotomy reservoir  15 , to which suction is applied at  15   a . The degree of suction should be sufficient to elevate the blood level into chimney  114 , even when the expandable chamber  118  is less than full. Thus, any air  623  entering inlet tube  111  would float to the top of first inlet chamber  112  and enter chimney  114 . The air would then displace the liquid in chimney- 114 , coalesce with air volume  114   a  that interfaces between the blood in chimney  114  and outlet  114   b  of chimney  114 , and the additional suction would pull the liquid up the chimney to its original level. This system requires that chimney  114  have an ID that facilitates upward movement of air bubbles, even large ones. The length of the chimney needs to be at least equal to the level of the expected liquid when suction is applied and expandable chamber  118  is full. Beyond that height, the outlet of chimney  114   b  can be connected via ¼″ ID tube- 116  to the cardiotomy reservoir. Air space  114   a  below chimney outlet  114   b  assures that the blood does not enter smaller diameter tube  116 . Suction, applied at  15   a , can be provided by the wall source, or suction pump  1114  (FIG. 1) connected to cardiotomy reservoir  15 , said suction regulated to appropriate levels as well known in the art.  
         [0122]    As described in the Description of the Prior Art, improved venous drainage can be achieved by applying some negative pressure on the venous blood. Another aspect of the invention allows the user to apply suction with a collapsible reservoir. FIGS. 8 a ,  8   b , and  8   c  illustrate venous reservoir  772 , previously described in reference to FIGS. 7 a ,  7   b , and  7   c , placed in generally elliptical, clear rigid, housing  88 . Housing  88  is open both at its bottom, defined by border  88   a , and at its top, defined by border  88   b , said borders having sealing gaskets  82  and  81  respectively. Disposable venous reservoir  772  incorporates rigid bottom cap  89 , said cap having lip  89   a  with its inside diameter matching outside diameter of housing  88  to form a seal along gasket  82 . Bottom cap  89  also is sealed to inlet tube  1  at  89   a  and outlet tube  5  at  89   b . A similar arrangement is made at the top of venous reservoir  772  where rigid disk  72   d  is sealed along top gasket  81  of housing  88 . Thus, the user would slip chimney  74  of disposable venous reservoir  772  into the bottom of housing  88 , push it up and insert it through opening  88   d  at the top of housing  88 . When lined up, rigid disk  72   d  is pushed against gasket  81  and bottom cap  89  seals against gasket  82 . The bottom and top seals are reinforced and maintained by cap  89  held against housing  88  by snaps  88   e ,  88   f ,  88   g  and  88   h  that lock onto ridge  89   d  of cap  89 . At the end of the case, snaps  88   e ,  88   f ,  88   g  and  88   h , each of which is hinged at its midpoint (e.g. see  88   i  of hinge  88   f ) are pushed inward, as shown by respective arrows  812  and  811  for snaps  88   f  and  88   e , causing the bottom of said snaps (e.g.  88   j  shown in FIG. 8 b ) to move outward, see for example  88   e ′ in FIG. 8 b , releasing said snaps from locking ridge  89   c  and  89   j  thereby allowing the removal of venous reservoir  772 .  
         [0123]    Chamber  87 , formed between venous reservoir  772  and rigid housing  88 , communicates via port  88   c  with vacuum regulator  813 , said regulator used to adjust the degree of suction applied to chamber  87  using knob  813   b . Gauge  813   a  can be used to indicate the applied suction. As described before, venous reservoir  772  responds to pressure differences across its walls  18  and  19  (FIG. 8 b ). Thus, diminished blood flow from patient  1102 , see FIG. 1, due to increased resistance to flow (e.g. smaller cannula) can be increased by applying suction to chamber  87 . The suction “pulls” walls  18  and  19  outward thereby pulling the blood into the blood chamber. For safety, housing  88  is sized to assure that venous reservoir  772  cannot over-expand beyond defined limits, said limits defined as a volume in blood chamber  8  that would result in a pressure measured at the top of blood chamber  8  being greater than 10 mmHg. Thus, as chamber  8  of venous reservoir  772  expands, walls  18  and  19  move towards the walls of housing  88  until they make contact, see  18   a  and  19   a  in FIG. 8 b . Once contact is made, further outward motion of walls  18  and  19  is limited by rigid housing  88 . To facilitate the use of the system, housing  88  incorporates pole clamp  810 , said clamp provides a simple connection of said housing to a heart-lung machine. It should be understood that a rigid component, such as rigid cylinder  72 , incorporating into venous reservoir  772 , see FIGS. 7 a  and  8   a , is required to facilitate both the introduction of said venous reservoir  772  into housing  88 , and the sealing of said reservoir against gasket  81 , shown in FIG. 8 a . To enhance the ability of the user to see the blood in venous reservoir  772 , light  80 , shown in FIG. 8 b , can be added to the back of housing  88 .  
         [0124]    [0124]FIG. 9 a  illustrates another embodiment for a nondisposable housing designed to allow venous augmentation with a collapsible venous reservoir. The concept is similar to that shown in FIG. 8 a  except that the seals and closure mechanism are different. Here, venous reservoir  772  is placed in container  98 , said container having a back plate and four walls forming first open box,  98   e , which accommodates venous reservoir  772 . Container  98  has a matching door  99  that is hinged at  99   f  by pin  98   f  to container  98  and is shown in FIG. 9 b  and  9   c . Door  99  has a front plate and four walls forming second box  99   e  that also accommodates venous reservoir  772 . To operate, venous reservoir  772  is placed in first box  98   e  and door  99  is closed thereby sealing said venous reservoir, along gasket  92 , within space  909  formed by first box  98   e  and second box  99   e . Port  98   c  in box  98  in fluid communication with the formed sealed space can be connected to a regulated vacuum source, much like the one described in reference to port  88   c  shown in FIG. 8 a  and  8   b . It should be understood that for proper function, the venous reservoir is free to expand within the sealed space  909  thus formed. For free expansion of venous reservoir  772 , seals of the venous reservoir within container  98  and door  99  are achieved at inlet tube  1 , between  92   a  and  99   a  (FIG. 9 b ), air-venting tube  4 , at  92   b  and  99   b  (FIG. 9 c ), and along outlet tube  5 , at  92   c  and  99   c  (FIG. 9 b ). When door  99  is closed, the ID of indentations  92   a  and  99   a  form a tight seal about the OD of inlet tube  1 . Similarly, indentations  92   c  and  99   c  form a tight seal about the outside of outlet tube  5  (FIG. 9 b ), and indentations  92   b  and  99   b  form a tight seal about the outside of air-venting tube  4  (FIG. 9 c ). To assure a tight seal, relievable latches  99   d  and  99   f  lock unto ridge  98   d , see FIGS. 9 a ,  9   b  and  9   c.    
         [0125]    To improve the seal along the inlet, outlet and gas exhaust port, each of said tubes preferably incorporates a secondary structure, see sealing structure  1   a  in FIG. 9 d  for inlet tube  1 . Sealing structure la has a flexible wall forming a wings  1   aa  and  1   ab  on the side of tube  1 , see FIGS. 9 e  and  9   d . The wings are tapered, being thickest at the base and thinnest at the tips, see FIG. 9 d . For effective sealing, gasket  92  accommodates wing  1   aa  at thinner section  92   aa  and wing  1   ab  at thinner section  92   ab , said accommodation providing a seal between container  98  and door  99  along gasket  92 . Gasket  92 , for example, can be made of a polyurethane sponge, which conform to the shape of said wings, see FIG. 9 d . Wing  1   a  preferably is bonded or welded to tube  1  and is therefore disposed when venous reservoir  772  is disposed. Similar designs can be incorporated into air-venting tube  4  and outlet tube  5 .  
         [0126]    [0126]FIG. 9 f  illustrates another preferred embodiment for sealing inlet tube  1  between housing  98  and door  99 . Here, gasket  93  is attached to door  99 , said gasket having indentation  93   a  to seal about the inlet tube  1  when door  99  is closed against housing  98 . This design also incorporates deeper indentation  98   a ′ in the housing, with a closed circumference greater than 225° and an inside diameter that is less than the OD of inlet tube  1 . When the venous reservoir is loaded into the housing, flexible inlet tube  1  is pushed into indention  98   a ′ where it is retained within said indentation by a pressure fit. This allows the user to load air-venting tube  4  and outlet tube  5 . It should be obvious that purge port should be loaded first thereby having the venous reservoir hanging from the top while the other two tubes are lined up before door  99  is closed.  
         [0127]    [0127]FIGS. 12 a ,  12   b , and  12   c  illustrate another preferred embodiment that is identical to that described in FIGS. 8 a ,  8   b  and  8   c  with two major exceptions. Gas removal port  74  and its associated seal  72   d  shown in FIG. 8 a  are replaced by gas removal tube  124  shown in FIG. 12 a . Tube  124  bends and extends to the bottom of bag  772 , see FIG. 12 a , and exits in the same direction as inlet tube  1  and outlet tube  5  thereby eliminating the need for top seal  72   d . Bag  772  in FIG. 8 a  has its gas removal port  74  extending straight up with its outlet ending above bag  772  and pointing opposite to said inlet and outlet tubing. Having all three tubes of bag  772  extend beyond blood chamber  8  and in one direction and exit along the same plane allows all three tubes to be threaded, preferably during manufacturing, through bottom supporting plate, or cover  89 . Thus, as shown in FIGS. 12 a ,  12   b , and  12   c , inlet tube  1  is threaded through cover  89  and is sealed at  89   a , outlet tube  5  is threaded through cover  89  and is sealed at  89   b , and gas removal  124  is threaded through cover  89  and is sealed at  89   e . Having all tubes extend beyond blood chamber sealed within single plate  89  significantly simplifies sealing bag  772  in housing  88 ; it allows sealing along a single plane of cover  89  against single O-ring  82  of housing  88 . It should be obvious that bottom plate  89  could incorporate perfusion connectors as described in reference to supporting plate  1389  in FIG. 13 f.    
         [0128]    The other innovative design, shown in FIGS. 12 a  and  12   b  but not in FIG. 8 a  or  8   b , incorporates an opening  88   k  in front wall  881  of housing  88  allowing the user to reach bag  772  without removing the bag from its housing. Reaching bag  772  was the purpose of the external means provided by aforementioned U.S. Pat. No. &#39;045 to massage the SSR with vibrator  36 . The present invention incorporates removable sealing means to front wall  881  of housing  88 , such as door  1288 , whose outside outline is shown as a dashed line in FIGS. 12 a  and  12   b . Door  1288  in its neutral state is supported by hinge  1202  hanging at on front wall  881 . The outside perimeter of opening  88   k , shown as a dotted line in FIGS. 12 a  and  12   b , of front wall  881  is surrounded by flexible seal  83 . Seal  83  assures that when door  1288  is closed, it seals opening  88   k  from atmospheric pressure. To open door  1288 , the user would release any negative pressure in closed chamber  87  then open door  1288  by pulling handle  1288   a  shown in FIG. 12 b . Closure of door  1288  against seal  83  can be facilitated by tilting front wall  881  either by design, or by tilting entire housing  88 , thereby allowing gravity to hold door  1288  against wall  881 . Design correctly, using gravity to push door  1288  against seal  83  can eliminate clamps that may be necessary otherwise. Gravity closing would allow hinged door  1288 , if it were not secured to rigid housing  88 , to also serve as a pressure relief valve should vacuum fail. As well known in the art of doors, mechanisms to maintain door  1288  open, or even temporarily remove the door, can be easily incorporated in the usual manner. To assure that vacuum is not applied accidentally, door closure is preferably designed such a complete seal occurs only when vacuum is applied and the user temporarily pushes against the door. The seal formed by the initial pushing force provided by the user, is then maintained once vacuum build within chamber  87 .  
         [0129]    [0129]FIGS. 13 a  and  13   b  illustrate another preferred embodiment of a soft shell reservoir with the very innovative features: top loading of the reservoir into its holder and easy secure sealing of the bag for vacuum assist. Venous bag  1366  is preferably made by RF welding polyvinylchloride or polyurethane film having thickness of 0.015 to 0.020″ along perimeter  1310 , to form expandable chamber  138  with walls  1318  and  1319 . Folded screen  1303  (e.g. Medifab from Tetko Inc. Depew N.Y., a polyester mesh with a pore size of 105μ and a 52% opening) is placed with fold (preferably not creased)  1303   a  facing downward and sealed along its vertical sides by welding its side edges between walls  1318  and  1319  along periphery  1310 . Screen fold  1303   a  defining the bottom of screen  1303 , preferably is placed at least ½″ from the bottom of blood chamber  138 . The top free edges  1303   b  and  1303   c  of screen  1303 , shown in FIG. 13 b , face upward and, at least partially, are not sealed along the top periphery  1310   a  and therefore an opening into pouch formed by fold  1303   a  and the two sealed sides of screen  1303 . The screen placement defines four sections, within expandable chamber  138 . Bottom or outlet section  138   a  defined as the section of blood chamber between screen fold  1303   a  and blood outlet tube  1305 . Mid or inlet section  138   b  defined as the section of blood chamber between the top of screen  1303  and its fold  1303   a . In inlet section  138   b , blood is completely surrounded by screen  1303 . Top, or bubble removal section  138   c , is defined as the section of blood chamber  138  above inlet section  138   b , between the top of screen  1303  and sealed top periphery  1310   a . Bubble removal section  138   c  has no screen. The “in-between” section,  138   d , is the section between walls  1318  and  1319  and screen  1303 . The four sections are in fluid communication with each other.  
         [0130]    As shown, four tubes enter bag  1366 . Inlet tube  1301  and infusion tube  1306  are in direct fluid communication with inlet section  138   b . Air removal tube  1304  is in direct fluid communication with inlet section  138   b  and air removal section  138   c . Outlet tube  1305  is in direct fluid communication with outlet section  138   a . Tubes  1301 ,  1306  and  1304  enter from the top of blood chamber  138 , are sealed along top perimeter of sealed section  1310   a , pass through air removal section  138   c , two screen edges  1303   b  and  1303   c  of screen  1303  and into inlet section  138   b . All tubes, except outlet tube  1305 , preferably have holes along their length positioned in inlet section  138   b . Gas removal tube  1304  also has holes,  1304   aa , along its length stationed in both air removal section  138   c  and inlet section  138   b.    
         [0131]    Inlet tube  1301  preferably enters blood chamber  138  at a top corner of blood chamber  138  and extends to the bottom of inlet section  138   b , preferably diagonally to a bottom corner opposite said top corner. Blood enters inlet tube  1301  at its inlet end  1301   a  in a downward direction, said inlet being above said blood chamber  138  and changes direction as it flows within curved inlet tube  1301 . Outlet end  1301   d  of inlet tube  1301  is preferably sealed, forcing blood out exiting holes  1301   b . Exit holes  1301   b  are preferably located only along the top length of tube  1301  situated in inlet section  138   b  that faces air removal section  138   c , see FIG. 13 a . Thus, venous blood, entering inlet tube  1301  in a downward flow at inlet  1301   a , is diverted from a downward flow to a more horizontal flow and then in an upward direction through exit holes  1301   b . The diversion in flow occurs within inlet tube  1301  distal to inlet  1301   a . The upward blood flow pushes bubbles towards air removal section  138   c . A venous bag for an adult patient would preferably have inlet tube  1301 , said tube preferably having an ID of 0.5″ and exit holes  1301   b  with a diameter of 0.5″ or larger.  
         [0132]    Blood entering inlet section  138   b  preferentially flows to outlet section  138   a  via screen  1303 , said screen, once wet, allowing liquid through but retaining bubbles within inlet section  138   b . Bubbles are pushed upwards by the direction of the blood exiting holes  1301   b  and by buoyancy. Bubbles rise towards air removal section  138   c  and then to access holes  1304   a  of air removal tube  1304 , where they are removed, is obstructed when wall  1318  collapses against its opposing wall, as happens with prior art SSR when blood volume is low. With the present SSR, as described in reference to FIG. 2 cc  and FIGS. 1 b  and  1   bb , channels are formed along the outside diameter of tubes  1301 ,  1306 , and  1304  providing a pathway for bubbles to move upward to air removal section  138   c  and on to access holes  1304   a  of air removal tube  1304 . Air removal efficiency is further improved by extending tube  1304 , and preferably also infusion tube  1306 , from the top of blood chamber  138  downward into inlet section  138   b , at least 50% of the vertical distance between the top and the bottom of inlet section  138   b  but preferably over 80% of the height inlet chamber  138   b . If no screen is used, then said extension downward from the top of blood chamber  138  is at least 50% of the height of blood chamber  138 .  
         [0133]    As shown in FIG. 13 a , air removal tube  1304  preferably extends in a diagonal direction within blood chamber  138   b  thereby providing a longer air removal channel than that possible with said tube extending only vertically. Tube  1306  serving as an infusion line, may be closed at its top and just serve as a spacer that provides air bubbles a pathway to air removal section  138   c  when low blood volume tends to collapse the blood chamber. In fact additional intermediate gas purge tubes (not shown), similar to tubes  1304  and  1306  may be incorporated in a similar manner to provide more numerous air removal channels. Having air channels from the bottom of the screen to the air removal section, not only eliminates the front plate of prior art venous reservoir, but also allows chamber  138  of bag  1366  to take its natural tear drop shape, much like that shown in FIG. 12 b . The teardrop shape provides a larger area of the screen (the bottom) for blood flow unhindered by contact with the walls of the bag.  
         [0134]    To assure that air bubbles can travel along the entire horizontal length of air removal section  138   c  towards air removal tube  1304 , spacer  138   cc  may be placed along the top of blood chamber  138 . Spacer  138   cc  prevents the flexible wall forming blood chamber  138  from completely collapsing against its opposing wall when the blood chamber is partially empty. As with the aforementioned air channels provided by tube  1304 , preventing said complete collapse increases the efficiency of gas from the top of blood chamber  138 .  
         [0135]    Another innovative design feature requires that the open ends of the all tubes of venous reservoir  1366  be above blood chamber  138 . Inlet tube  1301 , gas removal tube  1304  and infusion tube  1306  enter blood chamber  138  from its top. Outlet tube  1305  exits outlet blood chamber  138   a  in a direction that facilitates outlet flow to exit in an upward direction. For example, as shown in FIG. 13 a , tube  1305  exits outlet pocket  138   aa , the lowest portion of outlet  138   a , in a horizontal direction thereby requiring only 90° turn for changing the normally downward outlet flow to the desirable upward flow. Here the venous reservoir also incorporates supporting plate  1389  having a first and second planar surfaces, with said first planar surface facing blood chamber  138 . The tubes of venous reservoir: inlet tube  1301  at  1389   a , outlet tube  1305  at  1389   b , gas removal tube  1304  at  1389   c , and infusion tube  1306  at  1389   d  can be threaded through, solvent bonded and sealed during manufacturing to supporting plate  1389 .: (inlet tube  1301  at  1389   a , outlet tube  1305  at  1389   b , gas removal tube  1304  at  1389   c , and infusion tube  1306  at  1389   d .) Supporting plate  1389  can serve to support bag  1366  by dropping it into holder  1388 , as is done with prior art hard shell reservoir (e.g. Baxter holder p/n HSRH for hard shell reservoir p/n HSR4000). For this purpose, the perimeter of supporting plate  1389  is preferably larger than the perimeter of venous reservoir  1366 .  
         [0136]    Inlet  1305   a  of outlet tube  1305  tube may also be designed to prevent pocket  138   aa , shown in FIG. 13 a , from prematurely collapsing (i.e. while there is still blood in outlet chamber  138   a ) and uncollapsing once blood returns to outlet chamber  138   a . This is achieved by having the inlet of tube  1305  cut longitudinal to form a scoop-shape whose walls provide the resilience to maintain the walls of bag  1366  of section  138   aa  apart from each other. A similar design was described in reference the inlet  5   a  of outlet tube  5  shown in FIG. 2 a.    
         [0137]    Another advantage of having all the tubes for the SSR entering from its top is that the bottom of the bag is unhindered by tubing and can be placed lower on to the floor thereby allowing greater gravity drainage.  
         [0138]    It should be obvious that other designs of SSR  772  shown in FIG. 13 a  can be made without compromising the spirit of the present invention. For example, FIG. 13 d  is a line drawing of the bottom part of another preferred embodiment of a SSR, SSR  1362 . FIG. 13 dd  is a line drawing of a cross section taken of FIG. 13 d  along line  133 - 133 ′. SSR  1362  is identical to SSR  1366  shown in FIGS. 13 a  and  13   b  except its outlet section  1368   a  is shaped as a funnel and its outlet tube  1365  enters said outlet section through back wall  1362   a  via an angled connection. Here, as for outlet  138   a  of bag  1366 , outlet tube  1365  exits outlet section  1368   a  at lowest point, pocket  1368   aa . The angled connection can be made utilizing, for example, a Halkey-Roberts semi rigid connector #727AC (St. Petersburg, Fla.) RF welded to wall  1362   a  and then connecting outlet tube  1365  to said connector. This design with an angle connector eliminates the need for outlet tube  1365  to be bent, as is the case for the design of outlet tube  1305  shown in FIG. 13 a . Though not illustrated, it is also possible to have outlet tube  1305  contained within blood chamber  138  and exiting at the top of bag  1366 .  
         [0139]    [0139]FIG. 13 e  is a line drawing of the bottom part of another preferred embodiment of a SSR, SSR  1372 . FIG. 13 ee  is a line drawing of a cross section taken of FIG. 13 e  along line  134 - 134 ′. SSR  1372  is identical to SSR  1366  shown in FIGS. 13 a  and  13   b  except its outlet tube  1375  enters its outlet section  1378   a  through back wall  1372   a  via an angled connection. Here, as for outlet  138   a  of bag  1366 , outlet tube  1375  exits outlet section  1378   a  at lowest point, pocket  1378   aa . The angled connection can be made utilizing, for example, a Halkey-Roberts semi rigid connector #727AC (St. Petersburg, Fla.) RF welded to wall  1372   a  and then connecting outlet tube  1375  to said connector. This design with a semi rigid angle connector eliminates the need for outlet tube  1375  to be bent, as is the case for the design of outlet tube  1305  shown in FIG. 13 a.?    
         [0140]    [0140]FIGS. 13 a , and  13   b  also illustrate a line drawing of one preferred embodiment of a SSR holder that in combination with supporting plate  1389  of venous bag  1366  can form a closed housing that can be used for VAVD. Container  1388  can, in one embodiment, consist of continuous vertical walls (e.g. an extruded ellipsoid tube), a bottom and open top  1388   f  forming an internal chamber having an effective internal diameter (e.g. for an ellipsoid the effective diameter being a function of the major and minor diameters.) Open top  1388   f  preferably has a smaller opening than that of container  1388 , said opening sized to at least allow venous reservoir  1366  with its blood chamber  138  empty, to be dropped into container  1388 . The internal diameter of container  1388  is sized to prevent blood chamber  138  from over extending beyond aforementioned desirable limits. The perimeter of cover  1389  preferably is larger than opening  1388   f  so as to close said opening  1388   f  of container  1388  and form sealed chamber  1309 .  
         [0141]    When positioned properly, supporting plate, or cover,  1389  closes said opening  1388   f  forming housing  1309 . In one embodiment, cover  1389  preferably has two protrusions along its perimeter,  1389   e  and  1389   f , said protrusions forming a channel between accepting open perimeter  1388   a  of container  1388 . This combination lines up cover  1389  and container  1388 , provides a better seal, and hinders cover  1389  from sliding off container  1388 .  
         [0142]    Rim  1388   a  along the open perimeter of housing  1388  may incorporate sealing gasket  1382  against which cover  1389  can seal when vacuum is applied to chamber  1309 . When regulated vacuum is applied, via port  1308  shown in FIG. 13 b , SSR  1366  can be used to enhance venous drainage, as described in aforementioned VAVD. For VAVD, the cross section of container  1388  is preferably ellipsoid, a shape that accommodates the general shape of SSR  1366  and provides mechanical strength. It also serves to line up top of bag  1366  with its supported bottom, as well as preventing cover  1389  from rotating and thereby preventing the bag from twisting. Twisting along the vertical axis is also minimized by guides  1388   c  and  1388   b  extending from the bottom of container  1388 , accepting bag  1366 . Preferably, guides  1388   b  and  1388   c  support bag  1366  via outlet tube  1305 , which is stiffer than pliable wall  1319  and  1318 . Container  1388  preferably should be made from crystal clear, rigid, scratch resistance, tough material such as polycarbonate that can withstand an internal pressure of at least −250 mmHg. Since cover  1389  is disposable, it can be made from less expensive material, such as polyvinyl chloride, and need not be clear or scratch resistance. Cover  1389  required the physical strength to withstand the expected pressure differences across its wall when used for VAVD, preferably supporting a minimum internal pressure of −200 mmHg. Structures such as ribs  1389   f , shown in FIG. 13 a , can be used to reinforce cover  1389 . Reducing opening  1388   f  by extending  1388   g  shown in FIG. 13 b , to “just” allow loading of venous reservoir, reduces the area of cover  1389  that is exposed to vacuum and therefore reduces its required strength.  
         [0143]    The top loaded SSR  1366 , compared to the bottom loaded design shown in FIG. 8 b , has significant advantages. SSR  1366  can be easily placed in the housing with one hand. Once placed, it stays in the holder/housing without clamps (e.g.  88   g  and  88   h  in FIG. 8 a ). With top loading/support, the weight (gravity) of the blood in bag  1366  pulls down cover  1389  against seal  1382  rather than pulling away, thereby using gravity, at least partially, to initiate a seal between cover  1389  and container  1388 . Also, the support on top and the weight (blood volume) on the bottom tend to “straightens out” bag  1366 . Top loading also provides a single flat plane to seal the bag and its associated tubing within housing  1388 . This feature is extremely important to assuring simplicity, reliability, and cost effectiveness. Making one of the walls of the of the housing a disposable rather than the entire housing as shown in FIG. 9 of PCT &#39;16893, reduces costs significantly. Further reduction in costs is achieved by making the disposable wall, a wall with a small area (e.g. top or bottom wall). A smaller area requires lower force to support the same pressure difference and therefore allows use of thinner cover.  
         [0144]    Top loaded SSR has two additional advantages. First, when placing venous reservoir  1366  into its holder by hanging it by it supporting plate  1389 , blood in blood chamber  138  tends to settle at the bottom of blood chamber  138  lowering the center of gravity towards the bottom of the venous reservoir and far below, supporting plate  1389 . Thus, supported at its top and pulled down by weight of the blood, gravity is used to assist in maintaining the venous reservoir in a vertical position. Second, cover  1389  responds to pressure differences across its wall in a useful manner. Thus, when suction is applied to chamber  1309 , cover  1389  pulls tighter against seal  1382 ; the additional sealing force approximating the product of the area of  1389  exposed to the vacuum applied and the level of vacuum. For example, for a cover 2″ wide and 7.5″ long, when a suction of −50 mmHg (−1 psi) the sealing force would be 15 lbs. Similarly, should the vacuum fail, and cover  1389  was not secured to ridged housing  1388 , a build up of pressure within chamber  1309  would provide a force to open cover  1389  to relief pressure should it rise above atmospheric. Accidental pressure build up due to failed vacuum supply can also be achieved by introducing a small “leak” that prevents total sealing yet is small enough to allow suction in the operating room to overcome that leak and provide the desired regulated vacuum. Such a leak could for example be between 100 and 500 cc/min.  
         [0145]    It is obvious that the safety features described with respect to FIG. 8 b  apply to bag  1366  and housing  1388  shown FIG. 13 a . For example, housing  1388  is sized to assure that venous reservoir  1366  cannot over-expand beyond defined limits, said limits defined as a volume in blood chamber  138  that would result in a pressure measured at the top of blood chamber  138  of +10 mmHg. Should blood chamber  138  of venous reservoir  1366  expand, walls  1318  and  1319  would move outward until they make contact with the vertical walls of housing  1388 , as shown for walls  18   a  and  19   a  in FIG. 8 b . Once contact is made, further expansion of walls  1318  and  1319  is limited by the vertical walls of rigid housing  1388 .  
         [0146]    For non-VAVD applications container  1388  need not be sealed. For example, front wall  1388   e  of housing  1388  shown in FIG. 13 b , can be minimized or eliminated to allow the user to reach bag  1366  without removing the bag from the holder. This still provides a venous reservoir featuring easy top loading and connections of the inlet tube, outlet tube, and purge port to the extracorporeal circuit made by an end user from the top of the venous reservoir. Top connections are easier to make in the operating room than the side or bottom connections required with prior art soft shell venous reservoirs. It should also be obvious that bag  1366  can incorporate additional tubing (e.g. for cardiotomy return) in a manner similar to that shown for inlet tube  1301  and/or outlet tube  1305 . The advantage of top loading being maintained as long as said additions allow top cover  1389  to be used as shown. To simplify changing from a closed housing and open front wall housing, front wall  1388   e  of housing  1388 , can be designed as a removable wall as described in detail in reference to door  1288  of housing  88  in FIGS. 12 a  and  12   b.    
         [0147]    The aforementioned design of SSR incorporating a disposable supporting plate adds little cost compared to the added convenience and shorter set up time making it economical to use the bag for standard or VAVD procedures. This reduces cost of inventory and simplifies the user&#39;s set up and learning curve.  
         [0148]    It should be emphasized that all the designs for sealing a venous reservoir having at least one flexible wall within a rigid housing for example, as described in reference to FIGS. 8 b ,  9   b ,  10   b ,  12   b , or  13   b , allow the introduction of a venous reservoir into a rigid container without compromising the sterility of the blood contacting surfaces of the venous reservoir. As well known in the art, the blood contacting surfaces of a venous reservoir consist of at least the inside walls of the blood chamber as well as that of the inlet, the outlet, and the air removal tubes. Thus, the present invention overcomes one of the major obstacles, though not mentioned as such in the description of the prior art, inherent in prior art SSR intended to be sealed within a housing, see aforementioned U.S. Pat. No. &#39;045 and PCT &#39;08734.  
         [0149]    Cover  1389  may also incorporate tubing connectors  1389   aa ,  1389   bb ,  1389   cc,  and  1389   dd,  shown in FIG. 13 f , that facilitate assembly of bag tubing and eliminate the need for separate tubing connectors. Thus, inlet tube  1301  is sealed (e.g. solvent bonded) to the bottom of inlet connector  1389   aa , said inlet connector providing fluid communication between itself and said inlet tubing. Similarly, outlet tube  1305  is sealed to the bottom of outlet connector  1389   bb , said outlet connector forming fluid communication between itself and said outlet tubing. To further enhance the functionality of outlet connector  1389   bb , unidirectional valve  1305   c  may be placed within outlet connector  1389   bb . One-way valve  1305  is a safety feature that prevents back flow from the arterial line,  157  shown in FIG. 1, should arterial pump  1104  stop. Air removal tube  1304  is sealed to the bottom of air removal connector  1389   cc , said connector forming fluid communication between itself and said air removal tubing. Like connector  1389   bb , air removal connector  1389   cc  may incorporate unidirectional valve  1304   c . This valve assures that air cannot enter the bag via connector  1389   cc . Lastly, infusion tube  1306  is sealed (e.g. solvent bonded) to the bottom of infusion connector  1389   dd , said infusion connector forming fluid communication between itself and said infusion tubing. An additional advantage of incorporating rigid connectors into cover  1389 : they provide physical strength to the cover further preventing buckling under high vacuum.  
         [0150]    [0150]FIG. 13 f  also illustrates means that assure the pressure on the gas side  1105   c  of microporous oxygenator  1105 , not fall below that of chamber  1309 . This is achieved by applying the same suction to the outlet of gas port of oxygenator  1105  as is applied to chamber  1309  of FIG. 13 a . Thus, vacuum is provided by vacuum regulator  813  via tube  818  to three-way valve  1391 . Three-way valve  1391  channels the regulated vacuum to tube  1390   a , said tube in fluid communication with chamber  1309 , seen in FIG. 13 a  and  13   b , via connector  1308  placed in housing wall  1388 , see FIG. 13 f . Valve  1391  also channels the regulated vacuum to tube  1390   b , said tube in fluid communication with gas side chamber  1105   b  of oxygenator  1105 . Tube  1390   b  is also in fluid communication with one-way valve  1392 , caged in structure  1393   a  having opening  1393   b  to atmosphere, said one-way valve opening when pressure in tube  1390   b  exceeds atmospheric pressure. A similar one-way valve  1394 , is in fluid communication with tube  1390   a  connecting suction port  1308  of housing  1388  to said three-way valve  1391 . Valve  1394  opens when the pressure in tube  1390   a  exceeds atmospheric pressure. Both valves  1392  and  1394  provide safety and assure that in the event vacuum, applied to either tube  1390   a  or  1390   b , fail, the pressure in said tubes not be built but rather exhaust to atmosphere. It is important the valves  1392  and  1394  have very low cracking pressure, preferably below 10 mmHg. It is also important that these valves present a low resistance to gas flow, preferably requiring no more than 10 mmHg pressure drop at an air flow of 10 L/min. Similarly, vacuum regulator  813 , when used to apply suction to oxygenator  1105 , should accommodate gas flows exceeding that expected for oxygenator  1105 , or 12 L/min for adults. Three-way valve  1391  preferably allows the user to apply suction to chamber  1309  via tube  1309   a  but not to oxygenator  1105 , apply suction to both chamber  1309  and oxygenator  1105 , or not to apply suction to either chamber  1309  or oxygenator  1105 .  
         [0151]    Applying suction to the gas side of the oxygenator can reduce O 2  transfer rate because the partial pressure of O 2 , pO 2 , on the gas side is lowered by the percentage decrease in total pressure on the gas side. Thus, when suction of −50 mmHg is applied to the gas side, the total pressure is lowered by 50/760 or 7% thereby nominally reducing the O 2  exchange by 7%. Considering that the percent O 2  used in the sweep gas is less than 100%, it is possible to compensate for decreased total pressure by increasing the % of O 2  in the sweep gas. To avoid reduction in O 2  exchange, it is desirable to apply suction to the gas side only when there is none or very low blood flow. Low blood flow can be indicated by low pressure on the blood side. To achieve this desirable result, suction applied to the gas side of the oxygenator is throttled with valve  1391 , said valve responding to pressure readings taken of arterial line  157  shown in FIG. 1. For example, when the pressure in line  157  falls below 100 mmHg (a pressure indicating low blood flow), a signal is sent to direct valve  1391  to apply suction to gas exhaust line  1390   b  of oxygenator  1105  shown in FIG. 13 f . It should be pointed out that the decrease in O 2  exchange due to suction application on the gas side (i.e. reduction in pO 2 ) is compensated by longer residence time of the blood (lower blood flow). Applying vacuum to the gas side has no adverse affect on CO 2  exchange.  
         [0152]    The scope of the invention should not be limited to the aforementioned embodiments. The invention can be extended to other embodiments as illustrated with the venous reservoir having a single flexible wall assigned to Cordis Dow Corp and made by C. R. Bard (U.S. Pat. No. 4,424,190). Currently, there are no means to apply suction to the venous blood utilizing this Bard venous reservoir. With the present invention, applying suction to this design of a venous reservoir is simple. FIGS. 10 a , a three dimensional view,  10   b , a cross sectional view of  103 , and  10   c , a cross sectional view along lines  10   c  and  10   c ′ shown in FIG. 10 b , all illustrate a modification of the venous reservoir component shown in FIG. 1 of Pat. No. &#39;190. Blood enters venous reservoir  103  at inlet  101  into chamber  102 , said chamber formed by rigid wall  1019  and flexible wall  1018 , shown in a semi-full position. Wall  1018  is also shown in an almost empty position as indicated by dashed line  1018 ′. Flexible wall is sealed to rigid wall  1019  along periphery  1019   a , said seal made by solvent bonding, RF welding, ultrasonic welding or other appropriate method. Air entering expandable blood chamber  102  is extracted via gas exhaust port  104 . Gas exhaust port  104  may incorporate an automated gas removal means, as shown for example, utilizing a hydrophobic membrane as described in reference to FIG. 5 a . Blood exits via outlet tube  105 . For augmented venous return, the present invention adds face plate  108  that seals the external surface of flexible wall  1018  along periphery  108   a  of face plate  108 , forming sealed pressure chamber  107 . The seal  108   a  and seal  1019   a  therefore can sandwich the free ends of flexible wall  1018  and can be made simultaneously. Gas port  108   b  is in fluid communication with sealed pressure chamber  107 , and is preferably connected to vacuum regulator  813  shown and previously described in reference to FIGS. 8 a  and  12   a . Faceplate  108 , is preferably clear and rigid such as clear PVC, polycarbonate, polyethylene terephtalate (PET), polyethylene terephtalate glycol (PETG), polyester, or alike. Faceplate  108  does not have to be biocompatible because it does not contact blood. It should be clear that by incorporating sealing means between faceplate  108  and flexible wall  1018 , similar to those described in reference to FIG. 8 a , faceplate  108  could be made nondisposable. Whether disposable or not, faceplate  108  forming pressure chamber  107  allows the user to apply suction to chamber  107  via port  108   b , said suction transmitted to the blood via flexible wall  1018  thereby providing augmented venous return.  
         [0153]    [0153]FIG. 10 b  shows nondisposable cover  108  rests within lip  1019   aa  of disposable rigid structure  1019  where it is held lightly. When vacuum is applied to suction port  108   b  of nondisposable cover  108 , the user would hold cover  108  against periphery  1019   a  of structure  1019 . Seal material  1082   a , located along the periphery of cover  108 , is then compressed therebetween forming sealed chamber  107 . The suction within chamber  107  would pull disposable structure  1019  and nondisposable cover  108  together. Thus, the pressure difference across faceplate  108  is used for forming a tighter seal and holding cover  108 . As described in reference to cover  1389  shown in FIG. 13 a , should vacuum fail, any pressure buildup in chamber  107  would push faceplate  108  open to relieve said pressure.  
         [0154]    It should be understood that a comprehensive description of each of the applications of the invention is beyond the scope of a patent application and therefore the aforementioned descriptions are given as illustrations and should not be used to limit the intent, spirit, or scope of the invention. With that in mind,